JPH0410178B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention impregnates a porous nickel sintered substrate with an acidic nickel salt such as nickel nitrate, and then performs an alkali treatment to create an active material in the substrate. The present invention relates to a method for manufacturing a sintered nickel hydroxide electrode for alkaline storage batteries filled with a substance.

(b) Prior art A method for producing a nickel hydroxide electrode for an alkaline storage battery is to immerse a porous sintered nickel substrate as an active material holder in an acidic nickel salt impregnating solution such as nickel nitrate, thereby injecting the nickel salt into the pores of the substrate. 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 changing 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 filling the active material and simplify the manufacturing process, a molten salt impregnating liquid such as a high-temperature, high-concentration nickel nitrate aqueous solution is used as the impregnating liquid, 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 impregnating liquid became highly corrosive, corroding the substrate, and dissolving the nickel that made up the substrate, making the electrode plate brittle and causing a decline in cylindrical 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 nickel sintered substrate at high temperature in the presence of oxygen, thereby preventing corrosion of the substrate. Methods have been proposed to prevent this. 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, nickel oxide becomes conductive. Since the conductivity between the active material and the substrate is poor, there is a problem that the 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 a sintered nickel substrate in a high-temperature acidic impregnation solution and has excellent discharge characteristics. It is something to do.

(d) Means for Solving the Problems The method of manufacturing a nickel hydroxide electrode for an alkaline storage battery of the present invention involves producing cobalt hydroxide on the surface of a sintered nickel substrate, and then anodizing the cobalt hydroxide. After the surface of the nickel sintered substrate is coated with a cobalt oxide layer by changing it to cobalt oxide, an active material filling operation involving impregnation of the substrate with an acidic nickel salt is performed.

(E) Effect The above cobalt oxide layer acts as a protective film in the acidic nickel salt as a passive film, and stably prevents corrosion of the nickel sintered substrate even in the impregnation solution of the acidic nickel salt at high temperature and high concentration. and prevent vulnerability. In addition, cobalt oxide itself has good conductivity, and it is thought that conductivity is imparted to the interface between the cobalt oxide layer and the active material by solid solution of nickel and cobalt. There is no decrease in the utilization rate of the active material, unlike when a nickel oxide layer is formed.

(F) Example: Porosity of approximately 80 obtained by sintering in a reducing atmosphere
% nickel sintered substrate is immersed in a cobalt nitrate aqueous solution with a specific gravity of 1.25 at room temperature, thoroughly dried at 80°C, then immersed in a caustic soda solution to form a cobalt hydroxide layer on the substrate surface, and then Using the substrate as an anode in an alkaline aqueous solution consisting of caustic potash, an amount of electricity of 150% of the theoretical capacity of the amount of cobalt hydroxide generated on the surface of the substrate is applied for 30 minutes to change the cobalt hydroxide to cobalt oxide and sinter the nickel. The surface of the substrate is uniformly and completely coated with a cobalt oxide layer. Next, the substrate coated with this cobalt oxide layer was soaked in a nickel nitrate aqueous solution with a specific gravity of 1.75 at 80°C for 30 minutes.
A series of active material filling operations in which the nickel nitrate impregnated into the substrate is turned into an active material in a 25% caustic soda solution at 80°C is repeated five times to form a nickel hydroxide electrode (A) according to the method of the present invention. Manufactured.

For comparison, the substrate obtained by sintering in the reducing atmosphere described above was heat-treated in air at 400°C for 20 minutes to form a nickel oxide film on the surface, and then the active material filling operation described above was performed. electrode (B) obtained by using the substrate obtained by sintering in the above reducing atmosphere without any treatment and carrying out the above active material filling operation.
Electrodes (C) and electrodes (D) obtained by performing the active material filling operation described above were prepared using the substrates obtained in the above examples on which cobalt hydroxide was produced without oxidation treatment.

Figure 1 shows the substrate at the time of initial immersion into the nickel nitrate aqueous solution during the active material filling operation when producing the electrode (A) and reference electrodes (B) to (D) by the method of the present invention. It is a drawing showing potential. While the substrates of reference electrodes (B) and (C) reach the nickel dissolution potential during the first immersion, the substrate of the electrode (A) prepared by the method of the present invention always maintains a passive potential in the highly corrosive impregnating liquid. It has excellent corrosion resistance that does not reach the melting potential of nickel sintered substrates. In addition, Figure 2 shows the electrode produced by the method of the present invention, which showed good characteristics during the first immersion.
A drawing showing the substrate potential during each of the 1st to 5th immersion of (A) and the reference electrode (D) (the number of immersions is the first time, the second
(The number of times is indicated by the number inside the circle),
While the reference electrode (D) has a nickel dissolution potential after the third immersion, the substrate of the electrode (A) according to the method of the present invention remains passive even during the second to fifth immersion in the nickel nitrate aqueous solution. It can be seen that the corrosion resistance is very good.

Furthermore, a nickel-cadmium battery with a nominal capacity of 1.2 AH was manufactured by combining the above-mentioned nickel hydroxide electrodes (A) to (D) with a cadmium negative electrode of sufficiently large capacity manufactured under the same conditions, and the charge/discharge cycles of these batteries were The characteristics and discharge characteristics were measured. The results are shown in FIGS. 3 and 4, respectively, with the symbols corresponding to the electrodes (A) to (D) used as positive electrodes. The nickel electrode (A) made by the method of the present invention has a cobalt oxide layer that prevents the sintered nickel substrate from dissolving in the highly corrosive impregnating liquid during electrode fabrication, and has excellent electrode strength. The cobalt oxide layer prevents the nickel sintered substrate from becoming a corroded active material during charging and discharging in an alkaline aqueous solution, thereby suppressing the weakening of the substrate. As shown in Figure 3, the battery exhibited good cycle characteristics, and since the cobalt oxide layer itself is conductive, the resistance did not increase as when a large amount of nickel oxide was formed on the substrate surface. As shown in the figure, it shows good discharge characteristics.

Incidentally, when forming the cobalt oxide layer on the surface of the nickel sintered substrate, the same effect can be obtained by forming a thin nickel oxide film on the substrate surface in advance and forming the cobalt oxide layer on the surface. In this case, the conductivity does not decrease because the nickel oxide film is thin. In addition, as shown in the example, the cobalt inorganic acid salt solution used when forming 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 an inorganic acid salt solution.

(g) Effects of the Invention The method for manufacturing a nickel hydroxide electrode for an alkaline storage battery of the present invention involves generating cobalt hydroxide on the surface of a sintered nickel substrate, and then converting the cobalt hydroxide into cobalt oxide by performing anodic oxidation. After the surface of the nickel sintered substrate is coated with a cobalt oxide layer, this substrate is filled with active material by impregnating it with an acidic nickel salt. Since it acts as a passive film in salt, it has good conductivity between the substrate and active material, and prevents the substrate from becoming brittle due to corrosion caused by acidic nickel salts, making it an alkaline storage battery with excellent cycle and discharge characteristics. A nickel hydroxide electrode for use can be obtained.

[Brief explanation of drawings]

Figures 1 and 2 are drawings showing the relationship between the substrate potential and the immersion time of the substrate in a nickel nitrate aqueous solution during the preparation of the electrode according to the method of the present invention and the comparison electrode;
FIG. 4 is a cycle characteristic diagram and a discharge characteristic diagram of a battery using an electrode according to the present invention and a comparative electrode, respectively.

Claims (1)

[Claims] 1 Cobalt hydroxide is generated on the surface of the nickel sintered substrate, and then the cobalt hydroxide is changed to cobalt oxide by anodizing, the surface of the nickel sintered substrate is coated with a cobalt oxide layer, and then the substrate is acidified. A method for producing a nickel hydroxide electrode for an alkaline storage battery, comprising performing an active material filling operation accompanied by impregnation with a nickel salt.