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°) 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∙g⁻¹ after 8000 cycles), good rate performance (46.5% at 10 A∙g⁻¹), and high specific capacity (86.1 mAh∙g⁻¹ at 1 A∙g⁻¹, about 688.8 F∙g⁻¹ at 1 A∙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∙kg⁻¹ at a power density of 824 W∙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.