JPH10255782A - Hydrogen storage electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance low temperature and high efficiency discharge characteristics by setting a specific surface area of alloy powder of hydrogen storage alloy electrode which can store and discharge hydrogen reversibly in a specific range. SOLUTION: An alloy ingot of MmNi3.8 , Al10.3 , Co0.7 , and Mn0.2 is produced under inert atmosphere by a high frequency induction melting furnace, and a sample is obtained by annealing it at 1000 deg.C. In addition, Mn means mish metal which is a mixture of rare earth elements. This ingot is ground mechanically to a particle with a diameter of not more than 32μm to make hydrogen storage alloy powder. This alloy powder is immersed in acetic acid - sodium acetate buffer aqueous solution heated to 60 deg.C for 30 minutes and after agitating it, it is washed by water and dried to make an alloy powder sample treated by acetic acid. The hydrogen storage electrode is produced by making the alloy sample pasty, filling it in a porous nickel body and pressing it after drying. A specific surface area of the alloy powder used for the electrode is set at 0.2-1.0m<2> /g. As a result, a discharge capacity becomes large in 1C discharge at -20 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage electrode using a hydrogen storage alloy.

[0002]

2. Description of the Related Art In recent years, nickel hydride batteries using a hydrogen storage alloy as a negative electrode material have been increasing in energy density, and those having a volume energy density of 300 Wh / liter class have emerged, surpassing lithium ion batteries. Its applications are small portable devices such as mobile phones, including notebook computers. Nickel hydride batteries are also receiving worldwide attention as EV power supplies. Under the conditions used as these power sources, low-temperature characteristics are regarded as important in addition to life characteristics, high-rate discharge characteristics, and high-temperature characteristics. In particular, there is a demand for improved low-temperature characteristics of power supplies for mobile phones. Above all, the low-temperature high-rate discharge characteristics are greatly affected by the hydrogen storage electrode as the negative electrode, and it is essential to improve the low-temperature characteristics of the hydrogen storage electrode.

[0003]

However, the low-temperature characteristics of the conventional hydrogen storage electrode have not always been satisfactory. The present invention has been made in view of this problem,
An object of the present invention is to provide a hydrogen storage electrode having excellent low-temperature characteristics.

[0004]

The first aspect of the present invention is an electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the specific surface area of the hydrogen storage alloy powder is 0.2 to 1.
It is a hydrogen storage electrode characterized by being 0 m ² / g.

A second aspect of the present invention is a hydrogen storage electrode in which the hydrogen storage alloy has a transition metal rich layer mainly composed of nickel and cobalt on its surface.

A third aspect of the present invention is a hydrogen storage electrode in which the transition metal rich layer is formed by a surface treatment with an aqueous alkali solution or a surface treatment with an aqueous acetic acid-sodium acetate buffer solution.

A fourth aspect of the present invention is a hydrogen storage electrode in which the particle diameter of the hydrogen storage alloy is 32 μm or less.

Generally, as the temperature decreases, the activity of the substance tends to decrease. The same is true for the hydrogen storage electrode, and it is expected that the activity of the charge transfer reaction on the alloy surface will decrease in the low temperature range. In the present invention, an attempt was made to solve the above problem by using a hydrogen storage alloy having a large specific surface area and increasing the contact interface between the alloy surface and the electrolyte. As a technique, a specific surface area of 0.2 to 0.2 μm is formed by using a small particle having an alloy particle diameter of 32 μm or less and forming a porous transition metal rich layer on the alloy surface by surface treatment such as alkali treatment and acetic acid treatment. 1.0 m ² / g.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples.

First, MmNi _3.8 Al _0.3 Co _0.7 Mn
_A predetermined amount of each metal was weighed so as to have a composition of _0.2 , an alloy ingot was prepared in a high-frequency induction melting furnace under an inert atmosphere, and annealed at 1000 ° C. to obtain a sample. In addition, Mm
Means misch metal which is a mixture of rare earth elements. Half of this alloy ingot has a particle size of 32 μm or less,
The other half was mechanically pulverized to a particle size of 75 μm or less to obtain a hydrogen storage alloy powder. These powders are referred to as alloy powder A (having a particle size of 32 μm or less) and alloy powder B (having a particle size of 75 μm or less).

[0011] Alloy powder A and alloy powder B
3% in an aqueous solution of acetic acid-sodium acetate buffer heated to 0 ° C
After being immersed for 0 minutes and stirred, it was washed with water and dried to obtain an acetic acid-treated alloy powder sample. A thickener was added to the alloy sample to form a paste, and the paste was filled into a nickel porous body, dried and pressed to produce a hydrogen storage electrode. These are referred to as invention electrode A1 and invention electrode B1.

The alloy powder A and the alloy powder B are KO
H1 and LiOH were used and surface-treated with a high-temperature alkaline aqueous solution.
Inventive electrode A2 and comparative electrode B2 were produced in the same manner as in Example 1.

Further, a comparative electrode A3 and a comparative electrode B3 were prepared in the same manner except that the surface treatment was not performed on the alloy powder A and the alloy powder B.

Table 1 shows the results of measuring the specific surface area of the alloy used for each electrode by the BET method.

[0015]

[Table 1]

A charge / discharge test was performed at −20 ° C. using the electrode prepared as described above and a normal nickel hydroxide electrode as a counter electrode. The result is shown in FIG. As is clear from Table 1 and FIG. 1, the invention electrode A1, the invention electrode A2, and the invention electrode B1 have a specific surface area of 0.2 to 1.0 m ² / g.
It can be seen that the discharge capacity is larger at 1 C discharge at −20 ° C. than other comparative electrodes using an alloy having a smaller specific surface area.

FIG. 2 shows a discharge curve at -20.degree. As is clear from FIG. 2, the invention electrode A1, the invention electrode A2, and the invention electrode B1 whose specific surface areas are increased are:
Since the activity of the reaction on the alloy surface was increased, the effect of reducing the polarization at the initial stage of the discharge was obtained.

[0018]

As described above, in the hydrogen storage electrode of the present invention, since the hydrogen storage alloy powder having a large specific surface area of 0.2 to 1.0 m ² / g is used, low-temperature high-rate discharge characteristics at −20 ° C. And an extremely excellent effect of improving the

[Brief description of the drawings]

FIG. 1 is a relationship diagram between a discharge capacity and the number of cycles.

FIG. 2 is a relationship diagram between a discharge potential and a discharge capacity.

Claims (4)

[Claims] 1. An electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the specific surface area of the hydrogen storage alloy powder is 0.2 to 1.0 m ² / g. Hydrogen storage electrode. 2. The hydrogen storage electrode according to claim 1, wherein the hydrogen storage alloy has a transition metal rich layer mainly composed of nickel and cobalt on its surface. 3. The hydrogen storage electrode according to claim 2, wherein the transition metal rich layer is formed by a surface treatment with an alkaline aqueous solution or a surface treatment with an acetic acid-sodium acetate buffer aqueous solution. 4. The hydrogen storage alloy has a particle diameter of 32 μm.
The hydrogen storage electrode according to claim 1, wherein: