Coaxial spinning of Ti ₃ C ₂ T _X MXene fibers with spontaneous radial densification achieves simultaneous improvements in both mechanical strength and charge storage ability

Ti₃C₂T_X MXene has good mechanical strength, metallic conductivity and ultrahigh volumetric capacitance and is a promising candidate for developing advanced fibers for applications in fibrous supercapacitors (FSCs); however, the weak interlayer interaction, random stacking during coagulation and unsuitable channels for ion transport impose crucial difficulties in the continuous spinning of strong MXene fibers with desirable charge storage ability. Herein, we propose a coaxial spinning strategy accompanied by spontaneous radial densification for the simultaneous achievement of improved fiber mechanical strength and charge storage capability. The intercalation of sodium alginate (SA) in the core (S/M) expands the interlayer spacing and produces suitable paths for ion diffusion, while the presence of a SA/graphene oxide (S/G) sheath generates radial compression during dehydration because of capillary forces, enhances stress transfer within the fiber, and avoids short circuit in the FSC. The optimized S/M@S/G fiber exhibits a tensile strength of 238 MPa and a volumetric capacitance of 906 F cm^-3 at 1 A cm^-3. The assembled FSCs provide a capacitance of 153 F cm^-3 together with an energy density of 13.6 mWh cm^-3. Notably, owing to the improved mechanical properties, FSCs can be woven into gloves and provide power for an electronic watch.