Quenching singlet oxygen via intersystem crossing for a stable Li-O 2 battery.

Aprotic Li-O 2 batteries are a promising energy storage technology, however severe side reactions during cycles lead to their poor rechargeability. Herein, highly reactive singlet oxygen ( 1 O 2 ) 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 1 O 2 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 1 O 2 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 1 O 2 to the ground-state triplet oxygen to eliminate its derived side reactions, and the regeneration of TPA. These enable the Li-O 2 battery with obviously reduced overvoltages and prolonged lifetime for over 310 cycles when coupled with a RuO 2 catalyst. This work highlights the ISC mechanism to quench 1 O 2 in Li-O 2 battery.