Laser-induced gradient graphitization of polyimide on carbon fiber for structural supercapacitors

Carbon fibers (CFs) play a pivotal role in electrochemical/mechanical integrated technologies because of their concurrent high specific strength and excellent electrical conductivity. However, the inherently low specific surface area of CFs limits their charge storage capacity, hindering their commercialization in structural–electrochemical integrated systems. Therefore, the primary objective of modifying CF-based electrodes is to significantly enhance their electrochemical performance while preserving their intrinsic high mechanical properties. In this work, a laser-induced processing strategy, as an effective surface engineering tool, was used to optimize polyimide/activated carbon-coated CFs. This approach involves a gradient architecture consisting of a porous graphitized surface layer (shell) that transitions to a densely cross-linked subsurface region (core). This core-shell structure simultaneously enhanced the mechanical and electrical properties of the CF electrode. Moreover, we systematically investigated the laser processing parameters to break the trade-off between the dense protective layer and ion transport kinetics in the core and shell. Consequently, the modified CF electrode showed a 1.3-fold increase in tensile modulus and a 22.3-fold increase in specific capacitance, compared to the pristine counterpart.