Tailor-made polymer electrolytes based upon ionic liquids and their application in all-plastic electrochromic devices

A new type of tailor-made polymer electrolyte based on ionic liquids (ILs) and polymeric ionic liquids (PILs) analogues has been prepared by mixing 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonimide) [bmim][Tf2N], 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] and 1-butyl-3-methylimidazolium bromide [bmim][Br], with poly[1-vinyl-ethyl-imidazolium] bearing similar counter-anions [Tf2N], [BF4] and [Br]. The chemical affinity between PILs and ILs affords a completely compatible combination resulting in stable polymer electrolytes. The ionic conductivity of all these polymer electrolytes varies between 10−2 and 10−5 S cm−1 at room temperature, and shows high values of conductivity with increasing ionic liquid content. Finally, we have demonstrated that cycle life of electrochromic devices (ECDs) is significantly enhanced (up to 70,000 cycles) when this new type of tailor-made polymer electrolyte was used in PEDOT/electrolyte/PEDOT devices as compared to previously used poly(ethylene oxide) electrolytes.