JPH04312771A - Air battery - Google Patents

Abstract

PURPOSE:To improve the resistance to liquid leakage and liquid storing property by setting an oxygen selective permeable membrane, consisting of a thin film having a specified substitute group and a finely porous film supporting the former film. between an air taking-in side of a gas diffusion electrode and in the inner surface of a battery's container. CONSTITUTION:A fluoroalkyl group-containing polysiloxane composite membrane 11 is set between a PTFE porous film 2 and a porous film 4 to diffuse oxygen. The composite membrane is so set as to make the thin film side of the polysiloxane face to the air taking-in hole 3 of the finely porous film. Consequently. the oxygen transmitting speed is improved for the battery and also durable discharging properties under the high temperature and low humidity conditions together with over-discharging properties are improved while the steam and carbonic acid gas are shut from air.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery using oxygen as an active material, and more particularly to a hydrogen/oxygen fuel cell or a metal/air battery using an alkaline electrolyte.

0002

BACKGROUND OF THE INVENTION Examples of batteries equipped with gas diffusion electrodes and using oxygen as an active material include fuel cells and air cells (hereinafter referred to as air cells). In particular, in air batteries that use alkaline aqueous solutions or neutral aqueous solutions as electrolytes, water vapor flows in and out from the gas diffusion electrode (oxygen electrode) depending on the internal vapor pressure, which causes changes in the concentration and volume of the electrolyte in the battery. occurred, which affected various battery characteristics.

[0003] The situation will be explained below by taking the button type air cell shown in FIG. 3 as an example. In FIG. 3, 1 is an oxygen electrode (air electrode), 2 is a porous membrane that supports the oxygen electrode, and its material is polytetrafluoroethylene (PTFE), which has gas diffusivity but blocks liquid. 3 is an air intake hole from the outside, 4 is a porous membrane for air diffusion, 5 and 6 are separators, 7 is a negative electrode made of a mixture of potassium hydroxide aqueous solution and zinc chloride powder, 8 is a negative electrode container, 9 1 is an insulating gasket, and 10 is a positive electrode container.

[0004] 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 47%, evaporation of the electrolyte occurs, resulting in an increase in internal resistance and a decrease in discharge performance. Therefore, air batteries have problems with their characteristics after long-term storage because they are easily affected by the environmental atmosphere, and they are only designed for use in a specific field, which poses a major problem in making them more general-purpose. .

[0005] 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 limit the amount of oxygen supplied by making the air holes extremely small to prevent water vapor and carbon dioxide from entering the battery, but none of these methods can prevent liquid leakage or discharge. There remained major issues with performance, especially performance during long-term discharge. The main causes of these problems are dilution and volumetric expansion of the electrolyte due to the intrusion of water vapor from the air into the battery.
This is due to the inhibition of the discharge reaction due to the formation of carbonate by carbon dioxide gas and the blockage of the air circulation path.In contrast, when the outside air is low humidity, the loss of water in the electrolyte is the cause of the performance decline. . In order to eliminate these causes, in recent years,
A method of supplying air to an oxygen electrode through a membrane that suppresses the permeation of water vapor and carbon dioxide gas and selectively permeates oxygen with priority;
For example, a uniform nonporous thin film of polysiloxane, a composite film of polyorganosiloxane and an alkali-resistant microporous film, a thin film of a metal oxide or an organic compound containing metal atoms, and an appropriate porous film are integrated. A method using a film that has been modified has been proposed.

[0006]

[Problems to be Solved by the Invention] However, to date, satisfactory discharge performance has not been achieved due to the fact that sufficiently effective oxygen gas selective permeability has not been obtained and the permeation blocking ability for water vapor and carbon dioxide gas is not sufficient. Not obtained. In addition, since an alkaline electrolyte was used as the electrolyte, the hydrophilic properties of the various compounds and polymer membranes caused the electrolyte to be drawn along the inside of the battery container, causing leakage from the air intake holes. It has not yet been put into practical use.

The present invention has been made to solve the above-mentioned problems, and is intended to improve the storability and long-term use performance of batteries, and to obtain satisfactory discharge performance under discharge conditions ranging from light loads to heavy loads. Oxygen gas from the atmosphere is selectively introduced into the battery at a sufficient rate, but it also prevents water vapor and carbon dioxide from the atmosphere from entering the battery over a long period of time, and prevents electrolyte from leaking from the air intake hole. The object of the present invention is to provide an air battery configured as described above.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the air battery of the present invention is provided with a gas diffusion electrode having oxygen as an active material and a battery container having an air intake hole communicating with the outside air. An oxygen selectively permeable composite membrane formed from a thin film of polysiloxane having a fluoroalkyl group as a substituent between the air intake side of the diffusion electrode and the inner surface of the battery container, and a microporous membrane supporting the thin film. It is characterized by intervening.

The above polysiloxane is

0010

[Chemical formula 1]

It is represented by the structural formula: The thin film is a homogeneous thin film with no pinholes and has selective permeability for oxygen, and in order to obtain a sufficient oxygen permeation rate and water vapor and carbon dioxide permeation blocking ability, it is usually 1.0 μm or less, preferably 0.0 μm or less.
．． A thickness of 2 to 0.5 μm is suitable. The microporous membrane supporting this thin film is preferably a microporous membrane through which gas can easily permeate, and whose surface has a smoothness and pore size suitable for uniformly supporting the above-mentioned thin film. It is preferable that the average pore diameter is 3 to 0.01 μm.

The present invention focuses on the characteristics of a homogeneous thin film of polysiloxane as a thin film with excellent oxygen selective permeability, and furthermore,
For the microporous membrane that supports this thin membrane, we selected polyolefins such as polypropylene and polyethylene, which have excellent alkali resistance, fluororesin, polysulfone, etc., and completed the research after careful consideration. The microporous membrane may be a single layer, but in order to ensure strength during handling, manufacturing, or use, it may have a two-layer or more structure with an alkali-resistant nonwoven fabric further integrated as necessary. Also good.

Composite membranes in which the above-mentioned polysiloxane thin film is supported by a microporous membrane include polydimethylsiloxane and polysiloxane derivatives as disclosed in JP-A-54-56985, etc.; Practical applications are being considered for use, combustion aid, petroleum protein processing, waste liquid treatment aeration, medical exhalation, etc.
The main purpose is oxygen enrichment, and only the oxygen and nitrogen separation coefficient and oxygen permeation rate are evaluated. In order to apply these membranes to batteries that can obtain satisfactory discharge performance even under heavy load discharge conditions, it is important that the oxygen permeation rate be sufficiently high and that the permeation blocking ability of water vapor and carbon dioxide gas be excellent. However, until now, many of these characteristics have been unknown, and there have been few cases where their application to batteries has been considered. , polydimethylsiloxane-polyhydroxystyrene crosslinked copolymers have been proposed, but the oxygen permeation rate was insufficient and satisfactory performance could not be obtained in discharge under heavy loads.

As a result of intensive studies on various oxygen permeable membranes for use in batteries, the present invention has found that a composite membrane in which a polysiloxane thin film is integrated with a microporous membrane comprehensively satisfies the above-mentioned characteristics for use in batteries. They found that the performance of batteries to which this technology was applied was extremely excellent.

[0015]

[Function] Since the air battery of the present invention is constructed as described above, it has a high oxygen permeation rate for batteries, blocks water vapor and carbon dioxide from the atmosphere, and also has excellent leakage resistance and overdischarge characteristics. Therefore, it has excellent heavy load discharge characteristics and long-time discharge performance under high temperature and low humidity atmospheres.

[0016]

[Example] As an example of the present invention, polysiloxane

0
017]

[Case 2]

In [0018], R1 = CF2 H, R2 = C
A battery using a composite membrane using FH2, a battery using a single polydimethylsiloxane membrane, and a battery not using the above composite membrane were prototyped and evaluated. In addition,
In the case of a comparative example that does not use a composite membrane, the configuration is exactly the same as in Figure 3, and in the example and comparative example that uses a composite membrane, the composite membrane is provided as shown in the longitudinal cross-sectional view of Figure 1. The only difference from the battery in FIG. 3 is that the other configurations are exactly the same as those in FIG. 3.

As shown in the longitudinal cross-sectional view of FIG. 1, in this embodiment, the composite membrane 11 according to the present invention (partially enlarged in FIG. The only difference from the battery shown in FIG. 3 is that a battery (see figure) is provided. In the case of the comparative example, the diameter of the single membrane is set to porous membrane 2.
The composite membrane 11 is smaller and larger than the porous membrane 4, and the side of the polysiloxane thin film 12 is the microporous membrane 13.
The only difference from the battery shown in FIG. 3 is that the battery is disposed so as to face the air intake hole 3 of the battery. The supports in Examples were all microporous membranes (pore diameter: approximately 0.1 to 0.05 μm, thickness: approximately 30 μm).
15 μm), or a single layer of nonwoven fabric 14 (thickness: approximately 15
A thin film 12 was formed on the microporous membrane 13 side by using a composite layer in which 0 μm) was integrated.

[0020] The shape of the prototype battery was 11.6 mm straight.
The total height is 5.4mm, and the resistance is 20mm under relatively heavy load (75Ω).
℃ and normal humidity (60% RH) to evaluate the sufficiency of the rate of oxygen uptake from the air into the battery, and the same load was continued for 100 hours to evaluate overdischarge leakage resistance. Also, under relatively light load (3KΩ) at 20℃ and high humidity (90%)
RH) and low humidity (20% RH), the effects on battery performance include the intake of water vapor in the atmosphere, the dissipation of moisture within the battery, and the intake of carbon dioxide gas during the long-term discharge period. The degree was evaluated.

The details of the prototype battery are shown in Table 1.

[0022]

[Table 1]

Table 2 also shows the performance test results of the prototype batteries.

[0024]

[Table 2]

In Table 2, the discharge end voltages are all 0.
9V, and the weight change indicates an increase or decrease before and after the discharge test, and is a numerical value that mainly suggests the amount of moisture taken in or dissipated during discharge.

In Examples 1 to 5, relatively thin uniform thin films were formed within the range in which a uniform thin film without pinholes could be obtained, and in Examples 6 to 9, uniform thin films were formed. It is formed to be somewhat thick, and the former is designed primarily to increase the permeation rate of oxygen, while the latter is constructed with the primary purpose of blocking the permeation of water vapor and carbon dioxide gas. In these cases, the support of the composite membrane is composed of an alkali-resistant material. The effects of the present invention can be most clearly explained by comparing the characteristics of these batteries with Comparative Example 3 in which no composite membrane was used.

First, in a heavy load test at 20° C. and normal humidity, the discharge period is short and the effects of moisture uptake and dissipation and carbon dioxide gas are small, so the battery performance can be improved as long as the oxygen supply rate is sufficient. There is no need to give much consideration to preventing moisture and carbon dioxide from permeating. Therefore, under such conditions, excellent characteristics can be obtained even in Comparative Example 3. On the other hand, among the aforementioned Examples 1 to 5, discharge characteristics equivalent to Comparative Example 3 were obtained;
This shows that the rate at which oxygen permeates through the composite membrane sufficiently follows the rate at which oxygen is consumed in the discharge reaction. In Examples 6 to 9, although the discharge voltage and duration were slightly inferior, they exhibited comparable good characteristics, and the supply of oxygen was carried out almost satisfactorily.

On the other hand, in the case of light load discharge, the discharge period is long, and when the outside air is high or low humidity, moisture and carbon dioxide gas, especially moisture permeation prevention, is more important than the oxygen supply rate in order to obtain superior performance. The battery of Comparative Example 3, which does not have a mechanism to prevent water and carbon dioxide permeation, has a voltage drop during discharge due to depletion of water or, conversely, blockage of air holes due to leakage due to excessive water intake. However, the capacity obtained is only a portion of the discharge capacity obtained in the heavy load test. Furthermore, it goes without saying that liquid leakage during discharge is a fatal problem from a practical standpoint. On the other hand, the Examples showed extremely excellent performance, and a capacity almost equal to the heavy load capacity was obtained, and among them, Examples 6 to 9, in which the uniform thin film layer was relatively thick, were more excellent. These trends are the same whether the test atmosphere is high humidity or low humidity. This shows that, in the case of the example, the composite membrane sufficiently exhibits the permeation blocking effect of moisture and carbon dioxide gas. Also,
In Comparative Examples 1 and 2, the film thickness is thick, so the water vapor and carbon dioxide permeation blocking ability of the uniform thin film is sufficient, but the oxygen permeation rate is not sufficient, so the discharge characteristics under light load are different from those of the examples. However, the heavy load characteristics are significantly inferior to those of the example.

[0029] In summary, the prototype battery using a composite film of a uniform thin film of polysiloxane and a microporous film has excellent both heavy load characteristics and light load characteristics, and has good response to changes in the external atmosphere. In particular, it can be concluded that an excellent battery can be provided when the uniform polysiloxane thin film has a thickness of 0.2 to 1.0 μm and an alkali-resistant porous film is used as the support.

[0030] In the above example, R1 = C(F2)H, R2 = C(F)H2 as the polysiloxane.
We have explained a composite membrane using R1,
Part or all of R2 is CF3, C2 F3 H2
It has been confirmed that almost the same effect can be obtained with a composite membrane using polysiloxanes of , C2 F4 H, and C2 F5.

[0031]Also, in the above embodiments, a composite membrane was used in which a thin film of polysiloxane was coated or laminated on one side of a microporous support film or a support film in which a microporous film and a nonwoven fabric were integrated. According to the present invention, even in the case of a composite membrane in which thin films are formed on both sides of a support membrane, excellent battery performance can be obtained in the same way as described above if the total film thickness of polysiloxane is 0.2 to 1.0 μm. Furthermore, similar effects can be obtained by using other alkali-resistant microporous membranes (for example, nylon microporous membranes) as opposed to the microporous membrane supporting polysiloxane shown in the examples. Furthermore, in the examples, a case where the support was a composite layer in which a microporous membrane and a nonwoven fabric made of polypropylene were integrated was explained, but this nonwoven fabric was
Similar effects can be obtained with other alkali-resistant materials such as nylon.

Furthermore, in the above embodiments, the composite membrane of the present invention was installed between the battery container and the porous material for air diffusion, but the composite membrane of the present invention may be a microporous membrane, and in some cases, a nonwoven fabric may be further provided. It is composed of an integrated support body, and there is no difference even if a composite membrane is used instead of the porous body for air diffusion.

[0033]

[Effects of the Invention] As explained above, the air battery of the present invention has excellent discharge performance from heavy loads to light loads, and also has excellent leakage resistance and long-term storage. , is very effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a button-type zinc-air battery used to study examples and comparative examples of the present invention.

FIG. 2 is a partially enlarged view of the composite membrane in FIG. 1.

FIG. 3 is a vertical cross-sectional view of a conventional button-type zinc-air battery.

[Explanation of symbols]

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 (1)

[Claims] Claim 1: In an air battery comprising a gas diffusion electrode containing oxygen as an active material and a battery container having an air intake hole communicating with the outside air, there is a space between the air intake side of the gas diffusion electrode and the inner surface of the battery container. A thin polysiloxane film using a fluoroalkyl group as a substituent on one side of the microporous membrane, with a microporous membrane supporting an oxygen electrode made of a porous air-diffusing material such as a nonwoven fabric and a porous film such as polytetrafluoroethylene interposed therebetween. An air battery characterized by being provided with.