Ions Transport Control in Electrochromic WO3 Film for the Cyclic Stability Study

As a promising electrochromic material, WO3 frequently suffers from the cyclic degradation caused by trapped ions in the host structure. The intrinsic trapped sites in WO3 host structure usually are considered as the main contribution to the formation of trapped ions. In this study, by chronopotentiometry technology to quantify the diffused ions, we find that ions transport behavior plays a key role in the structural stability and the generation of trapped ions. Specifically, repeated insertion/extraction behavior will result in WO3 structure damage. As a result, the ions transport shows hysteretic kinetics in the subsequent reaction process, and the inserted Li+ ions in the coloration process can not be completely extracted, which contributes to the generation of the majority of trapped ions in film. Subsequently, the transmittance of the bleaching state and the optical modulation ability of WO3 film show serious decay. This work exhibits a new understanding of the degradation of electrochromic materials and offers an efficient method for WO3 to maintain a long-life performance. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.