Inductive-effect engineering of transition-metal–oxygen covalency and structural ordering in P2-type high-voltage sodium-ion cathodes

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P2-type layered oxides exhibit structural versatility and promising electrochemical properties as cathode materials for sodium-ion batteries (SIBs). In this work, we disclose a covalency-engineered P2-type layered Na 2/3 [Ni 2/3 Te 1/3 ]O 2 (NNTO) conceptualized through electronic structure engineering, achieving an exceptionally high average operating voltage of ∼3.75 V, which is among the highest reported values among Ni-based layered oxides. The incorporation of highly electronegative and redox-inactive Te 6+ as TeO 6 within the transition metal (TM) layer modifies the local TM–O covalency and electrostatic environment. This effect not only raises the operating voltage of the Ni 2+ /Ni 3+ redox couple but also stabilizes the electronic structure by lowering the O 2p energy. Unlike conventional P2 cathode materials in which Na + /vacancy ordering often impedes Na + diffusion, the ordered Ni/Te honeycomb arrangement stabilizes the long-range Na ordering without compromising Na + mobility. Operando X-ray diffraction analysis reveals that the NNTO undergoes a reversible P2–OP4 phase transition during de/sodiation. Comprehensive material characterization and density functional theory calculations demonstrate that the synergetic effects on TM–O covalency, cationic honeycomb ordering, and phase evolution are governed by the presence of TeO 6 covalency in the TM layer. This work provides a framework for designing high-voltage layered oxide cathode materials through electrostatic and electronic structure engineering, extending beyond polyanion-based approaches for SIBs.