JPS59132563A - Manufacture of nickel electrode for battery - Google Patents

Abstract

PURPOSE:To improve the utilization factor and the life of a nickel electrode by forming the nickel electrode while impregnating a porous electrode having nickel hydroxide as an active material with a weak acid salt solution of cobalt followed by heat resolution of its salt. CONSTITUTION:Nickel hydroxide, carbonyl nickel powder, graphite, fiber and carbonyl metal cobalt powder are mixed while adding a carboxymethylcellulose solution for forming paste to be applied to a punching metal for an electrode core material followed by dipping into the solution consisting of cobalt acetate, water and acetic acid while being heated in the air and then dipped into the running water for forming a paste type nickel electrode. Accordingly, the utilization factor and a life can be improved by simple operation while using cobalt having little corrosive action against the electrode and weak acid acetic cobalt having a big dissolution power and performing heat resolution of said salt.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing nickel electrodes used in nickel-cadmium storage batteries, nickel-iron storage batteries, nickel-hydrogen batteries, and the like.

Conventional structure and its problems The structure of this type of nickel electrode using water silacel as an active material used to be the pocket type, but recently the sintered type has been the mainstream. The pocket type, as is well known, is a steel container with many holes that is mechanically filled with nickel hydroxide along with a conductive material such as graphite.

Therefore, although the electrode has a robust appearance, since the active material exists only in contact with the conductive material and the container, polarization during large current discharge is large and the utilization rate is low. There are problems such as shortening the lifespan under harsh conditions such as rapid charging.

On the other hand, in the sintering method, the active material is firmly attached and embedded in the sintered body with micropores.
There are fewer problems than with the pocket type, and major improvements have been made in terms of large current discharge characteristics, rapid charging characteristics, and lifespan.

However, both the production of the sintered body and the filling of the active material are complicated, and there is a problem that the cost is considerably higher than that of the pocket type. Instead of the sintering method, a method has been developed in which a foamed metal with a large pore size and porosity is used as an active material support, and a paste-like active material, that is, nickel hydroxide, is directly filled into the foamed metal. Efforts are being made to simplify the process.

An even simpler method is the so-called paste method, in which a two-dimensional porous material such as a net, perforated plate, or expanded metal is used as the core material, and an active material and a binder are mixed with this material to form a paste. The coated material is applied, smoothed by passing it through slits or between rollers, and after drying, pressure is applied as necessary. This method is ideal as a manufacturing method because the core material is extremely inexpensive and filling with the active material is easy, and many proposals have been made. Paste-type electrodes have a long history, and although the manufacturing method is slightly different, paste-type lead electrode plates are extremely widely used. 1. Cadmium poles have also been put into practical use.

The following are the reasons why nickel electrodes have not been put into practical use despite many proposals.

(1) Nickel, that is, neither nickel oxyhydroxide as an active material during charging nor nickel hydroxide during discharging is an excellent conductor. Therefore, it is necessary to separately add a conductive material, and even if it is added, it is difficult to improve the utilization rate. Moreover, if too much is added, the absolute capacity will become small.

(Kon) Although the volume of the active material naturally changes due to repeated charging and discharging, nickel electrodes undergo severe swelling.

The above-mentioned factors are mainly preventing the widespread practical use of paste-type nickel electrodes.

In other words, as a method to first increase the strength (see below) and prevent the swelling and accompanying falling off of the active material, various binders have been considered, but in order to improve the strength, If a large amount of binder is added, the voltage characteristics will deteriorate and the utilization rate will decrease.In order to suppress this, nickel powder or graphite was added, or if a large amount is added, the proportion of active material decreases. However, if there were too few, there was a problem in that the utilization rate was low.

The addition of binders and other electrolyte-resistant fibers can improve the properties and lifespan of pasted or pressurized nickel electrodes, so-called non-sintered nickel electrodes, to some extent; It has not been widely used in practical use because it is far inferior to the conventional method.

As mentioned above, non-sintered nickel electrodes obtained by directly filling a support with nickel hydroxide, such as the Boke-Nt type 2 foam metal type, paste type, and pressurized type, are
Since strength and conductivity are contradictory factors, it is difficult to obtain high performance. Therefore, in order to improve the utilization rate, the addition of cobalt t or a cobalt compound is attracting attention. Generally, the addition method is to add metal cobalt hydroxide or oxide to the active material mixture, or to impregnate the active material with a cobalt salt solution and then immerse it in an alkaline solution. Another method is to convert the cobalt salt to cobalt hydroxide.

However, even with these methods, the utilization rate is not sufficiently improved. The latter method also has the disadvantage that washing with water to remove alkali requires a long period of time.

Purpose of the Invention In view of the above, the present invention aims to particularly improve the utilization rate of non-sintered nickel electrodes by adding a cobalt compound, and furthermore provides a method that does not cause electrode corrosion and is easy to wash with water. The purpose is to

Structure of the Invention The present invention is characterized in that a porous electrode containing nickel hydroxide as an active material is impregnated with a solution of a weak cobalt salt, and then the salt is thermally decomposed.

The method of the present invention does not use the generally used cobalt salts of strong acids such as nitric acid, sulfuric acid, and hydrochloric acid, but instead uses weak acid salts, so there is less risk of corrosion of the electrode during subsequent thermal decomposition, and it also reduces the risk of corrosion of the electrode during subsequent thermal decomposition. Since it is thermally decomposed without any residual acid, there is no need for a long water washing process to remove the alkali.In other words, even if water is washed after thermal decomposition, the time required is extremely long as the purpose is to remove the remaining weak acid. For example, it takes several hours to remove alkali using running water at room temperature.
In the case of the present invention, 10 to 20 minutes is sufficient.

Description of examples An example applied to a paste-type nickel electrode will be described.

One part nickel hydroxide with a particle size that can pass through a 200-millimeter sieve, 509 g of carbonyl nickel powder, 80 g of graphite, 100 g of diameter. lWm1. 20 g of acrylonitrile-vinyl chloride copolymer fibers having a length of 3 to 5 mm and 309 carbonyl metal cobalt powders were mixed, and 1 ky of a 3-weight polyhydric solution of carboquine methyl cellulose was added thereto to form a paste.

On the other hand, as the core material of the electrode, a punched metal plate with a hole diameter of 2mm and a center-to-center distance of 3mm in a 0.1-thick iron plate was used. The above paste was applied to both sides of this core material, passed through a slit, and the thickness after drying was set to 1.0±0.06. Then, 400 g of cobalt acetate was dissolved in 11 water, and 5 g of cobalt acetate was dissolved in this water.
Soaked in a solution of acetic acid and dried at 170°C for 2 hours.
Heated in air for 0 minutes. The nickel electrode obtained in this manner is designated as A, and the electrode that was immersed in running water at room temperature for 15 minutes is designated as B.

As a comparative example, the amount of carbonyl cobalt in the paste was 50 g, and the electrode without impregnation with cobalt acetate and subsequent treatment was 01. An electrode with cobalt oxide 709 instead of carbonyl cobalt in the paste was used as D. do. In addition, an electrode E is obtained by using a cobalt nitrate solution having a cobalt ion concentration or the same concentration as above, instead of the cobalt acetate, and subjecting it to the same impregnation and thermal decomposition and water washing treatments as B.

These plates are 120tmn in width and 63C in length.
It is then cut into pieces, then passed between rollers and pressurized to form an aqueous dispersion of polytetrafluoroethylene (resin content: 5% by weight).
was added and then dried. The thickness of the electrode was 0.7 mm.

This electrode had a width of 38 Tnm and a length of 220 mm.

A AA-sized sealed nickel-cadmium storage battery was used as a battery for comparing the characteristics.

The cadmium negative electrode manufactured as follows was used. 1. Apply a paste mainly composed of cadmium oxide to both sides of a nickel-plated iron punching metal, pass it through a slit set to a predetermined thickness, and go through a drying process to form a cylinder with a thickness of 0.7 mm. The electrode plate was obtained. Thereafter, a part of the cadmium oxide was changed into metal cadmium by partial charging in a 10% by weight aqueous solution of caustic potassium, and then washed with water.
After drying, it was pressurized to a thickness of 56 nm.

A polyamide non-woven fabric was used as the separator, and as the electrolytic solution, a small amount of lithium hydroxide was dissolved in a 25% by weight aqueous solution of caustic potash, and 6.5 CC was used per cell.

The charging capacity of these batteries, the utilization rate at each discharge, and the cycle life when the battery is discharged under the conditions of 0.15C for charging and 0.4C for discharge, and the life when the battery decreases to 60 times the initial capacity are as follows. Shown in the table.

As is clear from this table, battery A using the nickel electrode of the present invention has excellent utilization rate and life, and it can be seen that battery B, which includes a water treatment process, is further improved. In contrast, in /ζE using cobalt nitrate, the electrode is corroded during heating, resulting in a decrease in strength and a slightly shorter lifespan. In addition, with this level of treatment, the nitrate roots are not completely removed, so the utilization rate is also somewhat inferior.

As mentioned above, the salts of cobalt and weak acids that have little corrosive effect on electrodes, and the examples used, are inexpensive and have relatively high solubility.
Cobalt acetate, which is relatively easily decomposed, was used, but by adding this salt and thermally decomposing it, it is possible to provide nickel orange with extremely improved utilization and a long lifespan. In addition to cobalt acetate, phosphoric acid,
Salts of cobalt with arsenic acid, citric acid, oxalic acid, thiocyanic acid, phosphoric acid, etc. are used.

Note that salts of weak acids and cobalt generally have low solubility in water, so it is advisable to add metallic cobalt or a cobalt compound, especially an oxide, to the active material mixture in advance, as in the example.

Impregnate porous electrodeposit with cobalt weak acid salt solution and heat for 1 minute.
By doing so, it also serves to bind the cobalt compound (probably an oxide) or the active material, so nickel hydroxide as the active material can be directly bonded as in the paste type, pressurized type, foam metal type, and pocket type. It is suitable for filled nickel electrodes, which have relatively low strength.However, sintered type is also effective in improving the utilization rate.

Effects of the Invention As described above, according to the present invention, a nickel electrode with improved utilization rate and lifetime can be obtained with simple operation.

Claims (1)

[Claims] (1) A method for producing a nickel electrode for a battery, which comprises impregnating a porous electrode containing nickel hydroxide as an active material with a solution of a weak cobalt salt, and then thermally decomposing the salt. (A method for producing a nickel electrode for a battery according to claim 1, wherein the porous electrode holds metal cobalt, cobalt oxide 4, or cobalt hydroxide together with nickel hydroxide. Cobalt, cobalt citrate. Cobalt oxalate, cobalt formate' + cobalt IJ phosphate, cobalt arsenate, and cobalt thiocyanate. Manufacture of a nickel electrode for a battery according to claim 1. Law.