Bioinspired Redox Mediator in Lithium–Oxygen Batteries

LiO2 is an intermediate formed in aprotic Li–O2 and Li–air batteries during an oxygen reduction reaction (ORR). The soluble LiO2 triggers undesirable side reactions, such as a nucleophilic reaction and the formation of the byproduct Li2CO3 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–O2 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–O2 batteries, and the battery stability was significantly improved in the presence of OAC. Furthermore, the best Li–O2 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–O2 battery is ∼37.0 mAh cm–2.