Flexible Ti₃C₂T_x/Carbon Nanotubes/CuS Film Electrodes Based on a Dual-Structural Design for High-Performance All-Solid-State Supercapacitors

Freestanding and bendable films fabricated by two-dimensional (2D) MXene materials have demonstrated great potential as electrodes for energy storage devices owing to their paramount flexibility, structural stability, and high conductivity. Nevertheless, the unavoidable restacking of MXene sheets substantially limits their electrochemical performance. Here, a film electrode with a sandwich-like structure was fabricated by a dual-structural design through a layer-by-layer (LbL) method with alternating filtration of the Ti3C2Tx/carbon nanotube (CNT) hybrid and CuS dispersion. The introduced CNTs and pseudocapacitive CuS provide abundant active sites to augment the electrode storage capacity. The enlarged interlayer spacing facilitates the transport of electrolyte ions. As a result, the optimized Ti3C2Tx/CNTs/CuS-LbL-15 film electrode (1.7 mg/cm3) with a thickness of 17 μm still exhibits a high gravimetric capacitance (336.7 F/g) and volumetric capacitance (572.4 F/cm3) at 1 A/g in a poly(vinyl alcohol) (PVA)/H2SO4 gel electrolyte, both of which are among the highest within past reports at the same thickness. Meanwhile, the sample demonstrates an impressive rate capability with 57% capacitance retention at a current density of 9 A/g, ultrastable cycling by retaining 99.6% of the initial capacity after 5000 cycles at a high rate of 5 A/g, and good flexibility under different bending states. Besides, the all-solid-state symmetric supercapacitor exhibits an energy density of 12.72 Wh/L at a power density of 340 W/L. This work provides an effective route for assembling Ti3C2Tx/CNTs and CuS hybrid electrodes for high-performance energy storage devices.