“Carbon quantum dots-glue” enabled high-capacitance and highly stable nickel sulphide nanosheet electrode for supercapacitors

Abstract A facile “carbon quantum dots glue” strategy for the fabrication of honeycomb-like carbon quantum dots/nickel sulphide network arrays on Ni foam surface is successfully demonstrated. This design realizes the immobilization of nanosheet arrays and maintains a strong adhesion to the collector, forming a three-dimensional (3D) honeycomb-like architecture. Thanks to the unique structural advantages, the resulting bind-free electrode with high active mass loading of 6.16 mg cm-2 still exhibits a superior specific capacitance of 1130 F g−1 at 2 A g−1, and maintains 80 % of the initial capacitance even at 10 A g−1 after 3000 cycles. Furthermore, the assembled asymmetrical supercapacitor delivers an energy density of 18.8 Wh kg−1 at a power density of 134 W kg−1, and outstanding cycling stability (100 % of initial capacitance retention after 5000 cycles at 5 mA cm−2). These impressive results indicate a new perspective to design various binder-free electrodes for electrochemical energy storage devices.