Designing of surface-tailored vanadium oxide nanoparticles for high-performance Li-ion supercapacitors

V₂O₅ has immense potential as an efficient electrode material for pseudo-capacitors due to availability of multiple oxidation states, layered structure, and natural abundance. However, bulk V₂O₅ suffers from sluggish kinetics and poor electronic conductivity, which restricts its electrochemical performance. In this work, we have tailored V₂O₅ nanoparticles (NVO) from commercial V₂O₅ via a controlled chemical reduction strategy using oxalic acid. By systematically varying the oxalic acid concentration, we identified that 1:2 molar ratio of V₂O₅ and oxalic acid as optimal, which produced uniform nanostructures with abundant surface oxygen defects. The synthesized NVO exhibits a remarkable specific capacitance of 432 F/g at 5 mv/s and excellent cycling stability, retaining 86.7% of its capacitance with superior cyclability. The presence of oxygen vacancies, particularly near bridging oxygen sites, promotes facile Li⁺ transport into the interior structure, thereby enhancing rate capability and conductivity. A two-electrode device assembled with the optimized NVO delivered energy density of 15 Wh/kg and power density of 2397.6 W/kg. These results highlight that oxalic acid-engineered V₂O₅ nanoparticles are a promising contender for next-generation energy storage solutions such as Li-ion supercapacitors.