Molecular Dynamics Simulations of Lithium Alkyl Carbonates

A quantum chemistry-based many-body polarizable force field has been developed for two model solid-electrolyte interphase (SEI) components:  dilithium ethylene dicarbonate (Li2EDC) and lithium methyl carbonate
(LiMC). Molecular dynamics (MD) simulations of amorphous Li2EDC and LiMC were performed at
temperatures from 393 to 600 K. Simulations reveal that Li+ is coordinated by ∼4.6 oxygen atoms from
−COO- groups coming from different alkyl carbonate molecules. Charge transport in Li2EDC was found to
be almost entirely due to Li+. The temperature dependence of the ionic conductivity of the SEI model
compounds Li2EDC and LiMC was found to be significantly stronger than that of liquid electrolytes (e.g.,
ethylene carbonate + LiTFSI), yielding extrapolated conductivities of the Li2EDC on order of 10-10 S/cm at
−30 °C.