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

The optical and electrochemical properties of thin films of a nickel-vanadi um mixed oxide have been investigated as a new Li+ intercalation compound, to be used as an optically passive counterelectrode in electrochromic switc hing devices. The thin film samples were prepared by radio frequency (RF) s puttering under different preparation conditions, using targets with differ ent Ni/V ratios and a reactive (20% O-2) or, alternatively, non-reactive (p ure Ar) sputtering atmosphere. The optical properties of as-grown and Lit i nserted-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 voltammet ry, 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 durin g the electrochemical experiments. (C) 2001 Elsevier Science Ltd. All right s reserved.