Sulfur doped hollow carbon nanofiber anodes for fast-charging potassium-ion storage

Sulfur doping can bridge durable active sites to induce C S electron coupling to produce unparalleled Faraday conversion, breaking the limitations of ion storage capacitance, and therefore it is an effective way to design carbon materials with improved electrochemical performance. However, sulfur doping methods, especially how to design S-rich by atomic transition among carbon membered-ring structure of anodes remains a confusing topic. Herein, the linear relationship between sulfur and nitrogen content is found, and the tendency of sulfur to replace pyrrolic nitrogen is demonstrated. The sulfur replaces part of nitrogen atoms and form C S bonds with binds covalently to carbon skeleton, where S-rich hollow carbon nanofibers (NHCFs-S) are synthesized. The introduction of high sulfur doping in carbon results to the improvement of conductivity, Faraday reaction activity and pseudocapacitive adsorption behavior. For potassium-ion batteries, the fabricated NHCFs-S material delivers a 369 mAh/g high capacity at 1.0 A/g after 100 cycles with 80 % initial coulombic efficiency and a desirable rate capability of 261 mAh/g even at 5.0 A/g. This work provides a selection for high-performance anodes design and a reference for the future research of high sulfur doped in carbon materials.