A Universal Principle of Anionic Redox Chemistry in Li/Na Batteries

Oxygen redox chemistry provides a novel way to realize the high energy density of electrodes for Li/Na batteries. However, the reaction is accompanied by undesirable structural transformations and electrochemical degradation, which limits its practical use. In this regard, we explore the intimate interaction between local structural changes and oxygen redox chemistry during dynamic battery operation. It is demonstrated that the distinct evolution of oxygen-redox activity and reversibility is governed by the different cation migration mechanisms available within the structure of materials. We found that these cation mechanisms play an important role in determining the stabilization pathway of oxygen oxidation. Although π stabilization of oxygen in the absence of cation migration enhances the reversibility of oxygen chemistry, π-interacting oxygen is gradually replaced by σ-interacting oxygen as the electrochemical cycle progresses, resulting in significant structural changes with O–O dimer formation. These findings provide a unified picture for understanding the interplay between structural evolution and anionic redox chemistry and provide further guidance for designing high-energy Li/Na battery electrodes.