Films of Ce-Zr mixed oxide were produced by sol-gel and r.f. sputtering. These films can be used as 'passive' counter-electrodes in electrochromic smart windows because they retain their full transparency in both the oxidised and reduced state. Li intercalation was accomplished electrochemically using a liquid electrolyte. Electrochemical behaviour of the samples was found to be dependent on the heat treatment (sol-gel deposited film) and crystallite orientation (sputter deposited films). XRD analysis on sputter deposited films showed that the films are crystalline and grow following the orientation of the underlying tin doped indium oxide (ITO) film. Films of Ce-Zr mixed oxide lacking in (111) crystallite orientation show continuous evolution of the voltammograms and reach a maximum value for the cycled charge only after a large number of cycles. The lithium diffusion coefficient, calculated from GITT measurements. is in the range 10(-12)-10(-14) cm(2) s(-1) for sputter deposited films and becomes as low as 10(-15) cm(2) s(-1) for sol-gel deposited films. Optical constants of the thin films were calculated from reflectance and transmittance spectra, Refractive index values are in the range of 2.15-2.30 at lambda = 633 mn depending on the deposition method. A sharp absorption edge at about 320 nm is seen in accordance with CeO2 optical properties.