FTIR investigations on ion-ion interactions in liquid and gel polymeric electrolytes:: LiCF3SO3-PC-PMMA

FTIR spectroscopy and ionic conductivity measurements have been employed to study the solvation and conduction mechanism of lithium ions in aprotic liquid electrolytes of LiCF3SO3-PC (lithium trifluromethanesulfonate-propylene carbonate) and gel electrolytes containing poly(methylmethacrylate) (PMMA) additionally. Cation solvation occurs via interactions between Li+ ions with the ring oxygens as well as the carbonyl oxygen of PC molecules over the entire salt concentration range under investigation (0.025-2 M) for both liquid and gel electrolytes. The ionic conductivity decline for concentrations greater than or equal to0.8 M LiCF3SO3-PC is attributed to the formation of ion pairs and/or triplets. Presence of (a) free CF3SO3- ions in 0.025 and 0.05 molar LiCF3SO3-PC solutions, (b) the LiCF3SO3 structure with a monodentate coordinated lithium ion for concentrations greater than or equal to0.5 molar LiCF3SO3-PC systems and (c) ion triplets comprising two cations and an anion with a bidentate bridging structure in 2 M LiCF3SO3-PC electrolytes, has been established. Ionic conductivity performance concurs with our infrared results. Gel electrolytes containing upto 15 wt% of PMMA have been found to exhibit liquid like behavior but 2 M LiCF3SO3-PC systems that incorporate 25 wt% of polymer show a distinct Li+-O=C (of PMMA) interaction which is unambiguously determined from the remarkable changes observed for the nu(s)C=O) and nu(s)(SO3)-the symmetric stretching vibrational modes. (C) 2002 Kluwer Academic Publishers.