Electrochemical and optical characterization of RF-sputtered thin films of vanadium-nickel mixed oxides

The optical and electrochemical properties of thin films of a nickel-vanadium mixed oxide have been investigated as a new Li+ intercalation compound, to be used as an optically passive counterelectrode in electrochromic switching devices. The thin film samples were prepared by radio frequency (RF) sputtering under different preparation conditions, using targets with different Ni/V ratios and a reactive (20% O-2) or, alternatively, non-reactive (pure Ar) sputtering atmosphere. The optical properties of as-grown and Lit inserted-extracted electrodes were determined by computer fitting of the UV-Vis-NIR transmittance and specular reflectance spectra. The electrochemical measurements of Li+ insertion and extraction consisted of cyclic voltammetry, chronopotentiometry and potentiostatic intermittent titration technique. The samples showed interesting electrochemical and optical properties, a good electrochemical reversibility and ion-storage capacity exceeding 40 mC cm (-2), lasting for several hundreds cycles at a current of 50 muA cm (-2). The electrodes displayed an almost passive electrochromic behavior during the electrochemical experiments. (C) 2001 Elsevier Science Ltd. All rights reserved.