JPH0419962A - Cadmium negative electrode for use in alkaline storage battery - Google Patents

Abstract

PURPOSE:To enhance the charge efficiency of an electrode by providing conductive powder composed mainly of metal Cd in such a manner as existing through an active material layer and extending into conductive powder layers on both sides. CONSTITUTION:A Cd negative electrode for use in an alkaline storage battery compries a conductive base 1, an active material layer 2 compose mainly of Cd oxide applied to the base 1, and conductive powder layers 3 composed mainly of metal Cd and formed outside the active material layer 2, and conductive powder exists through the active material layer 2 and extends into the conductive powder layers 3 on both sides. In such a Cd negative electrode, the metal Cd functions as a reserved amount for discharge in constituting a battery and exists throughout the surface from the beginning and also exists in the active material composed mainly of Cd oxide which forms a portion not yet charged, and so the electron conductivity of the electrode is heightened and hence the chargeability of the negative electrode is heightened and also the electrode surface layer is kept in electric conduction to a conductive core.

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 a lot. However, since the electron conductivity of the electrode is inferior to that of a sintered cadmium negative electrode, the charging efficiency decreases as the charging current value increases, and hydrogen gas is more likely to be generated from the cadmium negative electrode.

In addition, the absorption performance of 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, the cadmium negative electrode is chemically converted to form metallic cadmium as a discharge reserve before it is incorporated into the battery, giving it electronic conductivity. The advantages of this 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 charging efficiency of the electrode was still insufficient.

On the other hand, it has been proposed that a paste-type cadmium negative electrode be impregnated with a fluororesin dispersion liquid 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, it still has not achieved the same oxygen gas absorption performance as a sintered cadmium negative electrode.

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks and provide a cadmium negative electrode for alkaline storage batteries that is relatively inexpensive and has better electrode charging efficiency and oxygen gas absorption performance. That is.

(Means for Solving the Problems) In order to achieve the above object, the cadmium negative electrode for alkaline storage batteries of the present invention includes a conductive substrate and an active material layer mainly composed of cadmium oxide coated on the conductive substrate. and a conductive powder layer mainly composed of metal cadmium formed on the outside of the active material layer, and the conductive powder passes through the active material layer and exists continuously in the conductive powder layers on both sides. It is characterized by being configured as follows. Furthermore, a fluororesin powder is added to the conductive powder.

(Function) In such a cadmium negative electrode, metal cadmium acts as a discharge reserve in the battery structure, and is ubiquitous on the surface from the beginning, and is also present in the active material mainly composed of cadmium oxide, which is the uncharged part. This increases the electronic conductivity of the electrode, thereby improving the charge acceptance of the negative electrode and keeping the electrode surface layer electrically connected to the conductive core.

- Because the fluororesin powder, which has strong and water repellent properties, is mixed in the conductive powder mainly composed of metal cadmium, the metal cadmium comes into contact with the electrolyte and oxygen gas, and as a result, the cadmium negative electrode absorbs oxygen gas quickly. It will be held in

(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 carboxymethyl cellulose 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. In this state, countless cracks were generated on the surface of the cadmium oxide electrode coated plate. Next, metal cadmium 10
A metal cadmium paste was obtained by kneading a mixture of 0 parts by weight of carboxymethylcellulose, 1 part by weight of carboxyl methyl cellulose, a fluororesin dispersion liquid, and ion-exchanged water. Coat this paste on both sides of the cadmium oxide electrode and apply it for about 15 minutes.
Cadmium negative electrode a according to the present invention was obtained by drying at 0°C.

As a comparative example of the cadmium electrode a according to the present invention, a cadmium electrode b1 in which the fluororesin dispersion liquid was not added in the metal cadmium paste was also pressed, and the surface of the cadmium oxide was smoothed and cracked by pressing a cadmium oxide electrode coated plate. Cadmium electrode C coated with the same metal cadmium paste as in the present invention after removing
1 was prepared respectively.

Each electrode a, b, c obtained in this way is hardened with resin,
It was cut in a direction perpendicular to the electrode surface and its cross-sectional view was observed. An enlarged view is shown in Fig. 1. Electrode C has an active material layer 2 mainly composed of cadmium oxide inside the electrode, and a conductive powder layer 3 mainly composed of metal cadmium only on both sides of the active material layer 2.
exists. However, electrode a was coated with metal cadmium paste 3 while the cadmium oxide electrode coated plate had cracks.

In b, it was found that the conductive material mainly composed of metal cadmium on both sides of the electrode penetrated through the inner layer 2 mainly composed of cadmium oxide and existed continuously with both sides. Note 1
is a conductive substrate.

In addition, batteries A, B, and B were made using these electrodes a, b, and c and a known paste nickel positive electrode, respectively.
Constructed C. Table 1 shows the increase in battery internal pressure after one cycle of charging and discharging these batteries.

As can be seen from Table 1 in Table 1 below, there was almost no increase in the internal pressure of batteries A and H. It is thought that in these electrodes, conductive powder was present in the active material layer mainly composed of cadmium oxide, so the charging efficiency of the active material layer mainly composed of cadmium oxide was improved, and no hydrogen gas was generated. On the other hand, the reason for the large increase in the internal pressure of battery C is considered to be that hydrogen gas was generated due to poor charging efficiency of the electrodes.

Furthermore, the internal pressure of each battery when overcharged by 300% of the nominal capacity using an IC is shown in FIG. It was found that battery A using a cadmium negative electrode to which a fluororesin dispersion liquid was added exhibited superior gas absorption performance compared to battery B to which no fluororesin dispersion liquid was added. This is thought to be because the presence of the fluororesin powder on the electrode surface increased the reaction area in contact with oxygen gas.

(Effects of the Invention) As explained above, according to the present invention, it is possible to improve the electrical conductivity of the active material layer mainly composed of cadmium oxide, thereby improving the charging characteristics of the battery, and to quickly remove oxygen gas generated during overcharging. Therefore, it is possible to provide a battery with high industrial value that is also compatible with rapid charging.

[Brief explanation of drawings]

Figure 1 is an enlarged cross-sectional view of cadmium electrode a of this example and cadmium electrodes s and c of comparative examples, and Figure 2 shows the equilibrium pressure of the batteries against overcharging for battery A of the invention and batteries B and C of comparative examples. This is a diagram. 1... Conductive substrate 2... Active material layer 3... Conductive powder layer

Claims (1)

[Claims] (1) A conductive substrate, an active material layer mainly composed of cadmium oxide coated on the conductive substrate, and a conductive powder layer mainly composed of metal cadmium formed on the outside of the active material layer. A cadmium negative electrode for an alkaline storage battery, characterized in that the conductive powder passes through the active material layer and is continuously present in the conductive powder layers on both sides.