JPH04121960A - Manufacture of metal hydride electrode - Google Patents

Abstract

PURPOSE:To make the pulverization of hydrogen storage alloy safe and and simple and restrain the oxidization of the alloy surface at the process of electrode manufacturing, by bringing the hydrogen storage alloy into contact with an acid solution, and then, bringing the alloy into contact with an alkaline solution at the time of pulverization or after pulverization. CONSTITUTION:Hydrogen storage alloy powder is immersed in water regulated to pH 5 by bubbling carbonic acid gas beforehand, and then, the alloy and solution are put in a ball mill, and ball mill pulverization is conducted, and in addition, the solution is added with an 0.1 M potassium hydroxide solution, and regulated to pH 9. After the water washing of the alloy powder, a slurry is obtained by regulating 20 wt parts of water and 1 wt part of polyethylene oxide to 100 wt parts of the alloy powder, and after painting on the surface of a conductive support body consisting of a punching metal, a metal hydride electrode is obtained by conducting drying and pressurization.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for manufacturing a hydrogen storage alloy electrode for an alkaline storage battery using a hydrogen storage alloy capable of absorbing and releasing hydrogen as a negative electrode material. It is.

(b) Conventional technology Storage batteries that have been commonly used include nickel-cadmium storage batteries and lead-acid batteries.
In recent years, nickel-hydrogen alkaline storage batteries have attracted attention because they are lighter, have higher capacity, and may have higher energy density than these batteries, and are equipped with a hydrogen-absorbing alloy electrode that uses a hydrogen-absorbing alloy as a negative electrode material.

The hydrogen storage alloy electrode used as the negative electrode of this alkaline storage battery is generally made by kneading a binder such as polytetrafluoroethylene or polyethylene oxide with hydrogen storage alloy powder, as shown in JP-A No. 61-66366. It is manufactured by preparing a paste, applying the paste to both sides of a core such as punched metal or expanded metal, and drying it. The hydrogen-absorbing alloy electrode produced in this way is usually placed in a battery case while being carried around in a spiral shape with a separator interposed between it and the sintered nickel positive electrode used in nickel-cadmium storage batteries. is housed in the battery to form a battery.

In this way, when a hydrogen storage alloy electrode mainly composed of hydrogen storage alloy powder and a binder is used as a negative electrode, the performance of the negative electrode is greatly influenced by the performance of the hydrogen storage alloy powder. Taking this point into consideration, Japanese Patent Application Laid-Open No. 154562/1983 proposes that the particle size of the hydrogen storage alloy is regulated to 20 to 149 μm to form an electrode, resulting in a long cycle life and high performance due to repeated charging and discharging. This makes it possible to provide batteries with

On the other hand, as a method for pulverizing this alloy,
As shown in Japanese Patent Publication No. 40668, there is a method of pulverizing hydrogen-absorbing alloy powder by forcibly absorbing and releasing hydrogen in a closed container, and as shown in Japanese Patent Application Laid-Open No. 154562-1982, Among them, there is a method of grinding a hydrogen storage alloy with a ball mill.

However, the former method is not preferred because it is difficult to crush a large amount of alloy at one time, requires complicated and expensive production equipment, and is dangerous because hydrogen gas is used. Even in the latter method, when pulverization is performed in air, the hydrogen storage alloy is active and is oxidized by oxygen in the air, resulting in a problem that the reactivity of charging and discharging (hydrogen storage and release) decreases. Furthermore, there is a method of suppressing the oxidation of the alloy by performing the above-mentioned crushing under an inert atmosphere, but in this case too, the oxides existing on the alloy surface before crushing remain as they are, and the oxides newly generated during the crushing. There was a problem that the active surface was oxidized when the alloy was taken out into the air, resulting in a decrease in the charging and discharging reactivity of the alloy.

(c) Problems to be Solved by the Invention The present invention solves the above-mentioned problems, and allows the hydrogen storage alloy to be pulverized safely and easily, and also prevents the oxidation of the surface of the hydrogen storage alloy in the electrode manufacturing process. The purpose is to provide a method for manufacturing a hydrogen storage alloy tL electrode that can suppress the amount of hydrogen absorbed.

A method for manufacturing a hydrogen storage alloy electrode of the present invention is a method for manufacturing an electrode by crushing a hydrogen storage alloy to a predetermined particle size.
After the alloy is brought into contact with an acidic aqueous solution, the alloy is brought into contact with an alkaline aqueous solution during or after the pulverization.

(E) Effects Hydrogen storage alloys before pulverization generally have oxides formed on their surfaces, and the alloy surface newly exposed by pulverization is extremely active and easily oxidized by oxygen. Therefore, even if pulverization is carried out under an inert atmosphere, when the alloy is taken out into the air, the surface of the alloy is oxidized and the reactivity of the alloy is reduced to low F.

On the other hand, when the alloy is brought into contact with an acidic aqueous solution by immersion or the like, the oxides present on the alloy surface are dissolved in the acidic aqueous solution and an active surface appears on the surface of the alloy. Furthermore, when the aqueous solution is made alkaline after being immersed in an acidic aqueous solution, the metal ions dissolved in the aqueous solution precipitate as hydroxides on the surface of the alloy to form a stable film.

As a result of a detailed study of this hydroxide film, it was found that unlike oxidation by oxygen in the air, it does not cause a decrease in charge/discharge reactivity.

Furthermore, even if this alloy is taken out into the air, the active surface of the alloy is covered with a film of the aquatic product, so the active surface is not exposed to the air, and this prevents it from being oxidized by oxygen in the air. This makes it difficult for the battery to receive the charge and discharge, and it is possible to suppress the low reactivity of charging and discharging.

In addition, the formation of a hydroxide film must be applied to the surface of the pulverized alloy in order to obtain a sufficient effect, so the contact between the alloy and the alkaline aqueous solution should be made at least once during or after pulverizing the alloy. There is a need to do. On the other hand, the alloy may be brought into contact with the acidic aqueous solution at any time before the alloy comes into contact with the alkaline aqueous solution.

(f) Examples Examples of the present invention will be shown below, and comparisons with comparative examples will be mentioned.

(Example 1) Commercially available Mitshumetal (Mm, a mixture of rare earth elements) as a raw material metal for a hydrogen storage alloy, nickel, cobalt, aluminum, and manganese were mixed in an elemental ratio of 1. O: 3.2
:1. After weighing at O: 0, 2: 0, 6, it is melted and cast in a high frequency induction furnace. This results in MmN i 3.
*An alloy with the composition CoA lo, tMno, s is obtained. Furthermore, this alloy was coarsely pulverized in a nitrogen atmosphere.
A powder with a size of 0 or less is obtained.

Next, this powder is adjusted to pH by bubbling carbon dioxide gas in advance.
After immersing the alloy in water adjusted to 5, the alloy and aqueous solution were placed in a ball mill consisting of an alumina pot and balls, and ball milled for 5 hours.
, 1M potassium hydroxide aqueous solution was added to reduce p I-1 to 9
Adjust to.

After washing the alloy powder with water, prepare a slurry by adjusting 100 parts by weight of the alloy powder to 20 parts by weight of water and 1 part by weight of polyethylene oxide, and apply it on the surface of a conductive support made of punched metal. After drying and pressurizing, the hydrogen storage alloy electrode a of the present invention was obtained.

Next, this electrode was used as a negative electrode, a sintered nickel electrode was used as a positive electrode, and a vortex electrode body was obtained by rotating the electrode with a separator made of nonwoven fabric interposed between the positive and negative electrodes. Then, insert this spiral electrode body into the battery outer can: 30
After injecting an aqueous solution of potassium hydroxide with a concentration of 10% as an electrolyte, the battery was sealed to assemble a sealed nickel-metal hydride battery A of the present invention having a nominal capacity of tloooomAh.

(Example 2) In Example 1, the alloy was immersed and ground in a ball mill in an aqueous solution adjusted to pH 3, pH 4, and pH 6 in advance, and then hydroxide J ram was added to this aqueous solution to adjust the pH to 9. The hydrogen storage alloys of the present invention, c and d, were produced under the same conditions except for the above, and the sealed nickel-metal hydride batteries B, C and D of the present invention were assembled in the same manner.

(Example 3) In Example 1, the alloy was immersed and ball milled in an aqueous solution whose pH was adjusted to 5 in advance, and then water;
Hydrogen storage alloy electrodes e, f, and g of the present invention were produced under exactly the same conditions except that the pH of the solution was adjusted to 8.10 and 11, and sealed nickel-hydrogen batteries E, F of the present invention were produced in the same manner. and G were assembled.

(Example 4) After immersing the alloy in the aqueous solution adjusted to pH 5 in Example 1, potassium hydroxide was added to this aqueous solution and p
Hydrogen storage alloy electrodes H and I of the present invention were produced under exactly the same conditions except that ball milling was carried out with H adjusted to 9 and 10, and sealed nickel-hydrogen batteries H and I of the present invention were produced in the same manner. assembled.

(Comparative Example 1) In Example 1, ball mill pulverization is performed in a nitrogen atmosphere without adding water, and after pulverization, this powder is taken out into the air, and polyethylene oxide and water as a dividing medium are added to prepare a slurry. A comparative hydrogen-absorbing alloy electrode tfij was produced under the same conditions except for that, and a comparative sealed nickel-metal hydride battery J was assembled.

(Comparative Example 2) A comparative example was prepared under exactly the same conditions as in Example 1, except that the alloy was immersed and ball milled in neutral water with a pH of 7, and then polyethylene oxide was added to the powder to prepare a slurry. A hydrogen storage alloy electrode K was fabricated, and a comparative sealed nickel-hydrogen battery K was assembled.

(Comparative Example 3) In Example 1, the alloy was immersed and ball milled in neutral water with a pH of 7, and then potassium hydroxide was added to this aqueous solution to adjust p)I to 9. A comparative hydrogen storage alloy t&+1 was produced under the same conditions, and a comparative sealed nickel-metal hydride battery was assembled.

A charge/discharge test was conducted on the hydrogen storage alloy electrode of the present invention and the comparative hydrogen storage alloy electrode in a 5 atm pressurized container filled with 30% KOH. The charging/discharging conditions at that time were to charge at a current value of 50 mA/g for 8 hours, then discharge at a current value of 50 mA/g, and the electrode potential reached 10
, 7 V v s Hg/Hg O, the discharge is stopped.

The results are shown in Table 1.

As is clear from Table 1 in Table 1 below, the discharge capacities of the hydrogen storage alloy electrodes a to l of the present invention are the same as those of the comparative hydrogen storage alloy t%NJ,
It can be seen that it is higher than k and l.

That is, in the electrode of the present invention, since the alloy is immersed in an acidic aqueous solution during or after pulverization, the oxides existing on the alloy surface even before pulverization are dissolved to form an active surface. By dissolving this oxide, the active surface that is the production opening and the active surface that is generated during pulverization are coated with a hydroxide film in the alkali J aqueous solution, which suppresses oxidation by oxygen and reduces reactivity during charging and discharging. This is because it is suppressed.

On the other hand, in comparison electrode J, the active surface on the surface of the alloy produced during pulverization is oxidized by oxygen in the air when the alloy is taken out, so it is thought that the reactivity during charging and discharging is reduced.

In addition, in the comparison electrode, the active surface generated by pulverization was exposed to the air during drying during the manufacture of the single electrode, and was oxidized by oxygen in the air, resulting in a decrease in charge/discharge reactivity.

On the other hand, in comparison electrode 1, the active surface generated during alloy pulverization is covered with a hydroxide film, and even if the alloy is exposed to air for drying, the active surface will not be oxidized. It is thought that the presence of oxides on the alloy surface caused a decrease in the charging and discharging reactivity of the alloy.

Next, after charging the sealed two-layer hydrogen batteries A to Comparative of the present invention and comparison with a current of 100 mA for 16 hours,
Discharge with a current of 200mA, and the battery voltage will be 1. A charge/discharge cycle test was conducted under cycle conditions in which discharging was stopped when OV was reached, and the cycle life was measured. In this cycle test, the cycle life was defined as the time when the capacity became 50% or less of the initial capacity.

In addition, after using the same battery and carrying out 5 cycles of charging and discharging, an opening was provided at the bottom of the battery outer can, and a pressure sensor for measuring the internal pressure was attached to this opening. This battery was charged with a current of 10,100 O, and after the battery voltage reached a peak value, charging was stopped when the battery voltage decreased by 10 mV from this peak value, and the internal battery pressure during this period was measured.

The results are shown in Table 2. However, the battery internal pressure is shown as the maximum value during the charging.

As shown in Table 2, it can be seen that the batteries A to I of the present invention have a long cycle life and a small increase in battery internal pressure. On the other hand, it can be seen that comparative batteries J, K, and L have a short cycle life and a large increase in battery internal pressure.

That is, in the battery of the present invention, the oxide present on the alloy surface is removed from the alloy in the hydrogen p and fL electrode of the negative electrode before it is crushed, and an active surface is formed, and this active surface is covered with a hydroxide film. It is believed that this coating suppresses the oxidation of the alloy due to oxygen, prevents a decrease in the reactivity of the negative electrode during charging and discharging, suppresses the rise in internal pressure of the battery, and maintains the battery capacity for a longer period of time. It will be done.

On the other hand, in the comparative battery, oxides are formed on the alloy surface and the reactivity of the negative electrode during charging and discharging is reduced, resulting in hydrogen generation during charging and an increase in the internal pressure of the battery.

Furthermore, as the cycle progresses, the internal pressure of the battery increases and the safety valve operates to release the gas inside the battery.Also, when this gas is released, the electrolyte is simultaneously released to the outside of the battery, reducing the amount of electrolyte inside the battery. It is thought that the cycle life was shortened due to a shortage.

Note that when the hydrogen storage alloy of the above embodiment is immersed in an acidic aqueous solution and metal ions are dissolved, the pH of the aqueous solution shifts to the alkaline side. Therefore, by adjusting the amount and pH of the acidic aqueous solution in which the hydrogen storage alloy is immersed, it is possible to make the pH of the aqueous solution alkaline without separately adding alkali, which is more effective.

(g) Effects of the Invention The method for producing an electrode using a hydrogen storage alloy of the present invention involves contacting the hydrogen storage alloy with an acidic aqueous solution and then contacting the alloy with an alkaline aqueous solution during or after pulverization. Since the surface of the alloy can be activated and oxidation of the surface can be suppressed, the reactivity of charging and discharging the electrode can be maintained at a high level. In addition, a battery using the electrode of the present invention as a negative electrode can suppress pressure increase within the battery, and can maintain battery capacity for a longer period of time.

Claims (1)

[Claims] (1) In a method of manufacturing an electrode by pulverizing a hydrogen storage alloy to a predetermined particle size, the alloy is brought into contact with an acidic aqueous solution, and then the alloy is brought into contact with an alkaline aqueous solution during or after the pulverization. A method for producing a hydrogen storage alloy characterized by: