Activating the Inert Na1 Sites in Na2FePO4F Toward High Performance Sodium Storage

Abstract Na 2 FePO 4 F, an iron‐based fluorophosphate with facile 2D sodium ion channels, is considered as a promising cathode material for sodium‐ion batteries because of low cost, resource abundance, and nontoxicity. However, its application is considerably restricted by the limited intrinsic electronic conductivity and specific capacity. Herein, a doping strategy represented by Cu 2+ is proposed to boost the electrochemical performance, attributed to the derivation of a new active Na3 site originated from the inert Na1 site and the band gap reduction due to the d‐orbital hybridization. Consequently, the as‐obtained Na 2 Fe 0.95 Cu 0.05 PO 4 F/C composite can deliver an excellent rate capacity of 74 mAh g⁻ 1 at 20 C and a decent specific capacity of 119 mAh g⁻ 1 at 0.1 C, which is superior to the previously reported Na 2 FePO 4 F‐based cathode materials. This study sheds new light on developing high performance fluorophosphates cathode materials via regulating the Na site and electronic structure.