Bioinspired Redox Mediator in Lithium–Oxygen Batteries

LiO 2 is an intermediate formed in aprotic Li–O 2 and Li–air batteries during an oxygen reduction reaction (ORR). The soluble LiO 2 triggers undesirable side reactions, such as a nucleophilic reaction and the formation of the byproduct Li 2 CO 3 upon reaction with the electrolyte and substrate, resulting in irreversible redox reactions and causing a low Coulombic efficiency with poor cycling durability. Inspired by superoxide dismutase (SOD) in biological systems, we hypothesized that SOD mimetics could likewise be applied in Li–O 2 and Li–air batteries, thereby prolonging the battery cycle life. Oxidized activated charcoal (OAC) is known to be one SOD mimetic with fast kinetics and a high turnover. Therefore, OAC was added to a dual polymer gel electrolyte as a redox mediator. The OAC redox mechanism is well illustrated in quasi-solid Li–O 2 batteries, and the battery stability was significantly improved in the presence of OAC. Furthermore, the best Li–O 2 battery containing OAC demonstrated stable galvanostatic charge/discharge performance for ∼300 cycles (3000 h) with a cutoff capacity of 0.4 mAh cm –2 . In addition, under a discharge cutoff potential of 2.0 V, the discharge capacity of the best Li–O 2 battery is ∼37.0 mAh cm –2 .