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FT-IR investigation of Ion association in plasticized solid polymer electrolytes
journal contributionposted on 08.02.1996, 00:00 authored by A Bishop, D MacFarlane, D McNaughton, Maria ForsythMaria Forsyth
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 ether (tetraglyme) and N,N‘-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 LiCF3SO3 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.