Copper sulfide nanoneedles on CNT backbone composite electrodes for high-performance supercapacitors and Li-S batteries

Hierarchical-structured copper sulfide nanoneedles were grown on multi-walled carbon nanotube backbone (denoted as CuS@CNT) as electrodes for supercapacitors via a facile template-based hydrothermal conversion approach and further by simply impregnating sulfur into CuS@CNT (S@CuS@CNT) as electrodes for Li-S batteries. The electrochemical measurements showed that the resultant CuS@CNT composite electrodes deliver outstanding electrochemical performance with a specific capacitance up to 566.4 F g−1 and cyclic stability of 94.5 % of its initial capacitance after 5000 cycles at a current density of 1 A g−1. A synergistic effect arising from the unique hierarchical structure was responsible for the electrode performance, including a large surface area of 49.3 m2 g−1 and active CuS ultrafine nanoneedles firmly bonded to the highly conductive carbon nanotube (CNT) backbone. When used as an electrode material for Li-S batteries, the S@CuS@CNT (S content 59 wt%) exhibited satisfying electrochemical performance. The S@CuS@CNT electrode showed that coulombic efficiency was close to 100 % and capacity maintained more than 500 mA h g−1 with progressive cycling up to more than 100 cycles even at a high current density. This strategy of stabilizing S with a small amount of copper sulfide nanoneedles can be a very promising method to prepare free-standing cathode material for high-performance Li-S batteries. The fabrication strategy presented here is low cost, facile, and scalable, which can be considered as a promising material for large-scale energy storage device. In particular, the use of CNT as backbone for the growth of active materials presents many potential merits owing to its lightweight, biodegradable, and stretchable characteristics.