A high mass loading electrode based on ultrathin CoS nanosheets for high performance supercapacitor

There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin CoS nanosheet decorated electrode (denoted as CoS/NF) with mass loading of 6 mg cm is successfully fabricated by using highly dispersive CoO nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3∼5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5∼1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g and large specific capacitances of 2415 and 1152 F g at 1 and 20 A g, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and CoS/NF electrode exhibits a high energy density of 79 Wh kg at a power density of 151 W kg, a high power density of 3000 W kg at energy density of 30 Wh kg and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g. More importantly, the formation process of the ultrathin CoS nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine CoO nanowires in the anion-exchange reaction. [Figure not available: see fulltext.]