JPH01146253A - Manufacture of cadmium electrode for battery - Google Patents

Abstract

PURPOSE:To improve charge-discharge performance in a sealed battery by combining a partially charging process in a caustic alkali aqueous solution and an immersing process in a caustic alkali aqueous solution for almost completely converting cadmium oxide into cadmium hydroxide. CONSTITUTION:A negative electrode mainly comprising cadmium oxide is cut, and then partially charged in a caustic alkali aqueous solution by using a nickel plate as a counter electrode. This negative electrode is immersed in a potassium hydroxide solution, washed, and dried. By this alkali treatment, redish-brown cadmium oxide is converted into yellow-brown cadmium hydroxide. Fluororesin dispersion is diluted with water, and the cadmium electrode is immersed in this dispersion at normal temperature, then dried. By this treatment, water repellency is given to the electrode. The cadmium electrode obtained is assembled in a battery. A sealed alkaline storage battery having high capacity and capable of quick charge is obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for manufacturing cadmium electrodes for batteries.

BACKGROUND OF THE INVENTION As is well known, storage batteries used as various power sources include lead storage batteries and alkaline storage batteries. A typical type of alkaline storage battery is a nickel-cadmium storage battery, and the sealed type is widely used because of its ease of handling.

The development of a sintered electrode for this nickel-cadmium storage battery brought about significant improvements in charge/discharge characteristics, lifespan, low-temperature characteristics, etc., and the development of a sealed type improved ease of handling.

However, it was not sufficient in terms of cost reduction and high energy density, so instead of the sintered type, foamed type electrodes and electrodes using fibrous porous materials were developed as nickel electrodes.

On the other hand, for cadmium electrodes, the paste method has become widely used, and has made some progress in lowering costs and increasing energy density to some extent.

In this case, the cadmium electrode is generally used partially charged for discharge compensation in order to enable so-called Neumann type hermetic sealing.

Such partial charging of a cadmium electrode is generally carried out by immersing a negative electrode mainly made of cadmium oxide in caustic alkali, charging it to a desired capacity, and then washing and drying it. This method enabled hermetic sealing and also provided excellent life characteristics.

Problems to be Solved by the Invention However, the above-mentioned means were not sufficient to cope with high capacity and even rapid charging.

Therefore, attempts have been made to form a fluororesin layer on the surface of the negative electrode in order to improve the rapid charging characteristics, and although considerable improvement has been seen, the current situation is that this is still not sufficient. Therefore, it is an object of the present invention to provide a sealed alkaline storage battery with high capacity and rapid charging.

Means to solve the problem As a cadmium electrode, we use a caustic alkaline aqueous solution to obtain excellent rapid charging characteristics and discharge performance when using an electrode mainly made of cadmium oxide, which is most easily mass-produced, and especially a paste type electrode. The partial charging process in the wafer is combined with the same immersion process in a caustic aqueous solution to almost completely convert uncharged cadmium oxide to cadmium hydroxide.

Note that the partial charge in the alkaline aqueous solution is approximately 5 to 20% of the cadmium electrode capacity. In this case, the negative electrode in the form of cadmium oxide appears to have a higher charging efficiency than after conversion to cadmium hydroxide, so partial charging first and then alkaline immersion is preferred. The immersion conditions may be about 3 to 10 hours at room temperature, and a shorter time at higher temperatures. For example, 5
At 0°C, it lasts for 0.5 to 3 hours.

In view of the above-mentioned problems, the present invention aims to improve the charging and discharging characteristics of this sealed battery by adding fluorine resin to the cadmium electrode in order to improve the rapid charging characteristics.

The reason why the combined use of cadmium for conversion to cadmium hydroxide is so effective in improving rapid charging characteristics is not clear. However, judging from the results, it seems that a considerable amount of cadmium oxide remained after partial charging as in the conventional method.
If a battery is constructed in this manner and an electrolyte is added, it is thought that non-uniformity in the electrolyte concentration within the battery will occur, whether cadmium oxide or cadmium hydroxide. It is presumed that this adversely affects the gas absorption characteristics of the negative electrode during the first charging, and that the adverse effect remains even if the electrolyte concentration becomes more uniform through repeated charging and discharging thereafter. In contrast, in the present invention,
Due to alkaline immersion, the conversion of cadmium to cadmium due to partial charging and cadmium hydroxide due to alkaline immersion is progressing before battery construction, so at least in the discharge phase, there is no movement of water, and therefore non-uniformity of electrolyte concentration occurs. do not have.

This is considered to be the reason why it has excellent gas absorption properties.

Note that the addition of a fluororesin imparts water repellency to the surface of the negative electrode, which contributes to improving the gas absorption characteristics of the negative electrode.

Example Commercially available cadmium oxide was mixed with 3% polyvinyl alcohol (
A paste is prepared by adding 5% polyethylene fine powder, 0.6% vinyl chloride-acrylonitrile short fibers, etc. in a 9% weight ratio of ethylene glycol solution of 1).

This is 0.15mm thick.

It is applied to a nickel-plated punched metal plate made of iron with a hole diameter of 1.8 mm and a porosity of 50%.

It is smoothed through a slit and then dried at 120° C. for 2 hours to obtain a paste-type cadmium electrode. The thickness is 0.5
It was 5 mm.

Next, the negative electrode mainly composed of cadmium oxide obtained in this way was used for 5ubC, that is, the width was 34 mm,
It was cut into a length of 200 mm. Using this negative electrode, partial charging was performed for 8 minutes at 150 mAh/cm2 in a caustic potassium aqueous solution with a specific gravity of 1.2 using a nickel plate as a counter electrode. In this state, only some parts show the gray color of metallic cadmium, while other parts show the reddish-brown color of cadmium oxide.

Then, it was immersed in a caustic potassium aqueous solution with a specific gravity of 1.3 at 45° C. for 4 hours, washed with water, and dried. With this alkali treatment,
The reddish brown color of cadmium oxide changed to yellowish brown due to the formation of cadmium hydroxide.

Next, a commercially available fluororesin dispersion was diluted to a 2% aqueous solution, and the cadmium electrode was immersed in this solution for 2 minutes at room temperature, and then dried at 120° C. for 1.5 hours. This treatment made the electrode surface water repellent. The cadmium electrode obtained in this way was incorporated into a battery.

Note that a foamed nickel electrode was used as the positive electrode. Foamed nickel with a porosity of 96%, an average pore diameter of 130 μm, and a thickness of 1.2 mm was used as a substrate, and a carboxymethyl cellulose aqueous solution containing 85 parts of nickel hydroxide, 8 parts of carbonyl nickel, and 7 parts of metal cobalt (by weight) was added to the substrate. filled with paste and pressurized in a semi-dry state to a thickness of 0.57
Adjusted to mm. Thereafter, it was impregnated with 2% fluorine resin dispersion, dried at 90° C. for 2 hours, and used.

As the battery, a 5ubC type sealed nickel-cadmium storage battery was used as an example, as described above.

A polyamide nonwoven fabric was used as the separator, and 20 g/L of lithium hydroxide was dissolved in a caustic potassium aqueous solution having a specific gravity of 1.20 as the electrolyte. Nominal capacity is 2.0A
It is h.

This battery was designated as A, and for comparison, a battery using a negative electrode obtained by forming cadmium for discharge compensation only by partial charging, washing with water, and adding fluororesin as in the past was added as B. Ta.

After constructing each battery, 0. After repeating IC charge-0°20 discharge three times, the IC was charged. Discharge was carried out at 0.5C in this case.

As a result, both batteries A and B exhibited a capacity of 2.1 Ah and an average voltage of 1.20V.

However, the maximum internal pressure inside the battery during charging was 3.2Kg/cm2 (average of 5 cells) for battery A, while it was the same for battery B, 7Kg/cm2 (5 cells).
cell average).

Furthermore, when 1.50 kg/cm2. Battery B
In this case, it was 9.1 Kg/Cm2.

By using a combination of partial charging and immersion in alkaline aqueous solution,
It is possible to provide a sealed alkaline storage battery that can be rapidly charged while maintaining superior discharge characteristics compared to conventional partial charging only cases.

Claims (2)

[Claims] (1) A cadmium battery for a battery, characterized in that the battery is constructed using a negative electrode mainly made of cadmium oxide, which is obtained by adding a step of immersion in an alkaline aqueous solution in addition to a partial charging step in an alkaline aqueous solution. How to make poles. (2) Claim 1 using a negative electrode obtained by adding fluororesin in addition to partial charging and immersion in an alkaline aqueous solution
A method for producing a cadmium electrode for batteries as described in Section 1.