Mechanistic Evolution of Aprotic Lithium-Oxygen Batteries

Aprotic lithium-oxygen (Li-O-2) batteries have attracted much attention in recent years. Considerable efforts have been devoted to understand the reaction mechanisms and improving battery performance. Here, various reaction mechanisms at the cathode are discussed, including the direct electrochemical formation and decomposition of Li2O2 and LiOH and the redox mediator (RM) assisted reactions in both the discharging and charging processes. Formation of Li2O2 in discharging processes is related to the electrolyte solvent property, and its following decomposition proceeds stepwise with the intermediate of Li2-xO2. Low overpotentials have been reported in LiOH-involved discharging and charging processes, and it can alleviate the instability of carbon against Li2O2 and provide new insights into the design of practical Li-air batteries. RMs are promising for Li-O-2 batteries, and the prerequisites in addition to the redox potentials should be taken into account. Perspectives on the development of Li-O-2 batteries are provided. The future deployment of Li-O-2 batteries relies on the continuous efforts of all the scientists around the world.