TRIFLATE ION ASSOCIATION IN PLASTICIZED POLYMER ELECTROLYTES

Ion association in plasticised solid polymer electrolytes (SPEs) has b een monitored using FT-IR spectroscopy. The SPEs were prepared from a random co-polymer of ethylene oxide (EO) and propylene oxide (PO) and the salt lithium trifluoromethane sulfonate (lithium triflate, LiTf). Tetraethylene glycol dimethylether (tetraglyme, epsilon similar to 5) and N,N'-dimethyl formamide (DMF, epsilon = 36.7) were chosen as model plasticisers. Decreased ion association resulted from plasticization with DMF, indicating that the addition of a higher dielectric constant solvent increases the fraction of dissociated ions in the SPE. The in corporation of tetraglyme into these SPEs results in increased ion ass ociation, despite the similar dielectric constants of the plasticiser and polymer host. The effects of salt concentration (0.05-1.25 mol dm( -3) solvent) upon ion association in SPEs was also investigated. There appears to be a minimum in the number of ''free'' ions at a LiTf conc entration of 0.2 mol dm(-3) solvent followed by a maximum at approxima tely 0.4 mol dm(-3) solvent, consistent with the molar conductivity be haviour previously observed in these electrolytes.