JPH0456066A - Electrode for sealed type nickel cadmium accumulator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sealed nickel-cadmium storage battery and its electrodes.

Conventional techniques There are three types of electrodes for nickel-cadmium storage batteries: pocket type, sintered type, and paste type.

In the pocket type, a pocket is made of a nickel plate with holes or a nickel plated iron plate, and the active material, introduction material, etc. are placed in the pocket and used as an electrode. Such electrodes are commonly used in open nickel cadmium storage batteries. The sintering method is an electrode obtained by sintering powdered nickel to form a porous body, and filling the porous body with an active material chemically or electrochemically.

The paste type electrode is obtained by applying a paste of active material, conductive material, etc. to nickel or nickel-plated punched iron metal and drying it. The electrodes used in sealed nickel-cadmium storage batteries are sintered or pasted.

Only about 60% of the active material can be filled. Therefore, it is difficult to increase the packing density of the active material. Paste-type electrodes are electrodes in which a paste of active material, conductive material, etc. is applied and dried, so it is possible to almost eliminate the voids that cannot be filled like in sintered-type electrodes, and it is possible to obtain electrodes with high packing density. . However, paste type electrodes have a problem in that the active material often falls off because the strength of the active material is weaker than that of sintered type electrodes. A solution to this problem would be to increase the thickness of the separator, but this would reduce the volume of electrodes that can be filled into the battery can, making it difficult to achieve the high packing density of the paste method. I can't say that.

Means for Solving the Problems In view of the above points, the present invention arranges a sheet-like current collector on both sides of a layer of active material, conductive material, etc., and has a highly packed structure in which the active material hardly falls off. density electrodes can be obtained.

On the other hand, the charging and discharging reactions at nickel electrodes and cadmium electrodes are as shown in the following equations (1) and (2).
++e-+-→Cd+20H (21 For this reason, the current collector must not be a complete sheet, but must have holes through which the electrolyte can enter and exit the active material layer. In particular, the electrolyte must be active through the holes in the current collector. Because it enters the material layer and diffuses during charging and discharging,
It is desirable that the current collector has a porosity of 50 to 60%.

Further, the size of the hole in the current collector is desirably one fin or less in view of the charging characteristics of the active material layer. Furthermore, in order to improve the adhesion between the active material layer and the current collector, the surface of the current collector on the active material side is subjected to an uneven treatment, thereby improving high rate discharge performance.

Furthermore, in the case of a wound electrode, since stress is applied to one current collector during winding, it is preferable to use a current collector that has some flexibility, such as foam metal or felt.

It is possible to obtain an electrode having a high packing density and having an electrode strength that prevents the active material from falling off.

Examples Example 1 The results of a comparison of the packing density of the active material of a sintered cadmium electrode and a paste cadmium electrode produced by a conventional manufacturing method and a cadmium electrode according to the present invention are shown in m 11;. Here, the active material composition of the conventional paste type cadmium electrode and the active material composition of the cadmium electrode according to the present invention are the same. As a result, it was possible to obtain a cadmium electrode according to the present invention with a packing density equivalent to that of a paste-type cadmium electrode. The active material was dropped from a height of 5 ornI, and the amount of the active material dropped was measured. The results are shown in Table 2.

The amount of shedding of the cadmium electrode according to the present invention is about 175 compared to that of the paste-type cadmium electrode, and the effect of the surface being covered with the current collector is clearly visible.

Table 1 Table 2 Example 2 FIG. 1 shows the results of comparing the porosity of the current collectors.

When the aperture ratio is 50% and 60%, the ratio of 3 cmA discharge capacity to 2 cmA discharge is about 80%, but when the aperture ratio is 65%. At 40%, the ratio drops to about 70%. The reason for this is thought to be that at a porosity of 40%, the scattering of the electrolyte is prevented, and at a porosity of 65%, the conductivity of the current collector decreases.

Example 3 The aperture diameter of the current collector was studied. FIG. 2 shows the relationship between the aperture diameter of the current collector and the battery internal pressure when charged for 90 minutes at cmA. When the opening diameter is 1W or less, the internal pressure is 4 to 6.
Kf/m, but above 1.3 wJJ, the internal pressure becomes 10 Kf/- or more.

As shown in Figure 3, as charging progresses, the current collector 1
0 If the opening diameter is 1m or less, metal cadmium 2° is also present in the opening.
This is thought to be due to the fact that it begins to generate.

A in Fig. 3 is the case where the opening diameter is 1.3 m, and B
The opening diameter is 1. Example 4, which is the case of Om. Using an electrode with a roughened current collector with a pore size of 50% and a pore diameter of 1 mm, the discharge capacity of 0.2 cmA was 3cn]A
The ratio of discharge capacity was compared. The results are also shown in FIG. Note that there was no difference in the 0.2 cmA discharge capacity due to the uneven treatment. The protrusions are made by plating for 10 μm protrusions, by sprinkling nickel powder on 20 μm and 4 μm protrusions and sintering them, and by thermal spraying for 100 μm protrusions.

The ratio of 7i￥ capacitance is about 80% when the unevenness treatment is 10ztm or less, but it is 86 to 88% when the unevenness treatment is 20μm or more.
It has been improved by %. The reason for this is thought to be that the adhesion between the active material and the current collector is improved.

Example 5 When using the electrode proposed by Akira in a flat type battery, there is no problem even if the same current collector is used on both sides of the active material), but when making this into a cylindrical battery, The drawback is that stress is applied between the active material and the core material, making them easy to separate. Table 3 shows the amount of active material during winding and unwinding.

Table 3 As can be seen from Table 3 above, a perforated plate with an uneven treatment is also effective, but the amount of active material falling off is 10 to 2.
0% is not practical. In addition, when one side of the current collector is made of felt or foam metal, which easily absorbs stress, the amount of active material falling off is less than a few percent. This shows that the method using is effective.

Effects of the Invention As described above, according to the present invention, an electrode with high strength can be obtained without reducing the packing density of the active material, and by processing the current collector for holes, irregularities, etc. ,
It has great industrial value, as it can improve charging and discharging characteristics.

4. Brief explanation of 1NIil Figure 1 is a curve diagram showing the relationship between the aperture ratio of the current collector and Q, and the ratio of 3cmA discharge capacity I to 2cmA discharge capacity, and Figure 2 is a curve diagram showing the relationship between the aperture diameter of the current collector and l A curve diagram showing the relationship between battery internal pressure when charged for 90 minutes at cmA, and Figure 3 is a schematic diagram showing the difference in how charging occurs depending on the aperture diameter. shows the case where the opening diameter is 1.0 mm. The fourth example is a curve diagram showing the relationship between the size of the protrusion of the current collector and the ratio of 3 cmA discharge capacity to 020 mA discharge capacity 1.

Claims (4)

[Claims] (1) An electrode for a sealed nickel-cadmium storage battery in which current collectors are placed on both sides of an active material layer, characterized in that the current collector has a porosity of 50 to 60% and an opening diameter of 1 mm or less. Electrodes for sealed nickel-cadmium storage batteries. (2) The electrode for a sealed nickel-cadmium storage battery according to item 1 above, characterized in that protrusions are formed on the surface of the active material layer of the current collector. (3) The size of the protrusions on the active material layer surface of the current collector is 20 to 10
The electrode for a sealed nickel-cadmium storage battery according to item 2 above, characterized in that the electrode has a diameter of 0 μm. (4) An electrode for a sealed nickel-cadmium storage battery, characterized in that one current collector of the wound group has protrusions formed on the surface of the active material layer, and the other current collector is made of foamed nickel or nickel felt.