Direct Growth of Birnessite-Type MnO2on Treated Carbon Cloth for a Flexible Asymmetric Supercapacitor with Excellent Cycling Stability

This paper reports a facile means of fabricating a flexible supercapacitor with excellent cycling stability, based on the use of carbon cloth (CC) activated and subsequently modified with birnessite-type MnO2. In this study, sections of commercially-available CC were treated using a simple wet method and then served as substrates for the direct growth of MnO2 via an electrochemical process. The resulting CC electrodes allowed the deposition of a large amount of MnO2 while maintaining its electrochemical utilization efficiency. The optimal mass loading of MnO2 was determined to be 4.27 mg cm−2, a level that gave an areal capacitance of 568 mF cm−2 at a scan rate of 2 mV s−1. This MnO2/CC material was employed in conjunction with an activated carbon-coated CC section as the positive and negative electrodes, respectively, in a solid-state asymmetric supercapacitor. The device generated a cell voltage of 2.0 V with a maximum volumetric energy density of 0.978 mWh cm−3 at a minimum power density of 3.52 × 10−3 W cm−3 and 0.439 mWh cm−3 at 0.158 W cm−3. This performance was maintained at 94.4% of the original level, even after 10,000 cycles, at a constant current density of 50 mA cm−2.