JPS5937659A - Manufacturing method for nickel electrode - Google Patents

Abstract

PURPOSE:To improve the rate of utilization and the reproducibility of an effect of the improvement of life span when such a process is applied, where nickel hydroxide is left alone under the coexistence of water together with nickel and cobalt and obtain an electrode with fixed quality, by using the nickel hydroxide cleaned by neutral or weak alkaline cleaner as the electrode. CONSTITUTION:Nickel hydroxide cleaned by alkaline or neutral cleaner is left alone under the coexistence of nickel, cobalt, and water. The desirable range of the alkaline amount that is made to adhere to nickel hydroxide and is left alone is some 7-8.5 in the pH of water after the amount of water twice as heavy is added to nickel hydroxide and is fully agitated. As a result, nickel hydroxide is cleaned until it becomes neutral or weak alkaline.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a nickel electrode for use in alkaline batteries. This invention relates to a method for manufacturing a nickel electrode to be filled into a sponge-like porous metal body.

Structures of conventional examples and their problems Regarding batteries used as power sources for various portable devices, in-vehicle use, -7- equipment, independent use in remote areas, etc., systems that use alkaline aqueous solutions as electrolytes have a positive electrode.
There are nickel electrodes, silver oxide electrodes, manganese dioxide electrodes, air electrodes, etc., and negative electrodes include cadmium camellia, iron electrodes, hydrogen electrodes, etc. Among positive electrodes, nickel electrodes are the most commonly used because they are particularly stable in alkaline aqueous solutions, have excellent charge/discharge reversibility, can be expected to have a long life, and are also excellent in terms of utilization. ing. In particular, nickel-cadmium batteries have been put into practical use as secondary batteries next to lead batteries, and demand is expected to continue to grow significantly in the future. In addition, nickel-zinc batteries and nickel-iron batteries are being developed especially for use in electric vehicles, and nickel-metal hydride batteries have entered the practical stage for special uses, mainly for space use.

As described above, nickel electrodes are widely used, and the electrode structure used to be a pocket type, but recently the sintered type has become mainstream. As is well known, the pocket type is obtained by mechanically filling a steel container with many holes with nickel hydroxide and a conductive material such as graphite. Therefore, although the electrode has a robust appearance, the active material exists only in contact with the conductive material and the container (pocket), so polarization during large current discharge is large and the utilization rate is low. . In addition, there are problems such as a shortened lifespan under harsh conditions such as rapid charging.

On the other hand, in the sintered type, the active material is firmly attached and embedded in the sintered body with micropores, so there are fewer problems like the pocket type described above, and it is difficult to handle large currents. Significant improvements have been made in terms of discharge characteristics, rapid charging characteristics, and lifespan.

Therefore, it can be said that the sintered type has reached the ideal stage from the viewpoint of characteristics alone. However, the production of sintered bodies,
The process for filling active materials is complicated.
The problem is that it is considerably more expensive than the pocket type. Instead of the sintering method, a method has been developed in which a sponge-like porous metal material with large pore size and porosity is used as an active material support, and a paste-like active material, that is, nickel hydroxide, is directly exposed to light. The filling process has been simplified.

An even simpler method is the so-called paste method, which uses a two-dimensional porous material such as a net, perforated plate, or expanded metal as the core material, and mixes the active material and binder with it to form a paste. Apply a layer of paint, smooth it 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 electrodes have a long history, and the manufacturing method is slightly different, but
Pasted lead plates are widely used. Cadmium electrodes 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) Neither nickel oxyhydroxide during charging nor nickel hydroxide during discharging as a nickel thin active material 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.

(2) Although the volume of the active material naturally changes due to repeated charging and discharging, nickel electrodes undergo severe swelling.The above-mentioned factors mainly prevent the widespread practical use of paste-type nickel electrodes. In other words, various binders have been considered in the past as a method of first increasing the strength and preventing the swelling as described in (2) and the accompanying shedding of the active material.

As a binder, there are groups such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, and fluororesins, which have high insulating properties but are expected to be strong, and polyvinyl alcohol, which has low insulating properties but is not expected to have much strength.

There are groups such as carboxymethyl cellulose and ethyl cellulose. Of course, the former group is superior in terms of electrolyte resistance and oxidation resistance, but if a large amount is added to improve strength, the voltage characteristics will be inferior and the utilization rate will decrease. To suppress this, nickel powder and graphite were added, but if too much was added, the proportion of active material would decrease, and if too little was added, the utilization rate would be 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 is far inferior to keishiki, so it has not been widely used in practice.

Therefore, the present inventors first developed a pocket-type electrode.

An excellent method that improves the electrode using a sponge-like porous metal material as the active material support or the paste-type electrode described above to bring the discharge characteristics and life close to those of the sintered type while retaining the advantage of being easily filled with active material. We proposed two manufacturing methods. That is, the method includes a step of mixing nickel and cobalt with nickel hydroxide, which is an active material, and leaving the mixture in the coexistence with water.

This method improves the utilization of the active material and therefore allows a long life with charging and discharging at a constant load.

When this method was investigated using various materials produced on an industrial scale, it became clear that the effectiveness of these methods in improving utilization rate and lifespan was inconsistent and that reproducibility was poor in some cases. .

Purpose of the Invention As described above, the present invention improves the reproducibility of the effect of improving the utilization rate and life when adopting a process in which nickel hydroxide is left in the coexistence of nickel and cobalt with water, and achieves a constant quality. The aim is to obtain electrodes of

Structure of the Invention The present invention is characterized by using nickel hydroxide that has been washed in a neutral or slightly alkaline trench.

Here, the preferable range of the amount of alkali remaining attached to nickel hydroxide is, for example, when about twice the weight of water is added to nickel hydroxide, and the pH of the water after stirring is about 7 to 8.5. be.

Since nickel hydroxide is generally produced by precipitation from nickel sulfate and caustic soda, the remaining alkali is caustic soda. This residual alkali is unavoidable to some extent, as the precipitate remains in the form of fine particles even after thorough water washing. Note that since it is actually used in the air, most of the caustic soda is converted to soda carbonate.

In any case, when water is added to cobalt, nickel, and nickel hydroxide and left, the pH has a great effect, and the pH becomes acidic (below 7) or alkaline (pH 11 or more), which can lead to improvements in utilization rate and lifespan. It was found that reproducibility deteriorated. Therefore, it is essential to wash nickel hydroxide until it becomes neutral or weakly alkaline.

Description of Examples A AA size sealed nickel-cadmium storage battery was used as a battery for performance comparison. The cadmium negative electrode manufactured as follows was used. First, a paste mainly composed of cadmium oxide is applied to both sides of a nickel-plated iron punching metal, passed between slits set to a predetermined thickness, and then dried to a thickness of 0.7 mm. Obtained the electrode plate. Thereafter, it was partially charged in a 10% by weight aqueous solution of caustic potassium to change some of the cadmium oxide into metal cadmium, and after washing and drying, it was pressurized to a thickness of 0.65 mm.

A non-woven polyamide fabric was used as the separator, and 6.6 cc of an electrolyte prepared by dissolving a small amount of lithium hydroxide in a 25% by weight aqueous solution of caustic potash was used per cell. In this embodiment, a paste type nickel electrode is used. As materials for trench paste, nickel hydroxide with a particle size that passes through a 200-mesh sieve, 10 g of carbonyl nickel powder, 1 25 g of graphite, 20 g of acrylonitrile-vinyl chloride copolymer with a diameter of 0.1 mm and a length of 3 to 5 layers. , polyethylene powder 26g, carbonyl metal cobalt powder 6゜1
1 and a 3% by weight aqueous solution of carboxymethyl cellulose (1 kg).

As the nickel hydroxide used in this paste, commercially available nickel hydroxide was further washed with boiled water and filtered three times. 1oog of nickel hydroxide to 2oocc of water
After stirring thoroughly, the pH was 10.2 immediately after obtaining the commercially available product, but it became 8.3 when the above paste was heated at constant temperature (about 23°C). I left it for days.

The core material used was a bunching metal plated with nickel, which was made of a steel plate with a thickness of 0.1 m + n, with holes of two diameters and three center-to-center pitches. The above paste is applied to both sides of this core material, passed through a slit, and the thickness after drying is 1.
○±0.06 key. Then 2oOg of cobalt acetate
After drying, the sample was immersed in a caustic potash aqueous solution, and cobalt hydroxide was added by a method of converting acetic acid into cobalt hydroxide.

The electrode plate thus obtained was first cut into pieces of 120 mm wide and 680 mm long. Then, pressure was applied between rollers, and an aqueous polytetrafluoroethylene disc (resin content: 6 parts by weight) was added, followed by drying. The thickness of the electrode was 0.7 mm. This electrode was further cut into 2 AA size pieces. In this case, the width was 38 mm and the length was 2.20 mm.

. Let's call this battery 8.

For comparison, a paste was prepared using commercially available nickel hydroxide as is, and a battery using an electrode obtained by the same manufacturing method as (8) will be referred to as (B).

When examining the external appearance of the paste used in battery (B) and (B), it was found that in (5), the dry or semi-dry areas turned brown due to being left, whereas in (B), such coloration Almost no changes were observed.

As a further comparison, a paste was prepared using commercially available nickel hydroxide and electrodes were immediately prepared.

A battery using this electrode (C1, as in (8), prepare a paste using water-washed nickel hydroxide and immediately use it as an electrode) is designated as q.

The charging capacity of these batteries (5) to p), the utilization rate at each discharge, and the charging and discharging conditions of 0.15C and 0.50C, and the life when the initial capacity decreases to 65% is the lifespan. The table below shows the cycle life.

It can be seen from the following margin that the battery using the nickel electrode according to the present invention has excellent utilization rate and life. Furthermore, in the presence of coexistence of nickel and cobalt, especially in the coexistence of cobalt, it is effective to wash the nickel hydroxide sufficiently with water. If it is not performed, it can be seen that there is no significant difference in the characteristics as shown in (q and p).

In addition, in the example, an example of leaving at room temperature (approximately 23°C) was shown, but if the temperature is higher than this, it is necessary to slow down the drying speed, and the drying time may be several hours, or below 2o°C. In this case, it is best to leave it for about 6 to 7 days. In addition, when constant stirring is performed, the time for standing can be shortened, and may be from several hours to one day at room temperature. In addition, it is effective to add metallic cobalt to a portion of nickel hydroxide that has been thoroughly washed with water and leave it to stand, but it is preferable to add cobalt oxide from the beginning in order to expect such an effect. I can't say that.

Further, in the embodiment, a paste type was described, but the same applies when a sponge-like metal porous body is used, and in the case of a pocket type, a dry one may be used.

Effects of the Invention As described above, according to the present invention, it is possible to improve both the utilization rate and the lifespan of a non-sintered nickel electrode, and moreover, it is possible to obtain a non-sintered nickel electrode of constant quality.

Claims (1)

[Claims] A method for producing a nickel electrode, which includes the step of making a paste of a mixture containing nickel hydroxide as a main component and nickel powder and cobalt powder. A method for manufacturing nickel electrodes that involves leaving them in the presence of water.