FT-IR investigation of ion association in plasticized solid polymer electrolytes

Andrea G. Bishop, Douglas R. MacFarlane, Don McNaughton, Maria Forsyth

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FT-IR spectroscopy has been utilized to monitor ion association in plasticized solid polymer electrolytes (SPEs). The SPEs were prepared from a random copolymer of ethylene oxide (EO) and propylene oxide (PO) and the salt lithium trifluoromethanesulfonate (lithium triflate, LiTf). Tetraethylene glycol dimethyl çther (tetraglyme) and /J.A-dimethylformamide (DMF) were chosen as model plasticizers. Despite having a'similar dielectric constant to that of the polymer host, ε ∼ 5, the incorporation of tetraglyme into the SPEs resulted in increased ion association. The addition of a higher dielectric constant solvent, DMF, ε = 36.7, resulted in decreased ion association in the SPE. The effects of salt concentration (0.05-1.25 mol dm-3) and temperature (25-100 °C) upon ion association in SPEs were also investigated. At low salt concentrations, ion association was found to increase with temperature, however, at 1.25 mol dm-3 the temperature dependence of ion association was dominated by concentration effects. There appears to be a maximum in the fraction of "free" ions at a LiCFaSC concentration of 0.4 mol dm-3, preceded by a minimum at approximately 0.2 mol dm-3, consistent with the molar conductivity behavior previously observed in these electrolytes.

Original languageEnglish
Pages (from-to)2237-2243
Number of pages7
JournalJournal of Physical Chemistry
Issue number6
Publication statusPublished - 1 Jan 1996

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