JPH0680586B2 - Alkaline secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alkaline secondary battery using a nickel electrode as a positive electrode, and more particularly to improvement of the positive electrode.

[Conventional technology]

Conventionally, in an alkaline secondary battery using a nickel electrode as a positive electrode, nickel hydroxide as an active material, a conductive auxiliary material / active material holding material obtained by nickel-plating a steel fiber, and a cobalt powder are kneaded together with a binder, and a predetermined amount of this is kneaded. A nickel electrode was produced by molding in the above-mentioned shape (for example, Japanese Patent Application No. 60-39843).

Cobalt in the nickel electrode is added in order to improve the utilization rate of the active material in the charge / discharge cycle of the electrode, but since it is added in the powder state, the dispersion of cobalt in the electrode is unsatisfactory. There was a problem that it would be enough. Further, since the conductive additive and the cobalt powder are used separately and the desired amount of each of them is added, there is a problem that the filling efficiency of the active material is lowered.

[Problems to be solved by the invention]

The present invention solves the problem that the conventional alkaline secondary battery has a low packing density of the active material, has a large packing density of the active material, and has a positive electrode with a nickel electrode excellent in utilization rate of the active material. It is intended to provide an alkaline secondary battery having

[Means for solving problems]

The present invention provides a nickel electrode produced by mixing a fibrous conductive auxiliary material and an active material to hold the active material in a network formed by the entanglement of the fibrous conductive auxiliary material. As a material, a steel fiber plated with cobalt is used, and the function of the cobalt powder, which has been added separately from the conductive additive in the past, is also imparted to the conductive additive. Therefore, the volume occupied by cobalt in the electrode in the past can be replaced with the active material, and the packing density of the active material can be increased to obtain an electrode having a high electricity density.

In producing the nickel electrode, nickel hydroxide or nickel oxyhydroxide is used as the active material.

The base material of the conduction aid is steel fiber, which has a wire diameter of 10 to 150.
It is preferable that the particle size is 0.5 μm and the length is 0.5 to 10 mm because the dispersion is good at the time of kneading with the active material and the binder, and the “entanglement” between the fibers becomes dense. When this steel fiber is used, it is usually plated with nickel and then plated with cobalt for reasons of cost. However, cobalt plating may be directly performed on the steel fiber. Using steel fiber as the base material of the conductive additive as described above,
This is because steel is cheap and has high strength. However, since steel fiber may be corroded, nickel plating was conventionally used to prevent it, but in the present invention, a part or the front part of the nickel plating is replaced with cobalt plating to replace the conventional cobalt powder. That is, the conductive auxiliary material has the function of improving the utilization rate of the active material that the conventional conductive material has.

As described above, in the present invention, the steel fiber as a base material of the conductive auxiliary material (generally 10 to 55% by weight and 5 to 25% by volume of the electrode material by weight) occupying a large proportion in the electrode material. Since the surface of cobalt is plated with cobalt, the dispersion of cobalt in the electrode material is better and the surface area of cobalt is increased compared to the case where cobalt powder is added as in the conventional case, thereby increasing the amount of cobalt in the electrode material. The amount of cobalt to be added can be reduced as compared with the case where conventional cobalt powder is added, and as a result, the packing density of the active material can be increased and a nickel electrode with a high electricity density can be obtained. Become. Even if the surface of the steel fiber is plated with cobalt as described above, the effect of the conductive additive is not impaired because cobalt has good electric conductivity. The amount of plating applied to the amount of steel fiber is usually the same as the weight of steel fiber in order to obtain a uniform plated layer without pinholes.
It is preferably 10% by weight or more, and particularly preferably 15% by weight or more.

As the binder, for example, ethylene-propylene-ethylidene norbornel terpolymer (hereinafter referred to as sulfonated EPDM) which is sulfonated and then neutralized with a metal carboxylate, carboxymethyl cellulose, polytetrafluoroethylene, or the like is used. EPDM is preferable because it has a strong binding force. The amount of these binders used is usually preferably 1 to 10% by weight in the electrode material.

The nickel electrode is prepared by kneading the active material, at least the cobalt-plated steel fiber on the uppermost layer, and the binder liquid, and then mixing the kneaded product with a metal such as expanded metal or punching metal that is usually used for the purpose of reinforcement. It is performed by applying it to a porous body, making it a predetermined thickness with a roll or the like, and then drying.

The nickel electrode manufactured as described above can be used as a positive electrode of a secondary battery using an alkaline electrolyte, such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery. Then, in the case of a nickel-cadmium battery, the cadmium electrode may be prepared by holding the active material with a cobalt-plated steel fiber and a binder, like the nickel electrode.

〔Example〕

45 parts by weight of nickel hydroxide and a wire diameter of 10 ~
It is in the range of 150 μm, 50% or more of which is 25-45 μm
The length is in the range of 0.1 to 1 mm, and 50% by weight or more
Steel fibers of 0.2 mm or less are first plated with 10% by weight of nickel based on the weight of the steel fibers, and then with 5% by weight of cobalt based on the weight of the steel fibers. EP
1.5 parts by weight of DM (in this example, sulfonated EPDM having a sulfonation ratio of 5 mol% and neutralized with stearic acid) was previously added to 14.1 parts by weight of hexane and 0.9 parts of methyl alcohol.
Part by weight mixture (weight ratio of hexane and methyl alcohol)
15.0 parts by weight of a binder solution dissolved in 94: 6) was kneaded, 0.8 g of this was sampled, and applied to expanded nickel (size 15 mm × 15 mm) having a porosity of 60%. Then, this was passed through a roll having a gap of 0.2 mm to make the thickness constant, and then dried to prepare a nickel electrode. The theoretical amount of electricity of this electrode is
It was 54.7 mAh. After this nickel electrode was immersed in a 30 wt% potassium hydroxide aqueous solution for 24 hours, a cadmium electrode was placed as a counter electrode, and the nickel electrode was used as a positive electrode and the cadmium electrode as a negative electrode, and charging and discharging were repeated 5 times at a constant current of 25 mA. After that, when charged at 5mA for 15 hours and then discharged at 10mA, 53mAh
The amount of discharge electricity of was obtained. The utilization rate of the active material was about 97%. Then, charging / discharging was repeated at 25 mAh for 1 hour, and every 100 times, charging was performed at 5 mA for 15 hours and discharging at 10 mA was performed to obtain the utilization rate of the active material.

For comparison, according to the conventional method, 50 parts by weight of a conductive auxiliary material obtained by nickel-plating 15% by weight of the same steel fiber as that of the above-mentioned example with 5 parts by weight of cobalt powder separately from the conductive auxiliary material. Nickel electrodes having the same dimensions were produced by adding the same amount of other active materials and the same amount of binder.
The theoretical electricity of this nickel electrode was 48 mAh. This nickel electrode was immersed in a 30 wt% potassium hydroxide aqueous solution for 24 hours as in the above-mentioned example, and then a cadmium electrode was placed as a counter electrode. The nickel electrode was used as a positive electrode and the cadmium electrode was used as a negative electrode, and charged / discharged at 25 mAh for 1 hour. The above operation was repeated, and every 100th cycle, the battery was charged at 5 mA for 15 hours and discharged at 10 mA to obtain the utilization rate of the active material.

FIG. 1 shows changes in the utilization rate of the active material according to charge and discharge of the battery of the above example and the battery using the nickel electrode prepared according to the conventional method as the positive electrode. In FIG. 1, A is the battery of the embodiment of the present invention, B is the conventional battery, and the utilization rate of the active material is represented by the electricity density.

As shown in FIG. 1, in the battery A of the example of the present invention, although the amount of cobalt used was about half that of the conventional battery B, the utilization rate of the active material changed with charging and discharging. As in the case of B, it was small, and the electricity density at each charge / discharge cycle number was higher than that of the conventional battery B.

〔The invention's effect〕

As described above, according to the present invention, by using a steel fiber coated with cobalt as the conductive auxiliary material, the conductive auxiliary material has two functions of improving the conductivity and the utilization rate of the active material. In addition, the addition of cobalt powder, which has been added separately from the conduction aid to improve the utilization rate of the active material for the charge / discharge cycle, becomes unnecessary, thereby increasing the packing density of the active material in the nickel electrode and The quantity density of electricity could be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in utilization rate of an active material according to charging and discharging of a battery of an example of the present invention and a conventional battery. A ... Batteries of the examples of the present invention, B ... Conventional batteries

Claims (3)

[Claims] 1. An alkaline secondary battery using a nickel electrode as a positive electrode, wherein the positive electrode comprises an active material held by a cobalt-plated steel fiber and a binder. 2. The steel fiber has a wire diameter of 10 to 150 μm.
The alkaline secondary battery according to claim 1, wherein m and the length are in the range of 0.5 to 10 mm. 3. An alkali according to claim 1 or 2, wherein the binder is an ethylene-propylene-ethylidene norbornel terpolymer which has been sulfonated and then neutralized with a metal carboxylate. Secondary battery.