Polypyrrole-Assisted Nitrogen Doping Strategy to Boost Vanadium Dioxide Performance for Wearable Nonpolarity Supercapacitor and Aqueous Zinc-Ion Battery

Fiber-shaped energy-storage devices with high energy and power density are crucial for powering wearable electronics. However, the improvement of their energy and power density is limited by the low mass loading of active materials and slow diffusion of ions, which further hinders the application as flexible energy-storage devices. Herein, a facile and cost-effective strategy is proposed to fabricate polypyrrole (PPy)-assisted nitrogen-doped vanadium dioxide/nitrogen-doped carbon (N-VO2@NC) heterostructures by the pyrolyzation of vanadium oxide (VOx)/PPy supported on carbon nanotube fiber (CNTF). The carbonization of PPy nanowire not only forms nitrogen-doped carbon 3D conductive scaffold for enhancing ion transport pathways and mass loading of N-VO2 but also provides source of nitrogen in situ doping into VOx to produce N-VO2 for improving electronic conductivity and energy-storage capacity. Consequently, the well-designed N-VO2@NC@CNTF electrode delivers impressive electrochemical performance and extraordinary mechanical flexibility both applied in all-solid-state fiber-shaped nonpolarity supercapacitors and aqueous zinc-ion batteries. Furthermore, the results of theoretical calculations discovered that the band gap of PPy-assisted N-VO2 can be significantly reduced from 0.55 to 0.23 eV and thus its conductivity is greatly enhanced. This work sheds light on the construction of high-performance free-standing electrodes for next-generation wearable aqueous energy-storage devices.