JPH01146252A - Manufacturing method of cadmium negative electrode for alkaline storage batteries - Google Patents

Abstract

PURPOSE:To increase gas absorbency without decrease in performance caused by self-discharge by applying active material powder on both sides of a conductive substrate, drying, and immersing in a nickel salt aqueous solution, and at the same time cathodically electrolysing to form a thin metallic nickel layer on the surface of cadmium active material. CONSTITUTION:Ethylene glycol solution of polyvinyl alcohol is added to cadmium oxide powder, and they are kneaded to form active material paste. The paste is applied to a neckel-plated perforated steel which is a conductive substrate to obtain a cadmium active material coated plate. This active material coated plate is immersed in a nickel sulfate aqueous solution and simultaneously cathodically electrolyzed at the current of a cadmium negative plate to form a thin metallic nickel film on the surface of a cadmium active material. The active material coated plate is charged about 40% of the theoretical capacity in an alkaline solution, washed, and dried to obtaine a cadmium negative electrode for an alkaline storage battery. The electrode having low self-discharge rate and excellent gas absorbency is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a cadmium negative electrode for an alkaline storage battery.

Conventional technology Paste-type negative electrodes, in which cadmium and electrodes for alkaline storage batteries are made by kneading active materials with binders and coating them on both sides of a conductive support, have a simple manufacturing process, low manufacturing costs, and It is widely used because it provides high energy density.

Problems to be Solved by the Invention Although such paste-type cadmium negative electrodes have advantages such as high energy density, they have poor electron conductivity and have a poor ability to absorb oxygen gas generated from the positive electrode due to overcharging. However, when used in a sealed battery, the internal chair pressure tends to increase. In addition, the solubility of cadmium hydroxide in a highly concentrated alkaline solution increases in a high temperature region (40'C or higher), and repeated charge/discharge cycles cause repeated leaching and precipitation of cadmium, resulting in deformation of the negative electrode and
It also has the disadvantage that it tends to have a relatively short lifespan due to a decrease in utilization rate, growth of dendrites, etc.

゛In order to solve these problems,
As seen in Publication No. 5149, it has been proposed to provide a metallic nickel layer on the surface of the stain electrode by electroless plating or electrolytic plating. Because of the precipitation, the residue of the nickel salt is likely to be mixed into the active material or the nickel layer, which has the problem of increasing self-discharge as a battery.

The object of the present invention is to solve these problems and to obtain a cadmium negative electrode for alkaline storage batteries that has excellent gas absorption characteristics and has a long life even in high temperature ranges without deterioration due to self-discharge.

Means for Solving the Problems In order to solve these problems, the present invention applies active material powder in the form of a paste or sheet to both sides of a conductive support, dries it, and then coats it with nickel chloride or nickel sulfate. This is a method for producing a cadmium negative electrode for an alkaline storage battery, which is characterized by forming a thin film layer of metallic nickel on the surface of a cadmium active material by immersing it in an aqueous nickel salt solution mainly consisting of nickel and electrolyzing it simultaneously.

Operation The oxygen gas absorption reaction by the cadmium negative electrode in a sealed alkaline storage battery is shown by the following equation.

Cd+I02+H2O-Cd(OH)2 001. (1
) In other words, it is a reaction at the three-phase interface of gas phase: liquid phase: solid phase, and the more the metal cadmium and oxygen gas come into contact, the more active the reaction is. However, in paste-type cadmium negative electrodes, the active material has low electrical conductivity, and the charging reaction progresses gradually from near the core toward the plate surface, so metallic cadmium is difficult to generate near the plate surface, away from the conductive core. It has become.

On the other hand, in a paste-type cadmium negative electrode in which a thin film of metallic nickel is provided on the surface of the active material layer, some of the metallic cadmium generated around the conductive core is transferred to the electrically conductive metallic nickel on the surface of the active material. When the thin film layer is reached, metal cadmium gradually precipitates preferentially in the entire vicinity of the negative electrode surface from the reached part along the metal nickel layer, improving the oxygen gas absorption ability.

Further, when the negative electrode is discharged in a high temperature region (40'C or higher), discharge products are eluted as cadmate ions, diffused in the alkaline electrolyte, and precipitated without returning to their original state when the battery is next charged. This is accelerated by repeated charge/discharge cycles, and the negative electrode is significantly deformed, resulting in a decrease in utilization rate, and the growth of dendrites causes the active material to penetrate into the separator, causing short circuits and shortening the life of the negative electrode. It causes this.

However, by forming a dense layer of extremely fine metal nickel particles on the electrode surface layer, it is possible to prevent the dissolution and diffusion of discharge products in high-temperature regions. The lifespan is greatly improved.

However, when forming a thin film of metallic nickel μ on the active material surface of a paste-type cadmium negative electrode by electroless plating or electrolytic plating, the active material, cadmium oxide or cadmium hydroxide, dissolves in the plating solution and replaces it. Nickel hydroxide or nickel oxide is produced as a reaction. The nickel hydroxide or nickel oxide produced here cannot be removed even by washing with water after plating and remains as a residue. It has been found that when this residue is mixed in, it increases the self-discharge of the battery. One of the causes of self-discharge in normal alkaline storage batteries is
The reaction of nitrate ions (NO3-) at the negative electrode is said to be as shown in the following equation.

Cd+H20+NO3--Cd(OH)2+NO2-・
(21 The NO2- ions generated here are oxidized at the positive electrode and become No3- again. The reaction of equation (2) is repeated and self-discharge progresses. Residues such as nickel hydroxide or nickel/I/oxides are It is estimated that this promotes self-discharge through catalytic action, significantly increasing self-discharge.

However, in the present invention, the formation of nickel hydroxide or nickel oxide is suppressed in order to form a thin film of metallic nickel on the surface of the cadmium active material by immersing the cadmium active material coated plate in a plating solution and at the same time performing negative electrolysis. can do.

In other words, conventionally, in electroless plating or electrolytic plating, when a cadmium active material coated plate is immersed in a plating solution, cadmium oxide or cadmium hydroxide starts to dissolve before a metal nickel layer is formed, and nickel hydroxide or nickel oxide is formed. However, in electroless plating, the immersion time in the plating solution is relatively long, and in electrolytic plating, the cadmium active material is dissolved, so H2 gas is generated due to a decrease in the conductivity of the surface. Its production is promoted by the fact that the vicinity of the surface of the cadmium active material becomes alkaline.

In contrast, in the present invention, since the cadmium active material-coated plate is immersed in the plating solution and electrolyzed simultaneously, metallic nickel begins to precipitate before the cadmium active material dissolves.
Furthermore, since electrical conductivity is ensured by the precipitated metal nickel, no H2 gas is generated. As a result, it is possible to suppress the generation of residues such as nickel hydroxide or nickel oxide, thereby suppressing an increase in self-discharge.

Example: Cadmium oxide powder with an average particle size of 1 μm is mixed with 1 t of ethylene glycol I solution of polyvinyl alcohol to form a paste. This paste was applied to a conductive support, a nickel-plated perforated steel plate with a thickness of 0.1
It was dried at 40° C. for 30 minutes to obtain a cadmium active material coated plate having a thickness of about 0.5 wn.

Next, this cadmium active material coated plate was coated with a concentration of 1%//ll.
r In a nickel sulfate aqueous solution with a liquid temperature of 25°C and a pH of 3, the apparent surface area of a cadmium negative electrode plate is 1 drrr? Current p 1 oA
Negative electrolysis was carried out for 5 minutes at a current of . At this time, the cadmium active material coated plate was immersed in the nickel sulfate aqueous solution and at the same time, electricity was applied. After a thin film of metallic nickel was formed on the surface of the cadmium active material by this method, it was charged in an alkaline solution to about 40% of its theoretical capacity, washed with water, and dried to obtain a cadmium negative electrode for an alkaline storage battery. Let this negative electrode be a.

On the other hand, it does not form a metallic nickel layer on the surface layer of the active material.
A conventional cadmium negative electrode having the same configuration as a was otherwise prepared. Let this be b.

Furthermore, as a comparative example using the electrolytic plating method, after 1 minute and 6 minutes of immersion in a nickel sulfate aqueous solution with a concentration of 1 mol/l, a liquid temperature of 26°C, and a pH of 3, negative electrolysis was performed for 6 minutes at a current density of 1 QA/dPF/. A metal nickel layer was formed on the surface of the active material, and cadmium negative electrodes c and d having the same structure as a were obtained in other respects.

A sealed storage battery was prototyped by combining the four types of cadmium negative electrodes a and -d with a sintered nickel positive electrode, and a battery internal pressure test during overcharging, a self-discharge test, and a cycle life test were conducted.

The battery internal pressure during overcharging was evaluated by the peak value of the battery internal pressure when overcharging at 20° C. with a current equivalent to %C to 3C.

The self-discharge characteristics were evaluated by the amount of self-discharge when the battery was charged at a current of 0.10 at 20°C for 15 hours and then left at a temperature of 45°C. Furthermore, the cycle life characteristics were evaluated by charging at 50° C. for 4.6 hours with a current equivalent to %C, repeating complete discharging with a resistance load equivalent to 1C, and evaluating the capacity decrease due to the cycles.

FIG. 1 shows the relationship between the charging rate and the peak value of the battery internal pressure. A battery using a cadmium negative electrode according to the present invention,
The oxygen gas absorption capacity is improved compared to c and d. This is due to the formation of a metal nickel layer on the surface of the active material of the cadmium negative electrode, which improves the oxygen gas absorption ability due to the metal cadmium precipitated preferentially throughout the vicinity of the negative electrode surface, and the fact that the metal nickel layer is formed on the surface of the cadmium active material. Comparative Examples c and d because nickel was precipitated in a uniform form as fine particles without the formation of nickel hydroxide or nickel oxide.
It is thought that the gas absorption capacity is improved.

FIG. 2 is a diagram showing the relationship between the remaining capacity rate, which indicates the amount of self-discharge, and the storage period. Battery a according to the present invention exhibits almost the same self-discharge characteristics as the conventional battery in which a metal nickel layer is not formed on the surface layer of the active material, whereas Comparative Examples c and d show a marked decrease in self-discharge characteristics. As mentioned earlier, in the present invention, 7) V
Alternatively, it is considered that the self-discharge characteristics do not deteriorate because the formation of nickel oxide residue is suppressed.

FIG. 3 is a diagram showing the relationship between the capacity retention rate and the number of charge/discharge cycles when the capacity at the first cycle is 1oO. As is clear from these results, cycle life characteristics are significantly improved when a cadmium negative electrode in which a metal nickel layer is provided on the surface of a cadmium active material (a, c, d) is used. Furthermore, when the cadmium negative electrode according to the present invention is used, the cycle life characteristics of a are also improved. This is thought to be because, as mentioned above, the metallic nickel forms a layer in the form of uniform fine particles, which prevents significant deformation due to dissolution and precipitation of the active material during charge/discharge cycles at high temperatures.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a cadmium negative electrode for an alkaline storage battery that has improved self-discharge characteristics, excellent gas absorption characteristics, and has a long life even in a high temperature region.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the peak value of battery internal pressure and charging rate, Figure 2 shows the relationship between capacity remaining rate and storage period, and Figure 3 shows the relationship between capacity retention rate and number of charge/discharge cycles. It is a figure showing a relationship. Agent's name: Patent attorney Toshi Nakao, and one other person (Fig. 1, eyebrows raised - ¥ - (C□c) Fig. 2, Ira Nobu J), and number 11 (3) Fig. 3 ridge] (Suifuru soft

Claims (1)

[Claims] A step of applying an active material powder mainly composed of cadmium oxide or hydroxide in the form of a paste or sheet to both sides of a conductive support and drying it to obtain a cadmium active material coated plate, and chlorinating the cadmium active material coated plate. A method for producing a cadmium negative electrode for an alkaline storage battery, comprising the steps of immersing it in an aqueous nickel salt solution containing nickel or nickel sulfate and at the same time electrolyzing it negatively to form a thin film layer of metallic nickel on the surface of a cadmium active material.