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

Abstract

Lithium–oxygen batteries promise high energy but suffer from poor cycle life owing to the generation of highly reactive singlet oxygen ¹O₂, which rapidly deactivates the electrode and the electrolyte. Here we demonstrate an effective strategy to suppress ¹O₂ using redox mediators. Using operando spectroscopy techniques, we show that 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), as a model redox mediator, drastically reduces ¹O₂ formation, increases the yield of ground state ³O₂, and reduces the by-product generation. The ¹O₂ 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 ¹O₂ suppression effect applies universally across six common redox mediators with up to three orders of magnitude higher ¹O₂ suppression efficiency compared to 1,4-diazabicyclo[2.2.2]octane (DABCO), the most efficient quencher used in Li–O₂ batteries to date. From the comparison of the investigated mediators we discuss the plausible governing principle dictating redox mediators’ effectiveness in suppressing ¹O₂. Our study achieves effective ¹O₂ suppression and provides guidelines for designing redox mediators for efficient and reversible lithium–oxygen batteries.