Temperature-dependent raman spectroscopy of lithium triflate-PEO complexes: phase equilibrium and component interactions.

Poly(ethylene oxide) and complexes of lithium trifluorosulfonate-poly(ethylene oxide) (LiTf-PEO) with 4 <or= O/Li <or= 18 have been studied by Raman spectroscopy from room temperature up to 160 degrees C. The Raman spectrum of the (PEO)(3)LiTf defined compound has been deduced from the experimental data. Subtraction of the Raman spectrum due to (PEO)(3)LiTf in each sample allowed us to determine for the first time the composition and the Li(+)-Tf(-) and Li(+)-PEO interactions in the part of the polymer not crystallized as (PEO)(3)LiTf. It is shown that the local interactions between cation and anion or between cation and PEO chain persist even in the melted state, up to near the liquidus temperature. In particular, the Li(+)-PEO interactions decrease significantly just below the liquidus temperature with a simultaneous strong increase in the ion pair concentration.