Hierarchically structured VO2@PPy core-shell nanowire arrays grown on carbon nanotube fibers as advanced cathodes for high-performance wearable asymmetric supercapacitors

摘要

Fiber-shaped asymmetric supercapacitors (FASCs) have emerged as intriguing energy storage devices for next-generation wearable electronics. However, the limited specific capacitances that arise from electrode materials severely restrict further enhancement of their energy densities. We successfully fabricated a hierarchically structured three-dimensional VO2@polypyrrole (VO2@PPy) core-shell nanowire array (NWA) on carbon nanotube fiber (CNTF) via a facile and cost-effective route. Such a composite structure not only enables a highly pseudo-capacitive VO2 core to provide a large surface area for reversible Faradic redox reactions, but also uses a highly conductive PPy shell to suppress the dissolution of VO2, thus making the hybrid fiber a new state of fibrous electrode with exceptional specific capacitance and rate behavior. To benefit from these superior features, we assembled a high-performance FASC with an operating voltage of 1.8 V and achieved a remarkable specific capacitance of 60.6 F/cm(3) and an extraordinary energy density up to 29.3 mWh/cm(3) at a current density of 0.25 A/cm(3). In addition, the FASC device exhibited excellent flexibility; its capacitance retention remained at 88.9% after bending 4000 times. Thus, these findings should help to develop advanced VO2-based cathodes for next-generation wearable energy storage devices. (C) 2018 Elsevier Ltd. All rights reserved.