Dielectric Constants for Quantum Chemistry and Li-Ion Batteries: Solvent Blends of Ethylene Carbonate and Ethyl Methyl Carbonate

This work reports measurements of the dielectric constants of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) blends between 25 and 60 degrees C. Dielectric constants were measured using a cylindrical capacitance cell and a frequency response analyzer. EC and EMC form nonideal mixtures that cannot be described by a simple linear mixing model. A quadratic mixing rule was instead adopted, and the mixing parameter is reported for 25-60 degrees C. The results of this research may be used to calculate the dielectric constant of any EC/EMC mixture over this temperature range with <= 4% estimated error. By modeling the ionic dissociation of lithium hexafluorophosphate (LiPF6) in various solvents, the significance of the dielectric constant on quantum chemistry simulations of chemical processes is explored. The effect of the dielectric constant accuracy on electrochemical processes was similarly evaluated by calculating the solvation energy of neutral and singly oxidized vinylene carbonate in various solvents. It is demonstrated that the exact value of the dielectric constant can significantly affect calculation accuracy when epsilon < 40, which is the case for the most commonly used EC/EMC blends.