Lithium trapping at excess oxygen in sputter-deposited a-WO3 films

The initial stages of electrochemical intercalation of lithium in sputter-deposited tungsten oxide thin films were studied. The as-deposited films show a substantial irreversible uptake of lithium without an electrochromic effect. This trapping of lithium is associated with the presence of excess oxygen in the film. The experimental results are consistent with a reaction of lithium and interstitial oxygen to form a neutral Li-2-O-i complex. Our findings are relevant for the manufacture of electrochromic devices, and the electrochemical titration method used may be applied to probe excess oxygen in other oxidic films as well. (C) 1999 American Institute of Physics. [S0021-8979(99)06003-X].