Suppressing singlet oxygen generation in lithium-oxygen batteries with redox mediators

Lithium-oxygen batteries promise high energy but suffer from poor cycle life owing to the generation of highly reactive singlet oxygen(1)O(2), which rapidly deactivates the electrode and the electrolyte. Here we demonstrate an effective strategy to suppress(1)O(2)using redox mediators. Usingoperandospectroscopy techniques, we show that 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), as a model redox mediator, drastically reduces(1)O(2)formation, increases the yield of ground state(3)O(2), and reduces the by-product generation. The(1)O(2)suppression effect is attributed to an increased intersystem crossing rate induced by redox mediators, with which the relaxation of a singlet-state intermediate to a triplet-state one is accelerated. We further show that this(1)O(2)suppression effect applies universally across six common redox mediators with up to three orders of magnitude higher(1)O(2)suppression efficiency compared to 1,4-diazabicyclo[2.2.2]octane (DABCO), the most efficient quencher used in Li-O(2)batteries to date. From the comparison of the investigated mediators we discuss the plausible governing principle dictating redox mediators' effectiveness in suppressing(1)O(2). Our study achieves effective(1)O(2)suppression and provides guidelines for designing redox mediators for efficient and reversible lithium-oxygen batteries.