Molecular dynamics simulations for liquid electrolytes of propylene carbonate with LiTFSI, LiPF₆, and LiBF₄ salts

Understanding the role that molecular interactions play on physicochemical properties of ionic solutions is of fundamental importance to design novel electrolytes used in devices to storage energy, such as lithium ion batteries. Several salts containing propylene carbonate are studied. The propylene carbonate and TFSI- anion force fields were previously parametrized by our group. Those of lithium (Li+), hexafluorophosphate (PF6- and tetrafluoroborate (BF4-) are developed in this work with ions carrying a charge of +/- 1e. The calculated properties are liquid density, dielectric constant, self-diffusion coefficient and viscosity. The results are excellent agreement with experimental data at different salt concentrations and temperatures. The dielectric constant of PC/LiBF4 is greater than that of the other two electrolytes because the ions form large clusters and the solvent molecules behave as a pure liquid. The predictions with the new parameters improve those from polarizable model for PC/LiTFSI and those from a machine learning force field for PC/LiPF6.