Interconnected Ni-Co sulfide nanosheet arrays grown on nickel foam as binder-free electrodes for supercapacitors with high areal capacitance

Binary metal sulfides have been considered as promising electrode materials for supercapacitors with excellent performance. Herein, we demonstrate a simple two-step hydrothermal method to grow the interconnected Co9S8/NiCo2S4 nanosheet arrays (denoted as Ni-Co sulfide NSAs) on nickel foam with robust adhesion for high performance supercapacitors. Remarkably, the as-synthesized Ni-Co sulfide binder-free electrode exhibits an ultrahigh areal capacitance of 7.4 F cm−2 for supercapacitors, which is about five times higher than 1.5 F cm−2 of the Ni-Co oxide electrode at the current density of 5 mA cm−2. The Ni-Co sulfide binder-free electrode also exhibits a good cycling stability, which still displays a high capacitance retention of 90.7% after 2000 cycles even at a high current density of 40 mA cm−2. The good electrochemical performance could be ascribed to the high electrical conductivity and porous nanosheet structure of the Ni-Co sulfide nanosheets, as well as the robust adhesion with the current collector. These electrochemical results suggest that such Ni-Co sulfide NSA binder-free electrode might hold some potential for electrochemical energy applications.