JPS62140359A - Electrode for cell - Google Patents

Abstract

PURPOSE:To improve the capacity density and reduce the unevenness of capacity, by using a foamy metal with one side of a high porousness and the other side of a low porousness as a foamy metal to fill an active substance. CONSTITUTION:A foamy metal with one side of a high porousness and the other side of a low porousness is used, and the highly porous side is placed upward. Then an active substance is filled, dried, and pressed so that falling off of the active substance is prevented, while the filling efficiency is improved by the high porousness of the one side. Since the falling efficiency of the active substance is good and the falling off of that is restricted, like this the level of the filling capacity density is improved and the unevenness of the capacity can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to electrodes used in secondary batteries such as nickel-cadmium storage batteries, and more particularly to electrodes for batteries constructed by filling a porous metal support with an active material. Regarding electrodes.

BACKGROUND OF THE INVENTION Electrodes for secondary batteries are generally made of a metal cylindrical bag or lattice support filled with an active material, or a metal sintered body filled with an active material. The former type, which uses a cylindrical bag-like support and a lattice, has the advantage of increasing the filling capacity, but has the disadvantage of poor high-rate discharge characteristics. The latter, which uses a sintered metal support, has the advantage of excellent high-rate discharge characteristics, but has the disadvantage of a small filling capacity. In order to improve both of these drawbacks, battery electrodes have recently been proposed in which a metal foam having a continuous three-dimensional network structure with high porosity is used as a support. This method of filling the foamed metal with an active material provides an electrode suitable for high capacity and high rate discharge.

The active material is usually filled into the foamed metal by directly filling the active material in powder form, or by kneading the active material in powder form with water or the like to form a paste. In any of the above cases, the higher the porosity of the foamed metal, the easier it is to fill with the active material, which is advantageous in terms of production volume.

Problems to be Solved by the Invention However, it is usually necessary to press the electrode plate after filling the active material in order to increase the packing density. Even when a paste-like active material is filled, this pressurization is performed with the electrode plate in a dry state in order to prevent the paste-like active material from flowing out during pressurization. In this pressurizing process or the drying process before pressurizing, if a highly porous foamed metal with good active material filling properties is used, the active material powder will fall off from the foamed metal support, resulting in a reduction in the capacity of the electrode. There were problems such as a decrease in capacity, an increase in capacity variation, and a loss of active material. The present invention solves the above problems by improving the structure of the foam metal.

Means to Solve the Problems In order to improve the above problems, the present invention uses a foamed metal with high porosity on one side and low porosity on the other side, and coats the foamed metal with powder or active material. It is filled in a paste state, dried, and processed.

The filling property of the active material is greatly influenced by the porosity of the foamed metal. This is true whether it is in powder form or in paste form. If the porosity of the foamed metal is low, the active material particles cannot pass through the foamed holes, resulting in extremely poor filling performance. However, when the porosity of the foamed metal reaches a certain level or more, the filling property rapidly decreases. This is because the active material particles can smoothly pass through the foamed holes.

Falling off of the active material has exactly the same relationship as filling.

That is, on the high porosity side, the foamed metal tends to fall off unenclosed, and on the low porosity side, there is almost no falling off. Conventional? The foamed metal used as the material support for lf Ikegawa had a uniform high porosity to facilitate filling.

For this reason, falling off after filling resulted in a major turning point.

The present invention improves the conventional problems by using a material with high porosity on one side and low porosity on the other side. That is, if the active material is filled with the highly porous side facing up and this direction is maintained until the drying and pressurizing steps, the active material will hardly fall off. As for the filling property, since it has one surface with high porosity, the filling property is good.

Examples Examples of the present invention will be described below using a nickel positive electrode.

5 Foamed metal used in nickel positive electrodes is usually made by nickel plating foamed polyurethane coated with carbon, which acts as a conductive material, and then treated at high temperature to burn out the foamed polyurethane, resulting in a foamed metal skeleton. Manufactured by leaving behind.

In the present invention, nickel plating is performed by placing anodes on both sides of polyurethane foam coated with carbon, whereas nickel plating is performed on the polyurethane foam coated with carbon by placing an anode only on one side. Nickel plating progresses from the surface where the anode is placed, so
The amount of nickel plating on the side where the anode is placed is large (
The opposite side has less nickel plating (low porosity).
porosity). In this way, a foamed metal 1 having high porosity on one side and low porosity on the other side was prepared.

FIGS. 1A, B, and C are schematic cross-sectional views of the foamed metal of the present invention and the conventional foamed metal for battery electrodes, as described above;
are of low porosity and high porosity, respectively.

To 6/ Each of the foamed metals A, B, and C above was filled with a powdered active material, and pressurized to a constant thickness using a conventional method. During the steps from filling to pressurization, the foamed metal was fixed horizontally, and in case of A, the low porosity surface was placed on the lower side.

Later, each electrode plate of A, B, and C was processed into a size of 6'''l x 6 cm, and the filling capacity density was calculated. Figure 2 shows the filling capacity density of A, B, and C, respectively. B is a diagram showing the level and dispersion of the filling capacity. B has good filling properties and therefore has a high level of filling capacity density, but the active material tends to fall off during the process, so it tends to unbalance downward. Due to the poor properties, the level of filling capacity density is low, and there is a large variation during the filling process, so the capacity variation as a final electrode plate is also poor.On the other hand, A according to the present invention has a good filling property of the active material. Since it is difficult for the material to fall off, the level of filling capacity density is high and there is little variation.

Effects of the Invention As described above, according to the present invention, it is possible to provide a battery electrode that uses foamed metal and has a high capacity density and less variation in capacity.

[Brief explanation of drawings]

FIG. 3 is a diagram showing a comparison between the electrode plate and the conventional electrode V% filling capacity density. 1... Foamed metal. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] A battery electrode in which a foamed metal having a continuous three-dimensional network structure is filled with an active material, the foamed metal having a high porosity on one side and a low porosity on the other side.