LAUSR

Abstract Sodium-ion supercapacitors (SICs) have attracted increasing scientific attention for mid-to-large-scale energy storage applications due to their high energy and power densities. Herein, an ultra-flexible and free-standing hybrid anode material consisting of sulfur-doped Nb2O5 quantum dots (~3 nm) uniformly embedded within nitrogen and sulfur co-doped microporous carbon nanofiber (S–Nb2O5@NS-PCNF) is successfully fabricated by electrospinning followed by a sulfidation treatment. The designed 3D microporous network not only offers a continuous conducting framework for electron-transport, but also provides more accessible channels for rapid Na-ions migration. Furthermore, the S-doping induced anionic oxidation of Nb2O5 (O2-2−→O−) and S-doping in microporous carbon nanofibers result in the formation of numerous oxygen vacancies and defects for enhanced electrical conductivity and surface pseudocapacitance. In particular, the oxygen vacancies induced by the S-doping on Nb2O5 have been firstly demonstrated. This S–Nb2O5@NS-PCNF film electrode exhibits superior rate capability (124 mAh g−1 at 4 A g−1) and ultralong cycling life (173 mAh g−1 after 10000 cycles at 2 A g−1). The SIC full-cell comprising a S–Nb2O5@NS-PCNF anode and an activated carbon cathode delivers a maximum energy density of 112 Wh kg−1 at 80 W kg−1 and a ultralong-term cycling stability. This strategy provides a promising application for highly efficient energy storage systems.