Tuning the Electronic Structure of Niobium Oxyphosphate/Reduced Graphene Oxide Composites by Vanadium‐Doping for High‐Performance Na+ Storage Application

ABSTRACT Sodium‐ion batteries have become a significant research focus in academia. As a novel sodium anode material, layered NbOPO 4 , consisting of octahedral NbO 6 units sharing oxygen atoms with tetrahedral PO₄ units, exhibits stability due to strong phosphorus‐oxygen covalent bonds that prevent oxygen loss from the framework. However, its inherently low electrical conductivity and sluggish charge transfer kinetics limit its electrochemical performance. To address these challenges, we designed and synthesized vanadium‐doped niobium oxyphosphate coated with reduced graphene oxide (V‐NbOPO 4 @rGO) via a microwave hydrothermal method followed by calcination. Vanadium doping effectively modulated the electronic structure of NbOPO 4 and significantly enhanced its conductivity, as corroborated by density functional theory (DFT) calculations. Consequently, the V 0.15 ‐NbOPO 4 @rGO electrode demonstrated exceptional rate capability, achieving 418 mAh g −1 at a low current density of 0.1 A g −1 and maintaining a reversible capacity exceeding 100 mAh g −1 even at an ultrahigh current density of 50 A g −1 . Furthermore, the reversible sodium storage mechanism of V 0.15 ‐NbOPO 4 @rGO was validated through in‐situ XRD, TEM, and XPS analyses. This study provides an effective strategy for improving the electrochemical performance of NbOPO 4 based anodes and deepens understanding of the sodium storage mechanism in V‐doped NbOPO 4 , emphasizing its potential for practical application in sodium‐ion batteries.