JPH0129310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a battery equipped with a gas diffusion electrode using oxygen as an active material.

Conventional Structure and Problems The so-called zinc-air battery is widely known as a battery that uses a gas diffusion electrode with oxygen as an active material for the positive electrode, an aqueous potassium hydroxide solution for the electrolyte, and zinc for the negative electrode. Traditionally, large batteries have been widely used for lighting buoys, traffic signals, etc. In recent years, with the spread of small button-type primary batteries, this battery system has attracted attention, and button-type batteries have begun to be used.
However, this battery uses oxygen as the positive electrode active material, and it is necessary to open a hole in a part of the battery to take in oxygen during discharge. Because of these pores, water vapor flows in and out depending on the vapor pressure of the internal electrolyte, causing changes in concentration and volume of the electrolyte in the battery, and affecting various characteristics of the battery. This situation will be explained using FIG. In the figure, 1 is an oxygen electrode (air electrode), and 2 is a polytetrafluoroethylene (PTFE) porous membrane that allows gas diffusion but blocks liquid. 3
4 is a porous body that supports the oxygen electrode and diffuses air, 5 and 6 are separators, and 7 is a negative electrode made of a mixture of an aqueous potassium hydroxide solution and zinc powder. be. Generally, the concentration of potassium hydroxide used as an electrolyte is 30 to 35% by weight.
When the relative humidity was higher than 47% to 59%, external moisture was taken in, causing a decrease in electrolyte concentration and volumetric expansion, resulting in a decrease in discharge performance and electrolyte overflow. On the other hand, when the relative humidity is below the above range, evaporation of the electrolytic solution occurs, resulting in an increase in internal resistance and a decrease in discharge performance. Therefore, button-type zinc-air batteries have been limited to applications in hearing aids where they are used up within a relatively short period of time, as they are susceptible to significant effects from the environmental atmosphere. In order to expand the uses of this battery, it is necessary to improve the characteristics with microcurrent, and one way to do this is to use a porous PTFE membrane.
Measures have been considered to reduce the air permeability of porosity, but it is difficult to adjust the porosity to a certain level, and satisfactory effects have not always been obtained. In the figure, 8 is a negative electrode container, 9 is an insulating gasket, and 10 is a positive electrode container.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems under minute operating currents, and aims to improve the environmental stability of batteries.

Structure of the Invention In other words, the present invention provides stable discharge characteristics when using a minute current and minimizes water vapor permeation by providing an oxygen selective permeable membrane and an oxygen permeable solution layer on the air intake side of the oxygen electrode. It is characterized by prevention.

Among the group of silicone resins and copolymers of silicone resins and other polymer resins, polydimethylsiloxane and polydimethylsiloxane-polyhydroxystyrene cross-linked membranes have high oxygen permeability but low water vapor permeation. type copolymers and polydimethylsiloxane-polyhydroxystyrene-polysulfone ternary crosslinked copolymers. Also,
Examples of oxygen permeable solutions include perfluorodecalin and perfluoromethylcyclohexane. The present invention uses these two materials with different properties, and the present invention will be explained in detail below using one example.

Description of Examples A polydimethylsiloxane-polyhydroxystyrene crosslinked copolymer was used as an oxygen-selective permeable membrane. This material has a porosity of 40% and a pore diameter of 0.3 μm.
on one side of a polypropylene porous body with a thickness of 50 μm.
Form a film to a thickness of 0.3 μm. On the other hand, a polypropylene nonwoven fabric (thickness: 50 μm) was impregnated with perfluorodecalin, and the battery shown in FIG. 2 was constructed using these two types of components. The construction method of the battery is almost the same as the conventional one, and the above-mentioned polypropylene porous body 1
The polydimethylsiloxane-polyhydroxystyrene copolymer film 11a provided on one side of the positive electrode container 10 is positioned on the air intake hole 3 side of the positive electrode container 10.

Furthermore, the above-mentioned perfluorodecalin-impregnated layer 12 is laminated thereon. After that, the PTFE membrane 2, the oxygen electrode 1, and the separators 5 and 6 are laminated, the mixture 7 of potassium hydroxide aqueous solution and zinc chloride powder is put into the negative electrode container 8, and the positive electrode part and the negative electrode part are combined.
The open end of the positive electrode container 10 was caulked to the negative electrode container 8 side via the gasket 9. R ₄₄ as an example
A battery of the same size (diameter 11.6 mm, height 5.4 mm) was constructed. In order to evaluate the environmental stability of this battery in detail, the results of continuous discharge at a temperature of 20°C and normal humidity (35 to 85% relative humidity) with a load of 68KΩ are shown in Figure 3A. Ta. For comparison with conventional products, conventional battery B using a PTFE membrane was discharged under the same conditions. As a result, conventional product B stopped discharging after about 2000 hours, while product A of the present invention stopped discharging about 8 times as long.
Discharged for 16,000 hours. As can be seen from this example, the product of the present invention is capable of discharging over a long period of time due to the double arrangement of an oxygen-selective permeable membrane and an oxygen-permeable layer that are less affected by water vapor, and is capable of performing electronic desktop calculations. When used in devices such as appliances and game watches, the above-mentioned results indicate that it can last for 1.5 to 2 years.

Effects of the Invention As described above, the present invention provides a battery with an oxygen-selective permeable membrane and an oxygen-permeable solution layer on the air intake side of the gas diffusion electrode, thereby making the battery less susceptible to environmental conditions and reducing the It has become possible to obtain extremely stable characteristics for current.

[Brief explanation of drawings]

Figure 1 is a cross-sectional structural diagram of a conventional button-type air battery, Figure 2 is a cross-sectional structural diagram of a button-type air battery in an embodiment of the present invention, and Figure 3 is a conventional button-shaped air battery in an embodiment of the present invention. It is a discharge characteristic diagram when compared with a product. 1... Gas diffusion electrode (oxygen electrode), 2... Polytetrafluoroethylene porous membrane, 3... Air intake hole, 4... Porous body that also serves as a support for the oxygen electrode,
5, 6... Separator, 7... Negative electrode, 8... Negative electrode container, 9... Insulating gasket, 10... Positive electrode container, 11... Polypropylene porous body provided with oxygen selective permeable membrane 11a, 12... Par Polypropylene nonwoven fabric impregnated with fluorodecalin.

Claims (1)

[Scope of Claims] 1. An air battery comprising a gas diffusion electrode using oxygen as an active material, and an oxygen-selective permeable membrane and an oxygen-permeable solution layer provided on the air intake side of the gas diffusion electrode. 2. The oxygen-selective permeable membrane is made of any material from the group consisting of polydimethylsiloxane, polydimethylsiloxane-polyhydroxystyrene crosslinked copolymer, and polydimethylsiloxane-polyhydroxystyrene-polysulfone ternary crosslinked copolymer. An air battery according to claim 1, comprising: 3. The air cell according to claim 1, wherein the oxygen permeable solution layer is made of perfluorodecalin or perfluoromethylcyclohexane.