Thin Film Counterelectrodes with High Li Charge Capacity for Electrochromic Windows

 Ce-V mixed oxide films have been deposited by RF sputtering with the aim of increasing the Li charge capacity of counter electrodes in smart windows. Such mixed oxides have shown high transmittance and optical passivity in the visible region. After electrode pre-conditioning by cyclic voltammetry, a good electrochemical reversibility in LiClO₄– propylene carbonate electrolyte was observed, and large Li-charge capacity under galvanostatic charging (up to 50 mCċcm⁻²) has been measured. The electrode charge capacity decreased after prolonged insertion-deinsertion cycles, whereas the photoptic transmittance remained about constant. After 800 cycles the Li-charge capacity decreased to 40 mCċcm⁻². The Li diffusion coefficient inside the films measured by electrochemical impedance and by galvanostatic titration ranged from 10⁻¹¹ cm²ċs⁻¹ to 10⁻¹³cm²ċs⁻¹. We observed that the Li charge capacity of the film electrodes is a function of the film deposition conditions, because it increased with the vanadium oxide concentration in the target and with the oxygen content in the sputtering atmosphere.