JPS6359228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sintered substrate for an alkaline storage battery.

Conventionally, methods for producing sintered substrates for alkaline storage batteries include a dry method and a wet method. In the dry method, a wire mesh or perforated plate made of nickel or iron as a core material and a powder of nickel or the like for sintering are arranged in a carbon frame and sintered in a reducing atmosphere. In the wet method, an aqueous slurry of sintering metal powder and an adhesive such as CMC is applied to the core material, dried, and sintered in a reducing atmosphere at 700 to 900°C. The dry method results in a slightly larger porosity of the sintered substrate than the wet method, but
Workability during manufacturing is poor, especially since continuous production is not possible, resulting in poor productivity. On the other hand, the wet method is superior in terms of productivity, but has the disadvantage of low porosity. Especially when applying slurry through a slit,
Since the fine nickel powder gathers near the slit during development, it has the disadvantage that the porosity near the substrate surface becomes small. Since a sintered substrate is used as an electrode by filling it with an electrode active material, the larger the porosity, the higher the capacity density, and the easier it is to fill, so various methods have been investigated to increase the porosity of the substrate. has been faced.

For example, in Japanese Patent Publication No. 52-15774, an attempt is made to increase the surface porosity by attaching combustible powder to the surface layer of a slurry obtained by a wet method and burning it off during sintering. Similarly, in Japanese Patent Publication No. 53-47492, sintering metal powder is attached to the slurry surface, and the porosity is increased by a mixed method of wet and dry methods. However, the porosity of the sintered substrate obtained by the wet method is generally around 70 to 78%, and although there is a slight increase in porosity due to an increase in surface porosity, it is difficult to create a substrate with higher porosity. Although it is possible, the process involves a powder adhesion step, which causes a decrease in productivity.

On the other hand, as shown in Japanese Patent Publication No. 37-8331, a method for obtaining an electrode substrate with extremely high porosity is to mix and sinter an expanding material that decomposes and expands near the sintering temperature, such as anhydrous magnesium salt or nickel salt. There is a method for manufacturing the substrate, but this method causes rapid decomposition, so when applied to slurry, the sintered layer may fall off from the core material, or the distance between the metal powders may be too large, resulting in low sintering strength. It's not a good thing to do.

In addition, as a method of obtaining a highly porous electrode substrate, a foamed polymer is sliced to a predetermined thickness, a conductive coating is applied to this, electrolytic plating is performed, and the polymer is then burned out to create a highly porous electrode substrate. There are some that yield a spongy porous substrate with a degree of pores. Similarly, a method of obtaining a spongy highly porous body by vibrationally filling a polymer foam with nickel powder and then sintering the same has been proposed. This method was developed by Guy Grespy et al.
Power Sources 7 (Research and
Development in Non-Mechanical Electrical
Power Sources (1979), but either method does not allow the core material to be placed inside the electrode substrate, so the strength of the substrate itself is weak.
Further, when used as an electrode, it is extremely difficult to take out the lead terminal, which is undesirable because there are many restrictions when manufacturing the electrode.

Furthermore, as shown in Japanese Patent Publication No. 53-8895, a highly porous spongy nickel porous body is obtained by molding a paste made by kneading nickel powder and resin balls, burning off organic matter, and then sintering it. be. In order to make a highly porous sintered substrate using this method, the volume of nickel powder is small, and most of the paste-like material is resin balls and adhesive. For this reason, even if nickel powder with a low apparent density is used, a highly porous sintered body cannot be produced unless resin spheres are mixed in at several times the volume of nickel. In addition, there are various active material filling methods, but in methods such as directly filling an active material paste into a porous substrate, the pore size of the porous body needs to be several tens to hundreds of microns; In order to obtain a large pore size, it is necessary to mix resin spheres with the required pore size, but if the sphere diameter becomes too large, the nickel powder and spheres will separate in the paste or get stuck in the slit, so the resin There is a natural limit to the size of the ball. In this way, a large amount of burnt material is required to obtain the intended sintered substrate, and there are restrictions on the hole diameter of the sintered substrate, so it cannot be said to be a method with good productivity.

In addition, a method of mixing air bubbles into a nickel slurry was shown in Japanese Patent Publication No. 14737/1982, but it was difficult to keep the air bubbles uniform over time.
This is not preferable since there are problems such as variations in bubble diameter due to differences in slurry viscosity.

The present invention eliminates the drawbacks of the above-mentioned substrate manufacturing method, and provides a highly porous and spongy sintered substrate at a low cost using almost the same process as the conventional wet method sintered substrate manufacturing method. The purpose is to provide an electrode plate with high capacity density.

The present invention involves applying a slurry obtained by mixing thermally expandable microcapsules containing low-boiling hydrocarbons, nickel powder, and an adhesive such as CMC to a porous metal core material such as a perforated iron plate through a slit. rear,
A three-dimensional spongy porous body having a core material is obtained by drying at a predetermined temperature taking into consideration the expansion ratio, etc., and simultaneously foaming the microcapsules and then sintering them. In this method, the thermally expandable microcapsules have different boiling points depending on the hydrocarbon in the encapsulating agent and different softening points depending on the resin used for the outer shell, so the expansion ratio varies depending on the temperature during drying. Therefore, by controlling various conditions, closed-cell skeletons of various sizes are formed, and the nickel powder trapped between the cells fuses into a spongy shape during sintering, simultaneously expanding the microcapsules and CMC. and other adhesives are burned out,
The result is a highly porous sintered substrate. This effervescent microcapsule has a resistance of 20 to 70% under atmospheric pressure.
It has a foaming ratio of twice as much, but if drying of the adhesive, such as CMC, takes priority, the foaming ratio decreases. Since the temperature is raised after the process, the foaming pressure is lower than the CMC membrane pressure, so foaming can be virtually prevented.

Examples of the present invention will be described below.

Example 1 100 parts by weight of carbonyl nickel powder (specific gravity 0.8 to 1.0 g/cc) as metal powder for sintering, 100 parts by weight of CMC aqueous solution with a concentration of 3% as adhesive, and mainly vinylidene chloride-acrylonitrile as foamable microcapsules. Three types of slurry were prepared by kneading 5 parts by weight, 10 parts by weight, and 15 parts by weight of particles with a particle size of 8 to 10 μ containing isobutane in the copolymer shell.
After applying this to a perforated steel plate (porosity 54%), it was heated at 120℃.
Dry for 20 minutes, followed by sintering at 920°C for 30 minutes,
Porous substrates A, B, and C each having a thickness of 0.7 mm were obtained.
In these sintered substrates, the foaming ratio was approximately 20 times, and the pore diameter was approximately 25 to 50 μm. The porosity was 92.5%, 95%, and 96.5%, respectively. A traced micrograph of the porous substrate thus obtained is shown in the figure. In the figure, the shaded area 1 is the sintered part of the nickel powder, and there are many small pores of several microns. In addition, the white areas 2 are pores with a pore size of several tens of microns generated by the foamable microcapsules.

Also, the substrates A, B, and C obtained in this way
and a conventional sintered substrate were filled with an active material using a 4 mol/a nickel nitrate aqueous solution using a commonly used chemical impregnation method to create a nickel positive electrode.As a result, the active material filling capacity of the conventional substrate was 360mAh/ cc
On the other hand, those using substrates A, B, and C according to the present invention have 420 mAh/cc, 450 mAh/cc, and 450 mAh/cc, respectively.
A plate with a capacity of 460 mAh/cc was obtained.

Further, although the microcapsules used in Example 1 are expected to expand approximately 50 times at 120° C. under atmospheric pressure, in reality, only an expansion ratio of approximately 20 times could be obtained. This is because it was dried at 120℃.
This is because the water in the CMC aqueous solution evaporated first at the boiling point (100°C), so the slurry dried before the microcapsules were sufficiently foamed.
In order to fully utilize the foaming ability of microcapsules, the following experiment was conducted.

Example 2 The conditions were the same as in Example 1, but using foamable microcapsules whose shell surfaces were colored black, slurries containing 5 parts by weight and 15 parts by weight of microcapsules were applied to the core material. After drying with an infrared heater, the material was sintered at 870°C to create a spongy porous substrate.
The porosity of the perforated plate produced in this way is
At 96.5% and 98%, the addition of 5 parts by weight was the same as the addition of 15 parts by weight of microcapsules in Example 1. Moreover, the pore diameter was about 50 to 100 microns. Note that heating with a far-infrared heater had the same effect.

A nickel positive electrode was prepared by filling the active material into the porous substrate prepared in Example 2 by sliding a paste consisting of nickel hydroxide powder, CMC aqueous solution, and nickel powder using the reciprocating motion of a spatula-like object. A plate with a capacity density of /cc was obtained. However, when the porosity was 98%, the substrate surface was destroyed when the active material was filled, and a sufficient amount of filling could not be obtained. In this example, microcapsules of 8 to 10 microns were used, but sintered substrates were obtained even when microcapsules of 100-odd microns were used. In addition, the encapsulating agent for the microcapsules was made with isobutane, but any combination of materials with a boiling point above room temperature that does not burn the adhesive and a material with a softening point close to that of the shell can be used. good.

As described above, the method for manufacturing a sintered substrate according to the present invention is as follows:
Highly porous sintered substrates can be easily produced by simply mixing a small amount of microcapsules containing low-boiling hydrocarbons into the slurry, without any changes to the conventional wet method sintered substrate manufacturing process. Porous substrates having various porosity and pore diameter can be obtained by simply changing the material of the microcapsules, the encapsulating agent, or the drying temperature. Furthermore, the present invention has a core material that cannot be obtained with the spongy porous substrate obtained by filling a foamed polymer with plating or metal powder by vibration, which has been widely used in the past, so it is strong and extremely strong. Since the plate lead can be easily taken out, it is extremely convenient to use it as an electrode plate. Further, according to the present invention, since the amount of foam used is small, there is an advantage that the amount of reducing gas used during sintering can also be reduced.

[Brief explanation of the drawing]

The figure is a traced micrograph of a cavernous porous substrate according to an example of the present invention. 1... Nickel powder sintered part, 2... Hole part.

Claims (1)

[Scope of Claims] 1. A step in which the slurry is made of a mixture of microcapsules containing hydrocarbons in a resin shell, nickel powder, and an adhesive, and the slurry is applied to a porous metal core material; The microcapsules are expanded by heating and drying the porous metal core coated with nickel, and then sintered in a reducing atmosphere to remove the nickel sintered part 1 and the pores 2 generated by the separation of the microcapsules. A method for manufacturing a sintered substrate for an alkaline storage battery, which comprises a step of providing a sintered substrate for an alkaline storage battery. 2. Sintering for an alkaline storage battery according to claim 1, wherein the shell surface of the microcapsules mixed in the slurry is black, and the porous metal core material coated with the slurry is heated and dried using infrared rays or far infrared rays. Substrate manufacturing method.