Anion Coordination Field Enables Ni/Mn Spin-Orbital Reconstruction for Stable High-Voltage Sodium Layer-Structured Cathodes.

Ni/Mn-based O3-typed layer-structured oxides are attractive for high-voltage cathodes toward sodium batteries; however, the deep-desodiation stability is constrained by transition-metal orbital instability and localized oxygen redox. The anion-coordination local-electronic network was thus reconstructed in single-crystalline Na[Ni0.3Mn0.5Cu0.1Ti0.1]O2 through a polyvinylpyrrolidone-assisted mild nitridation strategy. The resulting Ni-N-Mn coordination can enhance Ni/Mn 3d-N 2p orbital coupling, driving Ni-to-Mn charge redistribution and stabilizing the low-spin Mn3+-like states by increasing local crystal-field splitting. This coordination-induced spin/orbital reconstruction can further generate an extended TM-(O,N)-TM p-d charge network that disperses high-voltage ligand holes and stabilizes lattice oxygen. The modified cathode delivers reduced polarization, improved Na+-transport kinetics, and a durable cycling lifespan at high voltage, with 91% capacity retention after 300 cycles at 2 C coupled with hard carbon. These findings demonstrate anion-coordination reconstruction as a direct route to regulating orbital occupation and oxygen redox in high-voltage layer-structured cathodes.