Abstract

In this work, a series of VO2(B) samples were synthesized via a hydrothermal process by reducing V2O5 with different concentrations of oxalic acid. The prepared samples were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, and galvanostatic charge–discharge. Furthermore, the microdefects of VO2 samples were characterized by positron lifetime spectroscopy. The results revealed that VO2(B) was successfully prepared and the concentration of reducing agent had a certain influence on the microstructures and properties. The electrochemical performance measurements showed that all samples had good cycle stability in 2 mol/L KOH solution. The x = 1.50 sample displayed higher discharge capacitance of 149.5 F g−1 at 30 mA g−1 and the discharge capacitance remained about 67% even after 80 charge/discharge cycles. The positron lifetime spectra revealed that the main defects in VO2 samples were microvoids, and the defect concentration and size were affected by the C2H2O4 concentration.

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