The lifetime of the electrochromism of the W0,-TiO, films prepared by vacuum evaporation is found to exceed that of WO, films by a factor of five. X-ray difiactioo has revealed that the crystal structure of W0,-TiO, films stays amorphous, while crystalline compounds are formed in amorphous WO, films after colouring and bleaching. W0,-TiO, films stay amorphous after they are annealed at 40O0C, although WO, films crystallize. SIMS and XPS analyses have revealed that half the amount of lithium injected during a colouring cycle is stored as 0-Li bonds in the bleached film. In W0,-TiO, films the number of bonds such as W-OH and W=O in which lithium ions accumulate is reduced. We conclude that the lifetime of the electrochromism is prolonged for amorphous W0,-TiO, films, because lithium does not accumulate and the W0,-TIO, films stay amorphous.