JPS6237874A - Manufacture of nickel hydroxide electrode of alkaline storage battery - Google Patents

Abstract

PURPOSE:To prevent weakening of a base plate due to corrosion by heat- processing a sintered nickel base plate impregnated with cobalt inorganic acid salt under the presence of oxygen to cover the base plate surface with cobalt oxide layer, before making filling operation with active material. CONSTITUTION:A sintered nickel base plate impregnated with cobalt inorganic acid salt or a sintered nickel base plate with cobalt hydroxide generated on the surface is heat-processed at 150-250 deg.C under the presence of oxygen to cover the base plate surface with cobalt oxide layer. The base plate is then impregnated with acid nickel salt and undergoes filling operation with active material accompanied by impregnation with acid nickel salt which is made active through alkali treatment or the like, to form a nickel hydroxide electrode of alkaline storage battery. The cobalt oxide layer is made to serve as a protective coat to prevent corrosion and weakening of the base plate. Thus efficiently of filling operation with active material can be improved by using acid nickel salt of high concentration at a high temperature.

Description

Detailed Description of the Invention (a) Industrial Application The present invention impregnates a porous nickel sintered substrate with an acidic nickel salt solution such as nickel nitrate, and then performs an alkali treatment to improve the quality of the substrate. The present invention relates to a method of manufacturing a sintered nickel hydroxide electrode for an alkaline storage battery, which is filled with an active material.

(b) Conventional technology A method for manufacturing nickel hydroxide electrodes for alkaline storage batteries involves immersing a porous nickel sintered substrate as an active material holder in an acidic nickel salt impregnating solution such as nickel nitrate to infiltrate the pores of the substrate with nickel salt. There is a method of manufacturing a nickel hydroxide electrode by performing an active material filling operation in which the nickel salt is impregnated with nickel salt and then converted into an active material by converting the nickel salt into nickel hydroxide in an alkali. This active material filling operation cannot fill the nickel sintered substrate with a sufficient amount of active material in one operation, so it must be repeated several times to fill the required amount of active material. . Therefore, in order to increase the efficiency of active material filling and simplify the manufacturing process, a molten salt impregnating solution such as a high-temperature, high-concentration nickel nitrate aqueous solution is used as the impregnating solution, and the required amount of active material can be obtained with a small number of impregnations. However, in this case, as a matter of course, the corrosivity of the impregnating liquid becomes strong, which erodes the substrate and dissolves the nickel that makes up the substrate, making the electrode plate brittle and causing a drop in cycle performance. .

On the other hand, in JP-A-59-78457 and JP-A-59-96659, oxidation-resistant nickel oxide is generated on the surface of a 2.7 Kel sintered substrate at high temperature in the presence of oxygen. A method of preventing corrosion of the substrate W' has been proposed. However, even with this method, if the amount of nickel oxide produced is small, corrosion of the substrate cannot be sufficiently suppressed, and if the amount of nickel oxide produced is increased to obtain a sufficient effect, the amount of nickel oxide Since it has poor electrical conductivity, there is a problem in that the electrical conductivity between the active material and the substrate is significantly impaired and the active material utilization rate is reduced.

(c) Problems to be Solved by the Invention The present invention aims to provide a nickel hydroxide electrode for alkaline storage batteries that reliably prevents corrosion of nickel sintered substrates in high-temperature acidic impregnating liquid and has excellent discharge characteristics. It is something to do.

(2) Means for Solving the Problems The method for producing a nickel hydroxide electrode for alkaline storage batteries of the present invention is based on a di-Sikel sintered substrate impregnated with a cobalt inorganic acid salt or a nickel sintered substrate with cobalt hydroxide formed on its surface. Heat treating the substrate at 150 to 250°C in the presence of oxygen,
After coating the surface of the nickel sintered substrate with a cobalt oxide layer, the substrate is exposed to acid! - The active material filling operation involves impregnation with Tsukeru's salt and then impregnation with acidic nickel salt, which is converted into an active material by an alkali treatment or the like.

(E) Function The above cobalt oxide layer acts as a protective film in acidic nickel salt as a passivation film, and stably protects the nickel sintered substrate even in high-temperature, high-concentration acidic nickel salt impregnation solution. Prevents corrosion and weakening. In addition, cobalt oxide itself has good conductivity, and it is thought that conductivity is imparted by solid solution of nickel and cobalt at the interface between the cobalt oxide layer and the active material. There is no decrease in the utilization rate of the active material as in the case of forming a 4t nickel layer.

The heating temperature during the production of cobal oxide 1 is 150 to 160°C.
The lower limit is 150℃ because cobalt oxide is generated from
It must be. Further, when the temperature exceeds 230 to 250°C, the nickel on the substrate oxidizes and the formation of nickel oxide occurs, but below 250°C, almost no nickel oxide is generated, so the upper limit needs to be 250°C.

However, no adverse effects due to the formation of nickel oxide are observed at temperatures below 300°C.

(F) Example A nickel sintered substrate with a porosity of 80% obtained by sintering in a reducing atmosphere was immersed in a nitric acid:cobalt aqueous solution with a specific gravity of 1.25 at room temperature, and then thoroughly heated at 80°C. Dry and add 1
Heat treatment is performed in air at 80° C. for 30 minutes to uniformly and completely cover the surface of the nickel sintered substrate with a cobalt oxide layer. The substrate coated with this cobalt oxide layer was then coated with 8
The nickel nitrate impregnated into the substrate was immersed in a nickel nitrate aqueous solution with a specific gravity of 1.75 at 0°C for 30 minutes.
A nickel hydroxide electrode (A) according to the method of the present invention was manufactured by repeating a series of active material filling operations in which the active material was formed in a 25% caustic soda solution at 5°C. Note 1. The cobalt oxide obtained by the method described in
It was identified as O30,4).

For comparison, a substrate obtained by sintering in the reducing atmosphere described above was heated in air at 400°C for 20 minutes to form a nickel oxide film on the surface, and then the active material filling operation was performed as described above. The electrode (B) obtained by sintering in the above reducing atmosphere was used without any treatment, and the electrode (C) obtained by performing the above active material filling operation and the substrate obtained by sintering in the above reducing atmosphere were used. The obtained substrate was immersed in an aqueous cobalt nitrate solution in the same manner as in the example, dried, and then immersed in caustic soda to form a cobalt hydroxide layer on the substrate surface, and this substrate was then filled with the active material described above. Electrodes (D) were manufactured respectively.

Figure 1 shows the electrode (A) produced by the method of the present invention and the comparative electrode (
It is a drawing showing the substrate potential at the time of first immersion of the substrate in the above nickel nitrate aqueous solution in the active material filling operation when producing B) to (D>. While the substrate reaches the nickel dissolution potential when immersed for the first time, the substrate of the electrode (A) produced by the method of the present invention always shows a passive potential in the highly corrosive impregnating liquid, and the potential does not reach the dissolution potential of the nickel sintered substrate. It has excellent corrosion resistance.

In addition, Figure 2 is a diagram showing the substrate potential during each of the first to fifth immersions of the electrode (A) produced by the method of the present invention, which showed good characteristics during the first immersion, and the comparative electrode (D) (the number of immersions is The first time is shown by the number in C, and the second time is shown by the number in C, such as ``■'', and the comparison electrode (D) has a niragel dissolution potential after the third immersion, whereas the electrode according to the present invention (A It can be seen that the substrates with > exhibited a passive potential even during the second to fifth immersion in the nickel nitrate aqueous solution, indicating that they had very excellent corrosion resistance.

Furthermore, a nickel-cadmium battery with a nominal capacity of 1.2 AH was manufactured by combining the L-distributed nickel oxide electrodes (A) to (D) with a sufficiently large capacity cadmium negative electrode manufactured under the same conditions. Discharge cycle characteristics and discharge characteristics were measured.

The results are shown in Figures 3 and 4, respectively, with the symbols corresponding to the electrodes (A> to (D)) used as positive electrodes. The nickel sintered substrate can be prevented from dissolving in the highly corrosive impregnating liquid, and the electrode strength of 7° is extremely high, so there is little chance of the active material falling off due to charging and discharging. In order to prevent the nickel sintered substrate from becoming a corroded active material and to suppress the weakening of the substrate during charging and discharging inside the battery, batteries using this electrode as the positive electrode exhibit good cycle characteristics as shown in Figure 3. , and since the cobalt oxide layer itself is conductive, the resistance does not increase unlike when a large amount of nickel oxide is formed on the substrate surface, and it exhibits good discharge characteristics as shown in FIG. 4.

In addition, when forming a cobalt oxide layer on the surface of a nickel sintered substrate, the same effect can be obtained by forming a thin nickel oxide film on the substrate surface in advance and forming a cobalt oxide layer on that surface. . In this case, the conductivity does not decrease because the nickel oxide film is thin. Furthermore, as shown in the example, the cobalt/inorganic acid salt solution used to form the cobalt oxide layer is at room temperature and has a low concentration, so corrosion of the nickel sintered substrate hardly occurs. It also helps prevent corrosion of the substrate during impregnation with cobalt inorganic salts.

(G) Effects of the Invention The method for producing a nickel hydroxide electrode for alkaline storage batteries of the present invention is to heat-treat a cobalt inorganic acid salt or cobalt hydroxide at 150 to 250°C in the presence of 0 atoms to form a nickel sintered substrate surface. After covering the substrate with a cobalt oxide layer, this substrate is filled with an active material accompanied by impregnation with an acidic nickel salt, and the cobalt oxide layer itself is conductive and acts as a passive film in the acidic nickel salt. The present invention provides a nickel hydroxide electrode for alkaline storage batteries with excellent cycle characteristics and discharge characteristics because the conductivity between the substrate and the active material is good and the substrate is prevented from becoming brittle due to corrosion caused by the oxidizing nickel salt. be able to.

Further, since the heat treatment was performed at 150 to 250@C, there was no adverse effect due to the formation of nickel oxide, and the result was good.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the relationship between substrate immersion time and substrate potential in a nickel nitrate aqueous solution during the production of electrodes and comparison electrodes by the method of the present invention, and Figures 3 and 4 are diagrams by the method of the present invention. FIG. 2 is a cycle characteristic diagram and a discharge characteristic diagram of a battery using an electrode and a comparison electrode, respectively.

Claims (1)

[Claims] (1) A nickel sintered substrate impregnated with a cobalt inorganic acid salt or a nickel sintered substrate with cobalt hydroxide formed on the surface is heat-treated at 150 to 250°C in the presence of oxygen to oxidize the surface of the nickel sintered substrate. A method for manufacturing a nickel hydroxide electrode for an alkaline storage battery, which comprises coating the substrate with a cobalt layer and then performing an active material filling operation involving impregnation of the substrate with an acidic nickel salt.