Introducing a redox-active ferrocenyl moiety onto a polythiophene derivative towards high-performance flexible all-solid-state symmetric supercapacitors

A new design strategy of introducing redox-active metal-organic fragments onto the backbone of conductive polymers is proposed in this article towards conductive metallopolymers for flexible all-solid-state supercapacitor applications. Porous carbonaceous materials of high surface area act not only as the current collector but also as the substrate for potentiostatic electropolymerization. The as-prepared electrodes combine the advantages of pseudocapacitor electrode materials from metal-organic compounds and conductive polymers as well as electrical double-layer capacitor electrode materials from carbon fibers without involving composite formation. Moreover, the metallopolymer-coated carbonaceous electrodes are free-standing and binder-free, exhibiting splendid morphologies with cauliflower-like units consisting of open-top spheres at the micrometer scale. The controllable electrode preparation method together with the morphological study reveals the process of polymer growth responding to the imposed voltage. The highest areal specific capacitance of 2.97 F cm⁻² for the metallopolymer-coated carbonaceous electrodes surpasses those for almost all the flexible and binder-free supercapacitor electrodes reported so far. Two all-solid-state symmetric supercapacitor devices were assembled, and the flexible one exhibited ultrahigh capacitance (1.35 F cm⁻²), extraordinary cycling performance (88% retention after 15 000 cycles) and excellent mechanical stability. Moreover, both maximum energy densities (over 0.37 mW h cm⁻²) and maximum power densities (22.4 mW cm⁻²) of the devices are superior to those of all flexible all-solid-state symmetric devices in the literature and these values also stand out among the non-flexible ones.