Fast ion transport phenomena in oriented semicrystalline LiI-P(EO)n-based polymer electrolytes

We have employed a variety of experimental methods, including DC and AC con ductivity, scanning electron microscopy (SEM), atomic force microscopy (AFM ), differential scanning calorimetry (DSC), Fourier Transform Infrared (FTI R) spectroscopy, and pulsed field gradient nuclear magnetic resonance (NMR) , to investigate the poly(ethylene oxide):LiI system. The effect of stretch ing the polymer electrolyte on its DC conductivity is dramatic, resulting i n up to a 40-fold increase in the Lil P(EO)(7) composition. Structural orde ring imposed by the stretching is observed in SEM and AFM images, and the c ation solvation sheath (i.e., the helical PEO structure) is also affected b y stretching in a manner believed to favor enhanced transport, according to the FTIR results. The NMR results demonstrate unambiguously that Li+ diffu sivity is anisotropic and enhanced along the stretch direction. Although th e cation transport mechanism in polyether-salt polymer electrolytes is beli eved to rely heavily on polymer segmental mobility, this investigation sugg ests that other factors also contribute significantly. Such factors which c an be augmented by stretching are modest changes in the cation solvation sh eath and alignment of the helical structural units characteristic of PEO an d its salt complexes.