JPH0550100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for producing a nickel hydroxide electrode used in alkaline storage batteries such as nickel-cadmium storage batteries and nickel-zinc storage batteries.

(b) Conventional technology Conventionally, nickel hydroxide electrodes are produced by immersing a porous nickel sintered substrate in an impregnation solution of nickel nitrate aqueous solution, and then converting nickel nitrate into nickel hydroxide, which is a hydroxide, in an alkaline aqueous solution. They are manufactured by repeating the process of turning them into active materials and filling them with the required amount of active material. In order to increase the amount of active material filled per cycle of the above process and reduce the number of impregnations, an extremely highly concentrated aqueous solution of nickel nitrate hexahydrate is used as the impregnation liquid, and in order to reduce its viscosity, it is heated to a temperature higher than 60°C. A method of immersion at high temperatures is widely used. However, this method increases the concentration of free nitric acid in the aqueous nickel nitrate solution of the impregnating solution.
Moreover, the high temperature caused corrosion of the nickel sintered substrate, causing a decline in the strength of the electrode plate and electrode performance. Therefore, in order to suppress this corrosion, there is a method of forming a nickel oxide film on the surface of a nickel substrate (JP-A-59-78457, JP-A-59-96659, etc.), but the effect is not sufficient. do not have.

Therefore, the present inventor proposed in Japanese Patent Application No. 61-249115 that the pH of the nickel nitrate aqueous solution was adjusted to 1 to 2 in order to suppress the deterioration of electrode performance caused by corrosion during impregnation of the active material into the nickel sintered substrate. on the surface of the sintered substrate.
A method for manufacturing a nickel hydroxide electrode is proposed in which a film of Ni(OH) _2.2 (NO ₃ ) _{2.2H 2} O is formed. According to this method, the sintered nickel substrate becomes passivated by the impregnating liquid made of an aqueous nickel nitrate solution, making it possible to suppress corrosion of the substrate itself. However, this method is not without its problems. In other words, during the active material impregnation process, the amount of active material filled per cycle of a series of steps consisting of immersion, alkali treatment, and water washing is small and insufficient. The problem was that it was necessary.

(c) Problems to be Solved by the Invention The present invention has been devised in view of the above-mentioned problems, and aims to suppress the corrosion of the nickel sintered substrate, increase the filling amount of active material, and further improve electrode manufacturing. The purpose is to simplify the process.

(d) Means for Solving the Problems The method for producing a nickel hydroxide electrode for alkaline storage batteries of the present invention is to prepare a porous sintered nickel substrate coated with cobalt oxide at a temperature of 60 to 100°C and a pH of 0 to 2.
After immersing in a nickel nitrate aqueous solution adjusted to
The method is characterized in that the nickel nitrate is changed into nickel hydroxide by alkali treatment, and the porous sintered nickel substrate is filled with an active material.

(E) Effect The present inventors have discovered that when the surface of a porous nickel sintered substrate is coated with cobalt oxide, the passivation region can be expanded to PH0-2.
As a result, corrosion of the nickel sintered substrate during impregnation with the active material is suppressed at pH 0 to 2.

Furthermore, by lowering the PH range of the impregnating liquid, the turbidity of the impregnating liquid due to decomposition products generated in the nickel nitrate impregnating liquid is reduced. Conventionally, PH1~
In region 2, the pores of the nickel sintered substrate were clogged due to deposits on the surface of the nickel sintered substrate due to turbidity. This reduces the increase in the amount of impregnation (active material filling amount) in one cycle of the impregnation process. However, in the present invention, it is possible to lower the pH during impregnation to 0 to 1, which suppresses the formation of deposits on the surface of the nickel sintered substrate during impregnation, thereby suppressing clogging of the pores. can. Furthermore, although corrosion of the nickel sintered substrate is suppressed by coating with cobalt oxide even in the pH range of 0 to 1, some unnecessary active material on the surface of the nickel sintered substrate is dissolved during impregnation, and the pores are The penetration of the impregnating liquid becomes better than when the pH is 1 to 2. Due to this effect, the number of times of impregnation can be reduced, and the process can be simplified.

(F) Example As an impregnation liquid, an aqueous nickel nitrate solution having a specific gravity of 1.75, a temperature of 80° C., and a pH maintained at various pH values of −1 to 3 by adding nitric acid or nickel hydroxide was prepared. Next, after impregnating cobalt hydroxide into a nickel sintered substrate with a porosity of approximately 85%, the substrate coated with cobalt oxide by heating at 200°C and the uncoated substrate were each soaked in the nickel nitrate aqueous solution for 60 minutes. After soaking, immediately washing with water and drying, the weight was measured. Let the weight at this time be bg. This was immersed in an ammonium acetate-ammonia aqueous solution for 16 hours to extract the active material, washed with water, dried, and then weighed. Let the weight at this time be cg. Further, the weight of the nickel sintered substrate before being impregnated with the active material was defined as a. When α is the percentage of the substrate nickel dissolved in the impregnating liquid during filling of the active material, α is determined by the following formula.

α=ac/a×100% On the other hand, if β is the percentage of the amount of active material extracted by ammonium acetate-ammonia aqueous solution treatment, then
β is determined by the following formula.

β=b−c/a×100% When coated with cobalt oxide (according to the present invention), since cobalt oxide does not dissolve in ammonium acetate-ammonia aqueous solution, the nickel sintered substrate after coating with cobalt oxide The weight is a. Then, α determined from these indicates the degree of corrosion of the nickel sintered substrate, and β indicates the amount of nickel in the sintered substrate converted into an active material due to corrosion.

Figure 1 shows α when coated with cobalt oxide (●, ▲ in the figure) and when not coated (○, △ in the figure).
This shows the relationship between β and PH. This shows that when the substrate is coated with cobalt oxide, α and β are minimized in the PH range of 0 to 2, and corrosion of the substrate can be suppressed.

In addition, a sintered nickel substrate with a porosity of 85% is used.
Cobalt hydroxide of 1.35 is coated, heated at 200℃, coated with cobalt oxide, specific gravity 1.75 is immersed in an aqueous nickel nitrate solution adjusted to a temperature of 80℃ and a pH of 0 to 1, and then soaked in water at room temperature. Electrode A
was produced. Next, adjust the pH of the same impregnation solution to 1 to 2,-
Electrodes B, C, and D were manufactured in the same manner as electrode A except that the electrodes were adjusted to 1 to 0 and 2 to 3, respectively.

The electrode thus produced was immersed in an ammonium acetate-ammonia aqueous solution for 16 hours to extract the active material. A scanning electron micrograph showing the grain structure of the main part of the surface of the nickel sintered substrate at this time is shown in FIG. Here, electrode A corresponds to FIG. 2a, electrode B corresponds to FIG. 2b, and so on. It can be seen from this that corrosion such as pitting is suppressed in electrodes A and B compared to electrodes C and D.

Further, FIG. 3 shows the relationship between the number of times of impregnation during impregnation of the active material and the amount of impregnation (the amount of active material filled). From this, it can be seen that the amount of impregnation in electrode A increases greatly depending on the number of times of impregnation, compared to electrode B. This is due to the difference in pH during impregnation with the active material. That is, electrode A requires six impregnations, and electrode B requires eight impregnations. Therefore, the pH should be 0 to 1.
By setting the pH to 1 to 2, it is possible to reduce the number of impregnations compared to when the pH is set to 1 to 2. Note that the filling of the active material here involves repeating a series of steps in which the nickel sintered substrate is immersed in an active material impregnating liquid made of nickel nitrate, then immersed in an alkaline aqueous solution for alkali treatment, and then washed with water. It is.

(G) Effects of the Invention According to the present invention, corrosion of a sintered nickel substrate can be suppressed even in a high-temperature, high-concentration nickel nitrate aqueous solution in the pH range of 0 to 2, and in particular, by adjusting the pH to 0 to 1, the number of impregnation times can be reduced. Since it becomes possible to reduce the amount of carbon, the process can be simplified, and its industrial value is extremely large.

[Brief explanation of the drawing]

Figure 1 shows α, β and PH on a nickel sintered substrate.
2 and 2 are electron micrographs showing the particle structure of the main part of the surface of the nickel sintered substrate, a and b are according to the present invention, C and d
3 is based on a comparative example, and FIG. 3 is a diagram showing the relationship between the number of times of impregnation of the active material and the amount of active material filled.

Claims (1)

[Claims] 1. A porous nickel sintered substrate coated with cobalt oxide is immersed in a nickel nitrate aqueous solution adjusted to a temperature of 60 to 100°C and a pH of 0 to 2, and then treated with an alkali to remove the nitric acid. A method for producing a nickel hydroxide electrode for an alkaline storage battery, comprising changing nickel to nickel hydroxide, and filling the porous sintered nickel substrate with an active material. 2. The method for producing a nickel hydroxide electrode for an alkaline storage battery according to claim 1, wherein the pH is 0 to 1.