Mechanisms Controlling the Energy Barrier for Ion Hopping in Polymer Electrolytes

The present work studies the mechanisms controlling theenergybarrier for ion hopping in conducting polymers. Polymer electrolytesusually show Arrhenius-like temperature dependence of the conductivityrelaxation time (characteristic time of local ion rearrangements)at temperatures below their glass transition T ( g ). However, our analysis reveals that theArrhenius fit of this regime leads to unphysically small prefactors,& tau;(0) MUCH LESS-THAN 10(-13) s. Imposing avalue of 10(-13) s for this parameter renders thefairly unexpected result that the energy barrier for charge transportin these polymers has strong temperature dependence even below T ( g ). Our study also reveals significanttemperature variations of the dielectric permittivity and the instantaneousshear modulus in the glassy state of these polymers. Using the Andersonand Stuart model, we demonstrate that these variations provide strongjustifications for the temperature variation of energy barrier forion hopping. Most importantly, the proposed approach reveals thatthe energy barrier controlling ion hopping in polymer electrolytesis significantly (& SIM;30-40%) lower than that estimatedusing traditional Arrhenius fit. These new insights call for revisionsof many earlier results based on apparent Arrhenius fits, and thenewly proposed approach can provide more accurate guidance for thedesign of solid-state electrolytes with enhanced ionic conductivity.