Flexible all-solid-state micro-supercapacitor based on Ni fiber electrode coated with MnO 2 and reduced graphene oxide via electrochemical deposition

Flexible and micro-sized energy conversion/storage components are extremely demanding in portable and multifunctional electronic devices, especially those small, flexible, roll-up and even wearable ones. Here in this paper, a two-step electrochemical deposition method has been developed to coat Ni fibers with reduced graphene oxide and MnO2 subsequently, giving rise to Ni@reduced-graphene-oxide@MnO2 sheath-core flexible electrode with a high areal specific capacitance of 119.4 mF cm−2 at a current density of 0.5 mA cm−2 in 1 mol L−1 Na2SO4 electrolyte. Using polyvinyl alcohol (PVA)-LiCl as a solid state electrolyte, two Ni@reduced-graphene-oxide@MnO2 flexible electrodes were assembled into a freestanding, lightweight, symmetrical fiber-shaped micro-supercapacitor device with a maximum areal capacitance of26.9 mF cm−2. A high power density of 0.1 W cm−3 could be obtained when the energy density was as high as 0.27 mW h cm−3. Moreover, the resulting micro-supercapacitor device also demonstrated good flexibility and high cyclic stability. The present work provides a simple, facile and low-cost method for the fabrication of flexible, lightweight and wearable energy conversion/storage micro-devices with a high-performance.