MnO2/MWNT yarn supercapacitors

Abstract

Recently, there has been a great interest in miniaturized and flexible energy storage devices for portable applications. In terms of energy storage, electrochemical supercapacitors have attracted much attention because of their high power density, moderate energy storage property and long life cycles. Among the electrode materials, manganese dioxide (MnO2) is considered to be a promising transition metal oxide for the next generation of supercapacitors because of its ideal capacitor performance (1370 F/g), environmental friendliness, and high-power density. However the poor electric conductivity and the brittleness of the MnO2 limits the high power performance and flexibility of the device. In this work, we demonstrate a highly flexible and high power maintaining supercapacitor by fabricating a thin MnO2 coating on MWNT yarn by thermal decomposition method. Due to the high surface area to volume ratio and high conductivity of the MWNT yarn electrode, the MnO2/MWNT yarn supercapacitor showed specific capacitances of 398 F/g with a long-term cycle stability over 2500 cycles. It also exhibited an energy density of 9.64 Wh/kg and power density of 34.58 kW/kg. The MnO2/MWNT yarns also retain their capacitance and resistance value after bending and overhand knot, since the yarn exhibits tensile strength up to ~295 MPa and a Young's modules up to ~17.1 GPa/cm. These results represent that the MnO2/MWNT yarn can be a promising work for the lightweight and micro sized energy storage materials and device. Also these sample can be applied in bio-artificial muscle and bio-medical instruments.