JPH059902B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the manufacturing method of an alkaline battery,
The purpose of the present invention is to provide an alkaline battery with low internal resistance and high discharge capacity. For example, in a cylindrical alkaline manganese battery, the positive electrode can serving as a battery container also serves as a positive electrode current collector, so it is necessary to increase the current collecting ability of the inner surface of the positive electrode can. Therefore, it has been proposed to apply a conductive paint to the inner surface of the positive electrode can, and conductive paints used for this purpose include conductive additives such as nickel, silver, graphite, and acetylene black, as well as polyvinyl chloride and polyacetic acid. It has been proposed that synthetic resins such as vinyl and polystyrene are dissolved and dispersed in organic solvents such as toluene, xylene, methyl ethyl ketone, and ethyl acetate. However, the synthetic resin used there has excellent film-forming ability and excellent alkali resistance and oxidation resistance, making it very suitable as a binder. is covered with these synthetic resins, which remain stable for a long period of time and do not break down, which impairs the conductivity of the conductive aid. Therefore, attempts have been made to eliminate the above-mentioned drawbacks by reducing the amount of synthetic resin in the paint as much as possible, but this results in problems such as unevenness and peeling after coating and drying. The present invention overcomes the above-mentioned drawbacks of the prior art and achieves its objectives by using polyvinylpyrrolidone as a binder for graphite. Polyvinylpyrrolidone used in the present invention is a water-soluble polymer, but it is also soluble in alcohols such as methyl alcohol, ethyl alcohol, and butyl alcohol, and also soluble in halogenated hydrocarbons such as methylene chloride and chloroform. be. Furthermore, it has the unique property of being soluble in ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatic hydrocarbons such as toluene and xylene using alcohol as a co-solvent. In addition, polyvinylpyrrolidone is slightly soluble in weak alkaline aqueous solutions, but it dissolves in strong alkaline aqueous solutions such as those used as electrolytes in alkaline batteries.
Its dissolution is limited to a very small amount that causes swelling, and it is also chemically stable against strong oxidizing agents such as manganese dioxide as a positive electrode active material. Furthermore, polyvinylpyrrolidone has excellent film-forming ability, and when a polyvinylpyrrolidone solution is applied and dried, a transparent, glossy, and durable film is formed, which has an excellent effect of binding graphite particles together and adhering to the substrate. It has a good binder effect,
Moreover, since it swells upon contact with the electrolyte, it does not impede the conductivity of graphite. The present invention takes advantage of these properties of polyvinylpyrrolidone, uses polyvinylpyrrolidone as a binder for conductive paint, dissolves this polyvinylpyrrolidone in an organic solvent and disperses graphite to prepare a conductive paint, and replaces the conventional synthetic resin binder. Eliminates the drawbacks of the conductive paint used, and has low internal resistance.
Moreover, an alkaline battery with a large discharge capacity is provided. Polyvinylpyrrolidone is divided into four grades ranging from low molecular weight to high molecular weight, and is commercially available in powder form. Specific examples of commercially available products include General Aniline & Film Co.
Aniline & Film Corp.) or Badische Aniline & Film Corp.
Anilin & Soda Fabrik)
PVPK-15 (average molecular weight 10,000), PVPK-30 (average molecular weight 40,000), PVPK-60 (average molecular weight 160,000),
Examples include PVPK-90 (average molecular weight 360,000). The higher the molecular weight of these materials, the higher the viscosity of the paint. However, the viscosity can be increased by increasing the amount of low-molecular-weight ones, and there is no big difference between them and high-molecular-weight ones in terms of other properties. The conductive paint can be obtained by dissolving the polyvinylpyrrolidone in an organic solvent such as methyl alcohol, ethyl alcohol, butyl alcohol, and dispersing graphite. Dissolution of polyvinylpyrrolidone and dispersion of graphite are usually performed in the order of dissolving polyvinylpyrrolidone in an organic solvent and then dispersing graphite. and graphite can be dispersed at the same time, or graphite can be dispersed first and then polyvinylpyrrolidone can be dissolved. As the graphite, pyrolytic graphite, artificial graphite such as carbon black, natural graphite such as phosphorous graphite, earthy graphite, etc. are used. In the present invention, graphite was specifically selected as the conductive aid because graphite is relatively flexible, has high lubricity, has low contact resistance, is chemically stable, and is water repellent. This is because even after the polyvinylpyrrolidone swells, the electrolyte on the surface of the graphite is removed and good conductivity is exhibited. The composition of the conductive paint varies depending on the type of solvent and polyvinylpyrrolidone used, but it usually contains 5 to 10 parts of polyvinylpyrrolidone and 30 to 40 parts of graphite for 300 parts (by weight, the same applies hereinafter) of the solvent. A range of is preferred. The conductive paint as described above is usually applied by spraying or by pouring the conductive paint into the battery container and sucking out the excess paint. For example, in the case of a cylindrical alkaline battery, the coating may be performed on the surface of a positive electrode can serving as a battery container that comes into contact with the positive electrode mixture. Next, embodiments of the present invention will be described with reference to the drawings. Example 1 10 g of PVPK-90 (described above) was added little by little to 300 g of ethyl alcohol and dissolved, and 40 g of phosphorous graphite powder (viscosity 0.5 to 7 μm) was added thereto and well dispersed to prepare a paint. This paint was applied to the part of the nickel-plated cathode can 1 used as the battery container of the LR6 battery that would come into contact with the cathode mixture, and left to dry at room temperature for 20 hours.
A coating 2 was formed as shown in FIG. The obtained coating 2 is almost uniform, and its thickness is 40 μm on average.
It was hot. In the positive electrode can 1 on which the conductive film 2 has been formed in this manner, a ring-shaped positive electrode mixture molded body made by pressure-molding a positive electrode mixture powder consisting of manganese dioxide and graphite is placed along the inner wall of the positive electrode can 1. A core rod is inserted into the hollow part of the positive electrode mixture, and a punch slidably attached to the outer periphery of the core rod is lowered to pressurize the positive electrode mixture from above. was pressed onto the conductive film 2 formed on the inner surface of the positive electrode can 1. After crimping, pull up the punch, then pull out the core rod, bend the opening of the positive electrode can 1, form a groove near the opening end, and then insert the separator 4.
was inserted, and then an electrolytic solution was injected into the separator 4 to infiltrate the separator 4 and the positive electrode mixture 3. Next, the negative electrode material 5 is placed inside the separator 4 in the positive electrode can 1.
Then, the synthetic resin sealing body 8 equipped with the negative electrode lead rod 6 and washer 7 is inserted into the opening of the positive electrode can 1, and the portion beyond the groove of the positive electrode can 1 is tightened in the radial direction to close the sealing body 8. The opening of the positive electrode can 1 was sealed. Thereafter, the exterior was applied by a conventional method to produce an LR6 type alkaline manganese battery A as shown in Fig. 2. In Figure 2, 9 is a leaf spring, 10 is a negative terminal plate, 11 is an insulating ring, 1
2 and 13 are resin tubes, 14 is a positive terminal plate, 1
5 is a metal exterior can, and 16 is an insulating ring. Example 2 10 g of PVPK-90 was dissolved little by little in 200 g of ethyl alcohol, and then 100 g of toluene was added and mixed. Add 40% of the same phosphorous graphite powder as in Example 1 to this solution.
g was added and well dispersed to prepare a paint. This paint was applied to a positive electrode can for an LR6 type battery similar to that in Example 1, and dried to form a conductive film on the inner surface of the positive electrode can in the same manner as in Example 1.
LR6 type battery B was manufactured in the same manner. In this example, toluene was added to lower the viscosity of the paint and improve its fluidity when applied. Comparative Example 1 After dissolving 10 g of polystyrene in 300 g of toluene, 40 g of the same phosphorous graphite powder as in Example 1 was added and well dispersed to prepare a paint. This paint was applied to a positive electrode can for an LR6 type battery similar to that in Example 1, and dried to form a conductive film on the inner surface of the positive electrode can.
A type battery C was manufactured. Comparative example 2 300g of methyl ethyl ketone and 10% polyvinyl chloride
After dissolving 40 g of phosphorous graphite powder as in Example 1, the mixture was well dispersed to prepare a paint. This paint was applied to a positive electrode can for an LR6 type battery similar to that in Example 1, and dried to form a conductive film on the inner surface of the positive electrode can.
A type battery D was manufactured. Comparative Example 3 An LR6 type battery E was manufactured in the same manner as in Example 1 except that the conductive paint was not applied. Batteries A, B, C manufactured as above,
D and E initially, after 3 months storage at 45°C and 20
The open circuit voltage and short circuit current were measured after 12 months storage at °C. The results are shown in Tables 1 and 2. In addition, the discharge when the above five types of batteries were initially discharged at a final voltage of 0.9V with 2Ω intermittent discharge (5 seconds discharge/5 seconds pause) after storage at 45℃ for 3 months and after storage at 20℃ for 12 months. The times (net discharge time) are shown in Table 3.

【table】

【table】

[Table] As is clear from the results shown in Tables 2 and 3, Batteries A and B according to the present invention have low internal resistance and excellent discharge performance. The effects of the present invention are particularly noticeable in the properties after storage. Further, as shown in Table 1, batteries A and B according to the present invention
The open circuit voltage was the same as that of conventional batteries C and D, and no deterioration in battery characteristics due to the use of polyvinylpyrrolidone was observed.

[Brief explanation of the drawing]

1 and 2 are views showing an alkaline battery according to the present invention, and FIG. 1 is a cross-sectional view showing a state in which a conductive film is formed on the inner surface of a positive electrode can during manufacturing;
FIG. 2 is a partial sectional view showing the state after manufacture. 1... Positive electrode can, 2... Conductive coating.

Claims (1)

[Claims] 1. Production of an alkaline battery characterized by applying a conductive paint made by dissolving polyvinylpyrrolidone in an organic solvent and dispersing graphite powder to the inner surface of a battery container that also serves as a current collector and drying it to form a conductive film. Law.