Defect‐Regulated Electronic and Lattice Evolution in Na ₄ VMn(PO ₄ ) ₃ Toward High‐Performance Sodium Storage

NASICON‐type Na 4 VMn(PO 4 ) 3 (NVMP) is a promising high‐capacity cathode for sodium‐ion batteries, yet its practical deployment is hindered by Mn 3+ ‐driven lattice distortion, persistent oxygen vacancy defects, and sluggish Na + transport, collectively resulting in accelerated performance degradation. Here, we report a transition‐metal defect‐engineering strategy that introduces well‐controlled Mn vacancies into the Mn/V sublattice, yielding a defect‐regulated phase (Na 4 VMn 0.85 (PO 4 ) 3 ) with a reconstructed local electronic environment. Comprehensive structural analyses coupled with electrochemical evaluation demonstrate that the vacancy‐induced electronic redistribution enhances Mn/V redox reversibility, suppresses oxygen‐vacancy formation, and promotes the evolution of more open Na + diffusion pathways. Benefiting from this synergistic regulation, the optimized material delivers markedly improved rate performance (81.7 mAh g −1 at 20C) and long‐term cycling stability (81.8% capacity retention after 5000 cycles at 10C). Mechanistic investigations further reveal that the integrated “electron‐compensation and lattice‐self‐adaptation” response associated with cation defects governs the enhanced structural robustness and charge‐transfer dynamics. This study provides a viable defect‐chemistry‐guided design paradigm for high‐performance NASICON‐type cathodes and offers deeper insight into defect‐regulated electrochemical processes in polyanionic frameworks.