JP3173775B2 - Paste nickel positive electrode and alkaline storage battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a paste-type nickel positive electrode and an alkaline storage battery (for example, a nickel-cadmium storage battery, a nickel-metal hydride storage battery) provided with the paste-type nickel positive electrode.

[Problems to be Solved by Conventional Techniques and Inventions] Pasted nickel electrodes have many advantages over conventional sintered nickel electrodes, such as higher capacity and lower cost of production. In recent years, the demand has been increasing. At present, the mainstream of paste-type nickel electrodes is a method using a sponge-like metal porous body or a fibrous metal porous body for an electrode substrate. The sponge-like porous metal body is mainly obtained by coating the surface of a sponge-like resin with an alkali-resistant metal by a method such as electrodeposition or vapor deposition, and then thermally decomposing the resin component. It is obtained by a method in which a metal fiber obtained by chattering and shaking a metal ingot having mainly alkali resistance is formed into a nonwoven fabric and sintered. In addition, as shown in JP-B-48-25149 and JP-A-61-208756, the surface of a fibrous organic material is coated with an alkali-resistant metal by an electrodeposition or vapor deposition method and then thermally decomposed. There is a felt-like porous metal body that can be obtained by heating.

A comparison of the two types of substrates made of a sponge-like metal porous material and a fibrous metal porous material which are widely used among the above three types shows that a paste-type nickel electrode using a sponge-like metal porous material as an electrode substrate is first used. However, there is a disadvantage that the degree of capacity reduction particularly when a large current discharge is performed is more remarkable than that using a fibrous metal porous body.

This is largely due to the low current collecting performance caused by the sponge shape. Sponge-like porous metal body has a diameter of 500
Spherical or nearly spindle-shaped voids of ~ 600 microns exist continuously, and the rest is made up of metal, so the diameter of each metal grid is not uniform . Therefore, in a large current discharge, the diameter of the narrowest part defines the electron conductivity,
When compared at the same porosity, the electrical resistance tends to be higher than that of the fibrous metal porous body. In addition, the active material in the center of the spherical or substantially spindle-shaped void has a distance to the nearest substrate of 250 to 300 microns and a large reaction resistance during charge and discharge, which causes a decrease in capacity during large current discharge. Is considered to be significant.

On the other hand, in the case of a paste-like nickel positive electrode using a fibrous metal porous body as an electrode substrate, the rate at which the metal grid formed when spirally wound penetrates through the separator and contacts the counter electrode to cause an internal short circuit failure Has a disadvantage that it is significantly higher than that of a sponge-like porous metal body. The cause is considered to be that the outer diameter is as thin as 10 to 20 microns because one metal grid is formed by cutting, which facilitates penetration between separator fibers.

The present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to provide a paste-type nickel positive electrode that has a small capacity decrease at the time of large current discharge and a small internal short-circuit defect at the time of winding. .

Another object of the present invention is to provide an alkaline storage battery provided with a paste-type nickel positive electrode having a small internal short-circuit failure at the time of winding and having a reduced capacity reduction during large-current discharge.

[Means for Solving the Problems] The paste-type nickel electrode according to the present invention is obtained by coating a surface of a felt-like organic material with an alkali-resistant metal, and then thermally decomposing the organic material. In a paste-type nickel positive electrode in which a randomly arranged felt-like metal porous body is used as an electrode substrate and filled with a paste-like active material containing nickel hydroxide as a main component, the felt-like metal porous body has an effective gap. Rate 85-99
%, The average outer diameter of the hollow metal fibers is in the range of 30 to 70 μm, and the average distance between adjacent hollow metal fibers is 100 to 4%.
It is characterized by being in the range of 00 μm.

The alkaline storage battery according to the present invention is obtained by coating the surface of a felt-like organic material with an alkali-resistant metal, and then thermally decomposing the organic material, and forming a felt-like metal porous body in which hollow metal fibers are randomly arranged. Electrode board,
In an alkaline storage battery provided with a paste-type nickel positive electrode which is filled with a paste-like active material containing nickel hydroxide as a main component, the felt-like metal porous body has an effective porosity of 85 to 99% and a hollow metal. The average outer diameter of the fiber is 30-70
μm, and the average interval between adjacent hollow metal fibers is in the range of 100 to 400 μm.

[Operation] First, in order to suppress a decrease in capacity at the time of large current discharge, it is desirable that the average distance between the active material and the substrate is as small as possible.
Alternatively, if the number is the same, it is advantageous that the hollow metal fibers are uniformly distributed. Its value is at least 400
It is desirable that the particle size is not more than micron, but if it is too small, the ratio of voids that can be filled with the active material (hereinafter referred to as effective porosity) is reduced, so that the range of 100 to 400 microns is practically appropriate.

Further, in order to prevent the penetration of the separator by the hollow metal fiber, it is desirable that the outer diameter of the hollow metal fiber is as large as possible. This value is desirably at least 30 microns, but if it is excessively large, the effective porosity is reduced as described above, so that the range of 30 to 70 microns is practically appropriate. However, even within the above range, depending on the combination, the effective porosity is insufficient and the high capacity which is the original advantage of the paste type nickel positive electrode is impaired, or conversely, the porosity becomes so large that it cannot be used in terms of strength and the like. In some cases,
Practically, it is desirable that the effective porosity is 85 to 99%.

As the shape of the electrode substrate that satisfies these requirements, a fibrous metal porous material is more suitable than a sponge-like metal porous material in that the outer diameter of the metal grid and the spacing between adjacent metal fibers are uniform. I have. However, metal fibers formed by cutting have a problem that the outer diameter cannot be increased,
It is preferable that the surface of the above-mentioned felt-like organic material is coated with an alkali-resistant metal by a method such as electrodeposition or vapor deposition because the outer diameter can be freely adjusted. Examples of the organic material at that time include polyethylene, polyamide, and carbon fibers formed into a nonwoven fabric with an appropriate binder. However, since the organic material, particularly carbon, in the electrode has a negative effect on the self-discharge characteristics of the nickel positive electrode, etc.After coating the alkali-resistant metal by the above-mentioned electrodeposition or vapor deposition, it is necessary to thermally decompose and remove the organic material. desirable.

[Example] As a felt-like organic material, a material obtained by forming a pitch-diameter carbon fiber having an outer diameter of 13 microns into a felt shape using a binder was used. After coating the surface with nickel by electrodeposition, first heat it in the presence of oxygen to decompose the carbon,
Subsequently, a heat-annealing operation was performed in a reducing atmosphere to obtain a felt-like porous metal body. Using this felt-like porous metal body as an electrode substrate, 90 parts by weight of nickel hydroxide, 10 parts by weight of cobalt hydroxide, and 0.
5 parts by weight, filled with a paste-like active material consisting of 35 parts by weight of water, dried at a temperature of 80 ° C to a constant weight, and then pressed to a predetermined thickness by a roller press, the paste nickel of the present invention A positive electrode was obtained. In the process of producing the felt-like porous metal body, the outer diameter of the hollow metal fibers and the distance between adjacent hollow metal fibers were changed by adjusting the amount of carbon fibers and the amount of electricity supplied during electrodeposition. The values were calculated for the finished electrode and were in the range of 20-100 microns and 50-500 microns, respectively. Table 1 shows the effective porosity of the produced paste-type nickel electrode, and Table 2 shows the packing density per volume.

In the table, white outlines, particularly the upper right part, indicate locations where the porosity was excessive and could not be used as an electrode substrate in terms of strength. In general, when the outer diameter of the hollow metal fibers is large and the interval between adjacent hollow metal fibers is small, the effective porosity and the packing density per volume tend to decrease.

The obtained paste-type nickel electrode was wound with a cadmium electrode as a counter electrode to produce a nickel cadmium battery of AA (AA) size. FIG. 1 is a cross-sectional view showing the structure of this nickel cadmium battery, in which 1 is a metal can, 2 is an electrode group obtained by winding a paste-type nickel positive electrode 3 and a cadmium negative electrode 4 of the present invention via a separator 5, 6 is a metal sealing plate and 7 is a positive electrode terminal. The internal short-circuit defect at the time of winding was 90% or more when the hollow metal fiber had an outer diameter of 30 to 100 microns, while it was about 50% when the diameter was 20 microns.
Met. Subsequently, after charging and discharging the nickel cadmium battery, the battery was discharged at a rate of 3 C with respect to the theoretical capacity, and the utilization at that time was measured. The results are shown in Table 3. As shown in Table 3, when the distance between adjacent hollow metal fibers exceeds 400 microns, the utilization tends to decrease. Further, Table 4 shows the value obtained by multiplying the packing density per volume in Table 2 by the 3C discharge utilization rate in Table 3, that is, the effective capacity per volume.

In Table 4, the condition that the capacity per volume is large and the yield rate at the time of winding when producing a battery is high is such that the average outer diameter of the hollow metal fibers is 30 to 70 microns and the average distance between adjacent hollow metal fibers. Is in the range of 100-400 microns.

However, even in this range, the volume per volume is relatively small, which corresponds to the case where the effective porosity shown in Table 1 is less than 85%. If the effective porosity exceeds 99%, it cannot be used as an electrode substrate in terms of strength. Therefore, those having an effective porosity in the range of 85 to 99% are preferable.

At the same time, a sponge-like metal porous body having a continuous substantially spindle-shaped space with a diameter of 500 μm and a fibrous metal porous body with an outer diameter of about 20 μm per metal grid are used as electrode substrates, respectively. Produced a paste-type nickel positive electrode and a nickel cadmium battery in the same manner as in the Example. The one using a sponge-like porous metal had a utilization rate of 65% at 3c discharge and a felt-like porous metal. Showed lower results than those using. In the case of using the fibrous metal porous body, the yield rate after the internal shortening test at the time of winding was about 40%, which was also lower than that of the felt-like one.

[Effects of the Invention] As described in detail above, according to the present invention, there is provided a high-performance paste-type nickel positive electrode which has a high capacity even during a large current discharge and has few internal short circuit defects during winding. And its industrial value is great.

Further, according to the present invention, it is possible to provide an alkaline storage battery including a high-performance paste-type nickel positive electrode with few internal short-circuit defects at the time of winding and having a high capacity even when discharging a large current.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a nickel cadmium battery using the paste nickel positive electrode of the present invention. DESCRIPTION OF SYMBOLS 1 ... Metal can 2 ... Electrode group 3 ... Paste nickel positive electrode 4 ... Cadmium negative electrode 5 ... Separator 6 ... Metal sealing plate, 7 ... Positive electrode terminal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Kunihiko Miyamoto Inventor Toshiba Battery Co., Ltd. 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo (56) References JP-A-55-30180 (JP, A) JP-A-61-76686 (JP, A) JP-A-56-159066 (JP, A) JP-A-62-15764 (JP, A) JP-A-62-12067 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01M 4/80

Claims (2)

(57) [Claims] An electrode substrate is obtained by coating a surface of a felt-like organic material with an alkali-resistant metal and then subjecting the organic material to thermal decomposition to obtain a felt-like metal porous body in which hollow metal fibers are randomly arranged. In a paste-type nickel positive electrode obtained by filling a paste-like active material containing nickel hydroxide as a main component, the felt-like metal porous body has an effective porosity of 85 to 99%, which is outside the average of hollow metal fibers. A paste-type nickel positive electrode having a diameter in the range of 30 to 70 µm and an average distance between adjacent hollow metal fibers in the range of 100 to 400 µm. 2. An electrode substrate comprising a felt-like organic material which is obtained by coating the surface of a felt-like organic material with an alkali-resistant metal and then thermally decomposing the organic material, wherein hollow metal fibers are randomly arranged. In an alkaline storage battery provided with a paste-type nickel positive electrode obtained by filling a paste-type active material containing nickel hydroxide as a main component, the felt-like metal porous body has an effective porosity of 85 to 99%,
The average outer diameter of the hollow metal fibers is in the range of 30 to 70 μm, and the average distance between adjacent hollow metal fibers is 100 to 400 μm
Alkaline storage battery characterized by the following.