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. By altering aggressive superoxide (O2−) to moderate hydroperoxide (HO2−), addition of water effectively controls the side reactions during oxygen reduction. The reversible oxygen–peroxide redox reaction guarantees a low overpotential, which is superior to the electrochemistry occurring on the cathode/Li2O2 interface. The positive effect of water on both discharge and charge can remedy the inherent defects in aprotic Li‐O2 batteries.