Quenching singlet oxygen via intersystem crossing for a stable Li-O2 battery.

Aprotic Li-O2 batteries are a promising energy storage technology, however severe side reactions during cycles lead to their poor rechargeability. Herein, highly reactive singlet oxygen (1O2) is revealed to generate in both the discharging and charging processes and is deterimental to battery stability. Electron-rich triphenylamine (TPA) is demonstrated as an effective quencher in the electrolyte to mitigate 1O2 and its associated parasitic reactions, which has the tertiary amine and phenyl groups to manifest excellent electrochemical stability and chemical reversibility. It reacts with electrophilic 1O2 to form a singlet complex during cycles, and it then quickly transforms to a triplet complex through nonradiative intersystem crossing (ISC). This efficiently accelerates the conversion of 1O2 to the ground-state triplet oxygen to eliminate its derived side reactions, and the regeneration of TPA. These enable the Li-O2 battery with obviously reduced overvoltages and prolonged lifetime for over 310 cycles when coupled with a RuO2 catalyst. This work highlights the ISC mechanism to quench 1O2 in Li-O2 battery.