Sulfur covalently linked TiO2/C nanofiber as a high-capacity, ultrastable, and self-supported anode for sodium-ion capacitors

Abstract Sodium ion capacitors (SICs) have attracted extensive attention due to their combination of high-power electric-double-layer capacitors (EDLCs) and high-energy sodium ion batteries (SIBs). However, development of high-performance SIHCs has been plagued by the lack of superior Na+-storage anode materials to couple with the activated carbon (AC) cathode. In this work, we have prepared a sulfur-enriched self-supported TiO2/C nanofiber membrane using a simple and scalable electrospinning technique. In such S-TiO2/C structure, sulfur atoms (13%) are covalently linked with TiO2 nanodots (5–10 nm), which are homogeneously embedded in highly conductive N-doped carbon nanofibers. Chemically bonded sulfur can not only provide additional faradaic pseudocapacitance but also show robust structural stability. In terms of sodium storage performance, the as-made S-TiO2/C electrode exhibits high reversible capacity (410 mAh g‒1 at 0.1 A g‒1), high rate capability (173 mAh g‒1 at 15 A g‒1), and ultralong cycle life (no capacity degradation after 10000 cycles). When coupling with the AC cathode, the SIC full cell is capable of delivering high energy and power densities as well as long cycle life.