JPH06338355A - Air cell - Google Patents

Abstract

PURPOSE:To provide a highly reliable air cell having excellent electric discharging as well as anti-liquid-leak characteristic by providing a polytetrafluoroethylene(PTFE) porous film, in which a crack is not formed even when a gas diffusion electrode is bent, and by using the film. CONSTITUTION:A mixture of catalytic powder, activated carbon and fluororesin powder is filled in a net made of metal, and the filled net is formed into a sheet, a polytetrafluoroethylene porous film 4 is pressure-connected to the one side, and a gas diffusion electrode 5 is thus formed and used. The percentage of elongation of the PTFE porous film 4 in the extended (longitudinal) direction and in the perpendicular (lateral) direction is 200-2000%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air battery having an improved polytetrafluoroethylene (hereinafter abbreviated as PTFE) porous membrane used for a gas diffusion electrode.

[0002]

2. Description of the Related Art As a PTFE porous membrane used for a conventional gas diffusion electrode of an air battery, generally, one having micropores formed by uniaxial or biaxial stretching is used. A PTFE porous membrane that has good adhesion when the thickness, air flow rate, porosity, etc. are specified and when a mixture of catalyst powder, activated carbon and fluororesin powder is actually pressed against a catalyst sheet filled with a metal net. I was using it.

[0003]

As a typical example of an air battery, FIG. 1 shows a sectional view of a current button type air battery. As shown in FIG. 1, in one positive electrode case, 3 diffusion papers, 4 water repellent films, 5 gas diffusion electrodes, and 6 separators are punched out in the order of circles and arranged. By the way, when the vertical direction of the gas diffusion electrode using the PTFE porous membrane defined only by the basic physical properties is curved along a cylinder having a certain diameter, cracks are produced in the horizontal direction of the PTFE porous membrane. It could happen.

Therefore, when such a gas diffusion electrode is used, the gas diffusion electrode inside the bottom of the insulating gasket 9 is the negative electrode 7 when the battery is assembled, especially when the periphery of the positive electrode case 1 is caulked and sealed. Bent to the active substance side in a spherical shape,
Similarly to the above, the PTFE porous membrane is cracked, and the electrolytic solution in the negative electrode acting substance 7 leaks out from this portion through the catalyst layer. Then, this electrolyte is accumulated between the water-repellent film 4 (the PTFE porous film used as a single film, which is not pressure-bonded to the gas diffusion electrode), and the air that has entered through the diffusion paper 3 from the air holes 2 The inflow is interrupted, causing the gas diffusion electrode to suffocate, making discharge impossible. In addition, this electrolytic solution may seep out between the water repellent film of 4 and the positive electrode case of 1 and leak from the air holes of 2.

Generally, the bending of the gas diffusion electrode which occurs at the time of sealing becomes larger as the crimp pressure becomes higher, and the above-mentioned problem is more likely to occur. For this reason, the crimp pressure has to be set to a relatively low value, and the liquid leakage resistance between the sealing plate 8 and the insulating gasket 9 is also poor in sealing property, so good results cannot be obtained. Reference numeral 10 is a sealing tape that closes the air holes 2 before using the battery.

According to the present invention, even if the gas diffusion electrode is bent,
By using a PTFE porous film that does not cause cracks, the above problems are solved, and discharge and leakage resistance are excellent,
An object is to provide a highly reliable air battery.

[0007]

In order to solve this problem, the present invention is to fill a metal net with a mixture of catalyst powder, activated carbon and fluororesin powder, form a sheet, and then form polytetrafluoroethylene porous on one side. What is claimed is:
As an FE porous film, the elongation rate (according to JIS K6887) in the (horizontal) direction perpendicular to the stretching (vertical) direction is 2
The air battery is characterized in that it is from 0 to 2000%.

[0008]

According to this structure, even if the vertical direction of the gas diffusion electrode is curved along a cylinder having a certain diameter, no crack is generated in the horizontal direction of the PTFE porous membrane which is pressure-bonded, and the sealing is performed. Even at times, the PTFE porous membrane does not crack.

[0009]

EXAMPLES Examples of the present invention will be described. (1) Performance of Gas Diffusion Electrode Catalyst powder, activated carbon, and fluororesin powder are mixed and stirred, and the fluororesin powder is made into fibers, and the obtained mixture is passed through a rolling roller to obtain a sheet having a thickness of 0.4 mm. It was A nickel mesh current collector having a wire diameter of 0.15 mm and 40 mesh was pressure bonded to one surface of this sheet to form a catalyst layer. On the other surface of this catalyst layer (surface on the air supply side), a porosity of 30%, a thickness of 0.1 mm, an elongation of 200% in the vertical direction, and a horizontal direction, 8 kinds of PTFE porous membranes shown in Table 1 were overlaid and Was pressure-bonded with a roller at a constant pressure to prepare eight kinds of gas diffusion electrodes, and the following comparative examinations were conducted.

[0010]

[Table 1]

(I) Elongation in the horizontal direction and adhesive strength With respect to a test piece obtained by cutting each electrode into strips with a width of 1 cm, the adhesive strength between the catalyst layer and the PTFE porous membrane was measured by a tensile tester (Autograph S-500D, The peel strength was measured using Shimadzu Corporation). The results are shown in Table 2.

[0012]

[Table 2]

From this result, the adhesive strength between the catalyst layer and the porous PTFE membrane becomes stronger as the elongation in the horizontal direction becomes larger. By the way, it has been empirically understood that in the step of punching out the gas diffusion electrode at the time of production, the adhesive strength of 50 g or more is necessary to prevent peeling of the circumferential portion between the catalyst layer and the PTFE porous membrane. There is. When the gas diffusion electrode with peeling is assembled as a battery, the electrolyte easily permeates into that portion and interferes with the inflow of air, which hinders the battery reaction. Therefore, PTF
E The lateral elongation of the porous film needs to be 200% or more.

(Ii) Elongation rate in the horizontal direction and crack generation state due to bending. Each electrode was cut into a rectangle of 5 cm in the vertical direction and 3 cm in the horizontal direction, and a test piece was wound around the circumference of the cylinder in the vertical direction. It was curved by bending, and the appearance of cracks in the PTFE porous membrane was visually observed using a microscope (× 20). The results are shown in Table 3.

[0015]

[Table 3]

From this result, it is advantageous that the elongation in the horizontal direction is small so that cracks hardly occur. By the way, the crack of the PTFE porous film due to the bending of the electrode in the sealing (crimping) step during battery assembly can be substituted in the above test, and in order to prevent the crack from occurring, the diameter is practically 5 mm.
It is necessary to use a gas diffusion electrode that does not crack up to 0 mm or less. Therefore, the elongation rate in the horizontal direction of the PTFE porous membrane needs to be 2000% or less. It should be noted that the vertical and the horizontal have a mutual exchange relationship, and the vertical and the horizontal are the same even if they are interchanged.

(2) Performance of Battery The air battery in this embodiment has the same structure as the air battery shown in FIG. 1, and the gas diffusion electrodes shown in Table 1 differing only in the porous PTFE membrane were incorporated into the air battery. Button type air battery P
R44 (nominal capacity: 540 mAh) was prepared for each crimping pressure, and the following tests were conducted. The crimp pressure was the standard pressure and 20 kgf and 40 kgf added thereto.

(I) Continuous Discharge Test As an initial test and an acceleration test, a battery which was heated and stored at 60 ° C. for 20 days was stored in an environment of temperature 20 ° C. and relative humidity 60% Rh
Conducted a continuous discharge test with a load resistance of 250Ω, and as a result,
Table 4 shows the average values of the discharge capacities. The final voltage of 1.1
V, the number of tests n = 10.

[0019]

[Table 4]

After completion of the above test, the elongation percentage is 100-
When 150% of the batteries were disassembled and investigated, the catalyst layer and PTF were
E A part where the porous film was peeled off was generated, and the electrolytic solution was just accumulated at that part. Also, the elongation rate is 250
Similarly, when 0 to 3000% of the batteries were disassembled and investigated, cracks occurred in the PTFE porous film of the gas diffusion electrode, and the electrolytic solution was accumulated between the film and the water repellent film. That is, good results were obtained when the elongation rate was 200% to 2000%.

(Ii) Leakage resistance test A battery having an elongation rate of 200% and 2000% was tested at a temperature of 45%.
The sample was stored in an environment of ° C and a relative humidity of 93% Rh, and a leak resistance test between the sealing plate and the insulating gasket was carried out. The results are shown in Table 5. The number of tests n = 50.

[0022]

[Table 5]

[0023]

As is clear from the above description, the PT having an elongation of 200 to 2000% in the direction perpendicular to the stretching direction is obtained.
The air battery using the FE porous film is excellent in discharge and leakage resistance and can be highly reliable.

[Brief description of drawings]

FIG. 1 is a sectional view of a PR44 type button type air battery.

[Explanation of symbols] 1 positive electrode case 2 air holes 3 diffusion paper 4 water repellent film 5 gas diffusion electrode 6 separator 7 negative electrode active substance

Claims (1)

[Claims] 1. Air using a gas diffusion electrode which is formed by filling a metal net with a mixture of catalyst powder, activated carbon and fluororesin powder, forming a sheet, and then crimping a polytetrafluoroethylene porous membrane on one side. A battery, wherein the porous film has an elongation rate (according to JIS K6887) of 200 to 20 in a (horizontal) direction perpendicular to a stretching (vertical) direction.
An air battery characterized by being 100%.