Highly flexible all-solid-state cable-type supercapacitors based on Cu/reduced graphene oxide/manganese dioxide fibers

Abstract

Highly flexible all-solid-state cable-type supercapacitors based on Cu/reduced graphene oxide/manganese dioxide fibers (Cu/RGO/MnO₂) were successfully assembled by closely placing two Cu/RGO/MnO₂ fibers in a parallel direction and using PVA–KOH gel electrolyte, in which the Cu/RGO/MnO₂ fiber electrode, possessing good flexibility, excellent electrochemical properties, and high electrical conductivity was prepared by heating a glass pipeline filled with a Cu wire and a graphene oxide homogenous suspension at 230 °C for 2.5 h. The Cu/reduced graphene fiber was then refluxed in KMnO₄ solution at 70 °C for 120 min. As well as being used as a current collector, the Cu wire also served as the matrix for depositing active materials and improving the fiber flexibility, causing a high-quality interfacial contact between the current collector and the active materials. The optimized all-solid-state Cu/RGO/MnO_2(6.0) fiber supercapacitor showed a high specific capacitance of 140 mF cm⁻² at a current density of 0.1 mA cm⁻², enhanced capacitance retention of 97% after 500 bending cycles with a big angle of 120°, and relatively good stability (88% of initial capacitance values after 5000 cycles). Moreover, aside from its excellent electrochemical performance, it could light a LED lamp when connected with a battery, indicating that the assembled Cu/RGO/MnO₂ fiber supercapacitor could be used not only as an energy storage device, but also an electrical conduction cable, which could have a significant impact on future energy storage applications.