JPH1069908A - Hydrogen storage alloy, electrode and alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy whose hydrogen storage characteristic near room temperature, particularly hydrogen storage rate, is enhanced. SOLUTION: A hydrogen storage alloy includes two or more kinds of regions selected from among a first region in which its Mg content is not less than 50mol% to not more than 75mol% and its Ni content is not more than 50mol%; a second region in which its Mg content is not less than 0mol% to less than 50mol% and its Ni content is less than 75mol%; a third region in which its Mg content is not less than 75mol%; and a fourth region in which its Ni content is not less than 75mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy, an electrode, and an alkaline secondary battery.

[0002]

2. Description of the Related Art A hydrogen storage alloy is an alloy that can stably store and store hydrogen (as a normal temperature and normal pressure gas) having a volume of tens of thousands or more times its own volume. For this reason, the hydrogen storage alloy is regarded as promising as a material that can safely, easily store, store, and transport hydrogen as an energy source. The application fields of hydrogen storage alloys as new functional materials are:
Hydrogen storage / transport, heat storage / transport, thermo-mechanical energy conversion, hydrogen separation / purification, hydrogen isotope separation, batteries using hydrogen as active material, catalysts in synthetic chemistry, temperature sensors, etc. Have been proposed throughout.

Further, in recent years, nickel-hydrogen secondary batteries using a hydrogen storage alloy as a negative electrode material have a high capacity,
It has the characteristics of being resistant to overcharge and overdischarge, capable of high-rate charge / discharge, being clean, and being compatible with nickel-cadmium batteries. Attention has been paid to its application and practical application at present. Thus, the hydrogen storage alloy,
Utilizing its physical and chemical properties, it has potential for various applications and can be counted as one of the key materials in the future industry.

[0004] Metals that occlude hydrogen include metal elements that react exothermically with hydrogen, ie, can form stable compounds with hydrogen (eg, Pd, Ti, Zr, V, and other rare earth metal elements, alkaline earth elements). ) May be used alone, or these metal elements may be alloyed with other metals.

[0005] One advantage of alloying is that the bonding force between metal and hydrogen is appropriately reduced so that not only the occlusion reaction but also desorption (release) occurs.
The reaction should be relatively easy. The second advantage is the size of the hydrogen gas pressure (equilibrium pressure; plateau pressure) required for the reaction, the width of the equilibrium region (plateau region), the change in the equilibrium pressure during the process of absorbing hydrogen (flatness). Storage and release characteristics such as A third advantage is that chemical and physical stability is enhanced.

[0006] Conventional metal element capable of exothermically reacting with the above-mentioned hydrogen A is the composition of the hydrogen-absorbing alloy, when the other metal and B, (1) AB ₅ type (for example La
Ni _5, CaNi _5, etc.), ₍₂₎ AB 2 type (e.g. MgZ
n _2, ZrNi _2, etc.), (3) AB system (e.g. TiNi,
(4) A ₂ B-based (eg, Mg ₂ Ni, Ca
₂ Fe, etc.) can be roughly classified into (5) Others (e.g. cluster, etc.).

Among them, (1) LaNi ₅ , Laves phase alloys belonging to (2) or some alloys belonging to (3) can react with hydrogen near normal temperature and have relatively high chemical stability. Therefore, it has been widely studied as a material for an electrode of a secondary battery described above.

However, the Mg ₂ Ni-based hydrogen storage alloy (4) has the following various problems. Very high stability with hydrogen, hard to release hydrogen after occlusion. Unless the temperature is relatively high (about 200 to 300 ° C.), the occlusion / release reaction does not occur or the reaction is extremely slow. As a result, the Mg ₂ Ni-based hydrogen storage alloy has not been widely applied to uses other than storage and transportation. However,
Its potential hydrogen storage capacity is equal to or higher than that of other alloys per volume, and has excellent properties of 2 to several times per weight. Therefore, if the problems of the Mg ₂ Ni-based hydrogen storage alloy are solved, applications to various physical and chemical and industrial fields which have been using other alloy systems until now are expanded, and the hydrogen storage alloy is further used. It will also lead to the development of new fields.

Although the system of (5) has been reported academically, there are almost no systems which have reached the stage of practical application or practical application at present. As described above, among various hydrogen storage alloys, Mg ₂ Ni-based alloys are light-weight, large-capacity, and generally can be produced with a composition centered on alkaline earth metals and iron group metals, so that they are raw materials. It also has the feature of being inexpensive. However, the hydrogen storage alloy also has various problems as described above.

[0010]

The object of the invention is to solve the present invention, Mg ₂ Ni
An object of the present invention is to provide a hydrogen storage alloy having improved hydrogen storage characteristics near room temperature, particularly, a hydrogen storage speed, among various problems of a system alloy.

An object of the present invention is to provide an electrode containing a hydrogen storage alloy with an improved hydrogen storage rate and an alkaline secondary battery with improved charge / discharge cycle characteristics.

[0012]

According to the present invention, a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less; Mg content of 0 mol%
As described above, two types selected from a second region having a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a fourth region having a Ni content of 75 mol% or more. The hydrogen storage alloy is characterized by including the above regions.

According to the present invention, the Mg content is 50 mol%
First region in which the Ni content is not less than 75 mol% and 50 mol% or less; Mg content is not less than 0 mol% and 50 mol%
A second region having a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a Ni content of 7
Two or more regions selected from a fourth region of 5 mol% or more;
An electrode comprising a hydrogen storage alloy having the following formula:

According to the present invention, the Mg content is 50 mol%
First region in which the Ni content is not less than 75 mol% and 50 mol% or less; Mg content is not less than 0 mol% and 50 mol%
A second region having a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a Ni content of 7
Two or more regions selected from a fourth region of 5 mol% or more;
The present invention provides an alkaline secondary battery including a negative electrode including a hydrogen storage alloy having the following formula:

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the hydrogen storage alloy according to the present invention, a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less; Mg content of 0 mol% or more and less than 50 mol% In the second region, where the Ni content is less than 75 mol%, Mg
At least two or more regions selected from a third region having a content of 75 mol% or more and a fourth region having a Ni content of 75 mol% or more (hereinafter, referred to as a II region).

Here, the region is a homogeneous crystal grain region, a crystal grain region in which precipitated particles at a microscopic level are uniformly dispersed, an intergranular region existing between crystal grains, an aggregated region of microcrystals, and an amorphous region. A region, such as a region, that can be distinguished from the others in terms of composition and structure.

The alloy generally has a structure in which the second region is present in the first region. The boundary between the second region and the first region may be clear or unclear. In other words, the second region may be present as a phase in the alloy, or the boundary may not be clear, and the target composition gradually becomes the target from the periphery toward the center. It may be. In the alloy having such a structure, two or more alloys selected from the second to fourth regions may be in contact with each other.

Hereinafter, each area (first to fourth areas) will be described. (1) First Region The first region (M1) generally functions as a base for storing and releasing hydrogen. The Mg content in this region,
When the Ni content is out of the range, the hydrogen storage amount of the alloy decreases, and the hydrogen storage characteristics deteriorate. From the viewpoint of improving the hydrogen storage amount, the lower limit of the Ni content in the first region is preferably set to 25 mol%. The first region may be, for example, a region containing Mg ₂ Ni as a main component and containing less than 15 mol% of impurities. The alloy including the first region having such a composition can further improve the hydrogen storage capacity. As the impurities, Cr, Mo, Mn, Tc, Re, Fe, Ru, Os, Cr, Mo, Mn, Tc mixed during the preparation of the alloy or during the heat treatment because the Mg component in the alloy is large.
Examples include Co, Cu, Al, Ag, B, C, and Si.
Also, the oxide formed by each of the above elements is allowed to be mixed as an impurity. In particular, the first region is the M
It is preferable that the g content be 60 mol% or more and 70 mol% or less, and the Ni content be 20 mol% or more and 40 mol% or less. When the Mg content and the Ni content are in such ranges, it becomes easy to obtain the above-described region having a composition mainly composed of Mg ₂ Ni. (2) Second Region It is presumed that the second region (M2) functions to destabilize the stored hydrogen and promote the hydrogen release reaction. If the Mg content or the Ni content is out of the above range, the occluded hydrogen will be stably present in the alloy, and the hydrogen release characteristics of the alloy will be reduced. The second region may be, for example, a region containing MgNi ₂ as a main component and containing less than 15 mol% of impurities. An alloy including the second region having such a composition includes:
The hydrogen release characteristics can be further improved. The impurities include Rh, Ir, Pd, and Pd mixed during the alloy preparation or heat treatment due to the large amount of the Ni component in the alloy.
t, Au, Cd, Sn, Y, La, Ce, Pr, Sm,
Co and Fe are mentioned. Also, the oxide formed by each of the above elements is allowed to be mixed as an impurity. In particular, in the second region, it is preferable that the Mg content be 20 mol% or more and 40 mol% or less, and the Ni content be 60 mol% or more and 70 mol% or less. Mg
When the content and the Ni content are in such ranges, the above-described region of the composition containing MgNi ₂ as a main component is easily obtained. (3) Third Region This third region (M3) is assumed to function to increase the amount of hydrogen occlusion of the alloy. If the Mg content is outside the above range, the hydrogen storage capacity of the alloy decreases. Examples of the third region include a region containing Mg as a main component and containing less than 25 mol% of impurities. Examples of the impurities include Li, Na, K, which are mixed during alloy preparation or heat treatment.
Ca, Sr, Ba, Rb, Sc, In, Tl, Pb, S
b, Bi, Te, Ni, Co, Fe, Zr, and Hf. Particularly, when the Mg content is 80 mol% or more,
It is preferable that the content is not more than mol% because the hydrogen storage amount can be further increased. (4) Fourth Region This fourth region (M4) is assumed to act as a hydrogen dissociation catalyst when storing hydrogen. When the Ni content is out of the range, the hydrogen storage rate of the alloy decreases. The fourth region is made of, for example, Ni as a main component and 25%.
Those containing less than mol% of impurities are included. As the impurities, Ti mixed during alloy preparation or heat treatment,
V, Nb, Ta, Mg, Ga, Zn, Ge, N, O,
P, S, As, Se, and F are mentioned. In particular, the Ni
The content is set to 80 mol% or more and 95 mol% or less because
This is preferable because the hydrogen storage rate can be further increased.

The coexistence amount of the second region is 0.001 to 5
The content is desirably 0 mol%, more preferably 1 to 30 mol%. When the coexistence amount of the second region is less than 0.001 mol%, it becomes difficult to sufficiently increase the hydrogen storage rate of the hydrogen storage alloy at around normal temperature. On the other hand, if the coexistence amount of the second region exceeds 50 mol%, the hydrogen storage amount of the hydrogen storage alloy may decrease.

It is preferable that one component of the second region is a second region (M2). This second area (M2)
Is 0.1 to 90 mol% in the total compounding amount of the second region.
Preferably, it occupies.

[0021] The second region preferably comprises a second region (M2) and a third region (M3). Such an alloy including the second region can dramatically improve the hydrogen storage speed near normal temperature while maintaining a high hydrogen storage amount. It is preferable that the second region and the third region are present in the alloy at 1 to 10 mol%, respectively.

The first region (M1) and the second region (M1)
2 or more regions selected from M4), for example, a high frequency melting method, a liquid quenching method, an atomizing method, a sintering method, a plating method, a CVD method, a sputtering method, a rolling method, and a sol. -It is produced by a gel method or the like. The composition of each region can be analyzed using electron probe X-ray micro area analysis (EPMA), energy dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES), or the like.

The hydrogen storage alloy according to the present invention described above has a Mg content of 50 mol% or more and 75 mol% or less, and
a first region where the i content is 50 mol% or less; a second region where the Mg content is 0 mol% or more and less than 50 mol% and the Ni content is less than 75 mol%, and where the Mg content is 75 mol% or more. A conventional region of Mg ₂ , which includes a third region and at least two regions selected from a fourth region having a Ni content of 75 mol% or more.
The hydrogen storage characteristics, particularly the hydrogen storage speed, can be improved as compared with the Ni alloy.

In other words, when a hydrogen storage alloy comprising a region containing 50 mol% or more of Mg and 25 mol% or more of Ni is required, not only does it require a relatively high temperature (about 300 ° C.) when storing hydrogen, The storage speed is also very low,
No hydrogen can be absorbed at around normal temperature.
As in the present invention, at least two or more regions selected from the second to fourth regions coexist in the first region,
By using three or more phases, the dissociation reaction of hydrogen adsorbed on the surface of the hydrogen storage alloy is promoted, and the hydrogen storage characteristics, particularly the hydrogen storage speed, can be significantly increased.

Further, the hydrogen storage alloy according to the present invention has a larger amount of hydrogen storage per weight than conventional rare earth hydrogen storage alloys, and is inexpensive and lightweight. Next, an example of a cylindrical nickel-metal hydride secondary battery of the alkaline secondary batteries according to the present invention will be described with reference to FIG.

As shown in FIG. 1, an electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a bottomed cylindrical container 1. ing. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. Hole 6 in the center
The first sealing plate 7 having a circular shape is disposed at the upper opening of the container 1. Ring-shaped insulating gasket 8
Is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate 7 is connected to the container 1 through the gasket 8 by caulking to reduce the diameter of the upper opening inward. And airtightly fixed. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6.
The safety valve 11 made of rubber includes the sealing plate 7 and the positive electrode terminal 1.
It is arranged so as to close the hole 6 in a space surrounded by 0. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole of the holding plate 12. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described. 1) Positive electrode 2 The positive electrode 2 is prepared, for example, by adding a conductive material to nickel hydroxide powder as an active material, kneading the mixture with a polymer binder and water to prepare a paste, and filling the paste into a conductive substrate. After drying and drying, it is produced by molding.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, and carbon. Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polytetrafluoroethylene.

Examples of the conductive substrate include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

2) Negative electrode 4 This negative electrode 4 is obtained by adding a conductive material to a powder of a hydrogen storage alloy,
A paste is prepared by kneading with a polymer binder and water, and the paste is filled in a conductive substrate and dried,
It is produced by molding.

The hydrogen storage alloy is an alloy as described above, that is, a first region where the Mg content is 50 mol% or more and 75 mol% or less and the Ni content is 50 mol% or less; When the Ni content is less than 50 mol% and the Ni content is
At least two regions selected from a second region having a mol content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a fourth region having a Ni content of 75 mol% or more.

Examples of the polymer binder include those similar to those used in the positive electrode 2. Examples of the conductive material include carbon black.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a perforated rigid plate, and a nickel net; Can be mentioned.

[0034] Since such a negative electrode contains a hydrogen storage alloy having an improved hydrogen storage rate, the stability at the time of charge and discharge cycles can be improved. Further, the hydrogen storage alloy as the negative electrode material is cheaper and lighter than the rare earth-based hydrogen storage alloy, so that a low-cost and lightweight negative electrode can be realized.

3) Separator 3 The separator 3 is made of, for example, a polymer non-woven fabric such as a polypropylene non-woven fabric, a nylon non-woven fabric, or a non-woven fabric obtained by mixing polypropylene fibers and nylon fibers. In particular, a polypropylene nonwoven fabric whose surface has been hydrophilized is suitable as a separator.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

The above-described alkaline secondary battery has excellent charge / discharge cycle characteristics and lightness because it has an improved hydrogen storage rate near room temperature and is provided with a negative electrode containing a cheap and lightweight hydrogen storage alloy.

In FIG. 1 described above, an example of a cylindrical alkaline secondary battery is described. However, in the present invention, an electrode group and an alkaline electrolyte prepared by interposing a separator between a positive electrode and a negative electrode have a bottomed angle. The present invention can be similarly applied to a prismatic alkaline secondary battery having a structure housed in a cylindrical container.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. FIG. 2 is a schematic diagram showing a temperature scanning type hydrogen storage / release characteristic evaluation apparatus used for evaluating the hydrogen storage alloys of Examples 1 to 20 and Comparative Examples 1 to 4. The hydrogen cylinder 31 is connected to a sample container 33 through a pipe 32. The pipe 32 is branched on the way, and an end of the branch pipe 34 is connected to a vacuum pump 35. The pressure gauge 36 is attached to a pipe portion 34a further branched from the branch pipe 34. In the portion of the pipe 32 between the hydrogen cylinder 31 and the sample container 33, the cylinder 3
First from 1 side, the second valve 37 _1, 37 ₂ is interposed. The accumulator 38 is provided with the first and second valves 37.
It is connected to the pipe 32 portion between _1, 37 _2. The vacuum pump 35 is connected to the branch pipes 34a through the third valve 37 _3. The heater 39 is attached to the sample container 33. The thermocouple 40 is inserted into the sample container 33. A temperature controller 42 controlled by a computer 41 is connected to the thermocouple 40 and the heater 39, and adjusts the temperature of the heater 39 based on the temperature detected from the thermocouple 40. The recorder 43 controlled by the computer 41 is connected to the pressure gauge 36 and the temperature controller 42.

(Examples 1 to 20 and Comparative Examples 1 to 4) Hydrogen storage alloys having the compositions shown in Tables 1 to 3 below were prepared. In the following Tables 1 to 3, M1 is a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less, M2 is a Mg content of 0 mol% or more, A second region with less than 50 mol% and less than 75 mol% Ni content, M
3 is a third region where the Mg content is 75 mol% or more, and M4 is N
A fourth region where the i content is 75 mol% or more is shown. The coexistence amount (mol%) of each region (M2 to M4) was calculated assuming that the total amount of the regions existing in the hydrogen storage alloy was 100 mol%. Further, I1 to I4 in Tables 1 to 3 below indicate impurities in each region (M1 to M4). The contents of metals and impurities in each region (M1 to M4) were calculated assuming that the total amount of elements in each region was 100 mol%. The composition of each region (M1 to M4) was analyzed by EDX.

Further, the alloys of Examples 1 to 20 and Comparative Examples 1 to 4 are mainly composed of the first region, and two or more regions selected from the second to fourth regions in the first region. Existed. Also, the boundaries between the second to fourth regions were unclear. Each area (2nd to 4th area)
Was such that the desired composition was obtained from the periphery toward the center.

Next, each of the hydrogen storage alloys was stored in the sample container 33 (atmospheric temperature 25 ° C.) shown in FIG.
The first valve 37 ₁ is closed, and the second and third valves 37 ₂ ,
Open 37 _3, the pipe 32 by operating the vacuum pump 35
The air in the branch pipe 34 and the pressure accumulator 38 was exhausted. After closing the second and third valves 37 ₂ and 37 ₃ , the first valve 37 ₁ is opened to supply hydrogen from the hydrogen cylinder 31 to replace the inside of the pipe 32, the branch pipe 34, and the accumulator 38 with hydrogen. did. Subsequently, the first valve 37 ₁
Was closed, and at this time, the amount of hydrogen introduced was calculated from the pressure in the system indicated by the pressure gauge 36. The second valve 37 continues
₂ was opened, hydrogen was supplied into the sample container 33, and the temperature was monitored with a thermocouple 40. Thereafter, the sample container 33
Computer 4 so that the internal temperature rises at a constant rate
1 and the temperature controller 42, and the temperature was scanned using the heater 39 receiving the control signal. At this time, the pressure change in the container 33 was detected by the pressure gauge 36 and recorded by the recorder 43.

As described above, the amount of hydrogen (wt%) occluded in each hydrogen storage alloy up to one hour after the introduction of a fixed amount of hydrogen into the sample container 33 is changed by the pressure change in the container 33. Was measured by detection of These results are shown in Table 1 below.
To Table 3 together.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

As is clear from Tables 1 to 3, the hydrogen storage alloy made of the Mg ₂ Ni alloy as in Comparative Example 1 requires a considerably high temperature (about 300 ° C.) when reacting with hydrogen. Furthermore, since the reaction rate is extremely low, it does not react with hydrogen at around normal temperature at all, and it can be seen that the hydrogen storage amount is almost zero. Further, it can be seen that the hydrogen storage properties of the hydrogen storage alloy in which two phases coexist as in Comparative Examples 2 to 4 hardly improve.

On the other hand, as in Examples 1 to 20, M1
It can be seen that at least two types of regions M2 to M4 coexist in the region, that is, a hydrogen storage alloy of three or more phases has a remarkable increase in the storage speed and has excellent hydrogen storage characteristics.

(Examples 21 to 40 and Comparative Examples 5 to 8)
The hydrogen storage alloy powder having the composition shown in Tables 4 to 6 and the electrolytic copper powder were mixed at a weight ratio of 1: 1.
g using a tableting machine (inner diameter 10 mm) at a pressure of 1000
Pellets were produced by pressing for 5 minutes under the condition of 0 kg. This pellet is sandwiched between nickel meshes,
24 types of alloy electrodes (negative electrodes) were produced by spot welding the periphery and spot welding nickel lead wires. In the following Tables 4 to 6, M1 is a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less, M2 is a Mg content of 0 mol% or more,
A second region in which the Ni content is less than 75 mol% and less than 50 mol%, a third region in which the Mg content is 75 mol% or more, M 3
Reference numeral 4 denotes a fourth region in which the Ni content is 75 mol% or more. The coexistence amount (mol%) of each region (M2 to M4) is
The calculation was made assuming that the total amount of the regions existing in the hydrogen storage alloy was 100 mol%. Further, I1 to I4 in the following Tables 4 to 6 indicate impurities in each region (M1 to M4). The contents of metals and impurities in each region (M1 to M4) were calculated assuming that the total amount of elements in each region was 100 mol%.

Further, Examples 21 to 40 and Comparative Examples 5 to 8
Has the first region as a main component, and in the first region, two or more types of regions selected from the second to fourth regions exist. In addition, the second region to the fourth region
The boundaries of the area were unclear. Each area (2nd to 4th area)
Was such that the desired composition was obtained from the periphery toward the center.

Each of the negative electrodes was immersed in an 8 N aqueous potassium hydroxide solution together with a sintered nickel electrode as a counter electrode, and a charge / discharge cycle test was conducted at a temperature of 25 ° C.
The maximum discharge capacity was measured. The charge and discharge conditions were as follows: after charging for 10 hours at a current of 100 mA per 1 g of hydrogen storage alloy, resting for 10 minutes, and then charging at 20 mA per 1 g of hydrogen storage alloy.
The discharge cycle was repeated until the current reached −0.5 V with respect to the mercury oxide electrode. The results are shown in Table 4 below.
Also shown in Table 6.

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

As is clear from Tables 4 to 6, as in Examples 21 to 40, at least two or more regions of M2 to M4 coexist in the region of M1, that is, a hydrogen storage alloy of three or more phases is contained. It can be seen that the battery provided with the negative electrode has a significantly higher discharge capacity than the batteries of Comparative Examples 5 to 8, and has excellent charge / discharge characteristics.

[0056]

As described above in detail, according to the present invention, while maintaining a high hydrogen storage capacity, the hydrogen storage speed near normal temperature is improved as compared with the conventional Mg-Ni-based hydrogen storage alloy. Can provide occlusion alloys. Therefore, the hydrogen storage alloy of the present invention can be used in various application fields in which other alloy systems have been used, for example, storage / transport of hydrogen, storage / transport of heat, heat-transfer.
Mechanical energy conversion, separation and purification of hydrogen, separation of hydrogen isotopes, batteries using hydrogen as an active material, catalysts in synthetic chemistry, temperature sensors, etc. are further expanded, and further cultivation of new fields using hydrogen storage alloys It has remarkable effects such as being able to do.

Further, the electrode and the alkaline storage battery according to the present invention can be applied to the charge and discharge reaction of a magnesium-containing hydrogen storage alloy, which has been difficult in the past, so that the weight and cost can be reduced and the excellent charge can be achieved. It has remarkable effects such as having discharge characteristics. Further, the electrode according to the present invention can be used as an electrode for electrolysis (for example, a negative electrode for electrolysis of saline).

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a cylindrical nickel-metal hydride secondary battery which is an example of an alkaline secondary battery according to the present invention.

FIG. 2 is a schematic view showing a temperature scanning type hydrogen storage / release characteristic evaluation apparatus used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... container, 2 ... positive electrode, 4 ... negative electrode, 5 ... electrode group, 7 ... sealing plate, 31 ... hydrogen cylinder, 33 ... sample container, 35 ... vacuum pump, 36 ... pressure gauge, 39 ... heater, 41 ... computer, 42 ... temperature controller.

Claims (9)

[Claims] 1. a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less;
A second region having a Mg content of 0 mol% or more and less than 50 mol% and a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a second region having a Mg content of 75 mol% or more. A hydrogen storage alloy, comprising: two or more regions selected from four regions. 2. The hydrogen storage alloy according to claim 1, wherein one of the at least two regions is the second region. 3. The hydrogen storage alloy according to claim 1, wherein the two or more regions are present in an amount of 0.001 to 50 mol% in the alloy. 4. a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less;
A second region having a Mg content of 0 mol% or more and less than 50 mol% and a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a second region having a Mg content of 75 mol% or more. An electrode comprising a hydrogen storage alloy containing at least two regions selected from four regions. 5. The electrode according to claim 4, wherein one of the two or more types of regions is the second region. 6. The electrode according to claim 4, wherein said two or more kinds of regions are present in the alloy in an amount of 0.001 to 50 mol%. 7. a first region having a Mg content of 50 mol% or more and 75 mol% or less and a Ni content of 50 mol% or less;
A second region having a Mg content of 0 mol% or more and less than 50 mol% and a Ni content of less than 75 mol%, a third region having a Mg content of 75 mol% or more, and a second region having a Mg content of 75 mol% or more. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy containing at least two regions selected from four regions. 8. The alkaline secondary battery according to claim 7, wherein one of the two or more types of regions is the second region. 9. The alkaline secondary battery according to claim 7, wherein the two or more regions are present in an amount of 0.001 to 50 mol% in the alloy.