Binder-free cobalt-doped Cu₇S₄ nanorods as electrode for hybrid supercapacitor with high power density and stable cyclability

Copper-based transition metal sulfides are regarded as good supercapacitor electrode materials due to their cost-effectiveness and considerable theoretical capacity. However, their cycle stability, energy density and rate performance need to be improved. Herein, cobalt-doped Cu7S4 (Co-Cu7S4) nanorods are synthesized at room temperature using environment-friendly routes of co-precipitation and self-sacrifice template processes. Results obtained from electrochemical characterizations and density functional theory calculations can prove the excellent doping kinetics and ideal electrochemical behavior of cobalt ions. Impressively, a high specific capacity of 1302.0 C g(-1) (2367.3 F g(-1)) at 4 A g(-1) and rate capabilities of 90.0 % at 10 A g(-1) and 61.8 % at 40 A g(-1) are obtained. The assembled hybrid supercapacitor (Co-Cu7S4//Active carbon) exhibited superior cycle stability with no insignificant decay after 40,000 charge/discharge process at 5 A g(-1) and 20 A g(-1), and a maximum power density of 20.4 kW kg(-1) at 17.6 Wh kg(-1). These excellent electrochemical properties can be ascribed to the porous nanostructures formed by shrinkage during the sulfide process, the rapid electrochemical kinetics, as well as the synergistic effect due to the cobalt ions. This study can provide useful insight into the design and development of electrode materials for high-performance energy storage devices.