JPS61273866A - Manufacture of air electrode - Google Patents

Abstract

PURPOSE:To achieve a high resistance to the leak of liquid, enhance the diffusion of air to a catalyst layer and prevent a porous polytetrafluoroethylene film and the catalyst layer from separating from each other after they are press-bonded to each other, by press-bonding the unbaked film of a prescribed density to the catalyst layer to have another prescribed density. CONSTITUTION:After each of porous polytetrafluoroethylene films (porous PTFE films) of various densities (1.0 to 1.6g/cm<3>) is press-bonded to a catalyst layer, it turns out that the films of densities of 1.2 to 1.4g/cm<3> do not separate from the catalyst layers and do not crack. When it is then checked whether or not the leak of liquid from air holes occurs as to the films stored at a temperature of 60 deg.C for 30 days after the press-bonding and whether or not improper discharge occurs as to the films in continuous discharge at an electric resistance of 250OMEGA, it turns out that the films of densities of 1.5 to 1.7g/cm<3> are satisfactory. For these reasons, the porous PTFE film of the density good against the separation and the cracking is press-bonded to the catalyst layer, and the density is thereafter changed to be good against the liquid leak and for the discharge. The purpose is thus attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in the manufacturing method of an air electrode used in an air battery, particularly a button type battery.

BACKGROUND ART Air batteries, especially button-type air batteries, have a higher energy density than other alkaline batteries and are less polluting, so they are attracting attention as an alternative to mercury batteries.

However, while the air electrode used in air batteries takes in air from the atmosphere, it is necessary to prevent the electrolyte from leaking out of the battery.

For this reason, conventional air electrodes use an unfired porous polytetrafluoroethylene film (hereinafter referred to as porous PT) that has an excellent water-repellent effect and can supply air to the catalyst layer by diffusion.
FE film) was crimped onto the film. FIG. 1 shows a cross-sectional view of a button-type air battery using an air electrode. In Figure 1, 1 is zinc hydrate, 2 is nickel stainless steel.
A sealing plate using a three-layer steel clad plate, 3 is a sealing packing, 4 is a separator, 6 is an air electrode with a porous PTFE film crimped onto the catalyst layer, and 6 is an air diffusion device for the purpose of air diffusion to the air electrode. 7 is a positive electrode case, and 8 is an air hole for the purpose of introducing air from the atmosphere into the battery, and the hole is covered with a closing sheet when not in use. Also,
Figure 2 is an enlarged view of the air electrode marked A in Figure 1, where 9 is the catalyst layer and 1o is the one that prevents the electrolyte from leaking out of the battery and does not prevent air (oxygen) from diffusing into the catalyst layer. This is a porous PTHE film intended for this purpose. This film uses an unfired porous PTFE film and is pressed onto the catalyst layer. Further, the compression bonding is generally performed by sandwiching the catalyst layer and the porous PTFE film between two parallel rolls.

Problems to be Solved by the Invention However, simply pressing an unfired porous PTFE film onto the catalyst layer caused the following problems.

(1) Air (
A porous PTFE film is used that does not hinder oxygen (oxygen) diffusion, but if the pores are significantly crushed by pressure bonding, air will not be able to diffuse into the catalyst layer and sufficient discharge characteristics will not be obtained.

(2) Contrary to (1), porous PTFIi: If the pores of the film are too large, the electrolyte will pass through the PTFE film layer and leak out of the battery through the air holes.

(3) If the pressure bonding between the catalyst layer and the porous PTFE film is not sufficient depending on the pressure bonding conditions, peeling may occur.

During storage, electrolyte accumulates in this space, which prevents air from diffusing into the catalyst layer. For this reason, sufficient discharge performance cannot be obtained.

The present invention aims to solve the above-mentioned conventional problems and provide a method for manufacturing an air electrode that has excellent leakage resistance from air holes and does not hinder air diffusion to the catalyst layer. do.

Means for Solving the Problem In order to solve this problem, the present invention provides an initial density of 1.2.
This is a method for producing an air electrode in which a porous PTFE film of ~1.41//ctl is pressed onto a catalyst layer and its density is increased to 1.5 to 1.79/cIIl.

Effect: According to this configuration, the catalyst layer and the PTFE film are in close contact with each other, and the above-mentioned problem (3) does not occur. In addition, when the density after crimping is 1.5 to 1.71i/-, the above-mentioned (1
) or (2) will not occur. This makes it possible to provide an air electrode that does not cause liquid leakage from the air holes and does not hinder the diffusion of air into the catalyst layer.Examples The present invention will be described in detail below.

The configuration of the air electrode and air cell according to the present invention is the same as the conventional example shown in FIG.

The catalyst shown in Fig. 1 is a mixture of manganese oxide, activated carbon, acetylene black as a conductive material, and fluororesin, which is filled in a stainless steel screen with a mesh roughness of 400 to a thickness of 0.3 mm. It is. Various types of unfired porous PTFE are pressed onto this catalyst, and the density of the porous PTFE after pressing is set to 1.1 to 2. Ofi/crd
After storage at 60°C for 30 days, an air cell was created, and after storage at 60℃ for 30 days, liquid leakage from the air holes and 250Ω continuous discharge were performed to prevent air diffusion (defective discharge) due to the collapse of the pores of the porous PTFE due to pressure bonding. The results of the study are shown in Table 1. Note that the evaluation was performed using PH10.

Further, the density of porous PTFE was determined using the following formula.

From the results shown in Table 1, conventional problems (1) and (2) can be solved by setting the density of porous PTFE after pressure bonding to the catalyst layer to 1.5 to 1.71/-. I see that it is possible. In addition, in this study, the thickness of the porous PTFE after crimping was 0.1±(LO1wo++, but 0.3Tr
The trend is almost unchanged in the range up to rIn, 5,4
won.

Next, Table 2 shows the results of an investigation into the peeling between the catalyst layer and the porous PTFE film, which was described in (3) as a conventional problem.

Porous PTYE7 with various densities
Ile A (1,0-1, e#/i) as a catalyst...-'
#KEEIL, after arriving at 8E. Secret Ijf
1-101/c4 h L, fc.

J&,) Also, the thickness of the porous pTFE film after pressure bonding is □ , Both were set to 0.1±0.01 m.

ゝ1, Table 2: 1.1g/crIl 1.6. When compressed to jil/c1d, cracks occurred on the film surface.

From the above, the density of the porous PTFE film before pressure bonding is 1.
2-1.4. It was found that jil/ci was good.

Effects of the invention As is clear from the above explanation, the initial density was 162 to 1.
It is pressed onto a porous PTFE film catalyst layer of 4Ji'/crd, and its density is set to 1.5-1. An air electrode having a ratio of yg/i has no leakage from the air holes and does not hinder the diffusion of air into the catalyst layer, so that an extremely excellent air and air electrode can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an air battery according to an embodiment of the present invention and a conventional example, and FIG. 2 is an enlarged cross-sectional view of the mark A in FIG. 1...Zinc chloride, 2...Sealing plate, 3.
... Sealing packing, 4 ... Separator, 6 ... Air electrode, 6 ... Air diffusion paper,
7...Positive electrode case, 8...Air'l,
'l, ni';, l Hole, 9...Catalyst layer, 1o...Porous polytetraphyllium ``HIO.'', Fluoroethylene film 0°
Name of agent: Patent attorney Toshio Nakao
One other person □ □.゛, ゛+ ξ , ゛, pa j] S 7″1t. ,′ □ 〕 □ β −11 air comb

Claims (1)

[Claims] (1) An air electrode formed by pressing an unfired porous polytetrafluoroethylene film onto a catalyst layer, which is made of unfired porous polytetrafluoroethylene film having an initial density of 1.2 to 1.4 g/ccm^3. A method for producing an air electrode, characterized in that the density of fluoroethylene is adjusted to 1.5 to 1.7 g/cm^3 by pressing fluoroethylene onto a catalyst layer.