Vacuum-Filtered MXene/Carbon Nanotube Composite Films for Li-Ion Capacitors

MXene has garnered significant attention for its applications in electrochemical energy storage devices, such as supercapacitors and Li-ion capacitors, owing to its high electrical conductivity and relatively high capacitance/capacity in both aqueous and organic electrolytes. Utilizing its two-dimensional (2D) structure, this study prepared vacuum-filtered MXene/carbon nanotube (MXene/CNT) composite films for Li-ion capacitors. The incorporation of CNTs plays a critical role in mitigating the restacking of MXene flakes and enhancing the structural integrity of the films. The MXene/CNT films were first characterized by using various physicochemical methods and evaluated in electrochemical half-cells. A Li-ion capacitor was subsequently fabricated by using the MXene/CNT-12% film as the negative electrode and mesoporous carbon as the positive electrode. The fabricated Li-ion capacitor demonstrates a specific capacitance of 26 F g^-1, an energy density of 40.2 Wh kg^-1, and a power density of 375 W kg^-1 at a current density of 0.5 A g^-1. However, the electrochemical performance of the device is still limited by the layer-by-layer architecture of the MXene-based films, which hinders the efficient transport of electrolyte ions vertically through the layers.