Unravelling Water's Transition from Passivation to Electrochemical Participation in Aprotic Lithium‐Oxygen Batteries

Abstract Aprotic lithium‐oxygen (Li‐O ₂ ) batteries are considered promising next‐generation energy storage systems because of their high energy density, but their practical application is hindered by their limited discharge capacity. Water is regarded as significantly enhancing discharge capacity, but its effect on solvation and interfacial behavior is not fully understood. Herein, combined with molecular dynamics simulations, electron microscopy, and electrochemical analyses, it is elucidated that water‐driven solvation structure reconstruction dictates lithium peroxide (Li ₂ O ₂ ) nucleation behavior and enables crossover electrochemistry that governs Li anode corrosion. Specifically, moderate water introduction promotes Li ₂ O ₂ growth at the grooves of pre‐formed Li ₂ O ₂ deposits, expanding limited active sites on the cathode, thereby breaking the capacity ceiling. Furthermore, it is confirmed that Li anode corrosion, a controllable electrochemical reaction rather than chemical diffusion, is governed by cathode‐induced crossover electrochemistry. This previously overlooked coupling is initiated by water‐modulated solvation structures, effectively enhancing species mass transport while suppressing anode corrosion. This work provides fundamental insights into water‐mediated electrochemical processes and offers strategic guidance for optimizing Li‐O ₂ batteries.