JP2773253B2 - Manufacturing method of cadmium negative electrode for alkaline storage battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a cadmium negative electrode for an alkaline storage battery.

2. Description of the Related Art Conventionally, as a cadmium negative electrode for an alkaline storage battery, a paste type negative electrode in which an active material is kneaded with a binder and applied to a conductive support has a simple manufacturing process, a low manufacturing cost, and Widely used in that high energy density can be obtained.

Problems to be Solved by the Invention Such a paste-type cadmium negative electrode has advantages such as obtaining a high energy density, but has a poor ability to absorb oxygen gas generated from the positive electrode due to overcharge due to poor electron conductivity, When used in a sealed battery, there is a disadvantage that the internal gas pressure tends to increase. In the high-temperature region of 40 ° C or higher, the solubility of cadmium hydroxide in a high-concentration alkaline solution increases, and the charge-discharge cycle is repeated.
Dissolution and deposition of cadmium were repeated, and the disadvantage was that the life of the negative electrode was likely to be relatively short due to deformation of the negative electrode, reduction in the utilization factor, growth of dendrites, and the like.

In order to solve such problems, Japanese Patent Publication No. 48-25149
It is proposed to provide a metal nickel layer on the surface of an electrode by electroless plating or electrolytic plating as seen in Japanese Patent Publication No. The plating has a drawback that since the conductivity of cadmium oxide or cadmium hydroxide, which is an active material, is poor, the nickel layer of the metal tends to be nonuniform, and a sufficient effect as a battery cannot be obtained.

The present invention solves such a problem, and by obtaining a uniform thin film layer of metallic nickel, has excellent gas absorption properties,
An object is to obtain a cadmium negative electrode for an alkaline storage battery having a long life even in a high temperature region.

Means for Solving the Problems To solve such problems, the present invention provides a carboxyl group, a carbonyl group,
A mixture with carbon powder or carbon fiber having at least one quinone group is applied to a conductive support in the form of a paste or a sheet, dried, and then subjected to negative electrolysis in a nickel salt aqueous solution mainly composed of nickel sulfate. And a step of forming a microporous 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 the sealed alkaline storage battery is expressed by the following equation.

Cd + 1 / 2O ₂ + H ₂ O → Cd (OH) ₂ (1) That is, the reaction is at the three-phase interface of the gas phase, the liquid phase, and the solid phase, and the more the metal cadmium and oxygen gas are in contact, the more active the reaction It is. However, since the paste-type cadmium negative electrode has low conductivity of the active material and the charging reaction gradually proceeds from the vicinity of the core toward the electrode surface, metal cadmium is generated near the surface of the electrode away from the conductive core. It is hard to be done. On the other hand, in an electrode in which a metal nickel thin film is provided on the surface of an active material layer of a paste-type cadmium negative electrode, metal cadmium generated around the conductive core is reduced to a metal nickel thin film layer having the conductivity of the active material. When it reaches, metal cadmium is preferentially deposited from the reached portion along the metal nickel gradually over the entire vicinity of the negative electrode surface, and as a result, the oxygen gas absorbing ability is improved.

Further, when the negative electrode is discharged in a high temperature region of 40 ° C. or more, the discharge product elutes as cadmium ions, diffuses in the alkaline electrolyte, and precipitates without returning to the original state when charged next time. This is promoted by repeated charge / discharge cycles, and the negative electrode is remarkably deformed to lower the utilization factor, and the growth of dendrites or the like causes the active material to penetrate into the separator to cause a short circuit or shorten the life. However, by forming extremely fine metallic nickel particles as a dense layer on the electrode surface layer, it is possible to prevent the dissolution and diffusion of discharge products in a high-temperature region, and the charge / discharge cycle life of the battery is greatly increased. To improve.

However, when a thin layer of metallic nickel is formed on the surface of the paste-type cadmium negative electrode active material by electrolytic plating, the conductivity of the active material surface is low, so that the overvoltage of nickel deposition increases and hydrogen gas is discharged from the active material surface. Occur.
As a result, the vicinity of the cadmium active material surface becomes alkaline, and a nickel compound such as nickel hydroxide precipitates.
When this nickel compound is mixed into the metal nickel thin film layer, the conductivity of the nickel compound is low, so that the deposition reaction of the metal nickel tends to be nonuniform, and the metal nickel thin film layer becomes nonuniform. As a result, the distribution of metal cadmium deposited near the negative electrode surface during the charging reaction becomes non-uniform, and the oxygen gas absorbing ability is not sufficiently improved. Further, there is a disadvantage that the charge / discharge cycle life in a high temperature region cannot be sufficiently improved.

However, in the present invention, by mixing conductive carbon powder or carbon fiber into the cadmium active material, the conductivity inside and on the surface of the active material layer is improved, and the current density becomes uniform when performing negative electrolysis. , Nickel deposition tends to be non-uniform.

Further, by adding a carbon powder or a carbon fiber having at least one of a carboxyl group, a carbonyl group and a quinone group as a surface functional group to the cadmium active material, the functional group is present on the cadmium active material surface. These functional groups are generally known as functional groups contained in brighteners that improve the uniform electrodeposition and smoothness of nickel plating. By forming a complex with nickel ions, the overvoltage of nickel deposition is reduced, A uniform nickel plating layer can be obtained. That is, according to the present invention, the conductivity of the cadmium active material layer can be improved, and at the same time, the overvoltage of nickel deposition can be reduced, so that the active material surface layer consisting essentially of cadmium oxide or cadmium hydroxide, which has low conductivity, has a metal surface. The nickel microporous thin film layer can be formed uniformly, and the oxygen gas absorbing ability and the charge / discharge cycle life in a high temperature region can be improved.

Example Carbon black having an average particle size of 0.5 μm as carbon powder was heated in oxygen at about 400 ° C. for 10 minutes to give carboxyl groups and carbonyl groups on the carbon black surface.
5:95 by weight ratio with cadmium oxide powder having an average particle size of about 1 μm
And a solution of polyvinyl alcohol in ethylene glycol is added and kneaded to form a paste. The paste was applied to a nickel-plated apertured steel plate having a thickness of 0.1 mm as a conductive support and dried at about 140 ° C. for 30 minutes to obtain a cadmium active material coated plate having a thickness of about 0.5 mm. Next, this cadmium active material coated plate was subjected to a current density of 0.1 A / cm ² at a current density of 0.1 A / cm ² in a mixed solution of nickel sulfate + nickel chloride having a total amount of 1 mol / pH adjusted to PH3 and a liquid temperature of about 25 ° C. After performing a negative electrolysis for a minute to form a nickel plating layer on the surface of the cadmium active material, the substrate was washed with water and dried. Next, the electrode plate was charged to about 40% of the theoretical capacity in an alkaline solution, washed with water, dried, and cut into a predetermined size to obtain a cadmium negative electrode for an alkaline storage battery. This negative electrode is referred to as a.

In the same manner as above, an electrode using carbon black having no carboxyl group or carbonyl group on the surface without heat treatment in oxygen was applied to the electrode b, and only nickel plating was performed without adding carbon black. The electrode thus obtained was also referred to as a comparative product, in which carbon black was not added and nickel plating was not performed, and only the electrode charged in an alkaline solution was designated as d.

The above four types of cadmium negative electrodes were combined with a sintered nickel positive electrode to produce a sealed nickel cadmium storage battery, and a cycle life test and a battery internal pressure test during overcharge were performed.

The cycle life characteristics are 4.5 at 50 ° C and 1 / 3C equivalent current.
The battery was charged for a period of time, and was repeatedly charged and discharged to completely discharge with a resistance load equivalent to 1 C, and the capacity was reduced by the cycle.

In addition, the battery internal pressure characteristics at the time of overcharge were evaluated by the internal pressure of the battery when overcharged at 20 ° C. with a current equivalent to 2 C.

FIG. 1 shows the relationship between the capacity retention ratio and the number of charge / discharge cycles when the capacity of the first cycle is 100. In the figure, A shows a battery using the cadmium negative electrode a according to the present invention, B and C show batteries using comparative negative electrodes b and c, and D shows a battery using comparative negative electrode d.

As is clear from these results, the cycle life characteristics of a, b, and c, in which a nickel-based thin layer was provided on the surface of the electrode plate, were significantly improved as compared with Comparative Example d. It can be seen that the life time of a to which carbon black containing a carbonyl group is added is further improved.

As described above, by forming extremely fine metallic nickel particles as a dense layer on the electrode surface layer, dendrite growth outside the negative electrode due to dissolution and precipitation of the active material is prevented, and the life characteristics are improved. However, in Comparative Examples b and c,
Since the formation of the nickel fine particle layer is non-uniform, dendrite growth occurs in a portion where the nickel layer is small, resulting in a reduction in the life, and the life characteristics are inferior to those of a according to the present invention.

FIG. 2 shows a change in the internal pressure of the battery when charged at 20 ° C. with a current equivalent to 2 C. The discharge is 20
The test was performed at a temperature of 1 ° C and a current equivalent to 1C.

A negative electrode surface provided with a nickel microporous thin film layer a, b,
c has better internal pressure characteristics than Comparative Example d. Further, the battery A using the electrode a according to the present invention has further improved characteristics as compared with those using the comparative examples b and c. This is because, as described above, according to the present invention, a nickel microporous thin film layer is formed very uniformly on the cadmium active material surface, so that the distribution of metal cadmium deposited near the negative electrode surface in the charging reaction is uniform. It is considered that gas absorption is efficiently performed and the internal pressure characteristics of the battery are improved.

In this example, carbon black was used as the carbon powder. However, even if activated carbon, artificial graphite, or carbon fiber was used as the other powder, the surface functional group was imparted by heating at a high temperature in an oxygen atmosphere. By dispersing the cadmium active material well, the same effect as in the present embodiment can be obtained.

The presence of carboxyl, carbonyl and quinone groups as surface functional groups was identified and confirmed by chemical analysis, X-ray spectroscopy, secondary ion mass spectrometry, and the like.

Effects of the Invention As described above, according to the present invention, by forming a very uniform microporous thin film layer of metallic nickel on the surface of a cadmium active material, it has a long life even in a high temperature region and has excellent gas absorption characteristics. Thus, a cadmium negative electrode for an alkaline storage battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a capacity retention ratio of a sealed nickel cadmium storage battery and a charge / discharge cycle, and FIG. 2 is a diagram showing a battery internal pressure during charge / discharge.

Continuation of the front page (56) References JP-A-1-146252 (JP, A) JP-A-63-146360 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4 / 24 H01M 4/26

Claims (1)

(57) [Claims] A mixture of an active material powder mainly composed of cadmium oxide or cadmium hydroxide and a carbon powder or carbon fiber having at least one of carboxyl group, carbonyl group and quinone group as a surface functional group is formed into a paste or a mixture thereof. A step of applying a cadmium active material-coated plate by applying the cadmium active material-coated plate as a sheet, and subjecting the cadmium active material-coated plate to negative electrolysis in a nickel salt aqueous solution mainly composed of nickel sulfate to form a cadmium active material surface Forming a microporous thin film layer of metallic nickel on a cadmium negative electrode for an alkaline storage battery.