Sn/Sb Doping Induced Local Structure Transformation to Enhance the Lattice Oxygen Redox Activity of P2-Type Sodium-Ion Cathode Materials

Lattice oxygen redox (LOR) reactions in sodium-ion battery (SIB) layered oxides are considered a promising approach to overcoming capacity limitations. However, under high-voltage conditions, irreversible LOR-induced local structural distortions and phase transitions can lead to a significant degradation of electrochemical performance, limiting their practical application. In this study, Sn4+/Sb5+ were successfully introduced into layered cathode materials. It was found that Sn4+ doping maintained the ribbon-ordered superstructure of the transition metal (TMs) layers, while Sb5+ incorporation, through the formation of strong covalent Sb–O bonds, altered the ordering of the TMs layers, effectively alleviating lattice strain and suppressing structural collapse at high voltage. Moreover, the strong covalent bonds between Sb–O weakened the interaction between the O 2p orbitals and the TM 3d orbitals, activating the redox activity of lattice oxygen at high voltage and significantly improving energy density. This study proposes an effective method to enhance anionic redox activity, highlights the impact of superstructure transformations on the crystal structure and electrochemical performance, and provides fundamental mechanistic insights into element doping for anionic redox-active cathode materials.