Vanadium oxide nanospheres encapsulated in N-doped carbon nanofibers with morphology and defect dual-engineering toward advanced aqueous zinc-ion batteries

Vanadium-based electrodes are regarded as attractive cathode materials in aqueous zinc ion batteries (ZIBs) caused by their high capacity and unique layered structure. However, it is extremely challenging to acquire high electrochemical performance owing to the limited electronic conductivity, sluggish ion kinetics, and severe volume expansion during the insertion/extraction process of Zn²⁺. Herein, a series of V₂O₃ nanospheres embedded N-doped carbon nanofiber structures with various V₂O₃ spherical morphologies (solid, core–shell, hollow) have been designed for the first time by an electrospinning technique followed thermal treatments. The N-doped carbon nanofibers not only improve the electrical conductivity and the structural stability, but also provides encapsulating shells to prevent the vanadium dissolution and aggregation of V₂O₃ particles. Furthermore, the varied morphological structures of V₂O₃ with abundant oxygen vacancies can alleviate the volume change and increase the Zn²⁺ pathway. Besides, the phase transition between V₂O₃ and Zn_XV₂O_5−m·nH₂O in the cycling was also certified. As a result, the as-obtained composite delivers excellent long-term cycle stability and enhanced rate performance for coin cells, which is also confirmed through density functional theory (DFT) calculations. Even assembled into flexible ZIBs, the sample still exhibits superior electrochemical performance, which may afford new design concept for flexible cathode materials of ZIBs.