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 + (V 2+ -V 5+ ), a large number of vanadium(v)-based cathode materials, including vanadium oxides (e.g., V 2 O 5 and VO 2 ), vanadium bronzes (e.g., Na x VO 2 , NaV 3 O 8 , NaV 6 O 15 and δ-NH 4 V 4 O 10 ), V-based phosphates (e.g., Na 3 V 2 (PO 4 ) 3 , VOPO 4 , NaVOPO 4 , Na 7 V 3 (P 2 O 7 ) 4 and Na 2 (VO)P 2 O 7 ) and F-containing V-based polyanions (e.g., NaVPO 4 F, Na 3 V 2 (PO 4 ) 2 F 3 and Na 3 (VO x ) 2 (PO 4 ) 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.