Zn-Co Sulfide Microflowers Anchored on Three-Dimensional Graphene: A High-Capacitance and Long-Cycle-Life Electrode for Asymmetric Supercapacitors.

Abstract

Zinc-cobalt double-metal sulfides (ZCS) as Faradic electrode materials with high energy density have great potential for supercapacitors, but their poor transfer efficiency for electrons and ions hinders their electrochemical response. Herein, ZnCo2 (CO3 )1.5 (OH)3 @ZCS microflower hybrid arrays consisting of thin nanolayer petals were anchored on three-dimensional graphene (ZnCo2 (CO3 )1.5 (OH)3 @ZCS/3DG) by a simple hydrothermal method and additional ion-exchange process. A ZnCo2 (CO3 )1.5 (OH)3 @ZCS/3DG electrode delivered high capacitance (2228 F g-1 at 1 A g-1 ) and long cycling life (85.7 % retention after 17 000 cycles), which are ascribed to the multicomponent structural design. The 3DG conductive substrate improves the electron-transfer dynamics of the electrode material. Meanwhile, the microflowers consisting of thin nanolayer petals could not only provide many active sites for ions to improve the capacitance, but also alleviate the volume expansion to ensure the structural stability. Furthermore, an all-solid-state asymmetric supercapacitor based on a ZnCo2 (CO3 )1.5 (OH)3 @ZCS/3DG electrode achieved a high energy density of 27 W h kg-1 at 528.3 W kg-1 and exhibits exceptional cyclic stability for 23 000 cycles. Its ability to light a blue LED for 9 min verified the feasibility of its application for energy storage devices.