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., Na_xVO₂, NaV₃O₈, NaV₆O₁₅ and δ-NH₄V₄O₁₀), V-based phosphates (e.g., Na₃V₂(PO₄)₃, VOPO₄, NaVOPO₄, Na₇V₃(P₂O₇)₄ and Na₂(VO)P₂O₇) and F-containing V-based polyanions (e.g., NaVPO₄F, Na₃V₂(PO₄)₂F₃ and Na₃(VO_x)₂(PO₄)₂F_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.