Solvation and Ion Association Studies of LiBF₄−Propylenecarbonate and LiBF₄−Propylenecarbonate−Trimethyl Phosphate Solutions

Abstract

Concentrated LiBF4 solutions in propylenecarbonate (PC) or PC−trimethyl phosphate (TMP) were studied regarding the ion-association and solvation of Li+ ions in each solution from the measurements of conductivities, viscosities, Raman spectra, and diffusion coefficients by field gradient NMR spectroscopies. From the Walden product evaluated, the dissociation degree of LiBF4 in the LiBF4−PC solution was roughly deduced to be about 30% in concentrations over 1 mol dm-3. About 1.8 PC molecules were found bound strongly to a Li+ ion in the LiBF4−PC solution, and this number was smaller than 3 for LiPF6 in PC solutions. The small solvation number could be evidence of the formation of contact ion-pairs of Li+−BF4 -. The diffusion coefficients of BF4 - came closer to those of Li+ ions as concentrations increased, and this is also in accordance with the assumption that the contact ion-pairs are formed. In LiBF4−PC−TMP solutions, about 50% of LiBF4 dissociates at 1 mol dm-3. TMP as a Lewis base is expected to suppress the contact ion-pairs of Li+−BF4 - and to improve the conductivity.

Vibrational Spectroscopic and Density Functional Studies on Ion Solvation and Association of Lithium Tetrafluorobrate in Acetonitrile

“…However, if four AN molecules are coordinated to Li + in the first solvation shell and another one is in the secondary shell, a stable structure with C 3V point group is obtained. Moreover, the calculated value of ∆G for the reaction Li + (AN) 4 + AN f Li + (AN) 5 is positive, while that for Li + (AN) 4 + AN f Li + (AN) 4 (AN) is negative, suggesting that the solvation number of Li + in AN solution is four. This is in good agreement with the result obtained from the spectroscopic study mentioned above.…”

Dilution of Highly Concentrated LiBF4/Propylene Carbonate Electrolyte Solution with Fluoroalkyl Ethers for 5-V LiNi0.5Mn1.5O4Positive Electrodes

“…720 cm −1 ) increased. 13 Relative area ratios of ca. 710-and 720-cm −1 peaks are summarized in Table I 12 and served just as a diluent in the solution unlike conventional co-solvents such as diethyl carbonate (DEC) and dimethyl carbonate (DMC).…”

Pulsed-Field Gradient NMR Self Diffusion and Ionic Conductivity Measurements for Liquid Electrolytes Containing LiBF4 and Propylene Carbonate

“…Other methods have been employed to probe the ion-ion interactions such as Raman spectroscopy as well as using the Walden product and limiting molar conductivities [16,17], however the use of the Nernst-Einstein equation to predict conductivity was been proven to be effective for both liquid electrolytes [18,19,20,21,22,23] and polymer gel electrolytes [24,25,26,27] and has been shown to yield a good approximation of the ionic interactions.…”