N/S co-doping design promising coal pitch derived carbon nanofibers toward advanced all-carbon potassium ion hybrid capacitors

Heteroatom-doped carbon materials have shown great potential as anodes for potassium ion hybrid capacitors (PIHCs) thanks to their diverse merits. However, their practicability is limited seriously by sluggish reaction kinetics, short cycling life, and low initial Coulombic efficiency, primarily because of the large ionic radius of K+ and undesirable side reactions. Herein, the cost-efficiency low-softening-point coal pitch-derived one-dimensional N/S co-doped carbon nanofibers (N/S-CNFs) are smartly devised as competitive anodes for advanced PIHCs. The as-optimized N/S-CNF anode exhibits a compact morphology, abundant functional groups, and expanded interlayer spacing, rendering an improved initial Coulombic efficiency of 51.5%, high reversible capacities with 328.1 mAh g-1 at 0.1 A g-1 and 122.0 mAh g-1 at 5.0 A g-1, and robust cycling stability. Theoretical calculations authenticate that N/S co-doping significantly enhances the electric conductivity and K+ adsorption capability of fiber anodes. Detailed in-situ X-ray diffraction measurement unveils the intrinsic electrochemical K+-storage process of N/S-CNFs. Moreover, the assembled PIHCs depict an extremely high energy density of 106 Wh kg-1 at 250 W kg-1, and superb cycling performance with only 0.00016% capacity loss per cycle within 10,000 cycles, highlighting the superb practicality of our fabricated N/S-CNFs for next-generation PIHCs.