Carbon quantum dot-induced robust ε-MnO2 electrode by synergistic engineering of oxygen vacancy and low crystallinity for high- performance flexible asymmetric supercapacitor

Developing high-capacitance and robust electrode materials for robust flexible supercapacitors is an on-going challenge. To fabricate such energy storage devices, flexible electrodes with desired electrochemical and mechanical performances are crucial. Composition and structure tailoring of electrode materials play a significant role in exploiting high-performance flexible supercapacitors. Herein, CQDs-modified epsilon-MnO2 nanosheets with abundant oxygen vacancies and low crystallinity was uniformly grown on the skeletons of carbon cloth by a facile one-step electrodeposition strategy. Benefiting from the structural features and intrinsic defects, the obtained CQDs/epsilon-MnO2 electrode delivered outstanding mechanical property with tensile strength of 87 MPa and excellent electrochemical activity with high specific capacitance of 334.5 F g-1 at 1 A g-1 and remarkable rate capability as well as good cycling stability with 90% of capacitance retention after 6000 cycles at 5 A g-1, which was much better than pristine epsilon-MnO2 electrode. In addition, the assembled aqueous asymmetric supercapacitor (ASC) with good flexibility based on the CQDs/epsilon-MnO2 electrode could provide an energy density of 68.2 Wh kg-1 with power density of 990 W kg-1 at 5 A g-1 and long-term stability, outperforming most currently available flexible supercapacitors.(c) 2022 Elsevier B.V. All rights reserved.