Molecular Dynamics of Lithium Ion Transport in a Model Solid Electrolyte Interphase

TL;DR

This study uses molecular dynamics simulations with a non-polarizable force field to analyze lithium ion transport in a model solid electrolyte interphase, revealing distinct transport regimes and glassy behavior relevant for battery material design.

Contribution

It demonstrates the effectiveness of a non-polarizable MD model for studying Li+ dynamics in SEI layers, aligning with polarizable models and providing insights into trapping and transport mechanisms.

Findings

Identified three Li+ transport regimes: ballistic, trapping, and diffusive.

Trapping times in EDC are longer than in liquid EC and decrease with temperature.

Ethanol Dicarbonate exhibits glassy behavior affecting Li+ mobility.

Abstract

Li+ transport within a solid electrolyte interphase (SEI) in lithium ion batteries has challenged molecular dynamics (MD) studies due to limited compositional control of that layer. In recent years, experiments and ab initio simulations have identified dilithium ethylene dicarbonate (Li2EDC) as the dominant component of SEI layers. Here, we adopt a parameterized, non-polarizable MD force field for Li2EDC to study transport characteristics of Li+ in this model SEI layer at moderate temperatures. The observed correlations are consistent with recent MD results using a polarizable force field, suggesting that this non-polarizable model is effective for our purposes of investigating Li+ dynamics over long time scales. Mean-squared displacements distinguish three distinct Li+ transport regimes in EDC ballistic, trapping, and diffusive. Compared to liquid ethylene carbonate (EC), the nanosecond trapping times in EDC are significantly longer and naturally decrease at higher temperatures. New materials developed for fast-charging Li-ion batteries should have smaller trapping regions. The analyses implemented in this paper can be used for testing transport of Li+ ion in novel battery materials. Non-Gaussian features of van Hove self -correlation functions for Li+ in EDC, along with the mean-squared displacements, are consistent in describing EDC as a glassy material compared with liquid EC. Vibrational modes of Li+ ion, identified by MD, characterize the trapping and are further validated by electronic structure calculations.