Surface Nonbonding Oxygen State Regulation for Reversible Anionic Redox Chemistry in Li-Rich Mn-Based Layered Oxides

Activated by the Li–O–Li configuration with nonbonding O 2p state (lO_2p), anionic redox reaction (ARR) in Li-rich layered oxides (LLOs) contributes to additional capacity but exhibits significant irreversibility, leading to severe surface oxygen loss. Herein, surface nonbonding oxygen state (SNBOS) is regulated by the integrated surface structure engineering to suppress surface oxygen loss and enhance the reversibility of ARR. On the outermost layer, the conversion of layered structure into a LiLaO₂ layer and spinel phase structure eliminates lO_2p, thereby preventing the activation of ARR and suppressing side reactions between electrolyte and oxidized oxygen ions. Besides, by introducing 5d metal La on the near surface, the energy of lO_2p is decreased corresponding to the increased charge-transfer gap Δ and the d–d coulomb repulsion term U is reduced, making U/2 decrease close to Δ and enhancing ARR reversibility. Furthermore, it is demonstrated that the oxidized oxygen of the modified sample cannot become O₂ gas and escape, but rather exists more in the form of high-valence oxygen dimer anions (Formula presented.), reducing the reaction depth of surface ARR and inhibiting oxygen loss. Therefore, the designed material demonstrates outstanding cycling stability and kinetics performance. © 2025 Wiley-VCH GmbH.