Ion-polymer and ion-ion interaction in PEO-based polymer electrolytes having complexing salt LiClO4 and/or ionic liquid, [BMIM][PF6]

• Published in: Journal of Raman spectroscopy 2011-12, Vol.42 (12), p.2168-2172
• Main Authors: Chaurasia, Sujeet K., Singh, Rajendra K., Chandra, S.
• Format: Article
• Language: English
• Subjects: ion pairing; polymer electrolyte; Raman spectra
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.2999

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 + BMIMPF6) 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 + BMIMPF6 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. Laser Raman technique has been used to study the complexation of polymer PEO with the cations of salt LiClO4/ionic liquid BMIMPF6. The formation of contact ion pairs (Li+· ClO and BMIM+· PF) and cross‐contact ion pairs(Li+· PF and BMIM+· ClO) in this polymer electrolyte system is also reported.