JPH0410177B2 - - 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 solution such as nickel nitrate, and then performs an alkali treatment, etc. The present invention relates to a method for manufacturing a sintered nickel hydroxide electrode for alkaline storage batteries filled with an active material.

(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. Since a sufficient amount of active material cannot be filled into the nickel sintered substrate by this active material filling operation in one operation, the required amount of active material must be filled by repeating the process several times. . 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 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 reduction 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 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 for manufacturing a nickel hydroxide electrode for alkaline storage batteries of the present invention uses a nickel sintered substrate impregnated with a cobalt inorganic acid salt or a nickel sintered substrate on which cobalt hydroxide is formed. , 150-250 in the presence of oxygen
After the surface of the sintered nickel substrate is coated with a cobalt oxide layer by heat treatment at ℃, the substrate is impregnated with an acidic nickel salt, and then the active material is made into an active material by an alkali treatment etc. This is used for filling operations.

(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.

Heating temperature during cobalt oxide production is 150-160℃
The lower limit is
It needs to be 150℃. Further, when the temperature exceeds 230 to 250°C, nickel on the substrate oxidizes and nickel oxide is generated, 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 as low as 300°C.

(F) Example: Porosity of approximately 80% obtained by sintering in a reducing atmosphere
The nickel sintered substrate was immersed in a cobalt nitrate aqueous solution with a specific gravity of 1.25 at room temperature, thoroughly dried at 80℃, and then heat-treated in air at 180℃ for 30 minutes to coat the surface of the nickel sintered substrate with cobalt oxide. Cover evenly and completely with the layer. Next, the substrate coated with this cobalt oxide layer was immersed for 30 minutes at 80°C in a nickel nitrate aqueous solution with a specific gravity of 1.75, and the nickel nitrate thus impregnated into the substrate was turned into an active material in a 25% caustic soda solution at 80°C. 5 active material filling operations
The nickel hydroxide electrode produced by the method of the present invention was repeated several times.
(A) was produced. The cobalt oxide obtained by the above method was identified as tricobalt tetroxide (C ₀₃ O ₄ ) by X-ray diffraction.

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.
(C) and the substrate obtained by sintering in the above reducing atmosphere are 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, Electrodes (D) obtained by carrying out the above-mentioned active material filling operation on this substrate were manufactured.

Figure 1 shows the substrate at the time of initial immersion into the nickel nitrate aqueous solution in 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 sufficiently large cadmium negative electrode manufactured under the same conditions, and the charging and discharging of these batteries was performed. Cycle characteristics and discharge characteristics were measured. This effect is 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 corrosive impregnating liquid during electrode production, and has excellent electrode strength, which makes it easy to charge and discharge. The cobalt oxide layer prevents the nickel sintered substrate from becoming a corroded active material during charging and discharging in an alkaline 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 would occur when a large amount of nickel oxide was formed on the substrate surface. As shown in Figure 4, 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 when impregnated with inorganic acid salts.

(G) Effects of the Invention The method for manufacturing a nickel hydroxide electrode for an alkaline power storage device of the present invention heat-treats a cobalt inorganic acid salt or cobalt hydroxide at 150 to 250°C in the presence of oxygen to form a nickel sintered substrate surface. After being covered 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. Therefore, the conductivity between the substrate and the active material is good, and the weakening caused by corrosion of the substrate due to acidic nickel salt can be prevented, making it possible to obtain a nickel hydroxide electrode for alkaline storage batteries with excellent cycle characteristics and discharge characteristics. can.

Furthermore, since the heat treatment was carried out at 150 to 250°C, there was no adverse effect due to the formation of nickel oxide, which was good.

[Brief explanation of drawings]

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 showing the relationship between substrate potential and electrodes produced by the method of the present invention. FIG. 3 is a cycle characteristic diagram and a discharge characteristic diagram of a battery using a conventional electrode and a comparative electrode, respectively.

Claims (1)

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