JPH0620685A - Battery electrode and its manufacture - Google Patents

Abstract

PURPOSE:To prevent the dropping out of an electrode active material by providing a filamented fluorine resin layer on the surface of a battery electrode having a three-dimensional base as an electrode base. CONSTITUTION:An electrode formed by charging an active material 6 in a foamed nickel having a porosity of 96% followed by drying and pressure molding is continuously moved in one direction while heating to 60-80 deg.C. A first brush is fixed orthogonally to the moving direction, and a fluorine resin suspension is applied to the electrode surface while being penetrated from a tank above the brush. Simultaneously with the application, the filamenting of the fluorine resin is realized by the friction with the contact surface of the brush, and the filamenting is complicated by a second brush operated orthogonally to the moving direction of the electrode. The dropping out of the active material 6 in the electrode can be prevented by a complicatedly intertwined filamented fluorine resin 8 layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode of a three-dimensional substrate typified by foam metal as an electrode substrate, for example, an electrode of a nickel-cadmium battery or a nickel-hydrogen battery. It is related to falling prevention.

[0002]

2. Description of the Related Art Conventionally, in a nickel electrode, a sponge-like nickel, which is a three-dimensional substrate, is used as an electrode substrate, and a paste mixture containing nickel hydroxide powder, which is an active material, is filled in the electrode. To prevent the active material from falling off, for example, in Japanese Patent Application No. 53-40837, the active material is applied and filled in a sponge-like nickel porous body having a porosity of 97%, and then pressure molding is performed at a pressure of about 150 kg / cm ^2. After drying, it was impregnated with a fluororesin fine powder suspension of 1 to 15 wt% and dried, and a continuous or agglomerated porous layer of this fluororesin fine powder was provided inside the electrode.

[0003]

However, if the binder such as the above-mentioned fluororesin fine powder is mixed in the active material powder, the larger the amount thereof, the more the characteristics such as utilization factor, efficient discharge and battery life deteriorate. In JP-A-54-97739 for improving this, a thermoplastic resin such as polyethylene is melted on the electrode surface to form a net, and the net-like polyethylene is welded to the surface skeleton portion of the sponge-like nickel porous body. To prevent the active material from falling off. Also,
If a small amount of a binder such as a fine powder of fluororesin is impregnated after forming the reticulated polyethylene, the effect is enhanced, and the total amount of the binder is adjusted according to the conventional method (Japanese Patent Laid-Open No. 53-40.
No. 837 gazette).

However, the melting temperature of polyethylene is 1
The temperature becomes 20 ° C., and if this temperature is kept for a long time, the water of crystallization of the nickel hydroxide powder itself, which is the active material, may be decomposed, and this never gives a good effect. Also, it is extremely difficult to make the entire skeleton of polyethylene melted into a mesh smaller than the particle size of nickel hydroxide powder (average particle size 50 μm). Therefore, to prevent the mesh of polyethylene from falling out from the space, After forming the polyethylene, there has been a problem that the conventional working process of adding the electrode to the fluororesin fine powder suspension and drying it again has to be added.

An object of the present invention is to reduce the mixing amount of a binder such as a fluororesin fine powder in the active material powder, which leads to deterioration of characteristics such as utilization rate, high rate discharge and battery life, and to be an active material. An object of the present invention is to provide a battery electrode that is treated at a temperature that does not adversely affect the nickel hydroxide powder, and that is further provided with a fall prevention layer that is more effective in preventing the fall of the active material than conventional measures.

[0006]

In order to solve the above-mentioned problems, according to the present invention, a three-dimensional substrate such as foam metal is filled with an active material, and then a fluororesin is applied to the electrode surface, and at this time, , Fluorine resin powder is made into a filament by applying an external force such as friction to the coated surface. This fluororesin is a low-molecular weight tetrafluoroethylene resin fine powder, or a tetrafluoroethylene resin powder called dispersion or tetrafluoroethylene-
Even a suspension containing fine powder of propylene hexafluoride copolymer resin may be used as long as it is formed into a filament by mechanical force such as friction and vibration. Normally, the above-mentioned filamentation of the fluororesin powder is caused not only by mechanical force but also by heating, but the temperature is high because it is the softening point of the resin itself.

These fluororesins are the same as those described in JP-A-5353.
As proposed in JP-A-40837 and JP-A-54-97739, even if a layer is formed between the particles of the active material powder or on the surface of the particle layer of the active material powder by aggregating or connecting in a spherical shape. It has a binding property, but when made into a thread,
Its cohesive strength is strengthened. Therefore, it is possible to reduce the amount of the fluororesin used, as compared with the method of only impregnating and drying. Moreover, since the fluororesin is formed in the same direction as the direction in which the external force is applied, the binding force can be further strengthened by applying external force in two or more directions to the fluororesin.

When the filamentous fluororesin is in the form of a suspension and the suspension is permeable, the suspension is coated in advance with the electrode heated to 60 to 80 ° C. At the same time as the coating, the water content of the suspension is evaporated so that the fluororesin is present only on the electrode surface. Also, in the process in which this electrode is continuously moved in one direction to be manufactured, the electrode is fixed at a position orthogonal to the moving direction of the electrode, and a tank for storing the fluororesin suspension is provided above the brush. If the fluororesin suspension in the tank is dropped to the surface of the electrode using the capillaries of the brush to realize the coating, the brush and the surface of the electrode are simultaneously coated by the friction force. The fluororesin is made into a thread shape, and the direction of the thread is made complicated by a brush which operates so as to be orthogonal to the moving direction of the electrode.

[0009]

According to the above measures, since the filamentous fluororesin layer can be provided only on the electrode surface, the utilization rate and the efficiency, which are caused by the increase in the amount of the binder such as fluororesin mixed in the active material layer, can be improved. It becomes possible to prevent deterioration of characteristics such as discharge and battery life, and further, it is possible to perform treatment at a temperature at which the measures do not affect the active material. FIG. 1 shows a schematic view of a SEM photograph of the surface of the electrode according to the present invention. As you can see from this figure,
It can be confirmed that the active material particles are firmly fixed by the filamentous fluororesin having a wire diameter of 0.2 μm or less.

[0010]

EXAMPLE One example of the present invention will be described for a nickel electrode for a nickel-hydrogen battery. Nickel hydroxide powder (average particle size 15 μm) was added to the active material, 5 wt% of cobalt was added to it as an activator of the active material, and water was added at a ratio of 0.4 (weight ratio) to these mixed powders. Then, a slurry prepared by adding sodium carboxymethyl cellulose as a thickener at a ratio (weight ratio) of 0.004 to the mixed powder is pressed into nickel foam having a porosity of 96%, which is a three-dimensional substrate. The electrode filled with this slurry is passed through an air stream at 80 ° C. to evaporate the water content, and then pressure-molded at a pressure of 150 kg / cm ² . A filamentous fluororesin layer is formed on the surface of the pressure-molded electrode using the manufacturing apparatus shown in FIG. This manufacturing apparatus is composed of a heater 4 part for heating the electrode 1, a fixed brush 2 for coating and thread-forming the fluororesin, and an operating brush 3 which operates so as to be orthogonal to the moving direction of the electrode. As for the temperature of the heater 4, the electrode surface temperature is 8
Set it to 80 ° C or lower so that it does not exceed 0 ° C. Further, the presence or absence of contact between the heater 4 and the electrode 1 is not limited. The electrode 1 heated to 60 to 80 ° C. by the heater 4 was provided with a tank 5 storing the fluororesin suspension in the upper part, and contained the fluororesin suspension permeated from the tank 5. The fixed brush 2 is moved in the direction of the arrow while simultaneously receiving the coating and the friction. Further, in the operating brush 3 which operates so as to be orthogonal to this moving direction, after making the filamentation complicated so as to intersect with the yarn direction by the fixed brush 2, it is again 8
Dry in a stream of 0 ° C. The fluororesin suspension is obtained by adding water to a tetrafluoroethylene resin fine powder suspension (product name: Polyflon Dispersion D-1) manufactured by Daikin Industries, and diluting the fluororesin concentration to 3 wt%. . In this example, a tetrafluoroethylene resin fine powder suspension was used, but an external force such as tetrafluoroethylene-hexafluoropropylene copolymer resin fine powder suspension or low molecular weight tetrafluoroethylene resin fine powder was applied. It does not matter if it is a thread-like material. Further, the material, hardness, etc. of the brush of the above manufacturing apparatus can be adjusted by changing the moving speed of the electrode or the pressing force of the electrode of the brush, and is not particularly limited.

By combining the nickel electrode obtained by the above-mentioned method and the hydrogen electrode whose main component is a misch metal-based hydrogen storage alloy, an AA type nickel-hydrogen battery having a design capacity of 1050 mAh was prepared, and at 0.2 C 0.2 after charging for 15 hours
A cycle test of discharging at C was performed. The result is shown in Figure 3.
Shown in. a is a nickel electrode according to the present invention, and b is an AA with a design capacity of 1050 mAh using a nickel electrode whose electrode surface is covered with a fluororesin layer (PTFE) which is not thread-shaped.
The type nickel-hydrogen battery c is an AA type nickel-hydrogen battery having a design capacity of 1050 mAh which uses a nickel electrode impregnated with a polyethylene resin on the electrode surface and is impregnated with fluororesin (PTFE). As can be seen from this figure, the battery a using the nickel electrode according to the present invention has the highest capacity, and the capacity decrease due to the cycle test is the smallest. The capacity of the battery b using the non-filamentary nickel electrode was about the same as that of the product of the present invention, but as the cycle progressed, the capacity decrease, which is thought to be caused by the active material falling off, was large. The rate of capacity decrease in the cycle test of battery c having a polyethylene layer provided on the electrode surface was the lowest after a, but the initial capacity was most likely to be due to the performance deterioration of the active material, which is thought to be caused by heat treatment when providing the polyethylene layer. It was low.

[0012]

As described above, in the electrode of the present invention, the fluororesin layer can be provided only on the surface of the electrode, and the fluororesin layer is formed into a thread shape, and further, the threads are intricately entangled with each other. become. Further, since these treatments can be expressed simultaneously with the coating of the fluororesin and can be conducted at a temperature that does not adversely affect the nickel hydroxide as the active material, the conventional method of simply impregnating the fluororesin or heat treatment of polyethylene or the like Compared with the method in which a layer formed by melting a plastic resin and forming a mesh is provided on the electrode surface, and impregnated with a fluororesin,
It is excellent in that the manufacturing process can be simplified, the binding force of the active material can be strengthened, and the amount of fluororesin in the electrode can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view of an SEM photograph of the surface of a nickel electrode of a nickel-hydrogen battery according to the present invention.

FIG. 2 is a manufacturing apparatus according to the present invention.

[Explanation of symbols]

1 is an electrode, 2 is a fixed brush, 3 is a working brush, 4 is a heater, 5 is a tank

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[Procedure amendment]

[Submission date] August 20, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Added

[Correction content]

FIG. 3 is a curve diagram showing the relationship between the number of times charging and discharging a nickel-hydrogen battery and the battery capacity.

Claims (5)

[Claims] 1. An electrode in which a three-dimensional substrate is filled with an active material, wherein the electrode surface layer has a thread-like fluororesin layer, and the electrode for a battery. 2. The battery electrode according to claim 1, wherein the fluororesin is formed into a filament by a mechanical external force. 3. The method for producing a battery electrode according to claim 1, wherein the fluororesin in the electrode is formed into a filament shape at the same time as the fluororesin is applied to the electrode surface layer. 4. In a manufacturing process in which an electrode is continuously moved in one direction, a filament-shaped fluororesin is fixed so as to be orthogonal to the moving direction of the electrode, and a brush which is operated orthogonally to the moving direction. The method for manufacturing a battery electrode according to claim 3, which is performed. 5. The method for manufacturing a battery electrode according to claim 4, wherein the electrode moving in one direction is heated at least while the fluororesin is applied.