Anion–Cation Dual‐Site Co‐Doping Unlocking NASICON Na ₄ VMn(PO ₄ ) ₃ Cathodes Toward Advanced Sodium–Ion Batteries

ABSTRACT The Na ⁺ superionic conductor (NASICON)‐type Na ₄ VMn(PO ₄ ) ₃ (NVMP) is a highly promising cathode for sodium‐ion batteries (SIBs), but its commercialization is hindered by the Mn ³⁺ ‐induced Jahn‐Teller distortion and sluggish charge‐transferring kinetics. To meet such twofold challenges, an innovative Ti ⁴⁺ /Cl ⁻ dual‐site (i.e., Ti ⁴⁺ and Cl ⁻ occupying octahedral and tetrahedral sites, respectively) co‐doping methodology is first proposed here. Systematic physicochemical characterizations and first‐principles calculations corroborate that the introduction of both Ti ⁴⁺ and Cl ⁻ effectively enhances lattice stability and modulates local coordination environment of Mn ³⁺ , markedly suppressing Jahn‐Teller distortion. Moreover, the dual‐site co‐doping of NVMP improves electronic conductivity and substantially reduces the Na ⁺ migration barriers, thereby synchronously optimizing its electron/ion transport kinetics. Thanks to these distinct merits, the dual‐site doped cathode, i.e., tiny Ti/Cl co‐doped NVMP (i.e., Na ₄ V _0.95 MnTi _0.05 P ₃ O _11.9 Cl _0.1 ), delivers a high‐rate capacity of 80.6 mAh g ⁻¹ at 40C (2.7 times higher than pristine NVMP) and retains 94% capacity after 1000 cycles at 5C. The Na ₄ V _0.95 MnTi _0.05 P ₃ O _11.9 Cl _0.1 assembled SIBs obtain ultrahigh‐rate behavior (79.7 mAh g ⁻¹ at 30C) and robust wide‐temperature tolerance (–40°C to 50°C). Besides the unveiled microscopic mechanism of anion/cation synergistic doping, the in‐depth insights provide a new theoretical foundation for designing advanced cathodes toward next‐generation SIBs.