New Insights on FeNbO₄ Porous Nanofibers as NbO Based Anodes with Improved-Capacity for Li-Ion Batteries

NbO-based anodes for Li-ion batteries, such as Nb₂O₅, 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, FeNbO₄ 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 FeNbO₄ 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 Nb₂O₅ 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 Fe³⁺/Fe²⁺ and Nb⁵⁺/Nb⁴⁺, while their relatively high operating voltages contribute to the safety of FeNbO₄ PNFs as an anode material. This work provides a refined understanding of the FeNbO₄ electrode and offers fresh perspectives on the design of NbO-based anodes with improved-capacity.