One step synthesis of vesicular Na3V2(PO4)2F3 and network of Na3V2(PO4)2F3@graphene nanosheets with improved electrochemical performance as cathode material for sodium ion battery

•One-step synthesis of vesicular Na3V2(PO4)2F3.•Novel structure of vesicular Na3V2(PO4)2F3 was reported for the first time.•One-step synthesis of Na3V2(PO4)2F3@Graphene Nanosheets.•Na3V2(PO4)2F3@Graphene Nanosheets shows a highly connected network.•Na3V2(PO4)2F3@16%Graphene Nanosheets shows improved electrochemical property.