Di-ureasil xerogels containing lithium bis(trifluoromethanesulfonyl)imide for application in solid-state electrochromic devices

In this study we report the characterization of a prototype solid-state electrochromic device based on poly(ethylene oxide) (PEO)/siloxane hybrid networks doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymer networks prepared. designated as di-ureasils and represented as d-U(2000), were produced by a sol-gel procedure and are composed of a siliceous framework to which both ends of polyether chains containing about 40 -CH2CH2O- units are covalently bonded through urea linkages. Samples with compositions of 200 >= n >= 0.5 (where n is the molar ratio of -CH2CH2O- to Li+) were characterized by thermal analysis, complex impedance measurements and cyclic voltammetry at a gold microelectrode. Electrolyte samples were obtained as self-supporting, transparent, amorphous films and at room temperature the highest conductivity was observed with the d-U(2000)(35)LiTFSI composition (3.2 x 10(-5) Omega(-1) cm(-1)). We report the results of preliminary evaluation of these polymer electrolytes as multi-functional components in prototype electrochromic displays. Device performance parameters such as coloration efficiency, optical contrast and image stability were also evaluated. The electrolytes with n > 8 presented an optical density above 0.56 and display assemblies exhibited good open-circuit memory and stable electrochromic performances. (c) 2008 Elsevier Ltd. All rights reserved.