JPH05205784A - Oxygen permeable composite film and battery employing said composite film - Google Patents

Abstract

PURPOSE:To enhance storage properties and performance for a long use of a battery equipped with gas diffusing electrodes using oxygen as active material. CONSTITUTION:Mixture of fluorine contained resin soluble to solvent and metallic oxide powder is applied to a porous film to obtain an oxygen permeable film 11 which restrains vapor from being permeated and selectively takes in oxygen. By this constitution, satisfactory discharge performance required by a discharge condition for a range of low load to high load can be obtained, and battery excellent in storage properties and performance for long use can also be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen permeable composite membrane and a battery using the composite membrane, and more particularly to an oxygen permeable composite membrane for a battery equipped with a gas diffusion electrode using oxygen as an active material and the composite membrane thereof. Relates to a battery using.

[0002]

2. Description of the Related Art Batteries equipped with gas diffusion electrodes and using oxygen as an active material include air batteries and fuel cells. As the electrolyte, an alkaline, neutral or acidic electrolyte or a solid electrolyte is used.

Particularly, in a battery using a solution as an electrolyte, water vapor flows in and out of a gas diffusion electrode (oxygen electrode) in accordance with the vapor pressure of the electrolyte inside, so that the concentration change and volume change of the electrolytic solution in the battery occur. It happened, and this affected various battery characteristics. Taking a button type battery as an example, the situation will be described with reference to FIG. In the figure, 1 is an oxygen electrode (air electrode),
Reference numeral 2 is a polytetrafluoroethylene (PTFE) water-repellent film that has gas diffusivity but blocks liquid. 3 is an air intake hole from the outside, 4 is a porous film for supporting an oxygen electrode and diffusing air, 5 and 6 are separators, and 7 is a negative electrode composed of a mixture of an aqueous potassium hydroxide solution and zinc hydride powder. .. Generally, a potassium hydroxide aqueous solution is used as the alkaline electrolyte, and the concentration thereof is 30 to 35%. For this reason, when the relative humidity is higher than 47 to 59%, external humidity is taken in, the concentration of the electrolytic solution is reduced, and the volume is expanded, resulting in deterioration of discharge performance and leakage of the electrolytic solution. On the other hand, when the relative humidity is less than the above, evaporation of the electrolytic solution occurs, causing an increase in internal resistance and a decrease in discharge performance. Therefore, there is a problem in the characteristics after long-term storage because it is significantly affected by the environmental atmosphere, and air batteries and fuel cells are only designed for certain specific fields, and there is a major problem in generalization. Was. In the figure, 8 is a negative electrode container, and 9
Is an insulating gasket, and 10 is a positive electrode container (battery container).

In order to improve these problems, various countermeasures have been conventionally studied. For example, a substance that reacts with the electrolytic solution is inserted in a part of the periphery of the air hole to prevent the electrolytic solution from leaking to the outside of the battery. Alternatively, an electrolytic solution absorbent such as paper or a non-woven fabric made of a polymer material is provided to prevent leakage of the electrolytic solution to the outside of the battery. Furthermore, even if the air intake holes are made extremely small to limit the supply amount of oxygen, it has been proposed to prevent water vapor or carbon dioxide gas from entering the inside of the battery. However, all of the methods still have major problems in prevention of liquid leakage and discharge performance, especially in long-term performance. The main causes of these are the dilution and volume expansion of the electrolytic solution due to the entry of water vapor into the battery, and the inhibition of the discharge reaction based on the formation of carbonate due to the entry of carbon dioxide gas and the blockage of the air flow path. On the contrary, when the outside air is low in humidity, the evaporation of water in the electrolytic solution causes the performance deterioration. In order to eliminate this cause, in recent years, a method of suppressing the permeation of water vapor or carbon dioxide gas and supplying air to the oxygen electrode through a membrane that selectively preferentially permeates oxygen, for example, polysiloxane-based non-porous material A method using a homogeneous thin film, a metal oxide, or a thin film of an organic compound containing a metal atom and a film in which an appropriate porous film is integrated has been proposed.

[0005]

However, so far, satisfactory discharge performance is not obtained because sufficient effective oxygen gas selective permeability cannot be obtained and the ability to prevent permeation of water vapor and carbon dioxide is insufficient. There was a technical problem that it could not be obtained and could not withstand long-term use and storage.

Therefore, the present invention selectively improves the storability of the above-mentioned battery and the performance during long-term use, and selectively obtains oxygen gas in the atmosphere in order to obtain satisfactory discharge performance under discharge conditions from low load to high load. An object of the present invention is to provide an effective oxygen-permeable composite membrane which is incorporated into a battery and prevents invasion of water vapor and carbon dioxide gas in the atmosphere into the battery for a long period of time, and a battery using the composite membrane.

[0007]

To achieve this object, the oxygen-permeable composite membrane of the present invention is mainly composed of a porous polymer membrane coated with a mixture of a solvent-soluble fluororesin and a metal oxide. To do. A battery using the composite membrane of the present invention comprises a gas diffusion electrode having oxygen as an active material, and a battery container having an air intake hole communicating with the outside air, and the air intake side of the gas diffusion electrode and the battery container An oxygen-permeable composite membrane mainly composed of a porous polymer membrane coated with a mixture of a solvent-soluble fluorine resin and a metal oxide is interposed between the inner side and the inner side.

[0008]

[Function] Generally, it is known that a fluorine-based polymer substance has a high affinity for oxygen and water repellency, and is also excellent in alkali resistance among general polymer substances. Since it is chemically stable, it is insoluble in solvents and was not suitable for thin film formation such as coating method and spin coater method. In recent years, a solvent-soluble fluororesin has been developed, and by applying this resin to a porous film containing polyolefin, fluororesin or polysulfone as a main component, a film having alkali resistance and oxygen selective permeability can be obtained. Has been proposed (Japanese Patent Laid-Open No. Hei 3-225513).
In this case, since the affinity between the porous polymer film and the fluororesin is small, the fluororesin aggregates unevenly, and it is difficult to uniformly cover the entire surface of the porous film, especially when the coating amount is small. There was a problem. Therefore, in order to stably form a film in which the entire surface of the porous polymer film is covered with the fluororesin, it is necessary to increase the coating amount of the fluororesin to some extent, which can further improve the oxygen permeation rate. Have difficulty. In the present invention, it has been found that oxygen permeability is improved by mixing a solvent-soluble fluororesin and a metal oxide powder, which have excellent oxygen affinity, water repellency, and alkali resistance. According to the configuration, the above-mentioned composite membrane has a gas permeability measuring device and a gas permeation rate result by a cup method in Examples described below, and as is clear from the results of a battery test, a good oxygen permeation rate for a battery, Keeping the effect of blocking water vapor and carbon dioxide from the atmosphere in a satisfactory state, the high-load discharge performance required for a practical battery and the performance when discharged for a long time in an atmosphere of high humidity or low humidity Both will be satisfied.

[0009]

EXAMPLE An oxygen-permeable composite membrane and a battery using the composite membrane of an embodiment of the present invention will be described below with reference to the drawings.

Comparative Example 1 uses only a fluororesin-based porous film. Fluororesin-based porous membrane (16 cm ² )
Then, 1 ml of a solution of a solvent-soluble fluororesin (trade name: Cytop, manufactured by Asahi Glass Co., Ltd.) diluted with the perfluoro solvent (5% by weight) to 1/2 is applied and dried. The film thus formed is referred to as Comparative Example 2.

A perfluoro solution (5% by weight) of a solvent-soluble fluororesin (trade name: Cytop, manufactured by Asahi Glass Co., Ltd.) (5% by weight) was applied to a fluororesin-based porous membrane (16 cm ² ) with a perfluorosolvent for 2 minutes. A mixed solution of 20 mg of Al ₂ O ₃ powder having an average particle size of 20 μm was applied to 1 ml of the diluted solution of Example 1 and dried to form an oxygen permeable composite membrane (hereinafter referred to as a composite membrane) as Example 1.

Al ₂ O ₃ powder was added in the amount of 40 in Example 1 above.
A composite film obtained by adding 60 mg to the composite film applied in Example 2 was applied as Example 3, a composite film obtained by adding 80 mg in Example 3 was used as Example 4, and a composite film obtained by adding 100 mg as Example 5 is referred to as Example 5.

A perfluoro solution (5% by weight) of a solvent-soluble fluororesin (trade name: CYTOP, manufactured by Asahi Glass Co., Ltd.) was applied to a fluororesin-based porous membrane (16 cm ² ) with a perfluorosolvent for 2 minutes. A mixed solution prepared by applying 40 mg of TiO ₂ powder having an average particle size of 10 μm to 1 ml of the solution diluted to 1 and drying the composite film is referred to as Example 6.

A perfluoro solution (5% by weight) of a solvent-soluble fluororesin (trade name: Cytop, manufactured by Asahi Glass Co., Ltd.) (5% by weight) was applied to a fluororesin-based porous membrane (16 cm ² ) with a perfluorosolvent for 2 minutes. A composite film obtained by applying 40 mg of AgO powder having an average particle size of 10 μm to 1 ml of the diluted solution of Example 1 and drying the composite film is referred to as Example 7.

40 mg of Li ₂ WO ₄ powder (having a particle size of 32 μm or less) obtained by pulverizing massive Li ₂ WO ₄ in an agate mortar and sieving with a sieve having a sieve opening of 32 μm is used as a solvent-soluble fluororesin. (Product name: CYTOP, manufactured by Asahi Glass Co., Ltd.) A perfluoro solution (5% by weight) diluted with the perfluoro solvent to 1/2 was added to 1 ml of a mixed solution to give a fluororesin-based porous membrane ( Example 8 is a composite film applied to 16 cm ² ) and dried.

Example 9 is a composite film in which the powder screened in Example 8 is Li ₂ MoO ₄ powder.

A differential pressure type gas permeation rate measuring apparatus (Yanagimoto Seisakusho Co., Ltd.) was used to measure the oxygen permeation rate of the composite membranes of Examples 1 to 9 above.
Manufactured by GTR-10XD), and the water vapor transmission rate was measured by the cup method according to JIS-Z0208.

The above results are shown in (Table 1). The separation ratio in the table is (oxygen permeation rate) / (water vapor permeation rate), which indicates the selective permeability of oxygen to water vapor.

[0019]

[Table 1]

As described above, according to this example, a composite film in which a mixture of a solvent-soluble fluororesin and a metal oxide powder was applied to a porous polymer film was prepared, and thus a composite film for a battery was prepared. It is possible to obtain a composite membrane having both the oxygen permeability and the effect of blocking water vapor from the atmosphere. Although the examples show the case where the fluororesin-based porous membrane is used, it has been confirmed that the effect of this example does not change even when the polyolefin-based porous membrane or the polysulfone-based porous membrane is used. .. Further, it has been confirmed that the same effect can be obtained at any temperature as long as the drying temperature is from room temperature to the boiling point (100 ° C.) of the perfluoro solvent.

In order to confirm the effect of this embodiment,
A battery using the composite film produced in Comparative Example 2 and Examples 1 to 9 and a battery not using the composite film of Example (Comparative Example 1) were prototyped, evaluated, and examined. Comparative Example 2 and Example 1
9 to 9, the button type battery shown in FIG. 1 was constructed for the convenience of the test. In FIG. 1, the configuration other than the use of the composite membrane 11 is the same as that of the button type battery of FIG.
The description is omitted. First, in the case of Comparative Example 1 in which the composite film was not used, the structure was exactly the same as in FIG. In the embodiment using the composite film, as shown in FIG. 1, the composite film 11 of each embodiment is interposed between the water repellent film 2 of PTFE and the porous film 4 for diffusing oxygen. .. The size of the prototype battery was 11.6 mm in diameter and 5.4 mm in total height, and the oxygen in the air was discharged into the battery by continuous discharge at a relatively high load (75Ω) at 20 ° C and room temperature (60% RH). The sufficiency of the uptake rate was evaluated, and the load was 20 (3kΩ)
℃, high humidity (90% RH) and low humidity (20% RH)
By the long-term continuous discharge in the above, the degree of influence on the battery performance such as the uptake of water vapor from the atmosphere into the battery during the long-term discharge period, the evaporation of water in the battery and the uptake of carbon dioxide gas was evaluated. Table 2 shows the breakdown of the prototype battery.

[0022]

[Table 2]

In Table 2, the discharge end voltage is 0.9 V, and the weight change shows increase and decrease before and after the discharge test. Mainly, it is a numerical value that suggests the uptake of water during discharge or the amount of evaporation. is there. By comparing the characteristics of these batteries with Comparative Example 1 in which the composite film is not used, the effect of this example can be most simply explained. First, in a high-load test at 20 ° C and room temperature, the discharge period is short, and the effects of water uptake and evaporation and carbon dioxide gas are small, so the performance of the battery is that if the oxygen supply rate is sufficient, Permeation prevention does not need to be considered so much. Therefore, under such conditions, excellent characteristics can be obtained even in Comparative Example 1. On the other hand, in Examples 1 to 9 described above, discharge characteristics equivalent to those of Comparative Example 1 were obtained, and the rate at which oxygen permeated through the composite film sufficiently followed the rate at which oxygen was consumed in the discharge reaction. It is shown that. However, in the case of Comparative Example 2, the oxygen supply rate of the composite film is not sufficient, and satisfactory discharge characteristics cannot be obtained.

On the other hand, in the case of low-load discharge, the discharge period is long, and when the outside air has a high humidity or a low humidity, the battery characteristics are excellent in preventing the permeation of water and carbon dioxide gas, especially water, than the oxygen supply rate. The battery of Comparative Example 1 which does not have the function of preventing the permeation of water and carbon dioxide is important for obtaining the voltage, and the voltage drops during discharge due to the depletion of water or the clogging of air holes due to liquid leakage due to excessive intake of water. However, only the capacity corresponding to a part of the discharge capacity obtained in the high load test can be obtained. Needless to say, liquid leakage during discharge is a fatal problem in practical use. On the other hand, Examples 1 to 9 show extremely excellent performances, and these have capacities almost equal to the discharge capacity in the high load test. These tendencies are the same whether the test atmosphere is high humidity or low humidity. This means that in the case of the embodiment,
It is shown that the moisture permeation inhibiting effect of the composite membrane is sufficiently exerted.

Based on the above, the prototype battery using the oxygen permeable composite membrane in which the mixture of the solvent-soluble fluorine resin and the metal oxide powder is applied to the porous polymer membrane has a high load characteristic,
It can be concluded that an excellent battery can be provided because it has excellent low-load characteristics and is also good against changes in the external atmosphere. In the examples, the composite membrane was placed between the battery container and the porous membrane for air diffusion, but when the mechanical strength of the composite membrane was sufficient, the porous membrane for air diffusion was excluded. Has confirmed that there is no difference in battery characteristics. Further, the composite film was placed between the oxygen electrode and the water-repellent film supporting the oxygen electrode, but if the strength of the oxygen electrode is sufficient, the supporting water-repellent film can be omitted. Has confirmed that the battery characteristics do not change. In addition, it was confirmed that the same effect as the battery used in the alkaline electrolyte shown in the example was obtained for the air zinc battery using the neutral salt aqueous solution such as ammonium chloride and zinc chloride as the electrolyte. Therefore, the operation of the present invention can be explained for the same reason as in the embodiment.

[0026]

As is apparent from the above description of the embodiments, according to the oxygen-permeable composite membrane and the battery using the composite membrane of the present invention, the porous polymer membrane contains a fluorine-soluble resin soluble in a solvent. By applying the mixture with the metal oxide powder,
It is possible to realize an excellent oxygen-permeable composite membrane having not only the oxygen permeability for a battery but also the effect of blocking water vapor from the atmosphere. Further, it is possible to obtain an effect that excellent practical performance, excellent leakage resistance, and long-term storability can be provided in a wide range from high load to low load of a battery using a neutral or alkaline aqueous solution as an electrolytic solution. ..

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a button type zinc-air battery used for studying an oxygen-permeable composite membrane of an example of the present invention.

FIG. 2 is a vertical cross-sectional view of a conventional button-type zinc-air battery.

[Explanation of reference numerals] 1 oxygen electrode (gas diffusion electrode) 2 water repellent film 3 air intake hole 4 porous film 10 battery container 11 oxygen permeable composite film

Claims (8)

[Claims] 1. An oxygen-permeable composite membrane comprising a porous polymer membrane coated with a mixture of a solvent-soluble fluororesin and a metal oxide powder. 2. The porous polymer film contains, as a main component, any one of polyolefin, fluororesin and polysulfone.
The oxygen-permeable composite membrane as described. 3. A metal oxide powder is aluminum oxide (Al
₂ O ₃ ), titanium oxide (TiO ₂ ), silver oxide (AgO),
The oxygen-permeable composite membrane according to claim 1, which is one of lithium tungstate (Li ₂ WO ₄ ) and lithium molybdate (Li ₂ MoO ₄ ). 4. A gas diffusion electrode using oxygen as an active material, and a battery container having an air intake hole communicating with the outside air. A solvent is provided between the air intake side of the gas diffusion electrode and the inner surface of the battery container. A battery in which an oxygen permeable composite membrane in which a mixture of a soluble fluorine resin and a metal oxide is applied to a porous polymer membrane is interposed. 5. The porous polymer film contains, as a main component, one of polyolefin, fluororesin and polysulfone.
Battery described. 6. The metal oxide powder is aluminum oxide (Al
₂ O ₃ ), titanium oxide (TiO ₂ ), silver oxide (AgO),
The battery according to claim 4, which is one of lithium tungstate (Li ₂ WO ₄ ) and lithium molybdate (Li ₂ MoO ₄ ). 7. The oxygen-permeable composite film is coated with a mixture of a solvent-soluble fluororesin and a metal oxide, and the side of the oxygen-permeable composite film is brought into contact with the inner surface of the battery container having an air intake hole. The battery according to any one of claims 4 to 6, wherein the gas diffusion electrode is in direct contact with the porous polymer side of the membrane. 8. A solvent-soluble fluorine resin-mixed mixture of a metal oxide and a side of the oxygen-permeable composite membrane are directly in contact with a gas diffusion electrode, and a porous polymer membrane side of the oxygen-permeable composite membrane is air. The battery according to any one of claims 4 to 6, which is in contact with an inner surface of a battery container having an intake hole.