Soft matter electrolytes based on polymethylmetacrylate dispersions in lithium bis(trifluoromethanesulfonyl)imide/1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids

Ion transport in a polymer–ionic liquid (IL) soft matter composite electrolyte is discussed here in detail in the context of polymer–ionic liquid interaction and glass transition temperature. The dispersion of polymethylmetacrylate (PMMA) in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) resulted in transparent composite electrolytes with a “jelly-like” consistency. The composite ionic conductivity measured over the range −30 °C to 60 °C was always lower than that of the neat BMITFSI/BMIPF6 and LiTFSI-BMITFSI/LiTFSI-BMIPF6 electrolytes but still very high (>1 mS/cm at 25 °C up to 50 wt% PMMA). While addition of LiTFSI to IL does not influence the glass Tg and Tm melting temperature significantly, dispersion of PMMA (especially at higher contents) resulted in increase in Tg and disappearance of Tm. In general, the profile of temperature-dependent ionic conductivity could be fitted to Vogel–Tamman–Fulcher (VTF) suggesting a solvent assisted ion transport. However, for higher PMMA concentration sharp demarcation of temperature regimes between thermally activated and solvent assisted ion transport were observed with the glass transition temperature acting as the reference point for transformation from one form of transport mechanism to the other. Because of the beneficial physico-chemical properties and interesting ion transport mechanism, we envisage the present soft matter electrolytes to be promising for application in electrochromic devices