Superoxide Stabilization and a Universal KO2 Growth Mechanism in Potassium-Oxygen Batteries.

Rechargeable potassium-oxygen (K-O2 ) batteries promise to provide higher round-trip efficiency and cycle life than other alkali-oxygen batteries with satisfactory gravimetric energy density (935 Wh kg-1 ). Exploiting a strong electron-donating solvent, for example, dimethyl sulfoxide (DMSO) strongly stabilizes the discharge product (KO2 ), resulting in significant improvement in electrode kinetics and chemical/electrochemical reversibility. The first DMSO-based K-O2 battery demonstrates a much higher energy efficiency and stability than the glyme-based electrolyte. A universal KO2 growth model is developed and it is demonstrated that the ideal solvent for K-O2 batteries should strongly stabilize superoxide (strong donor ability) to obtain high electrode kinetics and reversibility while providing fast oxygen diffusion to achieve high discharge capacity. This work elucidates key electrolyte properties that control the efficiency and reversibility of K-O2 batteries.