Bidirectional Construction of 3D Flexible Ti3C2Tx MXene Films for High-Performance Lithium-Ion Capacitors

Lithium-ion capacitors (LICs) are considered ideal devices, which bridge the energy and power density gap between lithium-ion batteries (LIBs) and supercapacitors (SCs). However, the mismatched kinetics between the cathode and anode remains an obstacle to the development of LICs. Herein, an anode with excellent flexibility and fast electrochemical reaction kinetics is designed for advanced LICs by coupling highly conductive single-walled carbon nanotubes (CNTs) with the bidirectionally designed Ti3C2Tx MXene (KTi3C2-O). In such a composite (KTi3C2-O/CNTs), the bidirectional design of Ti3C2Tx MXene based on the interlayers of K+ ions intercalation and interfaces of −O terminal groups modification will increase the interlayer distance, provide more active sites, and improve Li+ ions storage capacity; the introduction of CNTs forming a three-dimensional (3D) interpenetrating structure with KTi3C2-O can alleviate Ti3C2Tx MXene interlayer stacking and offer fast charge transfer kinetics. When evaluated as a self-supported anode of LIC, the LIC displays a high power density of 15.63 kW kg–1, a high energy density of 138.89 Wh kg–1, and an exceptional capacity retention of 77.75% over 10 000 cycles at 5 A g–1. Such a bidirectional construction strategy based on interlayer and interfacial modification provides new ideas for the design of such two-dimensional (2D) materials that can be applied in advanced energy storage devices.