In situ synthesis of CoSx@carbon core-shell nanospheres decorated in carbon nanofibers for capacitor electrodes with superior rate and cycling performances

Transition metal sulfides coupled with carbon materials hold a promising application platform for high-performance supercapacitors. Herein, we report a strategy to fabricate a type of integrated CoSx hollow nanoparticles (HNPs)/C hybrid nanofibers via electrospinning technique combining with hydrothermal method. Results show that the in-situ formed CoSx HNPs were completely covered by a layer of onion-like carbon, which can not only increase their conductivity but also buffer their volume changes during the charging/discharging processes. Interestingly, this type of unique configuration will raise the synergistic effect from excellent electrical conductivity of porous carbon nanofibers (PCNFs) and high specific capacitance of CoSx, endowing the hybrids to be an excellent electrode for high-rate performance supercapacitors. The resultant CoSx/C hybrid electrodes exhibit a high specific capacitance (496.8 F g−1 at 0.5 A g−1), superior rate capability (remaining 66.1% at 100 A g−1), and good cycling stability (over 89.0% after 2000 cycles). Besides, the assembled asymmetric supercapacitors of CoSx/C hybrids//PCNFs show high energy density (15.0 W h kg−1 at power density of 413 kW kg−1) and high cycling stability (over 80% after 2000 cycles).