Free Volume Mediated Decoupling of Ionic Conduction from Segmental Relaxation Leading to Enhancement in Ionic Conductivity of Polymer Electrolytes at Low Temperatures

Coupling between segmental relaxation and ionic conduction has limited the ionic conductivity of flexible polymers like poly(ethylene oxide), PEO, based electrolytes especially at low temperatures where segmental relaxation becomes extremely slow. In the present study, we show that ionic conduction becomes decoupled from segmental relaxation in PEO-based electrolytes simply by loading succinonitrile (SN). As a result of SN interactions induced rigid chain packing of PEO, the semicrystalline morphology of PEO is completely altered along with the enhancement in number density of free volumes having smaller size and narrower size distribution. These free volumes provide additional pathways for ionic diffusion independent of segmental relaxations of PEO leading to decoupling of ionic diffusion from the segmental relaxation process. The decoupling finally leads to nearly two orders higher ionic conductivity (∼10^-11 Scm^-1)at glass transition temperature (<i>T</i>_g ∼ 210 K), than what is expected in the case of complete coupling.