JPS58175262A - Manufacture of nickel electrode for battery - Google Patents

Abstract

PURPOSE:To enhance the utilization rate of a nickel electrode and extend the life of the electrode by manufacturing moistened cobalt oxide or cobalt hydroxide which is then added to an active material. CONSTITUTION:Cobalt oxide (hydroxide) is prepared from an aqueous cobalt- acetate solution and an aqueous caustic-potash solution For instance, after 250g of cobalt acetate is dissolved in 2l of water, an excessive amount of 10wt% caustic-potash solution is added to the solution so as to make precipitates. Thus obtained precipitates are washed with water by the usual filtration until almost no alkali remains. Next, the above moistened precipitates are added to an active material mixture so as to make a paste. After that, a sealed nickel-cadmium battery of the single-2 type is constituted by using the convertional cadmium electrode, a non-woven polyamide fabric used as a separator, and a solution prepared by dissolving 20g of lithium hydroxide in 1l of 20wt% aqueous caustic- potash solution as electrolyte.

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. Further, nickel-zinc batteries and nickel-iron batteries are being developed particularly for use in electric vehicles, and nickel-hydrogen 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. 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, expanded metal, etc. is used as the core material, and an active material and a binder are mixed with this to paste. Apply a shaped material, smooth it by passing it through slits or between rollers, and after drying,
Pressure is applied as necessary.1 This method is ideal as a manufacturing method because the core material is extremely inexpensive and the active material can be easily prepared, and many proposals have been made. Paste-type electrodes have a long history, and although steam production is slightly different, paste-type lead electrode plates are extremely widely used. 1 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. Also, if you add too much, the absolute capacity will become smaller.

(2) Although the volume of the active material naturally changes due to repeated charging and discharging, severe swelling occurs in the nickel electrode.

The above-mentioned factors mainly prevent the widespread practical application 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, fluororesin, 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 decrease. To suppress this, nickel powder, graphite, etc. were added, but if too much was added, the proportion of 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 using a sponge-like porous metal material as an active material support, and paste-type electrodes using a two-dimensional core material to easily transfer active materials. The purpose is to provide a manufacturing method that maintains the advantage of being able to be filled and improves the utilization rate and lifespan.

There are ways to improve the utilization rate of this type of nickel electrode, such as adding nickel or graphite powder as a conductive material to the nickel active material, and adding lithium hydroxide in addition to potassium hydroxide to the electrolyte. There is an addition of cobalt to it. The present invention improves this method of adding cobalt. Conventionally, many proposals have been made regarding the addition of cobalt. Generally, there are methods such as directly adding metal cobalt, cobalt oxide, and cobalt hydroxide to an active material, or impregnating a cobalt salt solution and converting it into cobalt oxide or cobalt hydroxide with an alkali. Furthermore, improvements have been made to the method of adding cobalt, such as mixing it with the active material or adding it separately.

The present invention produces cobalt oxide or cobalt hydroxide from a cobalt salt such as an aqueous solution or a caustic alkali such as cobalt salt, cobalt nitrate, cobalt sulfate, or cobalt acetate. It is added to.

Of course, it is preferable to wash it with water before adding it.

That is, instead of adding cobalt hydroxide after powdering it as in the past, the precipitate is added to the nickel hydroxide powder or conductive material as it is without drying it.

The reason why the utilization rate improves with this method is not very clear, but the particles of (e)cobalt oxide made from cobalt salt or alkaline aqueous solution are small and bulky. When dried, the particles aggregate and their bulk decreases. Therefore, it is presumed that uniform mixing can be expected by adding the active material in a bulk state before agglomeration.

Hereinafter, the present invention will be explained using an example in which the present invention is applied to a paste type electrode.

First, make @cobalt oxide from an aqueous cobalt acetate solution or an aqueous potassium solution. For example, cobalt acetate 260y
is dissolved in water 22, and a 10% by weight aqueous solution of caustic potash is added in excess to form a precipitate. This is washed with water through normal filtration until almost no alkali is detected. After washing with water, it was added to the following active material mixture in a water-containing state to form a paste.

That is, 2.6 kg of nickel hydroxide, eoy of carbonyl nickel, 1 ooy of metallic cobalt, and 230 kg of phosphorous graphite.
p, acrylonitrile-vinyl chloride copolymer fiber (diameter o, 1MR9 length 3-5 mm) 505F.

Polyethylene powder 70y, water was 2.3Il including the water contained in the (t)cobalt oxide, and carboxymethyl cellulose was added to this to make a paste at 2.8% by weight. That is, in this example, metallic cobalt and the above-mentioned undried cobalt oxide were used together as cobalt, and the total cobalt equivalent was about 6.4% by weight based on nickel hydroxide.

As the core material, a punched metal plated with nickel was used, with holes made in a 0.1 m thick iron plate with a hole diameter of 2111+ and a center-to-center pitch of 3 ml. The above paste was applied to both sides of the plate while passing it through the slits. Then, it was heated for 20 minutes at 140° C., a temperature at which polyethylene melts. Finally, pressure was applied to reduce the initial thickness of 1.1 square meters to 0.63 m+.

This electrode is designated as A, and a known cadmium electrode and polyamide non-woven fabric are used as a separator, and a solution of 20f/Q lithium hydroxide dissolved in a 20% by weight aqueous solution of caustic potash is used as an electrolyte to seal the nickel-cadmium AA. The battery was configured.

Similarly, as a nickel positive electrode, a battery using an electrode in which metallic cobalt was omitted and 6.4% by weight of the above-mentioned α cobalt hydroxide was added to nickel hydroxide according to Cobalt Japanese Book was designated as B. Further, as a comparative example, batteries using electrodes containing metallic cobalt and electrodes containing cobalt oxide were designated as C and D, respectively, although the cobalt equivalent ratio was the same as above.

Charging capacity of these batteries A-D and eo% at each discharge
It is expressed as the number of cycles until the capacity decreases with i.

As is clear from the table, by using cobalt oxide produced from cobalt salt or alkali and containing water, it is possible to use cobalt oxide rather than metal cobalt or dcobalt oxide which has undergone a drying process. This makes it possible to produce superior nickel electrodes that have a high yield and therefore a long cycle life until they fall below eo% of their nominal capacity.

It should be noted that the cobalt salt is preferably one in which the remaining anions do not have an adverse effect as in the examples, but nitrates may also be used. The appropriate amount of addition is about 2 to 10% by weight of nickel hydroxide, equivalent to cobalt.

In addition, in the above example, cobalt (t)oxide containing water was used as a paste, but this (
e) After cobalt oxide is mixed with a paste material such as nickel hydroxide, it may be dried, so in a pressurized type or a pocket type, it may be dried before use.

As described above, according to the present invention, it is possible to improve the utilization rate of the nickel electrode and extend its life using a simple method.

Claims (1)

[Claims] Manufacture of a nickel electrode for a battery, which includes the step of preparing an active material mixture by adding cobalt oxide or cobalt hydroxide produced from a cobalt salt and an aqueous alkali solution to a mixture mainly consisting of nickel hydroxide powder S in a wet state. Law.