From O2- to HO2- : Reducing By-Products and Overpotential in Li-O2 Batteries by Water Addition.

The development of aprotic Li-O2 batteries, which are promising candidates for high gravimetric energy storage devices, is severely limited by superoxide-related parasitic reactions and large voltage hysteresis. The fundamental reaction pathway of the aprotic Li-O2 battery can be altered by the addition of water, which changes the discharge intermediate from superoxide (O2- ) to hydroperoxide (HO2- ). The new mechanism involving HO2- intermediate realizes the two-electron transfer through a single step, which significantly suppresses the superoxide-related side reactions. Moreover, addition of water also triggers a solution-based pathway that effectively reduces the voltage hysteresis. These discoveries offer a possible solution for desirable Li-O2 batteries free of aggressive superoxide species, highlighting the design strategy of modifying the reaction pathway for Li-O2 electrochemistry.