JPH0756799B2 - Method for producing hydrogen storage alloy negative electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage alloy negative electrode using a hydrogen storage alloy that reversibly stores and releases hydrogen.
It is possible to provide a pollution-free and high energy density alkaline storage battery.

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as secondary batteries among various power sources.

The most widely used alkaline storage battery is the nickel-cadmium storage battery. Although this battery is considerably superior in performance, there are still high expectations for high energy density and pollution-free, and new battery systems are being investigated.

For example, zinc has been taken up in place of cadmium as the negative electrode, but it is not widely used because it has a problem in life as well known. Recently, attention has been paid to alkaline storage batteries that use a hydrogen storage alloy that reversibly stores and releases hydrogen as the negative electrode. In this case, a battery can be constructed in the same way as cadmium and zinc, and the actual dischargeable capacity density can be made larger than that of cadmium, and there is no formation of dendrite such as zinc. Promising as a pollution-free alkaline storage battery.

However, the hydrogen storage alloy is further pulverized by repeating storage and release of hydrogen, and when this is used as a constituent material of a battery electrode, the electrode is deformed or comes off. Further, in a system that absorbs gas by the Neumann method in an alkaline storage battery, particularly a sealed alkaline storage battery, the surface is oxidized by oxygen gas generated from the positive electrode, and the hydrogen storage / release capacity is reduced.

Therefore, when using a hydrogen storage alloy for the negative electrode, advance the pulverization before making it into an electrode so that it will not be pulverized further even if charged and discharged in the battery, and the performance will be improved by oxygen gas. It is important to improve the oxidation resistance so as not to decrease. In order to solve these problems, it has been studied to pulverize the hydrogen storage alloy as finely as possible and to coat the surface of the hydrogen storage alloy with an oxidation resistant coating. Further, it has been considered to extend the life of the crushed hydrogen storage alloy by surface-treating it with an alkaline aqueous solution.

Problems to be Solved by the Invention An alkaline storage battery using a hydrogen storage alloy for a negative electrode is effective in improving high energy density as described above, but has problems in pulverization and oxidation.

It is an object of the present invention to provide a simple method for producing a hydrogen storage alloy while using the hydrogen storage alloy for a hydrogen storage alloy negative electrode of an alkaline storage battery to solve the problems such as pulverization and oxidation which have been problems so far. .

Means for Solving the Problems The present invention is characterized in that the step of mechanically crushing a hydrogen storage alloy is carried out in an alkaline aqueous solution, and then at least washing and drying are performed to obtain a hydrogen storage alloy negative electrode. It is a manufacturing method of an alloy negative electrode. And, preferably the alkaline aqueous solution is a caustic alkali having a specific gravity of 1.05 to 1.50, and the alkaline aqueous solution is heated to 30 to 80 ° C., and the step of mechanically pulverizing the hydrogen storage alloy is particularly a ball mill method. Is good.

By carrying out the grinding in an alkaline aqueous solution, the impurity phase, which is relatively hard to grind, is dissolved in the alkaline aqueous solution, so that finer grinding can be performed in a short time.

Example First, the structure of the present invention will be described conceptually. When a hydrogen storage alloy is used as a negative electrode of an alkaline storage battery, the hydrogen storage alloy obtained by melting the alloy has been previously pulverized by hydrogenation or mechanical means.

The present invention employs a wet mechanical pulverization method for this pulverization step, and is characterized in that it is carried out in an alkaline aqueous solution.

Up to now, it has been practiced to manufacture a hydrogen storage alloy, pulverize it into fine powder, and then subject the hydrogen storage alloy powder or the hydrogen storage alloy negative electrode to alkali treatment in an alkaline aqueous solution. This alkaline treatment will prolong the life of sealed batteries by removing components that are easily dissolved in caustic alkali, which is the electrolyte of alkaline storage batteries, or by accommodating the surface of the hydrogen-absorbing alloy powder into alkalis to make sealed batteries. It has the effect of being possible.

That is, the crushing step and the alkali treatment step, which have been performed separately respectively, are simplified at the same time, and at the same time, the two steps are simultaneously performed so that the crushing up to now can be performed more effectively. Is. What is important here is that the hydrogen storage alloy negative electrode obtained by crushing in a caustic alkali as in the present invention is superior to the hydrogen storage alloy negative electrode obtained by simply performing pulverization and alkali treatment separately. It is to exhibit life characteristics. It is presumed that the reason is that the crushed surface of the new alloy immediately comes into contact with caustic when crushing the hydrogen storage alloy. By performing the pulverization in the alkaline aqueous solution, the impurity phase which is relatively difficult to be pulverized is dissolved in the alkaline aqueous solution, so that finer pulverization can be performed in a short time.

Furthermore, the heat generated during crushing also has a positive effect. That is, crushing in alkali promotes heating without special heating.

Hereinafter, specific examples of the present invention will be described.

Commercially available raw materials such as Mn (Misch metal), Ni, Co, Mn, and Al are weighed to a certain composition ratio, and are measured by an argon arc melting furnace.
An MmNi _3.8 Co _0.5 Mn _0.4 Al _0.3 alloy was produced. The alloy was then heat treated in a vacuum heat treatment furnace according to known methods.

The alloy sample was placed in a ball mill consisting of an alumina pot and balls, and an aqueous potassium hydroxide solution having a specific gravity of 1.30 was added at a ratio of 50 ml to 100 g of the alloy. In this state, ball milling was performed for 10 hours at room temperature. The temperature in the ball mill at the end of this pulverization was about 40 ° C. The crushed hydrogen storage alloy powder was washed with water and then dried. When the particle size distribution of the alloy sample crushed in this alkaline aqueous solution was measured, it was found to be a fine powder of 50 microns or less.

The hydrogen storage alloy sample crushed in such an alkaline aqueous solution was then made into a paste together with a binder such as polyvinyl alcohol, and the paste was applied to a nickel-plated punching metal plate and dried to obtain a negative electrode plate A.

The negative electrode plate A thus obtained was incorporated into a battery.
As the battery, a C1-type cylindrical sealed nickel-hydrogen storage battery was taken as an example. Therefore, the negative electrode plate A thus obtained was cut into a width of 3.9 cm and a length of 26 cm, and the lead plates were attached by spot welding to two predetermined places. A well-known sintered nickel electrode was selected as the counter electrode and the width was 3.9c.
It was used as m and 22 cm in length. Also in this case, the lead plates were attached at two places.

As the separator, a polyamide nonwoven fabric, and as the electrolytic solution, 20 g of lithium hydride in a caustic potash aqueous solution having a specific gravity of 1.20.
L was used after dissolving. The nominal capacity is 3.0 Ah. This battery is designated as A.

Next, for comparison, the same MmNi
_3.8 Co _0.5 Mn _0.4 Al _0.3 alloy was selected and the hydrogen storage alloy was mechanically pulverized to a particle size of 50 microns or less. It took 24 hours. After that, a negative electrode plate B was obtained by immersing in an aqueous potassium hydroxide solution having a specific gravity of 1.30 at 40 ° C. for 10 hours and using the same method as a negative electrode plate B to obtain a battery B. Because of the capacity regulation of the positive electrode, the nominal capacity of this battery is 3.0 Ah.

For further comparison, the same hydrogen storage alloy as before was also used for 24
Negative electrode plate C was obtained by mechanically pulverizing for 50 hours or less without alkaline treatment, and similarly, battery C having a nominal capacity of 3.0 Ah was obtained.

The results of evaluating these batteries by a normal charge / discharge cycle test will be described.

Charge up to 130% at 0.2C (5-hour rate), discharge at 0.5C
The charging / discharging cycle was repeated at a final voltage of 1.0 V (at a rate of 2 hours). As a result, the discharge capacities of the three types of batteries A, B, and C were approximately 3.0 Ah up to about 100 cycles, except that the C battery had a slightly lower discharge terminal voltage than the A and B batteries. No big difference was found. However, when this charging / discharging cycle was further repeated, the discharge capacity of Battery C dropped sharply from the 142nd cycle. Battery B is
The decrease started at the 356th cycle. On the other hand, in Battery A of the present invention, no abnormality was observed up to 500 cycles.

From this, it was revealed that the battery A of the present invention has the most excellent life characteristics.

As described above, the method for producing the hydrogen storage alloy negative electrode of the present invention is
Since the pulverization step and the alkali treatment step of the hydrogen storage alloy that have been performed so far are performed at the same time, it is natural to simplify the manufacturing process, but it is particularly effective in improving the charge / discharge life of the battery.

Claims (4)

[Claims] 1. A method for producing a hydrogen storage alloy negative electrode, which comprises performing a step of mechanically pulverizing a hydrogen storage alloy in an alkaline aqueous solution, followed by at least washing and drying to obtain a hydrogen storage alloy negative electrode. 2. The hydrogen storage alloy negative electrode according to claim 1, wherein the alkaline aqueous solution is a caustic alkali having a specific gravity of 1.05 to 1.50, and the alkaline aqueous solution is heated to 30 to 80 ° C. Production method. 3. The method according to claim 1, wherein the step of mechanically pulverizing the hydrogen storage alloy is a ball mill method.
Item 6. A method for producing a hydrogen storage alloy negative electrode according to the item. 4. A particle size of 100 μm or less in the step of mechanically grinding the hydrogen storage alloy in an alkaline aqueous solution, wherein the particle size is 100 μm or less.
Item 6. A method for producing a hydrogen storage alloy negative electrode according to the item.