V₂O₅ embedded in vertically aligned carbon nanotube arrays as free-standing electrodes for flexible supercapacitors

Free-standing, three-dimensional (3D) V₂O₅ nanobelts coated with poly(3,4-ethylenedioxythiophene) (PEDOT) on vertically aligned CNTs (VA-CNTs)/graphene foam (GF) (PEDOT-V₂O₅-VA-CNTs/GF) are constructed for flexible energy storage devices. The well-aligned structure of VA-CNTs and light-weight, highly conductive GF lead to highly efficient ionic and electronic transport channels, which are of scientific and practical significance for energy storage/conversion applications. PEDOT-V₂O₅-VA-CNTs/GF delivers a specific capacitance of 1016 F g^-1 at a current density of 1 A g^-1 when tested in an aqueous electrolyte. All-solid-state asymmetric supercapacitor devices have been fabricated to demonstrate its flexibility in charging and discharging. Polypyrrole (PPy)/VA-CNTs/GF was used as the negative electrode, PEDOT-V₂O₅-VA-CNTs/GF as the positive electrode, and PVA/LiNO₃ as the solid electrolyte. The solid-state flexible supercapacitors exhibit a high specific capacitance of 48.83 F g^-1 at 1 A g^-1 and an energy density of 17.34 W h kg^-1 at a power density of 0.71 kW kg^-1 with good cycle stability as well. This work highlights the advantages of the VA-CNTs/GF substrate in the hybrid electrode with V₂O₅ embedded among the VA-CNT interstitials for high-performance flexible energy storage devices.