JPS5931833B2 - Manufacturing method for battery electrodes - Google Patents

Description

Detailed Description of the Invention The present invention provides a sponge-like porous metal body (hereinafter referred to as foam metal) having a three-dimensional structure and continuously connected pores.
The present invention relates to an improvement in a method for manufacturing a battery electrode, which includes a step of filling the pores with a paste-like active material.

The typical manufacturing method for battery electrodes in the past involves impregnating a sintered porous body with a salt solution of an active material, which is then subjected to electrolysis, thermal decomposition,
There are two methods: one is to convert it into an active material through chemical treatment, and the other is to apply a paste-like active material to a conductive porous body such as a grid or perforated plate.

When a sintered body is used, the electrode performance is excellent, but it has the disadvantage that impregnation and conversion must be repeated from several times to 10 or more times, making the process complicated. On the other hand, the method of applying paste to conductive porous bodies such as grids is easier to manufacture than sintered bodies, and can be used as conductive porous bodies such as screens, expanded metals, perforated plates, etc. Continuous manufacturing methods are also possible.

However, in this case, the active material is bound to the conductor using a binder, etc., and as a result, the contact with the conductor is much less, so it is not possible to use a sintered body in terms of both voltage and lifespan. It doesn't reach. Note that if the coating method can be adopted using a sintered body, the advantages of both methods can be utilized, but the pores of conventional sintered bodies are small, so it is difficult to uniformly fill the active material powder inside. That is impossible. However, in the case of foam metal, which has been attracting attention recently, even if the porosity is 90% or more, it is easy to make the pore size larger than the particle size of the active material, so this coating method is not suitable. Can be adopted.

In other words, if a paste-like mixture containing an active material powder, an optional conductive powder, a binder and its solvent is filled into a foamed metal, no conversion process is required as in the case of adding a salt solution of the active material. First, the process can be simplified, and since the foamed metal has a three-dimensional structure, an electrode with excellent conductivity can be obtained. However, this foamed metal is not suitable for ordinary screens with two-dimensional expansion.
Unlike a perforated plate, etc., it has a three-dimensional structure, so it requires some ingenuity to fill the pores with active material.

That is, it is not possible to use a paste with high viscosity, as in the case of coating a porous body with a two-dimensional structure, and it is necessary to use a paste with a high water content and high fluidity.
In this case, the binder added to the paste is preferably one that is used as a kneading agent for the paste, such as water-soluble carboxymethyl cellulose, and is not expected to have a permanent binding force. Electrodes filled with such a paste have the disadvantage that the active material may fall off during subsequent manufacturing processes or battery assembly. Therefore, a method is adopted in which a foamed metal is filled with an active material, dried, and then impregnated with a binder. According to this method, since the binder permeates into the pores formed in the active material layer after drying, it is possible to effectively prevent the active material from falling off with a small amount of binder. The binder used in this case is one that is resistant to electrolyte such as fluororesin or polyethylene, and a dispersion liquid that has excellent permeability into pores is suitable. However, there was a problem in that the active material fell off during the drying process to the binder impregnation process.

Particularly when using a binder dispersion, when the foamed metal is immersed in the dispersion, the air that escapes from the pores in the active material becomes bubbles, causing the active material near the surface of the foamed metal to fall off due to the bubbles. It turns out. As a result, it has been difficult to obtain electrodes of consistent quality. The present invention solves the above-mentioned conventional inconveniences by adding a step of spraying a solution or dispersion containing a binder on the surface of a paste-like active material filled in a foamed metal in a wet state. It is characterized by

According to the present invention, the binder that is sprayed while the active material is wet does not penetrate into the active material and forms a bond on the surface of the active material that is likely to fall off during the subsequent drying process and binder impregnation process. It can impart adhesion.

The binder impregnated after drying provides sufficient binding force to the active material inside the foam metal, resulting in a strong electrode that can withstand expansion and contraction during discharge. In a wet state, the binder does not penetrate into the interior, so it is not possible to impart binding force to the entire active material only by initially dispersing the binder liquid.

Therefore, it is preferable that the binder used here has a low concentration so as not to inhibit the impregnation of the binder after drying. The present invention will be explained below using examples.

FIG. 1 shows the manufacturing process of a nickel electrode.

1 is a paste-like active material, 2 is a container filled with this, 3
is a stirrer that is driven by a motor 4 and stirs the active material 1.

Reference numeral 5 is a band-shaped foamed metal driven by rolls 6 and 7, which is first introduced into the paste-like active material being stirred in the container 2, and then pores are removed from the surface by a plurality of flexible rubber plates 8. The active material is pressurized and filled into the inside.

9 is a fixture for fixing the rubber plate 8.

In this way, the foamed metal 5 filled with active material is slit 1.
0, excess active material adhering to the surface is removed, and then, when the active material on the surface is still wet, a dispersion containing a binder is thinly sprayed onto the surface by a sprayer 11. be done. Reference numeral 12 denotes a dryer, in which the active material is sufficiently dried and the dispersion medium of the binder sprinkled on the surface is also removed, so that the binding effect of the binder is exhibited.

Reference numeral 13 denotes a binder-impregnated container containing a binder dispersion 14, and the active material inside the foamed metal introduced therein is impregnated with the binder.

After passing through drying, pressure compression and cutting steps, the lead wire is attached and completed as an electrode. The manufacturing conditions implemented here are as follows.

First, is the foam metal 5 width 10? , length 200Cr1L1
A piece made of nickel with a thickness of 2.5 mrn1 and a porosity of 98% was used, and the moving speed was about 0.5 mm/sec. The paste-like active material is commercially available nickel hydroxide powder and conductive material nickel powder about 20% by weight? Approximately 70 kg of water with a water content of 35% by weight, which was obtained by adding an appropriate amount of water and an aqueous solution of carboxymethyl cellulose, was used. The binder dispersion sprayed from the sprayer 11 is a fluororesin dispersion with a resin content of 1.5% by weight, which is obtained by diluting a commercially available stock solution 40 times with water, and a binder dispersion 1.
In No. 4, a fluororesin dispersion having a resin content of 6.0% by weight was used, which was obtained by diluting a commercially available stock solution 10 times with water.

Further, the temperature of the dryer 12 was set at 100 to 150°C, so that drying could be performed in about 10 minutes. An alkaline storage battery A as shown in FIG. 2 was constructed using the nickel positive electrode constructed by the above manufacturing method and a known iron electrode as a negative electrode.

In Fig. 2, 21 is a positive electrode, 22 is a negative electrode, 23 is a separator, 24 is a battery container, 25 is an electrolytic solution, 26 is a lead terminal, 27 is a lid, and 28 is a liquid filling stopper, and the sizes of the electrodes are different from each other. 50x60m77! Each of them was made up of 4 sheets. This battery uses the positive electrode rule, and the capacity of the negative electrode is greater than the capacity of the positive electrode. As a comparative example, a battery using a nickel electrode manufactured in the same manner as described above except for the step of spraying the binder dispersion using the sprayer 11 was designated as B. Figure 3 shows that after charging these batteries with an amount of electricity equivalent to more than 150% of their discharge capacity,
The discharge characteristics when discharged with a current of 2A (discharge rate 0.2C) are shown.

As is clear from FIG. 3, the discharge capacity of battery A using the electrode according to the present invention is 10Ah on average, while the discharge capacity of battery B using the conventional electrode is 8Ah on average. It only shows capacity. As described above, the capacity of the battery employing the electrode manufactured by the manufacturing method of the present invention is increased by an average of 1.25 times compared to the battery employing the electrode manufactured by the conventional manufacturing method. Also, the battery of the present invention has a variation in capacity of 5? However, the conventional one showed a very large value of 10 to 20% or more, and it was confirmed that the cause of this was the dropout of the active material. Therefore, the manufacturing method of the present invention makes it possible to reduce variations in capacitance and to manufacture electrodes with uniform capacitance. This is due to the fact that a binder dispersion liquid is sprayed onto the active material on the surface in a wet state to strengthen the binding force between the active materials on the surface and in the vicinity thereof. In conventional products, the binding force between the active materials at or near the surface is weak, and there is only a small portion of the surface surrounded by the foam metal lattice.
When impregnated with a binder dispersion after the drying process, the active material on or near the surface falls into the dispersion, resulting in a decrease in the amount of active material actually filled into the foamed metal.
When conducting a discharge capacity test as an electrode, the discharge capacity decreases in proportion to the capacitance removed. At the same time, the dropout causes large variations in discharge capacity. In the present invention, the concentration of the binder dispersion sprayed on the surface of the foamed metal filled with a paste-like active material is set to a level low enough to prevent the active material from falling off during the subsequent drying and binder impregnation steps. Concentration is desirable.

If the concentration is too high, it is possible to prevent the active material from falling off, but on the other hand, the polarization of the electrode itself increases, leading to a decrease in discharge capacity and high rate discharge characteristics. This will inhibit the penetration of the binder into the interior. Is the amount of binder applied when the active material is wet compared to the amount of binder added after drying? ~wear. The concentration is about 0.5~
5.0 weight? A range of is appropriate. In addition, in the example,
Although a fluororesin dispersion was used as a binder to be added to the active material in a wet state and after drying, a dispersion of polyethylene or polystyrene may also be used. In addition to the above, an aqueous solution of carboxymethyl cellulose or methyl cellulose can be used as the binder added to the active material in a wet state. Further, although an example in which the present invention is applied to a nickel electrode has been described, it can also be applied to a cadmium electrode, an iron electrode, a lead electrode, or a carbon electrode.

As described above, according to the present invention, the active material filled on or near the surface of the foam metal does not fall off during the electrode manufacturing process, and as a result, the filling amount of the paste-like active material becomes uniform. In addition to this, it is also possible to improve the discharge capacity.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the manufacturing process of a nickel electrode in an example of the present invention, FIG. 2 is a longitudinal cross-sectional view of an alkaline storage battery, and FIG. 3 is a comparison of discharge characteristics. 1... Paste active material, 5... Foamed metal, 11... Sprayer for spraying binder, 12
...Dryer, 13...Binder impregnated container.

Claims (1)

[Claims] 1. Filling the pores of a sponge-like metal porous body with a three-dimensional structure with a paste-like active material, and spraying a liquid containing a binder onto the wet active material on the surface of the porous body. A method for manufacturing an electrode for a battery, comprising a step of drying the active material and then impregnating the active material with a binder after drying.