JPH04206455A - Oxygen permeating composite film and battery using composite film - Google Patents

Abstract

PURPOSE:To obtain the oxygen penetrating power and the shielding effect of steam from the atmosphere for a battery by coating polyamino phosphazen introduced with a substituent made of saturated aliphatic amine on porous fluororesin. CONSTITUTION:A composite film 11 is provided between a porous film 2 of polytetra fluoroethylene(PTFE) and a porous body 4 diffusing the oxygen. Polyamino phosphazen introduced with a substituent made of saturated aliphatic amine expressed by the formula I is coated on a porous polymer film to form the oxygen permeating composite film 11, where R, R' are an alkyl group or hydrogen. The good oxygen permeating speed and the shielding effect of water vapor or carbon dioxide from the atmosphere for a battery are kept in the satisfactory state, and the high-load discharge performance required for the practical battery and the performance when the battery discharged in the high- humidity or low-humidity atmosphere for a long time can be satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an oxygen permeable membrane for a battery equipped with a gas diffusion electrode using oxygen as an active material, and a battery using the membrane.

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. As the electrolyte, an alkaline, neutral, or acidic solution or a solid electrolyte is used.

In particular, in batteries that use a solution as an electrolyte, water vapor flows in and out from the gas diffusion electrode (oxygen electrode) depending on the vapor pressure of the internal electrolyte, causing changes in the concentration and volume of the electrolyte in the battery. This had an effect on the battery characteristics. Taking a button-type 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 porous membrane made of polytetrafluoroethylene (PTFE) that allows gas to diffuse but blocks liquid. 3 is an air intake hole from the outside, 4 is a porous membrane that supports the oxygen electrode and diffuses air, 5 and 6 are separators, and 7 is a negative electrode made of a mixture of potassium hydroxide aqueous solution and zinc oxide powder. Generally, an aqueous potassium hydroxide solution is used as the alkaline electrolyte, and its concentration is 30-35%. Therefore, if the relative humidity is higher than 47-59%, external moisture will be taken in and the electrolyte concentration will decrease. and volumetric expansion occur, resulting in a decrease in discharge performance,
The electrolyte was leaking. 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, 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.

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 by making the air holes extremely small to limit the amount of oxygen supplied. However, both methods had major problems in preventing leakage and discharging performance, especially in long-term use. The main causes of these are the dilution and volumetric expansion of the electrolytic solution 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 circulation path. Conversely, when the outside air is low-humidity, evaporation of water in the electrolyte causes a decline in performance. In order to eliminate this cause, in recent years, methods have been developed to supply air to the oxygen electrode through a membrane that suppresses the permeation of water vapor and carbon dioxide gas and selectively allows oxygen to permeate. A method using a film that integrates a uniform thin film of , a thin film of a metal oxide, or a thin film of an organic compound containing metal atoms with a suitable porous film has been proposed.

Problems to be Solved by the Invention However, until now, satisfactory discharge performance has not been achieved due to the inability to obtain sufficiently effective oxygen gas selective permeability and insufficient permeation blocking ability for water vapor and carbon dioxide gas. However, there were technical issues in that it could not withstand long-term use or storage.

Therefore, the present invention aims to improve the storability and long-term use performance of the above-mentioned battery, as well as to selectively inject oxygen gas from the atmosphere into the battery in order to obtain satisfactory discharge performance under discharge conditions ranging from low to high loads. The object of the present invention is to provide an effective oxygen-permeable composite membrane that prevents atmospheric water vapor and carbon dioxide from entering a battery over a long period of time.

Means for Solving the Problems In order to achieve the above objects, the oxygen permeable composite membrane of the present invention is a porous polymer membrane coated with polyaminophosphazene into which a substituent consisting of a saturated aliphatic amine is introduced. .

In the present invention, a polymer film is used to apply polyaminophosphazene, but in general, many phosphazene polymers exhibit a lower glass transition temperature than polymers such as polypropylene and polyhinyl alcohol. It is known to exhibit high oxygen permeability similar to polymers.

Furthermore, phosphazene polymers have better alkali resistance than siloxane polymers.

As mentioned above, the present invention was completed after intensive studies focusing on the high oxygen permeability and excellent alkali resistance of polyaminophosphazene.

Effect: Due to this structure, the above-mentioned composite membrane has good oxygen permeability for use in batteries, as is clear from the gas permeation rate results using a gas permeability measuring device and cup method in the examples described later, as well as from the results of battery tests. Maintaining satisfactory speed and effectiveness in blocking water vapor and carbon dioxide from the atmosphere,
This satisfies both the high-load discharge performance required of a practical battery and the performance when discharging for a long time in an atmosphere of high or low humidity.

Example An example of the present invention is shown below.

(Example 1) 5 g of hexachlorocyclophosphazene, 0.1 g of p-toluenesulfonic acid and 0.01 g of calcium sulfate were mixed into 1
．． Add 2.4-trichlorohenzene to 4 m Q and heat to 210°C under an inert gas atmosphere. When the solution becomes viscous, stop heating and cool to room temperature. This solution is poured into a dry n-hebutane solution to precipitate the polydichlorophosphazene, after which the polymer is filtered off and dried. The resulting polymer is dissolved in tetrahydrofuran, gradually added to a tetrahydrofuran solution containing equal amounts of isobutylamine and triethylamine, and then stirred day and night at room temperature to introduce amine groups into polydichlorophosphazene. Pour this solution into water,
After precipitation of the polymer, filtration and drying, polyaminophosphazene is obtained.

The polyaminophosphazene thus synthesized is dissolved in tetrahydrofuran, and an appropriate amount of this solution is applied to a porous fluororesin membrane and dried to obtain a composite membrane.

Example 2 is obtained by maintaining the conditions of Example 1 above, but replacing isobutylamine with a mixture of equal amounts of diethylamine and isobutylamine.

Example 3 is the same as in Example 1, except that isobutylamine is replaced with a mixture of equal amounts of sheen-n-propylamine and isobutylamine.

(Example 4) Isopropyl alcohol and sodium hydride were reacted in a tetrahydrofuran solution to form sodium isopropoxide, and after gradually adding a tetrahydrofuran solution of polydichlorophosphazene to this solution, the solution was heated under refluxing conditions for 24 hours. , an alkoxy group is introduced into polydichlorophosphazene by stirring. This solution was poured into water to precipitate the polymer, and after filtering and drying,
A polyalkoxyphosphazene is obtained.

Using the obtained polymer, a composite membrane is obtained in the same manner as in Example 1.

(Comparative example 1) Comparative Example 1 uses only porous fluororesin.

The oxygen permeation rates of the four types of composite membranes of Examples 1 to 4 and the membrane of Comparative Example 1 were measured using a differential pressure gas permeability measuring device (manufactured by Yanagimoto Seisakusho ■, GTR-10XD). The permeation rate was measured by the cup method according to JIS-20208.

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.

Examples 1 to 3 in which a substituent consisting of a saturated aliphatic amine was introduced
Comparing Example 3 and Example 4 in which an isopropoxy group was introduced, the oxygen permeability of each example is about the same, but the water vapor permeability of Example 4 is about 10 times that of Examples 1 to 3. The separation ratio between oxygen and water vapor is very low at 0.58. For this reason, it can be said that Example 4, in which isopropoxy groups were introduced, is inappropriate for the purpose of blocking water vapor from the atmosphere.

As described above, according to this example, by producing a composite membrane in which polyaminophosphazene is coated on a porous fluororesin, it has both oxygen permeability for battery use and the effect of blocking water vapor from the atmosphere. It is possible to obtain a membrane with

In addition, in order to confirm the effects of the present invention, a battery using the composite membrane produced in Examples 1 to 4 and a battery not using the composite membrane (Comparative Example 1) were prototyped, evaluated, and studied. First, in the case of Comparative Example 1 in which no composite membrane was used, the structure was exactly the same as that shown in FIG. 2.

Examples using composite membranes are almost the same as those shown in FIG. 2, and as shown in FIG. This is an intervening configuration.

The dimensions of the prototype battery are 11.6 mm in diameter and 5.4 m in total height.
m, at 20°C and normal humidity (6
The sufficiency of the oxygen uptake rate from the air into the battery was evaluated by continuous discharging at 0% RH), and at relatively low load (3Ω) at 20'C, high humidity (90% RH), Continuous discharge for a long period of time at low humidity (20% RH) may affect battery performance, such as the introduction of water vapor from the atmosphere into the battery, evaporation of moisture within the battery, and intake of carbon dioxide gas during the long-term discharge period. The degree of impact was evaluated.

Table 2 shows the performance test results of the prototype battery.

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

(Left below) The characteristics of these batteries are compared to Comparative Example 1, which does not use a composite membrane.
The present invention can be most clearly explained in detail by comparing it with the following.

First, in high-load tests at 20°C and normal humidity, the discharge period was short;
Since the effects of moisture uptake, evaporation, and carbon dioxide gas are small, there is no need to think too much about blocking moisture and carbon dioxide permeation in terms of battery performance as long as the oxygen supply rate is sufficient. Therefore, under such conditions, excellent characteristics can be obtained even in Comparative Example 1. In contrast, in Examples 1 to 4 described above, discharge characteristics equivalent to Comparative Example 1 were obtained, and the rate at which oxygen permeates through the composite membrane sufficiently follows the rate at which oxygen is consumed in the discharge reaction. It is shown that.

On the other hand, in the case of low-load discharge, the discharge period is long, and in addition, when the outside air is high or low humidity, it is necessary to obtain battery characteristics that are superior to moisture and carbon dioxide gas, especially moisture permeation prevention, rather than oxygen supply rate. The batteries of Comparative Example 1 and Example 4, which do not have a moisture or carbon dioxide permeation prevention mechanism, may experience problems during discharge due to depletion of moisture or, conversely, blockage of air holes due to leakage caused by excessive intake of moisture. The voltage decreases at
The capacity obtained is only a portion of the discharge capacity obtained in the high load test. Moreover, it goes without saying that liquid leakage during discharge is a fatal oversight from a practical standpoint. On the other hand, Examples 1 to 3 showed extremely excellent performance, and in these cases, a capacity almost equal to the discharge capacity in the high load test was obtained. These trends are the same whether the test atmosphere is high humidity or low humidity. This means that in the case of the example,
This shows that the moisture permeation blocking effect of the composite membrane is fully exhibited.

In summary, the prototype battery using an oxygen-permeable composite membrane made of porous fluororesin coated with polyaminophosphazene has excellent high-load and low-load characteristics, and changes in the external atmosphere well, making it an excellent battery. It can be concluded that it is possible to provide

In addition, although the example shows the case where the composite membrane is brought into contact with the air intake hole side, it has been confirmed that almost the same result is obtained even when the composite membrane is brought into contact with the gas diffusion electrode side.

Further, in the above embodiment, the composite membrane of the present invention was installed between the battery container and the porous body for air diffusion, but if the mechanical strength of the composite membrane of the present invention is sufficient, the air diffusion There is no difference in battery characteristics even if the porous material is removed. Furthermore, in the above example, the composite membrane of the present invention was installed between the oxygen electrode and the porous membrane supporting the oxygen electrode, but if the oxygen electrode has sufficient strength, the supporting porous membrane can be omitted. In that case, the battery characteristics remain unchanged. We also confirmed that air batteries using neutral salt aqueous solutions such as ammonium chloride and zinc chloride as electrolytes have the same effect as batteries using alkaline electrolytes as shown in the examples. Therefore, the present invention can be explained in detail for the same reason as the examples.

Effects of the Invention As described above, the present invention has a porous fluororesin coated with polyaminophosphazene into which a substituent consisting of a saturated aliphatic amine has been introduced, thereby improving oxygen permeability for batteries and at the same time removing water vapor from the atmosphere. This makes it possible to realize an excellent oxygen permeable composite membrane that also has a blocking effect.

As is clear from the above explanation, the oxygen permeable composite membrane of the present invention has excellent practical performance and excellent performance in a wide range from high to low loads of batteries using neutral or alkaline aqueous solutions as electrolytes. This provides the advantage of being able to provide liquid leakage resistance and long-term storability.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional view of a button-type zinc-air battery used for studying the embodiments of the present invention, and FIG. 2 is a half-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, 1o... Positive electrode container, 11...
...Composite membrane.

Claims (8)

[Claims] (1) An oxygen-permeable composite membrane characterized in that a porous polymer membrane is coated with polyaminophosphazene into which a substituent consisting of a saturated aliphatic amine represented by the following general formula is introduced. R, R'N- (However, R and R' are an alkyl group or hydrogen.) (2) Claim 1, wherein the saturated aliphatic amine is at least one saturated aliphatic amine selected from the group consisting of isobutylamine, diethylamine, and di-n-propylamine. The oxygen permeable composite membrane described. (3) The oxygen permeable composite membrane according to claim 1, wherein the porous polymer membrane has a fluororesin as a main component. (4) A gas diffusion electrode having oxygen as an active material and a battery container having an air intake hole communicating with the outside air are provided, and the following general formula is provided between the air intake side of the gas diffusion electrode and the inner surface of the battery container. 1. A battery characterized by interposing an oxygen-permeable composite membrane in which a porous polymer membrane is coated with polyaminophosphazene into which a substituent consisting of a saturated aliphatic amine is introduced. R, R'N- (However, R and R' are an alkyl group or hydrogen.) (5) Claim 4, wherein the saturated aliphatic amine is at least one saturated aliphatic amine selected from the group consisting of isobutylamine, diethylamine, and di-n-propylamine. Batteries listed. (6) The battery according to claim 4, wherein the porous polymer membrane has a fluororesin as a main component. (7) A composite membrane is brought into contact with the inner surface of the battery container having an air intake hole, and the porous polymer membrane side of the composite membrane is
The battery according to any one of claims 4 to 6, characterized in that the gas diffusion electrode is in direct contact with the battery. (8) In the composite membrane, the side coated with polyaminophosphatide introduced with a substituent consisting of a saturated aliphatic amine is in direct contact with the gas diffusion electrode, and the porous polymer membrane side has air intake holes on the inner surface of the battery container. The battery according to any one of claims 4 to 6, characterized in that the battery is in contact with the battery.