JP2002141061A - Hydrogen storage alloy electrode and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a hydrogen storage alloy electrode that is low in cost, has a high capacity, and is excellent in cycle life and output characteristics. SOLUTION: At least containing Ti, not containing Ni,
Having a body-centered cubic structure, and mixing a hydrogen storage alloy having a spherical particle shape with Ni powder, applying a shearing force to the resulting mixture to attach Ni to the surface of the hydrogen storage alloy, and A method for producing a hydrogen storage alloy electrode, comprising a step of heat-treating a hydrogen storage alloy having Ni attached to its surface to form an alloy layer containing at least Ti and Ni on a surface portion of the hydrogen storage alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using a hydrogen storage alloy capable of reversibly electrochemically storing and releasing hydrogen, and a method for producing the same.

[0002]

2. Description of the Related Art An electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen has a longer theoretical capacity density than a cadmium electrode, and has no deformation or dendrite formation like a zinc electrode. Future development is expected as a negative electrode for alkaline storage batteries that has a long life, no pollution, and has a high energy density.

Currently, hydrogen storage alloy that has been put to practical use as an electrode, AB ₅ type (A: La, Zr, Ti, etc.,
An element having a high affinity for hydrogen; B: an element having a low affinity for hydrogen, such as a transition element such as Ni, Mn, or Cr; and a La-Ni-based or Mm-Ni-based (Mm: misch metal-rare earth) element (Mixture of elements). However, this alloy is used at a capacity close to the theoretical value, and a great increase in capacity in the future is not expected. Therefore, a new hydrogen storage alloy material having a larger discharge capacity is desired.

[0004] As the hydrogen-absorbing alloy having a large hydrogen storage capacity than the AB ₅ type hydrogen storage alloy, Ti-V-N
There is an i-type hydrogen storage alloy. For example Ti _x V _y Ni _z electrode using a hydrogen storage alloy having a composition has been proposed (JP-A 6-228699, JP-A No. 7-2685
No. 13 and JP-A-7-268514). Japanese Patent Application Laid-Open No. 11-144728 also proposes a material obtained by coating a TiVCr-based hydrogen storage alloy with Ni and sintering it.

[0005]

The discharge capacity of an electrode using a Ti-V-Ni-based hydrogen storage alloy is larger than that of an electrode using a La-Ni-based or Mm-Ni-based multi-element alloy. And the theoretical discharge capacity of a Ti-V-Ni-based hydrogen storage alloy. Ti-V-Ni
The hydrogen storage alloy of the type has a problem that the phase not containing Ni is corroded by contact with the electrolytic solution, so that the corrosion resistance is poor and the cycle life and the output characteristics are apt to be reduced. Ni to Ti-V
The above-mentioned problems can be solved by a material coated on the surface of a Ni-based hydrogen storage alloy and sintered, but the uniformity and denseness of the Ni coating layer and the provision of the Ni coating layer There is room for improvement in these costs.

[0006]

The present invention provides at least T
Contains i, does not contain Ni, body-centered cubic structure (bcc structure)
And mixing a hydrogen storage alloy having a spherical particle shape with Ni (nickel) powder, applying a shearing force to the resulting mixture to attach Ni to the surface of the hydrogen storage alloy, and A method of heat-treating a hydrogen storage alloy having Ni adhered thereon to form an alloy layer containing at least Ti and Ni on a surface portion of the hydrogen storage alloy.

[0007] The hydrogen storage alloy of the general formula: Ti _a M ¹ _b
Cr _c M ² _{d Le} (M ¹ is at least one selected from the group consisting of V, Nb and Mo, M ² is Fe, Mn, C
o, at least one selected from the group consisting of Cu, Zn, Zr, Ag, Hf, Ta, W, Al and Si, L
Is at least one selected from the group consisting of rare earth elements and Y, 0.3 ≦ a ≦ 0.6, 0.05 ≦ b ≦ 0.
6, 0.1 ≦ c ≦ 0.6, 0 ≦ d ≦ 0.2, 0 ≦ e ≦
0.03, a + b + c + d + e + f = 1.0).

The average particle size of the hydrogen storage alloy is 20 to 50.
It is preferable that the average particle diameter is 80 μm or more and 80% by weight or more of the hydrogen storage alloy has a particle diameter within ± 15 μm of the average particle diameter. The average particle diameter of the Ni powder is preferably 5 μm or less. It is preferable that the compounding amount of the Ni powder is 5 to 20 parts by weight based on 100 parts by weight of the hydrogen storage alloy. The heat treatment of the hydrogen storage alloy having Ni adhered to the surface is performed under reduced pressure or in a reducing atmosphere at 550 to 700.
C. for 3 to 48 hours.

The present invention is also a hydrogen storage alloy electrode comprising a powder comprising a core alloy and a peripheral alloy covering the core alloy, wherein the core alloy contains at least Ti,
i, a hydrogen-absorbing alloy having a body-centered cubic structure and a spherical particle shape, wherein the outer peripheral alloy is
i and Ni, and 70% by volume or more of Ti
The present invention relates to a hydrogen storage alloy electrode having the same body-centered cubic structure as Ni. It is preferable that 98% or more of the surface of the core alloy is covered with the outer peripheral alloy.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a hydrogen storage alloy having a body-centered cubic structure containing at least Ti and not containing Ni and having a spherical particle shape is used. In the present invention, it is important that the raw material hydrogen storage alloy has a spherical particle shape. Then, Ni is attached to the surface of the hydrogen storage alloy as a core alloy by a method of applying a mechanical shearing force to the surface (mechanochemical method), and then a heat treatment is performed. As a result, a uniform and dense Ni-containing alloy layer can be formed on the surface of the hydrogen storage alloy, and the hydrogen storage amount and the discharge capacity can be increased. Then, it is possible to obtain an electrode having excellent corrosion resistance and a long life at low cost.

(1) Purpose of Forming an Alloy Layer Containing Ni on the Surface of the Hydrogen Storage Alloy Ni is an essential element for giving the hydrogen storage alloy a catalytic ability for an electrochemical reaction. However, when Ni is contained in a hydrogen storage alloy containing Ti and having a body-centered cubic structure, Ni penetrates into the crystal structure of the hydrogen storage alloy which is a parent phase, does not form a solid solution, and segregates as a second phase. I do. Therefore, the hydrogen storage amount of the hydrogen storage alloy decreases.

In order to improve this, it is necessary to include Ti and N
It is effective to attach Ni to the surface of a hydrogen storage alloy that does not contain i and has a body-centered cubic structure. But,
Simply attaching Ni decreases the capacity of the hydrogen storage alloy and the hydrogen diffusion rate. In addition, when Ni is not uniformly distributed on the surface of the hydrogen storage alloy, the discharge characteristics and the life characteristics of the electrode deteriorate. Therefore, it has been proposed to form a second layer that is an outer peripheral alloy by diffusing Ni atoms into a surface portion of a hydrogen-absorbing alloy containing Ti, not containing Ni, and having a body-centered cubic structure. . Containing Ti,
By using a hydrogen storage alloy that does not contain Ni and has a body-centered cubic structure as a core alloy and coats it with an outer alloy containing Ni, a material having excellent hydrogen storage capacity can be obtained.

The outer peripheral alloy is a Ti—Ni based alloy (for example, T
i ₂ Ni, TiNi, as long as the crystal structure of TiNi _3, etc.), catalytic activity for the electrochemical reactions, corrosion resistance, good balance of hydrogen storage characteristics, it is possible to obtain an excellent electrode. In particular, the outer peripheral alloy is particularly preferably made of an alloy phase having the same body-centered cubic structure as TiNi. When the alloy phase accounts for 70% by volume or more of the outer peripheral alloy, the improvement of the electrode characteristics is particularly remarkable.

In order to form the outer peripheral alloy, first, a hydrogen storage alloy containing at least Ti, not containing Ni, having a body-centered cubic structure, and having a spherical particle shape is mixed with Ni powder. Apply mechanical shear to the resulting mixture. Because a hydrogen storage alloy having a spherical particle shape is used,
At this time, Ni is thin on the surface of the hydrogen storage alloy, and
It adheres almost uniformly. Further, a part of Ni may diffuse to the surface portion of the hydrogen storage alloy. In order for the outer peripheral alloy to have the above composition, Ni
Is adhered, and then 550 under reduced pressure or in a reducing atmosphere.
Heating at ７００700 ° C. for 3 to 48 hours is effective.

In the portion of the surface of the hydrogen storage alloy that is not covered with the outer peripheral alloy, the electrode reaction does not proceed, so that the discharge characteristics of the electrode deteriorate. Further, since the hydrogen storage alloy comes into direct contact with the alkaline electrolyte, corrosion proceeds, and the life of the electrode is shortened. It is desirable that the surface of the hydrogen storage alloy be completely covered with the outer peripheral alloy, but it is actually difficult to completely cover the surface. However, if 98% or more of the surface of the hydrogen storage alloy is covered with the outer peripheral alloy, an electrode having excellent characteristics can be obtained.

(2) Influence of the particle shape of the hydrogen storage alloy The hydrogen storage alloy is mixed with the Ni powder, and a mechanical shearing force is applied to the obtained mixture. Ni adheres to the surface of the alloy,
i diffuses into the surface portion of the hydrogen storage alloy. Therefore, when the particle shape of the hydrogen storage alloy is irregular, such as a pulverized product, force concentrates on the corners of the particles, and it is difficult to uniformly attach Ni to the entire surface of the hydrogen storage alloy.
However, if a hydrogen storage alloy having a spherical particle shape is used, a shearing force is applied to the entire surface of the hydrogen storage alloy on average, and Ni can be uniformly attached to the surface.

(3) Method of attaching Ni to the surface of the hydrogen storage alloy The method of attaching Ni to the surface of the hydrogen storage alloy is as follows.
A method of applying electrolytic or electroless plating of Ni to the hydrogen storage alloy, a method of mixing the hydrogen storage alloy powder with the Ni powder, and a gas phase method (chemical vapor deposition (CVD), sputtering, etc.) can be considered. Among them, hydrogen storage alloy powder and N
The method of mixing with i-powder is a dry process, the raw material cost is relatively inexpensive, and a large amount of raw materials can be processed at once or continuously, so that the cost is low and simple compared with other methods. It is.

However, simply mixing the hydrogen storage alloy powder and the Ni powder does not sufficiently and uniformly adhere Ni to the surface of the hydrogen storage alloy. On the other hand, after mixing the hydrogen storage alloy with the Ni powder and then applying a mechanical shearing force to the resulting mixture, the adhesion between the hydrogen storage alloy and Ni is improved, and the surface of the hydrogen storage alloy is sufficiently and , Ni adheres uniformly. Devices for performing such processing include mechanofusion, theta composers, hybridization systems, and the like, and are commercially available.

The smaller the particle size of the Ni powder mixed with the hydrogen storage alloy powder, the better. If the particle size of the Ni powder is too large, a thin and uniform Ni is deposited on the surface of the hydrogen storage alloy.
It becomes difficult to form a coating layer. Specifically, it is preferable to use Ni powder having an average particle size of 5 μm or less. The average particle size of the Ni powder is preferably as small as possible. However, since the cost increases as the average particle size decreases, it is practically preferable to be about 1 μm.

(4) Composition of hydrogen storage alloy From the viewpoint of satisfying the hydrogen storage amount and the characteristics as an electrode,
As the hydrogen storage alloy represented by the general ^{_{formula: Ti a M 1 b Cr c}} M 2 d L
_e (M ¹ is at least one selected from the group consisting of V, Nb and Mo, and M ² is Fe, Mn, Co, Cu, Z
at least one selected from the group consisting of n, Zr, Ag, Hf, Ta, W, Al and Si; L is at least one selected from the group consisting of rare earth elements and Y;
3 ≦ a ≦ 0.6, 0.05 ≦ b ≦ 0.6, 0.1 ≦ c ≦
0.6, 0 ≦ d ≦ 0.2, 0 ≦ e ≦ 0.03, a + b +
Those having a composition represented by (c + d + e + f = 1.0) are preferably used.

In a hydrogen storage alloy containing Ni as a constituent element, Ni forms a second phase, and the hydrogen storage amount corresponding to the amount of Ni decreases. At this time, a small amount of Ni is dissolved in the parent phase, which causes an increase in the hydrogen equilibrium pressure, so that the hydrogen storage amount of the parent phase also decreases. Therefore, from the composition of the hydrogen storage alloy, Ni
Is preferably removed.

Since Ti has a large atomic radius, when it is included in the hydrogen storage alloy composition, the lattice size of the hydrogen storage alloy increases. At this time, the hydrogen equilibrium pressure also decreases, and the hydrogen storage amount of the hydrogen storage alloy increases. Also, in the case of forming an outer peripheral alloy in which Ni is diffused, the presence of Ti facilitates the diffusion of Ni at a low temperature. In the above general formula, when a is 0.3 or more, a remarkable effect is seen in the increase in the amount of hydrogen storage. However, when a exceeds 0.6, hydrogen in the hydrogen storage alloy is stabilized and hardly released.

V, Nb and Mo have a large atomic radius like Ti, and when they are included in the composition of the hydrogen storage alloy, they contribute to an increase in the lattice size of the hydrogen storage alloy. Further, these elements contribute to stabilization of the body-centered cubic structure of the hydrogen storage alloy. The effects of these elements are all the same and may be included alone in the composition of the hydrogen storage alloy,
A plurality may be included at the same time.

Cr facilitates activation of the hydrogen storage alloy and imparts corrosion resistance to the hydrogen storage alloy in an alkaline electrolyte. To obtain this effect, in the above general formula,
It is preferable that c is 0.1 or more. However, since Cr increases the hydrogen equilibrium pressure of the hydrogen storage alloy, the hydrogen storage amount decreases. Therefore, from the viewpoint of suppressing this, it is preferable that c is 0.6 or less.

By including a small amount of rare earth elements such as La and Ce or Y in the hydrogen storage alloy, the hydrogen storage amount of the hydrogen storage alloy can be further increased. This effect is considered to be due to these elements having an action of removing impurity oxygen contained in the hydrogen storage alloy.
If these elements are segregated as the second phase so that they are hardly contained in the mother phase, hydrogen storage can be performed without substantially affecting the composition of the mother phase and without changing the hydrogen equilibrium pressure and the like. The hydrogen storage capacity of the alloy can be increased. These elements account for 3 atomic% in the hydrogen storage alloy.
Even with the addition, no further improvement in the effect is observed.

Mn, Fe, Co, Cu, Zn, Zr, A
g, Hf, Ta, W, Al and Si are included in the hydrogen storage alloy in order to change the lattice size according to the atomic radius. At this time, simultaneously, the hydrogen equilibrium pressure of the hydrogen storage alloy can be controlled to increase the hydrogen storage amount. These elements may be included alone in the hydrogen storage alloy,
A plurality may be included at the same time. Mn, Ta or A
When l is contained in the hydrogen storage alloy, the effect of increasing the hydrogen storage amount of the hydrogen storage alloy is obtained, and Fe, Co, Cu, Z
When n, Zr, Ag, Hf, W or Si is included in the hydrogen storage alloy, an effect of increasing the electrochemical activity of the hydrogen storage alloy can be obtained. As a result, the discharge capacity and cycle life of the electrode are also improved.

(5) Particle Size Distribution of Hydrogen Storage Alloy The average particle size of the hydrogen storage alloy is preferably about 20 to 50 μm in consideration of the corrosion resistance and output characteristics of the alloy. Further, when the particle size distribution is large and the difference in particle size between particles is large, small particles enter gaps formed by large particles, so that mechanical shearing force does not work when Ni is coated on the surface, and Ni The adhesion between the alloy and the hydrogen storage alloy also tends to be weak. Therefore, it is desirable that the particle size distribution of the hydrogen storage alloy is as small as possible. Specifically, it is preferable that 80% by weight or more of the hydrogen storage alloy has a particle size within ± 15 μm of the average particle size. If a hydrogen storage alloy having such a particle size distribution is used, the ratio of the surface covered with the outer peripheral alloy is increased, and the electrode characteristics are also improved.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. << Example 1 >> (1) Production of hydrogen storage alloy A hydrogen storage alloy having a composition represented by Ti _0.4 V _0.4 Cr _0.2 was produced by a gas atomization method using a commercially available raw material. The particle shape of the obtained hydrogen storage alloy was spherical.
The obtained hydrogen storage alloy was heated at 1000 ° C. for 3 hours to homogenize the alloy structure, and then 55 μm and 20 μm
Classified with a sieve. As a result, 90% by weight of the whole was 2%.
A hydrogen storage alloy (alloy 1-1) as particles having a particle size of 3 to 53 μm was obtained. The average particle size was 38 μm.

In this embodiment, the hydrogen storage alloy is manufactured by the gas atomization method. However, if a hydrogen storage alloy having a spherical particle shape can be obtained, in addition to the gas atomization method, the water atomization method, the disk atomization method, and the centrifugal atomization method can be used. Method or the like may be used.

100 parts by weight of the alloy 1-1 were mixed with 10 parts by weight of Ni powder having an average particle diameter of 1 μm, and the mixture was treated with a mechanofusion apparatus (manufactured by Hosokawa Micron) for 30 minutes.
FIG. 1 shows the result of observing the surface of the alloy 1-1 after the treatment with an SEM. FIG. 1 shows that Ni is uniformly attached to the surface of the alloy 1-1 having a spherical particle shape. Next, the alloy 1-1 having Ni uniformly adhered to the surface thereof was removed under reduced pressure for 60 hours.
Heat treatment at 0 ° C. for 5 hours.
Was formed.

(2) Preparation of hydrogen storage alloy electrode and its evaluation
1 g and 0.4 g of Cu powder were mixed and pressed into a pellet. A Ni mesh is crimped on this, and Ni
The ribbon (lead) was welded to form an electrode (negative electrode).
Using the electrode, a nickel hydroxide electrode having an excess electric capacity as a counter electrode thereof, and an aqueous solution of potassium hydroxide having a specific gravity of 1.30 as an electrolyte, the capacity is regulated at the negative electrode, and the electrolyte is rich and open. A system battery was assembled and charged and discharged.

Charging is 100 mA / g of hydrogen storage alloy
12 hours for the first cycle and 5.5 for the second and subsequent cycles
The discharge was performed at 50 mA per gram of alloy until the terminal voltage reached 1.0 V. This charge / discharge cycle was repeated, and the discharge capacity of the electrode was examined. The capacity deterioration rate was calculated using the following formula. Table 1 shows the results. Capacity degradation rate (%) = {(maximum discharge capacity) − (50th cycle discharge capacity)} / (maximum discharge capacity) × 100

[0033]

[Table 1]

(3) Production of sealed battery and its evaluation Alloy 1-1 having an outer peripheral alloy formed by heat treatment was mixed with a dilute aqueous solution of carboxymethylcellulose to form a paste, which had a porosity of 95% and a thickness of 0.6 mm. Into a foamed nickel sheet. This was dried at 80 ° C., pressed with a roller, and further coated on its surface with a fluororesin powder to form a hydrogen storage alloy electrode.

The obtained electrode was cut to a width of 3.9 cm, a length of 10.5 cm, and a thickness of 0.40 mm, combined with a positive electrode and a separator and laminated in three layers, and wound so that the negative electrode was at the outermost periphery. It was turned into a cylindrical electrode group and housed in an AA-size battery case. At this time, as the positive electrode, a nickel electrode using a known foamed nickel core material was used to have a width of 3.9 c.
m, 7 cm long. A lead plate was attached to the positive electrode, and this was welded to the positive electrode terminal of the sealing plate. Also,
The outermost negative electrode was brought into contact with the inside of the outer can (container). As the separator, a polypropylene nonwoven fabric provided with hydrophilicity was used. Next, an electrolytic solution in which lithium hydroxide was dissolved in a potassium hydroxide aqueous solution having a specific gravity of 1.30 at a concentration of 30 g / liter was injected into the battery case. Then, the opening of the battery case was sealed with a sealing plate to obtain a sealed battery. This battery is regulated by the positive electrode capacity, with a nominal capacity of 1.3 Ah.

The obtained battery was charged at 25 ° C. with a current value of 0.1 C for 12 hours, discharged at a current value of 0.2 C, and left at 45 ° C. for 3 days. Thereafter, charge and discharge were performed for 5 cycles under the same conditions as above, and the capacity was confirmed.

The battery whose capacity was confirmed was 1 at a current value of 1C.
A cycle of discharging until the terminal voltage becomes 1 V at a current value of 1 C by repeating the cycle of 30% charging to a fully charged state,
The capacity deterioration rate after 0 cycles was calculated using the following formula. Table 1 shows the results. Capacity deterioration rate (%) = {(maximum discharge capacity) − (300th cycle discharge capacity)} / (maximum discharge capacity) × 100

The battery whose capacity has been confirmed is subjected to 1 C at 25 ° C.
And discharge at a current value of 0.2 C, and the discharge capacity at that time was determined. Then, the output of the battery was calculated using the following equation. Table 1 shows the results. Output (%) = (discharge capacity at 1 C discharge) / (discharge capacity at 0.2 C discharge) × 100

Comparative Example 1 A hydrogen storage alloy having the same composition as the hydrogen storage alloy manufactured in Example 1 was manufactured by arc melting. Then, after hydrogen crushing was performed by absorbing and releasing hydrogen into and from this, further mechanical crushing was performed. The obtained hydrogen storage alloy was not spherical, but was irregular and had a particle shape having many corners. This hydrogen storage alloy is referred to as alloy 1-2. Then, alloy 1-
Except that Sample No. 2 was used, the production and evaluation of a hydrogen storage alloy electrode and the production and evaluation of a sealed battery were performed in the same manner as in Example 1. Table 1 shows the results.

The alloy 1-2 was mixed with Ni powder and treated with a mechanofusion apparatus for 30 minutes.
The result of observing the surface of No. 2 by SEM is shown in FIG.

FIG. 2 shows that Ni is aggregated and adhered to the corners of the alloy 1-2. Also, from the results in Table 1, it can be seen that excellent electrode characteristics and battery characteristics are obtained by using alloy 1-1 rather than by using alloy 1-2. This is presumably because the surface of the alloy 1-1 is uniformly covered with Ni, so that the alloy 1-1 has a larger reaction area and higher corrosion resistance to the electrolyte than the alloy 1-2.

Example 2 In this example, the composition of the hydrogen storage alloy was examined. First, a hydrogen storage alloy having a composition shown in Table 2 was produced by a gas atomization method. Then, in the same manner as in Example 1, 10% by weight of Ni powder of the hydrogen storage alloy was adhered to the surface of the hydrogen storage alloy. Next, the hydrogen-absorbing alloy having Ni adhered to its surface was heated at 625 ° C for 4 hours.
Heating was carried out for a time to form a peripheral alloy containing Ni on the surface of the hydrogen storage alloy. The production and evaluation of a hydrogen storage alloy electrode were performed in the same manner as in Example 1, except that the obtained hydrogen storage alloy having the outer peripheral alloy was used. Table 2 shows the results.

[0043]

[Table 2]

In Table 2, element M ¹ is V unless otherwise specified.
And La was used as the element L unless otherwise specified.

From Table 2, in order to obtain an electrode having a high discharge capacity of 450 mAh / g or more and a capacity deterioration rate of 10% or less, the general formula: Ti _a M ¹ _b Cr _c M ² _{d Le} ( M ¹ is
At least one selected from the group consisting of V, Nb and Mo, M ² is Fe, Mn, Co, Cu, Zn, Zr,
L is at least one selected from the group consisting of Ag, Hf, Ta, W, Al and Si, and L is at least one selected from the group consisting of rare earth elements and Y, 0.3 ≦ a ≦
0.6, 0.05 ≦ b ≦ 0.6, 0.1 ≦ c ≦ 0.6,
0 ≦ d ≦ 0.2, 0 ≦ e ≦ 0.03, a + b + c + d +
It is found that it is effective to use a hydrogen storage alloy having a composition represented by (e + f = 1.0).

Example 3 Next, the influence of the average particle size and the particle size distribution of the hydrogen storage alloy was examined. First, the composition is Ti _0.4 Mo _0.15 Cr _0.45 by the gas atomization method.
Average particle size of 15, 20, 35, 50 and 60 respectively
A μm hydrogen storage alloy was produced. Then, particles having a large particle diameter and a particle having a small particle diameter were removed from each hydrogen storage alloy, and adjusted so that 80% by weight of the entire hydrogen storage alloy had a particle diameter within ± 15 μm of the average particle diameter. The obtained hydrogen storage alloys are referred to as alloys 3-1, 3-2, 3-3, 3-4 and 3-5, respectively. The average particle size is 35 μm, and 70% and 50% of the whole hydrogen storage alloy are ± 1% of the average particle size.
Those prepared so as to have a particle size of 5 μm or less were prepared. These hydrogen storage alloys are referred to as alloys 3-3 ′ and 3-3 ″, respectively.

Alloys 3-1 to 3-5 and alloy 3-
3 ′ and 3-3 ″, the average particle size was 1 μm as in Example 1.
m of Ni powder was mixed, and the mixture was treated with a theta composer for 1 hour to attach Ni to the surface of each alloy. As a result of observing each alloy to which Ni was attached by SEM, in the alloys 3-3 ′ and 3-3 ″ having a large particle size distribution, the attachment of Ni to particularly small particles was insufficient.

Each alloy before the heat treatment was treated with 6N (specified) KO
By immersing in an H aqueous solution (80 ° C.) and quantifying the amount of eluted Ti ions, the ratio of the portion of each alloy surface coated with Ni (hereinafter referred to as Ni coverage) was calculated. That is, when the hydrogen storage alloy not treated by the theta composer is immersed in an aqueous KOH solution, the elution amount of Ti ions is defined as the elution amount when the Ni coverage is 0%, and the elution amount of Ti ions is zero. And the amount of Ti ions eluted from each alloy as N
It was converted to i coverage. The obtained Ni coverage is the same as that of alloy 3-
3 is 98%, alloy 3-3 'is 95%, alloy 3-3 "is 8
7%.

Each alloy was heat-treated at 600 ° C. for 5 hours under reduced pressure to form a Ni-containing outer peripheral alloy on the surface of each alloy. At this time, it is considered that a peripheral alloy containing Ni is formed on the surface portion of each alloy at substantially the same ratio as the Ni coverage. However, since Ni also diffuses in the lateral direction,
It is considered that the ratio of the surface covered with the outer peripheral alloy is actually larger than the Ni coverage. Therefore, alloy 3-
In the case of No. 3, 98% or more of the surface, in the case of Alloy 3-3 ', 95% or more of the surface, and in the case of Alloy 3-3 ", 87% or more of the surface was covered with the outer peripheral alloy. .

Next, except that the alloys 3-1 to 3-5 and the alloys 3-3 ′ and 3-3 ″ after the heat treatment were used,
In the same manner as in Example 1, production of a hydrogen storage alloy electrode and its evaluation, and production of a sealed battery and its evaluation were performed. Table 3 shows the results.

[0051]

[Table 3]

As shown in Table 3, as the average particle size of the hydrogen storage alloy becomes smaller, the ratio of the outer peripheral alloy to the core alloy increases, so that the discharge capacity decreases. On the other hand, when alloy 3-5 having an average particle size of 60 μm is used, the output is reduced because the average particle size of the hydrogen storage alloy is too large and the specific surface area is small. Therefore, in order to obtain a battery having a high discharge capacity, a small capacity deterioration rate, and a high output, it is effective to use a hydrogen storage alloy having an average particle size of about 20 to 50 μm.

The alloys 3-3, 3-3 'and 3-
3 ", the larger the particle size distribution of the hydrogen storage alloy, the smaller the discharge capacity and the larger the capacity deterioration rate of the battery.
To increase the coverage and obtain an electrode with excellent properties,
It is effective that 80% or more of the entire hydrogen storage alloy has a particle size within an average particle size of ± 15 μm. Also, it can be seen that an electrode having particularly excellent characteristics can be obtained when the Ni coverage on the surface of the core alloy is 98% or more.

Example 4 Next, the amount of Ni adhering to the surface of the hydrogen storage alloy and the particle size of the Ni powder were examined.
First, 10% by weight of Ni powder having an average particle size of 0.05, 1, 5, and 10 μm were mixed with the alloy 3-3 used in Example 3, respectively. Similarly, treatment was performed for 1 hour using Theta Composer. Then, in the same manner as in Example 1 except that the hydrogen storage alloy after the treatment was used, production and evaluation of a hydrogen storage alloy electrode, and production and evaluation of a sealed battery were performed. Table 4 shows the results.

The average particle size of 3, 5, 10, 20, and 30% by weight of the alloy 3-3 used in Example 3 was 1%.
μm Ni powder was mixed with each other, and each mixture was prepared in Example 3.
1 hour with theta composer. And
Except for using the hydrogen storage alloy after the treatment, the production and evaluation of a hydrogen storage alloy electrode and the production and evaluation of a sealed battery were performed in the same manner as in Example 1. Table 4 shows the results.

[0056]

[Table 4]

In Table 4, as the average particle size of the Ni powder increases, the discharge capacity decreases and the capacity deterioration rate of the battery increases. This is because, as the average particle size of the Ni powder increases, the surface of the hydrogen storage alloy becomes thinner and more uniform.
It is considered that it becomes difficult to attach i. Further, the mixing amount of the Ni powder is 5 to 20 with respect to the hydrogen storage alloy.
Excellent characteristics are obtained in the case of weight%. If the mixing amount of the Ni powder is less than 5% by weight, it is considered that the Ni coverage is low and the capacity deterioration rate is high. On the other hand, when the content exceeds 20% by weight, N
It is considered that, because the ratio of the i amount is too large, the hydrogen storage amount decreases, and the discharge capacity decreases.

Example 5 Next, conditions for heat-treating a hydrogen storage alloy having Ni adhered to its surface were examined.
First, 10% by weight of Ni powder having an average particle size of 1 μm was mixed with the alloy 3-3 used in Example 3 and treated by mechanofusion as in Example 1. Then, the treated hydrogen storage alloy was heat-treated under vacuum under the conditions shown in Table 5. Next, except that the obtained hydrogen storage alloy was used,
Production and evaluation of a hydrogen storage alloy electrode were performed in the same manner as in Example 1. The discharge capacity of the electrode is 450 mAh / g
The results are shown in Table 5 where the case where the capacity deterioration rate is within 10% is ○ and the case where the capacity deterioration rate is other than that is ×.

[0059]

[Table 5]

From Table 5, it can be seen that if the heat treatment conditions are too mild,
It can be seen that the reaction between Ni and the hydrogen storage alloy becomes insufficient, and if the conditions are too severe, the reaction between Ni and the alloy proceeds too much and the characteristics of the electrode and the battery deteriorate. From Table 5, the heat treatment time is 3 to 48 hours, and the heat treatment temperature is 550 to 700 ° C.
Is effective.

When the hydrogen storage alloy after the heat treatment was analyzed by X-ray diffraction, it was found that, in addition to the peak attributed to the body-centered cubic structure, which is the parent phase, the peak attributed to TiNi and Ti ₂ Ni
And the peak attributed to metallic Ni were observed. From the intensity of these peaks, the ratio of the presence of these phases was roughly estimated. In Table 5, all of the heat-treated hydrogen-absorbing alloys marked with a circle were Ti
It was found that the ratio of the Ni phase was 70% by volume or more.
TiNi is an alloy having high electrochemical activity among Ti-Ni-based hydrogen storage alloys. Therefore, increasing the content of the TiNi phase in the hydrogen storage alloy is effective in obtaining an excellent electrode.

[0062]

According to the present invention, an alloy layer containing at least Ti and Ni can be efficiently formed on the surface of a hydrogen storage alloy. By using the powder made of the hydrogen storage alloy, it is possible to obtain a hydrogen storage alloy electrode having a low cost, a high capacity, and excellent cycle life and output characteristics.

[Brief description of the drawings]

FIG. 1 is a SEM photograph of the surface of a hydrogen storage alloy after mixing a hydrogen storage alloy having a spherical particle shape and Ni powder and treating the mixture with a mechanofusion device for 30 minutes.

FIG. 2 shows a hydrogen storage alloy having an irregular particle shape and Ni.
It is a SEM photograph of the surface of a hydrogen storage alloy after mixing with a powder and treating with a mechanofusion device for 30 minutes.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/24 H01M 4/24 J 10/30 10/30 Z // C22C 19/00 C22C 19/00 F C22F 1/00 621 C22F 1/00 621 641 641A 661 661C 691 691B 691C (72) Inventor Miho Kayama 1006, Ojimon, Kadoma, Osaka Pref. BC35 BD07 5H028 AA05 BB05 BB06 BB15 CC10 EE01 HH01 HH05 HH08 5H050 AA07 AA08 AA19 BA14 CA03 CB16 DA09 EA03 FA17 FA18 GA02 GA05 GA10 GA22 GA27 HA02 HA05 HA13 HA14 HA20

Claims (8)

[Claims] Claims: 1. At least contains Ti, does not contain Ni,
Having a body-centered cubic structure, and mixing a hydrogen storage alloy having a spherical particle shape with Ni powder, applying a shearing force to the resulting mixture to attach Ni to the surface of the hydrogen storage alloy, and A method for producing a hydrogen storage alloy electrode, comprising a step of heat-treating a hydrogen storage alloy having Ni attached to its surface to form an alloy layer containing at least Ti and Ni on a surface portion of the hydrogen storage alloy. 2. The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy has a general formula: Ti _a M ¹
_b Cr _c M ² _{d Le} (M ¹ is at least one selected from the group consisting of V, Nb and Mo, M ² is Fe, Mn, C
o, at least one selected from the group consisting of Cu, Zn, Zr, Ag, Hf, Ta, W, Al and Si, L
Is at least one selected from the group consisting of rare earth elements and Y, 0.3 ≦ a ≦ 0.6, 0.05 ≦ b ≦ 0.
6, 0.1 ≦ c ≦ 0.6, 0 ≦ d ≦ 0.2, 0 ≦ e ≦
2. The method for producing a hydrogen storage alloy electrode according to claim 1, having a composition represented by: 0.03, a + b + c + d + e + f = 1.0). 3. The hydrogen storage alloy has an average particle size of 20 to 5
2. The method for producing a hydrogen-absorbing alloy electrode according to claim 1, wherein the hydrogen-absorbing alloy electrode has a particle diameter of 0 μm and 80% by weight or more of the hydrogen-absorbing alloy has a particle diameter within ± 15 μm of the average particle diameter. 4. The method according to claim 1, wherein the average particle diameter of the Ni powder is 5 μm or less. 5. The compounding amount of the Ni powder is 5 to 20 parts by weight based on 100 parts by weight of the hydrogen storage alloy.
The method for producing a hydrogen storage alloy electrode according to the above. 6. The method according to claim 1, wherein the heat treatment is performed at 550 to 700 ° C. for 3 to 48 hours under reduced pressure or in a reducing atmosphere. 7. A hydrogen storage alloy electrode comprising a powder comprising a core alloy and an outer peripheral alloy covering the core alloy, wherein the core alloy contains at least Ti and does not contain Ni.
A hydrogen-absorbing alloy having a body-centered cubic structure and a spherical particle shape, wherein the outer peripheral alloy contains Ti and Ni;
A hydrogen storage alloy electrode wherein 0% by volume or more has the same body-centered cubic structure as TiNi. 8. The hydrogen storage alloy electrode according to claim 7, wherein 98% or more of the surface of the core alloy is covered with the outer peripheral alloy.