JPH04192271A - Air electrode for air battery - Google Patents

Abstract

PURPOSE:To extend the service life of a battery by using a graphite fluoride material of the composition CxF (5>=x>=2) as a hydrophobic component of an air electrode. CONSTITUTION:A gas feeding layer 2 and a collector electrode 3 are formed by mixing a CxF and polytetrafluoroethylene at the wt. ratio 7: 3, drying and powdering it, dispersing evenly in a high-pressure press pattern at the rate 10mg/cm<2>, spreading an Ni net thereover, and pressing at 100 deg.C 70kg/cm<2>. As an active layer 4, an activated carbon holding 2wt.% of platinum and polytetrafluoroethylene are dispersed in the water at the ratio 80:20, and powdered after drying and a heat treatment, loaded on the above layer at the rate 15 mg/cm<2>, and pressed at 300 deg.C 70kg/cm<2>. An air battery furnishing an equeous sodium hydroxide as the electrolyte 5 to the Ni negative electrode 6, can operates the CxF by its excellent hydrophobic property as the main component of the active layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an air battery and focuses on improving the air battery.

[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 positive and negative 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 211. 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. A metal screen that 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.

Deterioration of battery performance often culminates in irreversible electrode degradation due to excessive leakage of the electrode by electrolyte. Therefore, there remains a need for improved hydrophobic components for air electrodes that prevent electrode failure due to excessive leakage.

[Means to solve the problem]

The present invention uses CxF (5
It is characterized by using fluorinated graphite having a composition of >X>2).

[For production]

Compared to the carbon and hydrophobic resins currently employed in the “gas supply” layer of two-layer air electrodes, CxF(5>x>2)
Fluorinated graphite, having a composition of , has excellent hydrophobicity that inhibits aqueous electrolyte from soaking into the electrode while still allowing oxygen to pass through. In fact, the excellent hydrophobicity of these fluorinated graphites allows this material to serve effectively as the main component of the "active" layer without the use of a "gas supply" layer.

〔Example〕

An overall view of an air cell of the type described in the present invention is shown in FIG. 1 is the air inlet 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. For the present invention, the "gas supply" layer contains between 40% and 80% by weight of CxF (5≧X≧2), with the remainder consisting of a perfluorinated resin binder such as polytetrafluoroethylene. has been done.

(Example) "Gas supply" layers C and F are prepared by dispersing them in water. Polytetrafluoroethylene is then added as an aqueous dispersion to the C2F dispersion. The weight ratio of C2F and polytetrafluoroethylene is 7:3. The mixture is evaporated to dryness and then heat treated at 200° C. for 20 hours. The dry material is ground in a ball mill and uniformly distributed in a high-pressure press mold at a rate of 10 milligrams per square centimeter. C
Carefully lay the nickel screen over the 2F-binder mixture.

This combination was heated to 70kg/c for about 5 minutes at 100℃.
- Press. The "active" layer consists of activated carbon carrying platinum and polytetrafluoroethylene in a weight ratio of 80:
It is prepared by dispersing it in water at a ratio of 20:20, followed by evaporation and drying. Activated carbon contains 2% platinum by weight. This material is heat treated at 200° C. for 20 hours and then ground in a ball mill. This material was placed on top of the already produced "gas supply" layer at a rate of 15 mg/c- and 70 k at room temperature.
Press g/c-. Next, the composite two-layer electrode is heated at 300°C and pressed at 15 kg/c-. This electrode was tested in a heated stirred cell maintained at 80°C as an air cathode to a nickel counterelectrode. Aqueous sodium hydroxide (4N) was used as the electrolyte and circulated with a screw pump. A current of 450 milliamps per square centimeter was applied, being consumed at the oxygen or air cathode while being generated at the nickel anode.

The test was stopped when the voltage relative to the reversible hydrogen reference electrode fell below 0.55 volts. According to this criterion, the life of the tested electrode was 210 days.

(Comparative Example) An electrode was prepared in the same manner as described above except that acetylene black was substituted for C and F in the "gas supply" layer.

This was also 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〕

CxF (5>x
By using a fluorinated graphite material having a composition >2), the usable life of the battery is increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an air cell according to the present invention. 1...Air inlet port -2...Gas supply layer 3...Collector electrode 4...Active layer 5... Electrolyte 6...Metal negative electrode that's all Applicant: Seiko Epson Corporation

Claims (1)

[Claims] An air electrode for an air battery containing graphite fluoride consisting of a combination of C_xF (5≧x≧2) as a hydrophobic main component.