Enhanced Pseudo-Capacitive Contributions to High-Performance Sodium Storage in TiO/C Nanofibers via Double Effects of Sulfur Modification.

Pseudo-capacitive mechanisms can provide higher energy densities than electrical double-layer capacitors while being faster than bulk storage mechanisms. Usually, they suffer from low intrinsic electronic and ion conductivities of the active materials. Here, taking advantage of the combination of TiS decoration, sulfur doping, and a nanometer-sized structure, as-spun TiO/C nanofiber composites are developed that enable rapid transport of sodium ions and electrons, and exhibit enhanced pseudo-capacitively dominated capacities. At a scan rate of 0.5 mV s, a high pseudo-capacitive contribution (76% of the total storage) is obtained for the S-doped TiS/TiO/C electrode (termed as TiS/S-TiO/C). Such enhanced pseudo-capacitive activity allows rapid chemical kinetics and significantly improves the high-rate sodium storage performance of TiO. The TiS/S-TiO/C composite electrode delivers a high capacity of 114 mAh g at a current density of 5000 mA g. The capacity maintains at high level (161 mAh g) even after 1500 cycles and is still characterized by 58 mAh g at the extreme condition of 10,000 mA g after 10,000 cycles.