Recent progress on single-atom catalysts for lithium-air battery applications

Lithium-air batteries (LABs) have attracted extensive attention due to their high theoretical energy density based on the "Holy Grail", the lithium metal anode and the inexhaustible air as the cathode. However, their intrinsic low catalytic activity, including the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, undesirable high overpotential, low reversibility and poor cyclability hinder their development. Recently, single-atom catalysts (SACs) with high atom utilization and cost-effective prospects have shown excellent ORR/OER kinetics in various catalytic systems. Consequently, they have attracted increasing attention, especially in the past three years and achieved improvement in their electrochemical performances. With these in mind, this review first introduces the structure, characteristics, and synthesis methods of SACs and then summarizes the reported SACs for LABs based on both oxygen and carbon dioxide chemistry. The research progress of SACs in regulating the lithium metal anode is also discussed. Finally, challenges and opportunities for the synthesis, characterization, and application of SACs, as well as the structure-performance correlations are comprehensively summarized and corresponding perspectives are addressed.