Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems

Abstract The development of a flexible binder free electrode based on 3D vanadium dioxide (VO2) nano-architectures has materialized as an effective strategy for fabrication of advanced wearable, portable, and stretchable electronic devices. However, most of the stretchable energy storage devices based on VO2 suffer from a relatively low operating voltage, high weight, low specific capacitance, and thus low energy density. Here, a novel binder free supercapacitor electrode composed of hierarchical VO2 nanosheet arrays grown on porous carbon nanofibers (VO2@PCNFs) is designed using a simple hydrothermal method followed by annealing treatment. The electrochemical evaluation confirmed that the energy storage mechanism of the prepared VO2@PCNFs is based on the intercalation pseudocapacitance properties. The resulting VO2@PCNFs electrode displays a wide operation voltage (−1.0 to 1.1 V in three electrode systems), maximum specific capacitance of 778 F g−1 (at 1 A g–1), and excellent rate capability. Moreover, a novel all-solid-state asymmetric supercapacitor with good flexibility is assembled in a neutral Na2SO4− poly(vinyl alcohol) (Na2SO4/PVA) gel electrolyte using the VO2@PCNFs film as a positive electrode and PCNFs as a negative electrode. Due to the high capacitances and excellent rate performances of VO2@PCNFs and PCNFs, as well as the synergistic effects of the two electrodes, such asymmetric cell could be cycled reversibly in the voltage range of 0–1.7 V, and presents maximum energy density of 75.06 Wh kg−1, and excellent cycling durability, with 92.4% retaining in its specific capacitance even after 4000 cycles. These encouraging results confirm a great potential of our proposed electrode in developing energy storage devices based on VO2 electrode materials with superior performances for practical applications.