Several technologies for energy saving and storage rely on ion exchange between electrodes and electrolytes. In amorphous electrode materials, detailed knowledge of Li-ion intercalation is hampered by limited information on the structure and transport properties of the materials.Amorphous tungsten oxide is the most studied electrochromic material and suffers from iontrapping-induced degradation of charge capacity and optical modulation span upon extensive electrochemical cycling. In this paper, we investigate trapping and de-trapping processes in connection with performance degradation and specifically use real-time electro-optical monitoring to identify different trap energy ranges pertinent to the ion-intercalated system. Evidence is presented for three kinds of traps which degrade electrochromic tungsten oxide during ion intercalation: (i) shallow traps which erode the colored state, (ii) deep traps which lower the bleached-state transmittance, and (iii) irreversible traps. Importantly, Li-ion detrapping from shallow and deep traps takes place by different processes: continuous Li-ion extraction is possible from shallow traps, whereas a certain release time must be exceeded for de-trapping from deep traps. Our notions for ion trapping and de-trapping, presented here, may serve as a starting point for discussing ion intercalation in various amorphous materials of interest for energy-related applications.

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