JPS5973844A - Production method of cadmium negative pole plate for alkaline storage battery - Google Patents

Abstract

PURPOSE:To effectively improve the negative pole utilization factor and improve the cycle characteristics by depositing cobalt on the surface of cadmium crystal in relation to a paste-type cadmium negative pole plate for an alakline storage battery. CONSTITUTION:A negative pole plate made by coating a core material with paste not containing a conductive material, drying, and pressing it to a predetermined thickness is submerged in an aqueous solution of cobalt salt, and after drying it, chemical conversion treatment is performed. After the cobalt salt is deposited on the surface of cadmium crystal by impregnating and adding the cobalt salt to the pole plate having been pressed, it is made cobalt hydroxide at the same time as the chemical conversion treatment, thereby the cadmium crystal in its growth during charging and discharging is prevented from becoming coarse and the charging/discharging efficiency can be improved. Furthermore, no metal nickel, etc. as a conductive material is contained in paste, thus no solid solution of cobalt and nickel is generated. Therefore, the utilization factor of cadmium is increased effectively and largely, and as a result the cycle characteristics of the cell is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a paste type cadmium ram negative electrode plate for alkaline storage batteries.

Conventional configurations and their problems In recent years, for example, in sealed alkaline storage batteries, the battery capacity relative to the battery volume has been increasing, and as the capacity of nickel positive electrodes has increased, the limits on their capacity have also tended to increase. be. However, it is impossible to increase the volume of the negative electrode due to battery capacity limitations, and the negative electrode capacity cannot be decreased due to the balance between positive and negative electrode capacities.

Conventionally, there are two main methods for producing cadmium negative electrodes: One is the sintering method, in which carbonyl nickel powder is kneaded with a binder to form a paste, which is applied onto a conductive core material and sintered in a reducing atmosphere. It is porous.

Another method is to knead compounds such as CIO, Cd(OH)2, metal Ca, or metal powder with a short fiber binder and a solvent, and apply this paste directly to the conductive core material. This method is called a paste method, in which the material is coated, dried, and made into electrode plates.

Paste-type negative electrode plates have the advantage of being cheaper to manufacture and have a larger amount of active material per unit volume than sintered negative plates; Currently, it is better.

In the past, various methods have been used to improve the utilization rate of paste-type negative electrode plates. One is the addition of a conductive material. This is metal nickel, NIP, iron.

This is a method in which chromium or the like is kneaded with a cadmium compound or the like to form a paste to form a negative electrode plate. In this case, although the utilization rate is improved, the amount of effective active material per unit volume cannot be said to have been significantly improved due to the increase in volume due to the conductive material.

In addition, regarding the production of cadmium powder for pocket-type cadmium negative electrode plates, nickel or cobalt ions are added to cadmium ions in the electrolyte or solution used in the electrolytic method or chemical reduction method. There is also a method of precipitating fine powder at the same time as cadmium powder, but in this case, a satisfactory utilization rate could not be obtained because the fine nickel or cobalt powder would be soaked into a large amount of cadmium powder. .

Furthermore, there is also a method of mixing a strong cobalt salt into a cadmium paste, applying it, drying it, and then treating it with an alkali to form cobalt hydroxide. However, from a microscopic perspective, the cobalt hydroxide is surrounded by the cadmium powder in this case as well, which is disadvantageous to the effective cobalt addition when it adheres to the surface of the cadmium crystal.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to effectively improve the negative electrode utilization rate and improve the cycle characteristics by attaching cobalt to the surface of cadmium crystals.

Structure of the Invention In order to achieve the above object, in the present invention, a paste containing no conductive material is applied to a core material, dried, and pressed to a predetermined thickness. A negative electrode plate is immersed in a cobalt salt aqueous solution and dried. It is characterized by post-chemical conversion.

The present inventors added cobalt salt to the surface of the cadmium crystal by impregnating it into the electrode plate after pressing, and then converted it into cobalt hydroxide in the same way as chemical formation, thereby improving the properties of the cadmium during charging and discharging. We have discovered that it is possible to prevent coarsening of cadmium crystals during crystal growth and improve charge/discharge efficiency.

Furthermore, as described above, since the paste does not contain metal nickel or the like as a conductive material, no solid solution of cobalt and nickel is formed. Therefore, the utilization rate of cadmium is effectively and greatly increased, and as a result, the cycle characteristics of the battery are greatly improved.

Description of examples The present invention will be explained in detail below.

(Example 1) Cadmium oxide powder 100yvc with an average particle size of 1 to 2μ
, 1y of polyvinyl alcohol dissolved in 40cc of ethylene glycol solution was added, and kneaded for about a minute to form a paste. Apply this paste to a thickness of 0. After coating both sides of a nickel-plated steel perforated plate of I III, it was dried at 110°C for 1 hour, and a cadmium negative electrode plate with a thickness of 0.5 sm and the same amount and volume as this person was coated with 1 mol/l of cobalt nitrate. The sample was immersed in an aqueous solution for about 2 minutes, and then dried at 8 o'c for about 30 minutes.

Both A and B cadmium negative electrode plates were chemically formed by repeating charging and discharging three times each at a current density of approximately 10 mA/d in a caustic potassium aqueous solution with a concentration of 20% by weight.
After charging both cadmium electrode plates to 100%, they were completely discharged at the same current density, and the discharge capacity was compared with respect to the capacity theoretically calculated from the cadmium weight of the cadmium negative electrode plate.

The results are shown in FIG. In the figure, M indicates the utilization rate of the cadmium negative electrode plate according to the conventional method, and B indicates the utilization rate of the cadmium negative electrode plate containing cobalt nitrate in the above example.

As is clear from FIG. 1, the cadmium active material contained in the paste 2 cadmium negative electrode plate is fully utilized by the addition of cobalt salt.

(Example 2) Parts of both the A and B cadmium negative electrode plates prepared in Example 1 were cathodically polarized in a caustic potassium aqueous solution with a concentration of 10% by weight at a current density of about 100' Wr A/. A portion of it is converted into metallic cadmium and then dried.

The electrode plate fte obtained in this way has a thickness of 0.7n and a 6-
A single-bead sealed nickel-cadmium storage battery was created by combining a steel-type nickel positive electrode plate and a separator made of nylon nonwoven fabric, and using a caustic potassium aqueous solution with a concentration of 16% by weight as an electrolyte. Time charging, I 0
The cycle characteristics were compared by repeating a charge/discharge cycle of 1.6 hours of discharge and 0.6 hours of rest at a constant resistance equivalent to that of a human being.

The results are shown in FIG. B is a battery having a negative electrode plate according to the conventional method, and B is a battery having a negative electrode plate according to the present invention. As can be seen from FIG. 2, the cycle characteristics of the battery having the negative electrode plate according to the present invention are greatly improved. This is because in the case of a conventional negative electrode plate, repeated charge/discharge cycles cause the cadmium crystals to become coarse, which increases the amount of inert cadmium and deteriorates the charge/discharge characteristics. In the case of the negative electrode plate of the present invention, since the cobalt hydroxide contained in the electrode plate suppresses the coarsening of cadmium crystals, there is no decrease in the negative electrode utilization rate, and as a result, it exhibits good charge-discharge cycle characteristics. .

In addition, the effect of containing cobalt hydroxide in the cadmium negative electrode plate was confirmed by the O,OS weight staff.
If the amount is more than 6% by weight, the hardening of the electrode plate will not be significant.
This is disadvantageous for increasing capacity because it hinders battery production and increases the volume and weight of the electrode plate.

Although cobalt nitrate was used as the cobalt salt in the above embodiments, aqueous solutions of cobalt chloride, cobalt sulfate, cobalt acetate, etc. can also exhibit similar effects.

Effects of the Invention As is clear from the above explanation, in the present invention, in which cobalt hydroxide is contained in a paste-type cadmium negative electrode plate, the utilization rate of the negative electrode plate can be greatly improved, and the charge/discharge cycle characteristics can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the utilization rate of a cadmium negative electrode plate in an example of the present invention, and FIG. 2 is a diagram showing the charge/discharge cycle characteristics of a battery using the same cadmium negative electrode plate. M: Conventional product, B: Inventive product.

Claims (1)

[Claims] (1) An active material mainly composed of cadmium oxide, mixed with a binder and kneaded into a paste, is applied to a conductive core material.
A method for forming a negative electrode plate by drying and pressing it and then chemically forming it in an alkaline aqueous solution, the method comprising a step of impregnating Kono(ruto salt) between the pressing step and the chemical forming step. The method for producing a cadmium negative electrode plate for an alkaline storage battery according to claim 1, wherein the content is 0.05 to 6% by weight.