JPH0566714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a paste-type cadmium cathode used as a cathode for alkaline storage batteries such as nickel-cadmium storage batteries.

<Prior Art> Paste-type cadmium cathodes are widely used industrially as cadmium cathodes used in nickel-cadmium storage batteries and the like, as the process is relatively simple and manufacturing costs are low. This type of paste-type cadmium cathode uses an active material such as cadmium oxide powder or cadmium hydroxide powder as the main raw material, reinforcing fibers to give the electrode plate strength, and resins such as methylcellulose or CMC to bind them together. of,
The paste-like active material thus formed by kneading with a solvent is applied to both sides of a conductive core made of a perforated steel plate with nickel plating, etc. After drying, it is left as it is or subjected to chemical conversion treatment, and then the battery model is determined. It is obtained through the following steps: cutting it into the required dimensions according to the requirements.

<Problems to be Solved by the Invention> Incidentally, as described above, although the resin contained in the paste active material is added in a sufficient amount to bind the cadmium powder, reinforcing fibers, etc. to each other, There is naturally a limit to the amount added from the viewpoint of ensuring discharge capacity, etc., and the binding force of such a resin alone cannot sufficiently bind the conductive core having a metal surface and the active material layer. For this reason, although a structure is adopted in which the active material layer is held on the surface of the conductive core by binding the active material layers on both sides together through the pores of the porous conductive core, the active material layer and the conductive core Since the binding properties of the portions where they are in direct contact with each other remain unchanged, the active material layer may partially fall off from the conductive core when the unformed electrode plate is cut into the size of a battery.

In addition, since the binding between the active material layer and the conductive core is poor, the electrical contact resistance between the two increases. In the initial stage of charging, the potential of the electrode plate reaches the hydrogen generation potential and the hydrogen gas generation reaction progresses, resulting in low energy efficiency of charging electricity and poor charging efficiency during initial charging.

<Means for Solving the Problems> The method for producing a cadmium cathode of the present invention includes a conductive bond made of a conductive material containing at least one of metal powder or carbon powder and a binding resin on the surface of a conductive core. The gist is to apply an adhesive, and then apply a paste-like active material made of cadmium oxide or cadmium hydroxide as a main raw material, in which the conductive binding property is combined with a solvent that can be dissolved or dispersed. shall be.

Metal powders include copper and silver powders, carbon powders include carbon black, acetylene black, etc.
Examples include graphite.

Further, examples of the binding resin include polyvinyl alcohol, methylcellulose, CMC, and the like.

<Function> As in the above means, by first forming a layer made of a conductive binder on the surface of the copper electric core, and then forming a layer of paste-like active material thereon, conductive The presence of the binder significantly improves the binding properties between the surface of the conductive core and the active material layer. Also,
The electrical contact resistance between the active material layer and the surface of the conductive core is extremely low due to the improved binding between the active material layer and the conductive core and the presence of the conductive binder between them. Therefore, the hydrogen gas generation reaction is suppressed as much as possible, and the charging reaction starts extremely smoothly.

In addition, as a solvent for paste-like active materials,
Since we used a conductive binder that can be dissolved or dispersed, it can be used regardless of whether the conductive binder is dry or not.
After applying the paste-like active material, the conductive binder becomes in a swollen state, and the paste-like active material and the conductive binder are reliably bound together.

In addition, as a conductive material contained in the conductive binder,
By using a material (such as carbon) having a higher hydrogen overvoltage than the metal (such as nickel) forming the surface of the conductive core, the effect of suppressing the hydrogen gas generation reaction as described above is further increased.

<Example> As shown in Fig. 1, acetylene black (conductive material), polyvinyl alcohol (binder), and water were applied to both sides of a conductive core 1 made of a nickel-plated porous steel plate with a thickness of 0.08 mm. A conductive binder 12 in which solvents (solvents) were mixed in a weight ratio of 1:1:10 was applied. Next, 100 parts by weight of cadmium oxide (active material), 1 part by weight of synthetic fiber (active material reinforcing agent), 0.7 parts by weight of hydroxypropyl cellulose (active material binder) and 28 parts by weight of water were mixed to form a paste. The active material 3 was applied to the surface of the conductive binder 12 to form an electrode plate with a thickness of about 0.75 mm. After drying this electrode plate at 90° C. for 30 minutes, it was press-pressed to a thickness of 0.70 mm to produce electrode plate A according to the present invention. The amount of conductive binder applied is approximately 0.01mm thick after drying.
And so.

On the other hand, the conventional electrode plate B was prepared using the same process except that the conductive binder as described above was not applied, and instead of applying the conductive binder, a 10% aqueous solution of polyvinyl alcohol that did not disperse the conductive material was applied. Comparative electrode plates C were each manufactured using the same process except for the following steps.

The following tests 1 and 2 were conducted on the above three plates A to C.

Test 1 The electrode plates A to C were cut into predetermined dimensions using a punching press, and the state in which the active material of each electrode plate fell off during cutting was checked. As a result, while there was no such falling off in electrode plates A and C, in electrode plate B, as shown in FIG. ), the paste-like active material 3 was observed to come off. This is considered to be due to the fact that in the electrode plates A and C, the presence of polyvinyl alcohol increased the mechanical adhesive strength between the conductive core surface and the paste active material.

Test 2 Electrode plates A to C, each cut into 3cm x 5cm dimensions, were immersed in a 20% by weight aqueous solution of potassium hydroxide, charged at 200mA for 2 hours, then discharged at 200mA, and the amount of electricity charged (200mA ×2 hours = 400mAH)
The charging efficiency (%) determined from the ratio of the discharge capacity to the discharge capacity {(charged electricity amount/discharge capacity)×100} was calculated. The results are shown in the table below, and the discharge efficiency of plate A according to the present invention was about 10% higher than that of plates B and C. Plate A B C Charging Efficiency (%) 85 78 77 In addition, sufficiently overcharge Plate A to C separately (200 m
When the discharge capacity of each plate was measured after 5 hours), it was found that each plate had a discharge capacity of 700 mAH. Therefore, it can be seen that the charging efficiency shown in the above table is the charging efficiency of each electrode plate at the initial stage of charging. The reason that the charging efficiency of plate A is higher than that of plates B and C is that in plate A, the electrical connection between the conductive core and the paste-like active material is good, and hydrogen gas is generated in the early stage of charging. This seems to be due to the fact that it has been significantly suppressed.

In the above examples, the paste active material was applied without drying after applying the conductive binder to the surface of the conductive core, but after applying the conductive binder, it was dried. However, even when a paste-like active material is applied after that, the conductive binder swells again due to the solvent in the paste-like active material, and as a result, this and the paste-like active material are reliably bound. Needless to say, similar effects can be obtained.

<Effects of the Invention> According to the method for producing a cadmium cathode of the present invention configured as described above, the interposition of the conductive binder significantly improves the adhesion between the conductive core and the active material layer. , it is possible to increase the mechanical adhesion strength between the two, reliably prevent the active material from falling off when cutting the unformed electrode plate, and at the same time reduce the electrical contact resistance between the conductive core and the active material layer. This reduction improves the energy efficiency at the time of initial charging in the chemical formation process, and has the effect of improving charging efficiency.

Furthermore, since the solvent used for the paste-like active material is one in which the conductive binder can be dissolved or dispersed, there is an advantage that binding with the conductive binder can always be performed reliably.

In addition, since the energy loss during the initial charging of the cadmium cathode mainly appears as hydrogen gas generation at the start of charging, it is recommended to use a conductive material in the conductive binder that has a higher hydrogen overvoltage than the conductive core surface structure. If used, it becomes more difficult to generate hydrogen gas, which reduces energy loss and further improves charging efficiency during initial charging.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a cadmium cathode manufactured using the present invention, and FIG. 2 is a perspective view showing a state in which the cadmium cathode is cut by a conventional method. 1... Conductive core, 2... Conductive binder, 3...
Paste active material.

Claims (1)

[Claims] 1. A conductive binder consisting of a conductive material containing at least one of metal powder or carbon powder and a binder resin is applied to the surface of the conductive core, and cadmium oxide is applied on the surface of the conductive core. and cadmium hydroxide as the main raw materials,
A method for producing a cadmium cathode, comprising applying a paste-like active material prepared by kneading the conductive binder with a solvent in which it can be dissolved or dispersed. 2. The manufacturing method according to claim 1, wherein the hydrogen overvoltage of the conductive material is larger than the hydrogen overvoltage of the material constituting the surface of the conductive core.