Hierarchical Ni-Co-S@Ni-W-O core-shell nanosheet arrays on nickel foam for high-performance asymmetric supercapacitors

摘要

Nickel cobalt sulfides (Ni-Co-S) have attracted extensive attention for application in electronic devices owing to their excellent conductivity and high electrochemical capacitance.To facilitate the large-scale practical application of Ni-Co-S,the excellent rate capability and cyclic stability of these compounds must be fully exploited.Thus,hierarchical Ni-Co-S@Ni-W-O (Ni-Co-S-W) core/shell hybrid nanosheet arrays on nickel foam were designed and synthesized herein via a facile three-step hydrothermal method,followed by annealing in a tubular furnace under argon atmosphere.The hybrid structure was directly assembled as a free-standing electrode,which exhibited a high specific capacitance of 1,988 F·g-1 at 2 A.g-1 and retained an excellent capacitance of approximately 1,500 F·g-1 at 30 A.g-1,which is superior to the performance of the pristine Ni-Co-S nanosheet electrode.The assembled asymmetric supercapacitors achieved high specific capacitance (155 F.g-1 at 1 A.g-1),electrochemical stability,and a high energy density of 55.1 W.h.kg-1 at a power density of 799.8 W.kg-1 with the optimized Ni-Co-S-W core/shell nanosheets as the positive electrode,activated carbon as the negative electrode,and 6 M KOH as the electrolyte.