JPH03108256A - Battery - Google Patents

Abstract

PURPOSE:To increase the storage performance and discharge performance of a battery by placing a polyimide thin film between the air intake side of a gas diffusion electrode and the inner surface of a battery container. CONSTITUTION:A polyimide thin film 11 is placed between a gas diffusion electrode using oxygen as the active material and a battery container 8 having an air intake hole 3. As the supporter of the polyimide film 11, an alkali- resistant microporous film mainly comprising either one of polyolefin, fluororesin, and polysulfone is used. This makes oxygen permeability suitable for a battery and the penetration of water vapor and carbon dioxide is effectively blocked. The storage performance and discharge performance are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a gas diffusion electrode using oxygen as an active material, an electrolyte such as an alkaline aqueous solution, and a metal such as zinc, magnesium, or aluminum, or alcohol, hydrazine, or hydrogen. The present invention relates to a battery equipped with a negative electrode active material such as.

BACKGROUND OF THE INVENTION BACKGROUND ART Batteries equipped with gas diffusion electrodes and using oxygen as an active material include air cells, fuel cells, and the like. Especially alkaline aqueous solution,
In a battery that uses a neutral aqueous solution as an electrolyte, water vapor flows in and out from the gas diffusion electrode (oxygen electrode) depending on the internal vapor pressure, causing changes in the concentration and volume of the electrolyte in the battery, and this changes the battery characteristics. was influencing. Taking a button-type zinc-air battery as an example, the situation will be explained using FIG. 2. In the figure, 1 is an oxygen electrode (air electrode), and 2 is a polytetrafluoroethylene (polytetrafluoroethylene) that has gas diffusivity but blocks liquids.
This is a porous membrane that supports an oxygen electrode made of (PTFE). 3
4 is a porous body for supporting the oxygen electrode and diffusing air; 5 and 6 are separators; and 7 is a negative electrode made of a mixture of an aqueous potassium hydroxide solution and zinc chloride powder. Generally, an aqueous potassium hydroxide solution is used as the alkaline electrolyte, and its concentration is 30 to 35%. For this reason, when the relative humidity is higher than 47% to 59%, external moisture is taken in, causing a decrease in the concentration of the electrolyte and volume expansion, resulting in a decrease in discharge performance and leakage of the electrolyte. on the other hand,
When the relative humidity is below the above range, evaporation of the electrolyte occurs, resulting in an increase in internal resistance and a decrease in discharge performance. Therefore, since they are easily affected by the environmental atmosphere, there are problems with their properties after long-term storage. Air cells and fuel cells are only designed for use in a specific field, and there are major challenges in making them more general-purpose. had. In the figure, 8 is a negative electrode container, 9 is an insulating gasket, and 10 is a positive electrode container.

Problems to be Solved by the Invention In order to improve these problems, various countermeasures have been considered in the past. For example, a substance that reacts with the electrolyte is inserted into a portion around the air hole to prevent the electrolyte from leaking to the outside of the battery. Alternatively, an electrolyte absorbing material such as a nonwoven fabric made of paper or a polymeric material is provided to prevent leakage of the electrolyte to the outside of the battery. Furthermore, proposals have been made to prevent water vapor and carbon dioxide from entering the battery, even by making the air holes extremely small and limiting the amount of oxygen supplied, but none of these methods prevent liquid leakage. However, there remained major issues regarding discharge performance, especially performance during long-term discharge. The main causes of these are the dilution and volumetric expansion of the electrolyte due to the intrusion of water vapor from the air into the battery, and the inhibition of the discharge reaction due to the formation of carbonates due to the intrusion of carbon dioxide gas and the blockage of the air flow path. Conversely, when the outside air is low-humidity, evaporation of water in the electrolyte causes performance to deteriorate. In order to eliminate this cause, in recent years, methods have been developed to control the permeation of water vapor and carbon dioxide gas and to supply air to the oxygen electrode through a membrane that selectively allows oxygen to pass through, such as non-porous polysiloxane membranes. A method using a film that integrates a uniform thin film of , a thin film of a metal oxide or an organic compound containing metal atoms, and a suitable porous film has been proposed.

However, to date, it has not been possible to obtain satisfactory discharge performance due to the inability to obtain sufficiently effective oxygen gas selective permeability and insufficient permeation blocking ability for water vapor and carbon dioxide gas, and it has not been possible to obtain long-term use. It has not been put into practical use because of the technical issue of not being able to withstand storage.

Therefore, the present invention aims to improve the storability and long-term use performance of the above-mentioned battery, and to obtain satisfactory discharge performance under discharge conditions ranging from low to high loads. The purpose of this invention is to provide an effective means for preventing water vapor and carbon dioxide from the atmosphere from entering the battery over a long period of time.

Means for Solving the Problems The present invention provides a battery that includes a gas diffusion electrode using oxygen as an active material and a battery container having an air intake hole communicating with the outside air, and a battery having an air intake side of the gas diffusion electrode and an inner surface of the battery container. A polyimide membrane is interposed between them as an oxygen selective permeable membrane.

Furthermore, we selected polyolefins such as polypropylene and polyethylene, fluororesin, polysulfone, etc., which have excellent alkali resistance, as the porous base material to support this membrane, and after further investigation, we completed the project. Note that the microporous membrane may be a single layer, but
In order to ensure strength during handling, manufacturing, or use, a two-layer or more-layer structure may be formed by further integrating an alkali-resistant nonwoven fabric as necessary.

The present invention was completed after intensive studies on the use of polyimide membranes for batteries, and the discovery that they comprehensively satisfy the above-mentioned characteristics and that the performance of batteries to which the polyimide membranes are applied is extremely excellent.

Function: As is clear from the results of the battery test in the Examples described below, this configuration has a satisfactory oxygen permeation rate for batteries as well as the effect of blocking water vapor and carbon dioxide from the atmosphere. The battery satisfies both the high-load discharge performance required of a practical battery and the performance when discharged for a long time in an atmosphere of high or low humidity.

Example An example of the present invention is shown.

A battery using a polyimide membrane as an oxygen-selective permeable membrane, a battery using a polypropylene membrane as a support, and a battery not using the membrane as a comparative example were fabricated and evaluated.

In the case of a comparative example, the structure was exactly the same as that shown in FIG.

Examples 1 and 2 using polyimide membranes are almost the same as those shown in FIG. 2, and as shown in FIG. The only difference from FIG. 2 is that a composite membrane is interposed, and the composite membrane is arranged so that the side of the boimide membrane faces the side of the air intake hole 3.

The shape of the prototype battery is 11.6 mm in diameter and 5.4 meters in total height, and it can be used under relatively high load (75Ω) at 20℃ and normal humidity (60℃).
The sufficiency of the oxygen uptake rate from the air into the battery was evaluated by continuous discharging at a relatively low load (3KΩ).
) at 20℃, high humidity (90% RH) and low humidity (20% RH)
Due to long-term continuous discharge at RH), during the long-term discharge period, water vapor is taken into the atmosphere and water evaporates inside the battery.
We also evaluated the degree of influence on battery performance, such as carbon dioxide uptake.

The details of the prototype batteries are shown in Table 1. Table 2 also shows the performance test results of the prototype batteries.

In Table 2, the end-of-discharge voltage is 0.9 V in all cases, and the weight change shows the increase and decrease before and after the discharge test, and is a numerical value that mainly suggests the amount of moisture taken in or evaporated during discharge.

The support of the composite membrane of the present invention is composed of an alkali-resistant material. The present invention can be most clearly explained in detail by comparing the characteristics of these batteries with a comparative example that does not use a composite membrane. First, in high-load tests at 20°C and normal humidity, the discharge period is short, and the effects of moisture uptake, evaporation, and carbon dioxide gas are small. There is no need to give much consideration to blocking the transmission of. Therefore, under such conditions, excellent characteristics can be obtained even in the comparative example. On the other hand, in Examples 1 and 2 described above, discharge characteristics equivalent to those of the comparative example were obtained, indicating that the rate of oxygen permeating through the composite membrane sufficiently follows the rate of oxygen consumed by the discharge reaction. It shows.

On the other hand, in the case of low-load discharge, the discharge period may be long, but when the outside air is high or low humidity, the battery characteristics are better in preventing the permeation of moisture and carbon dioxide gas, especially moisture, than in the oxygen supply rate. This is important because the battery of the comparative example, which does not have a mechanism to prevent the permeation of moisture and carbon dioxide, has a voltage drop during discharge due to depletion of moisture, or conversely, blockage of the air holes due to leakage due to excessive intake of moisture. However, a capacity equivalent to only a portion of the discharge capacity obtained in the high-load test is obtained.Also, it goes without saying that liquid leakage during discharge is a life-saving problem in practical terms. The examples showed extremely usable performance, and a capacity almost equal to the discharge capacity in the high load test was obtained.These trends were the same whether the test atmosphere was high humidity or low humidity.

This shows that in the case of the example, the moisture permeation blocking effect of the composite membrane was sufficiently exhibited.

Taking all the above into account, the prototype battery using a composite membrane with a polyimide membrane on a microporous membrane has excellent high-load and low-load characteristics, changes well in the external atmosphere, and has particularly good alkali resistance. It can be concluded that an excellent battery can be provided when a porous membrane is used as a support. Furthermore, similar effects can be obtained with the microporous membrane supporting the polyimide membrane shown in the Examples with other alkaline microporous membranes (for example, nylon microporous membranes).

In addition, in the examples, it has been confirmed that almost the same results can be obtained even when the thin film side of the composite membrane is brought into contact with the air intake hole side.

In addition, in the above examples, the composite membrane of the present invention was installed between the battery container and the porous body for air diffusion, but the composite membrane of the present invention is a microporous membrane, and in some cases, a nonwoven fabric is further integrated into the composite membrane of the present invention. Since the cell is composed of a support, there is no difference in battery characteristics even if the porous body for air diffusion is removed.

We also confirmed that an air battery using an aqueous solution of neutral salts such as ammonium chloride or zinc chloride as the electrolyte has the same effect as the battery using an alkaline electrolyte shown in the example. Therefore, the present invention can be explained in detail for the same reason as the examples.

Effects of the Invention As is clear from the above explanation, the oxygen gas diffusion electrode according to the present invention has excellent practical performance over a range from high load to low load for batteries using a neutral or alkaline aqueous solution as the electrolyte, and excellent performance. Leak resistant.

The effect is that it can be stored for a long time.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a button-type zinc-air battery used to study examples and comparative examples of the present invention, and FIG. 2 is a cross-sectional view of a conventional button-type zinc-air battery that does not use a composite membrane. 1... Oxygen electrode (air electrode), 2... Water repellent membrane, 3... Air intake hole, 4... Porous membrane, 5, 6...・・・Separator, 7・・・・・・
Negative electrode zinc, 8... Negative electrode container, 9... Insulating gasket, 10... Positive electrode container, 11...
...Composite membrane.

Claims (2)

[Claims] (1) A gas diffusion electrode containing oxygen as an active material and a battery container having an air intake hole communicating with the outside air are provided, and a polyimide thin film is provided between the air intake side of the gas diffusion electrode and the inner surface of the battery container. A battery characterized by: (2) The battery according to claim 1, wherein an alkali-resistant microporous membrane whose main component is polyolefin, fluororesin, or polysulfone is used as a support for the polyimide membrane.