Revealing the Role of Niobium in Enhancing the Kinetics of Fe ₂ VO ₄ Nanomaterial Anodes for Stable Sodium-Ion Storage

Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage due to their cost-effectiveness and inherent safety. However, the lack of high-capacity and durable anode materials remains a critical challenge. Spinel-type ferrous vanadate (Fe 2 VO 4 ) nanomaterials have emerged as a potential anode material due to their high theoretical capacity and abundant resources, yet suffer from rapid capacity degradation and sluggish kinetics. In this study, niobium (Nb) was strategically incorporated into the Fe 2 VO 4 lattice via a scalable sol–gel method, thereby modulating charge compensation and the electronic structure to overcome intrinsic limitations. The optimized 7% Nb-doped Fe 2 VO 4 exhibits outstanding electrochemical stability, retaining 82.4% of its initial capacity after 500 cycles at 1 A·g –1, along with a superior rate capability (148 mAh·g –1 at 5 A·g –1 ), significantly outperforming pristine Fe 2 VO 4 . Systematic structural and electrochemical analyses suggest that Nb doping contributes to enhanced structural stability of the material during cycling. This behavior may be associated with the partial alleviation of structural strain induced by sodium ion intercalation/deintercalation, improved sodium-ion diffusion kinetics favored by partial pseudocapacitive charge storage, and enhanced electronic conductivity resulting from a narrowed bandgap. This study provides valuable insights into addressing the intrinsic challenges of Fe 2 VO 4 -based anodes, promoting the development of practical, cost-effective sodium-ion energy storage systems.