JPH04192270A - Manufacture of air electrode for air battery - Google Patents

Abstract

PURPOSE:To extend the service life of a battery by dissolving a polymer in an aqueous alcohol under the condition of a high temperature and a natural pressure in a sealed temperature and humidity cylinder, preparing a metastable solution, and processing the polymer after mixing the polymer with a carbon holding catalyst within an hour after the preparation. CONSTITUTION:As a binder to manufacture an active layer 4 of two-layer air electrode used for an air battery, a metastable ethanol water solution of a fluoride hydrophlic polymer, 1-propanol water solution, or 2-propanol water solution is used. The metastable solution is prepared by dissolving a polymer in an aqueous alcohol at a high temperature and a natural pressure in a sealed temperature and humidity cylinder, and the resultant solution is mixed with a carbon holding catalyst in an hour after the solution is prepared. Then, the mixture is processed in a normal method. As a result, a mixture with even combination of resin, activated carbon, and catalyst makes the catalyst particles into a complex effectively, and suppresses a loss of catalyst from the surface of the electrode. Consequently, an electrode with a good and long service life property can be obtained, and the service life of the battery is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an air battery, and focuses on improving a method for producing an air electrode.

[Conventional technology]

Air batteries generate electricity by electrochemically combining a reactive metal negative electrode with an air positive electrode through a suitable electrolyte solution. Air cathodes are typically laminar composite materials with opposing surfaces exposed to air and the cell's aqueous electrolyte, respectively.

Oxygen dissociates within the air electrode, while the metal at the negative electrode oxidizes. These half-reactions generate a useful current through an external circuit connected between the negative and positive electrodes. The air cathode must be permeable to air but relatively impermeable to water, and must contain electrically conductive elements to which an external circuit can be connected. Typically, an aqueous air cathode consists of two layers. The "active" layer exposed to the electrolyte typically contains activated carbon, catalyst, and binding resin. The "gas delivery" layer, which is exposed to air, typically contains carbon and a hydrophobic bonding resin. The metal screen, which acts as a conductive element, can be applied to one or both sides of the composite electrode, or sandwiched between two layers. A variety of negative electrode metals have been used including aluminum, iron, lithium, magnesium, and zinc.

Aluminum and its alloys are considered particularly advantageous due to their low cost, light weight, and ability to operate as the negative electrode of air electrodes using neutral electrolytes.

Considerable improvements have been made in developing efficient and economical air electrodes. 600 per square centimeter
Electrodes have been fabricated that exhibit fairly long-life performance at current densities in excess of milliamperes (European patent 029243).
1A2).

[Problem to be solved by the invention]

Despite the published improvements, a continuous drop in potential was typically observed over the life of the electrode.

One of the reasons for the decline in electrode performance is the gradual loss of catalyst from the "active" layer.

Fluorinated hydrophobic polymers are preferred for use as binding resins in the "active" layer due to their effectiveness in complexing and sequestering typically hydrophilic catalysts.

However, unless the fluorinated hydrophilic polymer-bound resin is intimately mixed with the catalyst and activated carbon, catalyst loss still occurs. Because of their high chemical stability and unique electrochemical properties, fluorinated hydrophilic polymers tend to be poorly soluble in common solvents and are usually not solution processable. When solutions can be obtained, fluorinated hydrophilic polymers tend to be unstable, precipitating solid polymers throughout. The resulting "active" layer from such a solution would be expected to be a heterogeneous mixture. Therefore, there is a need to develop improved processing methods to obtain a homogeneous mixture of fluorinated hydrophilic polymer bound resin, activated carbon, and catalyst for use as the "active" layer of an air electrode.

[Means for Solving the Problems] The present invention aims to improve the "activation" of a two-layer air electrode used in an air battery.
Metastable aqueous solutions of fluorinated hydrophilic polymers in ethanol, 1-propanol, or 2-propanol are used as binders to fabricate the layers. The metastable solution is characterized in that it is prepared by dissolving the polymer in aqueous alcohol at high temperature and under natural pressure in a sealed digestion bomb, and that the resulting solution is used within one hour of preparation.

[For production]

Compared to published methods of making the "active" layer of two-layer air electrodes used in air batteries, metastable alcoholic aqueous solutions of freshly prepared fluorinated hydrophilic resins as binders are advantageous.

In particular, the resulting more homogeneous mixture of binding resin, activated carbon, and catalyst effectively complexes the catalyst particles and suppresses loss of catalyst from the electrode surface. Thus, an electrode with good long-term performance is obtained.

〔Example〕

An overall view of the air battery of the present invention is shown in FIG. 1 is the air artificial port, 2 is the "gas supply layer" of the air electrode, 3 is the collector electrode of the air electrode, 4 is the "active" layer of the air electrode, and 5 is the electrolyte. , 6 is a metal negative electrode. In the context of the present invention, the "active" layer is comprised of 10% to 65% by weight fluorinated hydrophilic resin, with the remainder comprised of activated carbon and catalyst.

EXAMPLE A "dross feed" layer is prepared by dispersing 70 parts by weight of acetylene black in water. Then add 30% by weight of polytetrafluoroethylene as an aqueous dispersion to the acetylene black. The mixture is evaporated to dryness and then heated to 200°C.
Heat treated for 20 hours. The dry material is ground in a ball mill and placed in a high-pressure press mold at a rate of 1
Distribute uniformly to a degree of 0 milligrams. Carefully lay the nickel screen over the acetylene black-binder mixture. This combination was heated to 70kg/c for about 5 minutes at 100℃.
Press d. A copolymer of perfluorinated vinyl ether and tetrafluoroethylene having an ether chain low molecular weight oxidized polyhexafluoropropylene covered with tetrafluoroethylene/sulfonic acid terminal groups (NAFION NR5
0; DuPont) is used as the binding resin for the "active" layer. A digestion bomb is filled with fluorinated hydrophilic resin and 709152-brovanol/30% water in a weight ratio of 1:19.

Seal the bomb and heat at 230° C. for 5 hours. After cooling to room temperature, the bomb is opened and the solution is added to the activated carbon suspension in 2-propanol. It contains 296 parts by weight of dispersed platinum. The weight ratio of resin and activated carbon is 1;
It is 4. The suspension is evaporated to dryness with stirring and gentle heating under a stream of nitrogen. 20 pieces of this material
After heat treatment at 0°C for 20 hours, it is ground in a ball mill.

1 layer of this material on top of the already generated “gas supply” layer.
Load at a degree of 5e+g/cd and press at room temperature at 70kg/c-. Next, heat the composite two-layer electrode at 300℃ for 15 minutes.
Press in kg/cd. This electrode was tested in a heated stirred cell maintained at 80°C as an air cathode to a nickel counterelectrode. An aqueous sodium hydroxide solution (4N) was used as the electrolyte, and was circulated using a pumping pump. A current of 450 milliamps per square centimeter was applied, and oxygen was consumed at the air cathode while being produced at the nickel anode. The test was stopped when the voltage relative to the reversible hydrogen reference electrode dropped below 0.55 volts. According to this criterion, the life of the tested electrode was 170 days.

(Comparative Example) A commercially available fluorinated hydrophilic polymer bonded resin (A
The same electrodes as described above were prepared, except that a 100% molten metal chloride was used.

Use the solution as received for at least 30 days after manufacture.

The electrodes were tested in the same manner as outlined above.

According to the life criteria defined above, the life of the tested electrode was 130 days.

〔Effect of the invention〕

Use of a metastable aqueous ethanol, 1-propanol, or 2-propanol aqueous solution of a fluorinated hydrophilic polymer as a binder for the air electrode of an air battery within one hour of preparation extends the usable life of the battery.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an air cell according to the invention. 1... Air inlet port 2... Gas supply layer 3... Collector electrode 4... Active layer 5... Electrolyte 6... Metal negative electrode and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Suzu Ki Sanbe (and 1 other person) (v) SunLDcD

Claims (1)

[Claims] A method for producing an air electrode used in the production of an air battery, which uses a metastable aqueous ethanol solution, 1-propanol aqueous solution, or 2-propanol aqueous solution of a fluorinated hydrophilic polymer as a binder. The solution is prepared by dissolving the polymer in aqueous alcohol under autogenous pressure at high temperature in a sealed digestion bomb, the metastable solution is mixed with the carbon-supported catalyst within 1 hour after its preparation, and the mixture is then mixed with the carbon-supported catalyst. A method for producing an air electrode for an air battery, characterized by processing using a method well known in the industry.