Stretchable PU@CNT/MXene Fiber Fabricated by External Tension for High Performance Strain Sensor and Supercapacitor

Abstract Fiber‐based electronic devices can be woven into textiles to provide comfort, durability, and integrated multi‐functionality, and will be widely used in the intelligent wearable field. Herein, by introducing elastic substrates and regulating the external tension during spinning to control the helical structure and optimize mechanical properties, multi‐functional Polyurethane@carbon nanotube (PU@CNT) stretchable fibers with high extensibility and flexibility is prepared for human motion detection and energy storage. A multi‐layered structure consisting of alternating MXene sheets and CNT films is also designed, to promote the relative resistance change of PU@CNT/MXene fibers to 212% (4 times than PU@CNT) when acting as strain sensors, whereas their volume specific capacitance reaches 196 F cm −3 (increases ≈50 times). Additionally, the capacitance of our stretchable fibers supercapacitors maintains at 91.4% and 86.2% when stretched statically (170% strain) or after hundreds of cycles (50% strain), respectively. It is proposed that MXene sheets can fill gaps between CNTs, resulting in more uniform distribution in fibers, which can improve strain sensitivity and long‐cycle capacitance retention. These PU@CNT/MXene fibers with unique multi‐layered hybrid structure and superior performance have potential applications in portable, wearable, and body‐integrated sensors and energy storage devices.