Research progress on vanadium-based cathode materials for sodium ion batteries

Sodium ion batteries (SIBs) have attracted increasing attention as one of the most promising candidates for cost-effective, high-energy rechargeable batteries. Owing to their high theoretical capacity and energy density, and rich electrochemical interaction with Na+ (V2+-V5+), a large number of vanadium(V)-based cathode materials, including vanadium oxides (e.g., V2O5 and VO2), vanadium bronzes (e.g., NaxVO2, NaV3O8, NaV6O15 and delta-NH4V4O10), V-based phosphates (e.g., Na3V2(PO4)(3), VOPO4, NaVOPO4, Na7V3(P2O7)(4) and Na-2(VO)P2O7) and F-containing V-based polyanions (e.g., NaVPO4F, Na3V2(PO4)(2)F-3 and Na-3(VOx)(2)(PO4)(2)F-3 (2x)), have been explored for SIBs. In this review, we mainly summarize the basic structures, modified/optimized structures, synthetic methods and morphology control of V-based cathode materials for SIBs. Additionally, major drawbacks, emerging challenges and some perspectives on the development of V-based cathode materials for SIBs are also discussed.