JPH0987785A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hydrogen storage alloy high in hydrogen absorbing and discharging rate and of which initial activation can be carried out in a short time by specifying the compsn. composed of Zr, Ti, Mn, V, La, Ce, O and Ni and forming its structure into a specified one. SOLUTION: In the hydrogen storage alloy having the whole compsn. contg., by weight, 25 to 45% Zr, 1 to 12% Ti, 10 to 20% Mn, 2 to 12% V, 0.5 to 5% La and/or Ce and 0.2 to 1.7%. O, and the balance Ni (where the content is regulated to >=25%) with inevitable impurities, hydrogen-oxidation treatment product material phases are dispersedly distributed into the matrix phases of a Zr-Ni-Mn base alloy, and the main body of the hydrogen-oxidation treatment product material phases is composed of the oxides of La and/or Ce and an La and/or Ce-Ni base alloy. Furthermore, this alloy has a structure in which the above hydrogen-oxidation treatment product material phases are exposed to the inside faces of numberless cracks generated at the time of the hydrogen treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy having an extremely high hydrogen absorption and desorption rate and exhibiting excellent initial activation when used practically as an electrode of a battery, for example.

[0002]

2. Description of the Related Art Conventionally, a large number of hydrogen storage alloys have been generally proposed, and recently, 6-11 November 1994.
Hydrogen storage alloys were announced at the "International Symposium on the Fundamentals and Applications of Metal-Hydrogen Systems" held in Fujiyoshida, Japan. This hydrogen storage alloy has a Zr: 22.1 to 25.5% by weight (hereinafter,% means% by weight).
%, Ti: 11.6-13.4%, Mn: 23.7
~ 24.6%, Cr: 22.4 to 23.3%, L
a: 7.5% or less, the rest of which has a composition of Ni and inevitable impurities, and the representative structure of which is shown in FIG. It has a two-phase structure of a base phase of the alloy and a dispersed phase of the La-Ni alloy distributed along the grain boundaries of the base phase. In the conventional hydrogen storage alloy, the dispersed phase of the La-Ni alloy dissociates hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) by the catalytic action of the La-Ni alloy and dissociates the dissociated hydrogen atoms with Zr-. The Ni-Mn-based alloy absorbs at a much higher rate than the base phase, and thus the absorption of hydrogen atoms in the Zr-Ni-Mn-based alloy base phase is mainly caused by the La-N.
It is also known that it has a hydrogen absorption function performed through the dispersed phase of the i-based alloy, and hydrogen release is due to the opposite function. Further, the above conventional hydrogen storage alloy is prepared by preparing a Ni-based alloy molten metal having the above composition, casting it into an ingot, and heating the ingot to a predetermined temperature within a range of 950 to 1050 ° C. in a non-oxidizing atmosphere of vacuum or inert gas. It is manufactured by performing a homogenizing heat treatment under the condition of holding for a predetermined time. In general, when a hydrogen storage alloy is applied to, for example, an electrode of a battery, the hydrogen storage alloy has a sufficient discharge capacity with respect to the electrode in which the hydrogen storage alloy is incorporated, that is, the hydrogen storage alloy. The initial activation in which the charging and discharging are repeatedly performed is performed until the discharge capacity brought by is almost maximized, and this initial activation is put to practical use.

[0003]

On the other hand, in recent years, there has been a strong demand for higher output and higher performance and more energy saving of batteries and heat pumps to which many hydrogen storage alloys have been applied in recent years. It is strongly desired that alloys have an initial activation in a shorter time as well as a hydrogen absorption / desorption rate which is much higher than the hydrogen absorption / desorption rate of the conventional hydrogen storage alloy.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above viewpoints, as a result of research to improve the hydrogen absorption / desorption rate and initial activation of the hydrogen storage alloy, (a) First, Zr: 25 to 45%, Ti: 1
~ 12%, Mn: 10-20%, V: 2-12
%, La and / or Ce: 0.5 to 5%, and the balance was Ni-Zr alloy having a composition of Ni (however, 25% or more) and inevitable impurities were melted and cast. After that, when this Ni—Zr alloy ingot is subjected to homogenizing heat treatment under the same conditions as the above-mentioned conventional conditions, the crystal grains of the base phase of the Zr—Ni—Mn alloy are similar to the above-mentioned conventional hydrogen storage alloy. La and / or Ce-N along the world
The i-based alloy (hereinafter referred to as La (Ce) -Ni-based alloy) has a structure in which a dispersed phase is present. Further, following the homogenizing heat treatment, 400 to 7 in a hydrogen atmosphere.
When the hydrogenation treatment is performed under the condition of cooling at a predetermined temperature within a range of 00 ° C. for a predetermined time, the dispersed phase of the La (Ce) —Ni-based alloy formed by the homogenizing heat treatment preferentially acts with hydrogen in the atmosphere. In response to the reaction with La and / or Ce hydride (hereinafter referred to as La (Ce) hydride) and La and / or Ce-Ni based alloy (hereinafter referred to as La (Ce)-
(Indicated by a Ni-based alloy), and the hydrotreating product phase exhibits a large thermal expansion as compared with the base phase of the Zr—Ni—Mn-based alloy. Innumerable cracks are generated from the hydrogen reaction product phase as a starting point, and the hydrogenation product phase is exposed on the inner surface of the crack. Further, for example, in an oxidizing atmosphere, 400-500. When the oxidation treatment is carried out at a predetermined temperature within the range of ° C for a predetermined time, the La (Ce) hydride becomes La (Ce) oxide and, as a result, Ni-Zr
As shown in the schematic enlarged structure diagram of FIG. 1, the representative alloy of the system alloy has the hydrooxidized product dispersedly distributed in the matrix phase of the Zr—Ni—Mn alloy, and the hydrooxidized product phase is obtained. Is mainly composed of La (Ce) -Ni alloy and La (Ce) oxide, and has innumerable cracks, and the inside of the cracks has a structure in which the hydrooxidation product phase is exposed. To become.

(B) In the Ni-Zr alloy of (a) above, L of the hydro-oxidation treatment product phase constituting the alloy is formed.
a (Ce) -Ni-based alloy and La (Ce) oxide
While dissociating hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) by the same action as the dispersed phase of the La-Ni alloy in the conventional hydrogen storage alloy shown in FIG. The dissociated hydrogen atoms are absorbed at a much higher rate than the Zr-Ni-Mn-based matrix phase, and the release has an effect by the opposite mechanism, but the hydrooxidation product phase has numerous cracks. Many are exposed on the inner surface, and as a result the working area is expanded,
The rate of hydrogen absorption and desorption is much faster than the rate of hydrogen absorption and desorption in the conventional hydrogen storage alloy, and the absorption rate of hydrogen atoms in the matrix phase at the time of initial activation is significantly increased because it is performed in a wide action area. Therefore, it is possible to significantly promote the initial activation. The research results shown in (a) and (b) above were obtained.

The present invention was made based on the above research results, and Zr: 25-45%,
Ti: 1 to 12%, Mn: 10 to 20%, V:
2-12%, La and / or Ce: 0.5-5%,
Oxygen: 0.2-1.7%, with the balance being Ni (however, 25% or more) and inevitable impurities, and hydro-oxidation treatment of the base phase of the Zr-Ni-Mn alloy. The physical phase is distributed and distributed, the main component of the hydro-oxidation treatment product phase is a structure composed of La (Ce) oxide and La (Ce) -Ni based alloy, and there are innumerable cracks generated during the hydro-treatment. In addition, the present invention is characterized by a hydrogen storage alloy having a structure in which the hydrooxidized product phase is exposed on the inner surface of the crack, having a high hydrogen absorption / desorption rate and excellent initial activation.

Next, in the hydrogen storage alloy of the present invention, the reason why the composition of the Ni-Zr alloy constituting the hydrogen storage alloy is limited as described above will be explained. (A) Zr Zr component has a function of forming a base phase together with Ni and Mn to contribute to an increase in hydrogen storage amount, as described above.
If the proportion is less than 25%, the desired hydrogen storage capacity cannot be secured, while if the proportion exceeds 45%, the hydrogen storage capacity of the entire alloy will decrease, so It is set to 25 to 45%, preferably 32 to 40%.

(B) The Ti-Ti component has the function of making the equilibrium hydrogen dissociation pressure of the alloy lower than atmospheric pressure, for example, at room temperature, thereby contributing to the promotion of absorption and desorption of hydrogen, and also in the matrix phase. Although it has an effect of increasing the storage amount, if the ratio is less than 1%, the desired effect cannot be obtained, while if the ratio exceeds 12%, the equilibrium hydrogen dissociation pressure is again, for example, atmospheric pressure at room temperature. Since it rises above, and the absorption and release of hydrogen decreases, the ratio is 1 to 12%, preferably 4 to
8%.

(C) Mn The Mn component mainly has a function of forming a matrix phase to increase the hydrogen storage amount, but if the ratio is less than 10%, the desired effect is not obtained on the other hand. If the ratio exceeds 20%, the absorption and release of hydrogen will be hindered. Therefore, the ratio is 10 to 20%, preferably 14 to 1.
8%.

(D) The V V component has a function of stabilizing the equilibrium hydrogen dissociation pressure of the alloy and increasing the hydrogen storage amount, but if the ratio is less than 2%, the desired effect can be obtained in the above function. On the other hand, if the ratio exceeds 12%, the equilibrium hydrogen dissociation pressure becomes too low, and it becomes difficult to release the stored hydrogen, and as a result, a decrease in the hydrogen storage amount cannot be avoided. It was set to 2 to 12%, preferably 4 to 8%.

(E) La and Ce These components have the function of dissociating and absorbing hydrogen in the atmosphere at a much higher rate than the matrix phase as described above, and then recombining and releasing it into the atmosphere. -Ni-based alloy and La (Ce) are essential components for the formation of oxides, but if the proportion is less than 0.5%, the above La (Ce) -N is used.
If the proportion of i-based alloy and La (Ce) oxide formed is too small, a desired high hydrogen absorption / desorption rate cannot be secured. On the other hand, if the proportion exceeds 5%, the dispersed phase having a small hydrogen storage capacity is obtained. Is too large, and the hydrogen storage capacity of the entire alloy is reduced.
.About.5%, preferably 1 to 4%.

(F) Oxygen Oxygen is mainly La which constitutes the hydro-oxidation treatment product phase.
Along with the (Ce) -Ni-based alloy, hydrogen molecules (H
₂ ) dissociates and absorbs hydrogen atoms (H) at a faster rate than the base phase, and diffuses the absorbed hydrogen atoms into the base phase, while releasing hydrogen from the base phase to release hydrogen atoms quickly. La (Ce), which has the effect of rebinding to
It is an essential component for the formation of oxides, but its proportion is 0.
If it is less than 2%, the formation of La (Ce) oxide is too small to sufficiently exert the above-mentioned effects, and the formation of cracks is also insufficient, while the ratio exceeds 1.7%. When the ratio of La (Ce) oxide is relatively large, the strength is lowered and the tendency of pulverization is promoted. Therefore, the ratio is preferably 0.2 to 1.7%, Was determined to be 0.4 to 1.0%.

(G) Ni When the Ni component content is less than 25%, not only the formation of the hydro-oxidation treatment product phase is insufficient, but also the cracks generated during the hydro-treatment are insufficient. Since the desired hydrogen absorption / desorption rate and initial activation cannot be ensured, the content thereof is set to 25% or more.

The hydrogen-absorbing alloy of the present invention can be made into powder having a predetermined particle size by ordinary mechanical pulverization, and can be heated to a predetermined temperature within a range of 10 to 200 ° C. in a pressurized hydrogen atmosphere to absorb hydrogen. It is also possible to make powder by hydrogenation and pulverization of hydrogen released by evacuation, and each of the resulting powders has a structure whose representative structure is illustrated in FIG. Become.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the hydrogen storage alloy of the present invention will be specifically described with reference to examples. Ni, Zr, Ti, Mn, V, La, and Ce each having a purity of 99.9% or more as a raw material in a normal high frequency induction melting furnace.
And melted in Ar atmosphere to prepare Ni-Zr alloy melts having the compositions shown in Tables 1 and 2, respectively.
A water-cooled copper mold is cast into an ingot, and this ingot is subjected to a homogenizing heat treatment in a vacuum atmosphere at a predetermined temperature in the range of 950 to 1050 ° C. for 20 hours, and then in the range of 1 to 1.2 atm. In a hydrogen atmosphere at a predetermined pressure inside, first hold at room temperature for 1 hour, then start raising the temperature to 40
It is heated to a predetermined temperature within the range of 0 to 700 ° C., held at this temperature for 1 hour, then subjected to hydrogenation under the condition of forced air cooling with Ar gas, and further kept at 450 in the atmosphere for 1 hour. The hydrogen storage alloys of the present invention (hereinafter, referred to as the present invention alloys) 1 to 23 were manufactured by performing the oxidation treatment at 1. For the purpose of comparison, the composition of the molten Ni-based alloy is as shown in Table 2, and the conventional hydrogen storage alloy (hereinafter, Conventional alloy) was manufactured. The structure of the hydrogen storage alloy obtained as a result was observed with a scanning electron microscope.
No. 23 has innumerable cracks as shown in FIG. 1, and the inner surface of each crack has a hydrooxidation treatment product composed of La (Ce) -Ni alloy and La (Ce) oxide. The phase is exposed, and this hydro-oxidized product is Zr-Ni-
The structure of the Mn-based alloy is dispersed and distributed in the matrix phase, and the conventional alloy has a dispersed phase of the La-Ni alloy along the grain boundaries of the matrix phase of the Zr-Ni-Mn alloy as shown in FIG. Shows the distribution of the tissue.

Next, the hydrogen absorption rate and the hydrogen desorption rate of each of the above alloys 1 to 23 of the present invention and the conventional alloy were measured based on JIS H7202 "Hydrogen storage alloy hydrogenation rate test measuring method". Prior to the measurement, the alloys of the present invention 1 to 23 and the conventional alloy were sealed in a pressure vessel, the hydrogen atmosphere pressure was 8 atm, and the heating temperature was 200.
C., holding time: hydrogen absorption under the condition of 1 hour and hydrogen crushing consisting of hydrogen release by vacuum evacuation were performed to obtain 200me.
A powder having a particle size of sh or less was used, and measurement was performed using this powder under the following conditions.

First, regarding the hydrogen absorption rate, as shown in the schematic explanatory view of FIG. 4, (a) the powder is enclosed in a container immersed in a bath (oil or water), and the temperature of the bath is set to 200.
C, the valves Vb: closed, valves Va and Vc:
When opened, pressurized hydrogen is introduced into the system from a hydrogen cylinder. When the pressure in the system reaches 30 atm, the valve Va is closed, and the system is left until the pressure in the system drops to a constant pressure (hydrogen absorption by powder is completed). (B) When the pressure in the system drops to a constant pressure (about 20 atm), the valve V
b: Open, set the system to a vacuum atmosphere of 10 ^-2 Torr with a vacuum pump, set the bath temperature to 20 ° C, and set the valves Vb and Vc:
Close, valve Va: open and introduce hydrogen into the system excluding the container,
When the pressure reaches 30 atm, valve Va: closed, valve V
c: Open, pressure drop with respect to time in the system was measured in this state, and from the resulting pressure drop curve, the hydrogen storage amount at the time when the hydrogen storage amount of the powder became 80% and the time required until then were calculated. Then, (hydrogen storage amount at 80% storage) ÷ (80%
The time required for hydrogen storage) was calculated, and this value was used as the hydrogen absorption rate.

Regarding the hydrogen release rate, the state after the above hydrogen absorption rate measurement, that is, the valves Va and Vb:
Closed, valve Vc: open and the pressure in the system is constant (normally 20
(Atmospheric pressure), the bath temperature is set to an appropriate temperature for releasing hydrogen of powder in the range of 100 to 300 ° C., for example, 120 ° C., then the valve Vb is opened and the valve Vc is closed to remove the inside of the system. After exhausting to 10 ^-2 torr and then, with the valve Vb closed and the valve Vc open, the pressure rise over time in the system was measured and the resulting pressure rise curve showed that the hydrogen release of the powder was 80%. The amount of hydrogen released at the point of time and the time required up to that time were obtained, and (the amount of hydrogen released at the time of 80% release) / (the time required for the release of 80% hydrogen) was calculated. . The results are shown in Tables 1 and 2.

Further, for the purpose of evaluating the initial activation of the alloys 1 to 23 of the present invention and the conventional alloys, as described in detail below, these powders were incorporated into a battery as an active material, and the battery was discharged at maximum discharge. It is repeatedly charged and discharged until the capacity is reached, and 95% of the maximum discharge capacity is reached.
The number of times of charge and discharge until a discharge capacity corresponding to ± 1% was shown was measured. That is, first, a conventional alloy was coarsely crushed using a jaw crusher to obtain coarse particles having a diameter of 2 mm or less, and then the alloys 1 to 23 of the present invention and the coarsely crushed conventional alloy were finely crushed using a ball mill. Crushed 200
After making the particle size below the mesh and adding polytetrafluoroethylene (PTFE) as a binder and carboxymethyl cellulose (CMC) as a thickener to this to make a paste, a commercially available porous material having a porosity of 95% Quality N
i Sintered plate is filled, dried, pressed, and plane dimension: 30
mm × 40 mm, thickness: 0.40 to 0.43 mm (active material powder filling amount: about 1.8 g), and a Ni thin plate to be a lead is attached to one side of this by welding to form a negative electrode, On the other hand, the positive electrode uses Ni (OH) ₂ and CoO mixed in a weight ratio of 84:16 as an active material, and polytetrafluoroethylene (PTFE) as a binder is added thereto.
And carboxymethyl cellulose as a thickener (CM
C) is added to form a paste, which is filled in the above-mentioned porous Ni sintered plate, dried, and pressed to obtain a plane dimension: 30 mm ×
40 mm, thickness: 0.71 to 0.73 mm, and also formed by attaching a Ni thin plate to one side of this, and then, on both sides of the negative electrode, through a polypropylene polyethylene copolymer separator plate, respectively. In order to prevent the active material from falling off from the outer surface of each of the positive electrodes, the positive electrodes are arranged and integrated with a protective plate made of vinyl chloride, which is then placed in a cell made of vinyl chloride and placed in the cell. A battery was manufactured by charging a 30% KOH aqueous solution as an electrolytic solution. Then, in the above battery,
Charging rate: 0.15C, discharging rate: 0.15C, charge amount: 135% of the negative electrode capacity, charging and discharging are performed, the charging and discharging are counted as one charging and discharging, and the battery has the maximum discharging capacity. The charging / discharging was repeated until the process shown in FIG.
Tables 1 and 2 show the maximum discharge capacities measured as a result, and the number of times of charging and discharging required to show a discharge capacity of 95% of the maximum discharge capacities, thereby evaluating the initial activation.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

From the results shown in Tables 1 and 2, the alloys 1 to 23 of the present invention are exposed to the surface and the inner surface of numerous cracks, and as a result, are exposed to the atmosphere with a large surface area as a whole. La (C of the product phase of hydrooxidation treatment
e) -Ni-based alloy and La (Ce) oxide,
Hydrogen in the atmosphere is dissociated into hydrogen atoms and absorbed, and the absorbed hydrogen diffuses into the base phase of the Zr-Ni-Mn alloy to occlude hydrogen, but as described above, La has an extremely fast hydrogen absorption ability. (Ce) -Ni system alloy and La
Since the (Ce) oxide is distributed over a large surface area as a whole,
The hydrogen absorption rate is relatively extremely fast, and the initial activation is also significantly promoted. Also, since the hydrogen release is due to the opposite mechanism, the hydrogen release is performed at a high rate. In the conventional alloy,
The absorption and release of hydrogen is mainly due to the above La (Ce) -N.
This is performed by the dispersed phase of the i-based alloy and the La-Ni-based alloy having the same performance as the La (Ce) oxide, but the exposed area of the dispersed phase to the hydrogen atmosphere is such that active crack formation is performed by the hydrogenation treatment. Since it is relatively small, the rate of hydrogen absorption and desorption is inevitably slow, and the initial activation is also slow. As described above, in the hydrogen storage alloy of the present invention, the rate of hydrogen absorption and release is extremely fast, and it exhibits excellent initial activation in practical use. Therefore, high output of various mechanical devices to which the hydrogen storage alloy is applied is high. This greatly contributes to higher efficiency, higher performance, and energy saving.

[Brief description of drawings]

FIG. 1 is a schematic structure enlarged copy diagram illustrating a representative structure of a hydrogen storage alloy of the present invention.

FIG. 2 is a schematic structure enlarged copy diagram illustrating a representative structure of the hydrogen-absorbing alloy crushed powder of the present invention.

FIG. 3 is an enlarged schematic structure diagram illustrating a representative structure of a conventional hydrogen storage alloy.

FIG. 4 is a schematic explanatory diagram of an apparatus used for measuring a hydrogen absorption / desorption rate of a hydrogen storage alloy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Tamao 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Co., Ltd.

Claims (1)

[Claims] 1. By weight%, Zr: 25 to 45%, Ti: 1 to 12%, Mn: 10 to 20%, V: 2 to 12%, La and / or Ce: 0.5 to 5%, Oxygen: 0.2-1.7% is contained, the rest has a total composition of Ni (however, 25% or more is contained) and inevitable impurities, and hydrogen is contained in the base phase of the Zr-Ni-Mn alloy. The chemical oxidation treatment product phase is distributed and distributed, and the main component of the hydrooxidation treatment product phase has a structure composed of La and / or Ce oxide and La and / or Ce-Ni based alloy. Further, the hydrogen storage alloy has a structure in which there are innumerable cracks generated during the hydrotreating process, and the inner surface of the cracks has a structure in which the hydrooxidation treatment product phase is exposed.