Electrochemical properties of sol-gel deposited vanadium pentoxide films

Abstract

Microstructure, electrochemical and optical properties of sol-gel deposited vanadium pentoxide (V 2O 5) coatings were investigated. The films were deposited by spin coating on SnO 2:F/glass and quartz substrates from a polymeric solution of V 2O 5 derived from vanadium tri(isopropoxide)oxide. Process parameters were investigated for the deposition of V 2O 5 films exhititing high lithium insertion capability. Investigations were conducted by cyclic voltammetry, impedance analysis, optical spectroscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Structural investigations conducted by X-ray diffraction showed that the films fired at temperatures below 350 °C were amorphous, whereas those fired at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was V 2O 5. The electrochemical behavior and structural changes were investigated in 1 M LiClO4/propylene carbonate solution. The stability of V 2O 5 films upon cycling and switching between oxidized and reduced states was investigated by cyclic voltammetry, and in-situ spectroelectrochemistry. Cyclic voltammetric measurements showed that V 2O 5 films exhibit good electrochemical cycling reversibility. In-situ optical measurement revealed that these films exhibit an electrochromic effect in the spectral range 300 nm < λ < 2400 nm and change color between light yellow and light brown. The change in visible transmittance was 28% for 210 nm thick electrodes. XPS spectra indicate that V 5+ is reduced to a lower valance state V 4+ in a colored state with injected Li +. The bronze coloration is due to a simultaneous injection of electrons and Li + ions into V 2O 5. The sol-gel deposited V 2O 5 films are useful for transparent counter electrodes in electrochromic devices.