Thin films of vanadium oxide grown on vanadium metal: oxidation conditions to produce V2O5 films for Li-intercalation applications and characterisation by XPS, AFM, RBS/NRA

Abstract

Thin films of vanadium oxide were grown on vanadium metal surfaces (i) in air at ambient conditions, (ii) in 5 mM H2SO4 (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10−5 mbar) at temperatures between 350 and 550 °C and (iv) at near-atmospheric oxygen pressure (750 mbar) at 500 °C. The oxide films were investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed of V2O3. In air and in aqueous solution at RT, the oxide films are ultra-thin and hydroxylated. At 500 °C, nearly atmospheric oxygen pressure is required to form crystalline V2O5 films. The oxide films grown at pO2 = 750 mbar for 5 min are about 260-nm thick, and consist of a 115-nm outer layer of crystalline V2O5. The inner oxide is mainly composed of VO2. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 °C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well-crystallized V2O5 film, formed by oxidation for 5 min at 500 °C and 750 mbar O2, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright © 2005 John Wiley & Sons, Ltd.