JPH0697610B2 - Method for manufacturing electrode for alkaline battery - Google Patents

Description

The present invention relates to a method for manufacturing an electrode for an alkaline battery, and an object thereof is to improve the capacity density of the electrode.

The method of manufacturing an alkaline battery electrode is roughly classified into a sintering type,
There are 3 types: paste type and pocket type.

Currently, the most widely used method for small and closed nickel-cadmium storage batteries is the sintering method, which is expensive but has high capacity and long life. Sintered nickel substrates used as a support and a current collector for an active material of a sintered electrode are mainly manufactured by the following method. One of them is to spread carbonyl nickel in a heat-resistant mold such as graphite, then place a core metal such as nickel mesh, and further spread carbonyl nickel powder on both sides of the nickel mesh, and then remove excess powder. It is a loose sintering method in which the surface of powder dispersion is flattened and sintered in a non-oxidizing atmosphere. The other is to coat carbon nickel powder, solvent such as water, binder such as carboxymethyl cellulose or methyl cellulose, and thickening agent, which is a highly viscous nickel slurry, onto a core such as nickel net or nickel-plated perforated steel sheet. It is a slurry method in which after being deposited, it is dried and then sintered.

In the production of a sintered nickel substrate by the loose sintering method, sintering is started from a state in which carbonyl nickel powder is dispersed in a heat-resistant mold, that is, a state in which the bulk specific gravity of carbonyl nickel powder is close. Nickel powder with a large bulk specific gravity that is generally used industrially is Carbonyl Nickel "Type 255" manufactured by Inco, and its bulk specific gravity is 0.5 ~
The porosity of this state is 0.65, and the true density of nickel is 8.
At 85 g / cm ³ , this corresponds to 94.4-92.7%. Since the porosity decreases from this state due to sintering, the maximum value of the porosity of the sintered nickel substrate by the loose sintering method is about
It was 90%.

On the other hand, in the production of a sintered nickel substrate by the slurry method, the carbonyl nickel powder that holds a small bulk specific gravity in a three-dimensionally thinly stretched form during mechanical kneading of the nickel slurry is mechanically destroyed, Due to the large nickel powder, the maximum porosity of the sintered nickel substrate has been about 85%.

As described above, the porosity of the sintered nickel substrate manufactured by the loose sintering method or the slurry method has been conventionally controlled by considering the sintering temperature, the sintering time, the form of the raw nickel powder and the bulk specific gravity.

To manufacture a sintered electrode for an alkaline battery by filling a sintered nickel substrate manufactured by the loose sintering method or a slurry method with an active material, a nickel salt or a cadmium salt has conventionally been used in the pores of the sintered nickel substrate. Impregnated with water and then immersed in an aqueous solution of potassium hydroxide or sodium hydroxide to form nickel hydroxide or cadmium hydroxide by a chemical reaction. A chemical impregnation method is used to impregnate the pores of the substrate with nickel salt or cadmium salt and dry. Then, a thermal decomposition method of thermally decomposing at about 230 to 240 ° C to form nickel hydroxide or cadmium hydroxide, impregnating the nickel salt or cadmium salt in the pores of the substrate, and then potassium hydroxide or hydroxide. There has been a Fleischer method in which nickel hydroxide or cadmium hydroxide is formed by negatively decomposing in sodium. However, an aqueous solution of an acidic nickel salt or cadmium salt is used in the conventional chemical impregnation method of impregnating pores in a sintered nickel substrate with nickel salt or cadmium salt in the active material impregnation step, thermal decomposition method, Fleischer method, etc. Then, the nickel sintered body is corroded, and the strength of the manufactured electrode is reduced. In addition, the strength of the electrode is reduced even when the sintered nickel substrate is changed to an active material by a charge / discharge cycle.

If the porosity of the sintered nickel substrate is increased, the number of sintered parts of the individual nickel powders is reduced, and the strength of the sintered body itself is significantly reduced. Due to the decrease in strength, the porosity of conventional practicable substrates was about 85%.

In order to manufacture a sintered electrode of high capacity density, it is necessary to use a highly porous sintered nickel substrate, and in order to manufacture a highly porous sintered nickel substrate, as described above. The loose sintering method is more advantageous than the slurry method, but industrially, the sintered nickel substrate is mainly manufactured by the slurry method from the viewpoint of workability.

As described above, from the viewpoint of workability mainly in the manufacturing process of the sintered nickel substrate and the corrosiveness of the substrate in the process of filling the active material, conventionally, the manufacturing of the industrial sintered electrode for an alkaline battery has not been performed. It was performed using a sintered nickel substrate having a porosity of 85% or less obtained by a slurry method.

As a method for controlling the porosity of a sintered nickel substrate, the present invention is a result of studying the amount of nickel in the nickel slurry in the slurry method in addition to the sintering temperature, the sintering time, the form and bulk density of the raw nickel powder. By selecting the sintering conditions, it is possible to manufacture a substrate with a high porosity of about 90 to 95%, which has not been obtained in the past. By using this high porosity material, the filling conditions of the active material can be selected. It is based on the finding that an electrode for an alkaline battery having a high capacity density that is industrially practical can be obtained.

The result of the study on the amount of nickel in the slurry according to the present invention is shown in FIG. FIG. 1 shows the effect of the amount of nickel in the nickel slurry and the sintering conditions on the porosity of the sintered nickel substrate when using a carbonyl nickel powder having a bulk specific gravity of 0.50. Sintering was performed in H ₂ atmosphere. In the figure, A is a coated product, B is a dried product, and C to E are sintered products (C ...
(800 ℃ for 5 minutes, D… 900 ℃ for 3 minutes, E… 1000 ℃ for 1 minute)
Represents the porosity of the.

In the production of a sintered nickel substrate by a slurry method in which a nickel slurry is applied to a core body such as a perforated steel sheet and then dried and sintered, evaporation of a solvent such as water due to drying and the distance between nickel particles due to sintering are controlled. The shrinkage reduces the porosity of the slurry coating.

The state in which carbonyl nickel powder was sprayed in the mold in the loose sintering method corresponds to the dried state of the nickel slurry coating in the slurry method (B in FIG. 1),
The porosity in this state of the loose sintering method cannot be higher than that corresponding to the bulk specific gravity of nickel powder, but the porosity of this state in the slurry method is affected by gravity due to the action of a binder such as carboxymethyl cellulose or methyl cellulose. Since it can be reduced, it can be made more than that corresponding to the bulk specific gravity.

According to the present invention, for these reasons, a sintered nickel substrate having a high porosity of 90% or more, which could not be conventionally produced by the loose sintering method, can be produced by an industrially useful slurry method. It can be used to fabricate high capacity density electrodes.

As is clear from the figure, when a carbonyl nickel powder having a volume of 2 to 6% in a nickel slurry is sintered at a temperature of 800 to 950 ° C, a sintered body having a porosity of 90 to 95% can be obtained. . When the volume of the carbonyl nickel powder in the slurry is less than 2%, the dried body can be obtained, but the decomposed binder causes the dried body to collapse during the sintering process. I couldn't do it. Also, the sintering temperature is 10
At temperatures above 00 ° C (E in Fig. 1), the bond between nickel particles grows faster during sintering than at 800 ° C (Fig. 1C) or 900 ° C (Fig. 1D), and In the region where the volume of carbonyl nickel powder is small, the resistance to shrinkage of the distance between nickel particles is also small, so the shrinkage due to sintering is significantly large, and a sintered body with a porosity of 90% or more cannot be obtained. It was

Inco Carbonyl Nickel Powder, Type 255, has a bulk specific gravity of 0.50 to 0.65. Fig. 1 shows the case of using a carbonyl nickel powder having a bulk specific gravity of 0.50, but using a carbonyl nickel powder having a bulk specific gravity of 0.65. Even if there is, a relationship similar to that shown in FIG. 1 can be obtained.

As described above, according to the present invention, the volume of the carbonyl nickel powder in the nickel slurry is 2 by the slurry method.
It is possible to produce a sintered nickel substrate having a high porosity of 90 to 95% by sintering a material having a porosity of up to 6% at a temperature of 800 to 950 ° C in a non-oxidizing atmosphere. By selecting the filling condition of the active material using the body, an industrially practical electrode for alkaline battery can be obtained.

Next, production of a sintered nickel substrate for an alkaline battery according to the present invention will be described based on examples.

Inco Carbonyl Nickel Powder Type 255 (Bulk Specific Gravity
0.50) 5 kg is slurried with 10 l of a 3% aqueous solution of carboxymethyl cellulose.

The slurry was applied to a perforated steel plate plated with nickel as a core material, dried, and then sintered in an H ₂ atmosphere at 900 ° C. for about 3 minutes to obtain a substrate having a porosity of about 90% (see FIG. 1). This sintered nickel substrate was immersed in an aqueous solution of nickel nitrate with a specific gravity of 1.30 (80 ° C) adjusted to pH 4 to 5 with sodium hydroxide, and nickel nitrate was impregnated into the pores of the substrate, then the aqueous solution of sodium hydroxide was prepared. Immersion and chemical reaction formed nickel hydroxide. This operation of impregnation-reaction was repeated 6 times to obtain a positive electrode plate for an alkaline battery. In this embodiment, since the pH of the nickel nitrate aqueous solution is 4 to 5, the conventional pH 1 to 3 is used.
Although the amount of corrosion of the nickel substrate was smaller than that obtained by the method using the aqueous solution of 1., the porosity of the sintered nickel substrate usable in this example was up to about 90%.

The specific gravity of the positive electrode plate A manufactured according to this example and a sintered nickel substrate having a porosity of 78% adjusted to about pH 2 with nitric acid.
Specific gravity after impregnation with 1.30 (80 ℃) nickel nitrate aqueous solution
A conventional positive electrode plate B manufactured by repeating chemical impregnation 6 times of dipping in a 1.22 (20 ° C) sodium hydroxide aqueous solution, followed by washing with hot water and drying has a specific gravity of 1.25 (20
The discharge capacity was measured under the conditions that a nickel plate was used as a counter electrode in a potassium hydroxide aqueous solution (° C) for 16 hours to charge at 0.1 CmA and discharge to -1.0 V at 0.2 CmA. The results are shown in Table 1.

The capacity density of the positive electrode plate A according to this embodiment is the same as that of the conventional positive electrode plate B.
12% increase in capacity density.

The relationship between the porosity of the sintered nickel substrate and the capacity density of the positive electrode plate obtained from the results of the examples is shown in FIG. The figure shows that the capacity density of the positive electrode plate increases as the porosity of the sintered nickel substrate increases. Further, FIG. 3 shows a change in capacity density with charge / discharge cycles of each positive electrode plate. From the figure, it can be seen that the life of the positive electrode plate according to the present invention is superior to that of the conventional one.

A typical manufacturing flow chart of the electrode of the present invention is shown in FIG.

The relationships shown in FIG. 2 and FIG. 3 are also found in the negative electrode plate manufactured by using the cadmium nitrate aqueous solution in the same manner as in the examples, and it is understood that the present invention is effective also in the negative electrode plate.

As described above, according to the method of the present invention, in the production of the sintered nickel substrate by the slurry method, carbonyl nickel powder having a volume of 2 to 6% in the nickel slurry is 800 to 950 ° C. in a non-oxidizing atmosphere. 90 ~ 95 by sintering at the temperature of
% High porosity substrate was obtained and using this high porosity body,
By impregnating a substrate with a salt forming an active material using an aqueous solution of a salt forming an active material having a pH of 4 to 5, it is possible to prevent corrosion of the substrate during the step of impregnating the active material, and to have a practical high capacity density alkaline battery. It becomes possible to obtain an electrode for use and its industrial value is great.

[Brief description of drawings]

FIG. 1 shows the effect of the amount of nickel in the nickel slurry and the sintering conditions on the porosity of the sintered nickel substrate according to the present invention, and FIG. 2 shows the positive electrode plate A according to the present invention and the conventional method. FIG. 3 is a comparison diagram of the capacity densities of the positive electrode plate B, FIG. 3 is a comparison diagram of the capacity densities of the positive electrode plate A according to the present invention and the positive electrode plate B according to the conventional method with charge / discharge cycles, and FIG. It is a typical flowchart of a manufacturing process of an electrode.

Claims (1)

[Claims] 1. A carbonyl nickel powder is mixed with an aqueous solution of an organic polymer such as carboxymethyl cellulose or methyl cellulose to prepare a slurry in which the volume of the carbonyl nickel powder in the slurry is 2 to 6%. The slurry was applied to the core, dried, and then sintered in a non-oxidizing atmosphere to manufacture a nickel substrate, and then the nickel substrate was impregnated with an aqueous solution of a salt forming an active material having a pH of 4 to 5. A method for producing an electrode for an alkaline battery, which comprises forming an active material by immersing the active material in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.