JPS6238825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a battery electrode using a sponge-like porous metal material having a three-dimensionally continuous structure as a holder for an active material.

In addition to the method of manufacturing electrodes for batteries, in which the active material mixture is pressure-filled into a can as in the case of Lecrancier batteries, in general, in alkaline batteries and lead-acid batteries, the active material is placed in a metal container with micropores. Pocket type, in which a paste-like active material is applied to both sides of a screen, perforated plate, or lattice as a core material, and active material powder is pressed and integrated with a binder on both sides of the same core material. There are two methods, such as a sintering method and a sintering method in which an active material is filled into a porous sintered metal substrate. Although each method has advantages and disadvantages, sintered electrodes generally have excellent high-rate discharge characteristics due to their large current collection ability, and also have an excellent lifespan because they form a strong sintered base. On the other hand, a method that does not use a sintered substrate has the advantage that the manufacturing process is simple and that the active material can be filled with high density.

Recently, three-dimensional network-like sponge-like porous metal bodies have been produced, and electrodes have been proposed that have electrode characteristics similar to sintered electrodes and manufacturing methods similar to non-sintered electrodes. This method uses high porosity, unlike the sintering method, which impregnates the salt of the active material and converts it into an active material due to the fine pores.
For example, it is a method in which active material powder is directly filled into a 95% porous sponge-like metal body, and its high porosity makes it easy to pack at a high density. Another feature is that by selecting a sponge-like porous material, an electrode of any thickness can be obtained, and compared to non-sintered electrodes, the current collection ability is far superior, making it suitable for high-rate discharge.

The present invention relates to an improvement in a method for densely filling an active material using this sponge-like porous metal body.

The filling method that has been proposed so far is to fill a highly porous sponge-like porous metal body with a paste-like mixture of powders containing an active material, such as nickel hydroxide, and then create a paste that adheres to the surface of the porous body. There is a method of pressure molding after removing the active material, and during the pressure molding, pressure is applied in a semi-dry state to move a part of the active material during pressurization, and also to dissipate air to the outside of the electrode plate. This increases the overall packing density. However, when pressing a large electrode plate, for example, a 400×300 mm electrode plate, or pressing a continuous hoop-shaped electrode plate, this alone is insufficient.

In other words, in order to prevent the electrode plate from breaking during pressurization and to fill it with active material at a high density, air in the center of the electrode plate or a dispersion medium of active material powder in the paste must be dispersed along the pressure plate during pressurization. It was found that it was necessary to devise a way to quickly dissipate it to the outside. For this purpose, the first method to consider is to slow down the pressurization speed, but this alone would not only reduce productivity but also be insufficient to dissipate the air inside the electrode plate. .

The present invention eliminates the above-mentioned conventional disadvantages and provides a method for easily filling an active material at a high density without damaging the electrode plate during pressurization.

That is, in the present invention, a part of the sponge-like porous metal body is pressurized to form a plurality of grooves before being filled with the active material, and the pore diameter of the porous body in the pressurized portion is reduced so that most of the active material is not absorbed. This prevents it from being filled. According to this method, during pressure molding after filling the active material, the air inside the electrode filled with the active material and the dispersion medium in the paste easily pass through the groove and escape to the outside. Therefore, the packing density of the active material is improved and the electrode is not destroyed.

In order to uniformly pressurize a sponge-like porous metal material over a large area at a high density and at the same time, simply applying pressure using a flat mold is insufficient to achieve high-density and uniform filling. However, when the pressure is increased in order to achieve high density, cracks as shown in 2 occur in the porous substrate 1 due to the pressure of the internal air or dispersion medium, as shown in FIG. For this reason, when a sponge-like highly porous metal material is used as an electrode substrate, and the active material is filled uniformly and densely, and pressure molding is performed over a large area at once, the internal air or dispersion medium is forced out of the substrate. It needs to be easy to escape. For this reason, it is effective to provide appropriate grooves for the escape of air or dispersion medium even after pressure molding, that is, even if the thickness of the porous body becomes thinner after pressure molding.

The sponge-like porous metal body 1 used in this kind of electrode is different from those whose core material is a sintered body, screen, perforated plate, expanded metal, etc., and its skeleton 3 is as shown in Fig. 2. Average wire diameter 30~
It is made of long thin wires measuring 60 microns and approximately 100 microns long, so when mechanical force is applied during electrode manufacturing, the skeleton is cut by the pressure of the air or dispersion medium escaping. The present invention provides grooves in a sponge-like porous metal body by applying pressure.
This is intended to eliminate such inconvenience.

The present invention will be explained below with reference to Examples.

FIG. 3 shows a sponge-like porous metal body before being filled with an active material, in which a large number of grooves 4 are formed in the hoop-shaped porous body 1 in a direction perpendicular to its length by applying pressure. The interval between these grooves varies depending on the size of the electrode to be obtained, but is suitably about 30 to 70 mm or less. In other words, a porous material with a skeleton having a thick wire diameter of about 60 microns and large pores with a cell count of about 10/cm can be press-molded at high density with a groove spacing of about 70 mm, and the skeleton is 40. A porous material with a wire diameter of microns and small pores having a cell count of 30 cells/cm could be press-formed with high density up to a groove pitch of about 30 mm.

If the width of the groove is too small, it will not be effective, at least
0.5mm is necessary. Since the pressurizing part 5 of this groove forming part is not filled with active material, it is disadvantageous to make the groove width too large. It is also desirable that the grooves remain after pressure molding, and the appropriate pressure when forming the grooves is about 150 kg or more.

The grooves 4 may be provided not only on one side of the porous body 1 but also on both sides as shown in FIG. Furthermore, the corners of the cross section of the groove are preferably obtuse or rounded, as shown in FIG.

At least one end of the groove thus formed is
It must reach the end of the porous body during pressure molding.

Example 1 Porosity 95%, average wire diameter 50 microns, number of pores 22
pieces/cm, width 200mm, thickness 2mm long sponge-like porous nickel material, grooves 1mm wide at 40mm intervals almost perpendicular to the length direction from one side with a pressure of 300Kg/cm ² 0.7
After soaking to a depth of mm, the porous body contains an average particle size of 50 mm.
It is filled with a pasty mixture of micron (maximum 140 micron) nickel hydroxide and a 3% by weight aqueous solution of carboxymethyl cellulose (nickel hydroxide content 70% by weight). Thereafter, the active material powder in the grooves of the porous body is removed with a brush, and after semi-drying, pressure is applied between flat plates at a pressure of about 400 kg/cm ² . Removal of active material from the groove and pressurization are repeated as necessary. The thickness of the obtained electrode plate was 0.9 mm, and a groove about 0.2 mm deep remained.

Example 2 Similar grooves were provided in the same porous body as in Example 1, and 80% by weight of cadmium oxide with an average particle size of several microns, 19% by weight of carbonyl nickel, and 0.3% by weight of resin fibers were prepared.
A paste mixture containing 0.7% by weight of ethylene glycol and ethylene glycol was filled, and then pressure molded in the same manner as in Example 1.

FIG. 7A shows the relationship between the press pressure during pressure molding and the packing density of the active material in Example 1. B
shows a similar relationship in a comparative example using a porous body without grooves 4. Press pressure 350 in comparative example
Kg/cm ² sometimes caused cracks, but no cracks occurred in the examples of the present invention. As is clear from the figure, according to the present invention, the packing density of the active material can be improved, and the porous body is not destroyed during pressure molding.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the main parts of an electrode obtained by a conventional method, Figure 2 is an enlarged sectional view of a sponge-like porous metal body, and Figure 3 is a porous body before being filled with active material in an example of the present invention. 4 is a longitudinal sectional view of the porous body, 5 and 6 are longitudinal sectional views of porous bodies showing other examples, and 7 is the press pressure during pressure molding and the obtained electrode. FIG. 3 is a diagram comparing the relationship between the active material packing density and the active material packing density. 1...Porous body, 4...Groove.

Claims (1)

[Claims] 1. A step of pressurizing a sponge-like metal porous body having a three-dimensionally continuous structure to form a plurality of grooves on at least one side thereof, one end of which reaches an end of the porous body, and then applying an active material to the porous body. 1. A method for producing a battery electrode, comprising the steps of filling the active material in the groove, removing the active material in the groove, and press-molding the entire porous body after semi-drying.