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

Abstract

Na2FePO4F, 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 Cu2+ 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 Na2Fe0.95Cu0.05PO4F/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 Na2FePO4F-based cathode materials. This study sheds new light on developing high performance fluorophosphates cathode materials via regulating the Na site and electronic structure.