New Insights on FeNbO ₄ Porous Nanofibers as NbO Based Anodes with Improved‐Capacity for Li‐Ion Batteries

Abstract NbO‐based anodes for Li‐ion batteries, such as Nb ₂ O ₅ , are promising due to their minimal volume change and relatively high operation voltage, leading to extended cycling stability and reduced risk of Li‐dendrite formation. However, limited reversible capacity hinders their further development. Herein, FeNbO ₄ porous nanofibers (PNFs) are fabricated. These nanofibers consist of nanoparticles and numerous voids are left for electrolyte infiltration. When cycled within an optimized voltage window (0.50–3.00 V), the FeNbO ₄ PNF electrode exhibits reduced voltage hysteresis and improved energy efficiency compared to conventional wide‐range cycling (0.01–3.00 V). Moreover, it exhibits a lower activation energy and a substantially higher Li‐ion diffusion coefficient, resulting in a reversible capacity twice that of a Nb ₂ O ₅ anode. Ex situ characterizations on the intermediates suggest that LiFeO _x and LiNbO _x composites form during the first lithiation process via a conversion reaction, after which an insertion‐extraction reaction dominates the Li‐ion storage behavior. The enhanced capacity is attributed to the high reversible redox activity of Fe ³⁺ /Fe ²⁺ and Nb ⁵⁺ /Nb ⁴⁺ , while their relatively high operating voltages contribute to the safety of FeNbO ₄ PNFs as an anode material. This work provides a refined understanding of the FeNbO ₄ electrode and offers fresh perspectives on the design of NbO‐based anodes with improved‐capacity.