Electrostatically Shielded Transportation Enabling Accelerated Na+ Diffusivity in High‐Performance Fluorophosphate Cathode for Sodium‐Ion Batteries

Abstract

AbstractA typical polyanionic based material Na3V2(PO4)2O2F (Na3VPO2F) attracts much interest as a cathode for large‐scale sodium‐ion batteries in consideration of its stable structure and remarkable energy density. Nevertheless, the large coulombic attraction and repulsion suffered by the mobile Na+ from structural anions and surrounding Na+, respectively, result in a torpid reaction kinetics and inferior rate capability. Herein, Br−‐doped and Na+ vacancy preinstalled Na3−yVPO2−xBrxF is prepared to dilute the charges on and inside the Na+ transportation tunnel. In virtue of density functional theory analysis, Na3−yVPO2−xBrxF reveals a reduction in the bandgap and an increase in electronic conductivity. Meanwhile, the almost electrostatically shielded tunnel in Na3−yVPO2−xBrxF alleviates the coulombic hindrance imposed on Na+ during its (de)intercalation, which demonstrates a Na+ diffusivity about five times higher than that of Na3VPO2F. Consequently, the Na3−yVPO2−xBrxF cathode shows a superior rate capacity of 77.7 mAh g−1 under 50 C and great cycling property corresponding to a high capacity retention of 94.4% over 800 cycles at 10 C. The assembled Na3−yVPO2−xBrxF//hard‐carbon sodium‐ion full‐cell presents excellent specific energy/power (226 Wh kg−1@15424.2 W kg−1) as well as outstanding long‐term cyclic stability over 1000 cycles at 5 C.