Compressibility of Lithium Hexafluorophosphate Solutions in Two Carbonate Solvents.

Speed-of-sound measurements are performed to establish how the isentropic bulk modulus of the electrolyte system comprising lithium hexafluorophospate (LiPF) in blends of propylene carbonate (PC) and ethyl methyl carbonate (EMC) varies with salt molality , mass fraction of PC in the PC:EMC cosolvent , and temperature . Bulk moduli are calculated by combining acoustic time-of-flight data between parallel walls of a liquid-filled cuvette with densitometric data for a sequence of binary and ternary salt solutions. Correlations are presented to yield (, , ) accurately for nine compositions spanning the range = 0-2 mol kg and = 0-1, at temperatures ranging from 283.15 to 313.15 K. Electrolyte compressibility varies most with solvent ratio, followed by salt content and temperature, with ranging from 1 to 3 GPa. Composition-dependent acoustical properties elucidate the nature of speciation and solvation states in bulk electrolytes, and could be useful to identify the features of individual phases within solution-permeated porous electrodes.