JPS5951714B2 - Manufacturing method of paste-type electrode plates for alkaline storage batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a paste-type electrode plate.

Conventionally manufactured electrode plates for alkaline storage batteries include sintered electrode plates in which a nickel sintered substrate is filled with active material, and a molded mixture of active material and conductive material placed in a nickel porous container. , coated pocket-type electrode plates, and paste-type electrode plates in which active materials are kneaded with a synthetic resin binder (glue), coated on a porous metal support, and dried.

Among these, the sintered electrode plate is thin and has excellent thickness characteristics and high rate discharge characteristics, but on the other hand, the weight of the nickel substrate in the electrode plate is large and the volumetric efficiency is low. Furthermore, the pocket type electrode plate has low volumetric efficiency due to its large thickness and low active material utilization rate. On the other hand, paste-type electrode plates have a high active material utilization rate and a high volumetric efficiency, but they have problems with the binder, are weak against alkaline electrolytes, and have a short lifespan due to the significant shedding of the active material due to repeated charging and discharging. Each of them had their own problems. Among these, paste-type electrode plates are manufactured in relatively large numbers together with sintered-type electrode plates because of their high active material utilization rate and high volumetric efficiency.

Furthermore, in order to prevent the active material from falling off and extend the life of the active material, the use of various synthetic resin binders has been proposed. For cathodes that use cadmium as an active material, there are formulations that use polyvinyl alcohol as a glue, and some are even manufactured. However, when using polyvinyl alcohol, the amount added is 1w due to the characteristics of the cadmium cathode.
The limit is about t%, and if more than this is added, the active material utilization rate will decrease and the oxygen gas absorption ability will noticeably decrease in sealed batteries.

When added in a much smaller amount than 1wt%, polyvinyl alcohol has little effect as a binder.
It merely serves as a coating material to uniformly apply the paste to both sides of the metal support, and the strength of the electrode plate after application and drying is extremely weak. In response, attempts have been made to use various synthetic resin binders such as polyethylene and polytetrafluoroethylene to increase the strength and lifespan of the finished electrode plates, but similar to polyvinyl alcohol, they In order to obtain sufficient strength and service life, it is necessary to add about 5 to 10 Wt%, and the performance of the electrode plate will also be significantly reduced. For example, when polyvinyl alcohol is added at 0.38 wt% of the total weight of the electrode plate, the active material utilization rate is 70%.
However, when 5-10 wt% is added, 40-5
You end up getting only a 0% utilization rate. This tendency is common not only to cadmium cathodes, but also to paste-type electrode plates for alkaline storage batteries, such as zinc cathodes and nickel anodes. The present invention aims to increase the strength and lifespan of paste-type electrode plates while maintaining a high utilization rate.The present invention aims to achieve specified performance with a minimum amount of thermoplastic resin as a synthetic resin binder. It's what you're trying to get.

That is, the active material powder, the additive, and the thermoplastic resin are mixed to form a paste, and when kneaded, the temperature of the paste during kneading is maintained at or above the softening point of the thermoplastic resin to be added. In particular, the thermoplastic resin is uniformly diffused and the active material particles are firmly bound together.

Examples of the present invention will be described below.

(Example 1) A cathode plate for a sealed 4-type nickel-cadmium storage battery using cadmium oxide as the electrode active material was produced by the following method, and compared with a conventional example.

20 parts by weight of nickel powder per 100 parts by weight of cadmium oxide powder, and polyethylene powder with a particle size of 20 to 50 μm (softening point 120 to 130°C) as a thermoplastic resin 0 to 5
A solution of 0.4 parts by weight of polyvinyl alcohol dissolved in 30 parts by weight of ethylene glycol (boiling point 197°C) heated to 120 to 130°C was added to the mixed powder, and kneaded. While maintaining the mixing temperature at 120 to 130° C., the paste is sufficiently kneaded at high speed until the viscosity of the paste drops at a rate of 5 to 50 g/min through holes with a diameter of 10 mm. Apply this paste to both sides of a punched metal with a hole diameter of 2 mm, and after drying, press it to form a cathode plate A.
get. For this cathode plate A, for comparison, polyvinyl
Conventional Example 1 is a conventionally manufactured cathode plate using polyalcohol as a binder, and
An electrode plate was prepared as Conventional Example 2 by coating an electrode active material containing ~10 wwt% in a sheet shape on both sides of a metal support, press-molding the sheet, and heat-treating the sheet at a temperature of 150° C. for 2 hours.

For these cathode plates, the charge/discharge utilization rate in an alkaline solution, charge/discharge cycle life, and strength of the plates were determined.

The charge/discharge utilization rate was 15 hours at 0.1C, which is the theoretical capacity of the cathode plate, in a 7M KOH aqueous solution kept at 20℃, and discharged at 0.1C to -1.0 with respect to the nickel counter electrode. It was determined by charging and discharging. The results are shown in FIG. The charge/discharge cycle life was determined by repeating the above conditions. The results are shown in FIG. In addition, the present invention A uses 0 polyethylene.
．． 5 wt% added, Conventional Example 2 has 0 polyethylene added.
．． 5wt%, 2" is the addition of 7wt.The strength of the electrode plate is determined by covering the circumference of the cathode plate with a 0.2mm thick polyamide nonwoven fabric and wrapping it around a round bar with an outer diameter of 5mm.
The falling rate was determined from the ratio of the amount of active material falling off at this time. The results are shown in FIG. From these results, the cathode plate A in the present invention has an added amount of polyethylene powder of 0.2
In the range of ~1 Wt%, the charge/discharge utilization rate is 70-75%
Performance equivalent to that of the cathode plate of Conventional Example 1 was obtained, and in terms of charge/discharge cycle life and electrode plate strength, performance equivalent to that of the addition of 5 to 10 Wt% of polyethylene powder in the cathode plate of Conventional Example 2'' was obtained. It was confirmed that the effects of the present invention were significant. In addition to Example 1, similar effects were obtained with the following active materials and thermoplastic resins.

Representative examples are shown below. (Example 2) Instead of the polyethylene powder in Example 1, ethylene monovinyl acetate copolymer (polymerization ratio 100:0 to 90:1) was used.
A similar effect was obtained when the paste was similarly prepared using 0) to create a cathode plate.

(Example 3) The same effect can be obtained even if zinc or nickel is used instead of cadmium as the active material.

For example, for a zinc cathode as a cathode plate for a sealed nickel-zinc storage battery, 100 parts by weight of zinc oxide powder, 50 parts by weight of metal zinc powder, and 0.5 to 1 part by weight of polyethylene powder in Conventional Example 1 are uniformly mixed. Then, a solution obtained by melting and dissolving 1 part by weight of polyvinyl alcohol in 35 parts by weight of ethylene glycol heated to a temperature of 120 to 130°C was added to this powder, and the mixture was thoroughly mixed while keeping the kneading temperature at 120 to 130°C. After kneading, the resulting paste is applied to both sides of the punched metal, dried and pressed to obtain a zinc cathode plate, which is used to manufacture a sealed nickel metal plate using a sintered nickel electrode as the anode. When a zinc storage battery is made, the cycle life of this battery is approximately 1.5 times that of a battery using a conventional zinc cathode that does not contain polyethylene, and compared to a battery that uses a conventional zinc cathode that contains polyethylene. However, the lifespan is almost the same, and the utilization rate has improved, making it possible to improve energy and weight efficiency. On the other hand, the same is true when nickel is used as the electrode active material, and even when nickel hydroxide powder is used and the method of the present invention is used, the lifespan can be extended without reducing the utilization rate. .

The effects described in the above examples can be obtained by using thermoplastic resin,
By dissolving the glue that gives the paste tackiness in an organic solvent with a boiling point higher than the softening point, and adding the solution, the mixture is thoroughly kneaded with the electrode live electric current at a temperature higher than the softening point. This is due to the uniform diffusion of the thermoplastic resin into the electrode active material.

Therefore, even by adding a very small amount of resin, it is possible to increase the binding strength, improve the strength of the electrode plate, and extend its life. In addition, since the amount of resin added is small, there is almost no decrease in the active material utilization rate, and the effect is very large. As described above, the present invention improves the strength and life of the electrode plate, which are drawbacks of conventional paste-type electrode plates, without reducing the utilization rate.

[Brief explanation of the drawing]

FIG. 1 shows the charge/discharge utilization rate of a paste-type cadmium cathode plate made by the method of the present invention, FIG. 2 shows the charge/discharge cycle life, and FIG. 3 shows the plate strength.

Claims (1)

[Scope of Claims] 1. A thermoplastic resin is mixed into an electrode active material powder, and a solution of a glue dissolved in an organic solvent having a boiling point higher than the softening point of the thermoplastic resin is added to soften the thermoplastic resin. The paste obtained by kneading while heating at a temperature above the point,
1. A method for producing a paste-type electrode plate for an alkaline storage battery, which comprises coating on both sides of a porous support and drying. 2. The method for producing a paste-type electrode plate for an alkaline storage battery according to claim 1, wherein the thermoplastic resin is made of polyethylene or an ethylene-vinyl acetate copolymer. 3. The method for producing a paste-type electrode plate for an alkaline storage battery according to claim 1, wherein the electrode active material powder is one of the group consisting of cadmium oxide, cadmium hydroxide, and mixtures thereof. 4. The method for producing a paste-type electrode plate for an alkaline storage battery according to claim 1, wherein the electrode active material powder is zinc oxide or a mixture of zinc oxide and metal zinc. 5. The method for producing a paste-type electrode plate for an alkaline storage battery according to claim 1, wherein the electrode active material powder is nickel hydroxide.