PANI-Coated VO_x Nanobelts with Core-Shell Architecture for Flexible All-Solid-State Supercapacitor

As a typical pseudocapacitor material, VO_x possesses mixed valence states, making it an ideal electrode material for symmetric screen-printed supercapacitors. However, its high internal resistance and low energy density are the main hurdles to its widespread application. In this study, a two-dimensional PANI@VO_x nanobelt with a core-shell architecture was constructed via a two-step route. This strategy involves the preparation of VO_x using a solvothermal method, and a subsequent in situ polymerization process of the PANI. By virtue of the synergistic effect between the VO_x core and the PANI shell, the optimal VO_x@PANI has an enhanced conductivity of 0.7 ± 0.04 S/Ω, which can deliver a high specific capacitance of 347.5 F/g at 0.5 A/g, a decent cycling life of ~72.0%, and an outstanding Coulomb efficiency of ~100% after 5000 cycles at 5 A/g. Moreover, a flexible all-solid-state symmetric supercapacitor (VO_x@PANI SSC) with an in-planar interdigitated structure was screen-printed and assembled on a nickel current collector; it yielded a remarkable areal energy density of 115.17 μWh/cm² at an areal power density of 0.39 mW/cm², and possessed outstanding flexibility and mechanical performance. Notably, a "Xiaomi" hygrothermograph (3.0 V) was powered easily by tandem SSCs with an operating voltage of 3.1 V. Therefore, this advanced pseudocapacitor material with core-shell architecture opens novel ideas for flexible symmetric supercapacitors in powering portable/wearable products.