Polymer electrolytes in strong external electric fields: Modification of structure and dynamics

TL;DR

This study uses atomistic simulations to explore how strong electric fields affect the structure and ion transport in PEO-based polymer electrolytes, revealing a coil-to-stretch transition and nonlinear dynamics without enhanced ion mobility.

Contribution

It provides a detailed analysis of the structural and dynamical response of PEO electrolytes to high electric fields, including a new method to quantify their susceptibility to external stimuli.

Findings

Polymer chains undergo a coil-to-stretch transition under strong electric fields.

Ion transport does not improve; it actually slows down despite structural changes.

The study offers a microscopic explanation for the observed nonlinear behavior.

Abstract

We present the results from an extensive atomistic molecular dynamics simulation study of poly(ethylene oxide) (PEO) doped with various amounts of lithium-bis(trifluoromethane)sulfonimide (LiTFSI) salt under the influence of external electric field strengths up to $1\,$V/nm. The motivation stems from recent experimental reports on the nonlinear response of mobilities to the application of an electric field in such electrolyte systems and arising speculations on field-induced alignment of the polymer chains, creating channel-like structures that facilitate ion passage. Hence, we systematically examine the electric field impact on the lithium coordination environment, polymer structure as well as ionic transport properties and further present a procedure to quantify the susceptibility of both structural and dynamical observables to the external field. Our investigation reveals indeed a coiled-to-stretched transformation of the PEO strands along with a concurrent nonlinear behavior of the dynamic properties. However, from studying the temporal response of the unperturbed electrolyte system to field application we are able to exclude a structurally conditioned enhancement of ion transport and surprisingly observe a slowing down. A microscopic understanding is supplied.