Recent experiments demonstrating the concentration-dependent stability of aqueous and nonaqueous electrolytes have renewed interest in previously discounted solvents for viable energy storage technologies. Propylene carbonate provides a clear example of a solvent whose electrochemical stability is radically altered by increasing salt concentration beyond the standard 1.0 M recipe; however, the molecular origins of this effect remain unresolved. Prior studies have focused on changes in lithium-ion bulk solvation structure to capture the onset of electrolyte stability, yet the connection between bulk solvation and the environment of the electrode surface has not been considered. In this work we reexamine the liquid structure of a prototypical LiPF6+PC electrolyte over a range of concentrations (0.7–3.2 M) using nonreactive classical molecular dynamics to probe changes in ion solvation in transitioning from the bulk environment to the electrode interface. By application of a constant potential method to represent idealized electrodes, we show that the impact of the interface is to reduce ion pairing and that sufficient concentration is necessary to restore the strong ion association found in the bulk environment. Hence, we hypothesize that the switch in stability for PC electrolytes is dictated more so by the electrostatic interactions at the electrode interface, which can be overcome by sufficient salt content and is a direct result of the strong coordination of lithium ions by the PC solvent.
Bazurto et al. (Tue,) studied this question.