JPH0414461B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to an alkaline battery, and in particular to a method for producing a gelled zinc negative electrode thereof. Conventional structure and problems Conventionally, gelling agents used in the negative electrode of alkaline batteries include carboxymethylcellulose,
Water-soluble polymers include alginic acid, guar gum, polyacrylic acid and its salts, and polyvinyl alcohol. Among these, polyacrylic acid and its salts are preferable in consideration of oxidation and hydrolysis of the gelling agent by the alkaline electrolyte and positive electrode oxide during storage of the battery. Polyacrylic acid and its salts have two different structures depending on the polymerization method. One is the linear type, which is produced by aqueous solution polymerization of an aqueous monomer solution of acrylic acid or its salt using a redox catalyst that combines peroxide, persulfate, or a reducing agent such as a sulfite with these. It is. The other type is a cross-linked and branched type in which a cross-linking agent such as divinylbenzene is added and suspension polymerization is carried out in an organic solvent such as methanol or acetone. When polyacrylic acid or its salt obtained by the different polymerization methods described above is used alone in an alkaline battery, the results are as follows. In the case of linear polyacrylic acid and its salts, when the polymerization degree is 2500 or higher, a gel with high stringability and strong adhesiveness is formed, and the contact between the electrolyte, zinc, current collector, and separator is good, and the discharge Among them, the internal impedance of the battery is low and the closed circuit voltage characteristics are also good.
This is thought to be because the high contactability due to stringiness improves the diffusion of zincate ions during discharge. However, in batteries with a large sealing plate volume,
In the case of linear polyacrylic acid, zinc precipitates during storage and the effective area of zinc decreases, resulting in a large capacity loss. In the case of linear polyacrylic acid,
This is thought to be because when stress or load is applied to the gel state, the molecules align in the same direction, and there is no ability to maintain uniform dispersion. In addition, if linear polyacrylic acid with a degree of polymerization of 2500 or less and its salts are used alone, the addition rate will be high in order to obtain a certain gel strength, and the internal resistance will increase.
This will cause a decrease in battery performance. On the other hand, crosslinked dispersed polyacrylic acid and its salts have alkali resistance and a three-dimensional branched structure due to crosslinking reaction, so
Since it has almost no stringiness, exhibits thixotropic fluidity and a high yield value, it can prevent settling of a powdery negative electrode active material with a large specific gravity. Therefore, there is little deterioration in discharge performance due to long-term storage. However, unlike the linear type, this cross-linked branched type has almost no stringiness, has poor contact between the electrolyte, zinc, current collector, and separator, and has a higher internal impedance during battery discharge than the linear type. big,
When used in devices such as watches and cameras that require instantaneous large currents, the drop in closed-circuit voltage is large, which can cause problems at the end of discharge. Purpose of the Invention The present invention solves the above-mentioned drawbacks when using linear or cross-linked branched polyacrylic acid or its salt alone as a gelling agent, and provides an alkaline battery with constant quality and excellent performance. The purpose is to provide a method. Structure of the Invention The present invention involves dissolving linear polyacrylic acid or its salt with a degree of polymerization of 2500 or less in an alkaline electrolyte to create a viscous solution, and combining this viscous solution with cross-linked polyacrylic acid or its salt and zinc powder. It is characterized by injecting the liquid into a mixture with. The reason why linear polyacrylic acid or its salt with a degree of polymerization of 2500 or less is dissolved in an electrolytic solution is because linear polyacrylic acid with a degree of polymerization of 2500 or less has almost no stringiness and the workability of the process is good. be. In this way, by adding linear polyacrylic acid or its salt, it acts to fill the gap between the negative electrode and the separator composed of cross-linked branched polyacrylic acid or its salt and zinc, increasing the internal resistance during discharge. This also improves the closed circuit voltage characteristics. In addition, compared to a manufacturing method in which powders of linear polyacrylic acid or its salt and cross-linked polyacrylic acid or its salt are mixed with zinc and an electrolyte is poured into this mixture, the internal resistance of the battery is lower. Variations in closed circuit voltage characteristics, etc. are reduced. This is considered to be due to the difference in uniform miscibility between the two types of gelling agents, zinc, and electrolyte. Furthermore, by mixing the gelling agent, zinc, and electrolyte,
In the method of constructing a gel-like negative electrode and weighing it on a sealing plate, the weight accuracy varies widely and it is difficult to obtain a product of constant quality. In contrast, in the present invention, a mixture of cross-linked branched polyacrylic acid or its salt and zinc powder is weighed by the mass cutting method and filled into a sealing plate, and then linear polyacrylic acid or its salt is filled into a sealing plate. Since an electrolytic solution containing dissolved is injected, variations in weight accuracy can be reduced. In this way, according to the present invention, by taking advantage of the advantages of linear and cross-linked branched polyacrylic acids or their salts, it is possible to obtain a high-performance alkaline battery with constant quality. Description of Examples The figure shows a silver oxide battery SR1130. First, a positive electrode mixture 1 containing silver oxide as a main component is inserted into a positive electrode container 2 together with a positive electrode ring 3 and compression molded. Then, an alkali-resistant separator 4 and an electrolyte-impregnated material 5 are placed on the mixture. On the other hand, a linear sodium polyacrylate having a degree of polymerization of 2500 or less is dissolved in an aqueous solution of caustic potassium to form a viscous electrolyte. Further, zinc chloride powder and crosslinked branched sodium polyacrylate are mixed in a powder state, weighed by a mass cutting method, and filled into a sealing plate, and the viscous electrolyte is poured into this mixture. The sealing plate 7 provided with the gelled negative electrode 6 is combined with the positive electrode container 2 via the gasket 8, and the opening edge of the container 2 is tightened to form a sealed battery. Table 1 shows various negative electrode manufacturing methods and the ratio of gelling agent to negative electrode weight.

[Table] Table 2 shows a comparison of the weighed weight of the negative electrode, the average value of the initial internal resistance, and the standard deviation value indicating the dispersion thereof, which were measured for each of 100 batteries prepared by the above treatment method. Furthermore, Table 3 shows a comparison of the properties directly and after storage at 45°C for 3 months. In addition, the discharge time is when continuously discharging with a load of 7.5KΩ at 20℃.
The average value of 20 batteries up to 1.4V (standard deviation value is shown in square brackets). Also, the closed circuit voltage is 7.5KΩ
The average value of the lowest closed-circuit voltage of 15 batteries when discharged to a depth of discharge of 80% at 0°C for 5 seconds at 200Ω (the value in brackets is the standard deviation value) is shown.

【table】

【table】

[Table] From the above results, the silver oxide battery according to the present invention has
It can be seen that the negative electrode active material has excellent weighing accuracy, discharge characteristics, and low-temperature closed circuit voltage. In the examples, sodium polyacrylate was used as the gelling agent, but the same applies to polyacrylic acid and its salts, such as potassium salts.
Although caustic potash was used as the electrolyte, similar results were obtained with caustic soda. Effects of the Invention As described above, according to the present invention, an alkaline battery with constant quality and excellent performance can be obtained.

[Brief explanation of drawings]

The figure is a cross-sectional side view of a main part of a silver oxide battery in an example of the present invention. 1... Positive electrode, 4... Separator, 5... Electrolyte impregnated material, 6... Gel-like negative electrode.

Claims (1)

[Claims] 1. Dissolve linear polyacrylic acid or its salt with a degree of polymerization of 2500 or less in an alkaline electrolyte to create a viscous solution, and add this viscous solution to a mixture of cross-linked branched polyacrylic acid or its salt and zinc powder. A method for producing an alkaline battery comprising a step of forming a gelled zinc negative electrode.