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

Abstract

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.