JPH03274680A - Secondary battery - Google Patents

Abstract

PURPOSE:To prevent dendrite short and prevent the deterioration of a negative pole, and prevent the drop of the activity of MnO2 so as to improve cycle life, capacity, and output by making electrolyte contain Mn ions and carboxyl anions. CONSTITUTION:In a secondary battery where MnO2, as positive electrode substance, zinc sulfate aqueous solution, as electrolyte, and Zn, a negative pole active substance, are used, Mn ions and carboxyl anions are contained in the electrolyte. As the carboxyl ions, acetic acid ions, formic acid ions, or the like can be used. It is to be desired that the ions other than sulfuric acid ions, acetic acid ions, Mn ions, and Zn ions should not exist. It is to be desired that the concentrations of the Mn ions and carboxyl anions should be, though depending upon the concentration of sulfuric acid Zn, within 0.01 to 1M, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a secondary battery using manganese dioxide as a positive electrode active material, an aqueous zinc sulfate solution as an electrolyte, 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 electrical 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 been rapidly increasing.

Hitherto, in this type of field, nickel-cadmium secondary batteries have been commercialized, and alkaline zinc secondary batteries are also being researched. In particular, an alkaline zinc secondary battery using zinc as a negative electrode active material has 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.

In addition, it has recently become clear that a battery that uses 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, 61-248
370).

This type of secondary battery has the advantages of high energy density, low cost, and excellent economic efficiency, similar to alkaline zinc secondary batteries.

However, since this type of secondary battery also uses zinc as the negative electrode active material, due to subtle differences in the surface condition of the zinc electrode,
With repeated charging and discharging, zinc dendrites (
There was a problem in that crystals (resin-like) were formed and grew toward the positive electrode, eventually penetrating the separator and causing an internal short circuit (dendritic short), resulting in deterioration of the negative electrode.

Furthermore, this type of secondary battery has a problem in that the electrochemical reaction of manganese dioxide at the positive electrode decreases with repeated charging and discharging, resulting in a shortened cycle life of the secondary battery.

[Problems to be Solved by the Invention] The purpose of the present invention is to prevent deterioration of the negative electrode by preventing dendrite short circuit in secondary batteries that use zinc as the negative electrode active material, and to prevent deterioration of the negative electrode due to repeated charging and discharging. The object of the present invention is to provide a secondary battery with a long cycle life, high capacity, and high output by preventing the electrochemical activity of manganese dioxide from decreasing.

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors have developed a weakly acidic solution using manganese dioxide as a positive electrode active material, zinc sulfate as an electrolyte, and zinc as a negative electrode active material. The present inventors have discovered that the above-mentioned problems can be solved by incorporating manganese ions and carboxyl anions into the electrolyte of the secondary battery, and have completed the present invention. That is, the present invention provides 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, which is characterized in that the electrolyte contains manganese ions and carboxyl anions. Next battery.

The present invention will be explained in more detail below.

The electrolytic solution for the secondary battery of the present invention uses zinc sulfate as the main electrolyte, and is prepared by adding and dissolving a salt in which manganese ions and carboxyl anions coexist in the aqueous solution. Examples of such salts include, but are not limited to, adding manganese ions as acetates and sulfates, and adding carboxyl anions as manganese salts and zinc salts. Examples of carboxyl anions include acetate ions and formate ions. In addition, in order to further prevent a decrease in the electrochemical activity of manganese dioxide and a decrease in the efficiency of zinc precipitation and dissolution, as well as to further prevent a decrease in repeated stability, sulfate ions and acetate ions are added to the electrolyte. Since it is preferable that there be no ions other than manganese ions and zinc ions, it is preferable to add both manganese sulfate and zinc acetate or to add manganese acetate to the electrolytic solution. 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 for reasons such as large extraction current and extraction capacity. In addition, the concentration of manganese ion and carboxyl anion depends on the concentration of zinc sulfate, but each is 0.
．． Preferably, it is between 01M and IM. 0.01
If it is less than M, the effect of adding manganese ions and carboxyl anions may be negligible, while if it exceeds 2M, the solubility of zinc sulfate will decrease and the concentration of zinc ions present in the electrolyte will decrease, resulting in a decrease in the charging voltage. This may lead to increase in the amount of water, decompose the solvent water, and reduce cyclic stability. Furthermore, in order for manganese ions to be charged and oxidized at a low overvoltage, and for carboxyl anions to maintain a constant hydrogen ion concentration in the electrolyte, the molar ratio of manganese ions and carboxyl anions in the electrolyte should be 1:5.
It is preferable that the adjustment is made between 5=4.

Zinc used as the negative electrode active material of the secondary battery of the present invention is not particularly limited, but preferably has a purity of 99% or more. Further, although the shape is not particularly limited, it is preferable that the effective electrode surface area of the zinc electrode is large, so it is preferable to use granular zinc or a zinc electrode deposited by electrolysis.

Examples of manganese dioxide used as the positive electrode active material of the secondary battery of the present invention include natural manganese dioxide, chemical manganese dioxide, and electrolytic manganese dioxide. It is preferable to use Further, although these manganese dioxides can be used as they are, it is preferable to use them in combination with conductive carbon powder such as acetylene black, since it is possible to improve the conductivity and the retention of the electrolyte. Furthermore, these positive electrode active materials can be press-molded into a positive electrode, or made into a thin film by a method such as screen printing, and a binder or the like can be mixed with these positive electrode active materials in order to create a positive electrode in an arbitrary shape. good.

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

Example 1 The cell shown in Figure 1 was constructed 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 made of a 99% pure zinc plate. Created. This was impregnated with 3rrl of an aqueous solution consisting of 2M zinc sulfate and 0.5M manganese acetate as an electrolytic solution dropwise 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 1.9 V.

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 A battery was produced in the same manner as in Example 1, except that an aqueous solution consisting of 2M zinc sulfate, 0.2M zinc acetate, and 0.5M manganese sulfate was used as the electrolyte. A cycle life test was then conducted on this battery under the same conditions as in Example 1, and cycle changes in battery capacity were investigated. The results are also shown in Table 1.

Example 3 A battery was produced in the same manner as in Example 1 except that an aqueous solution consisting of 2M zinc sulfate, 0.5M zinc acetate, and 0.2M manganese sulfate was used as the electrolyte. A cycle life test was then conducted on this battery under the same conditions as in Example 1, and cycle changes in battery capacity were investigated. The results are also shown in Table 1.

Example 4 A battery was produced in the same manner as in Example 1 except that an aqueous solution consisting of 2M zinc sulfate and 0.5M manganese formate was used as the electrolyte. Example 1 for this battery
A cycle life test was conducted under the same conditions as above, and the cycle change in battery capacity was investigated. The results are also shown in Table 1.

Example 5 A battery was produced in the same manner as in Example 1 except that an aqueous solution consisting of 2M zinc sulfate, 0.5M zinc formate, and 0.2M manganese sulfate was used as the electrolyte. A cycle life test was then conducted on this battery under the same conditions as in Example 1, and cycle changes in battery capacity were investigated. The results are also shown in Table 1.

Example 6 A sample was prepared by sufficiently mixing 5 mg of electrolytic manganese dioxide and 2.5 mg of Ketchen Black. This was placed in the cell shown in Figure 2, the counter electrode was a 99% pure zinc plate, the reference electrode was a saturated sodium chloride calomel electrode, and 2M
The cyclic portammogram of manganese dioxide was investigated at room temperature in an electrolyte containing 0.5M zinc sulfate and 0.5M manganese acetate. The obtained portamogram is 0.6
FIG. 3 shows the relationship between the amount of reduction electricity of manganese dioxide and the number of repetitions, estimated by four-diagram integration in the potential range from V to -0.1 V versus a saturated sodium chloride calomel electrode.

Comparative Example 1 A battery was produced in the same manner as in Example 1 except that an aqueous solution consisting only of 2M zinc sulfate was used as the electrolyte. A cycle life test was then conducted on this battery under the same conditions as in Example 1, and cycle changes in battery capacity were investigated. The results are also shown in Table 1. As a result, it was found that the decrease in the cycle capacity of the battery was caused by the decrease in the activity of the positive electrode active material and the detachment of the electrode due to the generation of dendrites in the negative electrode.

Comparative Example 2 A cell similar to that of Example 6 was constructed except that 2M zinc sulfate was used as the electrolyte, and its cyclic portamogram was examined to examine the cyclic stability of manganese dioxide. The results are also shown in FIG.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, it is possible to prevent dendrite short circuit and deterioration of the negative electrode, and furthermore, it is possible to prevent deterioration of the negative electrode due to repeated charging and discharging. Since it is possible to prevent a decrease in electrochemical activity, cycle life can be extended,
In addition, a secondary battery with high capacity and high output can be obtained. Moreover, since this secondary battery contains manganese ions in the electrolyte, it is resistant to overcharging.

[Brief explanation of drawings]

Figure 1 is a diagram showing a cross section of the test cell used in Example 1, Figure 2 is a diagram showing a cross section of a cell used in Example 6, and Figure 3 is a diagram showing the relationship between the amount of electricity reduced and the number of repetitions of manganese dioxide. It is a figure showing a relationship. In the figures, the numbers indicate the following: DESCRIPTION OF SYMBOLS 1... Cell exterior, 2... Positive electrode current collector, 3... Positive electrode mixture, 4... Glass separator, 5... Negative electrode, 6...
... Negative electrode current collector, 7... Positive electrode terminal, 8... Negative electrode terminal, 9... Spacer, 10... Positive electrode current collector, 11...
・Teflon cell, 12...sample, 13...glass separator, 14...capillary

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 and carboxyl anions.