JPH0419963A - Cadmium negative electrode for use in alkaline storage battery - Google Patents

Abstract

PURPOSE:To enhance the strength and oxygen gas absorption performance of an electrode by forming on the active material layer of a negative electrode a surface layer made of a mixture of conductive powder of metal Cd and the like and fluororesin powder, and containing a binding agent only in the inner layers of the electrode. CONSTITUTION:This Cd negative electrode for use in an alkaline storage battery comprises an active material composed mainly of Cd oxide applied to a conductive base. A surface layer made of a mixture of conductive powder of metal Cd and the like and water-repellent fluororesin powder is further formed on the active material layer of the Cd negative electrode and a binding agent is contained only in inner layers except the surface layer. The binding agent is thus added only to the inside of the electrode so as to prevent the surface from being coated with the binding agent and a layer of metal cadmium to which the water-repellent fluororesin powder is added is formed and thereby the metal Cd can easily be brought into contact with an electrolyte and oxygen gas and as a result absorption of the oxygen gas promptly takes place while the strength of the electrode is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cadmium negative electrode used in alkaline storage batteries.

(Prior art) In recent years, paste-type cadmium negative electrodes have become more popular in alkaline storage batteries than sintered-type cadmium negative electrodes because they have advantages such as simpler manufacturing processes, lower costs, and higher energy density. It has come to be used. However, since the conductivity of the electrode is inferior to that of a sintered cadmium negative electrode, its ability to absorb oxygen gas generated from the positive electrode during overcharging is poor, and when used in a sealed battery, the internal pressure of the battery tends to increase. . For this reason, a method is used to chemically convert the cadmium negative electrode to form metal cadmium as a discharge reserve before incorporating it into a battery, giving it conductivity. The above advantages will be lost.

Therefore, in order to solve these problems,
As described in Publication No. 50843, it has been proposed that forming a metal cadmium layer on the surface of a paste-like active material layer provides excellent oxygen gas absorption performance and can omit the chemical formation process. Although the chemical formation process could be omitted, the electrode strength and oxygen gas absorption performance were still insufficient.

On the other hand, it has been proposed that a paste-type cadmium negative electrode be impregnated with a fluororesin dispersion to make the electrode active material water repellent and increase the reaction area between oxygen gas and electrolyte, thereby improving oxygen gas absorption performance and electrode strength. However, even with this method, it has not been possible to obtain oxygen gas absorption performance equivalent to that of a sintered cadmium negative electrode.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to provide a relatively inexpensive material with improved electrode strength and oxygen gas absorption performance. An object of the present invention is to provide a cadmium negative electrode for alkaline storage batteries.

(Means for Solving the Problems) In order to achieve the above object, the cadmium negative electrode for alkaline storage batteries of the present invention has a cadmium negative electrode for alkaline storage batteries in which an active material mainly composed of cadmium oxide is coated on a conductive substrate. In this method, a surface layer made of a mixture of a conductive powder such as metal cadmium and a water-repellent fluororesin powder is further formed on the active material layer of the cadmium negative electrode, and a binder is applied only to the inner layer excluding the surface layer. It is characterized by containing. However, the binder used here refers to a binder that has the ability to hold active materials by forming a film of itself, and should not swell in an aqueous solution after the film is formed. Therefore, since the fluororesin powder used for the surface layer holds the active material by turning the powder itself into fibers, it does not belong to the category of binder used in the present invention.

(Function) In such a cadmium negative electrode, the metal cadmium in the surface layer acts as a discharge reserve in the battery structure, and increases the conductivity of the electrode by being omnipresent on the surface from the beginning. but,
When a binder is added to improve the strength of the electrode, the binder film covers the entire electrode and prevents contact between the electrode surface and oxygen gas, which improves the strength of the electrode. However, its ability to absorb oxygen gas is inferior. Therefore, by adding a binder only to the inside of the electrode so that the surface is not covered with a film of binder, and by forming a layer of metal cadmium to which water-repellent fluorocarbon resin powder is added, the metal cadmium to make it easy to contact the electrolyte and oxygen gas,
As a result, oxygen gas can be absorbed quickly on the cadmium negative electrode while maintaining the strength of the electrode.

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

An active material paste obtained by kneading 95 parts by weight of cadmium oxide, 5 parts by weight of nickel powder, and fibers in an ethylene glycol solution containing carboxymethylcellulose was applied to a punched substrate plated with nickel as a current collector. , and dried at about 120° C. for 2 hours to obtain a cadmium oxide electrode.

Next, an aqueous solution of polyvinyl alcohol, which is a binder that hardly swells even in electrolyte while retaining the active material by forming a film, is prepared, and the solution is sprayed onto the cadmium oxide electrode and dried to form a bond. A cadmium oxide electrode with adhesive added was obtained. Furthermore, a mixture of 100 parts by weight of metal cadmium, 1 part by weight of carboxymethylcellulose, a fluororesin dispersion liquid, and ion-exchanged water was kneaded to obtain a metal cadmium paste. Coat this paste on both sides of the cadmium oxide electrode to which the binder was added,
A cadmium negative electrode a according to the present invention was obtained by drying at about 150°C.

As a comparative example of the cadmium negative electrode a according to the present invention, a cadmium negative electrode b1 where an aqueous solution of polyvinyl alcohol was not sprayed on the cadmium oxide electrode b1 Cadmium negative electrode a
A cadmium negative electrode C1 in which no fluororesin dispersion was added in the metal cadmium paste used in the above, and a cadmium negative electrode in which an aqueous solution of polyvinyl alcohol was not sprayed onto the cadmium oxide electrode and polyvinyl alcohol was added to the metal cadmium paste. d
was created.

FIG. 1 shows the amount of active material falling off from the negative electrodes when these negative electrodes a, b, c, and d were mixed with a known paste nickel positive electrode. The amount of cadmium negative electrode sludge that did not contain polyvinyl alcohol was significantly larger.
It was found that it did not have the strength suitable for the mass production process of electrodes.

Next, batteries A and B were made using these negative electrodes a, b, c, and d and a known paste nickel positive electrode, respectively.
B.

C and D were constructed. 3 ICs for each battery to nominal capacity
Figure 2 shows the internal pressure of the battery when overcharged to 00%. It was found that batteries A and B using a cadmium negative electrode to which a fluororesin dispersion liquid was added had lower internal pressures and exhibited superior gas absorption performance than battery C to which no fluororesin dispersion liquid was added. However, even with the addition of fluororesin powder, batteries with polyvinyl alcohol added to the conductive powder layer on the surface had high internal pressure and poor gas absorption performance. This is because the binder exists on the negative electrode surface and covers the metal cadmium particles with a film of the binder, reducing the reaction area that can come into contact with oxygen gas.Furthermore, the fluororesin powder is on the negative electrode surface. This is thought to be because the water-repellent effect due to this has also weakened.

On the other hand, in Battery A of the present invention, there is no binder to form a film on the surface of the negative electrode, and since there is fluororesin powder on the surface, the reaction area where the metal cadmium powder comes into contact with oxygen gas is larger than that of other negative electrodes. It is thought that this is because the gas absorption performance was even better.

In this example, the binder was added to the inner layer by spraying an aqueous solution, but the same effect as in this example can be obtained by impregnating the inner layer with an aqueous solution of the binder.

(Effects of the Invention) As explained above, according to the present invention, the workability in the battery manufacturing process is greatly improved, and since oxygen gas generated during overcharging is quickly absorbed, rapid charging is supported, and the battery life is extended. A stable battery with high industrial value can be provided.

[Brief explanation of the drawing]

Figure 1 is a diagram comparing the amount of negative electrode active material falling off relative to the total weight of the battery of the present invention and the comparative battery, and Figure 2 is a diagram showing the equilibrium pressure of the battery against overcharging of the battery of the present invention and the comparative battery. It is. (8733) Yoshiaki Patent Attorney General

Claims (1)

[Claims] (1) In a cadmium negative electrode for an alkaline storage battery in which an active material mainly composed of cadmium oxide is coated on a conductive substrate, the active material layer of the cadmium negative electrode is further coated with a conductive powder such as metal cadmium and a fluororesin powder. A cadmium negative electrode for an alkaline storage battery, characterized in that a surface layer is formed of a mixture, and a binder is contained only in the inner layer excluding the surface layer.