Lithium solvation and interfacial structure in a ternary carbonate electrolyte at electrified graphite interface: Constant charge vs constant potential molecular dynamics.

Multicomponent carbonate electrolytes are central to next generation electrochemical energy storage devices, and the choice of electrode model strongly shapes their predicted interfacial behavior. This study compares the constant charge method (CCM) and constant potential method (CPM) for modeling electrified interfaces in such electrolytes. Molecular dynamic simulations are performed for 1 M LiPF6 in an ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate ternary carbonate electrolyte sandwiched between two graphite electrodes. Results show that CCM and CPM give nearly identical interfacial structures at low and moderate polarization, with clear deviations emerging at ±1.35 V, equivalent to a 2.70 V cell voltage. This method-dependent response originates mainly from Li+ behavior at the negative electrode, where CCM promotes partial desolvation and contact-like adsorption, whereas CPM preserves solvent separated adsorption through dynamic charge redistribution and stronger interfacial solvent ordering. Meanwhile, PF6- distributions remain comparatively insensitive to electrode treatment. This study defines the polarization regime where CCM is sufficient and establishes when CPM is required to capture coupled Li+/solvent/electrode interactions in carbonate solvent-based energy storage electrolytes.