3D Network VO Electrodes in a Gel Electrolyte for High-Voltage Wearable Symmetric Pseudocapacitors.

A 3D network composed of VO nanofibers was manufactured on a novel conductive printing paper [urea-LiClO-PVA (ULP) deep eutectic solvent gel-doped graphite/printing paper, U-paper] for use as electrodes linked with a ULP neutral gel electrolyte for 3D network VO wearable symmetric pseudocapacitors (WSSCs). The function of the ULP gel is not only that it can be doped into the conductive ink to decrease the resistance of the conductive printing paper but also that it increases the stability of VO-based electrodes. Moreover, 3D network VO WSSCs containing the ULP gel can support high operating voltages of 4.0 V with great specific capacitance (160 F/g) and offer a high energy density (355 W h/kg at 0.2 kW/kg). The 3D network VO WSSCs exhibit a superior cycling stability/durability after 5000 cycles (capacitance retention of ∼91%). Operando X-ray absorption spectroscopy experiments show the reversibility and pseudocapacitive properties of VO from the ULP gel and offer the information of the oxidation states of vanadium during charge-discharge cycles. The 3D network VO WSSCs with the ULP gel electrolyte show great potential prospective candidates for smarter 3D wearable energy-storage devices and Internet-of-Things applications.