Ion-polymer and ion-ion interaction in PEO-based polymer electrolytes having complexing salt LiClO4 and/or ionic liquid, [BMIM][PF 6]

Abstract

Ion-polymer and ion-ion association in polymer electrolyte films of PEO complexed with salt LiClO4, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) and (LiClO4 + BMIMPF 6) have been studied by laser Raman spectroscopy. The cations (Li+ and/or BMIM+) of the dopant salt/IL are shown to complex with the ether oxygen of the polymer backbone (i.e. C-O-C bond of PEO). The polymer-cation complexation results in the appearance of an additional peak at ∼1131 cm-1 apart from the C-O-C stretching vibrations of PEO at ∼1062 and 1141 cm-1. This peak due to polymer-cation complexation is relatively strong for LiClO4 than BMIMPF6, indicating stronger interaction for the former. In the PEO:LiClO4 and PEO:BMIMPF6 spectra, Raman peaks at 937 and 747 cm-1, respectively related to Li+· ClO and BMIM+· PF 'contact ion pairs', have also been observed as a result of ion-ion association. In the polymer electrolyte PEO:LiClO4 + BMIMPF 6 which contained two different anions, viz. ClO and PF, an interesting observation of the formation of 'cross contact ion pairs' viz. Li+· PF and BMIM+· ClO is also reported. Copyright © 2011 John Wiley & Sons, Ltd.