Fe-containing CeVO4 films as Li intercalation transparent counter-electrodes

Iron containing CeVO4 films were prepared using the sol-gel method. The crystalline structure of powders and films with Fe/Ce/V ratios of 0.1:1:1, 0.3:1:1 and 0.5:1:1 were investigated by X-ray diffraction (XRD) and infrared (IR) spectroscopy. XRD revealed the predominance of a CeVO4-W (wakefieldite) crystalline phase with a small amount of monoclinic CeVO4, CeO2 and Fe2O3. Ex situ IR absorbance spectra of charged and discharged films show the changes in intensity of the V-O stretching mode at 770 cm(-1). Cyclic voltammetry showed that Li+ intercalation occurs in three steps with total capacities of 22 mC cm(-2) (Fe/Ce = 0.1), 32 mC cm(-2) (Fe/Ce = 0.3) and 37 mC cm (-2) (Fe/Ce = 0.5). The increase in the overall charge capacity with increasing Fe content is accompanied by a loss of capacity with cycling. The lithium diffusion coefficient: calculated by the galvanostatic intermittent titration method (GITT), the potentiostatic intermittent titration method (PITT) and electrochemical impedance spectroscopy (EIS), ranges from 10(-12) to 10(-14) cm(2) s(-1). UV-vis in situ transmittance spectra showed that these films are highly transparent with a photopic transmittance T-Vis similar to 0.85 for intercalated and deintercalated states. This suggests that Fe/Ce/V oxide films are good candidates for optically passive counter-electrodes in electrochromic (EC) devices. (C) 2001 Elsevier Science Ltd. All rights reserved.