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

Abstract

Developing high-capacitance and robust electrode materials for robust flexible supercapacitors is an ongoing 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 ε-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/ε-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 ε-MnO2 electrode. In addition, the assembled aqueous asymmetric supercapacitor (ASC) with good flexibility based on the CQDs/ε-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.