Redox Mediator-Enhanced Performance and Generation of Singlet Oxygen in Li-CO₂ Batteries

Rechargeable Li-CO₂ batteries as a novel system developed in recent years directly use CO₂ as the reactant, which enables deeper penetration of energy storage and CO₂ utilization. The Li-CO₂ battery system, however, is at an early stage, and many challenges remained to be overcome urgently, especially the problem of high over-potential during the charging process. Here, we report a redox mediator, phenoxathiin, to assist the decomposition of Li₂CO₃ during the charging process, which effectively reduces the over-potential and improves the cycling performance of the battery. Furthermore, we detect the presence of singlet oxygen during the oxidation of Li₂CO₃ by phenoxathiin, which reveals more of the underlying science of the reaction mechanism of the Li-CO₂ battery.