Novel materials for zinc-air batteries

The volumetric and specific energy density of Zn-air batteries is higher than that of lithium ion batteries. The aim of this project is to develop economically viable and environmentally friendly solutions for several problems which still have to be overcome for these batteries. The cathode is an electrode with a three-phase boundary (air-electrolyte-solid) which should combine good electrical conductivity and a high specific surface area. In this respect, porous carbon materials are of great interest due to their superior physical and chemical properties, like e.g. high surface areas, chemical stability and a low density. The properties of the gas diffusion electrode shall be improved by employing mesoporous carbon materials; hence, nickel foils shall be coated with the carbon materials by using different techniques to manufacture electrodes which shall be electrochemically characterized. To enhance the electrical conductivity of the mesoporous carbons, iron oxide-based catalytic graphitization shall be used to graphitize the amorphous carbon materials. First results show that the electrical resistance of the carbon coatings could be decreased if the carbon material have been graphitized before (Fig. 1). At this juncture, the graphitization temperature TG seems to be important.

The electrolyte shall be adapted by rather using neutral solutions instead of the commonly employed aggressive alkaline solutions which also lead to the undesired formation of carbonates. In this way, laboratory models of secondary Zn-air batteries shall be developed which will be tested electrochemically with regard to cycle stability, lifetime and for their suitability for daily use in industrial applications.

Fig. 1:  Electrical resistance for nickel foils (grey) and the carbon coated nickel foils. Red: amorphous mesoporous carbon; blue: T_G = 700 °C; green: T_G = 800 °C, yellow: T_G = 900 °C. T_G stands for graphitization temperature.