Synthesis and electrochemical characterization of crosslinked poly(ethylene oxide) containing LiN(CF3SO2)2

The ionic conductivity of polymeric electrolyte systems comprising a network of poly(ethylene oxide) (PEO) crosslinked with urethane functions and containing LiN(CF3SO2)(2) (TFSILi), was studied. Polyurethanes based on three different PEO molecular weights were prepared. Diffusion studies of TFSILi in swollen PEO-urethane membranes with acetonitrile were performed showing a diffusion coefficient for PEO2000 higher than that observed with LiClO4 in the same material, and were correlated with the variation of T-g's of the dried membranes which were determined as a function of salt concentration and crosslink density. The influence of a salt molecule on the T-g (for the TFSILi charged membranes) is equivalent to 25% of the influence of a covalent crosslink in the range of molecular weight between crosslinks used in this study. The relatively high slope for the plot T-g(-1) vs salt concentration for the network in PEO600 allows to consider a high chain rigidification due to the introduction of salt. The conductivity of network based on PEO2000 with a molar concentration ratio O/Li = 43 reached 10(-5) S cm(-1). (C) 1997 Elsevier Science Ltd.