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

Abstract A typical polyanionic based material Na 3 V 2 (PO 4 ) 2 O 2 F (Na 3 VPO 2 F) 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 Na 3−y VPO 2−x Br x F is prepared to dilute the charges on and inside the Na + transportation tunnel. In virtue of density functional theory analysis, Na 3−y VPO 2−x Br x F reveals a reduction in the bandgap and an increase in electronic conductivity. Meanwhile, the almost electrostatically shielded tunnel in Na 3−y VPO 2−x Br x F alleviates the coulombic hindrance imposed on Na + during its (de)intercalation, which demonstrates a Na + diffusivity about five times higher than that of Na 3 VPO 2 F. Consequently, the Na 3−y VPO 2−x Br x F 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 Na 3−y VPO 2−x Br x F//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.