Synergizing Electron and Ion Transports of Ti₃C₂T_X MXene Fiber via Dot-Sheet Heterostructure and Covalent Ti─C─Ti Cross-Linking for Efficient Charge Storage and Thermal Management

Ti₃C₂T_X MXene with the merits of metallic conductivity, superhigh volumetric capacitance, and efficient absorption of the electromagnetic wave is considered a promising building block for fiber fabrication; nevertheless, the simultaneous improvement in electrochemical charge storage and electrical conductivity/thermal management is seldom achieved for MXene-based fibers due to the contradictory in material design. Typically, aligned and densified packing of MXene fibers is highly desired for an enhanced intra-/inter-flake electron transport; however, the narrowed inter-layer spacing restricts the kinetics of ion diffusion (the intercalation/de-intercalation of electrolyte ions) and diminishes the accessible active sites for charge storage. Herein, the electron and ion transports of Ti₃C₂T_X MXene fiber are synergized via a unique dot-sheet heterostructure covalently bonded by Ti─C─Ti which provides the optimal inter-layer spacing for rapid ion diffusion and enhances the intra-/inter-flake cross-linking for fast electron transport. As a result, the obtained fiber offers an improved conductivity of 2405 S cm⁻¹, a desirable capacitance of 1597 F cm⁻³, an impressive energy density of 19.8 mWh cm⁻³ for the assembled supercapacitor, superior Joule heating performance, and a photo-thermal temperature. These remarkable attributes enable their practical applications in energy-supply scenarios, such as powering LEDs and wearable thermal management.