ELECTROCHEMICAL PROPERTIES OF SOL-GEL DEPOSITED VANADIUM PENTOXIDE FILMS

Microstructure, electrochemical and optical properties of sol-gel depo sited vanadium pentoxide (V2O5) coatings were investigated. The films were deposited by spin coating on SnO2:F/glass and quartz substrates f rom a polymeric solution of V2O5 derived from vanadium tri(isopropoxid e)oxide. Process parameters were investigated for the deposition of V2 O5 films exhibiting high lithium insertion capability. Investigations were conducted by cyclic voltammetry, impedance analysis, optical spec troscopy, scanning: electron microscopy, X-ray diffraction and X-ray p hotoelectron spectroscopy. Structural investigations conducted by X-ra y diffraction showed that the films fired at temperatures below 350 de grees C were amorphous, whereas those fired at higher temperatures wer e slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was V2O5. The electrochemi cal behavior and structural changes were investigated in 1 M LiClO4/pr opylene carbonate solution. The stability of V2O5 films upon cycling a nd switching between oxidized and reduced states was investigated by c yclic voltammetry, and in-situ spectroelectrochemistry. Cyclic voltamm etric measurements showed that V2O5 films exhibit good electrochemical cycling reversibility. In-situ optical measurement revealed that thes e films exhibit an electrochromic effect in the spectral range 300 nm < lambda < 2400 nm and change color between light yellow and light bro wn. The change in visible transmittance was 28% for 210 nm thick elect rodes. XPS spectra indicate that V5+ is reduced to a lower valance sta te V4+ in a colored state with injected Li+. The bronze coloration is due to a simultaneous injection of electrons and Li+ ions into V2O5. T he sol-gel deposited V2O5 films are useful for transparent counter ele ctrodes in electrochromic devices. (C) 1997 Elsevier Science S.A.