JPH09312157A - Hydrogen storage alloy electrode and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy electrode with its high capacity, efficient discharge characteristics, and cycle characteristics. SOLUTION: Hydrogen storage alloy granules are reduced with hydrogen gas or etched with fluoride hydrogen acid solution so that the thickness of an oxide film on the alloy surface is 0.15 micrometer or less, and this surface is applied with a mechanical stress or plating such as a ball mill so that nickel powder or porous nickel film is adhered thereto. Thus, an electrode is constituted by alloy granule adhered with Ni contributing to electrode activity. Further, characteristics can be improved by thermally treating this Ni-adhered alloy.

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 electrode used as a negative electrode of a nickel-hydrogen storage battery and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable equipment and cordless equipment, a battery as a power source thereof has been required to have higher energy density. In order to achieve this requirement, a nickel-hydrogen storage battery using a hydrogen storage alloy electrode for the negative electrode has been receiving attention. The hydrogen storage alloys currently in practical use are mainly Mm—Ni ₅ (Mm: mixture of rare earth elements) type AB ₅ type alloys, and AB ₂ Laves phase type alloys are partially used. However, there is a strong demand from the equipment side for higher capacity, and a hydrogen storage alloy material with a large discharge capacity is also desired. On the other hand, in recent years, the theoretical hydrogen storage capacity is larger than that of conventional AB ₅ type alloys, and high capacity can be expected in Z.
AB ₂ type Laves phase alloy composed of rTiMnMNi,
Solid solution type hydrogen storage alloy (hereinafter referred to as bcc alloy) of body-centered cubic structure such as TiVNi system, Mg ₂ Ni or MgN
Attention is paid to MgNi-based alloys such as i (for example, Japanese Patent Laid-Open No. 6-228699).

However, these hydrogen storage alloys are
There is the following problem in that the amount of Ni in the alloy is smaller than that of the AB ₅ type alloy. That is, the Ni content of the Mm-Ni ₅ type AB ₅ type alloy currently put into practical use is more than 50 w.
t%, whereas it is 3 for the AB ₂ type Laves phase alloy
It is 0% by weight, and 20% by weight or less in a solid solution type hydrogen storage alloy. Since Ni is a B-site element that does not absorb hydrogen, when a large amount of Ni is added like an AB ₅ type alloy, the discharge capacity is reduced, but on the other hand, the electrode activity is excellent, and even for an electrolyte mainly composed of KOH. Since it is stable, it has an advantage that it is excellent in high rate discharge characteristics and cycle characteristics. AB ₂ type Laves phase alloys and bcc alloys have a small amount of Ni,
Although the discharge capacity is high, the high rate discharge characteristics and cycle characteristics are poor. In the case of the MgNi-based alloy, the amount of Ni is considerably large, but Mg is easily oxidized and has problems in high rate discharge characteristics and cycle characteristics.

As countermeasures against these problems, plating of Cu or Ni on the surface of the alloy (JP-A-2-79369) and mechanical alloying of nickel fine powder (JP-A-64-636).
No. 6, JP-A-3-155049) and the like to coat the alloy surface, and further Ni firing and the like (JP-A-59-14).
No. 5752) has been proposed. But C
Due to the effect of the oxide film formed on the surface of the hydrogen storage alloy, the effect of improving the high rate discharge characteristics and cycle characteristics is small for the added amounts of u and Ni, and the addition of a large amount causes a decrease in the discharge capacity. It was

[0005]

In view of the above, the present invention improves the high rate discharge characteristics and cycle characteristics by effectively adhering Ni to the surface of the hydrogen storage alloy and improving the electrode activity and corrosion resistance. Another object is to provide a hydrogen storage alloy electrode.

[0006]

The hydrogen storage alloy electrode of the present invention has a fine nickel powder or a porous nickel film attached to the surface of the electrode through a thin oxide film which does not interfere with the electrode activity of 0.15 μm or less. It is composed of existing hydrogen storage alloy particles. This fine nickel powder or porous nickel film exists simply without having a chemical bond with the surface of the hydrogen storage alloy particles, or a part of the nickel powder or film exists in an alloyed state with the hydrogen storage alloy. . This nickel fine powder or porous nickel film can improve the high rate discharge characteristics and cycle characteristics of the hydrogen storage alloy electrode.

A hydrogen storage alloy for a negative electrode of a nickel-hydrogen storage battery is required to have a high capacity, a high electrode activity and an excellent cycle life. Further, it is effective to increase the ratio of the rare earth element and the A site element such as Zr in order to increase the capacity, but in terms of electrode activity and cycle life, N
It is effective to add a B site element such as i or Cu.
It is difficult to achieve both of these contradictory properties even if only the composition of the hydrogen storage alloy is examined. Therefore,
As the hydrogen storage alloy, it is suitable to use a composition with a small amount of Ni and a high capacity, and to cope with the electrode activity and the cycle characteristics on the alloy surface. Conventionally, a method of forming a nickel layer having excellent electrode activity by depositing Ni fine particles or nickel fine powder on the surface of the hydrogen storage alloy particles by a method such as a ball mill or mechanofusion has been studied.

As a result of various studies on the activation by the nickel layer, the present inventors found that the nickel layer formed as described above has a thickness of 0.15 existing on the surface of the hydrogen storage alloy.
Since it exists on the oxide film exceeding μm, it does not work very effectively for imparting the electrode activity, but when the oxide film becomes 0.15 μm or less, preferably 0.1 μm or less, the denseness of the film largely decreases and the oxidation It was found that the effect of adding Ni is remarkable because the film becomes porous. However, if the size of the added nickel fine powder exceeds 5 μm, it cannot contact the hydrogen storage alloy through the porous oxide film, and the effect of improving the characteristics is small.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Specific means for attaching fine nickel powder or porous nickel film to the surface of hydrogen storage alloy particles constituting the hydrogen storage alloy electrode of the present invention through an oxide film having a thickness of 0.15 μm or less. Will be described below. First, the first method removes at least a part of the oxide on the surface by subjecting the hydrogen storage alloy particles to reduction treatment in a high temperature hydrogen gas atmosphere or etching with a hydrofluoric acid aqueous solution. Specifically, the oxide film is thinned to 0.15 μm or less, preferably 0.1 μm or less. Next, it is a method in which fine nickel powder is adhered to the surface of the hydrogen storage alloy particles in an inert gas by a mechanical method such as mechanofusion, a ball mill or an air flow impact method. The nickel fine particles used here are carbonyl nickel, Raney nickel or Ni-X (X is Al, Sn, Mg, Ca and Z) consisting of Ni and an element soluble in a strong alkaline aqueous solution.
Nickel alloy fine particles represented by (at least one selected from the group of n) are prepared by a water atomizing method, a gas atomizing method, or a mechanical alloying method, and then immersed in a high-temperature strong alkaline aqueous solution to elute in the nickel alloy fine particles. Those produced by removing the components are used.

The second method is a method in which the oxide film on the surface of the hydrogen storage alloy particles is thinned in the same manner as described above, and then the porous nickel film is attached to the surface of the hydrogen storage alloy particles by electroless plating. A third method is to thin the oxide film on the surface of the hydrogen storage alloy particles as described above, and form the Ni-X alloy film by electroless plating on the surface of the hydrogen storage alloy particles,
Next, it is a method of dissolving the component X in the plating film to form a porous nickel film by immersing it in a strong alkaline aqueous solution.

In the fourth method, as in the above, the hydrogen storage alloy particles are reduced in a high-temperature hydrogen gas atmosphere or etched with a hydrofluoric acid aqueous solution to form an oxide film with an oxygen content of 0.
After thinning to 15 μm or less, preferably 0.1 μm or less, an electrode is formed by using the hydrogen storage alloy particles, and Ni—Zn or Ni—Sn is formed on the electrode surface by electrolytic plating.
And a method of forming a nickel alloy film selected from Ni-Co and then immersing the electrode in a strong alkaline aqueous solution to dissolve zinc, tin or cobalt in the plating film to form a porous nickel film. Is.

In the present invention, by reducing the hydrogen-absorbing alloy particles in a high-temperature hydrogen gas atmosphere or by etching with a hydrofluoric acid aqueous solution, the effect of covering the oxide particles on the surface of the alloy particles is greatly reduced, The effect of improving the electrode activity by Ni adhering to the surface of the hydrogen storage alloy is greatly improved. However, if left in the air for too long after the above-mentioned etching or the like, an oxide film is formed again. Therefore, it is preferable to perform the Ni treatment within 24 hours after the treatment. As described above, by sintering the hydrogen-absorbing alloy particles having the nickel fine powder or the porous nickel film attached to the surface in a vacuum, it is possible to further improve the high rate discharge characteristics. By sintering, nickel fine powder or a part of the porous nickel film diffuses into the hydrogen-absorbing alloy particles, and a part of them is alloyed to significantly improve the electrode activity. The characteristics are improved. Even when nickel fine particles are attached by a mechanical treatment such as a planetary ball mill or a mechanofusion method, a small amount of Ni diffuses in the hydrogen storage alloy.

AB ₂ Laves phase alloys, bcc alloys and MgNi-based high capacity hydrogen storage alloys are particularly effective as the hydrogen storage alloys. When mechanically attaching the fine nickel powder to the surface of the hydrogen storage alloy, it may be mixed in air using a mortar, but in an inert atmosphere, the mechanofusion method, (planetary) ball mill method, or airflow impact It is more preferable to use the method since a diffusion layer is formed and adhered on the surface of the hydrogen storage alloy.

[0014]

EXAMPLES Examples of the present invention will be described in detail below. << Example 1 >>) Ti _0.3 V _0.5 Cr _0.1 was used for the hydrogen storage alloy.
A bcc alloy of Ni _0.1 was used. This alloy is a commercial T
It was prepared by an arc melting method using i, V, Cr, and Ni metals as raw materials. Next, the alloy was sufficiently occluded with hydrogen and hydrogenated and pulverized.
m or less of hydrogen storage alloy particles were obtained. Next, 46% on the market
The hydrofluoric acid aqueous solution was diluted to prepare an etchant having a concentration of 0.5 wt%, 10 g of alloy particles was added to 100 cc of this etchant, and etching was performed at room temperature for 10 minutes while gently stirring. After that, washing with water and vacuum drying were performed to obtain hydrogen storage alloy particles. Since the surface of the hydrogen storage alloy particles cannot be directly observed, the alloy lump before crushing was embedded in resin, the surface was ground and degreased, and the surface was left for 24 hours as a standard, which was fluorinated under the same conditions as in this example. The product etched with an aqueous solution of hydrofluoric acid (standing time 2 hours) was subjected to Auger analysis. As a result, in the standard sample, the thickness of the surface oxide film is about 0.25 μm, and the thickness after etching is 0.1
μm. It was also found that the oxide film was thickened again to 0.15 μm when left for 24 hours after etching.

90 wt% of the above hydrogen-absorbing alloy particles and carbonyl nickel (INCO nickel powder Type 287 manufactured by Inco Limited Japan, average particle diameter 2.6-3.
(3 μm) 10 wt% was immediately (preferably within several hours) after the alloy etching treatment, mixed for 10 minutes with a planetary ball mill filled with argon gas to deposit fine nickel powder on the hydrogen storage alloy particles. 3% by weight of polyethylene powder as a binder was added to the hydrogen-absorbing alloy particles produced in this way, and made into a paste with ethanol, which had a porosity of 95%, a size of 2 cm × 2 cm, and a thickness of 0.6 m.
600kgf after being filled in a foamed nickel plate of m and dried.
/ Cm ² and pressurization at 130 ° C in vacuum at 1
The binder was melted by heating for a time to produce a hydrogen storage alloy electrode sheet. This electrode is about 1.0g of hydrogen storage alloy particles
Contains. A nickel lead wire was welded to this to form a negative electrode. In addition, the positive electrode mixture containing nickel hydroxide as the main component had the same porosity of 95% as the negative electrode and a size of 2 cm × 2 c.
A foamed nickel plate having a thickness of m and a thickness of 1 mm was filled and a nickel lead wire was welded to produce a positive electrode. The one negative electrode and the two positive electrodes thus produced were each wrapped with a hydrophilic polypropylene separator having a thickness of 0.15 mm, the negative electrode was sandwiched between the two positive electrodes, and an acrylic resin plate was placed from both sides. Tightened with. This was placed in a battery case, and about 200 cc of an electrolytic solution containing a potassium hydroxide aqueous solution (density 1.30 g / cm ³ ) as a main component was poured into the battery case. Thus, an open system liquid-rich battery whose capacity was regulated by the negative electrode was produced.

FIG. 1 shows the above battery at 10 ° C. for 10 hours.
4 shows a change in discharge capacity per 1 g of the negative electrode alloy when a charging / discharging cycle of charging at 0 mA for 6 hours and discharging at 50 mA to a final voltage of 0.8 V was performed. FIG.
Shows high rate discharge characteristics, and shows the capacity ratio when discharged at each discharge current density, with the capacity when discharged at a current of 50 mA / g per unit weight of the alloy being 1. Here, Comparative Example 1 uses an electrode composed of hydrogen-absorbing alloy particles which is not subjected to etching treatment or addition of nickel fine powder, and Comparative Example 2 is not subjected to etching treatment with a hydrofluoric acid aqueous solution. In addition, the same electrode as that used in Example 1 was used, which was composed of hydrogen storage alloy particles to which 10% by weight of carbonyl nickel was added.

In Comparative Example 1, the maximum discharge capacity is 280 mAh.
/ G / g, low cycle characteristics, 300 mA /
At a high rate of g, almost no discharge was possible. In Comparative Example 2, the discharge capacity was about 340 mAh / g, and the cycle characteristics were slightly improved as compared with the additive-free one. However, almost no improvement in capacity was observed at a discharge of 300 mA / g. On the other hand, in the case of this example, the maximum discharge capacity was greatly improved to 400 mAh / g, the cycle characteristics were also improved, and the high rate discharge characteristics were also markedly improved. This is because part of the nickel fine powder, which has excellent electrode activity and corrosion resistance, is in direct contact with the surface of the hydrogen storage alloy without passing through the oxide film, resulting in a significant improvement in electrode activity, an increase in discharge capacity, and a high rate discharge. It is considered that this is because the characteristics are improved and the cycle characteristics are also improved. Comparative Example 2
It is considered that, in the case where the nickel fine powder is simply adhered without etching treatment as described above, the direct bonding between the nickel fine powder and the surface of the hydrogen storage alloy is not sufficient, and the electrode activity is not improved so much. Therefore, it is considered that the current collecting property was slightly improved and the discharge capacity was slightly improved, but the high rate discharge property was hardly improved.

Example 2 Similar to Example 1, hydrogen-absorbing alloy particles were prepared by etching with a hydrofluoric acid aqueous solution and then mixing with carbonyl nickel powder in a planetary ball mill to deposit fine nickel powder on the surface. did. The hydrogen-absorbing alloy particles were made into a paste with ethanol, and the same foamed nickel plate as in Example 1 was filled and pressed to prepare an electrode,
This was heat-treated in vacuum at 800 ° C. for 30 minutes, and immediately quenched. As a result of analysis by EPMA (electron beam microanalyzer), some Ni (0.2 μm) was found in the alloy.
It was found to be diffused. If the holding time at high temperature is too long, the fine nickel powder on the surface will be completely diffused inside the hydrogen storage alloy, so about 30 minutes, and at most 1 hour or less was appropriate.

The characteristics of an open system liquid-rich battery using this electrode as the negative electrode are shown in FIGS. 1 and 2. In this example, further improvement in discharge capacity and high rate discharge characteristics was observed as compared with Example 1. Comparative Example 3 uses a negative electrode obtained by heat-treating an electrode composed of hydrogen-occlusion alloy particles to which 10% by weight of carbonyl nickel was added without heat treatment in vacuum at 800 ° C. for 30 minutes. Comparative Example 3 has a discharge capacity of 360 mAh / g and is 20 mA higher than Comparative Example 2 in which carbonyl nickel is added but not treated at high temperature.
It was improved by about h / g. However, no significant improvement was observed as compared with Example 2 (discharge capacity 430 mAh / g) which was subjected to etching treatment. It is considered that this is because the alloy surface has a strong oxide film, so that the nickel fine powder hardly diffuses to the surface of the hydrogen storage alloy even by the heat treatment, and the electrode activity is not significantly improved.

Example 3 Predetermined amounts of Zr, Mn, V and C
r and Ni were put in a crucible of a high frequency melting furnace and melted, and this was poured into a water-cooled mold, and the main alloy phase was a C15 type Laves phase AB ₂ type ZrMn _0.6 V _0.1 Cr _0.2 Ni _1.2. Was produced. The alloy produced in this way is vacuumed at 1100 ° C.
After heat treatment for 6 hours, mechanical pulverization gave alloy particles having a particle size of about 22 μm. 90% of these alloy particles in hydrogen gas
A reduction treatment was performed at 0 ° C. for 2 hours to thin the oxide film on the surface. As a result of Auger analysis performed in the same manner as in Example 1, the thickness of the oxide film was reduced from 0.2 μm to 0.08 μm. To 95 g of the hydrogen storage alloy particles, 5 g of nickel black (Ni, manufactured by Nippon Metallurgy Co., Ltd., particle size: 200 Å) was added, and mechanofusion (using Hosokawa Micron) for 20 minutes was performed in an argon atmosphere to deposit nickel black on the alloy surface. Let From the microscopic observation, it was found that nickel black adhered to the alloy surface almost uniformly.

Example 1 using the above hydrogen storage alloy particles
An electrode was prepared in the same manner as above, and an open system liquid rich negative electrode regulated battery was assembled. This battery is 100 at 100
The maximum discharge capacity per 1 g of the negative electrode alloy and the discharge capacity when discharged at 300 mA / g when the charging / discharging cycle of charging at a current of mA for 6 hours and discharging to a final voltage of 0.8 V at a current of 50 mA were performed. The results are shown in Table 1 below. The latter discharge capacity was used as an evaluation standard for high rate discharge characteristics. Comparative Example 4 uses a negative electrode composed of hydrogen storage alloy particles that is neither reduced nor added with nickel, and Comparative Example 5 is hydrogen added with nickel black in the same manner as in this Example without hydrogen reduction. A negative electrode composed of storage alloy particles is used. Comparative Example 4 has a small maximum discharge capacity of about 380 mAh / g and a capacity of 300 mA / g of 180 mAh / g.
g. Comparative Example 5 has a maximum discharge capacity of 395 mA.
The capacity at h / g and 300 mA / g was 210 mAh / g, and although some improvement was recognized, it was not so remarkable. On the other hand, in Example 3, the maximum discharge capacity was 420 mAh / g, and the capacity at 300 mA / g was 260.
It was improved to mAh / g.

Example 4 In the same manner as in Example 3, after hydrogen reduction treatment, hydrogen storage alloy particles having nickel black adhered to the surface were produced. Example 2 using these alloy particles
In the same manner as in (1), an electrode containing no polyethylene powder as a binder was prepared, and this was heat-treated in vacuum at 600 ° C. for 40 minutes. As a result of EPMA analysis, Ni was slightly contained in the alloy (0.
It was found that they were diffused (about 1 μm). Using the above electrode as a negative electrode, an open system liquid-rich negative electrode regulated battery similar to that of Example 1 was produced. This battery is 100 at 100
The maximum discharge capacity per 1 g of the negative electrode alloy and the discharge capacity when discharged at 300 mA / g when the charging / discharging cycle of charging at a current of mA for 6 hours and discharging to a final voltage of 0.8 V at a current of 50 mA were performed. The results are shown in Table 1 below. Comparative Example 6
An electrode composed of hydrogen storage alloy particles to which nickel black was added without hydrogen reduction treatment was subjected to the same heat treatment as in this example. Comparative Example 6 has a maximum discharge capacity of 410
The capacity at mAh / g and 300mA / g is 230mAh /
It was g, and some improvement was recognized. On the other hand, in Example 4, the maximum discharge capacity was 440 mAh / g,
The capacity at 300 mA / g was also improved to 290 mAh / g.

Example 5 The alloy particles were subjected to hydrogen reduction treatment in the same manner as in Example 3 and then subjected to the air flow impact method (NHS-produced by Nara Machine Co., Ltd.).
Nickel black was adhered to the surface of the hydrogen storage alloy particles by using 0 type, argon atmosphere, 5 minutes). The deposition rate of nickel black is 5 g per 95 g of alloy. An electrode was produced using the alloy particles in the same manner as in Example 1 to assemble an open system liquid-rich negative electrode regulated battery.
The maximum discharge capacity per 1 g of the negative electrode alloy when the battery was charged and discharged under the same conditions as above, and 300 mA
As shown in Table 1, the capacity at the time of / g discharge was almost the same as in Example 3, confirming the effect of the present invention.

<Examples 6 to 8> The same hydrogen storage alloy particles as in Example 1 were etched under the same conditions as in Example 1. On the other hand, as nickel fine powder attached to this,
The particles produced by the water atomizing method (jet pressure 1200 kgf / cm ² ) were classified, and the particle size was 3 μm, 5 μm, and 7
Three types of spherical nickel fine powder of μm were prepared. next,
This nickel fine powder is reduced with hydrogen at 800 ° C. for 10 hours,
The oxide film on the surface was almost removed. 85 g of the above-described hydrogen-absorbing alloy particles that had been subjected to the etching treatment and 15 g of nickel fine particles of each particle size were mixed for 1 hour in a ball mill filled with argon. In this way, hydrogen storage alloy particles to which the nickel fine powder was attached were prepared, and the particles were used to prepare an electrode in the same manner as in Example 1 to assemble a battery. Table 1 shows the characteristics of these batteries under the same conditions as described above. When the particle size of the nickel fine powder deposited on the hydrogen storage alloy particles was 3 μm (Example 6) and 5 μm (Example 7), the maximum discharge capacity and the capacity at 300 mA / g were improved. However, with 7 μm (Example 8), the capacity improving effect at 300 mA / g was weak. Therefore, the fine nickel powder to be attached to the hydrogen storage alloy particles preferably has a particle size of 5 μm or less. This is because as the particle size increases, the amount of direct contact with the hydrogen storage alloy through the porous part opened in the oxide film on the alloy surface decreases, and the contact point with the hydrogen storage alloy surface when the same weight is added decreases. It is thought to be because. The amount of the fine nickel powder added is limited to about 20 wt%, and the addition of Ni having no hydrogen storage capacity further lowers the discharge capacity.

Example 9 Mg particles 2 having a particle size of 200 μm
4 g and 58 g of carbonyl nickel having a particle size of several μm were mixed by a ball mill in an argon gas atmosphere for 3 days, and mechanical alloying was performed to obtain MgN having a particle size of about 10 μm.
An i alloy powder was prepared. This alloy was reduced in a hydrogen gas atmosphere at 360 ° C. for 10 hours and used as a master alloy. As a result of Auger analysis in the same manner as in Example 1,
The oxide film on the surface of the alloy was reduced from about 0.3 μm to about 0.15 μm. Next, Ni—Al particles having a particle size of about 70 μm were prepared as porous nickel by the gas atomizing method.
This was mechanically crushed by a mechanical grinder to have a particle size of about 15 μm, and then immersed in a KOH aqueous solution at 80 ° C. for 6 hours to elute Al, to produce a porous nickel powder. Porous nickel was added to 40 g of the above MgNi alloy.
0 g was added and mixed in a planetary ball mill for 10 minutes in an argon gas atmosphere to adhere porous nickel to the surface of the MgNi alloy. An open system liquid-rich negative electrode regulated battery having the same configuration as in Example 1 was produced using the hydrogen storage alloy particles to which the porous nickel was attached. Comparative Example 7 is one in which the electrode is made of a MgNi alloy which is not treated, Comparative Example 8
Is an electrode formed by depositing porous nickel on MgNi alloy particles in the same proportion without hydrogen reduction treatment.

The characteristics of these batteries are shown in Table 1. Comparative Example 7 has maximum discharge capacities of 410 mAh / g and 300 mA / g.
The capacity at 240 g was 240 mAh / g, and in Comparative Example 8, the maximum capacity was 435 mAh / g and the capacity at 300 mA / g was 2.
It was 60 mAh / g, and a slight improvement was recognized in each case. In Example 9, the maximum discharge capacity was 540 mAh / g,
The capacity at 300 mA / g was greatly improved to 410 mAh / g. In addition, an improvement effect was recognized also in cycle characteristics. As the method for producing the porous nickel particles, in addition to Ni-Al, Ni-Sn, Ni-Mg, or Ni-Ca alloy fine particles may be used by a gas atomizing method, a water atomizing method, or a mechanical arrowing method, or a Ni-Zn alloy. The fine particles can be produced by a mechanical arrowing method, and then mechanically pulverized if necessary, and Sn, Mg, Ca or Zn is eluted with a strong alkaline aqueous solution.

<Examples 10 to 12> Ti, V, Cr, L
Using a and Ni as raw materials, T by the arc melting method
A bcc alloy of i _0.3 V _0.4 Cr _0.1 La _0.1 Ni _0.1 was prepared. Particle size of 30μ
m hydrogen storage alloy particles. Next, the hydrogen storage alloy particles were subjected to etching treatment with a hydrofluoric acid aqueous solution in the same manner as in Example 1, and then an electrode was prepared in the same manner as in Example 1. Using this electrode as the negative electrode and the following plating bath,
Electroplating was performed for a minute to form a Ni-Zn alloy film on the surface. After rinsing with water, it was added to an etching solution at 100 ° C. in which LiOH was dissolved at a rate of 40 g / l in 31% KOH aqueous solution.
It was immersed for a time to elute Zn in the plated film. EPM
According to A observation, Ni- was formed on the surface of the negative electrode plate by electrolytic plating.
Although the Zn alloy was uniformly present, it was confirmed that Zn was almost completely eliminated by etching and that numerous minute cracks were contained.

Plating bath: NiSO ₄ .7H ₂ O 330 g / l NiCl ₂ .6H ₂ O 45 g / l ZnCl ₂ 20 g / l H ₂ BO ₃ 37 g / l pH 2 Anode Ni plate Current density 5 A / dm ²

A liquid-rich negative electrode regulated battery similar to that of Example 1 was assembled using the above electrode as a negative electrode. Comparative Example 9 uses the electrode before the plating treatment described above, and Comparative Example 10 configures the electrode with hydrogen storage alloy particles that are not subjected to etching treatment,
Comparative example 11 using an electrode subjected to the same Ni-Zn plating and etching treatment with a strong alkali as described above.
In the above, an electrode not subjected to etching treatment with a strong alkali after plating is used. The characteristics of these batteries are shown in Table 1. In Comparative Examples 10 and 11, the maximum discharge capacity and the high rate discharge characteristics were improved as compared with Comparative Example 9, but they were not significantly improved as compared with Example 10. Incidentally, instead of Ni-Zn plating, Ni-S
The same effect was observed even when using an electrode that was subjected to n-plating (Example 11) or Ni-Co plating (Example 12) and subjected to etching treatment with a strong alkali.

Example 13 The negative electrode plate of Example 10 was heat treated in vacuum at 900 ° C. for 10 minutes. Using this electrode, as shown in Table 1, further improvement in characteristics was observed as compared with Example 12.

<< Embodiment 14 >> Similar to Embodiment 10, Ti
A bcc alloy of _0.3 V _0.4 Cr _0.1 La _0.1 Ni _0.1 was prepared, and hydrogenated and mechanically ground to give particles having a particle size of about 30 μm, which were subjected to etching treatment with a hydrofluoric acid aqueous solution in the same manner as in Example 1. 2 g of 10 g of the hydrogen storage alloy particles
0 g / l SnCl ₂ · 2H ₂ O and 6N HCl for 10 m
Immerse in 1 / l treatment solution for 1 minute at 25 ° C, then 0.5
5 ml / g of PdCl ₂ .2H ₂ O and 6N HCl
It was immersed in a treatment liquid containing 1 l at 25 ° C. for 1 minute. After thoroughly washing with water, the surface was plated with nickel by immersing it in the electroless plating bath shown below at 60 ° C. for 30 minutes.

The electroless plating _{bath: NiSO 4 · 6H 2 O 25g} / l sodium pyrophosphate 50 g / sodium l phosphinate 25 g / l pH 11

As a result of EPMA analysis, it was confirmed that Ni was deposited on the surface of the hydrogen storage alloy particles in a porous form of about 0.5 μm. An electrode was prepared using the above hydrogen storage alloy particles in the same manner as in Example 1 to assemble a liquid-rich negative electrode regulated battery. As shown in Table 1, the characteristics of this battery are that the maximum discharge capacity is 500 mAh / g, 300 mA.
/ G capacity was improved to 260 mAh / g.

Example 15 The negative electrode plate of Example 14 was heat-treated in vacuum at 800 ° C. for 15 minutes. As shown in Table 1, the battery using this electrode showed further improvement in characteristics as compared with Example 14.

[0035]

[Table 1]

As described above, when nickel particles are attached to the surface of the hydrogen storage alloy particles, the thickness of the oxide film has a great influence on the electrode activity. It is difficult to completely remove the oxide film, but the thickness is 0.15 μm
When the thickness is less than 0.1 μm, the film becomes porous, and Ni adheres to improve the electrode activity. As a method for thinning the oxide film, reduction in a high-temperature hydrogen gas atmosphere and etching with a hydrofluoric acid aqueous solution are optimal.

[0037]

EFFECTS OF THE INVENTION In the hydrogen storage alloy electrode of the present invention, Ni having excellent electrode activity is present on the surface of the hydrogen storage alloy particles through a thin oxide film, and a part of Ni is alloyed with the hydrogen storage alloy. Therefore, it has high capacity, high rate discharge characteristics and excellent cycle characteristics.

[Brief description of drawings]

1 is an example of the present invention, and FIG. 1 is a comparative example.
FIG. 3 is a diagram showing a change in discharge capacity per 1 g of negative electrode alloy in the charge / discharge cycle of FIG.

FIG. 2 is a diagram showing high rate discharge characteristics of Examples 1 and 2 and Comparative Examples 1, 2 and 3.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toyoguchi ▲ Yoshi ▼ Toku 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] 1. A hydrogen storage alloy electrode comprising hydrogen storage alloy particles having a fine nickel powder or a porous nickel film attached to the surface thereof through an oxide film having a thickness of 0.15 μm or less. 2. The hydrogen storage alloy is an AB ₂ Laves phase alloy, a solid solution type alloy having a body-centered cubic structure, and MgN.
The hydrogen storage alloy electrode according to claim 1, which is selected from the group consisting of i-based alloys. 3. The hydrogen storage alloy electrode according to claim 1, wherein the fine nickel powder has a particle size of 5 μm or less. 4. The hydrogen storage alloy electrode according to claim 1, wherein the fine nickel powder is Raney nickel. 5. The nickel fine powder or a part of the porous nickel film is alloyed with hydrogen storage alloy particles.
The hydrogen storage alloy electrode as described in the above. 6. A step of reducing at least a part of oxides on the surface by subjecting the hydrogen storage alloy particles to reduction treatment with hydrogen gas or etching with a hydrofluoric acid aqueous solution, and the hydrogen storage alloy in an inert gas. The particle size is 5μ on the surface of the particle
A method for producing a hydrogen storage alloy electrode, comprising a step of depositing nickel fine powder of m or less by mechanofusion, a ball mill or an air flow impact method. 7. A step of reducing at least a part of surface oxides by subjecting the hydrogen storage alloy particles to reduction treatment with hydrogen gas or etching with a hydrofluoric acid aqueous solution, and electroless formation on the surface of the hydrogen storage alloy particles. A method for producing a hydrogen storage alloy electrode, comprising a step of depositing a porous nickel film by plating. 8. A step of reducing at least a part of oxides on the surface by subjecting the hydrogen-absorbing alloy particles to a reduction treatment with hydrogen gas or etching with a hydrofluoric acid aqueous solution, and producing an electrode plate from the hydrogen-absorbing alloy particles. The step of forming an alloy of Ni-Zn, Ni-Sn, and Ni-Co on the surface of the electrode plate by electrolytic plating, and immersing the plated electrode plate in a strong alkaline aqueous solution. A method for producing a hydrogen storage alloy electrode, comprising a step of dissolving zinc, tin or cobalt in the alloy. 9. The method for manufacturing a hydrogen storage alloy electrode according to claim 6, further comprising a step of sintering in vacuum. 10. A step of producing nickel alloy fine particles, wherein the fine nickel powder is nickel and an element soluble in a strong alkaline aqueous solution by a water atomizing method, a gas atomizing method or a mechanical alloying method, and the obtained nickel alloy fine particles are treated with a strong alkali. 7. The method for producing a hydrogen storage alloy electrode according to claim 6, wherein the hydrogen storage alloy electrode is manufactured by a step of immersing the electrode in an aqueous solution to remove elution components in the nickel alloy fine particles. 11. The nickel alloy fine particles are Ni—X.
(However, X is at least one element selected from the group consisting of Al, Sn, Mg, Ca, and Zn.) The method for producing a hydrogen storage alloy electrode according to claim 10.