Molecular Dynamics Simulations of Lithium Ion Transport through a Model Solid Electrolyte Interphase (SEI) Layer

Abstract

Lithium ion transport through a solid electrolyte interphase (SEI) layer in lithium ion batteries has eluded molecular simulation studies due to lack of compositional information and force field parameters for the organic SEI layer. In the last decade, experiments and ab initio simulations have identified dilithium ethylene dicarbonate (Li2EDC)as the primary component of SEI layers.We have applied a parameterized classical, non-polarizable force field to evaluate structural and transport properties of Li+ in an SEI layer of Li2EDC molecules at several temperatures (333, 500, 700 K).The correlations compare well with recent results using a polarizable force field, suggesting that this non-polarizabile model is effective. Mean-squared displacements distinctly show three Li+ transport behaviors in both EDC and in liquid ethylene carbonate (EC), namely, ballistic, trapping, and diffusive motions. The trapping regime is significantly broader in EDC compared with EC, but the temperature width diminishes with increased temperature.The non-Gaussian behavior of the self part of the van Hove time-dependent correlation function for Li+ in EDC, along with the mean-squared-displacement results, confirms that EDC is a glassy material compared with liquid ethylene carbonate.