Microfluidic regulation of graphene/MXene fiber architecture for high-performance fiber-shaped supercapacitors

Contraction–sudden-expansion flow regulates GO/MXene nanosheet assembly. • RGO3# combines preferential alignment with locally less compact stacking. • RGO3# achieves 270 MPa strength and 346 S cm −1 conductivity. • 5 wt% MXene boosts conductivity to 548 S cm −1 and capacitance to 650 F cm −3 . • The device delivers 361.1 mWh cm −3 with 96.09% retention after 15,000 cycles. The rapid development of flexible wearable devices has stimulated growing interest in graphene-fiber-based flexible supercapacitors for wearable electronics. Nevertheless, conventional wet spinning provides limited control over nanosheet orientation and local stacking, and subsequent coagulation and reduction can induce compact face-to-face restacking, restricting ion accessibility while limiting the simultaneous optimization of mechanical, electrical, and electrochemical properties. As a result, fiber-shaped supercapacitors assembled from these fibers often exhibit unsatisfactory energy density and are unable to meet the performance requirements of smart textiles. In this work, three gradient contraction–expansion microfluidic spinning channels were designed based on microfluidic wet-spinning technology. Graphene composite fibers were fabricated from graphene oxide (GO) and GO/nanosized titanium carbide (MXene) composite spinning dopes, and finite-element simulations were carried out to evaluate the shear and extensional flow fields within the microchannels. The influence of microchannel geometry on fiber microstructure, mechanical properties, electrical conductivity, and electrochemical performance was systematically investigated. The contraction–expansion channel enabled the graphene nanosheets to retain an overall preferentially aligned framework while locally disrupting compact face-to-face stacking through flow-induced nanosheet rearrangement, thereby favoring the formation of intersheet voids and mesoporous ion-transport pathways. The resulting reduced graphene oxide (RGO) fiber exhibited a WAXS-derived orientation degree of 0.64, a tensile strength of 270 MPa, and an electrical conductivity of 346 S cm −1 . This globally ordered yet locally porous architecture provides continuous pathways for electron transport while improving electrolyte accessibility and ion transport within the fiber. After incorporating only 5 wt% MXene, the electrical conductivity of the MXene/RGO composite fiber further increased to 548 S cm −1 . The symmetric supercapacitor assembled from this composite fiber delivered a volumetric capacitance of 650 F cm −3 at a current density of 0.1 A cm −3 , together with an energy density of 361.1 mWh cm −3 and a power density of 100 mW cm −3 . This study demonstrates a microfluidic structural-regulation strategy for constructing graphene-based energy-storage fibers with coexisting preferential nanosheet alignment and locally porous ion-transport domains, providing useful guidance for flexible wearable energy-storage devices.