Life-cycle design of polyimide-based composite porous fibers and the energy storage performance of their activated derived porous carbons

Life-cycle PI porous fibers: in-service reinforcement and end-of-life upcycling. • In situ PAN-to-panof forms a rigid network that stabilizes porous PI skeletons. • CNT bridge cracks, boosting strength, hydrophobicity, and flame resistance. • KOH-activated PPC-K optimizes porosity, N/O sites, and charge transport for high C. • Symmetric supercapacitors deliver high capacitance retention over 10,000 cycles. High-temperature protective and lightweight insulating fibers are important for fire safety, extreme thermal protection, and advanced functional textiles. However, highly porous fibers generally suffer from pore-wall collapse, thermal shrinkage, insufficient mechanical support, and limited recycling routes after service. To address these issues, a full-life-cycle design strategy was proposed for polyimide (PI)-based porous fibers synergistically reinforced by polyacrylonitrile (PAN) and carbon nanotubes (CNTs). PI-based porous fibers were fabricated through wet spinning, phase separation, freeze-drying, and thermal imidization, and were further converted into PI-derived carbons by carbonization and KOH activation for supercapacitors. The ladder-like network formed from PAN after heat treatment (panof, a product of PAN pre-oxidation) and the CNT bridging structure jointly constructed a multiscale reinforced framework, endowing the PI/panof/CNT fibers with high tensile strength (22.8 MPa), strong hydrophobicity (water contact angle of 159.0°), and excellent flame retardancy (LOI = 55.2%). Moreover, the precursor structure showed a clear inheritance effect after carbonization/activation. The carbon derived from PI/panof fibers (PPC-K) achieved a favorable balance between pore structure and surface chemistry, with a specific surface area of 880.14 m 2  g −1 and a capacitance of 263.17 F g −1 at 0.5 A g −1 in a three-electrode system. Its symmetric coin-cell supercapacitor retained 91.67% capacitance after 10,000 cycles at 3 A g −1 . This work provides an integrated route from porous-fiber reinforcement to end-of-life conversion into energy-storage materials. Download: Download high-res image (551KB) Download: Download full-size image