JPS5897266A - Manufacture of nickel electrode for battery - Google Patents

Abstract

PURPOSE:To provide an excellent manufacturing method for a non-sintered nickel electrode for an alkaline battery, which has a discharge characteristics and life performance close to those of a sintered electrode, by leaving a paste prepared from only nickel and cobalt, mixing nickel hydroxide and the like into said paste to make another paste, and using thus prepared paste for the electrode. CONSTITUTION:The pasted type is adopted for a nickel electrode. As to the composition of the paste, it consists of 1kg of granular nickel hydroxide which passes through a shieve of 200 mesh, 100g of carbonyl nickel powder, 10g of a graphite, 20g of acrylonitrile-vinylchloride copolymer fiber which has a diameter of 0.1mm. and a length of 3-5mm., 50g of carbonyl cobalt-metal powder and 1kg of 3wt% aqueous solution of carboxymethylcellulose. Of these materials, 100g of nickel powder and 50g of cobalt powder are added with 150cc of water, and the mixture is left to stand at 30 deg.C. According to performance comparison, a battery prepared by leaving the pasty mixture at 30 deg.C in such a manner as above, has a longer life than one which is prepared without leaving any pasty mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing non-sintered nickel electrodes for use in alkaline batteries.

In batteries used as various power sources, in systems that use alkaline aqueous solutions as electrolytes, there are nickel electrodes, silver oxide electrodes, manganese dioxide electrodes, air electrodes, etc. as positive electrodes, and cadmium electrodes as negative electrodes.

There are iron electrodes, hydrogen electrodes, etc. Among the positive electrodes, the nickel electrode is
It is most commonly used because it is particularly stable in alkaline aqueous solutions, has excellent charge/discharge reversibility, can be expected to have a long life, and is also excellent in terms of utilization rate. 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. Furthermore, nickel-zinc batteries and nickel-iron batteries are being developed particularly for use in electric vehicles, and nickel-metal hydride batteries have entered the practical stage mainly for special uses such as space applications.

As described above, nickel electrodes are widely used, and their electrode structure used to be the pocket type, but recently the sintered type has been the mainstream. As is well known, the pocket type is obtained by mechanically filling a steel container with many holes with nickel hydroxide together with 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. Become. Furthermore, there are problems such as 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. Discharge characteristics, rapid charge characteristics.

Significant improvements have been made in all aspects of lifespan.

Therefore, from the viewpoint of characteristics alone, it can be said that the sintered type has reached a fairly ideal stage. However, the steps involved in manufacturing the sintered body and filling it with the active material are complicated, and the cost is considerably higher than in the pocket type.

Pore size instead of sintering type.

A method has been developed in which a sponge-like porous metal material with high porosity is used as an active material support, and a paste-like active material, that is, nickel hydroxide, is directly injected into the material, which at least simplifies the process of filling the active material. It's being measured.

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. This is applied by applying a coating and pressing it through a suritan or between rollers. This method is ideal for manufacturing sintered sheets 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. 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) Nickel, that is, neither nickel oxyhydroxide as an active material during charging nor nickel hydroxide during discharging are excellent conductors. 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.

Examples of the binder include polyethylene, polypropylene, polyvinyl chloride, polystyrene resin, polyvinyl alcohol, carboxymethyl cellulose, and ethyl cellulose. Of course, the former 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 also decrease. To suppress this, nickel powder, graphite, etc. were added, but if too much was added, the proportion occupied by the 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 has not been widely used in practice because it is far inferior to the keishiki.

The present invention improves non-sintered electrodes such as pocket electrodes, electrodes that use a sponge-like porous metal material as an active material support, and paste-type electrodes that use a two-dimensional core material, so that they can be easily filled with active materials. The present invention provides an excellent manufacturing method that brings the discharge characteristics and lifespan closer to those of the sintered method while retaining the advantages of the sintered method.

The present inventors have discovered that by mixing nickel and cobalt into a paste positive electrode material mainly composed of nickel hydroxide, gradually drying it from a paste state and leaving it to stand, the utilization rate of the active material is improved. Therefore, it was previously proposed that charging and discharging under a constant load would extend the lifespan, and the present invention is directed to an improvement thereto. In other words, it was found that adding nickel and copal to nickel hydroxide and leaving it wet with water is effective in improving the utilization rate of nickel hydroxide. It has been found that several hours or more are required even if the addition is carried out, and that several days or more is preferable when it is not carried out continuously. This means that industrially it is necessary to process a large amount of paste, so the equipment, location, etc.
The drawback was that it required a lot of manpower.

Therefore, the present invention improves this and leaves only nickel and cobalt in the form of a paste, which is then used to form a paste with nickel hydroxide and the like for use in electrodes.

As a result, in terms of quantity, it is 1/10 of the case where the whole thing is left alone.
The following amount is sufficient, which is convenient for mass production.

The present invention will be explained in detail below.

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 perforated iron metal, passed through a slit set to a predetermined thickness, and then dried to a thickness of 0.
．． A 711M electrode plate was obtained. Thereafter, it was partially charged in a 10% by weight aqueous solution of caustic potassium to convert some of the cadmium oxide into metal cadmium, and after washing with water and drying, it was pressurized to a thickness of 0.66 mm.

As the layer solution, 6.3 cc of a small amount of lithium hydroxide dissolved in a 26% by weight aqueous solution of caustic potassium was used for each cell.

A paste type was adopted as the nickel electrode, and it was manufactured as follows. The paste composition is 2o.

Nickel hydroxide 1k particle size that passes through a mesh sieve
q and 1 oof carbonyl nickel powder, 1 og of graphite and acrylonitrile of diameter 0.1 vR, length 3-6 fl.
Vinyl chloride copolymer fiber 20f, carbonyl metal cobalt powder 50! j, and 1 kq of a 3% by weight aqueous solution of carboxymethyl cellulose.

Of these materials, 160cc of water was added to 10g of nickel powder and 509g of cobalt powder, and the mixture was left at 30°C. It was dried for two days while suppressing water evaporation. Note that the mixture was gently stirred once every 2 hours. The color changed from black to dark brown. This was lightly ground and the other ingredients mentioned above were added to make a paste.

The core material used was a punched metal plate with holes of 2 fl in diameter and 3 mm pitch between centers on a 40.1 m thick iron plate and plated with nickel. The above paste is applied to both sides of this core material, passed through a slit, and the thickness after drying is 1
．． 0±0.05 MM. Then 2 of cobalt acetate
Cobalt hydroxide was added by immersing the sample in an aqueous solution of 0.09/l, drying it, and then immersing it in an aqueous solution of caustic potash to convert cobalt acetate into cobanote hydroxide. The electrode plate obtained in this way was first cut to a width of 120 mm and a length of 680 mm.

The material was then pressed between rollers, impregnated with an aqueous dispersion of poly-47 nocaethylene resin (solid content: 16% by weight), and dried. The thickness of the electrode was 0.7 mm. This electrode was further cut into pieces. In this case, the width was 38 mm and the length was 220 mm.

This was combined with the aforementioned cadmium electrode and separator to form a complete battery. Let's say this battery is a person. As a comparative example,
A battery using a positive electrode constructed by leaving the entire paste in the same way as a human being is designated as B, and a battery using a positive electrode constructed from a paste that is not left in this way at all is designated as C.

As mentioned above, if a mixture of nickel and cobalt is left undisturbed, the entire mixture turns blackish brown. The reason for this is not clear, but it is thought that cobalt is diffusing into nickel while changing into an oxide. This reaction seems to be accelerated by exposure to oxygen while wet with water, and has been found to have little effect if left in solution or if a mixture of the two is rapidly dried. It was done.

The charging capacity of the battery M~C and the utilization rate at each discharge,
The following table shows the cycle life when the battery is charged and discharged under the conditions of O, 1SC for charging and 0.3C for discharge, and the life when the capacity decreases to 60% of the initial capacity.

As is clear from this table, the effect of the paste left is greater than that of the one used immediately without being left in the paste state. In addition, it was found that the method of the present invention, which involves the step of wetting nickel and cobal with water and leaving it for a while, has almost the same effect as the nickel and cobal water without leaving it for a long time. can be significantly reduced.

In addition, in the examples, the leaving temperature was 30°C, 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, and if the temperature is 20°C, the leaving temperature is one week. degree is optimal. In addition, when constant stirring is performed, the time for standing can be shortened, and may be about several hours even at room temperature. Furthermore, it is effective to add cobalt metal and leave it to stand as described above, but adding cobalt oxide from the beginning is not preferable in terms of expecting such an effect.

Further, in the embodiment, a paste-type electrode has been described, but the present invention can be similarly applied to an electrode in which a sponge-like metal porous body is filled with paste, and in the case of a pocket-type electrode, a dry one may be used.

By using a paste that has been left exposed to air for at least several hours, both the utilization rate and the lifespan of the electrode can be improved.

Claims (1)

[Claims] A method for manufacturing a nickel electrode that includes a process of turning an active material mixture containing nickel hydroxide, nickel powder, and cobalt powder into a paste, and a battery that includes a process of adding water to the nickel powder and cobalt powder and leaving them to dry. nickel electrode manufacturing method.