JPS61211957A - Manufacture of gas diffusion electrode - Google Patents

Abstract

PURPOSE:To firmly stick a catalytic layer to a water-repelling porous film by applying an adhesive on the surface of the catalytic layer while pressure is impressed to stick the adhesive to the catalytic layer and thereon a water- repelling porous film is placed for being stuck under pressure. CONSTITUTION:An adhesive is applied to a catalytic layer whereby the adhesive to be used is a water-repelling resin dispersion agent or water-repelling resin powder. Next, pressure is impressed from above an adhesive layer for firmly sticking the adhesion on the catalytic layer, whereby pressure impression is usually performed by using a roller. Thereafter, heat treatment of the whole at the temperature of 150-350 deg.C for 10-30min is desirable. Finally, a water- repelling porous film is placed on the formed adhesive layer for being press- stack under the prescribed pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a gas diffusion electrode used in air cells, fuel cells, etc., and more specifically relates to a method for producing a catalyst layer and a water-repellent porous Jf! gas diffusion electrode. This invention relates to a method for strongly adhering two films.

[Technical background of IJJ and its problems] For example, in an air battery that uses m elements in the air as a positive electrode active material, a gas diffusion electrode is housed. This gas diffusion′iTL
The poles are generally sheets of construction as shown in cross-section in FIG. In Figure 1, l is 411 as a current collector! For example, the nickel net 2 is a sheet of a catalyst layer formed by binding a catalyst material such as activated carbon with, for example, polytetrafluoroethylene (PTFE) resin. Reference numeral 3 denotes a water-repellent porous membrane in which fine air permeation holes are distributed, and this membrane is adhered to the catalyst layer 2 via an adhesive layer 4.

In the gas diffusion electrode having such a structure, the following method is conventionally known as a method for bonding and integrating the catalyst layer 2 and the water-repellent porous membrane 3.

For example, there is a method in which a water-repellent porous membrane is directly brought into contact with the surface of the catalyst layer and then pressure-bonded, or a catalyst layer is placed on one side of the water-repellent porous membrane as disclosed in Japanese Patent Application Laid-Open No. 57-145271. This method involves applying a paste consisting of powder and a water-repellent binder such as fluororesin, and heat-treating this at a temperature of 100 to 400°C.

However, in the former method, it is difficult to adjust the pressure applied when pressing the water-repellent porous membrane, and if this pressing force is too low, the catalyst layer and the water-repellent porous membrane may be damaged during storage or discharge of the battery. The electrolytic solution accumulates between the electrode and the battery, causing not only a decrease in the discharge characteristics of the battery but also a situation in which the electrolytic solution leaks from the air electrode side.

In addition, as another method, a catalyst layer or a water-repellent porous 1
After uniformly spraying, for example, 60% PTFE dispersion onto one side of the sheet and subjecting it to heat treatment.

A method of crimping and integrating the two is also known.

According to this method, the above-mentioned inconvenient situation can be solved to some extent. However, although the PTFE powder in the dispersion adheres to the water-repellent porous membrane, it does not blend with the surface of the catalyst layer due to other forces, so the adhesive force between the two in the integrated sheet is not necessarily sufficient.

In order to increase the adhesive strength between the two, it is possible to increase the force that presses them together, but in that case, the micropores in the water-repellent porous membrane will be crushed, and as a result, the inflow of oxygen will be suppressed. As a result, the required current cannot be extracted from the battery.

For these reasons, there is a strong demand for an improved method for firmly adhering a water-repellent porous membrane to a catalyst layer without crushing the micropores of the membrane.

[Object of the Invention] In response to the above-mentioned needs, the present invention aims to provide a method for manufacturing a gas diffusion electrode in which a catalyst layer and a water-repellent porous membrane are firmly bonded.

[Summary of the Invention] The method for producing a gas diffusion electrode of the present invention is a method for producing a gas diffusion electrode in which a catalyst layer and a water-repellent porous membrane are bonded together via an adhesive. Apply the agent,
The method is characterized in that pressure is applied to the adhesive-applied surface to adhere the adhesive to the catalyst layer, and then the water-repellent porous membrane is placed and pressure-bonded thereon.

The catalyst layer in the method of the present invention may be of any material that is normally used in air batteries, etc.; After mixing, this mixture was rolled and formed into a sheet!・Can be mentioned.

After this sheet is pressed onto a current collector such as a nickel net to integrate the two, an adhesive is applied to the other surface of the catalyst layer.

The adhesive used is a water-repellent resin dispersion or a water-repellent resin powder. A suitable example of the former is 20~
60% PTFE dispersion.

The latter may include PTFE powder with a particle size of 1 to 5. If the amount of these adhesives applied is too small, the thickness of the adhesive layer will become thin, leading to a decrease in the adhesive force between the catalyst layer and the water-repellent porous membrane described below. If the size increases, oxygen permeability decreases and battery performance deteriorates, so it is usually preferable that the coating amount be about 7 to 40 g/rn'. As a coating method, conventional methods such as spraying, printing, screen printing, etc. can be applied.

In the method of the present invention, pressure is then applied from above the adhesive layer to firmly adhere the adhesive to the catalyst layer. The greatest feature of the method of the present invention is that this step is essential.

This pressure application is usually carried out using a roller. At this time, it is effective not only to simply apply pressure to the adhesive layer, but also to add movement such as rubbing the adhesive into the catalyst layer, since this increases the adhesive force between the adhesive and the catalyst layer.

In addition, before or after applying pressure to the surface to which the adhesive is applied, it is preferable to heat-treat the entire adhesive at a temperature of 150 to 350°C for 10 to 30 minutes.
This treatment is effective for removing various surfactants contained in adhesives such as dispersions and increasing the adhesive strength between the catalyst layer and the water-repellent porous membrane described below. However, if the treatment temperature is higher than 350°C, the PTFE, which is the binder of the catalyst layer, will melt, causing a decrease in the strength of the catalyst layer and eventually resulting in a decrease in adhesive strength. High adhesive strength cannot be obtained even at a temperature of .

Finally, in the method of the present invention, a water-repellent porous membrane is placed on the adhesive layer formed in this way, and is crimped with a predetermined pressure.

The water-repellent porous membrane used may be any membrane as long as it is water-repellent and has fine pores distributed, but a porous membrane conventionally used in air batteries, such as a PTFE porous membrane, is suitable. .

The pressure applied during pressure E needs to be a pressure that does not crush the micropores of the water-repellent porous membrane, for example, 20
0~350kg/c7I! It is preferable to use a roller when applying pressure.

[Embodiments of the invention] (1) Production of gas diffusion electrode 70 parts by weight of activated carbon powder with an average particle size of 15 μs and 30 parts by weight of PTFE powder with an average particle size of 1− are mixed, and the resulting mixture is rolled. A catalyst layer sheet with a thickness of 0.3 mm was prepared.

This sheet ladle was crimped onto one side of a 60-mesh nickel net with l [lo, l vulcanization].

Next, apply 60% PTFE dispersion to the sheet surface opposite to the crimped surface with the nickel net in an amount of 7 g/
After coating with rn', the whole was heated in air at 300℃ for
Heated for 0 minutes.

Thereafter, a roller was scanned at a pressure of 240 kg/d over the dry coating surface of the 60% PTFE dispersion.

Next, a porous PTFE membrane with a thickness of 0.1 mm was placed on the coated surface, and a roller was run over the membrane at a pressure of 240 kg and 10 ff to perform an adhesion treatment, and gas diffusion according to the method of the present invention having the structure shown in Fig. 1 was performed. The electrode was manufactured.

For comparison, a gas diffusion electrode was also manufactured using a conventional method in which a porous PTFE membrane of the same type was directly stacked on the same catalyst layer sheet and pressed with a force of 240 kg/cm.

(2) Performance First, the adhesive strength between the catalyst layer and the PTFE porous membrane was measured. The measurement method was to cut the sample into pieces with a diameter of 1 cm, pull the PTFE membrane and catalyst layer in a 180° direction at a speed of 1 cs+/sin, and then measure the peel strength. As a result, the force in the case of the method of the present invention was 90 g force, and in the case of the comparative example, it was 10 g force. It has been found that the application of the undeveloped I51 method improves the adhesive strength by about 9 times.

Next, the manufactured gas diffusion electrode was R44 shown in Figure 2.
The battery was mounted on a No. 5 air battery, and the discharge performance and leakage rate of the battery were measured.

In FIG. 2, reference numeral 11 denotes a positive electrode can which also serves as a positive electrode terminal, and an air supply hole 12 is bored in the bottom thereof. 13 is a gas diffusion electrode, as shown in FIG.

It is an integrated product consisting of a nickel net on the top surface, a catalyst layer, a PTFE adhesive layer, and a PTFE porous pressure membrane. Reference numeral 14 denotes an electrolyte holding material, which is made of a nonwoven fabric having liquid holding properties and alkali resistance, holds a caustic alkaline electrolyte, and is in contact with the negative electrode 15 made of gelled zinc fine powder.

Reference numeral 16 is paper with excellent air permeability, the upper surface of which is in contact with the catalyst layer via the PTFE porous membrane of the gas diffusion electrode 13, and the lower surface of which is in contact with the bottom surface of the positive electrode can 11.

A negative electrode can 17 also serves as a negative electrode terminal, and the opening of the positive electrode can 11 is bent through a gasket 18 made of an insulating material to seal the entire battery.

100 such R44 type air batteries were heated at 20°C and 45°C.
Each battery was connected to a load of 250 Ω at a temperature of 0.degree. C. for continuous discharge, and the battery capacity at that time was measured. The average values are shown in the table.

Further, after the above continuous discharge, the battery was left in an environment with a temperature of 45° C. and a relative humidity of 90% for 14 days, and the presence or absence of leakage from the battery was observed at that time. The number of leaking batteries was counted to calculate the incidence rate, and the values are shown in the table.

Similar tests were conducted for the case where a conventional gas diffusion electrode was mounted, and the results are also listed in the table.

[Effects of the Invention] As is clear from the above explanation, the gas diffusion electrode manufactured by the method of the present invention has a significantly increased adhesive strength between the catalyst layer and the water-repellent porous membrane, and the air battery equipped with the same has a significantly increased adhesive strength. Compared to conventional products, its discharge performance is improved and the rate of leakage is significantly reduced, resulting in excellent long-term storage stability and high reliability.

Therefore, it can be said that the industrial value of the method of the present invention is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view for explaining the structure of a gas diffusion electrode, and FIG. 2 is a partial cross-sectional view of an air cell in which the gas diffusion electrode of FIG. 1 is mounted.

Claims (1)

[Claims] 1. A method for manufacturing a gas diffusion electrode in which a catalyst layer and a water-repellent porous membrane are bonded via an adhesive, comprising: applying the adhesive to the surface of the catalyst layer; A method for producing a gas diffusion electrode, which comprises applying pressure to a surface to adhere the adhesive to the catalyst layer, and then placing and pressing the water-repellent porous membrane thereon. 2. Prior to placing the water-repellent porous membrane, the adhesive layer is heated to a temperature of 150 to 350°C. Claim 1
The method for manufacturing the gas diffusion electrode described in Section 1. 3. The method for manufacturing a gas diffusion electrode according to claim 1 or 2, wherein the adhesive is a water-repellent resin dispersion or a water-repellent resin powder. 4. A method for producing a gas diffusion electrode according to claim 3, wherein the water-repellent resin dispersion is a polytetrafluoroethylene dispersion. 5. The water-repellent porous membrane is a polytetrafluoroethylene porous membrane. A method for manufacturing a gas diffusion electrode according to claim 1 or 2.