Conductance Study of Ion Pairing of Alkali Metal Tetrafluoroborates and Hexafluorophosphates in Acetonitrile

Abstract

High precision conductance measurements are reported for sodium, potassium, and rubidium tetrafluoroborate and hexafluorophosphate in acetonitrile at 25 °C. The results are analyzed using the expanded form of the Fuoss–Hsia conductance equation. The ion size parameter, d, was systematically varied to obtain the value which gave best fit of the data to the equation. All salts were found to be associated, and the trends in association are discussed in terms of the ability of acetonitrile to solvate cations and anions.

Ion Association Constants for Lithium Ion Battery Electrolytes from First-Principles Quantum Chemistry

“…Here the experimental trend is well reproduced by our computational model. As previously reported, 47 increasing alkali metal cation size results in decreasing solvent-cation electrostatic interactions, which in turn correlates with higher K A s. Two minor deviations from the relative experimental association strengths are noted. The experimental K A s indicate that Li + -AN is more associated than Na + -AN, in disagreement with the computed values.…”

Ion Correlations and Their Impact on Transport in Polymer-Based Electrolytes

“…Furthermore, we note that the impact of altering charge delocalization of the cation is often more complex than changing that of the anion, namely in solid polymer electrolytes where the cation and polymer host strongly interact. A larger cation has been shown to enhance transport in some cases 113,127 by minimizing cation−anion correlation, whereas in other cases the presence of free cations can mediate cross-linking of polymer chains and lead to reduced mobility. 128 L + − in Polymerized Ionic Liquids.…”

“…The simplest means of tuning the value of L + – is to alter the charge density of the electrolyte ions. To this end, several recent computational works have investigated the effect of altering ionic size and/or ion dipole strength on ion transport. ,− Cheng et al, for example, suggested that optimal conductivity in polymerized ionic liquids could be obtained by using large ions in the polymer chain and small counterions. Using both coarse-grained and atomistic MD simulations, they found that this design choice led to optimal decoupling of ion motion and segmental dynamics.…”

Conductivity studies of ion pairing in transition metal organics

“…19 Dissociation constants for simple alkali metal salts in CH3CN computed according to eq 5 were found by Yeager and Kratochvil to be relatively insensitive to the a value used. 23 Furthermore the a values reported in that study, which used high-precision conductance measurements and the analysis performed here, do not appear to be highly reproducible. (A0 and KA values were for the most part identical in multiple studies of the same salt.23) Hence the ion-pair contact distances reported in Table I1 for CH3CN solution are to be interpreted at best with much caution.…”