Multifunctional inorganic electrode materials for high-performance rechargeable metal-air batteries

This paper reports the application of Ni-Fe layered double hydroxides (LDHs) intercalated with CO32- (Ni-Fe CO32- LDH) to a catalyst layer of a rechargeable metal-air battery using an alkaline electrolyte. Ni-Fe CO32- LDH is found to play multifunctional roles in the catalyst layer as a mixed conductor with hydroxide ions and electrons, and also as an electrocatalyst. The air electrode with Ni-Fe CO32- LDH shows superior performance to all electrodes with other LDHs, indicating that Ni-Fe CO32- LDH forms more favorable triple-phase boundary regions in the catalyst layer of the air electrode. The Ni-Fe CO32- LDH addition to the catalyst layer of the reversible air electrode using alpha-MnO2 also improves the performance of a rechargeable zinc-air battery. The reversible air electrode with alpha-MnO2 shows good cycle stability during 40 cycles, indicating that Ni-Fe LDH as an ionomer remains stable in the reversible air electrode after cycles. There must be a limited influence of CO2 on Ni-Fe CO32- LDH which can exist stably in air. Consequently, these results demonstrate that Ni-Fe CO32- LDHs are promising materials for use as multifunctional ionomers with high durability. They are widely applicable to rechargeable metal-air batteries using alkaline electrolytes.