A Family of High‐Performance Cathode Materials for Na‐ion Batteries, Na3(VO1−xPO4)2 F1+2x (0 ≤ x ≤ 1): Combined First‐Principles and Experimental Study

Room‐temperature Na‐ion batteries (NIBs) have recently attracted attention as potential alternatives to current Li‐ion batteries (LIBs). The natural abundance of sodium and the similarity between the electrochemical properties of NIBs and LIBs make NIBs well suited for applications requiring low cost and long‐term reliability. Here, the first successful synthesis of a series of Na 3 (VO 1− x PO 4 ) 2 F 1+2 x (0 ≤ x ≤ 1) compounds as a new family of high‐performance cathode materials for NIBs is reported. The Na 3 (VO 1− x PO 4 ) 2 F 1+2 x series can function as high‐performance cathodes for NIBs with high energy density and good cycle life, although the redox mechanism varies depending on the composition. The combined first‐principles calculations and experimental analysis reveal the detailed structural and electrochemical mechanisms of the various compositions in solid solutions of Na 3 (VOPO 4 ) 2 F and Na 3 V 2 (PO 4 ) 2 F 3 . The comparative data for the Na y (VO 1− x PO 4 ) 2 F 1+2 x electrodes show a clear relationship among V 3+ /V 4+ /V 5+ redox reactions, Na + −Na + interactions, and Na + intercalation mechanisms in NIBs. The new family of high‐energy cathode materials reported here is expected to spur the development of low‐cost, high‐performance NIBs.