JPH05198318A - Air battery - Google Patents

Abstract

PURPOSE:To prevent the lowering of discharge characteristic of an air battery, in which a positive electrode catalyst layer is provided inside a positive electrode can having an air intake hole through the air diffused porous film and a water repellent film, even in the case where an air battery is preserved or used for a long time under the open condition by making a fluorine included high polymer covering film exist on the surface of the porous film. CONSTITUTION:An air diffused porous film 3 and a porous water repellent film 4 are interposed between an air intake hole 2 and a positive electrode catalyst layer 5 so as to support the catalyst layer 5, and the air flow to the catalyst layer 5 is secured. At this stage, the air diffused porous film 3 is made of nonwoven fabric such as polyethylene, polypropylene, nylon, and kraft paper, and the fluorine included high polymer covering film is formed on the surface of the film 3. As this high polymer material, the material, which can be formed easily into the film by the heating at a low temperature without generating the thermal decomposition of the porosity, is desirable, and for example, the material expressed by formulas I, II is used. At this stage, R<1> in the formula represents hydrogen, methyl, chlorine or fluorine, and R<2> represents R<f> or -(CHX)nR<f>, and R<f> represents a perfluoroalkyl group having 2-10 of carbon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air battery using oxygen as a positive electrode active material, and more particularly to an air battery having a small decrease in discharge performance even after long-term storage.

[0002]

2. Description of the Related Art An air battery is a battery that uses oxygen in the air as a positive electrode active substance, and its shape includes a button air battery, a square air battery, and a cylindrical air battery.
Among them, the button-type air battery is attracting attention as an alternative to a mercury battery because it has a larger electric capacity per unit volume than other battery systems and has low pollution, and is beginning to be used for hearing aids and the like.

The structure of the button type air battery will be described below as an example. As shown in FIG. 1, a positive electrode can (1) having an air intake hole (2) on the bottom and also serving as a positive electrode terminal is provided with a soft material such as non-woven fabric such as polyethylene, polypropylene, acetalized polyvinyl alcohol, or kraft paper. An air diffusion porous membrane (3), a porous water-repellent membrane (4) made of polytetrafluoroethylene or the like, a positive electrode catalyst layer (5) and a separator (6) are stacked in this order and housed. Furthermore, a negative electrode can (8), which is filled with a negative electrode mixture (7) composed of a negative electrode acting substance and an electrolytic solution on the separator (6) and also serves as a negative electrode terminal, has a positive electrode can opening through a gasket (9). And the periphery of the positive electrode can (1) is caulked inward.

Generally, an alkaline aqueous solution such as an aqueous potassium hydroxide solution is used as the electrolytic solution, and its concentration is 3
0 to 35%. With the structure as described above, since the air intake hole is open to the outside, if the relative humidity of the environment atmosphere is high, the concentration of the electrolyte solution decreases and the volume expands to take in the outside humidity, and the discharge performance is reduced. There was a drop and electrolyte leakage. On the other hand, when the relative humidity is low,
Evaporation of the electrolytic solution caused an increase in internal resistance and a decrease in discharge performance. Therefore, since the air battery is significantly affected by the environmental atmosphere, it has a problem in the characteristics after long-term storage and / or use, and it is designed only for a specific field, and is not suitable for generalization. It had a big problem.

In order to improve these problems, various countermeasures have been studied in the past. For example, a method of reducing the size of the air holes; a method of using a selective permeable membrane that preferentially permeates oxygen while limiting the permeation of water vapor; Method of preventing leakage of electrolytic solution to the outside; Method of preventing leakage of electrolytic solution to the outside of battery by providing electrolytic solution absorbing material such as paper or non-woven fabric made of polymer material; Proposals have been made for making the amount extremely small, limiting the amount of oxygen supply, and preventing water vapor and carbon dioxide gas from entering the inside of the battery.

However, all of the methods still have major problems in leakage prevention and discharge performance, especially in long-term discharge. For example, the smaller the air holes, the more restrictive the passage of oxygen and the lower the discharge performance; and also the selective permeable membrane, which can be used for a long time in the battery and shows satisfactory selectivity. On the contrary, in some cases, the oxygen permeation amount was insufficient and the battery performance was deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem and takes in oxygen in the atmosphere into the battery at a sufficient rate. It is an object of the present invention to provide an air battery configured to suppress infiltration and evaporation of an electrolytic solution for a long period of time. Another object of the present invention is to provide an air battery that maintains satisfactory discharge characteristics even when stored or used for a long period of time while the inside and outside of the battery communicate with each other through the air intake hole.

[0008]

In order to achieve this object, the present inventors have found that a film of a fluorine-containing polymer material is formed on the surface between the positive electrode catalyst layer and the air intake hole. The present invention has been completed by finding that inserting a diffusion porous membrane is extremely effective.

That is, the air battery of the present invention is an air battery having a positive electrode catalyst layer with an air diffusion porous film and a water repellent film inside a positive electrode can having an air intake hole, wherein the air diffusion porous film is used. Is characterized in that a film of a fluorine-containing polymer substance is present on the surface of.

In the present invention, an air diffusion porous membrane (3) is provided between the air intake hole (2) and the positive electrode catalyst layer (5).
And the porous water-repellent film (4) intervenes so as to support the positive electrode catalyst layer to ensure the flow of air to the positive electrode catalyst layer.

Examples of the air diffusion porous membrane include non-woven fabrics such as polyethylene, polypropylene, acetalized polyvinyl alcohol and nylon; paper such as kraft paper.
Of these, kraft paper is preferable in terms of workability.

A feature of the present invention is that a film of a fluorine-containing polymer substance is formed on the surface of the air diffusion porous film. As such a fluorine-containing polymer substance, a substance which can easily form a film at room temperature or at a low temperature such that the air-diffusing porous material does not undergo thermal alteration is preferable.

[0013]

[Chemical 1]

(Wherein R ¹ represents hydrogen, methyl, chlorine or fluorine; R ² represents R ^f or-(CHX) _n R ^f ;
R ^f represents a perfluoroalkyl group, preferably having 2 to 10 carbon atoms; X is a hydrogen atom, provided that in the R ² , one X is a methyl group, a hydroxyl group or an acetoxy group. Or n is a number of 1 to 3), a fluorine-containing ester of acrylic acid or a derivative thereof represented by formula; or formula (II)

[0015]

[Chemical 2]

A fluorine-containing amide of acrylic acid or a derivative thereof represented by the formula (wherein R ¹ and R ² are the same as above);
A homopolymer, a copolymer of two or more kinds of the above-mentioned fluorine-containing monomers, or an ester or amide of one or more kinds of these fluorine-containing monomers and acrylic acid or methacrylic acid having no fluorine atom in the molecule. Copolymers with are preferred. Further, as a part or all of the fluorine-containing monomer, it has two acrylic groups or methacrylic groups on both sides of the fluorine-containing molecular chain, for example, the compound represented by the formula (III)

[0017]

[Chemical 3]

(Wherein R ¹ is the same as above; R ³ represents a divalent group having a —CF ₂ — unit in the chain, and X represents —O—
Or a -NH-) is used, or a fluorine-containing polymer substance having a crosslinked structure formed by using a non-fluorine-based crosslinking monomer having a plurality of ethylenically unsaturated groups is also used. Can be used.

Still another type of fluorine-containing polymer substance is one in which a fluoroolefin polymer or the above-mentioned dibasic acid having R ^f as a substituent is cured by utilizing the reaction mechanism of a melamine resin or a urethane resin. Examples thereof include polymers of bisphenol-based epoxy compounds containing fluorine.

Of these fluorine-containing polymer substances, a uniform film having excellent water repellency can be formed on the surface of the air diffusion porous film by a simple treatment, and the film is used in a usual battery. A polymer of a fluorine-containing ester of acrylic acid or a derivative thereof is more preferable because it is not affected by an aprotic solvent or an electrolytic solution, and a homopolymer thereof is particularly preferable.

Such a fluorine-containing polymer or a composition containing the same is used as Florard (Sumitomo 3M Co., Ltd. trade name) Asahi Guard (Asahi Glass Co., Ltd. trade name), Tex Guard (Daikin Co., Ltd. trade name) and the like. Available.

The film of the fluorine-containing polymer material formed on the surface of the air diffusion porous film is formed in the range of 0.1 to 0.8 mg / cm ² with respect to the surface area of the porous film. Is preferred. If it is less than 0.1 mg / cm ² , the effect of suppressing the deterioration of discharge characteristics during storage and / or use is not sufficient depending on the purpose of use, and if it exceeds 0.8 mg / cm ² , the above discharge characteristics deteriorate. However, the initial discharge characteristics are not sufficient.

The method for forming such a film of a fluorine-containing polymer is not particularly limited, but examples of the coating method include dipping, padding, brush coating, knife coating, roll coating, spraying and the like. The fluorine-containing polymer substance or its precursor used for coating may be in the form of a polymer, a prepolymer or a reactive monomer, or a mixture thereof, and it may be dissolved in a solvent which dissolves them or polymerized in a solution. It is preferable to use as a treatment liquid obtained by forming a solution of a fluorine-containing polymer substance or suspending it in water, from the viewpoint of easy work.

Examples of the above-mentioned solvent include perfluorohexane, perfluoroheptane, perfluorooctane, perfluorononane, perfluorodecane, perfluorokerosene, perfluorocyclohexane, perfluoro (methylcyclohexane), perfluoro-1,4-dimethylcyclohexane, perfluoro-3, 3'-dimethyldicyclohexane, perfluorodecalin, perfluorotoluene, perfluorotributylamine, perfluorotripentylamine, perfluorotrihexylamine, perfluoro-N, N, N ', N'-tetrapropyldiaminopropane, perfluoro-4-isopropylmorpholine , Perfluorobutyl ether, perfluoro-2-ethyltetrahydrofuran, cyclic perfluoroether ( ₈ F ₁₆ O) fluorine-containing solvents such as;
Fluorine / chlorine-containing solvents such as trichlorotrifluoroethane, tetrachlorodifluoroethane and dichlorohexafluorobutene; chlorine-containing solvents such as 1,1,1-trichloroethane, tetrachloroethane and trichlorobutene are exemplified, but hygiene or global environment A fluorine-containing solvent is preferable because it does not contain a chlorine atom that causes the above problems, is inactive, and dissolves the fluorine-containing polymer substance well.

Such a fluorine-containing solvent is, for example, Fluorinert FC-70, FC-72, FC-75, FC.
-77, FC-40 and the like (both are trade names of Sumitomo 3M Limited).

A curing accelerator may be added to the above treatment liquid, if necessary, depending on the type of the fluorine-containing polymer substance and the treatment conditions. As a curing accelerator, a metal alcoholate,
Zirconium organic acid salt, acid anhydride, aziridine compound,
A carbodiimide compound is exemplified. These may be used alone or in combination of two or more.

After coating, depending on the type of fluorine-containing polymer and the composition of the treatment liquid, air-dry at room temperature, or
The coating of the fluoropolymer material is formed on the surface of the porous membrane by heating in a range that does not affect the material of the air diffusion porous membrane, for example, 70 to 100 ° C. for 2 to 10 minutes.

The water-repellent film used in the air battery of the present invention is not particularly limited, but polytetrafluoroethylene,
Porous membranes such as polyethylene and polypropylene are exemplified, and a porous membrane of polytetrafluoroethylene is preferable because it has excellent water repellency.

In the air battery of the present invention, the positive electrode catalyst layer usually comprises a catalyst, activated carbon and a binder, and as the catalyst, manganese oxide, platinum, silver, metal phthalocyanine or the like can be used. As the separator, a microporous membrane such as polypropylene is usually used.

In the air cell of the present invention, all other elements may be known ones. Further, other optional elements may be added without departing from the scope of the present invention. The present invention is not limited to the button type air battery,
It can also be applied to other types of air batteries such as prismatic type and cylindrical type.
Further, regarding the mechanism of the battery, air-zinc system, air-
It can be effectively applied to any of aluminum type and air-iron type.

[0031]

EFFECTS OF THE INVENTION According to the present invention, by forming a film of a fluorine-containing polymer on the surface of an air diffusion porous film, even if the pore size of the porous film is increased, the air diffusion porous film can be formed between the outside air and the positive electrode catalyst layer. It is possible to prevent the movement of water. therefore,
According to the present invention, invasion of water vapor in the atmosphere into the battery,
The concentration of the electrolytic solution is not changed by evaporation of the electrolytic solution, and the amount of air supplied to the positive electrode catalyst layer is not reduced. Therefore, the discharge performance hardly deteriorates due to the lack of the amount of oxygen permeated into the catalyst layer.

The air battery of the present invention is extremely excellent in both leakage resistance and overdischarge characteristics, and is also excellent in discharge characteristics under heavy and light loads and in discharge performance after being stored for a long period in an open state.

Therefore, the air battery of the present invention is particularly useful as a battery for electronic devices such as calculators that are discontinuously discharged and devices such as watches that are discharged with a relatively light load.

[0034]

EXAMPLES The present invention will now be described in detail with reference to Examples and Comparative Examples. In these examples, parts represent parts by weight. The invention is not limited by these examples.

Examples 1 to 6 As a mother liquor containing a fluorine-containing polymer, 2% by weight was used.
Poly (perfluoropentyl methacrylate) and 98
A solution consisting of wt% perfluorohexane was prepared. This solution was further diluted with perfluorohexane to prepare treatment liquids containing the above polymer and having various concentrations.

Kraft paper was immersed in this treatment liquid, taken out and air dried to obtain a kraft paper having a film of a fluorine-containing polymer substance as a water-repellent film. As described above, the amount of the fluorine-containing polymer substance coated on the kraft paper varies from 0.05 to 0.05 per unit area of the kraft paper by changing the amount of the polymer in the treatment liquid, as shown in Table 1. Varyed between 1.2 mg / cm ² .

The kraft paper having the water-repellent film thus obtained was used as the air diffusion porous film (3), the porous film of polytetrafluoroethylene was used as the water-repellent film (4), and the others were conventional. A button type zinc-air battery as shown in FIG. 1 was prepared using the same structure and material as the air battery.

Comparative Example A button-type zinc-air battery was prepared in the same manner as in the above example except that kraft paper not coated with a fluorine-containing polymer substance was used.

Test Examples The button type zinc air batteries prepared in Examples 1 to 6 and Comparative Example were stored at a temperature of 20 ° C. and a relative humidity of 60% with a sealing seal of air holes peeled off and stored for 1 month. The total weight of the battery after and after 2 months was measured to determine the weight change. Also,
For batteries before storage and after each period, 25
The continuous discharge of 0Ω was performed, and the discharge duration until the voltage dropped to 1.0 V was measured.

The results are shown in Table 1. However, regarding the discharge duration, the value of the battery of the comparative example before storage is 1
The relative value is set to 00.

[0041]

[Table 1]

As is clear from Table 1, by forming the water-repellent film by coating the air-diffusing porous film with the fluorine-containing polymer substance according to the present invention, excellent discharge sustainability can be achieved even after long-term storage or use. A time keeping air battery was obtained. The initial discharge duration did not decrease, and the discharge duration was maintained at a high level even after long-term storage. A range of / cm ² gives good results.

[0043]

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of a button type zinc-air battery produced in an example.

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Air intake hole 3 Air diffusion porous film 4 Water repellent film 5 Positive electrode catalyst layer 6 Separator 7 Negative electrode mixture 8 Negative electrode can 9 Gasket

Claims (2)

[Claims] 1. An air battery having a positive electrode catalyst layer via an air diffusion porous film and a water repellent film inside a positive electrode can having an air intake hole, wherein a fluorine-containing polymer is provided on the surface of the air diffusion porous film. An air battery characterized by the presence of a coating of material. 2. The air battery according to claim 1, wherein the amount of the fluorine-containing polymer substance on the surface of the air diffusion porous membrane is 0.1 to 0.8 mg / cm ² .