Determination of Transference Number and Thermodynamic Factor by use of Anion-Exchange Concentration Cells and Concentration Cells

Abstract

A method is described for the measurement of lithium ion transference number and thermodynamic factor of a binary electrolyte by the combined use of anion-exchange concentration cell measurements and concentration cell measurements. The measurements were carried out using cells consisting of LiTFSI salt, a poly(ethylene oxide) solvent, a polydiallyldimethylammonium bis(trifluoromethanesulfonyl)imide anion-exchange layer, and lithium foil electrodes. The transference number and thermodynamic factor were fit using expansions suggested by electrolyte theory. The thermodynamic factor was measured to lie within the range 0.3 to 6 at 80°C. The lithium ion transference number was measured to be 0.18 at infinite dilution and decreased with increasing concentration. Under ideal operation, the anion-exchange concentration cell directly measures the difference in the chemical potential of salt at two different concentrations. The accuracy of the approximation of ideal operation was estimated, showing that the method is more accurate as the salt has low partitioning into the anion-exchange layer and as the salt diffusivity in the anion-exchange layer is lower than in the solvent.

Measurement of Three Transport Coefficients and the Thermodynamic Factor in Block Copolymer Electrolytes with Different Morphologies

“…Choosing a different reference salt concen-tration results in a vertical shift of U. 77 We find that U is remarkably consistent across all five systems with ϕ c varying from 0.3 to 1 and N varying from 80 to 8000. This suggests that the presence of polystyrene does not affect the potential of the concentration cell, and a universal relationship can be used to determine U m d d ln for any SEO or PEO/LiTFSI mixture, regardless of morphology, ϕ c , or N. We fit a single curve through the data in Figure 8 to obtain the function:…”

“…The slope of U at a given value of ln m is independent of the reference salt concentration. Choosing a different reference salt concentration results in a vertical shift of U . Therefore, we can include data from previous studies by plotting U (ln m ) with a vertical offset, U ′, such that U ′(ln m ) = U (ln m ) + C .…”

Shifting-reference concentration cells to refine composition-dependent transport characterization of binary lithium-ion electrolytes

“…Most concentration-cell analyses assume the transference number to be constant, or use model-dependent numerical optimization to deconvolute the transference number and thermodynamic factor, introducing unwanted uncertainties [4][5][6][7][8]. All prior concentration-cell studies have employed fixed, arbitrary reference concentrations, which can introduce inaccuracies when measuring highly dilute or concentrated test concentrations [4][5][6][7][8][9][10][11][12][13][14].…”

Impact of Frictional Interactions on Conductivity, Diffusion, and Transference Number in Ether- and Perfluoroether-Based Electrolytes

“…[26][27][28][29]33,[38][39][40][41] Many recent publications emphasize the importance of another transport property, the transference number. 25,29,[42][43][44][45][46][47][48][49] In seminal work in 1987, Bruce and Vincent proposed a simple method for measuring the transference number. 50,51 They recognized that the transference number thus obtained is correct only in the case of ideal dilute electrolytes.…”