Flexible MXene-cellulose nanofiber based all-solid-state supercapacitors with high volumetric capacitance

All-solid-state supercapacitors (ASSCs) are critical for next-generation flexible and wearable electronic devices, but their development has been hindered by the challenge of balancing high energy storage performance with mechanical flexibility in wearable energy storage systems. MXene materials offer excellent electrical conductivity, large surface area, and outstanding charge storage capability, but their application in flexible devices is limited by poor mechanical stability and structural degradation. To overcome these challenges, we have developed MXene/cellulose nanofiber (CNF) composites. CNF is a cheap and environmentally friendly material with a huge storage capacity on earth. The doping of CNFs into a layered MXene material prevents the stacking of the MXene, improves the ionic transport speed, maintains the excellent electrochemical properties of the MXene, and enhances the structural reinforcement and flexibility. The flexible, binder-free ASSCs have excellent electrochemical properties with a volumetric capacitance of 94.21 F cm^-3. The electrochemical properties also showed no degradation in bending tests in the range of 30°-120°. The capacitance retention was 97.87% after 10 000 bending cycles at an angle of 60°. This work provides a scalable and green approach to fabricating high-performance MSCs and points the way to the next generation of wearable electronics.