Tuning Bulk O<sub>2</sub> and Nonbonding Oxygen State for Reversible Anionic Redox Chemistry in P2‐Layered Cathodes
Zhenrui Li, Weijin Kong, Yang Yu, Jicheng Zhang, Deniz Wong, Zijian Xu, Zhenhua Chen, Christian Schulz, Maciej Bartkowiak, Xiangfeng Liu
Abstract
Abstract Improving the reversibility of oxygen redox is quite significant for layered oxides cathodes in sodium‐ion batteries. Herein, we for the first time simultaneously tune bulk O 2 and nonbonding oxygen state for reversible oxygen redox chemistry in P2‐Na 0.67 Mn 0.5 Fe 0.5 O 2 through a synergy of Li 2 TiO 3 coating and Li/Ti co‐doping. O 2− is oxidized to molecular O 2 and peroxide (O 2 ) n − ( n <2) during charging. Molecular O 2 derived from transition metal (TM) migration is related to the superstructure ordering induced by Li doping. The synergy mechanism of Li 2 TiO 3 coating and Li/Ti co‐doping on the two O‐redox modes is revealed. Firstly, Li 2 TiO 3 coating restrains the surface O 2 and inhibits O 2 loss. Secondly, nonbonding Li−O−Na enhances the reversibility of O 2− →(O 2 ) n − . Thirdly, Ti doping strengthens the TM−O bond which fixes lattice oxygen. The cationic redox reversibility is also enhanced by Li/Ti co‐doping. The proposed insights into the oxygen redox reversibility are insightful for other oxide cathodes.