V2O5-TiO2 films as ion storage layers were proposed for electrochromic windows (ECWs) based on poly(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine). V2O5-TiO2 (V/Ti=70/30) films were fabricated by a sol-gel electrodeposition technique. The films were investigated by X-ray diffraction, a scanning probe microscope, and impedance spectroscopy. The cycling behaviors of the films were studied using cyclic voltammetry (CV) in 0.1 M LiClO4/propylene carbonate solution. Electrochromism of the films upon Li+ intercalation was investigated by transmittance measurements during the CV process. The V2O5-TiO2 film-based ECW was successfully processed and studied. The ECW exhibited its high electrochromic contrast, rapid switching speed, and long-term cyclic stability. Its contrast (Delta%T=T-max-T-min) was 68%T with a minimum transmittance, T-min=1%, at 580 nm wavelength. The ECW took 5 s to reach a fully colored state from a fully bleached state. It took 4 s to go to a fully bleached state. The asymmetry of coloring and bleaching time was explained by modeling the ECW as a simple equivalent circuit. The cyclic durability of the ECW was tested over 150,000 cycles. It revealed the contrast degradation of only 2% at 580 nm wavelength.