Cobalt disulfide/carbon nanofibers with mesoporous heterostructure and excellent hydrophilicity for high energy density asymmetric supercapacitor

Herein, a unique mesoporous heterostructure (average pore size: 15 nm) cobalt disulfide/carbon nanofibers (CoS2/PCNFs) composite with excellent hydrophilicity (contact angle: 23.5 degrees) is prepared using polyethylene glycol (PEG) as a pore-forming agent. The CoS2/PCNF electrode exhibits excellent cycle stability (95.2% of initial specific capacitance at 10 A center dot g(-1) after 8000 cycles), good rate performance (46.5% at 10 A center dot g-1), and high specific capacity (86.1 mAh center dot g(-1) at 1 A center dot g(-1), about 688.8 F center dot g(-1) at 1 A center dot g(-1)). Density functional theory (DFT) simulation elucidates that CoS2 tends to transfer substantial charges to CNF. As the center of positive charge, CoS2 is more likely to capture negative ions in the electrolyte, thus accelerating the ion diffusion process. The excellent properties of the electrode material can not only accelerate the electrochemical reaction kinetics, but also provide abundant redox-active sites and a high Faradaic capacity for the entire electrode due to the synergistic contributions of CoS2 nanoparticles, mesoporous heterostructure of PCNF, and admirable hydrophilicity of the composite material. A CoS2/PCNF-0.25//AC (AC: activated carbon) asymmetric supercapacitor is assembled using CoS2/PCNF-0.25 as the positive electrode and AC as the negative electrode, which possesses a high energy density (35.5 Wh center dot kg(-1 )at a power density of 824 W center dot kg(-1)) and superior cycling stability (maintaining over 98% of initial capacitance after 2000 cycles). In addition, the unique CoS2/PCNF electrode is expected to be widely used in other electrochemical energy storage devices, such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, etc.