High-energy and wearable fiber-shaped asymmetric supercapacitors based on the combination of fluorinated polyimide and Co₃O₄ on carbon fibers

This study reports a fiber-shaped asymmetric supercapacitor (f-ASC) made from carbonized fluorinated polyimide deposited onto carbon fiber (c-fPI@CF) as a negative electrode coupled with cobalt oxide-embedded c-fPI@CF (Co₃O₄@c-fPI@CF) as a positive electrode. The thermal decomposition of fPI evolves gases, mostly stemming from the fluorine-containing moiety (–CF₃) of fPI. This process leads to the formation of a distinct microporous structure characterized by small graphitic regions and a high specific surface area of 1071 m² g⁻¹. Asymmetric configuration enlarges the operating voltage of the f-ASC, contributing to the increase in energy density. The resulting f-ASC shows a capacitance of 56 F cm⁻³ at 0.5 A cm⁻³, exceeding other fiber supercapacitors and good cycle stability even under mechanical deformation, demonstrating its feasibility as a wearable power source. It also delivers a significant energy density of 10.0 mWh cm⁻³ and a power density of 1.16 W cm⁻³. According to first-principles calculations, the graphitic structure of c-fPI increases the conductivity of Co₃O₄@c-fPI and stabilizes the exposed metal spots of the Co₃O₄. Therefore, this f-ASC exhibits great potential for future wearable energy storage systems.