Heterogeneous cobalt polysulfide leaf-like array/carbon nanofiber composites derived from zeolite imidazole framework for advanced asymmetric supercapacitors

Developing new electrode materials is one of the keys to improving the energy density of supercapacitors. In this article, a novel cobalt polysulfide/carbon nanofibers (C, N -Co x S y /CNF) film derived from zeolitic imidazolate framework is first prepared by a facile strategy. The composite material with two-dimensional leaf-shaped nanoarray neatly grown on the surface of carbon nanofibers is composed of CoS, CoS 2 , Co 9 S 8 , N -doped carbon nanosheets, and carbon nanofibers. It is found that the composite can not only increase the contact area with the electrolyte but also provide abundant redox-active sites and a Faraday capacitance for the entire electrode. The C, N -Co x S y /CNF composite exhibits excellent electrochemical properties, including a high capacity of up to 1080F g -1 at 1 A g -1 and a good rate capability (80.4 % from 1 A g -1 to 10 A g -1 ). A C, N -Co x S y /CNF//AC asymmetric supercapacitor device is assembled using C, N -Co x S y /CNF as the positive electrode and activated carbon as the negative electrode, showing high energy density (37.29 Wh kg -1 @813.6 W kg -1 ) and good cycle stability (90.5% of initial specific capacitance at 10 g −1 after 5000 cycles). This C, N -Co x S y /CNF composite material may also be used as a potential electrode for future lithium-ion batteries, zinc-ion batteries, lithium-sulfur batteries, etc .