CN1162197A

CN1162197A - Hydrogen-storage alloy, alloy surface modifying method, cell and alkaline secondary cell negative electrode

Info

Publication number: CN1162197A
Application number: CN97100420A
Authority: CN
Inventors: 河野龙兴; 鹤田慎司; 神田基
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1996-01-22
Filing date: 1997-01-22
Publication date: 1997-10-15
Anticipated expiration: 2017-01-22
Also published as: CN1505189A; KR100241813B1; CN1505190A; CN1279637C; CN1279638C; KR970060558A; CN1154198C

Abstract

A hydrogen-absorbing alloy which is excellent in stability in an aqueous solution and in mechanical pulverizability is disclosed. This hydrogen-absorbing alloy contains an alloy represented by the following general formula (I): Mg2Mly, wherein M1 is at least one element selected (excluding Mg, elements which are capable of causing an exothermic reaction with hydrogen, Al and B) from elements which are incapable of causing an exothermic reaction with hydrogen; and y is defined as 1<y<=1.5.

Description

Hydrogen-absorbing alloy, method for modifying surface of alloy, battery and negative electrode for alkaline secondary battery

The invention relates to a hydrogen storage alloy, a hydrogen storage alloy surface modification method, a battery and an alkaline secondary battery cathode.

As it is well known that a hydrogen occluding alloy can stably absorb and store hydrogen in a volume of several ten thousand times itself (calculated as gas at normal temperature and pressure), and can safely and easily store, hold and transport hydrogen as an energy source, it attracts attention as a promising material. By taking full advantage of the differences in properties between different hydrogen storage alloys, their use in chemical heat pumps and compressors has also been studied, some of which have been developed to the practical stage of application. In recent years, research into the application of hydrogen storage alloys to electrode materials and metal hydride secondary batteries (e.g., nickel-hydrogen secondary batteries) has been widely conducted because hydrogen storage alloys have high catalytic activity in hydrogen absorption and desorption reactions, and batteries as energy sources operate on hydrogen stored in the alloys.

Since the physical and chemical properties of the hydrogen occluding alloy are likely to be applied in many fields, it is considered as one of important raw materials for the future industry.

The metal capable of absorbing hydrogen and constituting the hydrogen-absorbing alloy may be an elemental substance capable of reacting exothermically with hydrogen, i.e., a metal capable of forming a stable compound with hydrogen (e.g., platinum group elements, lanthanoid group elements, and alkaline earth metal elements); or an alloy comprising the above metal and other metals. One of the advantages of this alloy is that the bonding strength of the metal and hydrogen can be suitably weakened, with the result that the hydrogen absorption and desorption reaction proceeds relatively easily. The second advantage is that the relation between the hydrogen absorption and desorption characteristics of the alloy and the hydrogen pressure required by the reaction (equilibrium pressure, plateau pressure), the range of the equilibrium region (plateau region), the change of the equilibrium pressure during the hydrogen absorption process (flatness) and the like can be improved. The third advantage is that the physical and chemical stability of the alloy is improved.

Conventional hydrogen storage alloys fall into the following categories: namely, (1) AB₅Type (e.g. LaNi)₅、CaNi₅)；(2)AB₂Form (e.g. MgZn)₂，ZrNi₂) (ii) a (3) AB type (e.g., TiNi, TiTe); (4) a. the₂Type B (e.g. Mg)₂Ni、Ca₂Fe) and other types (e.g., clusters) wherein a represents a metal element capable of reacting exothermically with hydrogen and B is another metal element. Wherein the LaNi of the type (1)₅The Laves phase alloy of type (2) and some alloys of type (3) are reactive with hydrogen at normal temperature and chemically stable, so they have been widely studied as candidate materials for secondary battery electrodes.

But A is₂The type B hydrogen storage alloy has the following problems. That is, the alloy has a strong ability to adsorb hydrogen, 1Hardly releases hydrogen once adsorbedPlacing; the hydrogen absorption and desorption reaction can be carried out only at a relatively high temperature (about 200 ℃ C.); even if the reaction occurs, the reaction speed is very slow; the chemical stability is rather low, especially in aqueous solutions; such alloys are generally sticky and hard and therefore difficult to crush. In view of these facts, A is rarely used other than for storing and transporting hydrogen₂A type B hydrogen storage alloy. Although it absorbs hydrogen in a volume two to several times greater than other types of hydrogen storage alloys. So if A is above₂The problems of the B-type hydrogen storage alloy are solved, so that the B-type hydrogen storage alloy can be applied to the same field as other hydrogen storage alloys, and can also be usedin other new fields.

Incidentally, until now, there have been some theoretical papers on the type (5) hydrogen occluding alloys, but there have been almost no reports on practical use and experiments.

Meanwhile, Japanese patent publication No. 6-768.7 discloses a magnesium-based hydrogen storage alloy represented by the following formula: mg (magnesium)_2-xNi_1-yA_yB_x(wherein x is 0.1 to 1.5; y is 0.1 to 1.5; A is one of Sn, Sb and Bi; B is one of Li, Na, K and Al). Examples of such alloys are: mg (magnesium)_1.5Al_0.5Ni_0.7Sn_0.3(ii) a Or Mg_1.8Al_0.2Ni_0.8Sn_0.2. It is also disclosed in the publication that this hydrogen storage alloy is useful as a negative electrode material for alkaline secondary batteries. However, since the publication discloses a hydrogen occluding alloy mainly of A₂The B-type alloy has poor hydrogen absorption and desorption performance in a normal temperature range. Therefore, in order to make it possible to absorb and desorb hydrogen at normal temperature and pressure, the method disclosed in the publication is to coat the surface of the hydrogen absorbing alloy with a metallic nickel compound or a stonesen compound.

As explained above, A₂The type B hydrogen storage alloys have distinct characteristics from other types of hydrogen storage alloys: light weight, large capacity and low cost of raw materials. Since it is mainly composed of alkaline earth metals and iron group elements. But A is₂The B-type hydrogen occluding alloy also has the above-mentioned problems.

It is therefore an object of the present invention to provide a hydrogen occluding alloy which is chemically stable (especially in an aqueous solution) and which is easily mechanically crushed.

It is another object of the present invention to provide a hydrogen occluding alloy which is improved in hydrogen absorption performance, particularly at room temperature.

It is still another object of the present invention to provide a method for changing the surface activity of a hydrogen absorbing alloy so that the hydrogen absorbing alloy can easily absorb hydrogen sufficiently.

It is a further object of the present invention to provide a secondary battery negative electrode having a very stable electrode reaction and an alkaline secondary battery having improved charge and discharge cycle properties.

It is a further object of the present invention to develop a method for evaluating the failure rate of Mg-containing hydrogen storage alloys. Based on this method, it is possible to provide a negative electrode suitable for practical use, which is very high in reversibility and stability in electrode reactions and alkaline secondary batteries with such a negative electrode.

That is, according to the present invention, there is provided a hydrogen occluding alloy comprising an alloy represented by the following general formula (2):

Mg₂M1_y

wherein M1 is at least one element selected from the group consisting of elements (other than Mg, elements which exothermically react with hydrogen, Al and B) which do not exothermically react with hydrogen; y is in the range of 1<y<1.5.

According to the present invention, there is further provided a hydrogen occluding alloy comprising an alloy represented by the following general formula (II):

Mg_2-xM2_xM1_y……(II)

wherein M2 is an element selected from the group consisting of elements capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element of at least one element (other than Mg and M2) that is not exothermically reactive with hydrogen, x being in the range 0<x.ltoreq.1.0; y is in the range of 1<y<2.5.

Further, according to the present invention, there is provided a hydrogen occluding alloy comprising an alloy represented by the following general formula (III):

M_2-xM2_xM1_y……(III)

wherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Ti, Zr, Hf, Pd and Pt; m2 is an element selected from the group consisting of elements capable of reacting exothermically with hydrogen, at least one element (other than M) of Al and B M1 is at least one element selected from the group consisting of elements (other than Mg and M2) incapable of reacting exothermically with hydrogen; x is more than 0.01 and less than or equal to 1.0; y is in the range of 0.5<y.ltoreq.1.5.

Further, according to the present invention, there is provided a method comprising the step of treating the surface of a hydrogen occluding alloy with a solution containing an R-X compound, wherein R represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a substituent thereof; x represents a halogen element.

Further, according to the present invention, there is provided a hydrogen occluding alloy, wherein at least one of the three strongest peaks has a half-width (half-width) Delta (2 theta) in the range of 0.2 DEG to 50 DEG in an X-ray diffraction spectrum using CuK α as a radiation source.

Further, according to the present invention, there is provided a hydrogen occluding alloy containing 10% or more of Mg, which shows a half width Delta (2 theta) of a peak appearing in the vicinity of 20 DEG in an X-ray diffraction spectrum using CuK α as a radiation source₁) The range of (2 theta) is not less than 0.3 DEG₁) Less than or equal to 10 degrees; the half width Delta (2 theta 2) of a peak appearing in the vicinity of 40 DEG is in the range of 0.3 DEG to 10 DEG Delta (2 theta 2).

Further, according to the present invention, there is provided a method for surface modification of a hydrogen occluding alloy, comprising a step of mechanical treatment under vacuum or an inert gas or hydrogen atmosphere.

Also, according to the present invention, there is further provided a method for surface modification of a hydrogen absorbing alloy, comprising the step of subjecting the hydrogen absorbing alloy to mechanical treatment under vacuum or an inert gas or hydrogen atmosphere.

Further, according to the present invention, there is provided a battery negative electrode comprising a hydrogen storage alloy containing an alloy represented by the following general formula (I)

Mg₂M1_y……(I)

Wherein M1 is at least one element selected from the group consisting of elements that do not react exothermically with hydrogen (other than Mg, elements that react exothermically with hydrogen, Al, and B); y is more than 1 and less than or equal to 1.5.

According to the present invention, there is further provided an alkaline secondary battery whose negative electrode comprises a hydrogen storage alloy containing an alloy represented by the following general formula (I):

Mg₂M1y ……(I)

wherein M1 is at least one element selected from the group consisting of elements incapable of reacting exothermically with hydrogen (other than Mg, elements capable of reacting exothermically with hydrogen, Al and B); y is more than 1 and less than or equal to 1.5.

According to the present invention, there is provided a battery negative electrode comprising a hydrogen storage alloy containing an alloy represented by the following general formula (II);

Mg₂-xM2xM1y ……(II)

wherein M2 is selected from the group consisting of an element capable of reacting exothermically with hydrogen, at least one element of Al and B (other than Mg); m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than 0 and less than or equal to 1.0; y is more than 1 and less than or equal to 2.5.

According to the present invention, there is further provided an alkaline secondary battery whose negative electrode comprises a hydrogen storage alloy containing an alloy represented by the following general formula (II)

Mg_2-xM2xM1y ……(H)

According to the present invention, there is provided a negative electrode for a battery comprising a hydrogen-absorbing alloy having a half-width Δ (2 θ) of at least one of the three strongest peaks in an X-ray diffraction spectrum using CuK α as a radiation source in the range of 0.2 DEG to 50 deg.

According to the present invention, there is further providedan alkaline secondary battery having a negative electrode comprising a hydrogen storage alloy, wherein at least one of the three strongest peaks has a half-width Δ (2 θ) in the range of 0.2 ° or more and Δ (2 θ) or less than 50 ° in an X-ray diffraction spectrum using CuK α as a radiation source.

According to the present invention, there is provided a negative electrode for a battery comprising a hydrogen storage alloy containing an Mg element, wherein the negative electrode, when immersed in an alkaline aqueous solution of 6N-8N alkali metal hydroxide, has (a) an elution rate of magnesium ions into the aqueous solution of not more than 0.5Mg/kg alloy/hour at normal temperature and not more than 4Mg/kg alloy/hour at 60 ℃, and (b) an elution rate of component elements of the alloy into the aqueous solution of not more than 1.5Mg/kg alloy/hour at normal temperature and not more than 20Mg/kg alloy/hour at 60 ℃.

According to the present invention, there is also provided an alkaline secondary battery comprising a negative electrode of a hydrogen storage alloy containing Mg element placed in a case, a positive electrode placed opposite to the case and a separator disposed therebetween, and an electrolyte solution injected thereinto;

wherein the battery case is filled and sealed with an electrolyte, and after 30 days or more, the concentration of Mg ions in the electrolyte is not more than 2.2 Mg/L.

According to the present invention, there is further provided a hydrogen occluding alloy comprising an alloy represented by the following general formula (V):

(Mg_1-xM3_x)20-_yM4 ……(V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; m3 is at least one element selected from elements (other thanthe M4 element) having higher electronegativity than Mg; x is in the range of 0<x<0.5; y is in the range of 0-18.

Further, according to the present invention, there is provided a hydrogen occluding alloy which excludes an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 ………(VI)

wherein M5 is at least one element selected from the group consisting of elements having an atomic radius of 1 to 1.5 times that of Mg (excluding elements having higher electronegativity than Mg); m6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<0.5; y is in the range of 0-18.

Further, according to the present invention, there is provided a hydrogen occluding alloy formed of a mixture including:

an alloy having hydrogen storage properties, and

at least one additive selected from (a) at least one element of group IA elements, group IIA elements, group IIIA elements, group IVA elements, group VA elements, group VIA elements, group VIIA elements, group VIIIA elements, group IB elements, group IIB elements, group IIIB elements, group IVB elements, group VB elements, and group VIB elements, (b) an alloy formed by any combination of elements of (a), and (c) an oxide of any of elements of (a);

the mixture is mechanically treated under vacuum or an inert gas or hydrogen atmosphere.

Further, according to the present invention, there is provided a hydrogen occluding alloy comprising:

an alloy having hydrogen storage properties; and

0.01 to 50 vol.% of an additive which is a powder having a flat diameter of 0.01 to 100 μm and dispersed in the alloy,at least one element selected from the group consisting of (a) a group IA element, a group IIA element, a group IIIA element, a group IVA element, a group VA element, a group VIA element, a group VIIA element, a group VIIIA element, a group IB element, a group IIB element, a group IIIB element, a group IVB element, a group VB element and a group VIB element; (b) an alloy formed by a combination of any of (a) and (c) an oxide of any of (a);

further, according to the present invention, there is provided an alkaline secondary battery whose negative electrode comprises a hydrogen storage alloy containing an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 ……(V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; m3 is at least one element selected from elements (other than the M4 element) having higher electronegativity than Mg; x is in the range of 0<x<0.5; y is in the range of 0-18.

Further, according to the present invention, there is provided an alkaline secondary battery whose negative electrode comprises a hydrogen storage alloy containing an alloy represented by the following general formula (VI)

(Mg_1-xM5_x)_20-yM6 ……(VI)

Wherein M5 is at least one selected from the group consisting of elements having an atomic radius 1 to 1.5 times that of Mg (except for elements having higher electronegativity than Mg); m6 is at least one element selected from the group consisting of Fe, Ni, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<0.5; y is in the range of 0-18.

Further, according to the present invention, there is provided an alkaline secondary battery whose negative electrode contains a hydrogen storage alloy formed from a mixture comprising:

an alloy having hydrogen-absorbing properties; and

Further, according to the present invention, there is provided an alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy formed from a mixture comprising:

an alloy having hydrogen-absorbing properties; and

0.01 to 50 vol.% of an additive which is a powder having an average particle diameter of 0.01 to 100 μm and is dispersed in the alloy, at least one element selected from the group consisting of (a) group IA elements, group IIA elements, group IIIA elements, group IVA elements, group VA elements, group VIA elements, group VIIIA elements, group IB elements, group IIB elements, group IIIB elements, group IVB elements, group VB elements and group VIB elements; (b) an alloy formed by any combination of the elements in (a); and (c) an oxide of any of (a).

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may also be derived from the claims.

Brief description of the drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a phase diagram of a Mg/Ni alloy.

FIG. 2 is a phase diagram of La/Ni alloy.

Fig. 3 is a partial perspective view of a cylindrical type secondary battery of the present invention.

FIG. 4 is Mg₂Ni_yThe relationship between the value of y and the amount of Mg eluted.

Fig. 5 is a partial perspective view illustrating a test method by which the alloy strip can withstand maximum stress.

Fig. 6 is a block diagram illustrating a hydrogen absorption and desorption process temperature scanning type measuring device in an example of the present invention.

FIG. 7 is a graph showing a temperature rise versus a pressure change (pressure drop is proportional to the amount of hydrogen absorbed by the hydrogen absorbing alloy) for hydrogen absorbing alloys of examples 16 and 17 and comparative examples 3 and 17

FIG. 8 is a graph showing a temperature rise as a function of pressure for hydrogen occluding alloys of example 18 and comparative example 3

FIG. 9 Mg unmodified and surface modified at 25C₂Pressure change diagram of Ni hydrogen storage alloy in hydrogen absorption process.

Fig. 10 is a relationship between the cycle numbers of the simulated cells of the anode of example 151 and the anode of comparative example 20.

FIG. 11 is a graph of cycle number versus discharge capacity for simulatedbatteries of example 242 negative electrodes and comparative example 20 negative electrodes

FIG. 12 is a graph of mechanical treatment containing Mg₂An X-ray diffraction pattern of a hydrogen occluding alloy obtained from a mixture of Ni and Ni.

A hydrogen occluding alloy according to an embodiment of the present invention comprises an alloy represented by the following formula (I):

Mg₂M1_y……(I)

m1 is at least one element selected from the group consisting of elements that do not react exothermically with hydrogen (other than Mg, elements that react exothermically with hydrogen, Al and B); y is more than 1 and less than or equal to 1.5.

Examples of the M1 element are Fe, Ni, Co, Ag, Cd, Mn, In, Se, Sn, Ge and Pb. M1 may be a single element or a mixture of two or more of these elements. Preferred examples of M1 are elements having a higher electronegativity than Mg, i.e., Fe, Ni, Co, Ag, Cd, Mn, In, Se, Sn, Ge and Pb. In particular, hydrogen occluding alloys containing iron group elements such as Fe, Ni, and Co are preferable because such alloys are chemically stable and have excellent hydrogen occluding and releasing ability. The most preferred M1 element is an element with a higher electronegativity than Mg. Alloyed Mg formed when such an element is added in an amount of 10 atomic% or less as pure Mg_1-wM_1w(0<w.ltoreq.0.1) are smaller in unit cell volume than pure Mg, examples of these elements being: mn, Ag, Cd, and In.

Table 1 shows the unit cell volumes of alloys formed from the above-mentioned substituting elements and Mg and pure Mg. The data in table 1 were calculated by obtaining the lattice constants from the diffraction patterns using the alloy powder X-ray diffraction method, assuming that these crystal structures are all hexagonal like pure Mg.

In addition, if Mg_1-wM1_wW value in phase exceeding 0.1, Mg_1-wM1_wThe phase crystal structure and the hexagonal crystal structure are different, and the change in unit cell volume of Mg cannot be estimated accurately due to the addition of the element M1. Thus, the range of w is limited to 0<w.ltoreq.0.1. However, if even w exceeds 0.1, Mg_1-wM1_wThe phase still maintains the hexagonal crystal structure, and then the element M1 can be arbitrarily used in the range where the value of w exceeds 0.1. TABLE 1

Alloy composition	Crystal grainCell volume (nm³)
Alloy composition	Crystal grainCell volume (nm³)	Mg (pure Mg)	0.0462
Mg_0.99Ag_0.01	0.0459	Mg (pure Mg)	0.0462
Mg_0.99Ag_0.01	0.0459	Mg_0.9Cd_0.1	0.0452
Mg_0.95In_0.05	0.0460	Mg_0.9Cd_0.1	0.0452

The reason why the y value of the M1 element in the general formula (I) is defined to be in the range of 1<y.ltoreq.1.5 can be explained as follows in relation to the influence of (a) on the amount of hydrogen absorption; (b) chemical stability such as pulverizability and processability.

(a) Influence on the amount of hydrogen absorption

If the ratio of Mg to M1 (which hardly forms hydrides) having a hydrogen absorption capacity is set to 2: y, the value of y should be 1 (i.e., Mg) from the stoichiometric viewpoint₂M1). However, in practice, if the value of y is set to 1 or less, the resulting alloy may have problems in terms of chemical stability and mechanical crushability, which is the subject of the present invention. Conversely, if the value of y is too large, other undesirable problems may arise in actual use. For example, if the value of y is greater than 2, the resulting alloy appears, when observed microscopically, to be no longer Mg₂A crystal structure of M1 type to MgM1₂Type alloys, i.e. Laves phases. This MgM1₂Type alloys also have hydrogen absorption capacity, however, MgM1 is calculated by weight₂The hydrogen absorption capacity of the alloy is only Mg₂40-70% of M1 type alloy. An excessively large y value is disadvantageous in terms of capacity density.

(b) Influence on chemical stability and pulverizability

Typically, Mg is formed only when Mg: M1 is 2: 1₂Hydrogen storage alloys of the M1 type. Thus, if certain compositional fluctuations, such as an increase or decrease in Mg or M1 local to the alloy, are encountered, the Mg is completely retained₂The structure of the M1 type is not possible and the mechanism can be explained with reference to the following phase diagram. Mg shown in FIG. 1₂The phase diagram of Ni (Mg-Ni series) is Mg₂Typical examples of alloys of the M1 type. FIG. 2 shows AB₅Type alloy LaNi₅(La-Ni series) phase diagram. These phase diagrams appear in the binary alloy phase diagram (american society for metals, 1990 edition). From FIGS. 1 and 2, Mg can be seen₂Ni is represented by a vertical line in the Mg-Ni phase diagram, while Lavis is represented by enlarged regions in the La-Ni phase diagram. This can be attributed to the fact that LaNi is produced in the process of manufacturing₅In the production of the alloy, even if the melt composition fluctuates about the specified composition, the alloy can be practically and completely produced with LaNi₅The same alloy. But for Mg₂M1, Mg if the melt composition fluctuates above and below the specified composition₂A Ni solid solution and an extra component, a two-phase eutectic, i.e., in the equation Mg: Ni ═ 2: Y where Y represents a positive number, if Y<1, Mg₂Ni and excessive Mg form eutectic and are mutually soluble; if Y>1, Mg₂Ni and Mg₂Ni₂Or Mg₂Ni、Mg₂、Ni₂And Ni form a eutectic.

Mg is inferior to Ni in chemical stability such as corrosion resistance and oxidation resistance, and higher in toughness and plasticity than Ni. On the other hand, Mg₂Ni and Mg₂Ni₂In contrast, Mg₂Ni is more resistant to water and oxygen, especially in hydrogen-absorbing state, Mg₂The Ni structure has higher polarizability (ionization property). Therefore, when y<1, even if the value of y is lowered, Mg having high viscosity is present at the grain boundaries of the alloyAnd to resist mechanical stress, but is poor in chemical stability and pulverizability. On the contrary, when y is more than 1, the compound is not miscible with Mg, and Mg₂Ni surface is composed of Mg₂N1 or Ni, thereby improving chemical stability. Furthermore, when y>1, the result isThe alloy has high rigidity, but the grain boundary phase contains rich unnecessary low-viscosity Ni, and may easily cause brittle fracture. Crushing the alloy by mechanical means may be easily performed.

As explained above, when the ratio of Mg and M1 components is expressed as Mg: M1 ═ 2: y, one of the conditions for achieving improved mechanical pulverizability is y>1. At the same time, does not rely on MgM1 in order to maintain the effective capacity of the alloy₂The upper limit of y should be set to 1.5, and in order to ensure chemical stability of the alloy, the range of y should be set as follows: y is more than 1 and less than or equal to 1.5.

When the ratio of Mg to M1 components is expressed as Mg: M1 ═ 2: y, the lower limit of y is greater than 1 and is theoretically satisfactory. However, in fact, the alloy has composition fluctuations and segregation, so one of the conditions for obtaining the alloy is that each part of the alloy is composed of a uniform composition of y>1. In particular (a) if the alloy is produced by the so-called annealing method in which a melt of the component elements is poured into a mold vessel after being melted in an induction furnace or an electric arc furnace in the same manner as in the production of a normal metal ingot, the value of y is preferably 1.05 or more; (b) if the alloy is prepared by quenching the melt by contacting the melt with a low temperature/high heat capacity material such as rolls or liquid, or by casting the melt chilled in air or liquid to produce an alloy, the value of y is preferably 1.02 or more; and (c) mixing several pure metals or alloys according to a formulation to form an alloy having a predetermined composition, and then hot rolling, hot pressing or mechanically mixing (mechanical alloying) the mixture without using a melting method to make an alloy;the value of y is preferably 1.02 or more.

Since the cooling stage of the method (a) is slow, segregation is more likely to occur and it is difficult to obtain a uniform alloy, as compared with other methods, but since the production method thereof is quite simple, it is most widely used. According to the method (c), the uniformity of the alloy is more susceptible to the production conditions, so that the lower limit of y needs to be increased depending on the production conditions. In contrast, according to the method (b), an alloy having a relatively uniform quality can be obtained. The object of the invention is possible when the y-value is kept at 1.01 or higher if the homogeneity of the composition and structure can be improved by using optimized production conditions or by using post-production annealing treatment. The uniformity can be judged by various surface analysis methods (e.g., EDX, energy dispersive X-ray spectrometer or EPMA, electron probe microanalyzer), using electron microscopy or X-ray diffraction method. For example, according to the surface analysis method, the composition distribution test is applied to a partial alloy structure in which 90% or more of the surface is composed of the same phase, and the alloy can be regarded as uniform. On the other hand, according to the X-ray diffraction method, the ratio between the size of the diffraction peak of Mg or M1 or a single element in the master alloy and the size of the diffraction peak derived from these elements is expressed by percentage, and uniformity of the alloy can be regarded if the ratio does not exceed 5% as a whole.

From these results, even for alloys produced by other production methods, it is expected that the lower limit of y is in the range of 1.01 to 1.10.

The hydrogen occluding alloy of the present invention may be an alloy represented by the general formula (I) which contains more than 20 atomic% of elements of group VB and group VIB.

As explained above, the hydrogen occluding alloy of the present invention includes an alloy represented by the general formula (I): mg (magnesium)₂M1_y(wherein M1 is at least one of elements (excluding Mg, elements capable of reacting exothermically with hydrogen, Al and B) incapable of reacting exothermically with hydrogen, and y is in the range of 1<y.ltoreq.1.5). That is, the hydrogen occluding alloy represented by the general formula (I) is characterized in that y or M1 such as Ni is more than 1 and less than 1.5, is chemically stable, has excellent mechanical pulverizability, and exhibits A₂Type B alloys, e.g. Mg₂High hydrogen absorption capacity inherent to Ni.

Therefore, the hydrogen occluding alloy according to the present invention can maintain an excellent hydrogen absorption capacity even when reacted with a hydrogen gas containing a small amount of an oxidizing gas such as oxygen or water vapor. In addition, the hydrogen occluding alloy according to the present invention hardly changes its hydrogen absorption capacity even when it is contacted with an aqueous solution, thus expanding the range of use of the alloy.

Further, in general, the physical properties of the hydrogen absorbing alloy (such as bulk density, contact resistance and electrical conductivity) are changed as the absorption and desorption of hydrogen gradually cause the expansion and contraction of the crystal lattice of the hydrogen absorbing alloy. If these changes in physical properties cause problems, alloy powders that have been pulverized in advance may be used to avoid these problems. Because the hydrogen storage alloy proposed by the present invention is more similar to Mg than conventional ones₂A of Ni₂The type B alloys are more easily pulverized and the problems set forth above are easily solved.

As explained above, the hydrogen occluding alloy of the present invention represented by the general formula (I) is easily pretreated before use and can be easily and reliably controlled in use. Therefore, the hydrogen storage alloy represented by the general formula (I) is particularly suitable as an electrode material for secondary batteries.

A hydrogen occluding alloy according to another embodiment of the present invention comprises an alloy represented by the following formula (II):

Mg_2-xM2_xM1_y……(II)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B (except Mg); m1 is at least one element selected from the group consisting of elements that do not react exothermically with hydrogen (except Mg and M2); x is more than 0 and less than or equal to 1.0; y is more than 1 and less than or equal to 2.5.

As examples of M1, the same elements can be selected with reference to the general formula (I).

Examples of elements (other than Mg) capable of reacting exothermically with hydrogen or capable of forming hydrogen compounds spontaneously are alkaline earth metal elements such as Be, Ca and Ba; rare earth elements such as Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu; group IVA elements such as Ti, Zr and Hf; group VIIIA elements such as Pd and Pt. M2 may use a single element or a mixture of two or more of these elements.

M2 is preferably selected from Al, B and elements (other than Mg) that react exothermically with hydrogen and are more electronegative than Mg, i.e., M2 is at least one element selected from B, Be, Y, Pd, Ti, Zr, Hf, Th, V, Nb, Ta, Pa and Al. If the element selected by M2 has higher electronegativity than Mg, the difference of electronegativity between the alloy and hydrogen can be reduced, and hydrogen at the lattice position is unstable, thereby improving the hydrogen absorption performance of the alloy. In particular, Be, an alkaline earth metal, forms a chemically stable alloy with Mg. On the other hand, Ti, Zr and Hf, which are elements belonging to group IVA, have high reactivity to hydrogen and are capable of forming hydrides.

Further, M2 is preferably selected from Al, B and elements capable of reacting exothermically with hydrogen (except Mg), and if 10 atom% or less of M2 is added based on pure Mg, the Mg of the resulting alloy is_1-wM1_wThe unit cell volume of the phase (0<w.ltoreq.0.1) is smaller than that of pure Mg, i.e. M2 should preferably be at least one element selected from Li and Al.

The range of x in formula (II) is limited by the fact that when x is greater than 1.0, Mg₂M1_yThe hydrogen absorption property (hydrogen absorption capacity, flatness and reversibility of plateau region) of (A) is poor, and in some cases, the crystal structure cannot be maintained, so that the range of x is preferably 0.05. ltoreq. x.ltoreq.0.5.

The range of y in the general formula (II) is limited by the fact that when the value of y is set to more than 1, the same advantage can be obtained with reference to the explanation of the alloy represented by the general formula (I). On the other hand, when the value of y exceeds 2.5, not only the hydrogen absorption capacity of the hydrogen absorbing alloy is reduced but also the crystal structure itself is changed, so that y should preferably be 1.01. ltoreq. y.ltoreq.1.5, more preferably 1.02. ltoreq. y.ltoreq.1.5, particularly preferably 1.05. ltoreq. y.ltoreq.1.5.

The hydrogen occluding alloy of the present invention represented by the general formula (II) preferably contains at most 20 atomic% of the elements of group VB or group VIB.

As explained above, the hydrogen occluding alloy of the present invention represented by the general formula (II): mg (magnesium)_2-xM2_xM1_y(wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B (excluding Mg), M1 is at least one element selected from the group consisting of elements incapable of reacting exothermically with hydrogen (excluding Mg and M2), x is in the range of 0<x.ltoreq.1.0, and y is in the range of 1<y.ltoreq.2.5). That is, since the hydrogen occluding alloy represented by the general formula (II) is characterized in that a part of Mg is substituted by an element represented by M2, such as Al, in combination with general formula A₂Compared with the B-type hydrogen storage alloy, the hydrogen absorption performance of the B-type hydrogen storage alloy is improved particularly at lower temperature,while maintaining A₂High hydrogen absorption capacity inherent in type B hydrogen storage alloys. And the hydrogen occluding alloy represented by the general formula (II) has a larger hydrogen absorption capacity (by weight), a lower production cost and a lighter weight than the conventional rare earth-based hydrogen occluding alloy. Further, the hydrogen occluding alloy represented by the general formula (II) is characterized in that the Y value of M1 such as Ni is more than 1 and less than 2.5, and thus the alloy is chemically stable and excellent in mechanical pulverization property.

Therefore, the hydrogen occluding alloy of the present invention can maintain a large hydrogen absorption capacity even when it is reacted with a hydrogen gas containing a small amount of an oxidizing gas such as oxygen or water vapor. Furthermore, the oxygen absorbing alloy of the present invention hardly changes its hydrogen absorbing capacity even when it is brought into contact with an aqueous solution, and therefore the use of the alloy is expanded.

As explained above, the hydrogen occluding alloy of the present invention represented by the general formula (II) can lower the hydrogen absorption temperature while maintaining A₂High hydrogen absorption capacity inherent in type B hydrogen storage alloys. Furthermore, the pretreatment and control of the conditions in use before use are easy. Therefore, the hydrogen storage alloy represented by the general formula (II) is particularly suitable as an electrode material for secondary batteries.

A hydrogen occluding alloy according to another embodiment of the present invention comprises an alloy represented by the following formula (III):

M_2-xM2_xM1_y……(III)

wherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, En, Gd, Tb, Dy, Ho, Er, Tm, Lu, Ti, Zr, Hf, Pd and Pt; m2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B (other than M); m1 is at least one element selected from elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than 0.01 and less than or equal to 1.0; y is more than 0.5 and less than or equal to 1.5.

As examples of M2, the same elements can be selected with reference to the general formula (II).

M, M2 and M1 are examples of preferred combinations of ternary alloys comprising M for Zr, M1 for Fe and M2 for Cr and quaternary alloys comprising M, Ni for Zr and M1 for Co and M2 for V.

The ranges of y and x in formula (III) are limited based on the following facts. That is, when y is less than 0.5, M, M1 and M2 phases tend to precipitate, the characteristics inherent in the hydrogen absorbing alloy tend to be lost, and the chemical properties of the hydrogen absorbing alloy tend to be unstable, so the lower limit of the y value is preferably set not less than 1 (e.g., 1.01). Further, when the value of y exceeds 2.0, the hydrogen absorbing capacity of the hydrogen absorbing alloy is lowered and the crystal structure is changed, so the upper limit of the value of y is preferably set to 1.5.

If the value of x is less than 0.01, the hydrogen occluding alloy no longer has excellent low-temperature hydrogen absorption properties, and on the other hand, when x is more than 1.0, the hydrogen occluding alloy not only undergoes a change in crystal structure but also A₂The intrinsic properties of the B-type alloy disappear, so the preferred range of x values is 0.05 to 0.5.

As explained above, the hydrogen occluding alloy of the present invention includes an alloy represented by the general formula (III):

M_2-xM2_xM1_ywherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Ti, Zr, Hf, Pd and Pt; m2 is at least one element (except M) selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not undergo a exothermic reaction with hydrogen; x is more than 0.01 and less than or equal to 1.0; y is more than 0.5 and less than or equal to 1.5. That is, since the hydrogen occluding alloy represented by the general formula (III) is characterized in that a part of M such as Zr is substituted by an element represented by M2 such as A1, as compared with the general formula A₂The hydrogen absorption properties, particularly the property of lowering the hydrogen absorption temperature, of the type B hydrogen occluding alloy can be improved while maintaining the A hydrogen absorption properties₂High hydrogen absorption capacity inherent in type B hydrogen storage alloys. Further, the hydrogen occluding alloy represented by the general formula (III) has a larger hydrogen absorption capacity (by weight), a lower cost and a lighter weight than the rare earth-based hydrogen occluding alloy.

Therefore, the hydrogen occluding alloy of the present invention represented by the general formula (III) can lower the hydrogen absorption temperature while maintaining A₂The intrinsic large hydrogen absorption capacity of type B hydrogen storage alloys. Furthermore, because of the general formulaThe hydrogen occluding alloy represented by (III) may hold A₂The B-type hydrogen storage alloy has high hydrogen absorption capacity, and therefore, the alloy is particularly suitable as an electrode material for secondary batteries.

A hydrogen occluding alloy according to another embodiment of the present invention includes an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 ……(V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; m3 is at least one element selected from elements (other than M4) having higher electronegativity than Mg; x is in the range 0<x<0.5; y is in the range of 0. ltoreq. y<18.

Examples of M3 elements (other than M4) having higher electronegativity than Mg are Al (1.5), Mn (1.5), Ta (1.5), V (1.6), Cr (1.6), Nb (1.6), Ga (1.6), In (1.7), Ge (1.8), Pb (1.8), Mo (1.8), Re (1.9), AG (1.9), B (2.0), C (2.5), P (2.1), Ir (2.2), Rh (2.2), Ru (2.2), Os (2.2), Pt (2.2), Au (2.4), Se (2.4), S (2.5), Sc (1.3), Zr (1.4), Hf (1.3), Pd (1.8) and Tl (1.8). The data in brackets represent electronegativity data of each metal element, which is derived from the polarity value of each metal element, and these elements may be used alone or in combination.

The ranges of x and y in the general formula (V) are defined based on the following facts. That is, when x exceeds 0.5, the crystal structure of the alloy varies greatly while causing the deterioration of the properties of the Mg-based alloy, so that the preferable range of x is 0.01. ltoreq. x.ltoreq.0.4, and by limiting x within this range, the hydrogen absorption amount can be increased. On the other hand, when the value of y exceeds 18, the position of hydrogen storage in the alloy decreases, so the amount of hydrogen absorption decreases, so the preferable range of the value of y is 1. ltoreq. y.ltoreq.17.5.

The hydrogen occluding alloy containing the alloy represented by the general formula (V) and satisfying the above explanation has good hydrogen absorption and desorption properties.

The following is the change in bonding strength between the alloy and hydrogen observed from the electronegativity viewpoint, that is, the change in stability of hydrogen in the alloy is caused by the substitution of the Mg component in the above general formula (V) with an M3 element such as Pt and Zr.

In general, there is a relationship that, in most cases, the greater the difference in electronegativity between the metal element and hydrogen in the metal hydride, the greater the bonding strength between the metal and hydrogen, and it is also considered that the difference in electronegativity between the alloy and hydrogen increases, and the metal-hydrogen bond ion bonding performance increases, thereby strengthening the metal-hydrogen bond and thus improving the hydrogen absorption stability. In other words, when Mg is substituted with an M3 element having a higher electronegativity than Mg, such as Al and Ag, the difference in electronegativity between the metal and hydrogen becomes small, so that the stability of hydrogen in the crystal lattice is weakened.

Therefore, when the position of Mg is substituted with an M3 element such as Al and Ag, which are elements having higher electronegativity than Mg, hydrogen in the crystal lattice is unstable, thereby improving the hydrogen storage alloy properties and facilitating the production of the alloy.

On the other hand, M4 such as Ni in the above general formula (V) is effective for improving the properties of the hydrogen occluding alloy and promoting the release of hydrogen adsorbed in the alloy. Since M4 is more electronegative than Mg and is an element that does not react exothermically with hydrogen, i.e., does not form hydrides spontaneously.

As explained above, and general Mg₂The hydrogen absorbing alloy of the present invention containing the alloy represented by the general formula (V) can significantly improve the hydrogen absorption performance, particularly the hydrogen absorption amount, as compared with the Ni type alloy. Compared with the common rare earth metal type hydrogen storage alloy, the hydrogen storage alloy of the invention has the following practical advantages: the hydrogen absorption per unit weight is increasedThe production cost is reduced, and the weight is reduced.

A hydrogen occluding alloy according to another embodiment of the present invention includes an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 ……(VI)

wherein M5 is at least one element selected from the group consisting of elements having an atomic radius of 1 to 1.5 times that of Mg (except for elements having higher electronegativity than Mg); m6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<0.5; y is in the range of 0-18.

If the atomic radius of the element M5 exceeds 1.5 times that of Mg, it becomes difficult to form a single alloy phase, resulting in a decrease in the hydrogen absorption property of the alloy, and as the element represented by M5, Ca, Sr, K and Na may be used. Of these M5 elements, Ca and Sr are preferable.

The ranges of x and y in formula (VI) are defined based on the following facts. That is, when x exceeds 0.5, the crystal structure of the alloy varies greatly while the properties of the Mg-based alloy deteriorate, and a preferable range of x is 0.01. ltoreq. x.ltoreq.0.4, and when x is within this preferable range, the hydrogen absorption amount of the alloy increases. On the other hand, when the value of y exceeds 18, the hydrogen absorption site in the alloy is decreased, and the hydrogen absorption amount is decreased, and the preferable range of the value of y is 1. ltoreq. y.ltoreq.17.5.

The hydrogen occluding alloy comprising the alloy represented by the general formula (VI) and satisfying the above explanation has good hydrogen absorption and desorption properties.

That is, when the position of Mg in the alloy is substituted by an element having an atomic radius 1 to 1.5 times that of Mg atom such as Sr atom, the catalytic activity of the alloy for hydrogen increases, thus improving the hydrogen absorption property.

On the other hand, M6 such as Ni in the above general formula (VI) is effective in improving the hydrogen absorption properties of the hydrogen storage alloy and promoting the release of hydrogen absorbed in the alloy, because M6 is an element higher than electronegative Mg and does not react exothermically with hydrogen, i.e., does not spontaneously form hydride.

According to the above explanations, and Mg is commonly used₂The hydrogen absorption performance of the hydrogen occluding alloy of the present invention comprising the alloy represented by the general formula (VI) is remarkably improved, particularly the amount of hydrogen absorption is increased, as compared with the Ni type alloy. The hydrogen storage alloys of the present invention also have a number of practical advantages over conventional rare earth-type hydrogen storage alloys: the hydrogen absorption amount per unit weight is increased, the production cost is reduced, and the weight is reduced.

The method of surface modification of a hydrogen storage alloy of the present invention comprises the step of treating the hydrogen storage alloy with an R-X compound, wherein R represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a substituent thereof, and X is a halogen element.

Examples of such hydrogen occluding alloys are (1) AB₅Type (e.g. LaNi)₅、CaNi₅)；(2)B₂A₂Form (e.g. MgZn)₂、ZrNi₂) (ii) a (3) AB type (e.g., TiNi, TiFe); and (4) A₂Type B (e.g. Mg)₂Ni、Ca₂Fe)。

The method of the present invention can be applied to another hydrogen occluding alloy comprising an alloy represented by the following general formula (IV):

Mg_2-xM2_xM1_y……(IV)

wherein M2 is at least one element (except Mg) selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B; m1 is at least one element (other than Mg and M2) selected from elements that do not react exothermically with hydrogen; x is inthe range of 0-1.0; y is more than 0.5 and less than or equal to 2.5.

As examples of M1 in formula (IV), the same elements can be selected with reference to formula (I).

As examples of M2 in formula (IV), the same elements can be selected with reference to formula (II).

In the process of the present invention, the above-mentioned AB is preferably used₅Type A₂A hydrogen occluding alloy of type B or an alloy containing the general formula (IV).

The active sequence of the above R-X compounds is iodide>bromide>chloride, wherein R represents an alkylalkenyl, an alkynyl, an aryl or a substituent thereof and X represents a halogen. Examples of R-X compounds are: methyl iodide, vinyl bromide, 1, 2-dibromomethane and 1, 2-diiodomethane.

The R-X compound (halide) is preferably reacted with the hydrogen storage alloy in the presence of a solvent to modify the surface of the alloy.

Examples of such solvents are: diethyl ether, Tetrahydrofuran (THF), di-n-propyl ether, di-n-butyl ether, diisopropyl ether, diglyme, dioxane and Dimethoxyethane (DME). These solvents may be used alone or in combination, and diethyl ether and THF are preferred. When the R-X compound is an alkyl halide, alkenyl halide, aryl halide, an ether solvent is preferred. On the other hand, when the selected R-X compound is an alkenyl compound or an aryl compound, THF having a high coordination strength is preferably used. When the reaction is carried out in ether, the bromide and iodide in the R-X compound are easily reacted. The chloride or substituted bromide compounds are less active in these R-X compounds and can be reacted in THF.

The appropriate concentration of the above-mentioned R-X compound in the solvent is determined in consideration of the following factors

(1) The activity of the halide (when a less active halide is used, the concentration should be increased).

(2) The possibility of causing side reactions (when aryl chlorides and benzyl chlorides are used, coupling reactions may be caused, so these halide concentrations are low).

(3) Solubility and stability of the product (when the solubility of the halide is low, the halide concentration should be low, i.e. the solution is at a saturation concentration or higher, there may be solid matter precipitation when cooling, so that the inhomogeneity is increased).

In order to facilitate the reaction, a catalyst may be added to the solution containing the R-X compound. Examples of such catalysts are polycyclic condensed hydrocarbons, such as: pentalene (pentalene), indene, naphthalene, azulene,Heptylene, biphenyl, indacene, picene, acenaphthene, fluorene, phenalene, phenanthrene, anthracene, fluoranthene, acephatrylene, ylideneanthracene, terphenyl (triphenylene), pyrene, ya en, tetracene, Pleiadene, dinaphthylene, perylene, pentabenzene, tenetacene, tetracene, hexaphene, hexacene, rubicene, coronene, trinaphthalene, pentacene, heptacene, pinanthrene, and ovalene. Of these compounds, anthracene is most suitable. When a Mg-containing hydrogen storage alloy is treated with a THF solution of an anthracene-containing R-X compound, the mixture of anthracene and Mg reacts to form an equilibrium product therebetween. Therefore, anthracene is added as a catalyst only to the reaction system represented by the following reaction formula (3), and the reaction is certainly promoted to proceed in the forward direction, so that it is possible to perform the alloy surface modification more favorably.

The surface modification method of the present invention is advantageous in industrial applications in that R-MS (M: hydrogen storage alloy component) is previously added to a primary reaction system to dehydrate and activate the reaction system.

The method for surface modification of hydrogen storage alloy provided by the invention can improve the performance and activity of hydrogen storage alloy, especially compared with the alloy without surface modification.

Thus, one of the methods for improving the hydrogen absorption property of the hydrogen occluding alloy is to subject it to surface modification treatment, i.e., the activity of the hydrogen occluding alloy during hydrogen absorption is caused by a surface segregation mechanism, and therefore, the activity is considered to be related to the easiness of forming a catalytic layer on the surface of the alloy and the catalyst property when the hydrogen occluding alloy is treated with an R-X compound, the partial component element M constituting the hydrogen occluding alloy undergoes the following reaction, M + R-X → R-MX (1) or M + α R-X → α R-MX α (2)

When surface-treated by these reactions, slight segregation occurs at or near the surface of the hydrogen absorbing alloy to generate active sites thereon as a catalyst.

For example when treating Mg with bromoethane₂In the case of Ni type hydrogen occluding alloy, Mg in the hydrogen occluding alloy undergoes the following reaction

(3)

Following this reaction (surface modification), Mg₂The surface oxide film of Ni is removed, so that the exposed Ni acts as a catalyst for decomposing hydrogen while absorbing hydrogen, thereby improving the hydrogen absorption performance of the alloy.

Examples of the element (except Mg) capable of reacting with the R-X compound are rare earthelements Ln (Ln: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and ruthenium), these lanthanides and 1, 2-diiodoethane are produced in THF solution at room temperature under the following reaction formula LnI in an atmosphere of argon or nitrogen atmosphere₂

(4)

La, Nd, Sm and Ln are particularly active, and the active reactivity sequence of La, Nd, Sm and Ln and 1, 2-diiodoethane is La, Nd and Lu.

For example, when LaNi₅When the type hydrogen storage alloy is treated with 1, 2-diiodoethane, La in the hydrogen storage alloy undergoes the following reaction.

(5)

After this reaction (Table)Surface modified), covered with LaNi₅The oxide film on the surface is removed, so that the exposed Ni functions as a catalyst for decomposing hydrogen while absorbing hydrogen, thereby improving the hydrogen absorption performance of the hydrogen absorbing alloy.

After treatment with the R-X compound solution, only a small amount of halogen elements (e.g., less than 1%) remain on the surface of the hydrogen occluding alloy, with the result that the inherent properties of the hydrogen occluding alloy are not substantially impaired.

Another feature of the hydrogen occluding alloy of the present invention is that among the three strongest peaks in the X-ray diffraction pattern of CuK α as a radiation source, at least one peak has a half-width Δ (2 θ) in the range of 0.2 DEG.ltoreq.Δ (2 θ). ltoreq.50 deg.

An example of the composition type of the hydrogen occluding alloy is (1) AB₅Type (e.g. LgNi)₅、CaNi₅)；(2)AB₂Form (e.g. MgZn)₂、ZrNi₂) (ii) a (3) AB type (e.g., TiNi, TiFe); and (4) A₂Form B (e.g. Mg)₂Ni、Ca₂Fe)

The hydrogen occluding alloy is preferably a composition containing an alloy represented by the following formula (V):

Mg₂-xM2_xM1_y……(IV)

wherein M2 is at least one element (except Mg) selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B; m₁Is at least one element (other than Mg and M2) selected from elements that do not react exothermically with hydrogen; x is in the range of 0-1.0; y is in the range of 0.5<y<2.5.

Particularly, hydrogen storage alloys having a Mg content of 10% or more such as Mg₂Ni and a hydrogen occluding alloy represented by the general formula (IV) wherein, in an X-ray diffraction pattern using Cuk α as a radiation source, the half width Delta (2 theta 1) of a diffraction peak at around 20 DEG is in the range of 0.3 DEG to Delta (2 theta 1) to 10 DEG and the half width Delta (2 theta 1) of a diffraction peak at around 40 DEG is in the range ofTheta 2) is between 0.3 DEG and delta (2 theta 2) and 10 deg.

The half-width range is defined in accordance with the following fact. That is, if Δ (2 θ)<0.2 °, the hydrogen absorption speed of the alloy becomes very slow; on the other hand, if Δ (2 θ)>50 °, the hydrogen absorption capacity is decreased, so that the preferable half width is 0.3 ° ≦ Δ (2 θ) ≦ 10 °.

When D represents the crystal grain size of the hydrogen occluding alloy, it is preferably limited to 0.8 nm. ltoreq. D.ltoreq.50 nm. If a hydrogen occluding alloy having a crystal grain size within this range is used, the diffusion path of hydrogen is enlarged and the diffusion distance can be reduced, so that the hydrogen absorbing and releasing properties of the hydrogen occluding alloy can be improved. The reason for such control of the grain size is as follows: that is, if D is less than 0.8nm, the hydrogen absorption ability of the alloy may be reduced; in addition, if D is greater than 50nm, the diffusion path of hydrogen will be blocked.

The method for surface modification of a hydrogen absorbing alloy according to another embodiment of the present invention comprises a step of subjecting the hydrogen absorbing alloy to mechanical treatment under vacuum or an inert gas or hydrogen atmosphere.

The mechanical treatment for the surface modification described above can be achieved by the following method. That is, the hydrogen storage alloy is first placed in a ball mill vessel, such as an outward pendulum ball mill, a spiral ball mill, a rotary ball mill, or an attriter, and then the alloy is impacted by collision of the wall with the ball.

When the mechanical treatment is carried out in a closed vessel, the treatment may be carried out in a dry vessel filled with argon or an inert gas or evacuated, or sometimes filled with hydrogen. When using a sealed container, the sealing portion of the container will be loosened by the impact, since the impact is performed through the wall. Therefore, for the safety of sealing, double capping or cleaning the container with inert gas or vacuuming can be adopted. It is preferable to control the purity of the inert gas when forming the inert gas atmosphere. For example, it is preferable to control the oxygen content of the inert gas to be within 100ppm and the water vapor to be within 50 ppm. To prevent oxidation, the hydrogen occluding alloy particles are treated in an inert gas as are the metal particles.

Mechanical treatment was carried out for 1 to 1000 hours using an external pendulum ball mill and the like. If the treatment time is less than 1 hour, it is difficult to obtain a hydrogen absorbing property of the hydrogen occluding alloy; on the other hand, if the treatment time exceeds 000 hours, a slow oxidation process occurs and the production cost is also increased.

The hydrogen absorbing alloy should desirably have a particle size of 0.1 to 50 μm after mechanical treatment, and may be heat-treated if necessary. The processing temperature is determined by the hydrogen storage alloy composition. In this case, the temperature is preferably between 100 and 500 ℃. In some cases, there is a possibility that: after mechanical treatment, the elemental constituents incorporated in the mixture may agglomerate with the alloy. Such agglomeration may be effective in improving the hydrogen absorption properties of the alloy. In this case, the desired proportion of such aggregates is 10% by weight or more.

According to the method for surface modification of a hydrogen occluding alloy of the present invention, it is possible to greatly improve the initial activity, activity and hydrogen absorption property of the alloy. The method comprises the step of mechanically treating the hydrogen storage alloy under a vacuum or an inert gas or hydrogen atmosphere.

The hydrogen absorption property of the hydrogen occluding alloy can be improved by any of the following methods: (1) surface coating modification; (2) local chemical method modification; (3) modifying by a mechanochemical method; (4) coating modification; (5) in combination with the use of radiation. According tothe surface modification method of the present invention, the method of the (3) th method, i.e., mechanochemical method, can significantly improve the initial activity of the hydrogen absorbing alloy and the hydrogen absorbing property of the hydrogen absorbing alloy.

According to the mechanical modification method of the present invention, not only the basic structure of the alloy particles can be changed, but also the physical properties thereof can be changed by the change of the surface structure. In other words, the internal energy of the hydrogen occluding alloy can be changed. In addition, the surface energy may be increased due to the creation of a fresh surface as a result of the refinement of the particles.

According to the mechanical modification method of the present invention, changes are generated in the surface and structure of the hydrogen absorbing alloy, and thus stress is generated, which may result in structural destruction. The potential energy increases due to atomic or molecular migration and changes in lattice arrangement. Due to this series of effects, it is possible to improve the catalytic action and to improve the selectivity of the catalytic reaction.

One of the results of the modification treatment is crystal defects in the hydrogen occluding alloy. In this case, these defects include: plastic distortion, i.e., plastic deformation of the crystal caused by mechanical energy generated during the surface modification treatment, in addition to the allowable thermodynamic lattice defects in the ideal crystal; thermal distortion, i.e., deformation due to local heat generation due to temperature non-uniformity or phase change in the crystal; and distortion caused by phase change residual stress. It is also possible to improve the hydrogen absorption performance of the hydrogen occluding alloy by utilizing the above effects.

These hydrogen occluding alloy samples after the mechanical modification treatment are expanded in the X-ray diffraction peak profile obtained by using Cuk α as a radiation source, and usually the peak profile expansion is caused by (a) a change in the crystal grain size, (b) a non-uniform deformation (stain)

For (a), the grain size D can be expressed by the Scherrer's equation:

D＝(0.9λ)/(Δ(2θ)cosθ) (6)

d: grain size;

Δ (2 θ): displaying half width;

λ: the X-ray wavelength used;

θ: bragg angle of diffraction lines.

Also, the grain size ε can be expressed by the following Stokes and Wilson equations:

ε＝λ/(βicosθ) (7)

epsilon: grain size;

β i: integration width;

λ: the X-ray wavelength used;

θ: bragg angle of diffraction lines.

The hydrogen occluding alloy is subjected to the above mechanical treatment, and the X-ray diffraction peak becomes broad as can be seen from the above two equations because the mechanical treatment results in the reduction of the crystal grain size.

From (b), it is known that the grain deformation is also one of the causes of broadening of the X-ray diffraction peak, the grain deformation is caused by the change and fluctuation of interplanar spacings, and from the Stokes-Wilson equation, the relationship between the grain nonuniform deformation η and the diffraction line integral width β i' can be expressed by the following formula:

βi’＝2ηtanθ (8)

further, broadening of the peak profile due to both grain size variation and non-uniform deformation can be expressed by the following Hall equation:

β＝βi +β′i (9)

therefore, the broadening of the hydrogen absorbing alloy peak profile after mechanical treatment is a result of the change in the crystal grain size and the generation of non-uniform deformation. Accordingly, the hydrogen absorption properties of the alloy can be improved by controlling these two factors. That is, when the alloy crystal grains are refined by mechanical treatment, the diffusion path of hydrogen can be enlarged. The diffusion distance is shortened, and the hydrogen absorption and desorption performance of the hydrogen storage alloy can be improved. The preferred size of such grains is 0.8nm<D<50 nm. Further, the impact energy of the mechanical treatment is large enough to change the interplanar spacing of the hydrogen absorbing alloy, thereby causing asymmetry of the crystal lattice of the hydrogen absorbing alloy. In other words, the hydrogen absorption and desorption properties of the hydrogen absorbing alloy can be easily affected by changing the energy inside the crystal lattice due to the generation of crystal grain deformation.

The broadening of the peak profile of the hydrogen absorbing alloy after the mechanical treatment is expressed by the apparent half width (apprathalf-width) Delta (2 theta) as shown in equation (6), and is preferably in the range of 0.2 DEG.ltoreq.DELTA (2 theta) 50 DEG, more preferably 0.3 DEG.ltoreq.DELTA (2 theta) 10 deg.

Another embodiment of the hydrogen storage alloy of the present invention is formed from a mixture comprising:

an alloy having hydrogen-absorbing properties, and

at least one additive selected from at least one of (a) group IA elements (e.g., Li, Na, Rb, Ca, Sr, Ba, etc.), group IIA elements (e.g., Be, Mg, Rb, Cs, etc.), group IIIA elements (e.g., Sc, Y, etc.), group IVA elements (Ti, Zr, and Hf), group VA elements (V, Nb and Ta), group VIIA elements (Cr, Mo, and W), group VIIIA elements (e.g., Mn, Re, etc.), group VIIIA elements (Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, and Pt), group IB elements (Cu, Ag, and Au), group VB elements (Zn, Cd, and Hg), group IIIB elements (B, Al, Ga, In, Ti, etc.), group IVB elements (C, Si, Ge, Sn, and Pb), group VB elements (P, As, Sb, and Bi), and group IIB elements (e.g., S, Se, Te, etc.); (b) at least one member selected from the group consisting of an alloy of any combination of the above (a) elements and (c) an oxide of any of the above (a);

the above mixture is mechanically treated under vacuum or under an inert gas or hydrogen atmosphere.

As the above-mentioned alloy having hydrogen-absorbing property, A can be used₂The B type alloy or the alloys represented by the foregoing general formulae (IV) to (IV) (wherein A is selected from elements capable of reacting exothermically with hydrogen and B is selected from elements incapable of reacting exothermically with hydrogen.) in particular, the alloys represented by the general formulae (V) or (VI) are more preferable.

The element (a), the alloy (b) and the oxide (c) can serve as nuclei of the hydrogenation catalyst because they are strongly adsorbed to the alloy having a hydrogen-absorbing property.

In the above (a), those elements which exhibit high catalytic activity when reacted with hydrogen are preferably selected. If this element is considered for use in a battery, it is preferable to select an element that is positive (endothermic) in reaction with hydrogen, or an element having a larger exchange current density io in reaction at the negative electrode (hydrogen electrode). Examples of such elements are V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, Pd, Ni, Pt, Cu, Ag, Au, etc.

As for the alloy in the above (b), those exhibiting higher catalytic activity resulting from the synergistic effect of the component elements in the alloy in the hydrogen electrode reaction, which is higher than the sum of the catalytic activities derived from each component element, should be preferred. Examples of such alloys which are particularly suitable are Ti-Ni type alloys, Ni-Zr type alloys, Co-Mo type alloys, Ru-V type alloys, Pt-W type alloys, Pd-W type alloys, Pt-Pd type alloys, V-Co type alloys, V-Ni type alloys, V-Fe type alloys, Ti-Ni type alloys, Ni-Zr type alloys, Co-Mo type alloys, Ru-V type alloys, Pt-W type alloys, Pd type alloys, Pt-Pd type alloys, V-Co type alloys, V-Ni,Mo-Co type alloys, Mo-Ni type alloys, W-Ni type alloys, and W-Co type alloys. Of these alloys, MoCo₃、WCo₃、MoNi₃And WNi₃Is more preferred. Because of these alloysHas high catalytic activity and is suitable for improving the hydrogen absorption performance of the hydrogen storage alloy.

As the above-mentioned oxide of (c), those capable of providing a large exchange current density i are preferable_oAn oxide of (a). A preferred example of such an oxide is FeO₂、RuO₂、CoO、CO₂O₃、RhO₂、IrO₂And NiO.

The above-mentioned mixture preferably has a composition such that: the above-mentioned additive is contained in an amount of 0.01 to 70% by volume based on the volume of the alloy having hydrogen absorption characteristics. If the amount of the additive is less than 0.01% by volume, it becomes difficult to increase the hydrogen absorption rate of the hydrogen occluding alloy; on the other hand, if the additive is used in an amount of more than 70% by volume, the hydrogen absorption amount of the hydrogen occluding alloy decreases. The additive is more preferably contained in an amount of 1 to 50% by volume.

As the above-mentioned mechanical treatment method for surface modification, the same equipment as that described above, i.e., for example, an outward pendulum ball mill, a spiral ball mill, a rotary ball mill or a grinder, can be employed.

For example, in the case of an external pendulum ball mill, mechanical treatment is carried out for 1 to 1000 hours in the same manner as described above.

Since the hydrogen occluding alloy of the present invention is formed of a mixture comprising an alloy having hydrogen absorption properties and at least one additive selected from (a) at least one element selected from the group consisting of group IA elements, group IIA elements, group IIIA elements, group IVA elements, group VA elements, group VIA elements, group VIIIA elements, group IB elements, group IIB elements, group IIIB elements, group IVB elements, group VB elements, and group VIB elements; (b) at least one member selected from the group consisting of an alloy of any combination of the above (a) elements and (c) an oxide of any of the above (a); the resulting mixture is subjected to mechanical treatment in vacuum or inert gas or hydrogen gas, with the result that the initial activity and hydrogen absorption properties of the hydrogen occluding alloy can be significantly improved.

That is, the hydrogen absorption activity of the hydrogen storage alloy at the time of hydrogen absorption is affected by the ease of forming the catalytic layer and the performance of the catalytic layer. Due to these factors, it is possible to improve the hydrogen absorption properties of the hydrogen occluding alloy by utilizing the advantageous effects of the foregoing alloy surface modification method.

Accordingly, according to the hydrogen occluding alloy of the present invention, in order to further improve the hydrogen occluding property of the hydrogen occluding alloy, the above-mentioned additive is added in an amount of 0.01 to 70% by volume based on the volume of the hydrogen occluding alloy, and the resulting mixture is subjected to mechanical treatment in a vacuum or an inert gas or hydrogen atmosphere, thereby attaching a catalytic core for hydrogenation. By this mechanical treatment, the catalytic core is strongly adsorbed on the surface of the alloy having hydrogen-absorbing ability and in the vicinity of the surface thereof during hydrogen absorption, and the hydrogenation is promoted, whereby the initial activity of the alloy is enhanced, and therefore the initial activity and hydrogen absorption ability of the hydrogen-absorbing alloy can be significantly enhanced.

For example, Ni is mixed with Mg having hydrogen-absorbing property at a predetermined ratio₂Ni type alloy is mixed, and the resulting mixture is subjected to mechanical treatment in an inert gas (e.g., argon) atmosphere, so that Ni is adsorbed on the surface of the alloy and acts as a hydrogen decomposition catalyst during hydrogen absorption, resulting in an improvement in hydrogen absorption properties of the hydrogen absorbing alloy. In addition, after the mechanical treatment method is used, the grain size of the alloy is reduced, so that the interface proportion of alloy particles is increased, uneven deformation is generated in the crystal, and the absorption of hydrogen is further facilitated.

Another embodiment of the hydrogen storage alloy of the present invention comprises an alloy having hydrogen absorption characteristics and 0.01 to 70% by volume of at least one powder additive having an average particle size of 0.01 to 100 μm and dispersed In said alloy selected from the group consisting of (a) group IA elements (e.g., Li, Na, Rb, Ca, Sr, Ba, etc.), group IIA elements (e.g., Be, Mg, Rb, Cs, etc.), group IIIA elements (e.g., Sc, Y, etc.), group IVA elements (Ti, Zr, and Hf), group VA elements (V, Nb and Ta), group VIA elements (Cr, Mo, and W), group VIIA elements (e.g., Mn, Re, etc.), group VIIIA elements (Fe, Ru, Os, Rh, In, Ni, Pd, and Pt), group IIB elements (Cu, Ag, and IB), group Zn, Cd, and Hg), group IIIB elements (e.g., B, Al, Gu, Zn, Ti, etc.), group IVB elements (C), group IIB, Ag, and Au), group IIB elements (Zn, Ti, and Au), group IIB) elements, At least one element selected from Si, Ge, Sn and Pb), group VB elements (P, As, Sb and Bi) and group VIB elements (e.g., S, Se, Te, etc.); (b) an alloy comprising any combination of the elements (a) and (c) an oxide of any of the elements (a).

As the aforementioned alloy having hydrogen-absorbing ability, A₂Type B alloys (wherein A is an element capable of reacting exothermically with hydrogen and B is an element incapable of reacting exothermically with hydrogen) or alloys represented by the foregoing general formulae (IV) to (VI) can be used. Hydrogen occluding alloys containing an alloy represented by the general formula (V) or (VI) are more preferable.

All of the additives, i.e., the various elements of the foregoing (a), the alloy of (b) and the oxide of (c), can serve as hydrogenation catalyst cores when they are strongly adsorbed to the surface of the hydrogen storage alloy having hydrogen absorption properties. As these additives, the same types of materials as those described above for the hydrogen occluding alloy of the present invention can be used.

The reason for controlling the particle size of the additive powder is as follows. That is, if the additive powder particle size is less than 0.01. mu.m, it is difficult to improve the hydrogen absorption properties of the hydrogen occluding alloy; on the other hand, if the additive powder particle size is larger than 100 μm, the hydrogen absorption rate of the hydrogen occluding alloy is lowered. More preferably the additive powder has a particle size of 0.1 to 50 μm.

The reason for limiting the volume of the additive dispersed in the hydrogen occluding alloy having hydrogen absorption properties is as follows. That is, if the volume occupied by the powder additive is less than 0.01%, it is difficult to improve the hydrogen absorption rate of the hydrogen occluding alloy; on the other hand, if the powder additive occupies more than 70% by volume, the hydrogen absorption amount of the hydrogen occluding alloy will decrease. The volume occupied by the additive is more preferably 1-50%.

As a method for dispersing and adding the powder additive to the alloy having hydrogen absorption characteristics, there can be employed various methods such as a method of mixing the additive with the alloy and subjecting the mixture to mechanical treatment as described above, a method of adding the additive at the time of melting the alloy, a rapid quenching method, an atomizing sputtering method, an electroplating method, a CVD method, a cathode vacuum sputtering method, a mechanical alloying method, a roll method, a liquid-phase coagulation (sol-gel) method.

According to this embodiment of the hydrogen occluding alloy of the present invention, the foregoing additive having a certain particle size is dispersed in the alloy having hydrogen occluding property in a proportion of 0.01 to 70% by volume, resulting in adsorption of the hydrogenation catalyst core to the alloy, which significantly improves the initial activity of the alloy. Accordingly, the initial activity and hydrogen absorption performance of the hydrogen storage alloy can be significantly improved.

The alkaline secondary battery of the present invention is further explained with reference to a cylindrical nickel-hydrogen secondary battery.

Referring to fig. 3, an electrode assembly core 5, which isformed by winding a positive electrode 2, a separator 3 and a negative electrode 4, is placed in a cylindrical can 1, the negative electrode 4 is disposed at the outermost layer of the electrode assembly core 5 so as to be in electrical contact with the can 1, and an alkaline metal electrolyte is injected. A sealing cover 7 is disposed at an upper opening of the cylindrical shell 1; the sealing cover is a circular sheet with a hole 6 in the middle. An annular insulating gasket 8 is interposed between the outer edge of the sealing cap 7 and the upper inner wall of the open battery can 1. The edge of the end of the open cylindrical housing 1 is pressed inward, so that the sealing cap 7 is fixed to the housing 1 via the sealing ring 8. A positive electrode lead 9 has one end connected to the positive electrode 2 and the other end connected to the lower surface of the sealing cap 7, a positive electrode terminal 10 in the form of a top hat is mounted on the sealing cap 7 to cover the opening 6, and a rubber safety valve 11 is interposed between the sealing cap 7 and the positive electrode terminal 10 to seal the opening 6. The gasket 12 is a perforated circular insulating sheet that covers the positive terminal 10, whereby the projecting portion of the terminal 10 projects from the opening of the gasket 12. The packing tube 13 serves to pack all the periphery of the gasket 12, the outer wall of the battery case 1, and the bottom periphery of the battery case 1.

The cathode 2, the separator 3, the anode 4, and the electrolytic solution will be explained in detail below. (1) Positive electrode 2

The positive electrode 2 can be produced by adding a conductive material to nickel hydroxide powder as an active material, mixing the obtained mixture with a polymer binder and water to prepare a paste, filling the paste in an electrode matrix, drying the paste, and forming the dried paste into a predetermined shape.

Cobalt oxide or cobalt hydroxide may be used as the conductive material.

Examples of polymeric binders are carboxymethyl cellulose, methyl cellulose, sodium polyacrylate and polytetrafluoroethylene.

Examples of electrically conductive substrates are metallic nickel meshes, stainless steel meshes, nickel-plated stainless steel meshes or sponge-like, fibrous or felt-like porous metal bodies.

(2-1) negative electrode

The negative electrode can be prepared by adding a conductive material to hydrogen absorbing alloy powder, mixing the resulting mixture with a polymeric binder and water to prepare a paste, then filling the paste mixture into a conductive matrix, drying, and shaping into a predetermined shape.

Examples of the hydrogen storage alloy are alloys represented by the following items (1) to (5).

(1) The aforementioned hydrogen occluding alloy containing the alloy represented by the general formula (I), (II), (V), (VI).

(2) Among the three strongest peaks in an X-ray diffraction spectrum using Cuk α radiation as a radiation source, a hydrogen occluding alloy having at least one peak with a half width Delta (2 theta) of 0.2 DEG&lt,&gtDelta (2 theta)&lt,&gt 50 DEG, preferably 0.3 DEG&lt,&gtDelta (2 theta)&lt, 10 DEG, and having a crystal size D of preferably 0.8nm&lt, D&lt, 50 nm.

(3) Hydrogen storage alloys which have been mechanically treated under vacuum or under inert gas or hydrogen atmosphere conditions.

(4) A hydrogen storage alloy formed from a mixture comprising an alloy having hydrogen absorption characteristics; and at least one additive selected from (a) at least one element from the group consisting of group IA, group IIA, group IIIA,group IVA, group VA, group VIA, group VIIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, group VB and group VIB elements; (b) an alloy formed from a combination of any of the elements listed in (a); (c) (ii) oxides of any of the elements listed in (a); the mixture is mechanically treated under vacuum or under an inert gas or hydrogen atmosphere.

(5) A hydrogen occluding alloy comprising an alloy having hydrogen absorption properties and 0.01 to 50% by volume of a powdery additive having an average particle diameter of 0.01 to 100 μm, dispersed in said alloy, the additive being selected from (a) at least one element selected from the group consisting of group IA, group IIA, group IIIA, group IVA, group VA, group VIA, group VIIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, group VB and group VIB elements; (b) an alloy formed from a combination of any of the elements listed in (a); (c) (ii) oxides of any of the elements listed in (a).

Among the hydrogen storage alloys or alloys having hydrogen absorption characteristics in the above items (3) to (5), those containing alloys represented by the general formulae (IV) to (VI) are preferable.

As the polymeric binder, the same material as that used for the positive electrode can be used.

As the conductive material, for example, carbon black can be used.

Examples of electrically conductive substrates are two-dimensional substrates, such as punched metal, expanded metal, porous rigid plates, nickel mesh, and three-dimensional substrates, such as felt-like porous metal bodies, sponge-like metal substrates.

As a raw material of the negative electrode, a hydrogen absorbing alloy comprising alloys represented by the general formulae (I) and (II) is optimized to determine an optimum value of the magnesium content in the alloy, so as toimprove its reactivity and simultaneously improve the resistance to deterioration of the hydrogen absorbing alloy. That is, the stability of the hydrogen occluding alloy in hydrogen absorption/desorption or charge/discharge cycles is improved. Further, an alkaline secondary battery excellent in capacity and charge/discharge characteristics can be produced using such a negative electrode.

The hydrogen occluding alloys of the alloys represented by the aforementioned general formulae (V) and (VI) are characterized by a significant improvement in hydrogen absorption characteristics, particularly in comparison with conventional Mg₂The amount of hydrogen absorption increases when compared with the Ni-type alloy. Another feature of this hydrogen occluding alloy is that the hydrogen absorption amount per unit weight is larger, the manufacturing cost is cheaper, and the weight is lighter than that of the conventional rare earth element type hydrogen occluding alloy. Therefore, an alkaline secondary battery using a negative electrode containing such a hydrogen storage alloy as a negative electrode is particularly excellent in capacity and charge/discharge characteristics.

Further, an alkaline secondary battery having as the negative electrode a negative electrode of a hydrogen storage alloy containing the alloy represented by the above items (2) to (5) will exhibit a larger capacity and better charge/discharge characteristics. (2-2) negative electrode 4

Such negative electrode 4 includes a hydrogen storage alloy containing magnesium. When the negative electrode is immersed in an aqueous 6N-8N alkali metal hydroxide solution, (a) the elution rate of magnesium ions in the aqueous alkali metal hydroxide solution is not more than 0.5mg/kg alloy/hr at normal temperature, or the elution rate of magnesium ions in the aqueous alkali metal hydroxide solution is not more than 4mg/kg alloy/hr at 60 ℃,and (b) the elution rate of alloying component elements in the aqueous alkali metal hydroxide solution is not more than 1.5mg/kg alloy for 1 hour at normal temperature, or the elution rate of alloying component elements in the aqueous alkali metal hydroxide solution is not more than 20mg/kg alloy/hr at 60 ℃.

The inventors of the present invention have established a method for evaluating the degradation rate of magnesium-containing hydrogen storage alloys. Based on this method, the inventors found that the negative electrode comprising a hydrogen storage alloy has satisfactory reversibility and stability in electrode reaction.

The elution rate of the ions of the hydrogen storage alloy in an aqueous solution of an alkali metal hydroxide, i.e., the corrosion rate, is a parameter indicating the static stability of the alloy. It is therefore generally not possible to determine the stability of a dynamic cycle from this static stability alone. This is because the dynamic characteristics strongly affect the cycle stability of the hydrogen occluding alloy, and for example, the strain of the alloy lattice is affected by hydrogen between the alloy lattices during hydrogen absorption/desorption. In addition, the inherent static properties of the alloy can be determined by chemical or physical modification methods, by contact with external additives or by surface treatment.

In view of this, negative electrodes (hydrogen electrodes) were produced by several methods using a plurality of hydrogen storage alloys containing magnesium, differing in composition from each other, and treated by different methods, and the negative electrodes were evaluated. The results show that the hydrogen occluding alloy having higher reversibility is excellent in stability when subjected to the following conditions.

That is, the negative electrode is characterized in that when the negative electrode is immersed inan aqueous hydroxide solution of 6N to 8N, (a) the elution rate of magnesium ions in the aqueous alkali metal hydroxide solution is not more than 0.5mg/kg alloy/hr at normal temperature or not more than 4mg/kg alloy/hr at 60 ℃ in terms of magnesium alone, and (b) the elution rate of alloying component elements in the aqueous alkali metal hydroxide solution is not more than 1.5mg/kg alloy/hr at normal temperature or not more than 20mg/kg alloy/hr at 60 ℃ in terms of all elements.

The reason why the elution rate at a temperature of 60 ℃ was thus determined is as follows: that is, in the case of a hydrogen occluding alloy which is practically used, the ion elution rate of the alloy is low at ordinary temperature, in the order of 0.5mg/kg alloy/hour, and therefore the elution reaction rate needs to be accelerated to save the measurement time and improve the measurement accuracy.

Therefore, it is also possible to use another set value to represent an elution rate of virtually the same order of magnitude, which is to measure the elution rate at different temperatures to evaluate the characteristics of the negative electrode. However, the use of high temperatures exceeding 60 ℃ is not preferable. Because of the differences in alloy composition and processing, fluctuations in measurement temperature will cause side effects.

The most common method of making the negative electrode is to use a hydrogen storage alloy having the following characteristics: when the hydrogen occluding alloy is immersed in an aqueous solution of an alkali metal hydroxide of 6N to 10N, the elution rate of magnesium ions in the aqueous solution of the alkali metal hydroxide is not more than 0.5mg/kg alloy/hour at ordinary temperature, or the elution rate of magnesium ions in an alkaline aqueous solution of the alkali metal hydroxide is not more than 4mg/kg alloy/hour at 60 ℃, and the total elution rate of alloying component elements in a dehydrated solution of the alkali metal hydroxide is not more than 1.5mg/kg alloy/hour at ordinary temperature, or the total elution rate of alloying component elements in the dehydrated solution of the alkali metal hydroxide is not more than 20mg/kg alloy/hour at 60 ℃. (3) Diaphragm 3

The separator 3 may be composed of a polymer nonwoven fabric, for example, a polypropylene nonwoven fabric, a nylon nonwoven fabric, or a nonwoven fabric composed of polypropylene fibers and nylon fibers. In particular, a polypropylene nonwoven fabric surface-treated to be hydrophilic is more suitable as the separator. (4) Alkali metal electrolyte

Examples of the alkali metal electrolyte are an aqueous sodium hydroxide (NaOH) solution, an aqueous lithium hydroxide (LiOH) solution, an aqueous potassium hydroxide (KOH) solution, a mixed aqueous solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH), a mixed aqueous solution of potassium hydroxide (KOH) and lithium hydroxide (LiOH), and a mixed aqueous solution of sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH).

According to the present invention, an alkaline secondary battery comprises a negative electrode including a hydrogen storage alloy containing magnesium, a positive electrode opposed to the negative electrode, and a separator enclosed in a battery case, the separator being sandwiched between the positive and negative electrodes, an alkali metal electrolyte being filled in the battery case,

wherein, after the alkali metal electrolyte is filled into the battery case and sealed, the concentration of magnesium ions in the alkali metal electrolyte is not more than 2.2mg/l after 30 days or more.

The reason why the ion concentration in the electrolyte of the secondary battery is limited to such a range is referred to the case of an alkaline secondary battery.

In general, in an alkaline secondary battery, the amount of an electrolytic solution is limited, and therefore even a small amount of ions eluted into the electrolytic solution causes a significant increase in the ion concentration in the electrolytic solution. Furthermore, since the elution rate of ions decreases as the concentration of the eluting ions in the electrolyte increases, the rate of increase of the ion concentration in the electrolyte will decrease to a negligible extent in a relatively short time. Further, in the case of a negative electrode (hydrogen electrode) having a low degradation rate, as described in the negative electrode of the present invention, the elution rate of ions in the negative electrode is relatively low at the beginning. From these facts, it can be assumed that the ion concentration in the battery electrolyte remains substantially constant after 30 days after the electrolyte was charged. Thus, with respect to the electrolyte in the battery, the ion concentration in the electrolyte may be assumed as a parameter.

As explained above, according to another embodiment of the present invention, it is possible to manufacture an alkaline secondary battery having a negative electrode including a hydrogen storage alloy as a negative electrode with satisfactory reversibility and stability in an electrode reaction by establishing a method for detecting the degradation rate of a magnesium-containing hydrogen storage alloy. Therefore, it is possible to manufacture a high-capacity alkaline secondary battery in accordance with the present invention instead of the conventional alkaline secondary battery (a nickel-cadmium battery, or a nickel battery using LaNi 5-type hydrogen storage alloy).

Meanwhile, in the alkaline secondary battery, limiting the amount of magnesium ions eluted into the electrolyte also effectively suppresses internal short circuits caused by dendrite formation.

In the following, the invention will be described in more detail by means of preferred embodiments. Examples 1 to 5, comparative examples 1 to 6)

Mg and Ni were melted in a high-frequency heating furnace filled with argon gas, thereby preparing 11 kinds of alloy having Mg₂A hydrogen storage alloy of Niy composition (y values are listed in Table 2 below).

The diameters of the resulting 11 kinds of hydrogen occluding alloy particles were adjusted to 45 to 75 μm, and then a predetermined number of each alloy was immersed in an 8N aqueous solution of potassium hydroxide and heated to 60 ℃ for 5 hours. Subsequently, the concentration of magnesium ions eluted into such an aqueous solution was measured separately. From this measurement, the relative value of magnesium ions eluted and the concentration of magnesium ions eluted per mole of magnesium were calculated. The relative value of magnesium eluted was calculated by setting the elution concentration of pure magnesium to 100, and the results are shown in table 2 below. Fig. 4 shows a standard value obtained by dividing the amount of elution by the ratio of magnesium in the alloy.

On the other hand, each hydrogen occluding alloy pulverized into particles of 75 μm or less in diameter is placed in a pressure-resistant container, hydrogen gas is introduced into the container at 300 ℃ and 10atm, and after 24 hours, the amount of hydrogen occluded in the alloy is calculated from the decrease in pressure. The results are shown in table 2 below.TABLE 2

	Mg₂Niy composition		Eluted Mg concentration		Amount of hydrogen absorbed (Mg₂N_iyH_zZ in
	Mg₂Niy composition		Eluted Mg concentration			Mg∶Ni Atomic ratio	y	Relative value	Molar ratio of Mg in the alloy
	Comparative example 1	100∶0	0	100		Mg∶Ni Atomic ratio	y	Relative value	Molar ratio of Mg in the alloy	1.00	0
Comparative example 2	Comparative example 1	100∶0	0	100	75∶25	0.667	19	0.25	1.4	1.00	0
Comparative example 2	Comparative example 3	2∶1	1.000	18	75∶25	0.667	19	0.25	1.4	0.27	3.2
Example 1	Comparative example 3	2∶1	1.000	18	40∶21	1.050	8	0.12	3.4	0.27	3.2
Example 1	Example 2	64∶36	1.125	7	40∶21	1.050	8	0.12	3.4	0.11	3.5

Table 2 (continuation)

Example 3	5∶3	1.200	7	0.11	3.3
Example 3	5∶3	1.200	7	0.11	3.3	Example 4	8∶5	1.250	8	0.13	3.0
Example 5	4∶3	1.500	10	0.18	2.3	Example 4	8∶5	1.250	8	0.13	3.0
Example 5	4∶3	1.500	10	0.18	2.3	Comparative example 4	8∶7	1.750	105	1.97	0.7
Comparative example 5	50∶50	2.000	145	2.90	0.4	Comparative example 4	8∶7	1.750	105	1.97	0.7
Comparative example 5	50∶50	2.000	145	2.90	0.4	Comparative example 6	1∶2	4.000	240	7.20	0.5

As can be seen from Table 2, with respect to Mg₂Ni_yIn other words, when the value of y representing the amount of Ni is small, the amount of Mg ions eluted is smaller than that of pure Mg. However, when the y value exceeds 1.5, the amount of eluted Mg ions sharply increases. In particular, when the value of y in the hydrogen occluding alloy is in the range of 1<y.ltoreq.1.5, the amount of eluted Mg ions is reduced. Further, when the value of y representing the amount of Ni is in the vicinity of 1, Mg₂Ni_yThe hydrogen absorption characteristics of (a) are not significantly changed. However, when the value of y exceeds 1.5, the hydrogen absorption characteristics are drastically deteriorated. In view of these results, it can be seen that when Mg is used₂Ni_yWhen the value of y in (1) is more than y and less than or equal to 1.5, which is defined by the present invention, excellent chemical properties can be obtainedA hydrogen occluding alloy having stability and hydrogen absorption characteristics. (example 6 and comparative example 7)

Mg and Ni were melted in a high-frequency heating furnace filled with argon gas, thereby preparing two compositions of Mg₂Ni_1.5(example 6) and Mg₂Ni_0.84(comparative example 7).

Each hydrogen storage alloy block material is cut into five lath-shaped alloy samples by a diamond cutter. Since any defects or irregularities formed on the surface of the strip-shaped alloy may cause or promote alloy fracture, these test pieces were subjected to a surface polishing treatment with diamond refining having a grain size of 0.3 μm, followed by the following stress test. The maximum stress of each of the lath-shaped samples was measured as shown in fig. 5. That is, the lath-like test piece 21 is supported by a pair of support rods 22 arranged in parallel at a pitch of 20 mm. Then, on the lath-like test piece 21, a weight 23 is applied at the midpoint position of the pair of parallel support rods to cause the bending of the lath-like test piece 21, and the pressure required to cause the bending of the lath-like test piece 21 is measured, and on the basis of this measurement, the maximum stress is calculated.

The maximum stress was calculated according to the formula set out below. In this equation, w (mm) represents the width of the strip-shaped alloy specimen; t (mm) represents the thickness of the strip-shaped alloy sample; the distance between the support rods was set at 20mm, the force required for bending was defined as f/N, and σ represents the maximum stress. Sigma/10⁶N·m^-2Moment/section modulus

＝(20f/4)/(wt²/6)

＝5f/6wt²

The maximum stress of each strip alloy specimen determined in this way is shown in Table 3 below.TABLE 3

		Size of sample		Load at break N	Moment of force 10³NM	Modulus of section 10^-9m	Maximum stress 10⁶Nm^-2
		Size of sample						Thickness of (mm)	Width of (mm)
		Example 6	Sample No. 1					Thickness of (mm)	Width of (mm)	0.49	10.1	2.05	10.2	0.41	25.2
Sample No. 2	0.50		Sample No. 1	9.9	2.83	14.2	0.41	34.5		0.49	10.1	2.05	10.2	0.41	25.2
Sample No. 2	0.50		Sample No. 3	9.9	2.83	14.2	0.41	34.5	0.65	9.6	3.14	15.7	0.67	23.3
Sample No. 4	1.03		Sample No. 3	10.3	11.3	56.3	1.82	30.9	0.65	9.6	3.14	15.7	0.67	23.3
Sample No. 4	1.03		Sample No. 5	10.3	11.3	56.3	1.82	30.9	1.05	10.1	11.7	58.4	1.85	31.6
Comparative example 7	Sample No. 1		Sample No. 5	0.37	9.7	2.45	12.3	0.22	1.05	10.1	11.7	58.4	1.85	31.6	55.3
	Sample No. 1	Sample No. 2	0.60	0.37	9.7	2.45	12.3	0.22	10.6	6.20	31.0	0.64	48.7		55.3
	Sample No. 3	Sample No. 2	0.60	0.60	10.9	5.39	26.9	0.65	10.6	6.20	31.0	0.64	48.7	41.3
	Sample No. 3	Sample No. 4	1.22	0.60	10.9	5.39	26.9	0.65	10.5	26.9	134	2.60	51.8	41.3
	Sample No. 5	Sample No. 4	1.22	1.30	10.3	27.7	138	2.92	10.5	26.9	134	2.60	51.8	47.3

As can be seen from Table 3, the component is Mg₂Ni_1.5(example 6) strip Hydrogen absorbing alloyand composition Mg₂Ni_0.84(comparative example 7) the strip-shaped hydrogen occluding alloy sample had a low stress and excellent workability (including powderability) as compared with the former.

When the fracture surface of the hydrogen occluding alloy in example 6 was examined by Scanning Electron Microscope (SEM), it was confirmed from the obtained photograph that the fracture surface was composed of a large amount of Mg₂Ni phase and a small amount of Ni or other phase in Mg₂The grain boundaries of the Ni phase have a small amount of a phase with a high Mg content. The same structure was also confirmed in the EPMA (electron probe microanalyzer) test. Specifically, with respect to the hydrogen occluding alloy of example 6, the area of the high Mg content phase was 8 to 9% based on the entire area, and Mg₂The area occupied by the Ni phase and the phase composed of only Ni is 90% or more. In SEM photograph of the hydrogen occluding alloy of comparative example 7, Mg₂The Ni phase and the phase composed of only Ni occupy most of the area. At the same time, in Mg₂Considerable high Mg content phase was recognized at the grain boundary of the Ni phase. Specifically, the area of the high Mg content phase is 20% or more of the entire area.

From the results of example 6 and comparative example 7, it can be seen that the uniformity of the composition distribution (Mg) was measured at the fracture surface of the alloy₂Ni phase) of 90% or more, the stability and mechanical powderability thereof are excellent. (examples 7 to 14 and comparative examples 8 to 10)

11 composition Mg_2-xM2_xM1_yThe hydrogen occluding alloy blocks of (a) are shown in the following Table 4.

From these hydrogen occluding alloy blocks, a plurality of strip-shaped alloy samples having the same size as thesample of example 6 were prepared. The maximum stress of these samples was then measured using the test apparatus shown in fig. 5 and the calculation formula mentioned above. The results obtained are shown in Table 4.TABLE 4

	Hydrogen-storage alloy Mq_2-xM2_xM1_y	y value	Maximum stress 10⁶Nm^-2
	Hydrogen-storage alloy Mq_2-xM2_xM1_y	y value	Maximum stress 10⁶Nm^-2	Example 7	Mg₂Ni_0.95Fe_0.1	1.05	28.1
Example 8	Mg₂Ni_0.95Co_0.1	1.05	28.6	Example 7	Mg₂Ni_0.95Fe_0.1	1.05	28.1
Example 8	Mg₂Ni_0.95Co_0.1	1.05	28.6	Example 9	Mg₂Ni_0.9Cu_0.2	1.10	31.2
Example 10	Mg_1.9Ca_0.1Ni_1.1	1.10	28.2	Example 9	Mg₂Ni_0.9Cu_0.2	1.10	31.2
Example 10	Mg_1.9Ca_0.1Ni_1.1	1.10	28.2	Example 11	Mg_1.9La_0.1Ni_1.1	1.10	29.3
Example 12	Mq₂Ni_0.9Sn_0.25	1.15	30.2	Example 11	Mg_1.9La_0.1Ni_1.1	1.10	29.3
Example 12	Mq₂Ni_0.9Sn_0.25	1.15	30.2	Example 13	Mg₂Ni₁Se_0.1	1.10	34.9
Example 14	Mg_1.9Ca_0.1Ni_0.9Sn_0.15	1.05	30.8	Example 13	Mg₂Ni₁Se_0.1	1.10	34.9
Example 14	Mg_1.9Ca_0.1Ni_0.9Sn_0.15	1.05	30.8	Comparative example 8	Mg₂Ni_0.95Fe_0.05	1.00	44.8
Comparative example 9	Mg_1.9Al_0.1Ni_0.9	0.90	54.3	Comparative example 8	Mg₂Ni_0.95Fe_0.05	1.00	44.8
Comparative example 9	Mg_1.9Al_0.1Ni_0.9	0.90	54.3	Comparative example 10	Mg₂Ni_0.45Sn_0.45	0.90	53.3

As is apparent from Table 4, the composition is Mg_2-xM2_xM1_yWhen thevalue of y is greater than 1, the maximum stress obtainable is about 30X 106N m, as shown in examples 7 to 14^-2. In contrast, in comparative examples 8 to 10, y is not more than 1 and its maximum stress is about 50X 10⁶N·m^-2. This indicates that several tens of percent higher force is required in comparative examples 8-10 than in examples 7-14. (example 15)

Made by an annealing method to contain predetermined amounts of Mg and Ni and having a composition of Mg₂Ni_yThe hydrogen occluding alloy of (1). The alloy was then sealed in a quartz tube filled with argon. Slowly annealing at 500 deg.C for about one month, thereby obtaining Mg₂Ni_1.01The hydrogen occluding alloy of (1).

The prepared hydrogen absorbing alloy was immersed in an aqueous alkali metal hydroxide solution, and the amount of eluted magnesium ions was measured. As a result, the relative amount of magnesium ions eluted was 9, and the value obtained by dividing this amount by 66.4%, i.e., the amount of magnesium in the alloy, was 0.14, indicating that the alloy had excellent chemical stability.

FIG. 6 illustrates a temperature sweep type hydrogen absorption/desorption test apparatus for evaluating hydrogen occluding alloys prepared from example 16. Referring to fig. 6, a hydrogen cylinder 31 is connected to a sample container 33 through a pipe 32. The middle portion of the conduit 32 is bifurcated and the distal end of the branch pipe 34 is connected to a vacuum pump 35.A pressure gauge 36 is mounted on the branched portion of the branch pipe 34. A first valve 37 is arranged on the line 32 between the hydrogen cylinder 31 and the sample container 33₁A second valve 37₂Two valves are installed in this order (starting from the hydrogen cylinders 31). At the first valve 37₁And a second valve 37₂The portion of the conduit 32 therebetween is connected to an accumulator 38. In addition, a third valve 37₃Is mounted on a manifold 34 between a vacuum pump 35 and a pressure gauge 36. The sample container 33 is provided with a heater 39. The thermocouple 40 is inserted into the interior of the sample container 33. A temperature controller 42 controlled by a computer 41 is connected to the thermocouple 40 and the heater 39 to adjust the temperature of the heater 39 based on the temperature detected from the thermocouple 40. A computer controlled automatic recorder 43 is connected to the pressure gauge 36 and the temperature controller 42。

(examples 16 and 17, comparative examples 11 and 12)

Preparing the composition of Mg_2-xVarious hydrogen storage alloys of M2xM1y, but Mg_2-xM2_xAnd M1y and x and y are different from each other, i.e. they are each composed of, Mg_1.9Al_0.1Ni_1.05(M1-Ni, M2-Al, x-0.1, y-1.05; example 16), Mg_1.9Al_0.1Ni (M1 ═ Ni, M2 ═ Al, x ═ 0.1, y ═ 1; comparative example 11), Mg_1.9Mn_0.1Ni_1.05(M1-Ni, M2-Mn, x-0.1, y-1.05; example 17), Mg_1.9Mn_0.1Ni (M1 ═ Ni, M2 ═ Mn, x ═ 0.1, y ═ 1; comparative example 12) and Mg₂Alloy of Ni (comparative example 3).

Then, each hydrogen storage alloy is charged into the sample container 33, respectively. Thereafter, the first valve 37 is closed₁Opening the second valve 37₂And a third valve 37₃. In this case, the vacuum pump 35 is actuated to evacuate air from the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33. Then, the second valve 37 is closed₂And a third valve 37₃Thereafter, the first valve is opened to supply hydrogen from the hydrogen cylinder 31 to the pipe 32, the branch pipe 34, the accumulator 38 and the sample container33, thereby replacing them with hydrogen. Subsequently, the first valve 37 is closed₁At the same time, the amount of hydrogen gas to be input is calculated from the pressure displayed on the pressure gauge 36. Then, the second valve 37 is opened₂The input hydrogen gas is introduced into the sample container 33, and its temperature is controlled by the thermocouple 40, and the temperature in the sample container 33 is raised at a constant rate by the control of the thermocouple 40 and the temperature controller 42. At the same time, the heater 39, which receives such a control signal, records the temperature of the sample container 33. At this point, any change in pressure in the sample container 33 is detected by the pressure gauge 36 and recorded in the automatic recorder 43. The change in pressure due to the rise in temperature in the sample vessel 33 (the decrease in temperature is caused by hydrogen absorption by the hydrogen storage alloy) is shown in fig. 7.

As can be seen from FIG. 7, with Mg_1.9Al_0.1Ni hydrogen storageAlloy (comparative example 11) comparison, Mg_1.9Al_0.1Ni_1.05Hydrogen occluding alloy (example 16) can be operated at a lower temperatureAnd (4) absorbing hydrogen downwards. With Mg_1.9Mn_0.1Ni Hydrogen storage alloy (comparative example 12) in comparison with Mg_2.9Mn_0.1Ni_1.05The hydrogen occluding alloy (example 17) can also occlude hydrogen at a lower temperature. In particular, the hydrogen occluding alloy of example 16 in which M2 was replaced with Al was better in terms of lowering the hydrogen absorption temperature or the temperature suitable for hydrogen absorption than the hydrogen occluding alloy of example 17 in which M2 was replaced with Mn. And, with Mg₂The hydrogen occluding alloys of examples 16 and 17 have excellent hydrogen absorption capacity as compared with the Ni hydrogen occluding alloy (comparative example 3). It can thus be seen that when M2(Al or Mn) is substituted for a part of Mg, it is possible to lower the temperature suitable for hydrogen absorption while maintaining excellent hydrogen absorption capacity.

In another experiment, by using Mg_1.9Al_0.1Ni_1.05Example 16, Mg_1.9Mn_0.1Ni_1.05Example 17 Mg_1.9Al_0.1Ni (comparative example 11) and Mg₂The correlation between the hydrogen absorption concentration and the hydrogen absorption temperature was examined for the Ni (comparative example 3) hydrogen occluding alloy. From this, the temperature required until H/M becomes 0.1 (which means that the ratio of the number of hydrogen atoms absorbed to the number of atoms of the hydrogen absorbing alloy is 0.1) was measured. Further, the relative values of the magnesium concentration eluted in the alloys of examples 16 and 17 and comparative examples 11 and 3 and the concentration of magnesium eluted per mole of magnesium were determined in the same manner as described in example 1. In this case, the relative value of the concentration of magnesium ions eluted from pure magnesium was calculated by setting the relative value of the concentration of magnesium ions eluted from pure magnesium to 100. The results obtained are shown in Table 5.TABLE 5

	Hydrogen-storage alloy Mg_2-xM2_xM1_y	y value	Eluted Mg concentration		Temperature of (℃)
			Eluted Mg concentration			Relative value	Mg per gram of the alloy
			Example 16	Mg_1.9A1_0.1Ni_1.05		Relative value	Mg per gram of the alloy	1.05	7	0.11	70
Comparative example 11	Mg_1.9A1_0.1Ni	1.00	Example 16	Mg_1.9A1_0.1Ni_1.05	17	0.27	75	1.05	7	0.11	70
Comparative example 11	Mg_1.9A1_0.1Ni	1.00	Example 17	Mg_1.9Ni_1.06Mn_0.1	17	0.27	75	1.16	7	0.12	110
Comparative example 3	Mg₂Ni	1.00	Example 17	Mg_1.9Ni_1.06Mn_0.1	18	0.27	140	1.16	7	0.12	110

As is apparent from Table 5, when a hydrogen occluding alloy in which Mg is partially replaced with M2(Al or Mn) and the y value thereof is larger than 1 is used, it is possible to obtain a low hydrogen absorption temperature and to improve the chemical stability of the alloy. (example 18)

Prepared with the composition of Mg_1.9Al_0.1Ni_0.55(Mg_2-xM2_xM1_yM1 ═ Ni and Co, M2 ═ Al, x ═ 0.1, and y ═ 1.10) of the hydrogen storage alloys. Then, with the apparatus shown in FIG. 6, the pressure change due to the temperature rise of the sample vessel (temperature decrease due to hydrogen absorption by the hydrogen storage alloy) was tested in the same manner as in example 16. The characteristic curveof the alloy shown in FIG. 8 was obtained. From Mg₂The results obtained for the Ni hydrogen storage alloy are also shown in fig. 8.

As shown in fig. 8, replacement of M1 in the hydrogen storage alloy with Ni and Co enables lowering of the temperature suitable for hydrogen absorption while maintaining excellent hydrogen absorption capacity.

In another experiment, the relative values of magnesium concentration eluted and the concentration of magnesium eluted per mole of magnesium in the alloy of this example were tested in the same manner as described in example 1. In this case, the relative value of the magnesium ion concentration was calculated by setting the concentration value of magnesium ions eluted from pure magnesium to 100. As a result, the relative value of the eluted concentration was 8, and the concentration of magnesium eluted per mole of magnesium in the alloy was 0.13. Examples 19 and 20, comparative example 13)

Preparing various compositions of M_2-xHydrogen storage alloys of M2xM1y, but M thereof_2-xThere are differences in the M2x and M1 components and in the x and y values. I.e. alloy Zr_1.9V_0.1Fe_1.05(M ═ Zr, M1 ═ Fe, M2 ═ V, x ═ 0.1, y ═ 1.05; example 19), alloy Zr_1.9Cr_0.1Fe_1.05(M ═ Zr, M1 ═ Fe, M2 ═ Cr, x ═ 0.1, y ═ 1.05; example 20), (c) and the alloy Zr2Fe (comparative example 13). Then, with the experimental apparatus shown in FIG. 6, the pressure change due to the temperature rise of the sample vessel (temperature drop due to hydrogen absorption by the hydrogen storage alloy) was measured in the same manner as in example 16. At the same time, the temperature required for hydrogen absorption until H/M becomes 0.1 (which means that the ratio of the number of absorbed hydrogen atoms to the number of atoms in the hydrogen absorbing alloy is 0.1) was also measured. The results are shown in Table 6 below.TABLE 6

	Hydrogen-storage alloy Mg_2-xM2_xM1_y	Value of Y	Temperature (. degree.C.)
	Hydrogen-storage alloy Mg_2-xM2_xM1_y	Value of Y	Temperature (. degree.C.)	Example 19 Example 20 Comparative example 13	Zr_1.9V_0.1Fe_1.05 Zr_1.9Cr_0.1Fe_1.05 Zr₂Fe	1.16 1.16 1.00	340 295 380

As is apparent from table 6, when Zr ═ M, M2 (V and Cr) partially replaced M and

when the y value of M1 exceeds 1 (examples 19 and 20), the hydrogen absorbing temperature of the hydrogen occluding alloy constituted under the above conditions may be lowered.

(examples 21 to 26, comparative examples 3, 14 and 15)

First, Mg, Ni, Ag, Cd, Ca, Pd, Al, In, Co and Ti were melted In a high-frequency heating furnace filled with argon gas to prepare 9 kinds of hydrogen storage alloys. Composition of each alloy Mg₂-xM2xM1y is listed in Table 7.

Then, each alloy was put into the container 33 as a sample, respectively. Thereafter, the first valve 37 is closed₁Opening the second valve 37₂And a third valve 37₃. In this case, the vacuum pump 35 is actuated to evacuate air from the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33. Then the second valve 37 is closed₂And a third valve 37₃Opening the first valve 37₁So that the hydrogen gas in the hydrogen cylinder 31 is taken into the piping 32, the branch pipe 34, the accumulator 38 and the sample container 33, thereby completing hydrogen gas replacement. Subsequently, the first valve 37 is closed₁Thereafter, the second valve 37 is opened₂The input hydrogen gas is admitted into the sample container 33 and the pressure and temperature recorded in the automatic recorder 43 are checked.

With examples 21 to 26 and comparative examples 3, 14 and 15, the pressure of the hydrogen cylinder 31 was adjusted in advance so as to control the pressure (initial pressure) in the sample container 33 to be kept around 10atm when hydrogen gas was replaced, and the initial measurement temperature was set to room temperature (about 25 ℃).

Subsequently, the temperature in the sample container 33 was controlled to rise at a rate of 0.5 ℃ per minute by the control of the computer 41 and the temperature controller 42. At the same time, the heater 39 that receives such a control signal detects the temperature inside the sample container 33. At this time, changes in pressure and temperature in the sample container 33 are measured and recorded by the pressure gauge 36 and the automatic recorder 43.

On the other hand, the pressure change in the sample container 33, which is caused by the temperature rise in the above operation, is monitored. Based on this pressure drop, the temperature at which H/M is 0.1 (i.e., the number of hydrogen atoms absorbed per atom in the alloy reaches 0.1) was determined as a minimum temperature standard for allowing the hydrogen absorbing alloy to complete the hydrogen absorbing reaction, and the relative values of the magnesium concentration eluted in the alloys of examples 21 to 26 and comparative examples 3, 14 and 15 and the magnesium concentration eluted per mole of magnesium were measured in the same manner as described in example 1. In this case, the relative value of the concentration of magnesium ions eluted from pure magnesium was calculated by setting the relative value of the concentration of magnesium ions eluted from pure magnesium to 100.The results are shown in Table 7 below.TABLE 7

	Hydrogen-storage alloy Mg_2-xM2_xM1_y	y value (℃)	Eluted Mg concentration		Temperature of (℃)
			Eluted Mg concentration			Relative value	Molar ratio of Mg in the alloy
			Example 21	Mg₂Ag_0.22Ni_1.11		Relative value	Molar ratio of Mg in the alloy	1.11	7	0.11	120
Comparative example 14	Mg_1.9Al_0.1Ni	1.00	Example 21	Mg₂Ag_0.22Ni_1.11	17	0.27	75	1.11	7	0.11	120
Comparative example 14	Mg_1.9Al_0.1Ni	1.00	Example 22	Mg₂Co_1.24In_0.35	17	0.27	75	1.59	8	0.14	110
Example 23	Mg₂Co_1.11In_0.11	1.22	Example 22	Mg₂Co_1.24In_0.35	9	0.15	150	1.59	8	0.14	110
Example 23	Mg₂Co_1.11In_0.11	1.22	Example 24	Mg_1.5Ca_0.5Ni_1.5Ag_0.5	9	0.15	150	2.00	7	0.19	115
Example 25	Mg_1.76Ca_0.5Ni_1.5Ag_0.38	1.88	Example 24	Mg_1.5Ca_0.5Ni_1.5Ag_0.5	7	0.15	110	2.00	7	0.19	115
Example 25	Mg_1.76Ca_0.5Ni_1.5Ag_0.38	1.88	Example 26	Mg₂Ni_1.25In_0.25W_0.25	7	0.15	110	1.75	6	0.11	125
Comparative example 3	Mg₂Ni	1.00	Example 26	Mg₂Ni_1.25In_0.25W_0.25	18	0.27	140	1.75	6	0.11	125
Comparative example 3	Mg₂Ni	1.00	Comparative example 15	Mg₂Co	18	0.27	140	1.00	58	0.87	170

As is apparent from Table 7, it is possible to achieve a reduction in the hydrogen absorption temperature and an improvement in the chemical stability of the alloy using the hydrogen occluding alloys of examples 21 to 26 as compared with comparative examples 3, 14 and 15. (examples 27 to 38 and comparative example 16)

In Table 8, 13 hydrogen storage alloys are listed, each having (Mg)_1-xM3x)_20-yM4(x is defined as 0<x<0.5, y is defined as 0<y<18). They are placed in the sample containers 33, respectively. Then, the first valve 37 is closed₁Opening the second valve 37₂And a third valve 37₃In this case, the vacuum pump 35 is actuated to evacuate air from the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33. Then the second valve 37 is closed₂And a third valve 37₃Opening the first valve 37₁So that the hydrogen gas in the hydrogen cylinder 31 enters the pipe 32, the branch pipe 34, the accumulator 38 and the sample container 33, thereby completing hydrogen gas replacement. Then the first valve 37 is closed₁The amount of hydrogen gas input at this time is calculated from the system pressure indicated by the pressure gauge 36. Then the second valve 37 is opened₂The hydrogen gas thus supplied is introduced into the sample container 33. The temperature of the sample container 33 is detected by the thermocouple 40. At this time, the thermocouple 40 and the temperature controller 42 are controlled to keep the temperature inside the sample container 33 constant. In this case, the pressure change in the sample container 33 can be measured by the pressure gauge 36 and recorded on the automatic recorder 43.

The hydrogen absorption rate at 100C was determined for each hydrogen storage alloy by using the aforementioned test instrument. This hydrogen absorption rate is expressed as the amount of hydrogen (wt%) absorbed by the hydrogen storage alloy within 1 hour of the predetermined amount of hydrogen gas being input into the sample container. The results are shown in Table 8 below.TABLE 8

	Hydrogen-storage alloy	Rate of hydrogen absorption
	Hydrogen-storage alloy	Rate of hydrogen absorption	Comparative example 16	Mg₄Ni	1.0
Example 27	(Mg_0.5V_0.5)₂₀Zn_0.3Ni_0.7	7.2	Comparative example 16	Mg₄Ni	1.0
Example 27	(Mg_0.5V_0.5)₂₀Zn_0.3Ni_0.7	7.2	Example 28	(Mg_0.85Mn_0.15)₁₇Ni_0.9Cu_0.1	6.6
Example 29	(Mg_0.8S_0.2)_7.8Ni	4.7	Example 28	(Mg_0.85Mn_0.15)₁₇Ni_0.9Cu_0.1	6.6
Example 29	(Mg_0.8S_0.2)_7.8Ni	4.7	Example 30	(Mg_0.7C_0.3)₆Ni_0.5Co_0.5	4.5
Example 31	(Mg_0.6Ru_0.4)₄Ni_0.3Fe_0.7	4.0	Example 30	(Mg_0.7C_0.3)₆Ni_0.5Co_0.5	4.5
Example 31	(Mg_0.6Ru_0.4)₄Ni_0.3Fe_0.7	4.0	Example 32	(Mg_0.9Pt_0.1)₅Si_0.2Ni_0.8	4.2
Example 33	(Mg_0.5pd_0.5)₈Cu	5.0	Example 32	(Mg_0.9Pt_0.1)₅Si_0.2Ni_0.8	4.2
Example 33	(Mg_0.5pd_0.5)₈Cu	5.0	Example 34	(Mg_0.8Au_0.1Al_0.1)₁₄Ni	6.2
Example 35	(Mg_0.99Mn_0.01)_7.8Ni_0.8Fe_0.2	4.9	Example 34	(Mg_0.8Au_0.1Al_0.1)₁₄Ni	6.2
Example 35	(Mg_0.99Mn_0.01)_7.8Ni_0.8Fe_0.2	4.9	Example 36	(Mg_0.7Ti_0.3)₁₇Ni_0.3Co_0.7	6.5
Example 37	(Mg_0.9Nb_0.1)₁₀Ni	5.3	Example 36	(Mg_0.7Ti_0.3)₁₇Ni_0.3Co_0.7	6.5
Example 37	(Mg_0.9Nb_0.1)₁₀Ni	5.3	Example 38	(Mg_0.8Ag_0.2)₈Ni_0.8Fe_0.2	5.0

As is apparent from Table 8, by using the hydrogen occluding alloys of examples 27 to 28 having an increased magnesium content, the hydrogen absorption amount of the alloy can be significantly increased and the hydrogen absorption characteristics of the alloy can be improved, as compared with the hydrogen occluding alloy of comparative example 16. (examples 39 to 50 and comparative example 17)

Thirteen powdered hydrogen storage alloys, each having (Mg), are listed in Table 9_1-xM3x)_20-yM4(x is defined as 0<x<0.5, and y is defined as 0. ltoreq. y<18). First, these powdery alloys were mixed with electrolytic copper powder at a weight ratio of 1: 1, respectively, and 1g of the resulting mixture was pressed for 5 minutes in a pellet molding apparatus (inner diameter: 10mm) under a pressure of 10,000kg, thereby obtaining pellets. Then the product is mixed withThe particles were sandwiched between Ni screens, spot welded and compacted. Subsequently, the compact was connected to the Ni wire by spot welding. Thus, 13 different kinds of hydrogen absorbing alloy electrodes (negative electrodes) were produced.

The hydrogen absorbing alloy electrodes thus prepared were immersed in 8N aqueous potassium hydroxide solutions together with sintered nickel counter electrodes, respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, each cycle included the steps of charging at a current of 100mA per gram of hydrogen occluding alloy for 10 hours and, after 10 minutes, discharging at a current of 20mA per gram of hydrogen occluding alloy until the voltage relative to the mercury oxide electrode dropped to-0.5V. This charge/discharge cycle was repeated to obtain the maximum discharge capacity of each negative electrode. The results of this cycling test are set forth in Table 9 below.TABLE 9

	Hydrogen-storage alloy	Discharge capacity (mAh/g)
	Hydrogen-storage alloy	Discharge capacity (mAh/g)	Comparative example 17	Mg_3.5Ni	15
Example 39	(Mg_0.8Ta_0.2)_7.8Cu_0.4Ni_0.6	410	Comparative example 17	Mg_3.5Ni	15
Example 39	(Mg_0.8Ta_0.2)_7.8Cu_0.4Ni_0.6	410	Example 40	(Mg_0.6Os_0.4)₉Ni_0.5Cu_0.5	420
EXAMPLE 41	(Mg_0.7Re_0.3)₁₅Si_0.4Ni_0.6	710	Example 40	(Mg_0.6Os_0.4)₉Ni_0.5Cu_0.5	420
EXAMPLE 41	(Mg_0.7Re_0.3)₁₅Si_0.4Ni_0.6	710	Example 42	(Mg_0.98Ir_0.02)₁₀Ni_0.6Co_0.4	425
Example 43	(Mg_0.8Rh_0.2)₈Ni	405	Example 42	(Mg_0.98Ir_0.02)₁₀Ni_0.6Co_0.4	425
Example 43	(Mg_0.8Rh_0.2)₈Ni	405	Example 44	(Mg_0.97C_0.03)₃Ni_0.2Fe_0.8	120
Example 45	(Mg_0.9Ag_0.1)₁₄Cu	640	Example 44	(Mg_0.97C_0.03)₃Ni_0.2Fe_0.8	120
Example 45	(Mg_0.9Ag_0.1)₁₄Cu	640	Example 46	(Mg_0.5Al_0.5)_7.8Ni	420
Example 47	(Mg_0.94P_0.06)₁₀Ni_0.6Co_0.4	415	Example 46	(Mg_0.5Al_0.5)_7.8Ni	420
Example 47	(Mg_0.94P_0.06)₁₀Ni_0.6Co_0.4	415	Example 48	(Mg_0.9In_0.1)₈Ni	390
Example 49	(Mg_0.8Pt_0.2)₅Ni	180	Example 48	(Mg_0.9In_0.1)₈Ni	390
Example 49	(Mg_0.8Pt_0.2)₅Ni	180	Example 50	(Mg_0.8Au_0.2)₃Ni_0.2Fe_0.8	135

As is apparent from Table 9), it is apparent that the compound represented by the general formula (V) (Mg)_1-xM3_x)_20-yM4) and a hydrogen storage alloy having a higher Mg content than that of the hydrogen storage alloy of comparative example 17 is effective in increasing the hydrogen absorption amount of the alloy and significantly improving the hydrogen absorption characteristics of the alloy. (examples 51 to 60 and comparative example 18)

Table 10 below lists compounds having (Mg)_1-xM3_x)_20-yM4(x is defined as 0<x<0.5, y is defined as 0. ltoreq. y<18) of 11 alloys of the general formula (V), and the hydrogen absorption amounts at 25 ℃ of the 11 hydrogen occluding alloys were measured by using a hydrogen absorption/desorption characteristics testing apparatus as shown in FIG. 6, respectively. In this case, the amount of hydrogen absorbed by the hydrogen storage alloy (wt%) is expressed as the amount of hydrogen absorbed within 20 hours after the predetermined amount of hydrogen gas is input into the sample container. The results are shown in Table 10 below.Watch 10

	Hydrogen-storage alloy	Amount of hydrogen absorbed (wt％)
	Hydrogen-storage alloy	Amount of hydrogen absorbed (wt％)	Comparative example 18	Mg_3.2Ni	0.5
Example 51	(Mg_0.9Y_0.1)_7.8Zn_0.1Ni_0.9	4.8	Comparative example 18	Mg_3.2Ni	0.5
Example 51	(Mg_0.9Y_0.1)_7.8Zn_0.1Ni_0.9	4.8	Example 52	(Mg_0.7Sc_0.3)₅Cu_0.8Ni_0.2	4.2
Example 53	(Mg_0.6La_0.4)₃Ni_0.5Co_0.5	3.1	Example 52	(Mg_0.7Sc_0.3)₅Cu_0.8Ni_0.2	4.2
Example 53	(Mg_0.6La_0.4)₃Ni_0.5Co_0.5	3.1	Example 54	(Mg_0.6Hf_0.2Pt_0.2)₄Fe	4.0
Example 55	(Mg_0.5Zr_0.5)₁₀Cu_0.5Ni_0.5	5.3	Example 54	(Mg_0.6Hf_0.2Pt_0.2)₄Fe	4.0
Example 55	(Mg_0.5Zr_0.5)₁₀Cu_0.5Ni_0.5	5.3	Example 56	(Mg_0.8Pb_0.2)₅Ni	4.2
Example 57	(Mg_0.9Y_0.1)₈Sn_0.4Ni_0.6	5.0	Example 56	(Mg_0.8Pb_0.2)₅Ni	4.2
Example 57	(Mg_0.9Y_0.1)₈Sn_0.4Ni_0.6	5.0	Example 58	(Mg_0.4In_0.4W_0.2)_7.8Ni	4.8
Example 59	(Mg_0.7La_0.3)₁₇Cu_0.3Ni_0.7	6.6	Example 58	(Mg_0.4In_0.4W_0.2)_7.8Ni	4.8
Example 59	(Mg_0.7La_0.3)₁₇Cu_0.3Ni_0.7	6.6	Example 60	(Mg_0.9Tl_0.1)₉Si_0.05Co_0.95	5.0

As is apparent from Table 10, the use of the hydrogen occluding alloy containing Mg in an amount higher than that of the hydrogen occluding alloy of comparative example 17 is effective inincreasing the hydrogen absorption amount of the alloy and remarkably improving the hydrogen absorption characteristics of the alloy. (examples 61 to 71 and comparative example 19)

Table 11 below lists compounds having (Mg)₁-xM3x)_20-yM4(And x is defined as 0<x<0.5, and y is defined as 0. ltoreq. y<18). These powdery alloys were first mixed with electrolytic copper powder in a weight ratio of 1: 1, respectively, and 1g of the resulting mixture was pressed in a pellet molding apparatus (inner diameter: 10mm) under a pressure of 10,000kg for 5 minutes to obtain pellets. The particles were then sandwiched between Ni screens, spot welded and compacted. The compact was then spot welded to a Ni wire. Thus, 12 different kinds of hydrogen storage alloy electrodes (negative electrodes) were produced.

The hydrogen absorbing alloy electrodes thus prepared were immersed in an 8N aqueous solution of potassium hydroxide together with a sintered nickel counter electrode, respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, each cycle included the steps of charging at a current of 100mA per gram of hydrogen storage alloy for 10 hours, and after 10 minutes, discharging at a current of 20mA per gram of hydrogen storage alloy until the voltage relative to the mercury oxide electrode dropped to-0.5V. This charge/discharge cycle was repeated to obtain the maximum discharge capacity of each negative electrode. The results of this cycling test are set forth in Table 11 below.TABLE 11

	Hydrogen-storage alloy	Discharge capacity (mAh/g)
	Hydrogen-storage alloy	Discharge capacity (mAh/g)	Comparative example 19	Mg_4.0Ni	25
Example 61	(Mg_0.9Ce_0.1)₈Zn_0.3Ni_0.7	420	Comparative example 19	Mg_4.0Ni	25
Example 61	(Mg_0.9Ce_0.1)₈Zn_0.3Ni_0.7	420	Example 62	(Mg_0.85La_0.05C_0.1)₁₃Fe	510
Example 63	(Mg_0.7Pr_0.3)_7.8Ni	410	Example 62	(Mg_0.85La_0.05C_0.1)₁₃Fe	510
Example 63	(Mg_0.7Pr_0.3)_7.8Ni	410	Example 64	(Mg_0.25Zr_0.4Mo_0.35)₃Ni	125
Example 65	(Mg_0.8Sm_0.2)₅Si_0.3Cu_0.7	200	Example 64	(Mg_0.25Zr_0.4Mo_0.35)₃Ni	125
Example 65	(Mg_0.8Sm_0.2)₅Si_0.3Cu_0.7	200	Example 66	(Mg_0.5Y_0.4Al_0.1)₄Co	180
Example 67	(Mg_0.9Zr_0.1)₉Si_0.2Ni_0.8	390	Example 66	(Mg_0.5Y_0.4Al_0.1)₄Co	180
Example 67	(Mg_0.9Zr_0.1)₉Si_0.2Ni_0.8	390	68 examples of the present invention	(Mg_0.8In_0.2)_7.8Zn_0.4Cu_0.6	370
Example 69	(Mg_0.99Hf_0.01)₃Sn_0.2Ni_0.8	110	68 examples of the present invention	(Mg_0.8In_0.2)_7.8Zn_0.4Cu_0.6	370
Example 69	(Mg_0.99Hf_0.01)₃Sn_0.2Ni_0.8	110	Example 70	(Mg_0.8Hf_0.2)₄Ni	175
Example 71	(Mg_0.8Y_0.2)₈Cu_0.5Ni_0.5	390	Example 70	(Mg_0.8Hf_0.2)₄Ni	175

As is apparent from Table 11, the negative electrodes (examples 61 to 71) composed of the hydrogen occluding alloy represented by the general formula (V) of (Mg1-xM3x)20-yM4 and containing a higher Mg amount were effective in increasing the hydrogen absorption amount of the alloy and remarkably improving the hydrogen absorption characteristics of the alloy, as compared with the hydrogen occluding alloy of comparative example 19.

(examples 72 to 74)

Three hydrogen storage alloys of the general formula (VI) having the formula (Mg1-xM3x)20-yM4(x is defined as 0<x<0.5, and y is defined as 0. ltoreq. y<18) are listed in Table 12 below. By using the hydrogen absorption/desorption characteristic test apparatus as shown in fig. 6, the hydrogen absorption amounts at 25 ℃. In this case, the amount of hydrogen (wt%) absorbed by the hydrogen storage alloy is expressed as the hydrogen absorption amount within 20 hours of inputting a predetermined amount of hydrogen gas into the sample container. The results are shown in Table 12 below.

Further, the above powdery hydrogen occluding alloy was mixed with electrolytic copper powder in a weight ratio of 1: 1, respectively. In a pellet molding apparatus, 1g of the resulting mixture was pressed with a pressure of 10,000kg for 5 minutes to obtain pellets. The particles were then sandwiched between Ni screens, spot welded and compacted. The compact was connected to the Ni wire by spot welding. Thus, 3 different kinds of hydrogen absorbing alloy electrodes (negative electrodes) were prepared.

The hydrogen absorbing alloy electrodes thus prepared were immersed in an 8N aqueous solution of potassium hydroxide together with a sintered nickel counter electrode, respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, each cycle included the steps of charging at a current of 100mA per gram of hydrogen storage alloy for 10 hours, and after 10 minutes, discharging at a current of 20mA per gram of hydrogen storage alloy until the voltage relative to the mercuric oxide electrode dropped to-0.5V. This charge/discharge cycle was repeated to obtain the maximum discharge capacity of each negative electrode. The results of this cycling test are set forth in Table 12 below.TABLE 12

	Hydrogen-storage alloy	Amount of hydrogen absorption (wt%)	Discharge capacity (mAh/g)
	Hydrogen-storage alloy	Amount of hydrogen absorption (wt%)	Discharge capacity (mAh/g)	Example 72	(Mg_0.85Ca_0.15)₁₆Ni_0.8Cu_0.2	6.4	650
Example 73	(Mg_0.7Ca_0.3)₁₅Fe_0.3Co_0.7	6.0	720	Example 72	(Mg_0.85Ca_0.15)₁₆Ni_0.8Cu_0.2	6.4	650
Example 73	(Mg_0.7Ca_0.3)₁₅Fe_0.3Co_0.7	6.0	720	Example 74	(Mg_0.8Sr_0.2)₁₁Co_0.05Cu_0.95	5.5	580

As is apparent from Table 12, in the hydrogen occluding alloys of examples 72 to 74 in which the position of Mg was replaced by M5 or an element having an atomic radius of from 1 to 1.5 times as large as that of Mg (except for the element having a higher electronegativity than Mg), and M6 was at least one element of Ni, Fe, Co, Cu, Zn, Sn and Si, these alloys significantly increased the hydrogen absorption amount and improved the hydrogen absorption characteristics.

It is also understood that the negative electrode comprising the above hydrogen occluding alloy can increase its discharge capacity and improve its charge/discharge characteristics, respectively. (example 75)

Containing Mg₂Ni hydrogen storage alloy was placed in a round-bottomed flask equipped with a stirrer, a dropping funnel and a cooling tube, air in the flask was evacuated by a vacuum pump, and the projecting portion was heated by a heating gun and then filled with argon gas. Subsequently, THF was added to the flask while allowing argon to flow thereinto. 1-bromo-3-ethane was slowly dropped into the flask through a dropping funnel with stirring, and the hydrogen occluding alloy was allowed to react with 1-bromo-3-ethane. The stirring was stopped at the end of the dropwise addition to allow the hydrogen absorbing alloy to precipitate. And then filtering the precipitated hydrogen storage alloy to obtain the surface-modified hydrogen storage alloy.

The hydrogen absorption characteristics of the surface-modified and non-surface-modified hydrogen occluding alloys were measured by using a hydrogen absorption/desorption characteristics measuring apparatus shown in FIG. 6. This test was performed by controlling the pressure change in the reaction vessel when a predetermined volume of hydrogen was added to the reaction vessel.

Specifically, each hydrogen absorbing alloy is first placed in the sample container 33 separately. Then, the first valve 37 is closed₁Opening the second valve 37₂And a third valve 37₃In this case, the vacuum pump 35 is actuated to evacuate air from the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33. Then, the second valve 37 is closed₂And a third valve 37₃Opening the first valve 37₁So that the hydrogen gas in the hydrogen cylinder 31 enters the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33, thus completing hydrogen gas replacement. Then, while the first valve 371 is closed, the amount of hydrogen gas to be supplied is calculated from the pressure displayed on the pressure gauge 36. Thereafter, the second valve 37 is opened₂Allowing the input hydrogen to enter the sample containerIn 33, the temperature of the sample container 33 is detected by a thermocouple. At this time, the thermocouple 40 and the temperature controller 42 are controlled to keep the temperature inside the sample container 33 constant. The pressure change in the sample container 33 is observed from the pressure gauge 36 and recorded in the automatic recorder 43. Mg before and after surface modification at 25 DEG C₂The pressure change of the Ni hydrogen storage alloy due to hydrogen absorption (the temperature decrease is caused by hydrogen absorption by the hydrogen storage alloy) is shown in fig. 9.

As is apparent from fig. 9, in the case of the hydrogen occluding alloy which is not surface-modified, no significant pressure change is found even if a predetermined hydrogen pressure is applied, thereby maintaining a constant pressure. However, the book of changesSurface modified Mg₂In the case of a Ni hydrogen storage alloy, the application of a predetermined hydrogen pressure abruptly changes its internal pressure. It was thus confirmed that a large amount of hydrogen was absorbed by the alloy. In addition, the surface-modified hydrogen occluding alloy is likely to lower the hydrogen absorption temperature by about 200 ℃ as compared with the conventional hydrogen occluding alloy. That is, with conventional Mg₂For Ni hydrogen occluding alloys, the hydrogen absorption/desorption reaction will not occur or will be very slow unless the temperature is quite high (200 ℃ C. -300 ℃ C.). In contrast, when the surface-modified hydrogen occluding alloy as in example 75 is used, it is possible to conduct the hydrogen absorption/desorption reaction at around room temperature. (examples 76 to 106)

Hydrogen occluding alloys having the compositions listed in the following tables 13 to 15 were treated in the same surface modification method as example 75. The change in their hydrogen absorption characteristics was tested before and after surface modification. In this test, a hydrogen absorption/desorption characteristic test apparatus as shown in fig. 6 was used. The results are shown in the following tables 13 to 15, in which the symbol x represents the number of hydrogen atoms, i.e., MHx absorbed in the hydrogen occluding alloy.Watch 13

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 75	Mg₂Ni	0	3.0
Example 76	Mg₂Cu	0	2.0	Example 75	Mg₂Ni	0	3.0
Example 76	Mg₂Cu	0	2.0	Example 77	Mg₂Co	0	3.5
Example 78	Mg₂Fe	0	4.0	Example 77	Mg₂Co	0	3.5
Example 78	Mg₂Fe	0	4.0	Example 79	LaNi₅	0.1	6.0
Example 80	MnNi₅	0	3.0	Example 79	LaNi₅	0.1	6.0
Example 80	MnNi₅	0	3.0	Example 81	CaNi₅	0	4.0
Example 82	TiFe	0.1	0.5	Example 81	CaNi₅	0	4.0
Example 82	TiFe	0.1	0.5	Example 83	TiCo	0	0.5
Example 84	ZrMn₂	0.1	3.0	Example 83	TiCo	0	0.5
Example 84	ZrMn₂	0.1	3.0	Example 85	ZrNi₂	0.1	3.0

TABLE 14

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 86	Mg₂Ni_0.8Co_0.2	0	2.3
Example 87	Mg₂Ni_0.9Co_0.2	0	2.9	Example 86	Mg₂Ni_0.8Co_0.2	0	2.3
Example 87	Mg₂Ni_0.9Co_0.2	0	2.9	Example 88	Mg_2.1Ni_1.8Fe_0.1	0	3.0
Example 89	Mg₂Ni_0.7Mo_0.2Rh_0.2	0	3.1	Example 88	Mg_2.1Ni_1.8Fe_0.1	0	3.0
Example 89	Mg₂Ni_0.7Mo_0.2Rh_0.2	0	3.1	Example 90	Mg_1.8Zr_0.2Ni	0	2.5
Example 91	Mg_1.3Y_0.5Ni	0	2.0	Example 90	Mg_1.8Zr_0.2Ni	0	2.5
Example 91	Mg_1.3Y_0.5Ni	0	2.0	Example 92	Mg₂Ir_0.1Ni	0	2.4
Example 93	Mg_1.9Al_0.1Ni_0.9Mn_0.2	0	3.5	Example 92	Mg₂Ir_0.1Ni	0	2.4
Example 93	Mg_1.9Al_0.1Ni_0.9Mn_0.2	0	3.5	Example 94	Mg₂Cu_0.5Cd_0.5	0	1.6
Example 95	Mg₂Cu_0.8Pd_0.4	0	2.0	Example 94	Mg₂Cu_0.5Cd_0.5	0	1.6

Watch 15

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 96	Mg₂Ti_0.1Ni	0	2.3
Example 97	Mg₂Nb_0.1Ni_1.2	0	3.1	Example 96	Mg₂Ti_0.1Ni	0	2.3
Example 97	Mg₂Nb_0.1Ni_1.2	0	3.1	Example 98	Mg₂Ta_0.1Ni_1.8	0	2.8
Example 99	LaAl_0.3Ni_3.8Mn_0.4Co_0.5	0.5	5.0	Example 98	Mg₂Ta_0.1Ni_1.8	0	2.8
Example 99	LaAl_0.3Ni_3.8Mn_0.4Co_0.5	0.5	5.0	Example 100	NmAl_0.6Ni_3.7Mn_0.3Zr_0.4	1.0	5.0
Example 101	CaAl_0.4Ni_4.0Mn_0.5Si_0.1	0.7	4.5	Example 100	NmAl_0.6Ni_3.7Mn_0.3Zr_0.4	1.0	5.0
Example 101	CaAl_0.4Ni_4.0Mn_0.5Si_0.1	0.7	4.5	Example 102	TiFe_0.4Mn_0.5	0.2	2.1
Example 103	TiMn_1.6Co_0.1	0	2.6	Example 102	TiFe_0.4Mn_0.5	0.2	2.1
Example 103	TiMn_1.6Co_0.1	0	2.6	Example 104	ZrCo_1.1Mn_1.3	0.2	3.0
Example 105	Zr_0.6Ti_0.4V_0.6Ni_1.1Mn_0.2	0.1	3.5	Example 104	ZrCo_1.1Mn_1.3	0.2	3.0
Example 105	Zr_0.6Ti_0.4V_0.6Ni_1.1Mn_0.2	0.1	3.5	Example 106	ZrMn_0.6V_0.2Ni_1.5Co_0.1	0.2	3.1

As is apparent from tables 13 to 15, when the surface of the hydrogen occluding alloy is modified, the surface thereof is activated, and thus the hydrogen absorption characteristics of the alloy can be improved.

(example 107)

Mg₂Ni hydrogen storage alloy and stainless steel ball are put together into a reactorA stainless steel container covered, and thereafter filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water. After sealing with an O-ring, the stainless steel vessel was ball milled (a mechanical treatment) for 100 hours at a rotational speed of 200 rpm.

The hydrogen absorption characteristics of the hydrogen occluding alloy which was mechanically treated and which was not mechanically treated were measured by a hydrogen absorption/desorption characteristics measuring apparatus shown in FIG. 6. The test was conducted by controlling the pressure change in the reaction vessel when a predetermined volume of hydrogen was fed into the reaction vessel.

Specifically, each hydrogen occluding alloy is first charged into the sample container 33, and then the first valve 37 is closed₁Opening the second valve 37₂And a third valve 37₃. In this case, the vacuum pump 35 is actuated to evacuate air from the piping 32, the branch pipe 34, the accumulator 38, and the sample container 33. Then the second valve 37 is closed₂And a third valve 37₃Opening the first valve 37₁So that the hydrogen gas in the hydrogen cylinder 31 is taken into the piping 32, the branch pipe 34, the accumulator 38 and the sample container 33, thereby completing hydrogen gas replacement. Subsequently, the first valve 37 is closed₁At the same time, the amount of hydrogen gas to be input is calculated from the pressure indicated by the pressure gauge 36. Then the second valve 37 is opened₂The hydrogen gas is introduced into the sample container 33, and the temperature of the sample container 33 is detected by the thermocouple 40. At the same time, thermocouple 40 and temperature controller 42 are controlled so as to keep the temperature inside sample container 33 constant. At this time, the pressure change in the sample container 33 is measured by the pressure gauge 36 and recorded in the automatic recorder 43.

The hydrogen absorption characteristics of the hydrogen occluding alloy particles before and after mechanical treatment at 25 ℃ are shown in Table 16 below.

(example 108)

0.5 mol of Mg₂The Ni hydrogen storage alloy was mixed with 0.5 mol of Ni powder as a catalyst nucleus, and the resulting mixture was put into a stainless steel vessel with a double lid together with a stainless steel ball. Thereafter, the vessel is filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water, and after sealing with a packing, the vessel is made of stainless steelThe vessel was ball milled (a mechanical treatment) for 100 hours at a rotational speed of 200 rpm.

The Mg treated mechanically and not treated mechanically was measured by a hydrogen absorption/desorption characteristics testing apparatus shown in FIG. 6₂Hydrogen absorption characteristics of the Ni hydrogen storage alloy. The hydrogen absorption characteristics of this hydrogen occluding alloy at 25 ℃ are shown in Table 16 below. Example 109-

Hydrogen occluding alloys having compositions listed in the following tables 16 to 19 were subjected to mechanical treatment in the same manner as in example 107, and their changes in hydrogen absorption characteristics before and after surface modification were measured. In this test, a hydrogen absorption/desorption characteristic test apparatus shown in fig. 6 was used. The results are shown in tables 16 to 19 below. In these tables, the symbol x represents the number of hydrogen, i.e., the number of absorbed MHx in the hydrogen storage alloy.TABLE 16

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 107	Mg₂Ni	0	3.0
Example 108	Mg₂Ni (Ni mixed)	0	3.5	Example 107	Mg₂Ni	0	3.0
Example 108	Mg₂Ni (Ni mixed)	0	3.5	Example 109	Mg₂Cu	0	2.5
Example 110	Mg₂Co	0	3.8	Example 109	Mg₂Cu	0	2.5
Example 110	Mg₂Co	0	3.8	Example 111	Mg₂Fe	0	4.4
Example 112	LaNi₅	0.1	6.0	Example 111	Mg₂Fe	0	4.4
Example 112	LaNi₅	0.1	6.0	Example 113	MmNi₅	0	3.5
Example 114	CaNi₅	0	4.5	Example 113	MmNi₅	0	3.5
Example 114	CaNi₅	0	4.5	Example 115	TiFe	0.1	1.6
Example 116	TiCo	0	1.8	Example 115	TiFe	0.1	1.6
Example 116	TiCo	0	1.8	Example 117	ZrNi₂	0.1	3.2
Example 118	ZrNi₂	0.1	3.6	Example 117	ZrNi₂	0.1	3.2

TABLE 17

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 119	Mg₂Ni_0.7Cu_0.3	0	2.9
Example 120	Mg₂Ni_0.9Co_0.2	0	3.4	Example 119	Mg₂Ni_0.7Cu_0.3	0	2.9
Example 120	Mg₂Ni_0.9Co_0.2	0	3.4	Example 121	Mg₂Ni_0.8Fe_0.1	0	3.5
Example 122	Mg₂Ni_0.7Rh_0.2Ru_0.2	0	3.7	Example 121	Mg₂Ni_0.8Fe_0.1	0	3.5
Example 122	Mg₂Ni_0.7Rh_0.2Ru_0.2	0	3.7	Example 123	Mg_1.9Zr_0.1Ni	0	3.0
Example 124	Mg_1.8Cr_0.1Ni	0	2.6	Example 123	Mg_1.9Zr_0.1Ni	0	3.0
Example 124	Mg_1.8Cr_0.1Ni	0	2.6	Example 125	Mg₂Mo_0.1Ni	0	2.4
Example 126	Mg_1.9V_0.1Ni_0.9Mn_0.2	0	3.4	Example 125	Mg₂Mo_0.1Ni	0	2.4
Example 126	Mg_1.9V_0.1Ni_0.9Mn_0.2	0	3.4	Example 127	Mg₂Cu_0.5W_0.5	0	1.6
Example 128	Mg₂Cu_0.7Cd_0.4	0	2.0	Example 127	Mg₂Cu_0.5W_0.5	0	1.6

Watch 18

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 129	Mg₂Y_0.1Ni_1.1	0	2.3
Example 130	Mg₂Ir_0.1Ni_1.5	0	3.1	Example 129	Mg₂Y_0.1Ni_1.1	0	2.3
Example 130	Mg₂Ir_0.1Ni_1.5	0	3.1	Example 131	Mg₂Pt_0.1Ni_1.9	0	2.8
Example 132	LaAl_0.3Ni_3.5Mn_0.4Co_0.7	0.5	6.0	Example 131	Mg₂Pt_0.1Ni_1.9	0	2.8
Example 132	LaAl_0.3Ni_3.5Mn_0.4Co_0.7	0.5	6.0	Example 133	MmAl_0.3Ni_4.1Mn_0.3Co_0.3	1.0	6.0
Example 134	CaAl_0.3Ni_4.3Mn_0.4	0.6	5.5	Example 133	MmAl_0.3Ni_4.1Mn_0.3Co_0.3	1.0	6.0
Example 134	CaAl_0.3Ni_4.3Mn_0.4	0.6	5.5	Example 135	TiFe_0.6Mn_0.3	0.3	2.1
Example 136	TiMn_0.6Co_0.4	0	2.5	Example 135	TiFe_0.6Mn_0.3	0.3	2.1
Example 136	TiMn_0.6Co_0.4	0	2.5	Example 137	ZrCo_0.9Mn_1.1	0.1	3.5
Example 138	Zr_0.5Ti_0.5V_0.7Ni_1.3	0.2	3.9	Example 137	ZrCo_0.9Mn_1.1	0.1	3.5
Example 138	Zr_0.5Ti_0.5V_0.7Ni_1.3	0.2	3.9	Example 139	ZrMn_0.5V_0.3Ni_1.5	0.1	3.4

Watch 19

	Hydrogen-storage alloy	X (before treatment)	X (after treatment)
	Hydrogen-storage alloy	X (before treatment)	X (after treatment)	Example 140	(Mg_0.8Al_0.2)₃Ni	0	2.0
Example 141	(Mg_0.6V_0.4)₈Fe_0.7Cu_0.3	0	2.6	Example 140	(Mg_0.8Al_0.2)₃Ni	0	2.0
Example 141	(Mg_0.6V_0.4)₈Fe_0.7Cu_0.3	0	2.6	Example 142	(Mg_0.5Ba_0.25Cr_0.25)₁₀Co	0	3.1
Example 143	(Mg_0.9Mn_0.05Ti_0.05)₄Si_0.6Zn_0.4	0	2.8	Example 142	(Mg_0.5Ba_0.25Cr_0.25)₁₀Co	0	3.1
Example 143	(Mg_0.9Mn_0.05Ti_0.05)₄Si_0.6Zn_0.4	0	2.8	Example 144	(Mg_0.7Mo_0.3)₅Cu_0.8Ni_0.2	0	2.5
Example 145	(Mg_0.8Ca_0.2)₁₁Ni	0	2.2	Example 144	(Mg_0.7Mo_0.3)₅Cu_0.8Ni_0.2	0	2.5
Example 145	(Mg_0.8Ca_0.2)₁₁Ni	0	2.2	Example 146	(Mg_0.5Sr_0.5)₆Co_0.5Fe_0.5	0	3.0
Example 147	(Mg_0.7Li_0.3)₇₂n_0.5Ni_0.5	0	2.1	Example 146	(Mg_0.5Sr_0.5)₆Co_0.5Fe_0.5	0	3.0
Example 147	(Mg_0.7Li_0.3)₇₂n_0.5Ni_0.5	0	2.1	Example 148	(Mg_0.8La_0.1Y_0.1)₁₅Cu	0	2.9
Example 149	(Mg_0.8Na_0.05K_0.15)₉Ni_0.9Cu_0.1	0	3.2	Example 148	(Mg_0.8La_0.1Y_0.1)₁₅Cu	0	2.9
Example 149	(Mg_0.8Na_0.05K_0.15)₉Ni_0.9Cu_0.1	0	3.2	Example 150	(Mg_0.6Sr_0.2La_0.2)₁₃Ni_0.8Cu_0.2Co_0.2	0	2.9

As is apparent from tables 16 to 19, mechanical treatment of the hydrogen occluding alloy activates the surface of the alloy, and therefore improves the hydrogen absorption characteristics of the hydrogen occluding alloy. (example 151)

The hydrogen occluding alloy powder prepared in example 108 was mixed with electrolytic copper powder in a weight ratio of 1: 1. In a pellet molding apparatus (inner diameter: 10mm), 1g of the resulting mixture was pressed by applying a pressure of 20 tons for 3 minutes to obtain pellets. The particles were then sandwiched between Ni screens, spot welded and compacted. Subsequently, the compact was connected to the Ni wire by spot welding. Thus, a hydrogen absorbing alloy electrode (negative electrode) was produced. Comparative example 20

Except using Mg without mechanical treatment₂A hydrogen storage alloy electrode (negative electrode) was produced in the same manner as in example 151, except that Ni hydrogen storage alloy was used as a raw material.

The negative electrodes of example 151 and comparative example 20 were immersed in an 8N aqueous potassium hydroxide solution together with a sintered nickel counter electrode, respectively, and then subjected to charge/discharge cycle testing at a temperature of 25 ℃. In this charge/discharge cycle test, 100mA of current was charged per gram of hydrogen storage alloy for 10 hours, and after 10 minutes, 100mA of current was discharged per gram of hydrogen storage alloy until the voltage dropped to-0.5V with respect to the mercuric oxide electrode. This charge/discharge cycle was repeated, and the result is shown in fig. 10. In fig. 10, symbol a indicates the charge/discharge characteristic curve of the negative electrode in comparative example 20 without mechanical treatment.Symbol B is the charge/discharge characteristic curve of the negative electrode subjected to mechanical treatment in example 151.

As is apparent from fig. 10, in the case of comparative example 20 (charge/discharge characteristic curve a), it was impossible to perform charge/discharge at normal temperature, indicating that it had no discharge capacity. In contrast, for example 151 (charge/discharge characteristic curve B), the discharge capacity was 750mAh/g at the first cycle. It is clear that it is possible to significantly increase the discharge capacity by mechanical treatment. Therefore, it can be generally considered that the mechanical treatment is a method effective for improving the discharge characteristics of a battery (equipped with a negative electrode containing a hydrogen storage alloy). Example 152-155 and comparative example 20

Mixing Mg₂The Ni hydrogen occluding alloy is put into a stainless steel container having a double lid together with a stainless steel ball, and then the stainless steel container is filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water content. After sealing with an O-ring, the stainless steel vessel was ball-milled for 2 hours, 50 hours, 200 hours, and 800 hours, respectively(a mechanical treatment) their rotation speed was controlled to 200 rpm. Thus, four kinds of surface-modified hydrogen occluding alloy powders were prepared.

A hydrogen absorbing alloy electrode (negative electrode) was prepared from the hydrogen absorbing alloy which had been mechanically treated and which had not been mechanically treated in the same manner as described in example 151. These negative electrodes were immersed in 8N aqueous potassium hydroxide solutions together with counter electrodes, respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, charging was performed in the same manner as in example 151. Their maximum discharge capacity was measured. The results of this charge/discharge cycle test are shown in Table 20, and the average particle diameters of these hydrogen occluding alloy powders and those of the hydrogen occluding alloy powder in comparative example 20 are also shown in Table 20. Watch 20

	Time of treatment (h)	Average particle size Diameter of (μm)	Discharge capacity (mAh/g)
	Time of treatment (h)	Average particle size Diameter of (μm)	Discharge capacity (mAh/g)	Comparative example 20	0	80	0
Example 152	2	20	115	Comparative example 20	0	80	0
Example 152	2	20	115	Example 153	50	6	523
Example 154	200	2	617	Example 153	50	6	523
Example 154	200	2	617	Example 155	800	1	658

As is apparent from Table 20, the average particle diameter of the hydrogen occluding alloy decreases proportionally with the increase in the mechanical treatment time. It is therefore possible to increase the discharge capacity.

(example 156-162 and comparative example 20)

Mg₂The Ni hydrogen occluding alloy is put into a stainless steel container having a double lid together with a stainless steel ball, and then the stainless steel container is filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water. After sealing with an O-ring, the stainless steel container was ball milled (a mechanical treatment) for 3 hours, 40 hours, 300 hours, 650 hours, 800 hours, 900 hours and 1000 hours, respectively. Their rotation speed was controlled to 200 rpm. Thus, seven kinds of surface-modified hydrogen-absorbing alloy powders were prepared.

The same procedure was followed as in example 151 except that the hydrogen occluding alloy was mechanically treated and not mechanically treatedThe method prepares the hydrogen storage alloy electrode (cathode). These negative electrodes were immersed in 8N aqueous potassium hydroxide solutions together with a counter electrode (sintered nickel electrode), respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, charging was carried out in the same manner as in example 151, and their maximum discharge capacity was measured. The results of this charge/discharge cycle test are set forth in Table 21. Delta (2 theta) of the Hydrogen occluding alloys in example 156-162 and comparative example 20₂) (the half-widths of at least one of the three strongest lines in the X-ray diffraction pattern obtained using CuK α radiation as the radiation source) are also shown in Table 21. Table 21

	Treatment time (h)	Δ(2θ2) (°)	Discharge capacity (mAh/g)
	Treatment time (h)	Δ(2θ2) (°)	Discharge capacity (mAh/g)	Comparative example 20	0	0.1	0
Example 156	3	0.5	142	Comparative example 20	0	0.1	0
Example 156	3	0.5	142	Example 157	40	1.2	503
Example 158	300	3.4	631	Example 157	40	1.2	503
Example 158	300	3.4	631	Example 159	650	5.1	649
Example 160	800	9.5	653	Example 159	650	5.1	649
Example 160	800	9.5	653	Example 161	900	25.1	630
Example 162	1000	41.3	535	Example 161	900	25.1	630

As is apparent from Table 21, as the mechanical treatment time increased, the crystal grain size of the hydrogen occluding alloy powder was proportionally decreased while increasing Δ (2 θ)₂) The value is obtained. It is thus possible to increase the discharge capacity.

(example 163-167 and comparative example 20)

Mixing Mg₂The Ni hydrogen occluding alloy is put into a stainless steel container having a double lid together with a stainless steel ball, and then the stainless steel container is filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water. After sealing with an O-ring, the stainless steel container was ball-milled (a mechanical treatment) for 0.5 hours, 2.5 hours, 15 hours, 250 hours, and 700 hours, respectively. Their rotation speed was controlled to 200 rpm. Thus, 5 kinds of surface-modified hydrogen absorbing alloy powders were prepared.

The hydrogen occluding alloy electrode (negative electrode) was prepared in the same manner as in example 151 using the hydrogen occluding alloy which had been mechanically treated and had not been mechanically treated. These negative electrodes were immersed in 8N aqueous potassium hydroxide solutions together with a counter electrode (sintered nickel electrode), respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃. In this charge/discharge cycle test, charging was carried out in the same manner as in example 151, and their maximum discharge capacity was measured. The results of the charge-discharge cycle test and the grain sizes of the hydrogen occluding alloys in example 163-167 and comparative example 20 are shown in Table 22 below. TABLE 22

	Time of treatment (h)	Size of crystal grain (nm)	Discharge capacity (mAh/g)
	Time of treatment (h)	Size of crystal grain (nm)	Discharge capacity (mAh/g)	Comparative example 20	0	111.5	0
Example 163	0.5	56.2	13	Comparative example 20	0	111.5	0
Example 163	0.5	56.2	13	Example 164	2.5	37.5	124
Example 165	15	23.2	323	Example 164	2.5	37.5	124
Example 165	15	23.2	323	Example 166	250	5.1	626
Example 167	700	2.2	651	Example 166	250	5.1	626

As is apparent from Table 22, as the mechanical treatment time increased, the crystal grain size of the hydrogen occluding alloy was proportionally decreased, and thus it was possible to increase the discharge capacity.

(example 168-172 and comparative examples 21 and 22)

Mg₂The Ni hydrogen storage alloy is placed in a stainless steel vessel with a double lid together with a stainless steel ball, and the stainless steel vessel is treated under seven atmosphere conditions, i.e., vacuum, inert gas (nitrogen, argon, or helium), hydrogen, oxygen, and air. After sealing with a packing, the stainless steel vessel was subjected to ball milling treatment (a mechanical treatment) for 100 hours, and their rotation speed was controlled to 200 rpm. Thus obtaining seven surface-modifiedA hydrogen storage alloy powder.

These mechanically treated hydrogen storage alloys were used to prepare hydrogen storage alloy electrodes (negative electrodes) in the same manner as described in example 151. These negative electrodes were immersed in 8N aqueous potassium hydroxide solutions together with a counter electrode (sintered nickel electrode), respectively, and then subjected to charge/discharge cycle tests at a temperature of 25 ℃ in the same manner as in example 151 and their maximum discharge capacities were measured. The results of this charge/discharge cycle test are set forth in Table 23. TABLE 23

	Treatment atmosphere	Discharge capacity (mAh/g)
	Treatment atmosphere	Discharge capacity (mAh/g)	Example 168	Argon (99.999%)	605
Example 169	Vacuum	402	Example 168	Argon (99.999%)	605
Example 169	Vacuum	402	Example 170	Nitrogen (99.999%)	513
Example 171	Helium (99.999%)	526	Example 170	Nitrogen (99.999%)	513
Example 171	Helium (99.999%)	526	Example 172	Hydrogen (99.99999%)	650
Comparative example 21	Oxygen (99.999%)	0	Example 172	Hydrogen (99.99999%)	650
Comparative example 21	Oxygen (99.999%)	0	Comparative example 22	Air (a)	0

As is apparent from examples 168-172 in Table 23, it is desirable to perform the mechanical treatment under vacuum or under an atmosphere of an inert gas or hydrogen. If the mechanical treatment is carried out under such an atmosphere, it is possible to increase the discharge capacity.

(example 173-219 and comparative example 20)

The hydrogen occluding alloys having the compositions listed in the following tables 24 to 27 were subjected to mechanical treatment under various conditions, thereby completing the surface treatment.

These mechanically treated hydrogen storage alloys were used to prepare hydrogen storage alloy negative electrodes in the same manner as described in example 151. Then, these negative electrodes were immersed in 8N aqueous potassium hydroxide solutions together with a counter electrode (sintered nickel electrode), respectively, and their maximum discharge capacities were measured by charge/discharge cycle tests at a temperature of 25 ℃ in the same manner as in example 151, and the results are shown in tables 24 to 27. The maximum discharge capacities of comparative example 20 are also shown in tables 24 to 27.Watch 24

	Having the function of storing hydrogen Alloy of properties	Additive agent	Treatment of Time of day (h)	Discharge capacity (mAh/g)
	Having the function of storing hydrogen Alloy of properties	Additive agent	Treatment of Time of day (h)	Discharge capacity (mAh/g)	Comparative example 20	Mg₂Ni	--	--	0
Examples 173	Mg₂Ni	Ni	100	751	Comparative example 20	Mg₂Ni	--	--	0
Examples 173	Mg₂Ni	Ni	100	751	Examples 174	Mg₂Ni	--	1	78
Examples 175	Mg₂Ni	--	25	452	Examples 174	Mg₂Ni	--	1	78
Examples 175	Mg₂Ni	--	25	452	Examples 176	Mg₂Ni	--	100	605
Examples 177	Mg₂Ni	Ni	500	825	Examples 176	Mg₂Ni	--	100	605
Examples 177	Mg₂Ni	Ni	500	825	Examples 178	Mg₂Ni	Co	100	752
Examples 179	Mg₂Mi	Fe	100	703	Examples 178	Mg₂Ni	Co	100	752
Examples 179	Mg₂Mi	Fe	100	703	Examples 180	Mg₂Ni	WCO₃	100	642
Examples 181	Mg₂Ni	IrO₂	100	750	Examples 180	Mg₂Ni	WCO₃	100	642
Examples 181	Mg₂Ni	IrO₂	100	750	Examples 182	Mg₂Cu	Cu	100	502

TABLE 25

	Having the function of storing hydrogen Alloy of properties	Additive agent	Treatment of Time of day (h)	Discharge capacity (mAh/g)
	Having the function of storing hydrogen Alloy of properties	Additive agent	Treatment of Time of day (h)	Discharge capacity (mAh/g)	Examples 183	Mg₂CO	CO	100	712
Examples 184	Mg₂Fe	Fe	100	745	Examples 183	Mg₂CO	CO	100	712
Examples 184	Mg₂Fe	Fe	100	745	Examples 185	LaNi₅	--	--	274
Examples 186	LaNi₅	Pt	100	321	Examples 185	LaNi₅	--	--	274
Examples 186	LaNi₅	Pt	100	321	Examples 187	LaNi₅	MoCo₃	100	325
Examples 188	LaNi₅	CoO	100	290	Examples 187	LaNi₅	MoCo₃	100	325
Examples 188	LaNi₅	CoO	100	290	Examples 189	MmNi₅	Rh	100	123
Examples 190	CaNi₅	MoNi₃	100	150	Examples 189	MmNi₅	Rh	100	123
Examples 190	CaNi₅	MoNi₃	100	150	Examples 191	TiFe	Pd	100	154
Examples 192	TiCo	FeO	100	111	Examples 191	TiFe	Pd	100	154
Examples 192	TiCo	FeO	100	111	Examples 193	ZrMn₂	Wni₃	100	148
Examples 194	ZrNi₂	Au	100	85	Examples 193	ZrMn₂	Wni₃	100	148

Watch 26

	Alloy with hydrogen storage characteristics	Additive agent	Time of treatment (h)	Discharge capacity (mAh/g)
	Alloy with hydrogen storage characteristics	Additive agent	Time of treatment (h)	Discharge capacity (mAh/g)	Example 195	Mg₂Ni_0.8Co_0.2	Ag	100	650
Example 196	Mg₂Ni_0.6Co_0.5	Ir	100	730	Example 195	Mg₂Ni_0.8Co_0.2	Ag	100	650
Example 196	Mg₂Ni_0.6Co_0.5	Ir	100	730	Example 197	Mg₂Ni_0.7Fe_0.2	V	50	360
Example 198	Mg₂Al_0.2Ni_0.8Mn_0.2	CoO	100	850	Example 197	Mg₂Ni_0.7Fe_0.2	V	50	360
Example 198	Mg₂Al_0.2Ni_0.8Mn_0.2	CoO	100	850	Example 199	Mg_1.9B_0.1Ni	NiO	100	605
Example 200	Mg_1.8C_0.1Ni	Pd	500	625	Example 199	Mg_1.9B_0.1Ni	NiO	100	605
Example 200	Mg_1.8C_0.1Ni	Pd	500	625	Example 201	Mg₂Au_0.1Ni	Cr	200	652
Example 202	Mg_1.8A1_0.2Ni_0.8Cr_0.2	Ni	100	800	Example 201	Mg₂Au_0.1Ni	Cr	200	652
Example 202	Mg_1.8A1_0.2Ni_0.8Cr_0.2	Ni	100	800	Example of an example cell 203	Mg₂Cu_0.8Co_0.2	Mn	100	503
Example 204	Mg₂Cu_0.7Sn_0.5	Co₃O₄	100	524	Example of an example cell 203	Mg₂Cu_0.8Co_0.2	Mn	100	503
Example 204	Mg₂Cu_0.7Sn_0.5	Co₃O₄	100	524	Example 205	Mg₂Au_0.1Ni_1.3	Ru	100	605
Example 206	Mg₂Ni_1.6Ag_0.1	Mo	100	553	Example 205	Mg₂Au_0.1Ni_1.3	Ru	100	605
Example 206	Mg₂Ni_1.6Ag_0.1	Mo	100	553	Example 207	Mg₂Al_0.1Ni_1.9	RhO₂	100	502

Watch 27

	Alloy with hydrogen storage characteristics	Additive agent	Time of treatment (h)	Discharge capacity (mAh/g)
	Alloy with hydrogen storage characteristics	Additive agent	Time of treatment (h)	Discharge capacity (mAh/g)	Example 208	Mg₂Fe_0.5Ni_0.6Zn_0.1	W	100	645
Example 209	LaAl_0.3Ni_3.7Mn_0.5Co_0.5	VCO₃	100	285	Example 208	Mg₂Fe_0.5Ni_0.6Zn_0.1	W	100	645
Example 209	LaAl_0.3Ni_3.7Mn_0.5Co_0.5	VCO₃	100	285	Example 210	LaAl_0.4Ni_4.4Zr_0.2	Ru	100	231
Example 211	LaAl_0.3Ni_3.7Mn_0.5Co_0.5	VNi₃	100	265	Example 210	LaAl_0.4Ni_4.4Zr_0.2	Ru	100	231
Example 211	LaAl_0.3Ni_3.7Mn_0.5Co_0.5	VNi₃	100	265	Example 212	MmAl_1.0Ni_3.5Si_0.5	Nb	100	284
Example 213	MmNi_3.6Mn_0.4Ti_0.3Co_0.7	WPt₃	100	205	Example 212	MmAl_1.0Ni_3.5Si_0.5	Nb	100	284
Example 213	MmNi_3.6Mn_0.4Ti_0.3Co_0.7	WPt₃	100	205	Example 214	MmAl_0.2Ni_3.8Mn_0.5Cu_0.5	Ta	100	250
Example 215	TiFe_0.8Mn_0.1	Co₂O₃	100	211	Example 214	MmAl_0.2Ni_3.8Mn_0.5Cu_0.5	Ta	100	250
Example 215	TiFe_0.8Mn_0.1	Co₂O₃	100	211	Example 216	TiCo_0.6Mn_0.5	V	100	260
Example 217	Zr_0.6Ti_0.4V_0.6Ni_1.3	Au	100	390	Example 216	TiCo_0.6Mn_0.5	V	100	260
Example 217	Zr_0.6Ti_0.4V_0.6Ni_1.3	Au	100	390	Example 218	ZrCo_1.0Mn_1.3	RuO₂	100	350
Example 219	ZrV_0.3Ni_1.4Mn_0.6	Ta	100	380	Example 218	ZrCo_1.0Mn_1.3	RuO₂	100	350

As is apparent from tables 24 to 27, when the hydrogen occluding alloy is mechanically treated, the discharge capacity of the alloy is increased and the charge-discharge characteristics are remarkably improved.

(example 220)

Mg obtained by high-frequency smelting₂Ni alloy and 20% (by volume) (Mg)₂Ni alloy based) powder of Ni (an additive) functioning as a catalyst was mixed, and then the mixture was put into a stainless steel container with a double-covered stainless steel ball. The vessel was filled with argon gas containing 1ppm or less of oxygen and 0.5ppm or less of water, and thereafter the vessel was sealed with an O-ring and ball-milled (mechanically treated) for 100 hours with a rotation speed controlled at 200 rpm.

Then, the hydrogen absorption rate of the evaluation alloy was measured at 25 ℃ by using a hydrogen absorption/desorption characteristic evaluation apparatus shown in FIG. 6. The hydrogen absorption rate V of the alloy is expressed as the amount MHV of hydrogen absorbed by the alloy within 10 hours after a predetermined amount of hydrogen has been fed into the reaction vessel. The results are shown in Table 28.

(examples 221 to 241)

As shown in table 28, the alloys having hydrogen absorption characteristics were mixed with a certain volume percentage (based on the hydrogen storage alloy) of the additives functioning as catalysts, respectively, and subjected to mechanical treatment under the same conditions as in example 220.

The hydrogen storage rate was measured at 25 ℃ in the same manner as in example 220 using the hydrogen absorption/desorption characteristic evaluation apparatus shown in FIG. 6. Mechanically treated alloys with Mg without mechanical treatment₂The results of the Ni alloy (comparative example 20) are shown in table 28.Watch 28

	Alloy with hydrogen storage characteristics	Additive agent	Total amount of additives (Vol％)	Before V mechanical treatment	After V mechanical treatment
	Alloy with hydrogen storage characteristics	Additive agent	Total amount of additives (Vol％)	Before V mechanical treatment	After V mechanical treatment	Comparative example 120	Mg₂Ni	-	-	0	-
Example 221	Mg₂Ni	Ni	20	0	3.3	Comparative example 120	Mg₂Ni	-	-	0	-
Example 221	Mg₂Ni	Ni	20	0	3.3	Example 221	Mg₂Ni_0.5Cu_0.5	Pd	51	0	2.7
Example 222	Mg₂Ni_0.75Co_0.25	MoCo₃	32	0	3.9	Example 221	Mg₂Ni_0.5Cu_0.5	Pd	51	0	2.7
Example 222	Mg₂Ni_0.75Co_0.25	MoCo₃	32	0	3.9	Example 223	Mg₂Ni_0.75Fe_0.25	RuO₃	61	0	3.2
Example 224	Ti₂Ni	MmNi₅	5	0	1.9	Example 223	Mg₂Ni_0.75Fe_0.25	RuO₃	61	0	3.2
Example 224	Ti₂Ni	MmNi₅	5	0	1.9	Example 225	LaNi₅	V	37	0.1	6.0
Example 226	MmNi₅	MqZn₂	21	0	3.6	Example 225	LaNi₅	V	37	0.1	6.0
Example 226	MmNi₅	MqZn₂	21	0	3.6	Example 227	CaNi₅	Hf	9	0	4.8
Example 228	MgNi₂	La₃Ni	42	0	3.4	Example 227	CaNi₅	Hf	9	0	4.8
Example 228	MgNi₂	La₃Ni	42	0	3.4	Example 229	VNi₂	ZrFe₂	13	0	3.7

(continuation)Watch 28 (continuation)

	Alloy with hydrogen storage characteristics	Additive agent	Total amount of additives (vol％)	Before V mechanical treatment	After V mechanical treatment
	Alloy with hydrogen storage characteristics	Additive agent	Total amount of additives (vol％)	Before V mechanical treatment	After V mechanical treatment	Example 230	TiNi	Ir	46	0	1.9
Example 231	LaNi	V₄Ti	84	0.1	2.6	Example 230	TiNi	Ir	46	0	1.9
Example 231	LaNi	V₄Ti	84	0.1	2.6	Example 232	Vni	Ni	29	0.1	2.3
Example 233	LaNi₃	Ca₂Fe	34	0.1	4.2	Example 232	Vni	Ni	29	0.1	2.3
Example 233	LaNi₃	Ca₂Fe	34	0.1	4.2	Example 234	Vni₃	Mg₂Ni	55	0	4.1
Example 235	Ia₂Ni₇	pt	42	0.1	7.6	Example 234	Vni₃	Mg₂Ni	55	0	4.1
Example 235	Ia₂Ni₇	pt	42	0.1	7.6	Example 236	Zr₂Ni₇	Mg₂Cu	63	0	6.9
Example 237	La₂Ni₃	ZrNi₂	2	0.2	3.6	Example 236	Zr₂Ni₇	Mg₂Cu	63	0	6.9
Example 237	La₂Ni₃	ZrNi₂	2	0.2	3.6	Example 238	Ca₂Ni₃	Mo	27	0.1	3.1
Example 239	La₇Ni₃	TiNi	13	0.1	4.2	Example 238	Ca₂Ni₃	Mo	27	0.1	3.1
Example 239	La₇Ni₃	TiNi	13	0.1	4.2	Example 240	La₃Ni	Co₃O₄	73	0.2	8.1
Example 241	V₃Ni	Co	58	0	7.6	Example 240	La₃Ni	Co₃O₄	73	0.2	8.1

As is apparent from Table 28, the hydrogen absorption rate and hydrogen storage characteristics of the hydrogen absorbing alloys of examples 220 to 241, which were obtained by mechanically treating a mixture comprising a hydrogen absorbing alloy containing Ni in an amount of not less than 5% by volume and an additive such as a metal additive, were significantly improved.

(example 242)

The hydrogen occluding alloy powder of example 220 was mixed with electrolytic copper powder in a weight ratio of 1: 1, and 1g of the resulting mixture was charged into a mold having an inner diameter of 10mm and pressed under a pressure of 20000kg for 3 minutes to obtain pellets. The particles were sandwiched in a Ni mesh and the periphery was spot welded and compacted, respectively. Subsequently, the compact was connected to a Ni lead wire by spot welding, thereby producing a hydrogen absorbing alloy electrode (negative electrode).

The hydrogen electrode thus produced was immersed in an 8N potassium hydroxide solution together with a sintered nickel counter electrode. The charge-discharge cycle test was then carried out at 25 ℃. Each charge-discharge cycle consists of several steps: charging at 100mA current for 10 hours per gram of hydrogen storage alloy, and discharging at 20mA current per gram of hydrogen storage alloy after charging for 10 minutes until the voltage relative to the mercuric oxide electrode is reduced to-0.5V.

Comparison of the cycle discharge capacity characteristics of the negative electrode of comparative example 20 (containing Mg2Ni which had not been subjected to the foregoing mechanical treatment) with those of the negative electrode of example 242 is indicated by curves a and b, respectively, in fig. 11. As is apparent from FIG. 11, Mg contained without the aforementioned mechanical treatment₂The negative electrodeof Ni cannot be charged and discharged at normal temperature (curve a). On the other hand, the negative electrode comprising the hydrogen storage alloy of example 220 had a discharge capacity at the first cycle of 832 mAh/g. This shows a significant increase in discharge capacity with the mechanically treated material.

(examples 243 to 253)

Nickel was added to Mg in the weight ratios shown in Table 29₂Mixing Ni alloy to obtainTwelve hydrogen occluding alloys, and the resulting mixture was treated in the same manner as in example 220.

Subsequently, the hydrogen absorption rate of each hydrogen occluding alloy was measured by the same method as in example 220.

Thereafter, a negative electrode was produced in the same manner as in example 242 using each hydrogen storage alloy. The negative electrode thus obtained was immersed in 8N KOH alkaline solution together with the sintered nickel counter electrode, respectively, and subjected to charge-discharge cycles at 25 ℃ to measure the maximum discharge capacity.

The results obtained are shown in Table 29 together with the results of comparative example 20.

Figure 12 shows XRD diffractogram as a function of Ni. In FIG. 12, A shows the sample Mg₂Diffraction pattern of Ni + 5% Ni by volume; b shows sample Mg₂Diffraction pattern of Ni + 10% by volume of Ni; c shows sample Mg₂Diffraction pattern of Ni + 15% (by volume) Ni; d shows sample Mg₂Diffraction pattern of Ni + 18% Ni by volume; e shows sample Mg₂Diffraction pattern of Ni +22 vol% Ni; f shows sample Mg₂Diffraction pattern of Ni + 25% Ni by volume; g shows sample Mg₂Diffraction pattern of Ni + 33% Ni by volume. As is apparent from FIG. 12, as the Ni content increases, the amount of Ni in Mg increases₂In the X-ray diffraction spectrum of Ni, the peaks at 20 ℃ and 40 ℃ were widened in proportion, which significantly increased the apparent half-width value Δ (2 θ)₂₀And 2 theta₄₀°)。Watch 29

	Content of nickel (vol％)	Hydrogen absorption rate V	Discharge capacity (mAh/g)
	Content of nickel (vol％)	Hydrogen absorption rate V	Discharge capacity (mAh/g)	Comparative example Example 20	0	0	0
Example 243	5.1	2.1	525	Comparative example Example 20	0	0	0
Example 243	5.1	2.1	525	Example 244	9.7	2.2	544
Example 245	13.9	2.5	645	Example 244	9.7	2.2	544
Example 245	13.9	2.5	645	Example 246	17.7	3.0	751
Example 247	21.2	3.1	790	Example 246	17.7	3.0	751
Example 247	21.2	3.1	790	Example 248	24.4	3.2	805
Example 249	30.0	3.3	832	Example 248	24.4	3.2	805
Example 249	30.0	3.3	832	Example 250	34.5	3.4	850
Example 251	39.2	3.6	900	Example 250	34.5	3.4	850
Example 251	39.2	3.6	900	Example 252	49.8	3.7	920
Example 253	65.9	2.8	700	Example 252	49.8	3.7	920

As is apparent from Table 29, the hydrogen absorption rate and the discharge capacity become good as the Ni content increases, and the Ni content may be 50% by volume at the maximum. However, when the Ni content exceeds 50% by volume, the hydrogen absorption rate is greatly lowered.

(examples 254 to 275)

Various additives were mixed with various alloys having hydrogen storage characteristics in the volume ratios listed in Table 30, and the resulting mixtures were subjected to mechanical treatment in the same manner as described in example 220 to prepare twenty-two hydrogen storage alloys.

Then, using each of the hydrogen storage alloys thus obtained, a negative electrode was prepared in the same manner as in example 242, and the negative electrode thus obtained was immersed in a KOH alkaline solution of 8N together with a sintered nickel counter electrode. Then, charge and discharge cycles were performed at 25 ℃ to measure the maximum discharge capacity.

The results obtained are shown in Table 30 together with the results of comparative example 20.Watch 30

	Alloy with hydrogen storage characteristics	Additive agent	Additive Total amount (vol%)	(mAh/g) Discharge capacity
	Alloy with hydrogen storage characteristics	Additive agent	Additive Total amount (vol%)	(mAh/g) Discharge capacity	Comparative example 20	Mg₂Ni	-	-	0
Example 254	Mg₂Ni	Ni	65	820	Comparative example 20	Mg₂Ni	-	-	0
Example 254	Mg₂Ni	Ni	65	820	Example 255	Mg₂Ni_0.5Cu_0.5	wNi₃	31	728
Example 256	Mg₂Ni_0.75Co_0.25	Ni₂O	27	826	Example 255	Mg₂Ni_0.5Cu_0.5	wNi₃	31	728
Example 256	Mg₂Ni_0.75Co_0.25	Ni₂O	27	826	Example 257	Mg₂Ni_0.75Co_0.25	LaNi₅	48	850
Example 258	Ti₂Ni	Au	3	302	Example 257	Mg₂Ni_0.75Co_0.25	LaNi₅	48	850
Example 258	Ti₂Ni	Au	3	302	Example 259 Example 260	LaNi₅	V₂O₅	63	350
MmNi₅	ZrFe₂	22	285			LaNi₅	V₂O₅	63	350
MmNi₅	ZrFe₂	22	285	Example 261		CaNi₅	Os	38	350
Example 262	MgNi₂	TiNi	52	Example 261	442	CaNi₅	Os	38	350
Example 262	MgNi₂	TiNi	52	Example 263	442	VNi₂	Wco₃	8	419

Watch 30 (continuation)

	Alloy with hydrogen storage characteristics	Additive agent	Additive Total amount (vol%)	(mAh/g) Discharge capacity
	Alloy with hydrogen storage characteristics	Additive agent	Additive Total amount (vol%)	(mAh/g) Discharge capacity	Example 264	TiNi	Zr₂Ni₇	26	374
Example 265	LaNi	Ti	64	355	Example 264	TiNi	Zr₂Ni₇	26	374
Example 265	LaNi	Ti	64	355	Example 266	VNi	Ni	14	480
Example 267	LaNi₃	RuO₂	17	450	Example 266	VNi	Ni	14	480
Example 267	LaNi₃	RuO₂	17	450	Example 268	VNi₃	Co	56	401
Example 269	La₂Ni₇	Ta	35	360	Example 268	VNi₃	Co	56	401
Example 269	La₂Ni₇	Ta	35	360	Example 270	Zr₂Ni₇	Na₂Ni	2	364
Example 271	La₂Ni₃	ZrNi₂	42	222	Example 270	Zr₂Ni₇	Na₂Ni	2	364
Example 271	La₂Ni₃	ZrNi₂	42	222	Example 272	Ca₂Ni₃	LaNi	29	211
Example 273	La₇Ni₃	V₃Ni	51	503	Example 272	Ca₂Ni₃	LaNi	29	211
Example 273	La₇Ni₃	V₃Ni	51	503	Example 274	La₃Ni	Co₂O₃	38	450
Example 275	V₃Ni	Rf	7	700	Example 274	La₃Ni	Co₂O₃	38	450

As is apparent from table 30, the hydrogen occluding alloy treated mechanically increases the discharge capacity, remarkably improving the charge-discharge characteristics.

(examples 276 to 279 and comparative example 20)

Mg obtained by high-frequency melting method₂Ni alloy and LaNi₅The alloys were mixed together in a volume ratio of 80: 20. The resulting mixture was mechanically treated for different periods of time in the same manner as in example 220 to obtain 4 different hydrogen occluding alloys.

Then, the Δ (2 θ 2) value (half-width value of the peak in the vicinity of 40 ° in the X-ray diffraction spectrum using Cuk α as a radiation source) and the hydrogen absorption rate of each hydrogen storage alloy were measured, respectively.

In the same manner as in example 242, a negative electrode was produced from each hydrogen absorbing alloy, and the negative electrode and a sintered nickel counter electrode were immersed in 8N KOH alkaline solution, followed by charge-discharge cycling at 25 ℃ to measure the maximum discharge capacity.

The results obtained are comparable to the Mg of comparative example 20 which has not been treated by mechanical means₂The results for Ni are listed together in Table 31.Watch 31

	Treatment time (h)	Δ(2θ₂)(°)	Hydrogen absorption rate V	Discharge capacity (mAh/g)
	Treatment time (h)	Δ(2θ₂)(°)	Hydrogen absorption rate V	Discharge capacity (mAh/g)	Comparative example 20	0	0.07	0.6	150
Example 276	5	0.60	1.9	463	Comparative example 20	0	0.07	0.6	150
Example 276	5	0.60	1.9	463	Example 277	50	1.50	2.4	621
Example 278	400	3.70	3.4	860	Example 277	50	1.50	2.4	621
Example 278	400	3.70	3.4	860	Example 279	700	6.10	3.5	871

As is apparent from Table 31, the longer the mechanical treatment time, the smaller the diameter of the crystal grains and the nonuniform distortion occurred in the crystal. Thus, Δ (2 θ)₂) The value is increased and the hydrogen storage rate and discharge capacity are also greatly increased.

(examples 280 to 284 and comparative examples 23 and 24)

70% by volume of Mg₂The Ni alloy and 30% by volume of Co powder were placed in a stainless steel container with a double lid together with a stainless steel ball. Then in seven different atmospheresMechanical treatment was carried out in the same manner as in example 220 under the conditions of vacuum, argon, nitrogen, helium, hydrogen, oxygen and air, to prepare 7 kinds of surface-modified hydrogen absorbing alloy powders.

The hydrogen absorption rate of these modified hydrogen occluding alloy powders was then measured.

Thereafter, negative electrodes were prepared using these modified hydrogen occluding alloys, respectively, in the same manneras in example 242, and the obtained negative electrodes were immersed in 8N KOH alkaline solution together with a sintered nickel counter electrode, followed by charge-discharge cycling at 25 ℃ to measure the maximum discharge capacity.

The results are shown in Table 32.Watch 32

	Process gas	Hydrogen absorption rate V	Discharge capacity mAh/g)
	Process gas	Hydrogen absorption rate V	Discharge capacity mAh/g)	Example 280	Argon (99.999％)	2.4	610
Example 281	Vacuum	2.0	415	Example 280	Argon (99.999％)	2.4	610
Example 281	Vacuum	2.0	415	Example 282	Nitrogen(99.999％)	2.2	550
Example 283	Helium(99.999％)	2.1	531	Example 282	Nitrogen(99.999％)	2.2	550
Example 283	Helium(99.999％)	2.1	531	Example 284	Hydrogen(99.99999％)	2.7	672
Comparative example 23	Oxygen(99.999％)	0	0	Example 284	Hydrogen(99.99999％)	2.7	672
Comparative example 23	Oxygen(99.999％)	0	0	Comparative example 24	Air (a)	0	0

As is apparent from Table 32, the hydrogen absorption rate of the hydrogen occluding alloys subjected to mechanical treatment under vacuum, inert gas or hydrogen atmosphere conditions was greatly improved, and the discharge capacity of the negative electrodes containing these hydrogen occluding alloys was also greatly improved.

Example 285 to 306

Powder additives of a predetermined particle size were added to the alloys having hydrogen storage characteristics as shown in Table 33, and the resulting mixtures were subjected to the same mechanical process as in example 220 for different periods of time to obtain 22 different hydrogen storage alloys.

Then, the hydrogen absorption rate of each alloy was measured in the same manner as in example 220.

Thereafter, negative electrodes were made of these hydrogen storage alloys in the same manner as in example 242, and the obtained negative electrodes were immersed in a 8N KOH alkaline solution together with a sintered nickel counter electrode, followed by charge-discharge cycles at 25 ℃ to measure the maximum discharge capacity.

The results obtained are listed in table 33 together with the dispersion of the powder additive described previously and the results of comparative example 20.Watch 33

	Alloy having hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)
	Alloy having hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)	Comparative example 20	Mg₂Ni	-	-	0	0	0
Example 285	Mg₂Ni	Ni	0.001	30	3.0	743	Comparative example 20	Mg₂Ni	-	-	0	0	0
Example 285	Mg₂Ni	Ni	0.001	30	3.0	743	Example 286	Mg₂Ni_0.6Cu_0.4	Zr	0.513	17	2.8	700
Example 287	Mg₂Ni_0.7Cu_0.3	MoNi₃	8.15	0.4	3.3	824	Example 286	Mg₂Ni_0.6Cu_0.4	Zr	0.513	17	2.8	700
Example 287	Mg₂Ni_0.7Cu_0.3	MoNi₃	8.15	0.4	3.3	824	Example 288	Mg₂Ni_0.85Fe_0.15	Co₂O₃	0.692	16	3.4	856
Example 289	Ti₂Ni	Ag	3.68	0.7	3.0	290	Example 288	Mg₂Ni_0.85Fe_0.15	Co₂O₃	0.692	16	3.4	856
Example 289	Ti₂Ni	Ag	3.68	0.7	3.0	290	Example 290	LaNi₅	ZrNi₂	5.1	30	5.0	381
Example 291	MmNi₅	W	35.7	4.3	5.5	256	Example 290	LaNi₅	ZrNi₂	5.1	30	5.0	381
Example 291	MmNi₅	W	35.7	4.3	5.5	256	Example 292	CaNi₅	ZrFe₃	0.325	17	5.8	348
Example 293	MgNi₂	V	0.013	32	3.1	431	Example 292	CaNi₅	ZrFe₃	0.325	17	5.8	348
Example 293	MgNi₂	V	0.013	32	3.1	431	Example 294	VNi₂	Mg₂Ni	12.0	0.5	3.8	409
Example 295	TiNi	TC	1.35	2.5	2.0	368	Example 294	VNi₂	Mg₂Ni	12.0	0.5	3.8	409

Watch 33 (continue)

	Having the function of storing hydrogen Alloy of properties	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)
	Having the function of storing hydrogen Alloy of properties	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)	Example 296	LaNi	Mg₂Cu	2.31	26	2.7	351
Example 297	VNi	LaNi₅	0.052	1.8	3.0	360	Example 296	LaNi	Mg₂Cu	2.31	26	2.7	351
Example 297	VNi	LaNi₅	0.052	1.8	3.0	360	Example 298	LaNi₃	Ti₂Ni	0.016	45	4.8	425
Example 299	VNi₃	TiFe	0.894	3.6	4.9	431	Example 298	LaNi₃	Ti₂Ni	0.016	45	4.8	425
Example 299	VNi₃	TiFe	0.894	3.6	4.9	431	Example 300	La₂Ni₇	Zr₂Fe	0.953	23	10.1	367
Example 301	Zr₂Ni₇	IrO₂	22.3	0.02	9.5	356	Example 300	La₂Ni₇	Zr₂Fe	0.953	23	10.1	367
Example 301	Zr₂Ni₇	IrO₂	22.3	0.02	9.5	356	Example 302	La₂Ni₃	MmNi₅	0.413	8.9	3.6	218
Example 303	Ca₂Ni₃	Rh	40.5	48	3.8	209	Example 302	La₂Ni₃	MmNi₅	0.413	8.9	3.6	218
Example 303	Ca₂Ni₃	Rh	40.5	48	3.8	209	Example 304	La₇Ni₃	WCo₃	35.36	0.06	4.0	482
Example 305	La₃Ni	Ru	0.156	31	8.5	503	Example 304	La₇Ni₃	WCo₃	35.36	0.06	4.0	482
Example 305	La₃Ni	Ru	0.156	31	8.5	503	Example 306	V₃Ni	Cr	8.91	15	9.0	690

As is apparent from Table 33, although Mg₂The hydrogen absorption rate V of Ni is about 0 to 0.5 at normal temperature, and when a powder additive such as Ni powder is added to a hydrogen absorbing alloy having hydrogen storage characteristics, for example, the hydrogen absorbing alloys of examples 285 to 306, the hydrogen absorption characteristics of the alloy at normal temperature are improved, and the charge and discharge characteristics of the negative electrode are also greatly improved. Example 307 to 326

Powders of predetermined particle diameters were added to the alloys having hydrogen absorption characteristics of the general formulae (V) and (VI) shown in Table 34, and the resulting mixtures were mechanically treated for different periods of time in the same manner as in example 220, thereby obtaining 20 different hydrogen occluding alloys.

Then, the hydrogen storage rate of each hydrogen storage alloy was measured separately in the same manner as in example 20.

Thereafter, negative electrodes were produced from these hydrogen occluding alloys, respectively, in the same manner as in example 242, and the obtained negative electrodes were immersed in a 8N KOH alkaline solution together with a sintered nickel counter electrode, followed by charge-discharge cycles at 25 ℃ to measure the maximum discharge capacity.

The results are shown in Table 34 together with the dispersion volume of the powder additive described above.Watch 34

	Alloy with hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)
	Alloy with hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)	Example 307	(Mg_0.8Mn_0.2)₄Ni	Co	5	3.2	2.8	456
Example 308	(Mg_0.6Cr_0.4)₁₂Co_0.3Cu_0.7	CaNi₅	20	15.3	3.0	391	Example 307	(Mg_0.8Mn_0.2)₄Ni	Co	5	3.2	2.8	456
Example 308	(Mg_0.6Cr_0.4)₁₂Co_0.3Cu_0.7	CaNi₅	20	15.3	3.0	391	Example 309	(Mg_0.8Al_0.1B_0.1)₄Fe	TiFe	35	8.6	1.6	530
Example 310	(Mg_0.9Mo_0.1)₁₁Si	Ni	0.1	25.2	3.1	700	Example 309	(Mg_0.8Al_0.1B_0.1)₄Fe	TiFe	35	8.6	1.6	530
Example 310	(Mg_0.9Mo_0.1)₁₁Si	Ni	0.1	25.2	3.1	700	Example 311	(Mg_0.7Ru_0.3)₁₃Sn_0.5Zn_0.5	V	3	40.1	2.6	621
Example 312	(Mg_0.8Pd_0.1W_0.1)₁₀Ni	Ti₂Ni	18	55.3	2.2	313	Example 311	(Mg_0.7Ru_0.3)₁₃Sn_0.5Zn_0.5	V	3	40.1	2.6	621
Example 312	(Mg_0.8Pd_0.1W_0.1)₁₀Ni	Ti₂Ni	18	55.3	2.2	313	Example 313	(Mg_0.7Zr_0.3)₅Ni_0.9Cu_0.1	Co₃Mo	50	1.2	2.1	215
Example 314	(Mg_0.9C_0.1)₁₅Ni_0.9Co_0.1	Ni	0.9	11.6	2.9	400	Example 313	(Mg_0.7Zr_0.3)₅Ni_0.9Cu_0.1	Co₃Mo	50	1.2	2.1	215
Example 314	(Mg_0.9C_0.1)₁₅Ni_0.9Co_0.1	Ni	0.9	11.6	2.9	400	Example 315	(Mg_0.7Ge_0.3)₉Fe	ZrMnNi	23	31.2	3.1	390
Example 316	(Mg_0.8P_0.1Ti_0.1)₃Cu	Pt	11	0.6	2.6	280	Example 315	(Mg_0.7Ge_0.3)₉Fe	ZrMnNi	23	31.2	3.1	390

Watch 34 (continuation)

	Alloy with hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)
	Alloy with hydrogen storage characteristics	Additive agent	Particle diameter (μm)	Rate of dispersion (vol％)	Rate of hydrogen absorption	Discharge capacity (mAh/g)	Example 317	(Mg_0.9K_0.1)₃Ni	NiP	0.5	19.3	2.2	431
Example 318	(Mg_0.6Ca_0.4)₁₄Co_0.5Ni_0.5	Mo	1.3	60.2	1.3	320	Example 317	(Mg_0.9K_0.1)₃Ni	NiP	0.5	19.3	2.2	431
Example 318	(Mg_0.6Ca_0.4)₁₄Co_0.5Ni_0.5	Mo	1.3	60.2	1.3	320	Example 319	(Mg_0.8Ca_0.1Sr_0.1)₁₂Zn	Pd	5	45.3	2.9	800
Example 320	(Mg_0.5Ba_0.5)₁₀Cu_0.7Ni_0.3	V₄Ti	13	1.2	3.0	293	Example 319	(Mg_0.8Ca_0.1Sr_0.1)₁₂Zn	Pd	5	45.3	2.9	800
Example 320	(Mg_0.5Ba_0.5)₁₀Cu_0.7Ni_0.3	V₄Ti	13	1.2	3.0	293	Example 321	(Mg_0.8Na_0.2)₁₆Fe	NiB	8	16.3	2.2	411
Example 322	(Mg_0.7La_0.2Li_0.1)₅Si	LaNi₄Al	15	21.6	2.6	393	Example 321	(Mg_0.8Na_0.2)₁₆Fe	NiB	8	16.3	2.2	411
Example 322	(Mg_0.7La_0.2Li_0.1)₅Si	LaNi₄Al	15	21.6	2.6	393	Example 323	(Mg_0.8Y_0.1Ca_0.1)₂₀Ni_0.8 Co_0.1Cu_0.1	Ni	0.05	30.3	2.5	516
Example 324	(Mg_0.6Sr_0.4)₅Cu	Au	21	9.6	2.1	290	Example 323	(Mg_0.8Y_0.1Ca_0.1)₂₀Ni_0.8 Co_0.1Cu_0.1	Ni	0.05	30.3	2.5	516
Example 324	(Mg_0.6Sr_0.4)₅Cu	Au	21	9.6	2.1	290	Example 325	(Mg_0.9Li_0.1)₈Ni	B	0.8	51.2	1.3	410
Example 326	(Mg_0.6La_0.4)₄Co	CaAlNi₄	3	3.2	2.2	391	Example 325	(Mg_0.9Li_0.1)₈Ni	B	0.8	51.2	1.3	410

As is apparent from Table 34, the hydrogen storage alloys of examples 307 to 326, which were obtained by adding a powder additive such as Ni powder to the alloys having hydrogen storage characteristics represented by the general formulae (V) and (VI) at room temperature, exhibited greatly improved hydrogen storage characteristics. (examples 327 to 332 and comparative examples 25 to 27)

With an axial composition of Mg_1.9Al_0.1Ni_1.05Carbon powder and polytetrafluoroethylene are added into the hydrogen storage alloy according to different proportions. The resulting mixture was rolled into a sheet shape, and the sheet was attached to a Ni net with pressure. 9 kinds of hydrogen electrodes (negative electrodes) were prepared. The hydrophobicity and ion elution rate of the hydrogen electrode vary with the composition of the electrode, such as the polytetrafluoroethylene content and the pressure at which the composite sheet is formed with the Ni mesh.

The hydrogen electrode thus obtained was immersed in an 8N KOH alkaline solution, and then subjected to a charge-discharge cycle test at normal temperature. In the charge and discharge, the charge is carried out for 10 hours at 100mA per gram of hydrogen storage alloy, and the discharge is carried out at 200mA per gram of hydrogen storage alloy until the voltage of the hydrogen storage alloy relative to the mercuric oxide electrode is reduced to-0.5V. Capacity of 20 th cycle discharge andthe proportional relationship of the discharge capacity at the 3 rd cycle and the ion elution rate are shown in table 35. The ion elution rate is obtained by immersing a hydrogen electrode in an aqueous alkali metal hydroxide solution for 5 hours and then measuring the amount of the eluted component by an ICP (inductively coupled plasma) spectrometer. The amount of aqueous alkali metal hydroxide solution used in the hydrogen electrode was approximately 100ml per gram of alloy.Watch 35

	Ion species	Alkali solution	Temperature of the solution ℃	Elution Rate Mg/kg alloy/hr	Elution Rate (%) 20 th/3 rd cycle
	Ion species	Alkali solution	Temperature of the solution ℃	Elution Rate Mg/kg alloy/hr	Elution Rate (%) 20 th/3 rd cycle	Example 327	Mg	8N KOH	25	0.3	70
Example 328	Mg	6N KOH	25	0.5	65	Example 327	Mg	8N KOH	25	0.3	70
Example 328	Mg	6N KOH	25	0.5	65	Example 329	Mg	7N KOH 1N LiOH	25	0.4	77
Example 330	Mg	9N KOH		60	1.2	Example 329	Mg	7N KOH 1N LiOH	25	0.4	77	75
Example 330	Mg	9N KOH		60	1.2	Example 331	Mg+Al	8N KOH	25	1.0	72	75
Example 332	Mg+Al	8N KOH		60	3.4	Example 331	Mg+Al	8N KOH	25	1.0	72	68
Example 332	Mg+Al	8N KOH		60	3.4	Comparative example 25	Mg	8N KOH	25	0.7	32	68
Comparative example 26	Mg	9N KOH		60	2.3	Comparative example 25	Mg	8N KOH	25	0.7	32	43
Comparative example 26	Mg	9N KOH		60	2.3	Comparative example 27	Mg+Al	8N KOH	25	4.8	30	43

(examples 333 to 341)

The hydrogen storage alloys shown in Table 36 were mixed with carbon powder and polytetrafluoroethylene in different proportions, and then the mixture was rolled into a sheet, which was adhered to a Ni mesh with pressure to prepare 8 kinds of hydrogen storage alloy electrodes.

The hydrogen electrode thus obtained was immersed in an 8N KOH aqueous solution, and a charge-discharge cycle test was performed at room temperature in the same manner as in example 327. The proportional relationship between the capacity of the 20 th cycle discharge and the capacity of the 3 rd cycle discharge and the ion elution rate were measured in the same manner as in example 327, and the results are shown in table 36.Watch 36

	Hydrogen-storage alloy	Ion species
	Hydrogen-storage alloy	Ion species	Example 333	Mg₂Ni_1.125	Magnesium alloy
Example 334	Mg₂Co_1.1In_0.11	All elements	Example 333	Mg₂Ni_1.125	Magnesium alloy
Example 334	Mg₂Co_1.1In_0.11	All elements	Example 335	MgNi_1.11Ag_0.22	Magnesium alloy
Example 336	Mg_1.8Al_0.3Ni_0.9Pd_0.3	Magnesium alloy	Example 335	MgNi_1.11Ag_0.22	Magnesium alloy
Example 336	Mg_1.8Al_0.3Ni_0.9Pd_0.3	Magnesium alloy	Example 337	Mg_1.8Al_0.3Ni_0.9Pd_0.3	Magnesium alloy
Example 338	Mg_1.6Al_0.3NiMn_0.2	All round cables	Example 337	Mg_1.8Al_0.3Ni_0.9Pd_0.3	Magnesium alloy
Example 338	Mg_1.6Al_0.3NiMn_0.2	All round cables	Example 339	Mg_1.6Al_0.3Ni_0.7Mn_0.2Co_0.2	All elements
Example 340	Mg_1.8Al_0.3Ni_0.9Pd_0.3 (the powder was immersed in 001N hydrochloric acid for 30 seconds)	Magnesium alloy	Example 339	Mg_1.6Al_0.3Ni_0.7Mn_0.2Co_0.2	All elements
Example 340		Magnesium alloy	Example 341	Mg_1.8Al_0.2Ni_0.95pt_0.05	Magnesium alloy

Watch 36

	Alkali solution	Temperature of the solution ℃	Elution Rate Mg/kg alloy/hr	Elution Rate Twentieth/third cycle
	Alkali solution	Temperature of the solution ℃	Elution Rate Mg/kg alloy/hr	Elution Rate Twentieth/third cycle	Example 333	8N KOH	25	0.2	65
Example 334	8N KOH	25	2.1	-72	Example 333	8N KOH	25	0.2	65
Example 334	8N KOH	25	2.1	-72	Example 335	8N KOH	25	0.2	76
Example 336	8N KOH	25	0.2	78	Example 335	8N KOH	25	0.2	76
Example 336	8N KOH	25	0.2	78	Example 337	8N KOH	60	4.2	77
Example 338	7N KOH 1N LiOH	60	0.5	70	Example 337	8N KOH	60	4.2	77
Example 338	7N KOH 1N LiOH	60	0.5	70	Example 339	9N KOH	60	3.4	80
Example 340	8N KOH	25	0.2	76	Example 339	9N KOH	60	3.4	80
Example 340	8N KOH	25	0.2	76	Example 341	8N KOH	25	0.2	74

As shown in tables 35 and 36, a simulated battery was constituted by using a hydrogen electrode (examples 327 to 341) containing a hydrogen occluding alloy as a negative electrode, wherein when the negative electrode was immersed in a 6 to 8N aqueous solution of an alkali metal hydroxide, (a) the elution rate of Mg ions in the aqueous solution of an alkali metal hydroxide at normal temperature was not more than 0.5Mg per kg of alloy per hour, and at 60 ℃, the elution rate of Mg ions in the aqueous solution of an alkali metal hydroxide was not more than 4Mg per kg of alloy per hour; (b) at normal temperature, the elution rate of the component elements of the alloy in the alkali metal hydroxide aqueous solution is not more than 1.5mg per kilogram of the alloy per hour, and at 60 ℃, the elution rate of the component elements of the alloy in the alkali metal hydroxide aqueous solution is not more than 20mg per kilogram of the alloy per hour; it has a higher capacity as compared with a simulated cell having a hydrogen electrode of a hydrogen occluding alloy not satisfying the above conditions (comparative examples 25 to 27) as a negative electrode composition. (examples 342 to 348 and comparative example 28)

On the hydrogen electrodes (negative electrodes) obtained in examples 327, 333 to 335, 338 to 340 and comparative example 27, respectively, a pasted Ni electrode (positive electrode) was stacked with nylon nonwoven fabric interposed therebetween. Then, the resultant composite was wound into a cylinder to thereby prepare 8 kinds of electrode groups. These electrode groups were inserted into AA type battery cases, followed by the addition of 8N KOH solution. Then, it was sealed with a cap provided with a safety valve, thereby obtaining 8 AA type nickel-hydrogen secondary batteries.

The thus-obtained battery was subjected to a charge-discharge cycle test under the following conditions. Charging was carried out at a current of 50mA per gram of hydrogen occluding alloy for 10 hours, and discharging was carried out at a current of 20mA per gram of hydrogen occluding alloy until the voltage thereof dropped to 0.9V with respect to the mercury oxide electrode. This cycle was repeated, and the capacity at the 3 rd cycle was compared with the capacity at the 20 th cycle. Thereafter, the battery was disassembled after 30 days. The amount of magnesium ions eluted into the electrolyte was measured with an ICP (inductively coupled plasma) spectrometer. The results are shown in Table 37.Watch 37

	Hydrogen electrode for use	Ion species	Concentration of mg/l	Elution Rate (%) 20 cycles/3 rd cycle
	Hydrogen electrode for use	Ion species	Concentration of mg/l	Elution Rate (%) 20 cycles/3 rd cycle	Example 342	Example 327	Mg	1.2	68
Example 343	Example 333	Mq	1.1	63	Example 342	Example 327	Mg	1.2	68
Example 343	Example 333	Mq	1.1	63	Example 344	Example 334	Mq	1.7	57
Example 345	Example 335	Mq	1.2	62	Example 344	Example 334	Mq	1.7	57
Example 345	Example 335	Mq	1.2	62	Example 346	Example 338	Mg	1.3	59
Example 347	Example 339	Mg	1.2	66	Example 346	Example 338	Mg	1.3	59
Example 347	Example 339	Mg	1.2	66	Example 348	Example 340	Mg	1.4	78
Comparative example 28	Comparative Example 27	Mg	2.8	34	Example 348	Example 340	Mg	1.4	78

As is apparent from table 37, the following conditions are satisfied: that is, the batteries of examples 343 to 349, in which the concentration of Mg ions in the electrolyte was not more than 2.2Mg/l after 30 days when the alkali metal electrolyte was added to the battery case and sealed, had higher capacity than the battery of comparative example 28, which did not satisfy the above conditions.

As described above, the hydrogen occluding alloy of the present invention not only has the characteristics of light weight and high capacity, but also has an increased applicable range due to the excellent low-temperature hydrogen occluding property and excellent chemical stability, and can be applied to various fields (e.g., storage and transportation of hydrogen, storage and transportation of thermal energy, conversion of thermal energy and mechanical energy, separation and purification of hydrogen, separation of hydrogen isotopes, batteries containing hydrogen as an active material, catalysts for synthesis chemistry and thermal sensors, etc.) other than the application fields of conventional alloys. Many new applications or fields of application can also be developed using most of these alloys.

Further, according to the hydrogen occluding alloy and the surface modification method of the present invention, it is possible to easilyactivate the alloy and improve the hydrogen occluding property thereof. Therefore, by using such an alloy as a battery negative electrode, a battery having a high capacity can be obtained.

Further, according to the negative electrode and the alkaline secondary battery of the present invention, the charge-discharge reaction of the magnesium-containing hydrogen storage alloy is made possible, whereas the conventional magnesium-containing hydrogen storage alloy has not been able to perform the charge-discharge reaction so far. In addition, it can maintain charge and discharge stability for a long time while maintaining a high capacity.

Other advantages of the invention and modifications thereof will be apparent to those skilled in the art. The scope of the invention is not to be restricted, therefore, to the specific details, representative apparatus, and illustrative examples described herein. Accordingly, various modifications may be made without departing from the spirit or general concept as defined by the appended claims and their equivalents.

Claims

1. A hydrogen occluding alloy comprising an alloy represented by the following general formula (I):

Mg₂M1y (I)

wherein M1 is at least one element selected from the group consisting of elements (other than Mg, elements which react exothermically with hydrogen, and Al and B) which do not react exothermically with hydrogen, and y is in the range of 1<y.ltoreq.1.5.

2. A hydrogen occluding alloy as recited in claim 1, wherein said M1 is an element selected from the group consisting of (other than Mg, an element capable of reacting exothermically with hydrogen, Al and B) being incapable of reacting exothermically with hydrogenand having a higher electronegativity than Mg.

3. A hydrogen occluding alloy as recited In claim 2, wherein said M1 is at least one element selected from the group consisting of Ag, Cd, Mn, In, Fe, Ni and Co.

4. A hydrogen occluding alloy as recited in claim 1, wherein in the general formula (I), said y is in the range of 1.01. ltoreq. y.ltoreq.1.5.

5. A hydrogen occluding alloy as recited in claim 1, wherein in the general formula (I), said y is in the range of 1.02. ltoreq. y.ltoreq.1.5.

6. A hydrogen occluding alloy as recited in claim 1, wherein in the general formula (I), said y is in the range of 1.05. ltoreq. y.ltoreq.1.5.

7. A hydrogen storage alloy comprising an alloy represented by the following general formula (II):

Mg₂-xM2_xM1y (II)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of (excluding Mg and M2) elements which are not exothermically reactive with hydrogen, X being in the range 0<X.ltoreq.1.0 and y being in the range 1<y.ltoreq.2.5.

8. A hydrogen occluding alloy as recited in claim 7, wherein said M1 is an element other than Mg and M2, selected from the group consisting of elements incapable of exothermic reaction with hydrogen, having higher electronegativity than Mg, and if used in an amount of 10 atomic% or less based on pure magnesium, the Mg of said alloy is obtained_1-wM1_wThe unit cell volume of the phase is smaller than that of pure Mg (w is more than 0 and less than or equal to 0.1).

9. A hydrogen occluding alloy as recited In claim 7, wherein said M1 is at least one element selected from the group consisting of Ag, Cd, Mn, In, Fe, Ni and Co.

10. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (II) is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (excluding Mg), Al and B, and has higher electronegativity than Mg.

11. A hydrogen occluding alloy as recited in claim 10, wherein said M2 is at least one element selected from the group consisting of B, Be, Y, Pd, Ti, Zr, Hf, Th, V, Nb, Ta, Pa and Al.

12. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (II) is at least one element selected from the group consisting of Al, B and an element capable of reacting exothermically with hydrogen, except Mg, and Mg of the resulting alloy is contained in an amount of 10 atom% or less based on pure Mg_1-wM1_wThe unit cell volume of the (0. ltoreq. w.ltoreq.0.1) phase is smaller than that of pure magnesium.

13. The hydrogen occluding alloy as recited in claim 12, wherein said M2 is at least one element selected from the group consisting of Li and Al.

14. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (II) is an element selected from the group consisting of Al, B and an element capable of reacting exothermically with hydrogen (excluding Mg), which has a higher electronegativity than Mg, and if it is used in an amount of 10 atomic% or less based on pure Mg, the alloy obtained isMg_1-wM1_NThe unit cell volume of the (0. ltoreq. w.ltoreq.0.1) phase is smaller than that of pure magnesium.

15. A hydrogen occluding alloy as recited in claim 7, wherein X in the general formula (II) is in the range of 0.01. ltoreq. X.ltoreq.1.0.

16. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (II) is in the range of 1.01. ltoreq. y.ltoreq.2.5.

17. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (II) is in the range of 1.02. ltoreq. y.ltoreq.2.5.

18. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (II) is in the range of 1.05. ltoreq. y.ltoreq.2.5.

19. A hydrogen occluding alloy comprising an alloy represented by the following general formula (III):

M_2-xM2M1_y(III)

wherein M is at least one element selected from Be, Ca, Sr, Ba, y, Ra, Ca, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Ti, Zr, Hf, Pd and Pt; m2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen energy (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M) that do not react exothermically withhydrogen; x is more than 0.01 and less than or equal to 1.0; y is more than 0.5 and less than or equal to 1.5.

20. A hydrogen occluding alloy as recited in claim 19, wherein said M2 is selected from the group consisting of Al, Mn, Cr and V.

21. The hydrogen occluding alloy of claim 19, wherein said M is Zr, said M1 is Fe, and said M2 is Cr.

22. A hydrogen occluding alloy as recited in claim 19, wherein said M is Zr, said M1 is Fe, and M2 is V.

23. A hydrogen occluding alloy as recited in claim 19, wherein, in the general formula (III), x is in the range of 0.05. ltoreq. x.ltoreq.0.5.

24. A hydrogen occluding alloy as recited in claim 19, wherein in the general formula (III), y is in the range of 1<y.ltoreq.1.5.

25. A method for surface modification of a hydrogen storage alloy, the method comprising the step of treating the hydrogen storage alloy with an R-X compound, wherein R represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or a substituent thereof; x is a halogen atom.

26. The method according to claim 25, wherein said hydrogen storage alloy comprises an alloy represented by the following formula (IV);

Mg_2-xM2xM1y (IV)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is atleast one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than or equal to 0 and less than or equal to 1.0, and y is more than 0.5 and less than or equal to 2.5.

27. The method of claim 25 wherein said alloy is a₂An alloy of type B, wherein A is an element capable of reacting exothermically with hydrogen and B is an element incapable of reacting exothermically with hydrogen.

28. The method of claim 25, wherein said alloy is AB₅Type alloy wherein A is an element capable of reacting exothermically with hydrogen and B is an element incapable of reacting exothermically with hydrogen.

29. The method of claim 25, wherein said R-X compound is reacted with said hydrogen storage alloy in the presence of an organic solvent.

30. The process of claim 29 wherein said organic solvent is tetrahydrofuran.

31. The process according to claim 29, wherein the organic solvent is diethyl ether.

32. The process of claim 29 wherein said R-X compound is dissolved in an organic solvent and a catalyst is added thereto.

33. The process of claim 32 wherein the catalyst is a condensed polycyclic hydrocarbon.

34. A hydrogen occluding alloy characterized in that at least one of the three most intense peaks in an X-ray diffraction spectrum using Cuk α radiation as a radiation source has a half width [ delta](2 theta)]in the range of 0.2 DEG or more and [ delta](2 theta) or less and 50 DEG or less.

35. A hydrogen occluding alloy as recited in claim 34, wherein said alloy contains Ni as a component of the alloy.

36. A hydrogen occluding alloy as recited in claim 34, wherein said hydrogen occluding alloy comprises an alloy represented by the general formula (IV):

Mg_2-xM2_xM1_y(IV)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than or equal to 0 and less than or equal to 1.0, and y is more than 0.5 and less than or equal to 2.5.

37. A hydrogen occluding alloy as recited in claim 34, wherein at least one of said three strongest peaks has a half width Δ (2 θ) in a range of 0.3 ° ≦ Δ (2 θ) ≦ 10 °.

38. Hydrogen occluding alloy containing 10 wt% or more of Mg and exhibiting a half width Delta (2 theta) of a peak in the vicinity of 20 DEG in an X-ray diffraction spectrum using Cuk α as a radiation source₁) Delta (2 theta) is less than or equal to 0.3 DEG₁) In the range of ≦ 10 ° or in the vicinity of 40 ° (2 θ)₂) Delta (2 theta) is less than or equal to 0.3 DEG₂) Is less than or equal to 10 degrees.

39. The hydrogen occluding alloy as recited in claim 38, wherein said gold-containing alloy is a₂An alloy of type B, where A is an element that reacts exothermically with hydrogen and B is an element that does not react exothermically with hydrogen.

40. The hydrogen storage alloy according to claim 38, wherein said hydrogen storage alloy comprises an alloy represented by the following formula (IV):

Mg_2-xM2_xM1_y(IV)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen energy (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than or equal to 0 and less than or equal to 1.0, and y is more than 0.5 and less than or equal to 2.5.

41. A method for surface modification of a hydrogen absorbing alloy, which comprises the step of subjecting the hydrogen absorbing alloy to mechanical treatment in vacuum or in an inert atmosphere, or in a hydrogen atmosphere.

42. A method according to claim 41, wherein said hydrogen storage alloy comprises Ni as a component of the alloy.

43. The method of claim 41, wherein said hydrogen storage alloy is A₂An alloy of type B, wherein A is an element which reacts exothermically with hydrogen and B is an element which does not react exothermically with hydrogen.

44. The method according to claim 41, wherein said hydrogen storage alloy comprises an alloy represented by the following formula (IV):

Mg_2-xM2_xM1_y(IV)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) which do not react exothermically with hydrogen, x being in the range of 0. ltoreq. x.ltoreq.1.0, and y being in the range of 0.5. ltoreq. y.ltoreq.2.5.

45. The method according to claim 41, wherein said hydrogen storage alloy comprises an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 (V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si, M3 is at least one element selected from the group consisting of (except for M4) elements having a higher electronegativity than Mg, and x is in the range of 0<x<0.5; y is in the range of 0-18.

46. The method according to claim 41, wherein said hydrogen storage alloy comprises an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM₆(VI)

wherein M5 is at least one element selected from the group consisting of elements having an electronegativity higher than that of Mg and an atomic radius 1 to 1.5 times that of an Mg atom; m6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<0.5; y is in the range of 0-18.

47. A negative electrode for a battery comprising a hydrogen storage alloy comprising an alloy represented by the following general formula (I):

Mg₂M1_y(I)

wherein M1 is at least one element selected from the group consisting of elements (other than Mg, elements which react exothermically with hydrogen, Al and B) which do not react exothermically with hydrogen; y is more than 1 and less than or equal to 1.5.

48. The negative electrode of claim 47, wherein M1 is Ni.

49. An alkaline secondary battery using a negative electrode comprising a hydrogen storage alloy as a negative electrode, said hydrogen storage alloy comprising an alloy represented by the following general formula (I)

Mg₂M1_y(I)

50. A negative electrode for a battery comprising a hydrogen storage alloy, said hydrogen storage alloy comprising an alloy represented by the following general formula (II):

Mg_2-xM2_xM1_y(II)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (otherthan Mg and M2) that do not react exothermically with hydrogen; x is more than 0 and less than or equal to 1.0, and y is more than 1 and less than or equal to 2.5.

51. The negative electrode of claim 50, wherein M1 in formula (II) is Ni or Pt, or a mixture of Ni and Pt.

52. The anode of claim 50, wherein M2 in formula (II) is Pd.

53. The negative electrode according to claim 50, wherein y in the general formula (II) is in the range of 1.01. ltoreq. y.ltoreq.1.5.

54. An alkaline secondary battery using as a negative electrode containing a hydrogen storage alloy containing an alloy represented by the following general formula (II):

Mg_2-xM2_xM1_y(II)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than 0 and less than or equal to 1.0, and y is more than 1 and less than or equal to 2.5.

55. A negative electrode for a battery comprising a hydrogen occluding alloy, characterized in that said alloy has a half width Delta (2 theta) of at least one of the three most intense peaks in an x-ray diffraction pattern using Cuk α radiation as a radiation source in the range of 0.2 DEG to Delta (2 α) to 50 deg.

56. An alkalinesecondary battery using a negative electrode containing a hydrogen storage alloy as a negative electrode, characterized in that the half width Delta (2 theta) of at least one of the three most intense peaks in an x-ray diffraction pattern of the alloy using Cuk α rays as a radiation source is in the range of 0.2 DEG to Delta (2 theta) to 50 deg.

57. A battery negative electrode comprising a hydrogen storage alloy containing magnesium, wherein when the negative electrode is immersed in a 6-8N KOH aqueous solution, (a) the elution rate of magnesium ions in an alkali metal hydroxide aqueous solution is less than 0.5mg/kg alloy/hour at normal temperature, or the elution rate of magnesium ions in an alkali metal hydroxide aqueous solution is less than 4mg/kg alloy/hour at 60 ℃, (b) the elution rate of component elements of the alloy in an alkali metal hydroxide aqueous solution is less than 1.5mg/kg alloy/hour at normal temperature, and the elution rate of component elements of the alloy in an alkali metal hydroxide aqueous solution is less than 20mg/kg alloy/hour at 60 ℃.

58. An alkaline secondary battery having a negative electrode containing a hydrogen storage alloy containing magnesium, said negative electrode being housed in a battery case, and a positive electrode being housed in the battery case in such a manner as to face the negative electrode with a separator interposed therebetween, to which an alkali metal electrolyte is added, characterized in that:

after adding the alkali metal electrolyte into the container and sealing for 30 days, the concentration of magnesium ions in the alkali metal electrolyte is less than 2.2 mg/L.

59. A hydrogen occluding alloy comprising an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 (V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn, and Si; m3 is at least one element selected from the group consisting of elements (other than M4) having a higher electronegativity than Mg, and x is in the range of 0<x<0.5; y is in the range of 0-18.

60. A hydrogen occluding alloy as recited in claim 59, wherein x in the formula (V) is in the range of 0.01. ltoreq. x.ltoreq.0.4.

61. A hydrogen occluding alloy as recited in claim 59, wherein y in the general formula (V) is in the range of 1. ltoreq. y.ltoreq.17.5.

62. A hydrogen occluding alloy comprising an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 (VI)

wherein M5 is at least one element selected from the group consisting of elements having an atomic radius 1 to 1.5 times as large as the atomic radius of magnesium (excluding elements having higher electronegativity than magnesium), M6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si, and x is 0<x<0.5; y is more than or equal to 0 and less than 18.

63. A hydrogen occluding alloy as recited in claim 62. Wherein M5 in formula (VI) is selected from Ca, Sr and mixtures of Ca and Sr.

64. A hydrogen occluding alloy as recited in claim 62, wherein x in the formula (VI) is in the range of 0.01. ltoreq. x.ltoreq.0.4.

65. A hydrogen occluding alloy as recited in claim 62, wherein y in the formula (VI) is in the range of 1. ltoreq. y.ltoreq.17.5.

66. A hydrogen storage alloy formed from a mixture comprising:

an alloy having hydrogen storage characteristics; and

at least one additive selected from (a), (b), and (c), wherein: (a) is at least one element selected from the group consisting of elements of group IA, group IIA, group IIIA, group IVA, group VA, group VIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, group VB and group VIB;

(b) an alloy formed by any combination of the elements in (a); (c) is an oxide of any of the elements recited in (a);

the mixture is mechanically treated in a vacuum, inert gas or hydrogen atmosphere.

67. A hydrogen occluding alloy as recited in claim 66, wherein said mixture contains 0.01-50% by volume of said additive with respect to said alloy having hydrogen occluding properties.

68. A hydrogen occluding alloy as recited in claim 66, wherein said alloy having hydrogen occluding properties is A₂Type B alloys in which A is an element which reacts exothermically with hydrogen and B is an element which does not react exothermically with hydrogen.

69. A hydrogen occluding alloy as recited in claim 66, wherein said alloy having hydrogen occluding properties comprises an alloy represented by the following general formula (IV):

Mg_2-xM2_xM1_y(IV)

wherein M2 is at least one element selected from the group consisting of an element capable of reacting exothermically with hydrogen (other than Mg), Al and B; m1 is at least one element selected from the group consisting of elements (other than Mg and M2) that do not react exothermically with hydrogen; x is more than or equal to 0 and less than or equal to 1.0, and y is more than 0.5 and less than or equal to 1.5.

70. A hydrogen occluding alloy as recited in claim 66, wherein said alloy having hydrogen occluding property comprises an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 (V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; m3 is at least one element selected from the group consisting of elements (other than the M4 element) having higher electronegativity than magnesium; x is in the range of 0<x<0.5; y is in the range of 0-18.

71. A hydrogen occluding alloy as recited in claim 66, wherein said alloy having hydrogen occluding properties comprises an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 (VI)

wherein M5 is at least one element selected from the group consisting of elements having an atomic radius 1 to 1.5 times as large as the atomic radius of magnesium (excluding elements having higher electronegativity than magnesium); m6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<0.5; y is in the range of 0-18.

72. A hydrogen occluding alloy as recited in claim 66, wherein at least one element defined by (a) is selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, Pd, Ni, Pt, Cu, Ag and Au.

73. A hydrogen occluding alloy as recited in claim 66, wherein the alloy defined by (b) is selected from the group consisting of MoCo₃、WCO₃、MoNi₃And WNi₃。

74. According to claimThe hydrogen occluding alloy of claim 66, wherein the oxide defined by (c) is selected from FeO and RuO₂、CoO、Co₂O₃、Co₃O₄、RhO₂、IrO₂And NiO.

75. A hydrogen storage alloy comprising:

an alloy having hydrogen storage characteristics; and

0.01-50% by volume of at least one additive, which is a powder having an average particle diameter of 0.01-100 μm, and which is dispersed in the alloy and is selected from (a), (b) and (c), wherein (a) is at least one element selected from the group consisting of elements of IA group, IIA group, IIIA group, IVA group, VA group, VIA group, VIIA group, VIIIA group, IB group, IIB group, IIIB group, IVB group, VB group and VIB group; (b) is an alloy formed from a combination of any of the elements defined in (a); (c) is an oxide of any of the elements defined in (a).

76. A hydrogen occluding alloy as recited in claim 75, wherein said alloy having hydrogen occluding property contains Ni as a component thereof.

77. A hydrogen occluding alloy as recited in claim 75, wherein said alloy having hydrogen occluding property comprises an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 (V)

78. A hydrogen occluding alloy as recited in claim 75, wherein said alloy having hydrogen occluding properties comprises an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 (VI)

79. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy, said hydrogen storage alloy comprising an alloy represented by the following general formula (V):

(Mg_1-xM3_x)_20-yM4 (V)

wherein M4 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; m3 is at least one element selected from the group consisting of elements (other than theM4 element) more electronegative than magnesium; x is in the range of 0<x<0.5; y is in the range of 0-18.

80. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy, said hydrogen storage alloy comprising an alloy represented by the following general formula (VI):

(Mg_1-xM5_x)_20-yM6 (VI)

wherein M5 is at least one element selected from the group consisting of elements having an atomic radius 1 to 1.5 times as large as the atomic radius of magnesium (excluding elements having higher electronegativity than magnesium); m6 is at least one element selected from the group consisting of Ni, Fe, Co, Cu, Zn, Sn and Si; x is in the range of 0<x<05; y is in the range of 0-18.

81. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy obtained by mechanically treating a mixture in a vacuum, an inert gas or a hydrogen atmosphere, the mixture comprising:

an alloy having hydrogen storage characteristics; and

at least one additive selected from the group consisting of (a), (b) and (c), wherein (a) at least one element selected from the group consisting of elements of group IA, group IIA, group IIIA, group IVA, group VA, group VIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, group VB and group VIB; (b) an alloy formed from a combination of any of the elements defined in (a); (c) is an oxide of any of the elements defined in (a).

82. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy, said hydrogen storage alloy comprising:

an alloy having hydrogen storage characteristics; and

0.01-50 vol% of at least one additive powder with an average particle size of 0.01-100 μm, wherein the additive is dispersed in the alloy and is selected from (a), (b) and (c), and the (a) is selected from IA group, IIA group, IIIA group, IVA group and VA group. At least one element selected from the group consisting of elements of group VIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, group VB and group VIB; (b) an alloy formed from a combination of any of the elements defined in (a); (c) is an oxide of any of the elements defined in (a).