Sulfur-deficient flower-like zinc cobalt sulfide microspheres as an advanced electrode material for high-performance supercapacitors

Transition-metal sulfides boast a high theoretical capacity and have been regarded as a kind of prospective electrodes for supercapacitors; nevertheless, their inherent poor conductivity and low electrochemical active sites limit the practical applications of the materials.Herein, flower-like zinc cobalt sulfide (ZCS) microspheres with rich sulfur vacancies (ZCSδ) have been synthesized by a three-step procedure of hydrothermal, post-annealing and room-temperaturesulfuration treatments. The flower-like microspheres self-assembled by ultrathin nanosheets bring the active material fully contact with electrolyte, facilitating ion diffusion during charging and discharging. Furthermore, defect engineering of sulfur vacancies at the atomic level raises the intrinsic conductivity and increases active sites for electrochemical reactions. As a result, the obtained sulfur-deficient ZCS microspheres possess an excellent specific capacitance of 2709 F g-1 at 1 A g-1 and an exceptional cycling lifespan of maintaining 90.9% of the initial capacitance over 3000 cycles. In addition, the hybrid supercapacitor employing (HSC) sulfur-deficient flower-like ZCS microspheres as the positive electrode present a high energy density of 28 Wh kg-1 at the power density of 800 W kg-1. This investigation proposes an efficient strategy to significantly and synergistically enhance the electrochemical performance of the electrodes for hybrid supercapacitor by the comprehensive engineering of defect and morphology.