Interlayer and intralayer co-modified flexible V2CTX MXene@SWCNT films for high-power Li-ion capacitors

As an emerging member of the two-dimensional (2D) material family, V2CTX MXene shows great potential in the application of lithium-ion capacitors (LICs) due to its unique structure and excellent electrical conductivity. However, severe nanosheets stacking and intra-layer transport barriers have limited the further development of V2CTX MXene-based materials. Herein, we prepared K+ ions and –O functional group co-modified V2CTX MXene (VCT-K) and further incorporated it with single-walled carbon nanotube (SWCNT), obtaining freestanding V2CTX composite films ([email protected]) with the 3D conductive network. Significantly, K+ ions were introduced into V2CTX MXene to stabilize the interlayer structure and prevent the aggregation of nanosheets, the terminal group of –O was controllably modified on the surface of MXene to improve the Li+ ions storage reversible capacities and the SWCNT acted as the bridge between MXene nanosheets to opens up the channels for ion/electron transportation in the longitudinal direction. Benefited from the synergistic effect of VCT-K and SWCNT, the [email protected] exhibits superior reversible specific capacities of 671.8 mA h g−1 at 0.1 A g−1 and 318 mA h g−1 at 1.0 A g−1. Furthermore, the assembled LICs with [email protected] anode coupling activated carbon (AC) cathode deliver an outstanding power density of 19.0 kW kg−1 at 67.4 Wh kg−1, a high energy density of 140.5 Wh kg−1 at 94.8 W kg−1 and a stable capacitance retention of 86% after 6000 cycles at 10 A g−1. Such unique structures and excellent electrochemical properties are expected to pave the way for the large-scale application in LICs of MXene-based materials.