Molecular Dynamics Simulation Studies of the Structure of a Mixed Carbonate/LiPF6 Electrolyte near Graphite Surface as a Function of Electrode Potential

Abstract

Molecular dynamics (MD) simulations of an electrolyte comprised of ethylene carbonate (EC), dimethyl carbonate (DMC), and LiPF 6 salt near the basal face of graphite electrodes have been performed as a function of electrode potential. Upon charging of the electrodes, the less polar DMC molecule is partially replaced in the interfacial electrolyte layer by the more polar EC. At negative potentials, the carbonyl groups from the carbonate molecules are repelled from the surface, while at positive potentials, we find a substantial enrichment of the surface with carbonyl groups. PF 6 – rapidly accumulates at the positive electrode with increasing potential and vacates the negative electrode with increasing negative potential. In contrast, Li + concentration in the interfacial layer is found to be only weakly dependent on potential except at very large negative potentials. Hence, both composition of the electrolyte at the electrode surface and solvent environment around Li + are observed to vary dramatically with the applied potential with important implications for oxidation/reduction of the electrolyte and the process of Li + intercalation/deintercation.