Interface modification based on MnO2@N-doped activated carbon composites for flexible solid-state asymmetric supercapacitors

Abstract

One of the key issues to improve the energy density of supercapacitors is optimizing the performance of electrode materials. In this work, urea is used to modify the activated carbon (NAC), and then MnO2 are introduced on the surface of NAC by hydrothermal treatment to form three-dimensional structure composites (MnO2@NAC). After interface modification, the NAC has strong interactions with MnO2, which can ensure rapid charge transfer. The electrode material exhibits an excellent electrochemical performance (408.5 F g−1 at 0.5 A g−1) and a long-term stability (88.2% after 10,000 cycles). The 1.6 V flexible solid-state asymmetric supercapacitor is assembled with NAC as the anode, MnO2@NAC as the cathode, and PVA-KOH as the electrolyte with a superior specific capacitance (75 F g−1 at 1 A g−1), a high energy density (26.7 Wh kg−1 at 400 W kg-1) and an excellent rate performance (89.5% retention after 10,000 cycle). The density functional theory is used to calculate charge density difference, N-doping can strengthen the interactions at the interface of MnO2 and NAC, and enhance the charge transfer at the two-phase interface. This research can provide a thought for the rational design of carbon/metal oxide composites with excellent electrochemical properties in the future.