JPH01187767A - Manufacture of cadmium negative electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To provide excellent gas absorbing characteristic and prolong the lifetime even in high temp. range by using a current collecting roller, and accomplishing a film layer of uniform metal nickel. CONSTITUTION:Active substance powder is turned into paste or sheet and coated on both sides of a conductive support followed by drying, and the resultant is immersed in aqueous solution containing at least one of sulfuric acid and hydrochloric acid, put in contact with a current collecting roller in this aqueous solution, immesed in an aqueous solution containing nickel sulfate, nickel chloride, and boric acid, followed by current supply to the current collecting roller, and thereby the product is negative electrolyzed to form a film layer of metal nickel continuously on the surface of cadmium active substance. Thus a film layer of uniform metal nickel is obtained excellent in gas absorbing characteristic and with long life even in high temp. range.

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 Conventionally, as a cadmium negative electrode for alkaline storage batteries, a paste-type negative electrode in which an active material is kneaded with a binder and coated on both sides of a conductive support has a simple manufacturing process and low manufacturing cost. In addition, it is widely adopted 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 poor ability to absorb oxygen gas generated from the positive electrode due to overcharging. When used in a closed type, the internal gas pressure tends to increase.

In addition, in a high temperature region of 40°C or higher, the solubility of cadmium hydroxide in a highly concentrated alkaline solution increases, and repeated charge/discharge cycles cause repeated leaching and precipitation of cadmium, resulting in deformation of the negative electrode and reduction in utilization rate. It has the disadvantage that it tends to have a relatively short life due to the growth of dendrites, etc.

In order to solve these problems, the special public
As seen in Publication No. 49, it has been proposed to provide a metal nickel layer on the surface of the electrode by electroless plating or electrolytic plating, but electroless plating requires complicated steps such as activation treatment, and Since metal nickel is precipitated after being immersed in an aqueous solution, residues of the nickel compound are likely to be mixed into the active material or the nickel layer. When these residues are mixed in, the metal nickel layer tends to become non-uniform, resulting in a drawback that a sufficient effect as a battery cannot be obtained.

The object of the present invention is to solve these problems and obtain a cadmium negative electrode for alkaline storage batteries that has excellent gas absorption characteristics and has a long life even in high temperature regions by obtaining a uniform thin film layer of metallic nickel.

Means for Solving the Problems In order to solve these problems, the present invention provides active material powder that is applied in the form of a paste or sheet to both sides of a conductive support, dried, and then treated with boric acid, sulfuric acid, or hydrochloric acid. After being immersed in an aqueous solution containing at least one of these and simultaneously brought into contact with a current collector roller in this aqueous solution, it is subsequently immersed in an aqueous solution containing nickel sulfate, nickel chloride, and boric acid, and the current collector roller is energized. This method of producing a cadmium negative electrode for an alkaline storage battery is characterized by carrying out negative electrolysis to continuously form a thin film layer of metallic nickel on the surface of a cadmium active material.

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

Cd + 1402+ H,, O-+ Cd (OH)
2. - Song (1) In other words, it is a reaction at the three-phase interface of gas phase and liquid 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 conductivity, and the charging reaction progresses gradually from the vicinity of the core toward the surface of the plate. Therefore, metallic cadmium is charged near the surface of the plate, away from the conductive core. It becomes difficult to generate. In contrast, 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, the metallic cadmium generated around the conductive core reaches the active material's conductive thin film of metallic nickel. Once reached, metal cadmium gradually precipitates preferentially in the entire vicinity of the negative electrode surface from the reached part along the metal nickel, and as a result, the oxygen gas absorption ability improves.

Is the negative electrode released in a high temperature region of 40℃ or higher? [t,
7': If the discharge product is eluted as cadmate ion,
It diffuses in the alkaline electrolyte and precipitates without returning to its original state when it is next charged. This is accelerated by repeated charging and discharging 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 lifespan.

However, by forming a dense layer of extremely fine gold and nickel particles on the electrode surface layer, it is possible to prevent the dissolution and diffusion of discharge products in high-temperature regions, thereby extending the charge-discharge cycle life of the battery. Significantly improved.

However, when a thin film layer of metallic nickel is formed on the active material surface of a paste-type cadmium negative electrode by electrolytic plating, the overvoltage for nickel deposition is high due to the low conductivity of the active material surface, and H2 gas is removed from the active material surface. occurs. As a result, the vicinity of the surface of the cadmium active material becomes alkaline, and nickel compounds such as nickel hydroxide are precipitated. When this nickel compound is mixed into a thin film layer of metallic nickel, the precipitation reaction of metallic nickel tends to be uneven because the nickel compound has low conductivity, and the thin film layer of metallic nickel becomes uneven. As a result, the distribution of metal cadmium deposited near the surface of the negative electrode during the charging reaction becomes uneven, resulting in a decrease in oxygen gas absorption ability. Further, there was a drawback that the charge/discharge cycle life in a high temperature region could not be sufficiently improved.

However, in the present invention, the cadmium active material surface is kept acidic by electroplating after immersing the cadmium active material coated plate in an aqueous solution containing at least one of boric acid, sulfuric acid, or hydrochloric acid. The production of nickel hydroxide can be suppressed. Furthermore, since the inside of the active material is also impregnated with the aqueous solution in advance, the formation of nickel hydroxide inside the active material is also suppressed. Furthermore, by energizing the cadmium active material-coated plate in an aqueous solution containing at least one of boric acid, sulfuric acid, or hydrochloric acid, and by contacting it with the roller assembly, the cooling effect of the current collector roller and new No addition process is required, making the process extremely simple. Further, boric acid, sulfuric acid, or hydrochloric acid are included in the composition of the plating electrolyte, and even if they are mixed into the plating electrolyte, there will be no effect.

EXAMPLE An ethylene glycol solution of polyvinyl alcohol is added to cadmium oxide powder having an average particle size of about 1 μm, and the mixture is kneaded to form a paste. This paste was applied to a conductive support, a nickel-plated perforated steel plate with a thickness of 0.1, and dried at about 140°C for 30 minutes to obtain a coating of cadmium active material with a thickness of about 0.5. Ta. Next, this cadmium active material coated plate 1 is immersed in a 0.5 mol/E boric acid aqueous solution 3 while being guided by a current collecting roller 2 in the manner shown in FIG.
Subsequently, it was immersed in a nickel plating solution 6 consisting of an aqueous solution of 1 mol/E nickel sulfate, 0.1 mol/l nickel chloride, and 0.6 mol/β boric acid, and passed between a pair of nickel counter electrodes 4. Negative electrolysis was carried out by applying current to the current collecting roller 2 immersed in the boric acid aqueous solution. In addition,
The negative electrolysis conditions were such that the apparent surface of the cadmium negative electrode plate was [1 dm
The plate feeding speed and current value were set so that the current was applied to 10 people per person for 2 minutes.

After forming a thin film of metallic nickel on the surface of the cadmium active material by this method, about 40% of the theoretical capacity is
%, 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, as a comparative example of the electrolytic plating method, a cadmium negative electrode plate obtained by negative electrolysis without being immersed in a boric acid aqueous solution is designated as b. Further, C is a cadmium negative electrode of a comparative example having the same structure as a except that a metal nickel layer is not formed on the active material surface layer.

A sealed storage battery was prototyped by combining the above three types of cadmium negative electrodes, z, b, and c, with a sintered nickel positive electrode, and a battery internal pressure test during overcharging 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 was performed at 20° C. with a current equivalent to Ha to 3C. Furthermore, the cycle life characteristics were determined by charging for 4.5 hours under SO'C at a current equivalent to 1/13C, and repeating complete discharge under a resistive load equivalent to 1G.

FIG. 2 shows the relationship between the charging rate and the peak value of the battery internal pressure. Battery a using a cadmium negative electrode according to the present invention is b
, c has improved oxygen gas absorption ability. This is due to the fact that by forming a metallic nickel layer on the surface of the active material of the cadmium negative electrode, the oxygen gas absorption ability is improved due to the metallic cadmium precipitated throughout the vicinity of the negative electrode surface, and the metallic nickel layer is formed on the surface layer of the cadmium active material. However, the metal cadmium is precipitated in a uniform form as fine particles without the formation of nickel compounds such as nickel hydroxide, and the distribution of metal cadmium precipitated near the negative electrode surface is uniform, so the gas absorption capacity is higher than that of the comparative example. It is thought that this has improved.

FIG. 3 shows the relationship between the capacity retention rate and the number of charge/discharge cycles when the capacity at the first cycle is 1Q○. As is clear from these results, when using a cadmium negative electrode with a metal nickel layer on the surface of the cadmium active material, a and b
The cycle life characteristics have been significantly improved. Furthermore, when the cadmium negative electrode according to the present invention is used, the cycle life is improved compared to the conventional example. This is because, as mentioned above, a layer of metallic nickel is uniformly formed as fine particles on the electrode surface, which prevents significant deformation of the cadmium active material due to dissolution deposition of the active material during charge/discharge cycles at high temperatures. It is thought that this is because of this.

In this example, a boric acid aqueous solution was used, but the same effect can be obtained by using a sulfuric acid or hydrochloric acid aqueous solution.

Effects of the Invention As described above, according to the present invention, by obtaining a uniform thin film layer of metallic nickel through a very simple process, cadmium for alkaline storage batteries has excellent gas absorption characteristics and has a long life even in high temperature regions. A negative electrode can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the electrolytic plating device 4 used in the method of the present invention, Figure 2 is a diagram showing the relationship between the peak value of battery internal pressure and charging rate, and Figure 3 is a diagram showing the relationship between the capacity retention rate and the number of charge/discharge cycles. FIG. 1... Active material coated plate, 2... Current collector roller, 3... Boric acid aqueous solution, 4... Nickel counter electrode, 5... Nickel plating liquid. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
Cheap Buy #J7 Board 2 --- It Flora --- One's Heri Meku A Glass 4- Nikke) L Ga Import 5- Nikke Nine So Hanji Aodai Jlliff? Figure 2 Charging rate (CmA) Figure 3 Charging/discharging rate (CmA)

Claims (1)

[Claims] A step of applying an active material powder mainly composed of cadmium oxide or hydroxide in paste or sheet form to both sides of a conductive support and drying it to obtain a cadmium active material coated plate; After being immersed in an aqueous solution containing at least one of acid, sulfuric acid or hydrochloric acid and at the same time being brought into contact with a current collecting roller in the aqueous solution, successively immersing in an aqueous solution containing nickel sulfate, nickel chloride and boric acid, 1. A method for producing a cadmium negative electrode for an alkaline storage battery, comprising the step of carrying out negative electrolysis by energizing a current collecting roller to continuously form a thin film layer of metallic nickel on the surface of a cadmium active material.