JPS6251164A - Positive mixture for alkaline battery - Google Patents

Abstract

PURPOSE:To increase the moldability of the positive mixture by adding a metal salt of stearic acid to the mixture. CONSTITUTION:A metal salt of stearic acid is contained in a positive mixture 1 for an alkaline battery. Calcium stearate, zinc stearate or the like is used as the metal salt of stearic acid. As the result, the frictional resistance produced between the metallic mold and the surface of the mixture during its molding greatly decreases and also it is possible to greatly suppress the spring back produced during removal of the mixture from the metallic mold. Consequently, it is possible to significantly reduce the generation of defects such as breakdown or separation of the mixture and to increase the moldability of the mixture.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a positive electrode mixture for alkaline batteries.
The present invention relates to a positive electrode mixture for cylindrical alkaline batteries in which moldability is improved and the active material content in the mixture is increased by incorporating a specific substance into the mixture.

<Prior art> Among alkaline batteries constructed using a negative electrode formed by dispersing powdered zinc in gel form with an alkaline electrolyte such as KOH or Na0t-1 and a gelling agent such as carboxymethylcellulose, cylindrical alkaline batteries In a battery, the negative electrode is filled into the hollow part of a hollow cylindrical positive electrode mixture via a polypropylene separator, and the negative electrode is housed together in a positive electrode can.

As a positive electrode mixture, a granular material made by mixing a positive electrode active material such as manganese dioxide with scaly graphite as a conductive agent, carbon such as Grapheye 1~, and an appropriate binder is used on the top and bottom of the diamond. The material used is molded under high pressure using a mold made of pashchi, core rod, etc. As the above-mentioned granules, there is a tendency to widely use granules with high density made by so-called compression granulation, which improves the compacted density of the mixture and increases the content of positive electrode active material in the battery. As is well known, this has the advantage that the discharge capacity increases accordingly and the battery discharge performance can be improved.

The role of carbon in the positive electrode mixture used in such alkaline batteries is to increase the conductivity between the particles of positive electrode active material such as manganese dioxide, and to improve the conductivity between the positive electrode mixture and the positive electrode can. This reduces the internal resistance of the battery and increases the short-circuit current. By the way, if such carbon is included in the mixture, the content of the positive electrode active material in the mixture will decrease and the battery discharge capacity will decrease, so the lower the carbon content, the better, but if it is too low, the internal resistance will become extremely high. For example, in the case of a cylindrical alkaline battery, the carbon content (usually particles with an average particle size of about 25 to 50 μm are used) is the sum of manganese dioxide and carbon. It had to be 10% by weight or more based on the amount. Therefore, for example, as described in Japanese Patent Application No. 59-96670,
The applicant has determined that the average particle size of the carbon used in the mixture is 2 to 2.
It was proposed that by using graphite powder in the range of 20 μm, the carbon content in the mixture could be 3 to 8% by weight without deteriorating battery performance.

<Problems to be solved by the invention> However, when the carbon content is reduced as described above, the friction between the positive electrode mixture surface and the mold surface increases by the amount of the decrease in carbon content during mixture molding. As a result, there is a problem in that the proportion of surface peeling and vertical cracking in the mixture increases significantly, and the moldability of the mixture becomes extremely poor.

In particular, when the granules used in positive electrode mixture molding are made by compression granulation, the springback when taking out the mixture from the mold increases by the increased molding density. , the degree of deterioration of mixture moldability also increases.

<Means for Solving the Problems> The gist of the positive electrode mixture for alkaline batteries of the present invention is that it contains a metal salt of stearic acid.

Examples of the above metal salts of stearic acid include calcium stearate, zinc stearate, and the like.

By the way, metal salts of stearic acid such as calcium stearate and zinc stearate have excellent lubricity, good dispersibility, and a high melting point, so when they are contained in a mixture in excess of an appropriate amount, they can be The moldability of the mixture is improved quickly, and it is possible to spread it uniformly into the mixture, and it does not decompose even under high temperatures during compression in dry compression granulation, and therefore lubrication is maintained during pressure molding of the mixture. On the other hand, because it has strong hydrophilicity, if it is used at too high a valence level, the amount of alkaline electrolyte absorbed by the mixture will be noticeably reduced, resulting in a significant decrease in battery discharge performance. There is. - Regarding this point, according to the research of the present inventor, when the content of the metal salt of stearic acid in the mixture is 0.2 to 0.6% by weight based on the amount of manganese dioxide, the battery discharge performance is improved. It is known that the moldability of the mixture can be improved to a level that poses no problem in practical use without causing a decrease in the difference.

<Function> In this way, by including the metal salt of stearic acid in the positive electrode mixture, the lubricity between the mixture surface and the mold surface is improved, so the frictional resistance is significantly reduced and the mold Spring back when removed can be reduced.

<Example> FIG. 1(A) shows a hollow cylindrical positive electrode mixture 1 for an alkaline mankan battery according to the present invention, and this positive electrode mixture 1 mainly contains manganese dioxide and carbon. Granules made by dry compression granulation of the mixed powder are prepared using a die 2, an upper punch 3, a lower punch 4, and a core rod 5 as shown in Fig. 1 (
As shown in B), it is molded under high pressure. After pressure molding, first move the upper punch 3 in the direction of the arrow shown in FIG. 1 (B) to the position shown in FIG. , then the same figure (C)
The lower punch 4 is moved in the direction of the arrow shown in the figure to the position shown in FIG.

Using one or more, for example, three pieces of the positive electrode mixture 1 obtained by pressure molding in this way, the positive electrode mixture 1 is poured into the positive electrode can 6 from the opening of the positive electrode can as shown in FIG. ), press-fit the
After that, the separator 7 negative electrode 8, the sealing gasket 9, the negative electrode terminal 10, the negative electrode current collector 11, the sealing cap 12, etc. are housed or placed in the positive electrode can 6, and finally the beading and curling of the opening of the positive electrode can is removed. If this process is carried out, an alkaline manganese battery shown in FIG. 2(C) can be obtained.

Next, calcium stearate was used as a metal salt of stearic acid, and 02O51,0,2,
0,4,0,6,0,8,1,0 type group% (fffffi% with respect to the amount of manganese dioxide in the positive electrode mixture; the same applies hereinafter)
Positive electrode mixture for LR6 batteries (carbon-containing i6
．． 5@% by volume; those using dry compression granulation) were each 100%
Table 1 shows the number of pieces that cracked the mixture when they were made one by one. From the same table, it can be seen that when the content is less than 0.2% by weight, the number of cracks in the mixture increases rapidly.

In addition, five LR6 batteries were made using positive electrode mixtures molded with different calcium stearate contents, and these batteries were continuously discharged at a temperature of 20'C at a constant resistance of 110Ω to a final voltage of 0.9V. Discharge time (H
Table 2 shows the results (average values of 5 samples each) of the samples.

From the same table, it can be seen that when the content is greater than 0.16% by weight, the discharge time becomes suddenly shorter.

From these results, it was determined that the calcium stearate-containing wings were
．． It was confirmed that by setting the amount in the range of 2 to 0.6% by weight, it was possible to improve the moldability of the mixture without any disadvantage in terms of battery discharge performance.

<Effects of the Invention> According to the positive electrode mixture for alkaline batteries of the present invention configured as described above, the inclusion of a metal salt of stearic acid reduces friction between the mold and the mixture surface during molding of the mixture. Since the resistance is drastically reduced and the springback when the mixture is removed from the mold can be significantly suppressed, the occurrence of defects such as cracking and peeling of the mixture can be significantly reduced, and the moldability of the mixture can be improved. In addition, this makes it possible to reduce the carbon content in the mixture to about 3 to 8% by weight, or to use materials made by the above-mentioned high-density dry granulation when molding the mixture, without any practical problems. This has the advantage that the active material content in the positive electrode mixture increases, contributing to improving battery discharge performance.

[Brief explanation of the drawing]

FIG. 1(A) is a cross-sectional view showing an example of the positive electrode mixture according to the present invention, FIGS. 1(B) to (D) are explanatory diagrams of the molding process of this positive electrode mixture, and FIG. 2(A) -(C) are explanatory diagrams of the assembly process of a cylindrical alkaline battery constructed using the positive electrode mixture. 1... Positive electrode mixture, 2... Die, 3... Upper punch,
4... Lower punch, 5... Core rod, 6... Positive electrode can, 8... Negative electrode. Figure 1 (A) (C) (D) Figure 2 (A)

Claims (1)

[Claims] 1. A positive electrode mixture for alkaline batteries, characterized by containing a metal salt of stearic acid. 2. The positive electrode mixture for alkaline batteries according to claim 1, wherein the metal salt of stearic acid is calcium stearate or zinc stearate. 3. Contains manganese dioxide as a positive electrode active material and carbon as a conductive agent, and the content of the metal salt of stearic acid is 0.2 to 0.6 with respect to the amount of manganese dioxide.
The positive electrode mixture for alkaline batteries according to claim 1 or 2, characterized in that the amount is % by weight. 4. The positive electrode mixture for alkaline batteries according to claim 3, wherein the amount of carbon is 3 to 8% by weight based on the total amount of manganese dioxide and carbon. 5. Claims 1 and 2, characterized in that the product is formed by pressure molding granules produced by dry compression granulation.
Positive electrode mixture for alkaline batteries according to item 3 or 4