JPH0675397B2 - Method for producing paste type cadmium negative electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a paste type cadmium negative electrode for an alkaline storage battery.

Conventional technology Paste type cadmium negative electrodes for alkaline storage batteries are generally composed mainly of cadmium oxide or cadmium hydroxide,
Conductive powder such as carbonyl nickel and graphite, a binder such as polyvinyl alcohol and carboxymethyl cellulose, and a solvent such as water and ethylene glycol are added and kneaded to form a paste. The core material is manufactured by drying and then chemical conversion in an alkaline solution.

The purpose of the chemical conversion step is to convert a part or all of the cadmium compound in a discharged state such as cadmium oxide and cadmium hydroxide used as the active material into metal cadmium in a charged state to provide a precharged portion in the negative electrode. Especially.

Problems to be Solved by the Invention As described above, the paste type cadmium negative electrode has advantages that it is easier to manufacture and has a higher capacity density than the sintering type, but there is a conductive matrix like the sintering type. Therefore, the growth of metal cadmium generated during battery charging occurs in the vicinity of the core material, and it is difficult to reach the electrode plate surface layer. For this reason, the reaction with the oxygen gas generated from the positive electrode is not performed efficiently during overcharge, and when used in a sealed battery, the internal pressure of the battery becomes high.

The present invention is intended to improve the oxygen gas absorption capacity of the paste type cadmium negative electrode and enable high current charging (short time charging).

Means for Solving the Problems The present invention has an alkali-resistant and conductive material such as carbon or nickel powder after applying an active material paste mainly containing cadmium oxide powder or cadmium hydroxide powder to a conductive core. By forming a mixture layer of a powder and a fluororesin on the above-mentioned electrode plate and then adding metal cadmium as a precharge amount in the chemical conversion step, the oxygen gas income capacity of the negative electrode can be improved.

Cadmium metal oxide is electrochemically generated in the electrode plate when the electrode plate coated with the active material paste containing cadmium oxide or cadmium hydroxide as the core material is subjected to negative electrolysis in an alkaline solution. This step is a chemical conversion step that is generally performed to give a preliminary charge amount.

The metal cadmium formed in the chemical conversion step is usually formed in the vicinity of the conductive core body. However, when a conductive layer is formed on the surface of the electrode plate as in the present invention, it proceeds from the conductive layer on the surface of the electrode plate, and a layer of metal cadmium is formed on the surface of the electrode plate. In a sealed battery, it is important that the negative electrode absorbs oxygen gas generated from the positive electrode during overcharge. If this oxygen absorption is bad, the internal pressure of the battery will rise when overcharged.
Cannot charge with high current. In other words, it cannot be charged for a short time. Since oxygen gas is absorbed by the metal cadmium of the negative electrode, it is advantageous that a large amount of metal cadmium is distributed on the surface of the electrode plate as in the case of the present invention.

Further, the absorption of oxygen gas in the negative electrode is performed by the metal cadmium of the negative electrode. At this time, the existence of a three-phase interface between the metal cadmium, the electrolytic solution, and the oxygen gas is important. The greater the degree of formation of the three-phase interface, the more efficiently oxygen gas absorption proceeds. As is well known, since the fluororesin has large water repellency, the coating layer of the fluororesin according to the present invention
The formation of the three-phase interface becomes easy, and the absorption efficiency of oxygen gas is
In addition to the effect of the conductive matrix, it is further improved.

Examples Hereinafter, examples of the present invention will be described.

Cadmium oxide powder having an average particle size of about 1 μm was kneaded with an ethylene glycol solution of polyvinyl alcohol to form a paste, which was applied to a nickel-plated iron plate having holes and dried to form an electrode plate having a thickness of about 0.5 mm.

Next, the above electrode plate was immersed in a solution prepared by dispersing 100 g of nickel powder having a particle size of about 1 μm and 50 g of fluororesin powder in 1 distilled water, and dried. Next, this electrode plate was subjected to negative electrolysis in a sodium hydroxide aqueous solution having a specific gravity of 1.20 to perform chemical conversion to give metal cadmium, washed with water and dried.

This electrode plate was cut into a predetermined size and combined with a sintered nickel positive electrode to form a sealed storage battery corresponding to 1200 mAh, and the battery characteristics were tested.

The test was carried out a battery internal pressure test during overcharge to evaluate the oxygen gas absorption of the negative electrode, the battery internal pressure test, at 20 ℃, at the peak of the battery internal pressure when charged with a current equivalent to 1 to 3C evaluated.

The figure shows the relationship between the charging rate and the peak of the battery internal pressure.
“A” shows a battery using the negative electrode of the above-mentioned example, and “b” shows a battery using the negative electrode of the comparative example in which the chemical conversion process of the conventional example was performed. In the negative electrode according to the present invention, metal cadmium is likely to be distributed on the surface of the electrode plate during charging, and a three-phase interface is formed due to the presence of the fluororesin, so that the oxygen gas absorption capacity is high and therefore the battery
Has a low battery pressure and can be charged at a high rate.

Effects of the Invention As described above, according to the present invention, a large amount of metal cadmium is distributed on the surface of the electrode plate, so that oxygen gas can be efficiently absorbed. Moreover, since the degree of formation of the three-phase interface between the metal cadmium, the electrolytic solution and the oxygen gas is large, the oxygen gas can be absorbed more efficiently. Therefore,
It is possible to suppress an increase in battery internal pressure that occurs during overcharging.

[Brief description of drawings]

The figure is a diagram showing the relationship between the charging rate of a nickel-cadmium storage battery and the peak pressure in the battery.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenzo Kawashima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Minor Yamaga 1006 Kadoma, Kadoma City Osaka Prefecture, Matsuda Electric Industrial Co., Ltd. 56) References JP-A-60-216449 (JP, A)

Claims (1)

[Claims] 1. A step of coating a conductive core material with a paste mainly containing cadmium oxide or cadmium hydroxide, and a powder and fluorine having alkali resistance and conductivity such as carbon powder or nickel powder on the coated electrode plate. A method for producing a paste-type cadmium negative electrode, which comprises a step of forming a mixed layer with a resin powder and a chemical conversion step of subsequently performing negative electrolysis in an alkaline electrolyte to give a precharge amount.