JPS62139254A - Manufacture of nickel electrode for alkaline battery - Google Patents

Abstract

PURPOSE:To obtain a nickel electrode whose peeling off of active material is reduced and life is increased by performing press-molding in a two-step process, after brushing the surface of the electrode, of prepressing in a water content of 10-15% and press-molding in a water content of 0-7%. CONSTITUTION:Press-molding is performed in a two-step process, after brushing the surface of electrode, of prepressing in a water content of 10-15% and press-molding in a water content of 0-7%. For example, paste is prepared by adding water to a mixture of nickel hydroxide serving as main active material, metallic nickel powder, metallic cobalt powder and cadmium hydroxide powder, so as to have a water content of 35%. The paste is impregnated in a spongy, porous nickel, then the active material on pores of the substrate is removed by brushing, and water content is controlled, then prepressing and press-molding are performed to obtain a nickel electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing nickel electrodes for use in alkaline batteries.

Conventional technology Nickel electrodes used in alkaline batteries are usually made by filling a porous nickel welded substrate with active materials such as nickel hydroxide or cobalt hydroxide using electrolysis or chemical impregnation methods. is used. In addition, a nickel electrode with high capacity has been proposed in which a sponge-like nickel porous body is filled with an active material paste mainly composed of nickel hydroxide.

The conventional active material filling process for sintered nickel electrodes includes impregnation and alkali treatment, such as chemical impregnation method.

A large number of steps such as washing with water and drying are required, and in order to obtain a high-capacity electrode, it is necessary to repeat these steps several times, which is very complicated.

On the other hand, a sponge-like porous nickel material (porosity: 90-9
5), by selecting a material with a large pore diameter, the active material in paste form can be directly filled into the porous body, and high capacity can be achieved through a simple process of just performing pressure processing after filling. It is possible to manufacture nickel electrodes with

Problems to be Solved by the Invention However, in the method of using a sponge-like porous nickel material as a substrate, one with a large pore diameter can be selected.

Although it is possible to directly fill the active material in paste form, because the pores are large and the particles of the active material are not bound together, the active material may fall off during the manufacturing process, worsening the environment, and may cause problems in charging and discharging. There was a problem in that the active material fell off due to repeated steps and the characteristics deteriorated. Regarding this, a method using CMC as a binder and a method of coating the surface by immersing the electrode plate in a dispersion solution of fluorine resin and drying have been proposed. Although the method of using CMC as a binder was effective against shedding of the active material during the manufacturing process, it was hardly effective against deterioration of characteristics due to repeated charging and discharging. On the other hand, the method of immersing and drying a fluororesin dispersion solution was effective for all of the above problems, but it had the disadvantage that it was difficult to manage the dispersion solution because the fluororesin easily aggregated. Was.

Means for Solving the Problems The present invention can be used in the manufacturing process by regulating the treatment before pressure molding and the conditions of pressure molding without using a binder such as CMC or surface coating with fluororesin or the like. This is intended to prevent material from falling off and property deterioration due to repeated charging and discharging.

That is, in the method of manufacturing a nickel electrode by filling a sponge-like porous nickel body with a paste made by adding active material powder mainly composed of nickel hydroxide and kneading it with water as a solvent, and forming it under pressure. Molding is carried out in two steps: after brushing the electrode surface, preliminary pressure is applied at a moisture content of 10 to 15 degrees, and then pressure molding is performed at a moisture content of 0 to .gamma.

In order to prevent the active material from falling off from the working electrode, it is sufficient to make the pore size of the nickel base on the electrode surface sufficiently smaller than the particle size of the active material powder. If the active material is filled into the pores of the nickel base on the electrode surface, the pore size of the nickel base on the electrode surface is always larger than the particle size of the active material. This results in the active material falling off during the manufacturing process and repeated charging and discharging.56
-It causes characteristic deterioration when exposed to heat. In order to prevent this, it is necessary to remove the active material from the pores of the nickel base on the electrode surface by an operation such as brushing before pressure molding.

Furthermore, it is necessary to selectively pressurize only the base layer without active material on the surface of the electrode to reduce the diameter of the pores on the surface of the electrode. In order to selectively apply pressure to the nickel base layer without active material on the electrode surface, the layer filled with active material inside the electrode must be sufficiently hard. To harden the inner layer of the electrode, increase the water content when pressurized. In other words, all you have to do is fill the gaps between the living materials with water, but if the water content is too high, water will permeate and fill the electrode surface layer where there is no active material when pressurized, causing the electrode surface to It is not possible to make the pore size sufficiently small. Therefore, the water content during pressurization is such that the layer filled with active material inside the electrode is sufficiently hard compared to the base layer without active material on the electrode surface.
Moreover, it must be of a proper type that does not allow water to penetrate.

By the way, the main purpose of pressure molding is to make the electrode an appropriate thickness for the battery. If pressure is applied in one step, problems such as cracks or distortions may occur in the electrodes. Therefore, it becomes necessary to carry out two steps: pre-pressurizing to reduce the pores of the substrate without active material on the electrode surface, and then applying pressure to adjust the moisture content and achieve the final thickness. be.

Example The present invention will be explained in detail below with reference to Examples.

A sponge-like porous nickel body was filled with a paste containing a mixture of nickel hydroxide as the main active material, metallic nickel powder, metallic cobalt powder, and cadmium hydroxide powder, and water added to the active material powder to give a water content of 35%. Thereafter, the active material in the pores of the substrate on the surface of the electrode was removed by brushing, the moisture content was adjusted to various levels, and preliminary pressing and subsequent pressure molding were performed to obtain a nickel electrode.

Table 1 shows the extent to which cracks and distortions occurred in the nickel electrode at this time.

Table 1 In the table, a 0 mark indicates that no crack or distortion occurred, and an X mark indicates that a crack or distortion occurred. It can be seen that when the moisture content at the time of final pressure molding is 7 degrees or more, cranks and distortions occur in the electrode.

Next, FIG. 1 shows the relationship between the moisture content during final (second stage) pressure molding and the amount of active material falling off during the process. From the figure, it can be seen that when the water content at the time of pre-pressurization is 10 to 15 degrees, the amount of active material falling off decreases. FIG. 2 is a diagram showing the relationship between the number of times of charging and discharging until the life of the battery when charging and discharging is repeated, and the content percentage during pressurization. The numbers in the figure represent the moisture content at the time of pre-pressurization. The lifespan is evaluated using 20'C lithium hydroxide.
In an aqueous solution of potassium hydroxide with a specific gravity of 1.30, 1C
After charging with a corresponding current for 1.5 hours, the battery was discharged with a current corresponding to 1 C until the final voltage reached OV with respect to the Hg/HgO electrode. In addition, to determine the lifespan, the initial capacity is
oo, and the life was reached when the capacity became 80% of the initial capacity. A nickel electrode with a moisture content of less than 10% and higher than 15V+ at the time of pre-pressurization has a charging/discharging frequency of about 1ooo cycles or less before reaching the end of its life, which is not sufficient. Further, even if the water content during preliminary pressurization is 10 to 16 inches, if the water content during final pressurization exceeds 7 inches, the life characteristics will deteriorate. This is because, as shown in Table 1, cracks occur during the final pressurization. In addition, after conventional pressure molding, immersion in a fluororesin dispersion solution
The life of the dried nickel electrode was 185o cycles.

Effects of the Invention 96- As described above, according to the method of the present invention, a nickel electrode with good life characteristics and less shedding of the active material can be obtained.

[Brief explanation of drawings]

Figure 1 shows the relationship between the moisture content during pressure molding and the amount of active material falling off, and Figure 2 shows the relationship between the moisture content during final pressure molding and the number of charges and discharges until the end of the life. It is a figure showing a relationship. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure o s to /S 21:) Concentrated final pressure gintsu moisture content (2)

Claims (1)

[Claims] A method for manufacturing a nickel electrode in which a sponge-like porous nickel body is filled with a paste prepared by kneading an active material powder mainly composed of nickel hydroxide with water as a solvent, and then pressure molded. A step of pre-pressurizing at a moisture content of 10 to 15% after brushing the electrode surface, a step of pre-pressurizing at a moisture content of 0
A method for producing a nickel electrode for alkaline batteries, characterized in that it is carried out in two steps: pressure molding at ~7%.