JPH0978167A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the hydrogen absorption/discharge rates and initial activation by using an Ni-Zr alloy contg. Ti, Mn, V, La and Ce and allowing specified dispersed phases and cracks to exist in the matrix phases of a Zr-Ni-Mn alloy. SOLUTION: An Ni-Zr alloy 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 0.01 to 0.2% hydrogen, and the balance Ni (>=25%) is melted and cast. The obtd. ingot is subjected to homogeneous heat treatment to form into a structure in which the dispersed phases of the La (Ce)-Ni alloy are present along the grain boundaries of the matrix phases of the Zr-Ni-Mn alloy. Successively, it is subjected to hydrogeneration treatment under the conditions of holding to a prescribed temp. in the range of 400 to 700 deg.C for prescribed time in a hydrogen atmosphere and thereafter executing cooling to form into hydrogen reaction product phases essentially consisting of La (Ce) hydrides and the La (Ce)-Ni alloy, and furthermore, numberless cracks in which the above hydrogen reaction product phases are exposed to the inside face are generated.

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, La is formed by the homogenizing heat treatment as shown in FIG. The dispersed phase of the (Ce) -Ni-based alloy preferentially reacts with hydrogen in the atmosphere to form La and / or Ce hydride (hereinafter referred to as La (Ce) hydride) and La.
And / or Ce-Ni alloy (hereinafter, La (Ce))
-Ni-based alloy), and the hydrogen reaction product phase shows a large thermal expansion as compared with the base phase of the Zr-Ni-Mn-based alloy. Means that innumerable cracks are generated from the hydrogen reaction product phase as a starting point, and the hydrogen reaction product phase is exposed on the inner surface of the crack.

(B) In the Ni--Zr alloy of (a) above, the hydrogen reaction product phase La (C
e) -Ni system alloy, same action as the dispersed phase of the La-Ni-based alloy in a conventional hydrogen storage alloy shown in FIG. 3, i.e. the hydrogen molecules in the atmosphere in the catalytic action possessed by this (H ₂₎
Is dissociated into hydrogen atoms (H), the dissociated hydrogen atoms are absorbed at a much higher speed than the matrix phase of the Zr-Ni-Mn system, and the release exhibits an action by the opposite mechanism. Most of the hydrogen reaction product phase is exposed on the inner surface of a myriad of cracks, and as a result, the action area is expanded. Therefore, the above La (Ce) hydride also has an absorption hydrogen atom and a desorption hydrogen atom. Combined with having the effect of promoting the progress of diffusion, the hydrogen absorption and desorption are much faster than the hydrogen absorption and desorption rates of the conventional hydrogen storage alloys described above, and further, the hydrogen atoms in the base phase at the time of initial activation. Since the absorption rate of is also increased over a wide area of action, the initial activation can be significantly promoted. 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%,
Hydrogen: 0.01-0.2%, the balance Ni (25% or more) and inevitable impurities, and a hydrogen reaction product phase in the base phase of the Zr-Ni-Mn alloy. Are dispersed and distributed, and the main component of the hydrogen reaction product phase is La
(Ce) A structure composed of a hydride and a La (Ce) -Ni-based alloy, and further, there are innumerable cracks generated during the formation of the hydrogen reaction product phase, and the hydrogen reaction product phase is formed on the inner surface of the crack. It is characterized by a hydrogen storage alloy having an exposed structure, a high hydrogen absorption / desorption rate, and an 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 was set to 25 to 45%, preferably 32 to 38%.

(B) Ti The 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 promotion of absorption and desorption of hydrogen, and also hydrogen storage in the base material. Although it has an effect of increasing the 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 higher than atmospheric pressure at room temperature, for example. The hydrogen absorption rate and the hydrogen absorption rate and the release rate of hydrogen decrease. Therefore, the ratio is 1 to 12%, preferably 4 to 8%.
Defined as%.

(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. La (C), which has the function of promoting the formation of a Ni-based alloy and the diffusion of absorbed hydrogen into the matrix phase and the diffusion of hydrogen released from the matrix phase.
e) It is an essential component for the formation of hydride, but if the proportion is less than 0.5%, the production rate of the La (Ce) -Ni-based alloy and La (Ce) hydride is too small and the desired fast hydrogen is obtained. If the absorption / desorption rate cannot be secured, and if the ratio exceeds 5%, the proportion of the dispersed phase with a small hydrogen storage amount becomes too large, and the hydrogen storage amount of the entire alloy decreases. The ratio was set to 0.5 to 5%, preferably 1 to 4%.

(F) Hydrogen Hydrogen is mainly composed of La (Ce).
The La (Ce) -Ni-based alloy, which also forms a hydride and forms a hydrogen reaction product, dissociates and absorbs the dissociated and absorbed hydrogen and transfers it into the matrix phase at a high diffusion rate, while releasing the hydrogen from the matrix phase quickly. The La (Ce) —Ni-based alloy has an effect of diffusing, but if the ratio is less than 0.01%, the ratio of La (Ce) hydride that exerts the effect is too small to sufficiently exhibit the effect. On the other hand, if the proportion exceeds 0.2%, the proportion of La (Ce) hydride becomes too large as compared with the La (Ce) -Ni alloy, and the proportion of La (Ce)-is relatively large. Since the amount of Ni-based intermetallic compound decreases and the hydrogen absorption / desorption rate and the initial activation decrease, the ratio is 0.01 to 0.2%,
It is preferably set to 0.04 to 0.12%.

(G) Ni When the content of Ni component is less than 25%, not only the formation of the hydrogen reaction product phase becomes insufficient, but also cracks generated during the formation become insufficient, which is desirable. Since it becomes impossible to secure the hydrogen absorption / desorption rate and the initial activation of, the content thereof was 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 within a range of 950 to 1050 ° C. for 20 hours, and then 1 to 1.2. In a hydrogen atmosphere of a predetermined pressure within the range of atmospheric pressure, first hold at room temperature for 1 hour, then start heating and heat to a predetermined temperature within a range of 400 to 700 ° C., and hold at this temperature for 1 hour. From the above, the hydrogen storage alloys of the present invention (hereinafter, referred to as the present invention alloys) 1 to 22 were produced by performing a hydrogenation treatment under the conditions of forced air cooling with Ar gas. 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 referred to as the conventional alloy) is used under the same conditions except that the hydrogenation treatment after the homogenizing heat treatment is not performed. ) Was manufactured. As a result of observing the structure of the resulting hydrogen storage alloy with a scanning electron microscope, the alloys 1 to 22 of the present invention all have innumerable cracks as shown in FIG. 1, and the inner surfaces of the cracks are present. Reveals a hydrogen reaction product phase composed of La (Ce) -Ni alloy and La (Ce) hydride, and this hydrogen reaction product is distributed in the matrix phase of the Zr-Ni-Mn alloy. As shown in FIG. 3, the conventional alloy has an L-structure along the grain boundary of the matrix phase of the Zr—Ni—Mn alloy.
The structure in which the dispersed phase of the a-Ni alloy was distributed was shown.

Next, the hydrogen absorption rate and the hydrogen desorption rate of each of the alloys 1 to 22 of the present invention and the conventional alloys 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 22 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 22 of the present invention and the conventional alloys, as described in detail below, the powders were powdered and 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 22 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, in the alloys 1 to 22 of the present invention, they are exposed to the surface and the inner surface of numerous cracks, and as a result, they are exposed to the atmosphere with a large surface area as a whole. La (Ce) -N in the hydrogen reaction product phase
Through the i-based alloy, hydrogen in the atmosphere is dissociated into hydrogen atoms and absorbed, and the absorbed hydrogen is directly or
Although hydrogen is absorbed by diffusing into the base phase of the Zr—Ni—Mn-based alloy via the (Ce) hydride, the La (Ce) -Ni-based alloy having an extremely fast hydrogen absorption ability is generally used as described above. Since it has a large surface area, the hydrogen absorption rate is relatively fast, and the initial activation is also significantly accelerated. Also, hydrogen release is due to the reverse mechanism, so that the hydrogen absorption rate is high. While hydrogen is released, in the conventional alloy, absorption and release of hydrogen are mainly performed by the dispersed phase of the La-Ni alloy having the same performance as that of the La (Ce) -Ni alloy. The exposed area of the dispersed phase to the hydrogen atmosphere is relatively small because active crack formation by hydrogenation is not performed, and as a result, the hydrogen absorption and desorption rates must be slow. And that becomes initial activation is slow is clear. 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%, Hydrogen: 0.01 to 0.2% 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-based alloy. The reaction product phase is dispersed and distributed, and the main component of the hydrogen reaction product phase is La
And / or Ce hydride and a structure composed of La and / or Ce-Ni based alloy, and further, there are innumerable cracks generated during the formation of the hydrogen reaction product phase, and the inner surface of the crack. Has a structure in which the hydrogen reaction product phase is exposed in the hydrogen storage alloy.