Stretching-induced changes in ion-polymer interactions in semicrystalline LiI-P(EO)_n polymer electrolytes

Ionic conductivity, which is the most important polymer electrolyte (PE) property, is considered to be higher in the totally amorphous matrix, and ion transport is assumed to be mediated primarily by the motion of polymer segments. Despite this conventional wisdom, we suggest that fast ion transport occurs preferentially along the PEO helical axis, at least in the crystalline phase. In this work, we have studied the effect of hot and room-temperature stretching on the structural properties, ion-polymer interactions and ionic conductivity in dilute and concentrated LiI:P(EO)_n (3 ≤ n ≤ 100) PEs. SEM and XRD data show evidence of the formation of a more oriented polymer-electrolyte structure. Significant changes in the FTIR spectra of the diluted LiI:P(EO)_n electrolytes are found for the skeletal vibration mode of the C-O-C groups. The effect of stretching on the FTIR spectra of concentrated PEs was found to be less pronounced than that of the dilute PEs. The stretching process was found to influence the conductivity in the direction of the force more strongly than does an increase in temperature.