Identification of a better charge redox mediator for lithium–oxygen batteries

Abstract Soluble redox mediators (RMs) are one of the most promising approaches for reducing charging overpotentials in Li–O2 batteries. However, this auspicious strategy still in its infancy and raises new scientific problems needing to be clarified, such as the influence of RMs with different charge–transfer or different molecular structure (same redox functional group) on Li2O2 oxidation behavior. Herein, the realities of Li2O2 oxidation by some RMs, including lithium bromide, tetrathiafulvalene, 2,2,6,6–tetramethyl–1–piperidinyloxy, and 2–azaadamantane–N–oxyl, were investigated using detailed experimental results and first–principles calculations. Among these RMs studied, single electron–reaction RMs exhibited a more stable charging curve at lower potential than that of multiple electron–reaction RMs. Besides, the RM molecular with smaller steric effects and higher electron–donating power exhibited higher catalytic activity thus a lower charging overpotential. These findings offered a guidance direction for subsequent explorations and optimization of high performance RMs, which might further facilitate development for Li–O2 batteries.