Lithium solvation in a PMMA membrane plasticized by a lithium-conducting ionic liquid based on 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

The Raman and Infrared (IR) spectra of poly(methyl methacrylate) (PMMA) membranes plasticized by ionic liquids of the (1-x)[1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)],xLiTFSI type, where BMI+ is the 1-butyl-3-methylimidazolium cation and TFSI- the bis(trifluoromethanesulfonyl)imide anion, are analyzed for a lithium bis(trifluoromethane sulfone)imide (LiTFSI) mole fraction x = 0.23 and PMMA contents from 0 to 50 wt%. The lithium is found to have an average coordination of about three C=O groups and less than one TFSI- anion. It plays the role of a cross-linker between the ester groups of PMMA and the nonvolatile ionic liquid. Addition of PMMA to the (1 - x)(BMITFSI),xLiTFSI ionic liquid lowers the conductivity but might improve the lithium transference number by transforming the [Li(TFSI)(2)](-) anionic clusters present in the pure ionic liquid into a mixed coordination by ester groups and TFSI- anions. Copyright (c) 2008 John Wiley & Sons, Ltd.