New approach to the understanding of ion transport in semicrystalline polymer electrolytes

Despite the conventional wisdom that ion transport in polymer electrolytes is mediated primarily by polymer segmental motion, we have performed measurements on semicrystalline complexes of poly(ethylene oxide) (PEO) with LiI which suggest that transport occurs preferentially along the PEO helical axis, at least in the crystalline phase. The principal basis for this claim is an observed enhancement by a factor of 5-20 in electrical conductivity in stretched polymer electrolyte films. The effect of uniaxial stress on the polymer electrolyte long and short range structures was investigated by X-ray diffraction and ⁷Li nuclear magnetic resonance (NMR) spectroscopy. Stretching results in partial alignment of the PEO helices and also induces small but observable changes in the Li⁺ solvation sheath. These results are correlated with the ionic conductivity enhancement in the stretched polymer.