Flexibility-Engineered Nb2O5 Carbon Nanofiber Film Anodes: Concentration-Dependent Optimization for Mechanically Robust and Stable Sodium Storage

This study systematically investigates the correlation between the concentration of niobium oxide (Nb2O5) in carbon nanofibers (CNFs) and the microstructural characteristics and electrochemical performance of the composites. Through rational optimization of Nb2O5-to-CNFs mass ratios, we demonstrate that 50% Nb2O5 CNFs composite achieves an optimal balance between enhanced rate capability and structural stability. The composites transition from brittle to flexible with increasing Nb2O5 content, achieving unprecedented bending durability at 50% loading. This mechanical–electrochemical synergy positions Nb2O5 CNFs as viable candidates for flexible energy storage devices. Comprehensive characterization reveals that appropriate Nb2O5 incorporation significantly improves specific capacity (181 mA h g−1 at 0.1 A g−1) and rate performance compared to pristine CNFs. However, excessive Nb2O5 doping (>50%) induces detrimental hydrolysis reactions during synthesis, compromising both material processability and electrochemical reversibility. This work contributes to the development of flexible self-supporting frameworks that are superior to hard carbon for constructing high-performance flexible sodium-ion batteries.