Interfacial Structure and Dynamics of the Lithium Alkyl Dicarbonate SEI Components in Contact with the Lithium Battery Electrolyte

Molecular dynamics simulations were performed on the dilithium ethylene dicarbonate (Li2EDC) and dilithium butylene dicarbonate (Li2BDC) components of the lithium battery solid electrolyte interphase (SEI) in contact with mixed solvent electrolyte: ethylene carbonate (EC):dimethyl carbonate (DMC) (EC:DMC = 3:7) doped with LiPF6. The many-body polarizable APPLE&P force field was used in the simulations. Examination of the SEI-electrolyte interface revealed an enrichment of EC and PF6- molecules and a depletion of DMC at the interfacial layer next to the SEI surface compared to bulk electrolyte concentrations. The EC and DMC molecules at the interfacial layer next to the SEI demonstrated a preferential orientation of carbonyl oxygens directed toward the SEI surface. The process of the Li+ ion desolvation from electrolyte and intercalation into the SEI was examined. During the initial desolvation step, the Li+ cation showed a preference to shed DMC molecules compared to losing the EC or PF6- moieties. The PF6- anion was involved in the Li+ cation desolvation process at high temperatures. The activation energies for the Li+ solvation-desolvation reaction were estimated to be 0.42-0.46 eV for the Li2EDC-electrolyte and Li2BDC-electrolyte interfaces.