Synthesis and investigation of sodium storage properties in Na3V1.9Fe0.1(PO4)2F3@N-CNTs cathode material for sodium ion batteries

Na3V2(PO4)2F3 (NVPF) has consistently stood out as one of the most popular cathode materials for sodium ion batteries (SIBs) because of its impressive theoretical specific capacity, high energy density and controllable structure. However, its application has been hindered by two major challenges: its low electron conductivity and poor diffusion kinetics caused by large Na+ radius. In this study, iron-doped Na3V2-xFex(PO4)2F3 was prepared by hydrothermal solvothermal method to solve those issues. The iron doping facilitates the transfer of Na+ and alleviates structural deterioration. Simultaneously, the establishment of a three-dimensional carbon framework, constructed from N-CNTs and carbon layer, further enhances electron transport. Therefore, Fe0.1-NVPF@N-CNTs exhibited the initial discharge capacity reaching 105 mAh g−1 at 0.1C, maintaining approximately 74.53% of its capacity after 1000 cycles at 2C, and a noteworthy capacity retention rate of 83.38% after 1200 cycles at 5C. The incorporation of Fe-doped NVPF coated with carbon layer and N-CNTs holds great promise in advancing the electrochemical performance of SIBs.