Mechanisms of charge diffusion in polyethylene oxide based electrolytes: insights from molecular dynamics simulations

The future of a number of technologies requires significant improvements in energy storage techniques. Batteries with a higher energy density, which are safer, more efficient, less expensive, and greener, are essential. In this context, lithium-ion (Li-ion) batteries based on a solid polymeric electrolyte are promising candidates, being much safer and less expensive than current liquid-based technologies. Designing optimal polymer/salt mixtures for battery applications requires us to gain a deeper understanding of the fundamental ionic transport mechanisms at play in these systems. Here, through classical molecular dynamics simulations, we investigate charge diffusion in systems consisting of a mixture of polyethylene oxide (PEO) and lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt. In particular, we take into account the effect of ionic interactions, and show that at typical salt concentrations, there is a strong departure from the infinite dilution limit. We also investigate how specific chemical modifications of the polymer chain can influence charge transport, and provide guidelines for the design of efficient PEO-based polymer electrolytes.