Interlayer Manipulation for Accelerating Ion Diffusion Kinetics in Ti₃C₂T_X MXene Fiber toward Enhanced Supercapacitance with High Rate Capability

Polymer incorporation has been proven effective to enhance the mechanical strength of MXene fibers via interfacial cross-linking, yet the simultaneous improvement in electrochemical performance, particularly output capacitance and high rate capability, remains a challenge, and the major obstacle is identified as the sluggish ion diffusion kinetics. Herein, interlayer manipulation in Ti₃C₂T_X fiber is proposed, and the roles of substitutional groups in celluloses are examined. The addition of cellulose can obviously improve the spinnability of MXene dope and effectively bridge the adjacent Ti₃C₂T_X nanosheets via hydrogen bonds. Moreover, hydroxyethyl cellulose with a suitable group size and moderate adsorption ability is preferred for diminishing the steric effect and facilitating rapid proton transport. Simultaneous improvements in capacitance (1531 F cm^-3 at 2 A cm^-3) and strength (∼76 MPa) are achieved for the optimized M-HEC-1.0% fiber together with a superior high rate capability retaining 89.2% at 15 A cm^-3.