Theory-guided cation engineering overcome V-based polyanion cathode kinetic performance limitation

As a prominent member of NASICON-type cathodes, Na₃V₂(PO₄)₃ (NVP) has aroused substantial concerns, on account of low cost and excellent ionic conductivity. However, the VO octahedra tend to localize electrons, leading to intrinsically poor electrical conductivity, which constitutes a major bottleneck for improving its kinetic performance. In this work, guided by crystal field theory and Density Functional Theory (DFT) predictions, Mn²⁺ ions with strong electron-donor effect were employed to directionally remodel the overall charge distribution in NVP, narrowing the intrinsic bandgap and enhancing electron delocalization. Ultraviolet photoelectron spectroscopy served as direct evidence, confirming that Mn²⁺ effectively raises the valence band maximum (VBM), thereby reducing the bandgap, while lowered work function facilitates electron escape at interfaces. In-situ Electrochemical Impedance Spectroscopy-Distribution of Relaxation Times (EIS-DRT) analysis dynamically decoupled the complex electrochemical processes, revealing that the optimized NVP exhibits significantly lower charge-transfer and ion-diffusion resistances. Experimentally, the reconstructed charge distribution within the system by Mn²⁺ effectively enhances the kinetic performance. Differential charge density and Bader charge population calculations further elucidated the charge transfer changes induced by Mn²⁺ incorporation, providing microscopic explanation for the simultaneous narrowing of the bandgap and strengthening of VO bond hybridization. Accordingly, the NVMP-0.5 cathode exhibits an exceptional rate capability of 102.9 mA h g^-1 at 50C and significant long-standing stability of 70.2% capacity retention following 1000 cycles at 50C. This work provides valuable insights for the rational design of high-performance NASICON cathodes for sodium-ion batteries through crystal-field-theory-guided and DFT-predicted strategies.