Design and synthesis of sandwich-like CoNi2S4@C@NiCo-LDH microspheres for supercapacitors

Novel sandwich-like hollow nickel cobalt sulfides@carbon@nickel cobalt double hydroxides (CoNi2S4@C@NiCo-LDH) are synthesized using a facile microwave-assisted hydrothermal method and investigated as promising electrode materials for supercapacitors. The in-between highly conductive carbon layer simultaneously serves as uniform cover for CoNi2S4 and large-area support for ultrathin NiCo-LDH, which can restrain the microstructure change during the cyclic charge-discharge process and enhance the transmission rate of electrons and electrolyte ions. The especially nanostructured CoNi2S4@C@NiCo-LDH nanocomposites exhibit outstanding supercapacitive performances including excellent gravimetric specific capacitance (1183mAhg(-1) at 1Ag(-1)) and high rate capability (85.8% retention rate at 20Ag(-1)). More importantly, the assembled CoNi2S4@C@NiCo-LDH//graphene asymmetric supercapacitor can deliver a superhigh specific capacitance of 550mAhg(-1) at 1Ag(-1), prominent energy density of 111.9Whkg(-1) and long cycling stability with 93.8% of its initial capacitance after 10,000cycles at 5Ag(-1).