JPS60211770A - Positive electrode plate for alkaline battery - Google Patents

Abstract

PURPOSE:To remarkably improve the performance of a paste type positive electrode plate in which cobalt powder is added as a bonding agent by covering the surface of a conductive support body with cobalt metal or using the support body made of cobalt metal. CONSTITUTION:The mixed powder between the nickel hydroxide powder containing cobalt hydroxide, carbonyl nickel powder as conductive material, and the cobalt powder as a bonding agent obtained by hydrogen-reducing cobalt oxalate is pasted in a carboxymethylcellulose aqueous solution. Then, both surfaces of nickel net to which electrolytic cobalt plating is applied is coated with this paste and the thickness is adjusted, then the paste is dried by hot air. Furthermore, a positive electrode plate is obtained by immersing the said plate in a polytetrafluoroethylene dispersion solution and then drying, pressurizing, and molding it. The exfoliation of an active material is suppressed and life performance and discharge performance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a positive electrode plate for alkaline batteries in which a paste-like positive electrode active material is directly coated on both sides of a conductive support, and the conductive support is coated with cobalt. The purpose is to improve the performance of the positive electrode plate by coating it or using a support made of cobalt metal.

Conventionally, a sintered body of nickel powder has been used as the substrate for the positive electrode plate of alkaline batteries, but its porosity is between 70 and 70.
The porosity is approximately 80%, and if the porosity is increased beyond this level, its mechanical strength will be significantly reduced, and therefore, when the positive electrode active material is filled into the voids, deformation of the substrate, cracking, and peeling of the active material may occur. There were drawbacks that came with it. In addition, when filling the active material, a method called vacuum impregnation is usually used, in which the substrate is impregnated with an aqueous solution of salts such as nickel nitrate or nickel sulfate under reduced pressure, then treated with an alkaline aqueous solution, and then roughly washed with hot water. A method is used in which the steps of drying are repeated. However, the amount filled in the first operation is small, and the amount filled from the second time onward gradually decreases, so it is usually necessary to repeat the operation 4 to 10 times. This has the disadvantage that the manufacturing process is complicated and manufacturing costs are high.

Therefore, in recent years, a positive electrode active material in paste form has been applied directly to both sides of an active material support such as a nickel mesh or a porous nickel plate.
People who do li are attracting attention.

A positive electrode plate made by directly applying a paste active material to both sides of a nickel mesh, etc., has a very small ratio of the volume of the active material support to the volume of the electrode plate, so it is difficult to increase the capacity of the positive electrode plate. In addition to this, the manufacturing method is extremely simple and can be carried out continuously, making it economically advantageous.

However, when the positive electrode active material is held only by a binder such as an organic polymer, the binding force of the binder is small, and the active material may fall off due to expansion of the active material or gas generation during charging and discharging. This has the disadvantage that the life of the electrode plate is significantly shortened. Therefore, it has been proposed to add cobalt powder to increase the binding strength of the active material. When cobalt powder is added, the electrode plates harden during charging, increasing the bonding force between active material particles and significantly reducing the shedding of active material particles, but since the bonding force between the active material layer and the support is weak, filling When the discharge is repeated, the active material layer peels off from the support and JJ52
There is the inconvenience of falling.

The present invention has been made to solve the above-mentioned drawbacks, and in a paste-type positive electrode plate containing cobalt powder as a binder, the surface of the conductive support is coated with cobalt metal, or cobalt metal is added as a binder. This is based on the discovery that by using a support made of metal, the bonding force with the positive electrode active material support can be improved and the performance of the positive electrode plate can be significantly improved.

Examples of the present invention and its effects will be described in detail below.

A positive electrode plate according to the present invention was manufactured as follows.

First, 60 parts of nickel hydroxide powder containing 3% cobalt hydroxide and 20 parts of carbonyl nickel powder as a conductive material.
A mixed powder of 20 parts of cobalt powder obtained by hydrogen reduction of cobalt oxalate as a binder is made into a paste with a 1.0% carboxymethyl cellulose aqueous solution. Next, this paste was applied to both sides of a 20-mesh nickel mesh plated with electrolytic cobalt to a thickness of 1.0III.
After adjusting the temperature to Ill, it was dried with hot air at 80° C. for 1 hour. Further, this electrode plate was immersed in a 5% polytetrafluor A ethylene dispersion and dried again at 80°C for 1 hour.
A positive electrode plate A according to the present invention was obtained by pressure molding to a thickness of 0.65 mm. For comparison, a positive electrode plate B was manufactured using a conventional method in which the nickel mesh was not plated with cobalt.

One of these positive electrode plates, two sintered cadmium negative electrode plates as counter electrodes, and S, G, 1.250 (2
0'C) KO+-1 aqueous solution was used to construct a flat type battery. Then, this battery was charged for 10 hours with a current of 138111A per gram of metal cobalt to change the metal [Pal l-] into cobalt oxyhydroxide, and then the theoretical capacity of nickel hydroxide was 0. 1 at IOA current
After charging for 6 hours, the battery was discharged to 1.0μ at 0.20A to determine the active material utilization rate. A comparison of the discharge characteristics of these batteries is shown in FIG. The figure shows that the battery according to the present invention has a high discharge voltage and a high active material utilization rate.

Next, using 10 cells each of these batteries, T O
, IOAte, 16:00 Ill if L tc after 0,2
CAr 1. Figure 2 shows changes in the active material utilization rate when a charge/discharge cycle test was performed in which the battery was discharged to OV.

From the figure, it can be seen that battery A according to the present invention has extremely superior life performance compared to battery B according to the conventional method. In the case of battery B manufactured by the conventional method, the positive electrode active material sometimes completely peeled off from the support as the cycle progressed, but in the case of the battery according to the present invention, the active material particles slightly fell off. There was no battery in which the active material completely peeled off.

The reason why coating the support surface with cobalt prevents the active material from peeling off and significantly improves the electrode plate performance is thought to be due to the following reasons.

In other words, if cobalt powder is added when manufacturing a paste-type positive electrode plate, cobalt oxyhydroxide will form inside the electrode plate due to crystal growth when the cobalt is oxidized to cobalt hydroxide and roughly to cobalt oxyhydroxide during charging. It is believed that a conductive network structure is formed by the oxidation process, the electrode plate is hardened, and one particle of the active material is firmly held. In each active material layer coated on both sides of a support such as a nickel mesh, the active material particles are held sufficiently strong due to the above-mentioned effects, but in the vicinity of the support, the support is It is considered that due to the presence of the active material layers, the contact area between the active material layers sandwiching the supports is reduced by the area of the supports, and a sufficient bonding force cannot be obtained. That is, the bonding force between the active material particles in the electrode plate is the weakest near the support. For this reason, it is thought that the active material falls off during charging and discharging, which tends to occur near the support, leading to the collapse of the electrode plate due to peeling of the active material layer. However, according to the present invention,
It is thought that the binding force between the active material particles in the electrode plate is rather strongest near the support due to the strong bond between the metal cobalt present on the surface of the support and the cobalt particles in the active material. For this reason, it is thought that exfoliation of the active material is suppressed to improve life performance, and discharge performance is also improved by improving current collection performance.

In addition, when the surface of the support is coated with cobalt as in the present invention, the oxygen overvoltage of the support becomes large, which suppresses oxygen generation from the support at the end of charging, and has the effect of suppressing peeling of the active material due to gas generation. It is thought that there are also.

In the examples, electrolytic cobalt plating was used as a means of coating the surface of the support with cobalt, but other methods may be used, such as electroless cobalt plating, spraying slurry-formed cobalt powder, or drying after coating. A similar effect can be obtained by using .

As described above, in a paste-type positive electrode plate for an alkaline battery using cobalt powder as a binder, a positive electrode plate with excellent performance can be obtained by coating the surface of the active material support with cobalt.

It should be noted that since the above effects can be obtained at least if metal cobalt is present on the surface of the active material support, it goes without saying that the same effect can be obtained even if a support made entirely of cobalt metal is used. Nor.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams comparing the discharge characteristics and life performance of a battery according to the present invention and a battery according to the conventional method, respectively. △・・・Invention product, B・・・Conventional product physical strength
Banquet Toshikawahira (%) O 2nd class Family 1! Buifurusan (1!7)

Claims (1)

[Claims] 1. A paste made of a mixed powder of nickel hydroxide powder, conductive material powder, and cobalt powder as a binder is made into a paste, and a support made of cobalt metal or at least its surface is coated with cobalt metal. A positive electrode plate for an alkaline battery, characterized in that it is coated on both sides of a coated conductive support, such as a net or a porous plate. 2. The positive electrode plate for an alkaline battery according to claim 1, wherein the conductive support coated with cobalt metal is a conductive support plated with cobalt. 3. The positive electrode for an alkaline battery according to claim 1, wherein the conductive support coated with cobalt metal is obtained by spraying or coating slurry cobalt powder on the surface of the conductive support and then drying it. Board.