Low-cost gel polymeric electrolytes for electrochromic applications

Solid-state ionic conductors embodying either protons or lithium ions are very attractive for large-area electrochromic (EC) devices. In this work, aiming at the preparation of a gel polymer electrolyte (GPE), two cheaper and non-toxic commercial resins are used: a urethane-based prepolymer (NOA65) and a vinyl acetate-based resin (MASTIFLEX). They are employed as host matrices to trap the liquid constituents, made of lithium perchlorate-propylene carbonate (LiClO4-PC). Thermogravimetric analyses indicate that both resins show excellent thermal performance. Several GPE formulations are investigated with respect to electrical and optical properties, varying the polymer-to-liquid ratio and LiClO4 concentration. The EC devices made with the two GPEs are also characterized in terms of optical contrast, switching kinetics and repetitive switching cycles. These activities made it possible to find the best formulations finally employed for the fabrication of 100 cm2 large area EC devices. The obtained results demonstrate that low-cost GPEs based on commercial polymers are electrochemically stable as ion-conducting media for EC devices.