Spinning Dope Modulation Via pH-Triggered Multiscale Sheet-Wire Linkages for Constructing Strong Ti₃C₂T_X MXene Fibers with High Volumetric Capacitance

Due to their ultrahigh volumetric capacitance, metallic conductivity, and excellent mechanical properties, Ti₃C₂T_X MXene nanosheets are considered promising building blocks for the construction of advanced fibers toward the practical applications of fibriform supercapacitors (FSCs) that emerge as an important power supplying system for wearable electronics. However, because of the incompatible interfacial and microstructural design concepts, synergistic improvement in output capacitance and tensile strength remains a critical challenge for Ti₃C₂T_X fibers. Herein, a versatile pH-triggered strategy is presented for modulating Ti₃C₂T_X spinning dope toward the construction of high-performance MXene fibers with simultaneous enhancement in electrochemical capacitance and mechanical strength. Carboxylated cellulose nanofibers (CNF-C) are selected as the additives in Ti₃C₂T_X stock and multiscale sheet-wire linkages are arbitrarily formed via nucleophilic substitution and dehydration reactions by adjusting the pH value. The nematic LC behavior and the spinnability of Ti₃C₂T_X dope are significantly improved with the good ordering of MXene nanosheets. Impressively, the optimized MCC4 fiber achieves an electrical conductivity of 3007 S cm⁻¹, a specific capacitance of 1253 F cm⁻³ and a tensile strength of 258 MPa. The solid-state FSCs assembled from MCC4 fibers exhibit a remarkable energy density of 22.78 mWh cm⁻³ together with excellent charge/discharge reliability and outstanding robustness.