Construction of hierarchical core-shell ZnCo2O4@Ni-Co-S nanosheets with a microsphere structure on nickel foam for high-performance asymmetric supercapacitors

The hierarchical core-shell ZnCo2O4@Ni-Co-S nanosheets with microsphere structures for supercapacitors were prepared through a facile three-step method including hydrothermal reaction, subsequent annealing and electrodeposition process. The influences of deposition cycles on its structure and electrochemical performances were studied in detail. On account of a synergistic effect of the ZnCo2O4 and Ni-Co-S composite and its unique core-shell nanostructure, the as-prepared electrode reveals excellent supercapacitor properties. The ZnCo2O4@ Ni-Co-S with 6 electrodeposition cycles (ZCO@NCS-6) shows high specific capacitance values of 1762.6 F g(-1) at 1 A g(-1), outstanding rate performance with 81.3% at 50 A g(-1), and remarkable long-term stability of 18.6% capacity loss through 5000 cycles. Moreover, the asymmetric supercapacitor (ASC) device was further constructed by using of ZCO@NCS-6 and active carbon to evaluate the practical values of the fabricated composite materials. The assembled ASC device shows the maximum voltage window up to 1.7 V, high energy density of 37.1 W h kg(-1) and the excellent cycling life-span (only 9.71% capacitance loss after 8000 cycles). All these results suggest that ZnCo2O4@Ni-Co-S could be the hopeful electrode materials for energy storage devices.