The durability problem of electrochromic devices (ECD) in Li ion-conducting electrolytes may be due to the degradation of the ECD electrode matrix and irreversibly reacting Li ions during cycling. With this hypothesis, we investigated the performance Of WO3 film with an inorganic solid electrolyte, lithium phosphorous oxynitride (UPON), protective layer and of the ECD composed Of WO3 and V2O5 with a UPON protective layer prepared by RF magnetron sputtering. WO3 and ECD (glass/ITO/V2O5/LiPON/electrolyte/LiPON/WO3/ ITO/glass) with a protective layer not only showed improved durability with continuous potential cycling, but also demonstrated a good memory effect under voltage-off, good response times and high coloration efficiency (CE). Our results demonstrated that UPON layers are electrochemically stable, enhance the electrochromic properties in Li ion-conducting electrolytes, and can be used as a protective layer for ECD. (c) 2005 Elsevier B.V. All rights reserved.