Synthesis and Electrochemical Performance of the Na3V2(PO4)3 Cathode for Sodium-Ion Batteries

Rhombohedral Na3V2(PO4)3 with a Na+ superionic conductor structure was synthesized using a solid-state reaction method. Citric acid was used as a carbon resource for carbon-thermal reduction reaction to reduce the oxidation state of vanadium. The shape of Na3V2(PO4)3 particles is irregular and its average diameter is in the range 30–50 nm. The Na3V2(PO4)3 exhibits a superior cycling ability and rate capability. The discharge capacity retains 74.3% of the discharge capacity of its first cycle with coulombic efficiency of 99.3% after 100 cycles. The discharge capacity of Na3V2(PO4)3 at 10 C is 48.87 mAh g−1, which is 58.4% of the cell cycled at 0.1 C. Furthermore, the structure of Na3V2(PO4)3 is stable for a considerable amount of Na+ ions (2 mol of Na+ ions) insertion and extraction with only 0.42% difference of unit-cell volume between fully charged and discharged states. Na3V2(PO4)3 is a potential cathode material for sodium-ion battery applications.