JPH0384868A - Secondary cell - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the electrochemical activity of the manganese dioxide, and to obtain a secondary cell of a long cycle life, a high capacity, and a high output, by including manganese ions in the electrolyte. CONSTITUTION:In a secondary cell in which manganese dioxide is used as the positive electrode active substance, zinc sulfate water solution is used is the electrolyte, and zinc is used as the load active substance, manganese ions are included in the electrolyte. That is, the electrolyte of this secondary cell is made mainly of zinc sulfate, and by adding a salt including manganese ions as cations. As a result, the deterioration of the electrochemical activity of the manganese dioxide following the repeating charge and discharge is prevented, the cycle life is extended, and a secondary cell of a high capacity and a high output can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an aqueous solution secondary battery using manganese dioxide as a positive electrode active material and zinc as a negative electrode active material.

[Prior Art] Batteries are widely used as power sources for electronic and electrical equipment. BACKGROUND ART Recently, as various electric and electronic devices have become smaller and more sophisticated, portable, and personalized, the demand for economical secondary batteries that can be used for a long time has rapidly increased.

Conventionally, in this type of field, research has been carried out on nickel-cadmium secondary batteries, alkaline zinc secondary batteries, etc. especially,
Alkaline zinc secondary batteries that use zinc as a negative electrode active material have the advantages of high energy density, low cost, and excellent economic efficiency.

However, alkaline zinc secondary batteries have the drawbacks of large deterioration of the zinc electrode characteristics and short cycle life.
It has not been commercialized yet.

Recently, it has become clear that a battery using manganese dioxide as the positive electrode active material and zinc as the negative electrode active material can be used as a secondary battery by using a zinc sulfate aqueous solution as the electrolyte (for example, JP-A-61 -2483
(see issue 70).

Similar to alkaline zinc secondary batteries, this type of secondary battery has the advantages of high energy density, low cost, and excellent economic efficiency. However, with repeated charging and discharging, the electrochemical activity of manganese dioxide decreases, resulting in a problem that the cycle life of the secondary battery is shortened.

[Problems to be Solved by the Invention] An object of the present invention is to prevent the electrochemical activity of manganese dioxide from decreasing due to repeated charging and discharging, and to provide a high-capacity, high-output battery with a long cycle life. Our goal is to provide the next battery.

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors used manganese dioxide as the positive electrode active material, a zinc sulfate aqueous solution as the electrolyte, and zinc as the negative electrode active material. The present invention was completed based on the discovery that the above-mentioned problems can be solved by incorporating manganese ions into the zinc sulfate electrolyte in weakly acidic secondary batteries. That is, the present invention is a secondary battery that uses manganese dioxide as a positive electrode active material, a zinc sulfate aqueous solution as an electrolyte, and zinc as a negative electrode active material, and is characterized in that the electrolyte contains manganese ions. .

The present invention will be explained in more detail below.

The electrolytic solution of the secondary battery of the present invention is produced by using zinc sulfate as the main electrolyte and adding a salt having manganese ions as cations to this electrolyte. Examples of salts with manganese ions as cations include manganese sulfate, manganese chloride,
Examples include manganese acetate, but are not limited thereto. The concentration of zinc sulfate, which is the main electrolyte, may be at any concentration between 0.5M and saturation, but it is preferably 2M or more because the extraction current and extraction capacity are large. Further, the concentration of manganese ions is preferably between 0.01M and 2M. If it is less than 0.01M, there is almost no effect of adding manganese ions, and if it exceeds 2M, the solubility of zinc ions decreases, resulting in poor zinc reversibility, shortening the cycle life, and causing secondary damage. There is a risk that the battery will no longer function.

Although the zinc used as the negative electrode active material of the secondary battery of the present invention is not particularly limited, it is preferable that its purity is 99% or more. Further, since it is preferable that the effective electrode surface area of the zinc electrode is large, it is preferable to use granular zinc or a zinc electrode deposited by electrolysis.

Manganese dioxide used as the positive electrode active material of the secondary battery of the present invention includes natural manganese dioxide, chemical manganese dioxide, electrolytic manganese dioxide, etc. Among these, electrolytic manganese dioxide, which has high activity, can be used as the positive electrode active material of the battery. These manganese dioxides can be used as they are, but it is preferable to use them in combination with conductive carbon powder such as acetylene black because this improves conductivity and electrolyte retention. . Furthermore, such positive electrode active materials can be press-molded into positive electrodes, or made into thin films by methods such as screen printing.
A binder or the like may be mixed with these positive electrode active materials in order to obtain a positive electrode of any shape.

C Examples] Examples are given below to explain the present invention in more detail, but the present invention is not limited thereto.

Example 1 A first test using a positive electrode mixture consisting of 1 g of electrolytic manganese dioxide and 0.1 g of Ketchen Black, a separator made of glass fiber filter paper, and a negative electrode consisting of zinc electrolytically deposited on a lead current collector. A cell as shown in the figure was fabricated. This was impregnated with 3 ml of an aqueous solution consisting of 2M zinc sulfate and 0.5M manganese sulfate as an electrolyte to produce a battery.

A discharge test of the battery prepared as described above was carried out at 25°C.
The discharge end voltage was 0.3V, and the discharge was carried out at a constant current of 10mA. After discharging, charging was performed at 10 mA until the charging voltage reached 1.9V. A cycle life test of the battery was performed using this discharging/charging operation as one cycle, and cycle changes in battery capacity were investigated. The results are shown in Table 1.

Example 2 2.5M zinc sulfate and 0.5M zinc sulfate as electrolyte. A battery similar to Example 1 was constructed except that 2M manganese sulfate was used. Then, a cycle life test was conducted on this battery under the same conditions as in Example 1, and the cycle change in battery capacity was investigated. The results are also shown in Table 1.

Example 3 A battery similar to Example 1 was constructed except that 2M zinc sulfate and 0.2M manganese chloride were used as the electrolyte.

Then, a cycle life test was conducted on this battery under the same winter cropping conditions as in Example 1, and the cycle change in battery capacity was investigated. The results are also shown in Table 1.

Comparative Example A battery was constructed in the same manner as in Example 1, except that 2M zinc sulfate was used as the electrolyte. Then, a cycle life test was conducted on this battery under the same conditions as in Example 1 to examine the cycle change in battery capacity. The results are also shown in Table 1.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, it is possible to prevent the decrease in the electrical activity of manganese dioxide that occurs due to repeated charging and discharging, thereby increasing the cycle life. , and a high capacity, high output secondary battery can be obtained. Furthermore, since this secondary battery contains manganese ions in the electrolyte, it is resistant to overcharging.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a cross section of a test cell. In this figure, each number indicates the following. ■Cell exterior ■Positive electrode current collector ■Positive electrode mixture ■Glass separator ■Negative electrode
■Negative electrode current collector ■Positive electrode terminal ■Negative electrode terminal ■Spacer Figure 1

Claims (1)

[Claims] (1) A secondary battery using manganese dioxide as a positive electrode active material, a zinc sulfate aqueous solution as an electrolyte, and zinc as a negative electrode active material, characterized in that the electrolyte contains manganese ions.