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

Abstract

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.