JPH0416905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a positive electrode plate for an alkaline battery, which comprises filling a sponge-like porous nickel material with a three-dimensionally continuous structure with an active material, in which cobalt powder is used as an additive. The purpose is to obtain a positive electrode plate with excellent performance by carrying out a series of manufacturing steps in an inert atmosphere or a reducing atmosphere.

Conventionally, the substrate for the positive electrode plate of alkaline batteries is
A sintered body of nickel powder is used, but its porosity is about 70 to 80%, and increasing the porosity beyond this will significantly reduce its mechanical strength, and therefore When filled with a positive electrode active material, there were drawbacks such as deformation and cracking of the substrate and peeling of the active material. In addition, when filling the active material,
Normally, a method called vacuum impregnation method is used, in which the substrate is impregnated under reduced pressure with an aqueous solution of salts such as nickel nitrate or nickel sulfate, treated with an alkaline aqueous solution, and then washed with hot water and dried. There is. However, the amount to be filled in one operation is small, and the amount to be filled in the second operation gradually decreases, so it is usually necessary to repeat the operation 4 to 10 times. Therefore, the manufacturing process is complicated and the economic cost is high.

Therefore, in recent years, attention has been paid to methods in which a sponge-like porous body made of nickel metal having a three-dimensionally continuous structure is directly filled with a positive electrode active material in the form of a paste.

Sponge-like porous nickel material with a three-dimensional continuous structure has a high porosity of 90 to 98%.
Moreover, it has high mechanical strength. Moreover, since the pore size is large, filling this porous body with an active material can increase the capacity of the positive electrode plate, and the filling process is extremely simple, allowing a continuous process, which is economically advantageous. However, due to the large pore diameter of the porous body, sufficient electrical contact between the nickel porous body serving as the current collector and the active material powder and between the active material particles cannot be obtained, resulting in a low utilization rate. Therefore, attempts have been made to improve the utilization rate by adding conductive materials such as nickel powder and various additives. Although it has been proposed to use metallic cobalt powder as this additive, its effect is not necessarily sufficient and there is a drawback that a large amount must be added in order to obtain a high active material utilization rate.

The present invention was made to solve the above-mentioned drawbacks, and when a series of manufacturing steps are performed in an inert atmosphere or a reducing atmosphere when cobalt powder is used as an additive, the performance of the electrode plate will be improved. This is based on the discovery that the results are significantly improved.

Examples of the present invention and its effects will be described in detail below.

A positive electrode plate according to the present invention was manufactured as follows. First, nickel hydroxide powder 90% in nitrogen atmosphere
Cobalt powder was added to a mixed powder of 10 parts of nickel powder and 10 parts of nickel powder, which was made into a paste with an aqueous carboxymethyl cellulose solution.
It is filled into a sponge-like porous nickel material having a three-dimensional continuous structure with a porosity of 0.3 mm and a thickness of 96% and a thickness of 1.2 mm. Next, it is dried with hot air in a nitrogen stream, further immersed in a fluororesin dispersion, dried again with hot air in a nitrogen stream, and then pressed at a pressure of 500 kg/cm ² .
In this way, all steps were performed in a nitrogen atmosphere to obtain a positive electrode plate A according to the present invention.

For comparison, positive electrode plate B was manufactured using a conventional method in which a series of manufacturing steps were performed in air. A flat-type battery was manufactured using one of these positive electrode plates, two sintered negative electrode plates as counter electrodes, and an SG1.250 (20℃) potassium hydroxide aqueous solution as an electrolyte.
After charging at 0.1CA for 20 hours, the plates were discharged to 1.0V at 0.2CA and the performance of the plates was compared. Figure 1 shows a comparison of charging characteristics when the amount of cobalt added is 10 wt%. The terminal voltage of the positive electrode plate using the conventional method is 0.2V.
It can be seen that the amount of electricity required to oxidize cobalt, which corresponds to around 1.0V, is small, but the positive electrode plate according to the present invention requires an extremely large amount of electricity. Next, FIG. 2 shows changes in the active material utilization rate when the amount of cobalt added is changed. From the figure, it can be seen that according to the present invention, an extremely high utilization rate can be obtained even with the addition of a small amount of cobalt.

The reason why the performance of the electrode plate is significantly improved when a series of manufacturing steps are performed in an inert atmosphere when cobalt is used as an additive is considered to be due to the following reason.

That is, since cobalt is easily oxidized electrochemically unlike nickel, it is considered that cobalt is easily oxidized chemically by oxygen in the air.
In addition, as shown in Figure 1, because the amount of electricity required to oxidize cobalt in the conventional positive electrode plate manufactured in air is small, the surface of the cobalt powder is oxidized and becomes passivated during the manufacturing process, and therefore during charging. It is presumed that cobalt is not sufficiently oxidized in this process. According to the present invention, the surface of the cobalt powder is almost never chemically oxidized during the manufacturing process, so the cobalt is sufficiently oxidized during charging, making it highly effective as an additive. It is thought that a high utilization rate can be obtained.

As described above, according to the present invention, a positive electrode plate with excellent performance can be obtained by adding a small amount of cobalt.

In this example, a series of manufacturing steps were performed in an inert atmosphere using nitrogen, but similar effects could be obtained even if the steps were performed in an argon atmosphere or a reducing atmosphere using hydrogen.

[Brief explanation of drawings]

FIG. 1 is a comparison diagram of charging characteristics between a positive electrode plate according to the present invention and a conventional positive electrode plate, and FIG. 2 is a diagram comparing changes in active material utilization when the amount of cobalt added is changed. A...Product of the present invention, B...Conventional product.

Claims (1)

[Claims] 1 A series of manufacturing steps for a positive electrode plate consisting of a sponge-like nickel porous body with a three-dimensionally continuous structure filled with a paste-like active material mainly composed of nickel hydroxide powder and cobalt powder, that is, mixing of the active materials A method for producing a positive electrode plate for an alkaline battery, characterized in that pasting, filling, drying, binding agent impregnation, and pressing are performed in an inert atmosphere using nitrogen or argon, or in a reducing atmosphere using hydrogen.