Li+ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations

A fundamental understanding of solid electrolyte interphase (SEI) properties is critical for enabling further improvement of lithium batteries and stabilizing the anode-electrolyte interface. Mechanical and transport properties of two model SEI components were investigated using molecular dynamics (MD) simulations and a hybrid MD-Monte Carlo (MC) scheme. A many-body polarizable force field (APPLE&P) was employed in all simulations. Elastic moduli and conductivity of model SEIs comprised of dilithium ethylene dicarbonate (Li2EDC) were compared with those comprised of dilithium butylene dicarbonate (Li2BDC) over a wide temperature range. Both ordered and disordered materials were ordered materials showing higher conductivity in the conducting plane compared to conductivity of the disordered analogues. Li2BDC was found to exhibit softening and onset of anion mobility at lower temperatures compared to Li2EDC. At 120 degrees C and below, both SEI model compounds showed single ion conductor behavior. Ordered Li2EDC and Li2BDC phases had highly anisotropic mechanical properties, with the shear modulus of Li2BDC being systematically smaller than that for Li2EDC.