Na3V2O2(PO4)2F/graphene sandwich structure for high-performance cathode of a sodium-ion battery

Abstract

A Na₃V₂O₂(PO₄)₂F/reduced-graphene-oxide (RGO) sandwich structure has been synthesized by a facile one-step solvothermal method. Cubic Na₃V₂O₂(PO₄)₂F nanoparticles are homogeneously trapped between conductive RGO sheets during its growth and assembled into a compact sandwich structure, which allows the electrically insulating Na₃V₂O₂(PO₄)₂F nanoparticles to be wired up to a current collector through the underlying graphene conducting layers. As a sodium-insertion cathode material, the structure exhibits a high reversible capacity of 120 mA h g⁻¹ at a discharge rate of C/20 with a capacity retention of 100.4 mA h g⁻¹ at 1 C and an excellent cyclic retention of 91.4% after the 200th cycle at C/10. These results highlight the importance of anchoring Na₃V₂O₂(PO₄)₂F on a conducting scaffold for maximum utilization of the electrochemically active Na₃V₂O₂(PO₄)₂F particles in a high-performance sodium-ion battery.