Nickel-Cobalt-Sulfide Prepared by One-Step Electrodeposition on Expanded Graphite for High-Performance Supercapacitors

Supercapacitors can supply power for vehicles alone or by combination with lithium ion batteries or fuel cells due to their high power density. Here, an electrodeposition method was applied to obtain nickel-cobalt-sulfide (Ni-Co-S) nanoparticles inN,N-dimethylformamide solvent containing a small amount of water. Scanning electron microscopy and transmission electron microscopy images show that Ni-Co-S nanoparticles are uniformly distributed on commercial expanded graphite (EG). No strong peaks of x-ray patterns are observed, as the Ni-Co-S particles exist in an amorphous state. The Ni-Co-S/EG electrode demonstrates a specific capacitance of 1516.5 F g(-1)at current density of 1 A g(-1), capability of 74.2% as the current density increases from 1 to 20 A g(-1), and capacitance loss of 15.6% after 1000 cycles at 10 A g(-1). The electrode exhibits superior supercapacitive performance due to synergistic effect between Ni-S and Co-S, as well as layer-by-layer architecture of the Ni-Co-S/EG composite. The electrode with high specific capacitance, excellent rate performance, and superior cycle stability will provide prospective applications in the field of fast charge/discharge energy storage.