Gel electrolyte candidates for electrochromic devices (ECDs)

A comparison of key parameters of seven different gel electrolytes for use in electrochromic devices (ECD) is reported. The ionic conductivity, transmittance, and stability of the gel electrolytes are important considerations for smart window applications. The gel electrolytes were prepared by combining polymethylmethacrylate (PMMA) with a salt and a solvent combination. Two different salts, lithium perchlorate (LiClO4) and trifluorosulfonimide (LiN(CF3SO2)2), and three solvent combinations, acetonitrile and propylene carbonate (ACN and PC), ethylene carbonate and propylene carbonate (EC and PC), and Gamma-butyrolactone and propylene carbonate (GBL and PC) were investigated. Results show that gel electrolytes composed of a LiClO4 and GBL+PC combination and a LiClO4 and EC+PC combination are the best candidates for a smart window device based on its high conductivity over time and various temperatures, as well as its electrochemical stability and high transmittance.