Optimal cobalt oxide (Co3O4): Graphene (GR) ratio in Co3O4/GR as air cathode catalyst for air-breathing hybrid electrolyte lithium-air battery

Abstract

This study assembles lithium-air batteries with aqueous/aprotic hybrid electrolytes designed for ambient air-breathing in a high relative humidity environment. Cobalt oxide/graphene (Co3O4/GR) nanocomposites are synthesized for improved oxygen reduction and oxygen evolution reaction functionalities. The Co3O4/GR composites with Co3O4 loads of 33.7 wt%, 48.2 wt%, and 62.5 wt% are prepared using hydrothermal synthesis. The Co3O4/GR composites’ catalytic activities on oxygen reduction reaction and oxygen evolution reaction is shown to reduce the polarization of pristine carbon cloth electrode by 40% and serve as a good cathode catalyst. Lithium/air batteries are assembled with a lithium metal/organic electrolyte/ceramic lithium-ion conductive membrane/aqueous electrolyte/air cathode configuration. These batteries with the developed catalysts demonstrate good long-term stability over 120 h when fed with high (70–100%) relative humidity ambient air. More importantly, the results indicate the Co3O4/GR composite in 48.2:51.8 (w/w) is the optimal load for the hybrid electrolyte lithium-air battery due to its balanced amount of catalytic Co3O4 and charge-transfer mediated graphene, and good dispersibility of the nanocatalyst on the planar graphene surface.