JPH0320966A - Manufacture of hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To simply, safely pulverize a hydrogen storage alloy and to prevent an electrode from oxidation by pulverizing the alloy in water and holding it in a conductive support. CONSTITUTION:A negative electrode of a metal hydrogen alkaline storage battery is formed by pulverizing a hydrogen storage alloy with its surface covered with water and holding it in a conductive support. By pulverizing in water, fine particles are simply and safely obtained without use of a ball mill in an inert atmosphere which is necessary for avoiding use of dangerous hydrogen. Since tine particles are held in the support before drying without exposing in the air, oxidation is prevented and good negative electrode is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is a hydrogen absorbing material which is used as a negative electrode of an alkaline storage battery and can store and release hydrogen in a reverse manner.
The present invention relates to a method for manufacturing an electrode.

(Expression) Jubei's technology Storage batteries commonly used since Jubei include nickel-cadmium storage batteries and lead-acid batteries.
In recent years, metal-hydrogen alkaline storage batteries, which have a hydrogen storage electrode made of a hydrogen storage alloy on the negative electrode, have been the focus of attention because they are lighter, have higher capacity, and have the potential to have higher energy density than these batteries. There is.

Hydrogen storage alloys used in the negative electrode of this type of battery include:
LaNi. and its improvement LaNitCo. LaN
Alloys such as i, Cu, and LaN i+ aFeot are known, and are generally produced by the following method. In other words, hydrogen is obtained by weighing and mixing metals as raw materials used in hydrogen storage alloys to a certain Mi ratio, placing them in an arc melting furnace, subjecting them to arc discharge in a reduced pressure argon atmosphere, and heating and melting them. After coarsely pulverizing an ingot of storage alloy, it is made into fine powder using a ball mill or the like. Then, the hydrogen storage alloy thus produced is formed into an electrode by forming it into a slurry using a binder or the like, and spreading or filling the slurry onto a conductive support.

By the way, in this type of hydrogen storage TTFI, the hydrogen storage alloy becomes atomized by repeating charging and discharging cycles. t
A phenomenon occurs in which it falls off from ffL and the cycle life is shortened. Therefore, in order to prevent further pulverization as the charge/discharge cycle progresses, and to increase the surface area of the hydrogen storage alloy to improve reactivity,
Consideration has been given to pulverizing the hydrogen storage alloy in advance before holding it on a conductive support.

As a method of pulverizing this hydrogen storage combination,
As shown in Japanese Patent Application No. 0-40668, there is a method of atomizing hydrogen-absorbing alloy powder by forcibly absorbing and releasing hydrogen in a container, and as shown in Japanese Patent Application Laid-Open No. 154562-1982. Another method involves pulverizing a hydrogen storage alloy in air using a pole mill.

However, the former method is not preferred because it is difficult to crush a large amount of alloy at once, requires complicated and expensive production equipment, and is dangerous because it uses hydrogen gas. Even in the latter method, there is a problem that if atomization is carried out in air, the hydrogen +1 & chloride alloy is active and therefore easily reacts with oxygen, causing ignition. For this reason, when mechanically grinding with a ball mill or the like, oxidation of the hydrogen storage alloy is prevented by doing it in an inert atmosphere, but in this case, there are various restrictions such as the need for larger equipment. Therefore, it cannot be said that it is preferable in terms of the electrode manufacturing process.

(c) Problems to be Solved by the Invention The present invention provides a hydrogen storage system that can safely and easily atomize a hydrogen storage alloy and suppress oxidation of the surface of the hydrogen storage alloy throughout the electrode manufacturing process. The present invention attempts to provide a method for manufacturing an electrode.

(2) Means for Solving the Problems The method for manufacturing a hydrogen-absorbing Ht electrode of the present invention involves crushing the hydrogen-absorbing alloy with its surface covered with water and applying it to a conductive support without drying it. It is characterized by being held.

(E) Function By pulverizing the water X storage alloy, the newly exposed alloy surface is extremely active and easily oxidized by oxygen. For this reason, if pulverization is carried out in air, such as during pulverization, in which many active alloy surfaces are exposed, ignition may occur.

On the other hand, when a hydrogen storage alloy is crushed with its surface covered with water, ignition does not occur and the alloy is less likely to come into contact with oxygen than when it is in the air.
Oxidation of the alloy can be suppressed, and active alloy surfaces can be prevented from being covered with an inert oxide film. Moreover, since the powder is simply ground in water, there is no need to use a complicated and large-sized device, and the powder can be easily ground with a simple device.

After pulverizing, the hydrogen 11 & storage alloy is held on a conductive support such as punched metal or foamed nickel without drying, so it is constantly wet with water during the production of the t-electrode. Therefore, the hydrogen storage alloy can maintain a state in which it is difficult to come into contact with oxygen, as in the case of the above-mentioned pulverization, and oxidation of the alloy can be suppressed. Further, oxidation of hydrogen storage alloys tends to proceed when there is an interface of three phases of water, oxygen, and alloy, and if a rise in temperature is added to this, it can be said that the state becomes particularly easy to oxidize. In other words, when the alloy is dried from a wet state, it is most likely to be oxidized.

In the present invention, the hydrogen storage alloy is not dried before the slurry is prepared after pulverization, and it is only necessary to dry the alloy once after holding it on a conductive support, so that inactivation due to oxidation of the hydrogen storage alloy is suppressed as much as possible. Is possible.

(f) Examples In the following, a comparison between the present invention and comparative examples will be described in detail.

[Example] Weighed commercially available misch metal (Mm), nickel, cobalt, and aluminum raw materials to a certain composition ratio,
MmN i ICO+ using an argon arc melting furnace,
5Aj! +3+ alloy was produced. This alloy sample and 40 mR of water per 100 g of the alloy were placed in a ball mill consisting of an alumina pot and balls and ball milled for 5 hours, and then dehydrated so that 100 g of the alloy contained 10 ml of water. In this state, the alloy surface is covered with water. Next, an aqueous solution of polyethylene oxide was added and mixed so that 1 g of polyethylene oxide was added to 100 g of the alloy to prepare a slurry. The slurry is applied to the surface of the support by passing through and pulling up the conductive support made of punched metal coated with nickel into the lip holding the slurry, and drying and pressurizing the slurry to form an electrode of the present invention. I got it.

This electrode is used as the negative electrode, and a well-known sintered nickel electrode used in nickel-cadmium batteries is used as the positive electrode, and by rotating it with an alkali-resistant separator between the positive and negative electrodes, the spiral electrode After obtaining the electrode body and inserting the electrode body into a battery can, an alkaline electrolyte was applied and the cap was sealed to assemble a battery with a nominal capacity of 1200+nAH.

The battery thus produced is designated as A.

[Comparative Example 1] In the above example, the alloy was ground and dried, and then the dried alloy was used to prepare a similar slurry, and a battery was prepared under the same conditions except for the battery B, which was designated as Battery B.

[Comparative Example 2] In the above example, the alloy was pulverized in a dry state without adding water in a nitrogen atmosphere, and then a similar slurry was prepared using this alloy, and a battery was then manufactured under exactly the same conditions. This is called battery C.

Each of the batteries thus prepared was charged with a current of 360 mA for 4 hours, and then discharged with a current of 360 mA, so that the battery voltage was i. FIG. 1 shows the change in discharge capacity when charging and discharging were repeated under cycle conditions in which the discharge was stopped when the battery reached ov. In the figure, the symbols A to C correspond to the batteries used.

As is clear from FIG. 1, the discharge capacity of each battery increases as the cycle progresses, but in particular, battery A using the hydrogen storage electrode of the present invention shows a small decrease in discharge capacity at the beginning of the cycle. It can also be seen that the number of cycles required for the discharge capacity to reach its maximum value is short. This is because the oxidation of the alloy in the hydrogen storage electrode in battery A is suppressed compared to batteries B and C, and the active part of the alloy that was covered with an oxide film at the beginning of the cycle changes as the cycle progresses. This is thought to be due to the fact that it becomes exposed relatively quickly.

Next, each of the batteries A to C was charged with a current of 360 mA for 4 hours, and then discharged with a current of 1200 mA, and a discharge characteristic diagram at this time is shown in FIG. In addition, each of the spiral electrode bodies used in Batteries A to C above was used, and these electrode bodies and the mercury reference electrode were immersed in an excessive amount of electrolyte to perform discharge, and the hydrogen storage electrode of the negative electrode and the reference electrode were The potential difference between them was measured and the discharge characteristics of the negative electrode were investigated. The results are shown in FIG. From the results shown in FIGS. 2 and 3, battery A using the electrode of the present invention
i! It can be seen that the battery voltage is higher than batteries B and C, and the negative electrode performance is also superior in terms of discharge capacity and potential.

(g) Effect of invention 4-. The invention involves pulverizing a hydrogen storage alloy in water,
During pulverization, the formation of an oxide film on the alloy surface can be suppressed, and there is no risk of ignition, and it can be easily pulverized using a safe and simple device. In addition, since the crushed alloy is held on a conductive support without drying, the alloy is always kept wet with water and difficult to come into contact with oxygen, which suppresses oxidation of the alloy surface. I can do it.

[Brief explanation of drawings]

Figure 1 is a cycle characteristic diagram, Figure 2 is a battery discharge characteristic diagram,
FIG. 3 is a diagram showing the discharge characteristics of the negative electrode. A: Invention battery, B, C: Comparative battery.

Claims (1)

[Claims] (1) A method for producing a hydrogen storage electrode, which comprises pulverizing the hydrogen storage alloy while its surface is covered with water, and holding the alloy on a conductive support without drying it.