Cation Transport in Polymer Electrolytes: A Microscopic Approach

TL;DR

This paper develops a microscopic theory for cation diffusion in polymer electrolytes, linking molecular dynamics simulations with polymer-specific properties to predict lithium ion diffusion without entanglement effects.

Contribution

It introduces a microscopic model that explicitly relates cation diffusion to polymer dynamics, extending previous phenomenological approaches.

Findings

The model accurately predicts chain length dependence of D_{Li}

Cation jumps are characterized as renewal processes

Predictions align with experimental data

Abstract

A microscopic theory for cation diffusion in polymer electrolytes is presented. Based on a thorough analysis of molecular dynamics simulations on PEO with LiBF$_4$ the mechanisms of cation dynamics are characterised. Cation jumps between polymer chains can be identified as renewal processes. This allows us to obtain an explicit expression for the lithium ion diffusion constant D_{Li} by invoking polymer specific properties such as the Rouse dynamics. This extends previous phenomenological and numerical approaches. In particular, the chain length dependence of D_{Li} can be predicted and compared with experimental data. This dependence can be fully understood without referring to entanglement effects.