Triggering the Reversible Reaction of V³⁺/V⁴⁺/V⁵⁺in Na₃V₂(PO₄)₃by Cr³⁺Substitution

Sodium-ion batteries (SIBs) have grabbed worldwide attention as an alternative to lithium-ion batteries on account of the abundance and accessibility of the sodium element in nature. For the sake of meeting the requirements for various applications containing grid-scale energy storage system, electric vehicles, and so forth, a stable and high-voltage cathode is decisive to enhance the energy and power density of SIBs. In this research, sodium super ionic conductor structured Na3V1.5-xCr0.5+x(PO4)3 with different V/Cr ratios to balance the V3+/V4+ and V4+/V5+ redox couples was investigated as the potential cathode for SIBs. Among these candidates, Na3V1.3Cr0.7(PO4)3 manifested high energy density together with good cycling performance and rate capability. Combining the structural analysis and density functional theory calculation, the underlying mechanism of V3+ substitution by Cr3+ was uncovered, accounting for the improvement of electrochemical performance.