Core-shell MnO2@CoS nanosheets with oxygen vacancies for high-performance supercapattery

Low-cost manganese dioxide (MnO2) with a high theoretical capacity is a promising electrode in a supercapattery; however, the insufficient active sites and low electronic conductivity of bulk MnO2 increase the internal resistance and reduce the capacitance of the supercapattery. Here, we prepared a CoS and MnO2 composite electrode (MnO2-x@CoS) with a core-shell structure by coating CoS on the MnO2-x arrays with a simple electrodeposition method. Both the oxygen vacancies of MnO2-x generated at a high temperature and the metallic CoS coating increase the electronic conductivity of the composite electrode. The high surface area of the composite electrode also provides enough active electrochemical sites for the supercapattery. The prepared MnO2-x@CoS has a high specific capacitance of 781.1 C g−1 at 2 mA cm−2. A supercapattery (SCT) with MnO2-x@CoS composite electrode shows a high areal capacitance of 1064 mF cm−2 and a high energy density of 34.72 Wh kg−1 at 597.24 W kg−1. Besides, the SCT displays excellent cycling stability with a capacitance retention of 89.6% after 9000 cycles. These superior electrochemical properties of the present materials are comparable to those of state-of-the-art MnO2-based electrodes for supercapattery.