Electrochemical properties of superflexible CNTs/MXene/Cu-doped V₂O₅buckypaper electrodes and wide-voltage all-solid-state supercapacitors

Most flexible supercapacitors have limited applications due to their narrow voltage windows. Here, V₂O₅ nanosheets were in situ grown on and between MXene layers via a hydrothermal method. A superflexible CMV-Cu buckypaper composed of carbon nanotubes (CNTs), MXene, and Cu²⁺-doped V₂O₅ was fabricated via a directional pressure filtration technique, and then assembled into an asymmetric flexible all-solid-state supercapacitor (FSSC) with a wide voltage window. CNTs and MXene synergistically constructed a superflexible porous conductive network, and V₂O₅'s multivalent state transitions broadened the voltage window and contributed most of the pseudocapacitance. Cu²⁺ doping in V₂O₅ enhanced conductivity and ionic mobility, further widening the voltage window. The sheet-like MXene effectively supported and protected V₂O₅, enhancing the cycling and mechanical stability. The CMV-Cu_9.9 electrode with a Cu²⁺ doping ratio of 9.9 mol% had a 1.6 V voltage window and 472 F g⁻¹ specific capacitance at 1 A g⁻¹. It had a tensile strength of 1.6 MPa with only 0.117 mm thickness, and could be curled into a 2 mm radius circle. The assembled FSSC had a wide voltage window of 2.4 V, a specific capacitance of 170 F g⁻¹ at 1 A g⁻¹, and an energy density of 136 Wh kg⁻¹ at a power density of 1197 W kg⁻¹, with 84% capacitance retention after 10 000 cycles, without degradation in electrochemical performance after 200 folding–unfolding cycles along sharp creases. This work paves the way for the potential application of high-performance energy storage devices in wearable electronics.