Asymmetric-Orbital-Hybridization Induced Electron Redistribution Enabling Stable Sodium Layered Oxides

Layered transition metal (TM) oxides have garnered great attention as viable cathodes for sodium-ion batteries (SIBs), but the challenges of complicated multiphase transitions, severe structural deterioration and unstable oxygen redox reaction still hamper their practical application. Herein, a universal electron redistribution strategy based on the orbital hybridization regulation is proposed and NaNi_0.5Mn_0.35Ti_0.15O₂ (NNMTO) is introduced as a model cathode considering the distinct electronegativity between Ni and Ti. The nonequivalent electron distribution induced by the covalency competition within asymmetric Ni_3d-O_2p-Ti_3d backbone (Ni─O─Ti charge transfer via the bridging oxygen atom) delocalizes the electrons between Ni and O and modulates the local chemical environment around O. The enhanced orbital coupling combined with increased Ni─O covalency can not only suppress the over-oxidation of lattice oxygen and improve the reversibility of oxygen redox, but also alleviate the cooperative Jahn–Teller distortion of Ni³⁺O₆ octahedron and prevent the phase transition from O3′ to the detrimental O3″ phase by constructing a more rigid TM─O framework. As a result, NNMTO shows a sustained reversible capacity and remarkable cycling stability that is rooted in reversible oxygen and TM redox processes. This study provides an alternative avenue to construct high-performance SIBs from the perspective of local chemistry and orbital hybridization modulation.