Morphology and ionic conductivity of some lithium ion complexes with poly(ethylene oxide)

Deposition of LiBF4-PEO crystalline complexes from methanol gives a material (phase II) melting at ∼340K while deposition from acetone-chloroform mixtures gives a material with a melting point of ∼433K (phase I). Both materials have the same 1:4 stoichiometry (Li+:ethylene oxide) and each gives the same wide-angle X-ray scattering pattern though phase II has the broader reflections. The observations are interpreted in terms of a double helical model with long sequences of the same helical sense for phase I, but with less long range order and frequent reversals of helical sense for phase II. The presence of both phases in LiCF3SO3 complexes is attributed to the contribution of the anion towards complex stability in methanol. The conductivities of the semicrystalline materials are compared with those of amorphous PEO gels complexed with LiBF4. The highest ambient temperature conductivities are obtained from complexed gels.