Polymer geometry and Li+ conduction in poly(ethylene oxide)

We study the effect of molecular shape on Li+ conduction in dilute and concentrated polymer electrolytes (LiI:P(EO)n(3 ⩽ n ⩽ 100)). We model the transport-diffusion of interacting Li+ ions in the helical PEO molecule as Brownian motion in a field of electrical force. Our model demonstrates that ionic conductivity of the amorphous PE structure is increased by mechanical stretching due to the unraveling of loops in the polymer molecule and to increased order. The enhancement of the ionic conductivity in the stretch direction, observed in our Brownian simulations, is in agreement with experimental results. We find an up to 40-fold increase in the LiI P(EO)7 conductivity, which is also in agreement with experimental results. The good agreement with experiment lends much credibility to our physical model of conductivity.