Interconnected Vanadyl Pyrophosphate Nanonetworks as a Flexible Electrode for High-Voltage and Long-Life Li-Ion Supercapacitors

Engineering vanadium-based materials with high conductivity, superior redox performance, and high operating voltage has attracted widespread attention in energy storage devices. Herein, we demonstrated a simple and feasible phosphorization technique to design three-dimensional (3D) network-like vanadyl pyrophosphate ((VO)₂P₂O₇) nanowires on flexible carbon cloth (CC) (VP-CC). The phosphorization process enabled the VP-CC to increase the electronic conductivity, and the interconnected nano-network of VP-CC opens pathways for fast charge storage during the energy storage processes. Specifically, the 3D VP-CC electrodes and LiClO₄ electrolyte designed as a Li-ion supercapacitor (LSC) demonstrate a maximum operating window of 2.0 V with a superior energy density (E_d) of 96 μWh cm^-2, power density (P_d) of 10,028 μW cm^-2, and outstanding cycling retention (98%) even after 10,000 cycles. In addition, a flexible LSC assembled utilizing VP-CC electrodes with a PVA/Li-based solid-state gel electrolyte exhibits a high capacitance value of 137 mF cm^-2 and excellent cycling durability (86%) with a high E_d of 27 μWh cm^-2 and P_d of 7237 μW cm^-2. Considering excellent energy storage features, the highly conductive vanadium-based material has been utilized as an ideal electrode for various flexible/wearable energy storage devices with superior performance.