Zinc Cobalt Sulfide Microspheres as a High-Performance Electrode Material for Supercapacitors

Fast charging/discharging rate, sustained cycle life, and high power density are irreplaceable virtues of supercapacitors (SCs), and these merits can be achieved by selecting suitable active materials and designing the rational microstructure. In this work, zinc cobalt sulfde (ZCS) microspheres have been synthesized by a simple two-step method involving an ethylene glycol (EG) mediated solvothermal approach and subsequent sulfidation treatment. The formation mechanism of the microspheres is also proposed in detail by analyzing the time-dependent SEM observations. Compared to ZCS nanosheets, ZCS microspheres achieve better electrochemical storage performance due to their satisfactory mesoporous feature, conductivity, and effective transport/diffusion paths for ions and electrons. When used as the electrode material of supercapacitor, ZCS microspheres not only obtain a large specific capacitance of 1516 F g(-1) (211 mAh g(-1)) at 1 A g(-1) with good rate capability of 1080 F g(-1) (150 mAh g(-1)) at 10 A g(-1), but also exhibit exceptional cycling stability with a capacitance reduced 6% of the initial specific capacitance at 10 A g(-1) after 4000 cycles. An asymmetric supercapacitor using ZCS microspheres as the cathode and activated carbon (AC) as the anode is assembled, which achieves high specific capacitance (489.3 F g(-1)), energy density (152.9 Wh kg(-1)), and power density (750 W kg(-1)) at 1 A g(-1) with the capacitance retention of 79% at 5 A g(-1) after 2000 cycles. This work illustrates the promising application potential of the ZCS microspheres as the electrode material for electrochemical capacitors.