Growth of yolk-shell CuCo2S4 on NiO nanosheets for high-performance flexible supercapacitors

A poor electrical conductivity and short cycle life limits the wide application of transition metal oxides in energy storage applications. In this study, yolk-shell structured CuCo 2 S 4 was grown on NiO nanosheets (NiO@CuCo 2 S 4 ) via a hydrothermal method and vulcanization , which combined the synergistic interactions between Ni, Co, and Cu. The effect of varying the amount of the vulcanizing agent (thiourea) on the electrochemical performance of NiO@CuCo 2 S 4 was also investigated. Moreover, the amount of thiourea not only tuned the morphology of the composite, but significantly influenced its electrochemical performance. When the Cu 2+ : Co 2+ : thiourea molar ratio in the precursor solution was 1:2:6, the obtained NiO@CuCo 2 S 4 exhibited the best electrochemical performance of the various systems examined, with a specific capacitance of 1658 F g −1 being achieved at 1 A g −1 . Density functional theory calculations further confirmed the excellent synergistic effect between NiO and CuCo 2 S 4 . In addition, the asymmetric supercapacitor composed of a NiO@CuCo 2 S 4 positive electrode reached an ultrahigh energy density of 73 Wh kg −1 at a power density of 802 W kg −1 , as well as excellent cycling stability (i.e., 91% capacitance retention after 5000 cycles). These results suggest that NiO@CuCo 2 S 4 is a promising candidate for use in energy storage applications.