Flexible composite films constructed of MXene/cellulose nanofibers/natural fiber-based activated carbon fibers for high-performance flexible supercapacitors.

Traditional activated carbon fibers (CF) based supercapacitors suffer from low mechanical strength, inherent brittleness that induces stress concentrations, and bulky architectures from binder/conductive additive requirements. To overcome these limitations, cellulose nanofibers (CNF) are synergistically integrated with Ti₃C₂Tₓ MXene and CF, forming a mechanically reinforced composite film via hydrogen bonding and van der Waals interactions. The CNF/CF network expands the interlayer spacing of MXene, which enhances the ion-accessible surface area and enables rapid ion transport. The resulting Ti₃C₂Tₓ/CNF/CF composite film demonstrates exceptional electrochemical performance, achieving a specific capacitance of 420.99 F g at 0.5 A g, with 84.56 % retention at 10 A g. As a self-supporting flexible electrode (0.49 mm thickness), it delivers an areal capacitance of 214 mF cm at 0.3 mA cm and an energy density of 14.5 μWh cm at 30.2 μW cm. The hierarchical CNF/CF network simultaneously suppresses MXene restacking through spatial confinement while optimizing mechanical flexibility and stress distribution via interfacial bonding. This assembly strategy enables scalable fabrication of ultrathin MXene-based supercapacitors suitable for flexible electronics and grid-scale storage systems.