JPS61128462A - Manufacture of hydrogen absorption electrode - Google Patents

Abstract

PURPOSE:To simplify the manufacture of a hydrogen absorption electrode by activating a hydrogen absorption alloy having high equilibrium pressure and hydrogenating a hydrogen absorption alloy having low equilibrium pressure within a sealed container in which hydrogen pressure can be controlled. CONSTITUTION:A hydrogen absorption alloy which electrochemically absorbs and desorbs hydrogen in an alkaline solution is used for a negative electrode as hydrogen absorption electrode. Two or more kinds of hydrogen absorption alloy powder having different hydrogen equilibrium pressure are placed in a sealed container. The hydrogen atmosphere in the container is controlled higher than hydrogen absorption pressure of the hydrogen absorption alloy having low hydrogen equilibrium pressure and lower than hydrogen absorption pressure of the hydrogen absorption alloy having high hydrogen equilibrium pressure to perform hydrogenation and activation respectively. An alkali resistant polymer binder is added to the alloy powder, then they are molded together with a current collector. Thereby, the high performance electrode is obtained and the manufacturing process is simplified and the cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a battery negative electrode, a so-called hydrogen storage electrode, using an alloy that reversibly stores and releases hydrogen, which is used as a battery negative electrode active material.

2. Description of the Related Art In general, certain hydrogen storage alloys have the property of electrochemically storing hydrogen in an alkaline solution, fcD, and releasing it, so that they can be used as hydrogen storage electrodes.

Conventionally, in order to improve the discharge capacity of this hydrogen storage electrode, a manufacturing method has been proposed in which the hydrogen storage electrode is made by repeatedly storing and desorbing hydrogen and using pulverized powder of an alloy produced by hydrogenation (Unexamined Japanese Patent Publication No. (Sho 63-103910). This method requires prior hydrogenation of the alloy. Therefore, in handling the alloy powder during hydrogenation and after hydrogenation, the manufacturing process becomes somewhat complicated due to problems such as measures to prevent oxidation. Moreover, although the initial discharge capacity is excellent, it also has shortcomings such as a short charge/discharge cycle life.

Therefore, a method of manufacturing an electrode by mixing a hydrogen storage alloy and its hydride has been proposed (Japanese Patent Application No. 171,819/1981). Although this method has improved the charge/discharge cycle life, it still has the same problems as the former in the process of hydrogenating hydrogen storage alloys.

Problems to be Solved by the Invention In all of the above conventional methods, hydrogenation (
A hydrogen storage electrode was produced by making a finely divided hydrogen storage alloy powder, used alone or mixed with an alloy powder, and then bonding it to a conductive electrode support with a binder. This method complicates the manufacturing process and increases manufacturing costs due to the time required for hydrogenation and mixing of the alloy, equipment required to prevent oxidation of the alloy powder, etc. Furthermore, the discharge capacity, cycle life, etc. of the hydrogen storage electrode are not sufficient.

The present invention solves the above problems, and aims to simplify the manufacturing process, reduce manufacturing costs, and improve the performance of the electrode.

Means for Solving the Problems The present invention provides two or more types of hydrogen storage alloy powders with different hydrogen equilibrium pressures in a closed container, and the hydrogen absorption pressure is higher than the hydrogen storage pressure of the hydrogen storage alloy with a lower hydrogen equilibrium pressure. After hydrogenation and activation treatment in a hydrogen atmosphere below the hydrogen storage pressure of the hydrogen storage alloy with high equilibrium pressure, an alkali-resistant polymer binder is added and pressure formed to form a current collector. It is to be united with.

Effect As mentioned above, hydrogen storage alloys with high equilibrium pressure undergo hydrogen activation (
Hydrogen storage alloys with low equilibrium pressure are subjected to hydrogenation (hydrogen storage reaction), so they have excellent electrochemical hydrogen storage and release performance and can extend cycle life. . Furthermore, since the hydrogenated alloy is surrounded by the unhydrogenated alloy, there are few parts exposed to the atmosphere, which also serves to weaken reactions such as oxidation. In this way, there is less rapid expansion and bending of the electrode due to initial hydrogenation, improving the performance of the electrode and simplifying the manufacturing process.

Cost reduction becomes possible.

Example MmN 12 as a hydrogen storage alloy with high hydrogen equilibrium pressure
, a CO2, s (Mxn: mixture of rare earth metals), and LaNi as a hydrogen storage alloy with low hydrogen equilibrium pressure.
3Co2 is used. Each alloy was obtained by weighing each element so as to have a predetermined composition, and arc melting it in an arc melting furnace. Furthermore, it is crushed in a dry box in an argon atmosphere and sieved to produce an alloy powder that passes 300 mesh.
Both alloy powders are mixed in an appropriate ratio, for example, alloy 40 with high hydrogen equilibrium pressure and alloy 60 with low hydrogen equilibrium pressure. This mixed powder is placed in a closed container, and MmN i 2.5Co 2
．． The hydrogen storage pressure of L aN i 3Co2 (20°C) is 3 atm or less, and the hydrogen storage pressure of L aN i 3Co2 (20°C)
) We chose 2 atm as the hydrogen applied pressure above 0.5 atm. 0 Only LaNi3Co2 with low hydrogen equilibrium pressure was hydrogenated, and MI with high hydrogen equilibrium pressure! IN 12.5CO2,s
was activated. Here, activation means that hydrogen is adsorbed only on one unoccluded surface, or a part of the surface is reduced to create an active state.

This mixed powder is mixed with an aqueous dispersion of fluororesin as a binder at a solid content of approximately 5% by weight to form a paste, which is then filled into a 1-nickel foam porous material under pressure and dried under reduced pressure at room temperature to form an electrode. And so. The size of this electrode is 40 x 50 ms
, the thickness is 1.5 mm, and the filling amount of the alloy mixed powder is about 6?
It is. An alkaline storage battery was assembled using this electrode as a negative electrode and a known nickel oxide electrode as a positive electrode, and the charge/discharge performance and cycle life were measured.

As a comparative example, electrode iA was produced by using only LaNi3Co2 as an alloy and completely hydrogenating it, and the hydrogenated alloy powder and MmNi2.5CO2,5 alloy powder i50 were prepared.
An electrode using the mixture at a weight ratio of :50 is designated as B, and an electrode according to the present invention is designated as C.

The charging/discharging current was 2 oomA, and the following table shows a comparison of the initial capacity and the capacity after 100 cycles.

As shown in the table, A has an excellent initial capacity, but 100
The capacity of the first cycle has decreased significantly.

On the other hand, B has a low initial capacity, but the capacity at the 100th cycle is about twice as good as that of A. However, it is still insufficient for practical use. In the electrode C according to the present invention, the initial capacity is improved in the B direction, and the capacity at the 100th cycle is also improved. By simultaneously hydrogenating and activating a mixture of alloys with different hydrogen equilibrium pressures, it is possible to simplify the production process and improve electrode performance.

In the example, alloy 40 with high hydrogen equilibrium pressure was mixed with alloy 60 with low hydrogen equilibrium pressure, but the optimal range for the proportion of alloy with low hydrogen equilibrium pressure is 40 to 80% by weight, If it is less than 80% by weight, the effect of the hydrogenated alloy will be small and the discharge capacity will be reduced, and if it is more than 80% by weight, the cycle life will be significantly shortened. Furthermore, for production purposes, it is desirable to include a hydrogen storage alloy whose hydrogen equilibrium dissociation pressure at room temperature is 1 atm or less, and it is particularly suitable that the hydrogen equilibrium dissociation pressure of an alloy with a low hydrogen equilibrium pressure is 1 atm or less as in the example.

On the other hand, it is preferable that hydrogen is not dissociated as much as possible compared to a hydrogenated alloy, but even if hydrogen is partially removed from a friend alloy by hydrogenation, it is still better than the conventional method. In any case, after hydrogenation, 1
The effect of the present invention lies in the fact that hydrogen is occluded more than once.

The hydrogen storage alloy is not limited to those mentioned above, and other alloys may be used. Although a fluororesin is used as the binder, heat-welding type binders such as polyethylene and solution type binders such as methyl cellulose and polyvinyl alcohol can also be used.

Effects of the Invention As described above, according to the present invention, the manufacturing process of a hydrogen storage electrode can be simplified, the manufacturing cost can be reduced, and the electrode performance can be improved.
It becomes possible to manufacture high-performance alkaline storage batteries.

Claims (3)

[Claims] (1) Two or more types of hydrogen storage alloy powders with different hydrogen equilibrium pressures are placed in a closed container, and the hydrogen storage alloy with the high hydrogen equilibrium pressure absorbs hydrogen at a hydrogen storage pressure higher than the hydrogen storage pressure of the hydrogen storage alloy with the lower hydrogen equilibrium pressure. After hydrogenation and activation treatment in a hydrogen atmosphere within a range of pressure or less, an alkali-resistant polymer binder is added, and the product is press-molded to be integrally bonded to the current collector. Method for manufacturing hydrogen storage electrodes. (2) The method for producing a hydrogen storage electrode according to claim 1, wherein the proportion of the alloy having a low hydrogen equilibrium pressure in the mixture of hydrogen storage alloy powder is 40 to 80% by weight. (3) The method for manufacturing a hydrogen storage electrode according to claim 1, wherein the mixture of hydrogen storage alloy powders contains a hydrogen storage alloy with a hydrogen equilibrium pressure of 1 atm or less at room temperature.