Concentration Polarization of Salt‐Containing Liquid Electrolytes

Abstract

Using the example of Li-battery electrolytes, the importance of the concept of conservative ensembles for polarization behavior and transference measurements of salt-containing liquid electrolytes is stressed. The conventional evaluation of the stationary values fails if the ion pair is mobile and can act as a vehicle of a single ion such as Li + . The necessary generalization is considered. While the analytical form of the time dependence of voltage or current is not affected provided the ion pairing is suffi ciently fast, the diffusion coeffi cient contains nontrivial extra contributions. Finally, soggy-sand electrolytes are inspected, in which polarization occurs in the space-charge zones.

Dynamic Ion Correlations in Solid and Liquid Electrolytes: How Do They Affect Charge and Mass Transport?

“…[58] The strongly negative value of s þÀ enhances the total ionic conductivity [Eq. (17)], but lowers the stationary Li + ion current under anion-blocking conditions [Eq. (22)].…”

Single Alkaline‐Ion (Li+, Na+) Conductors by Ion Exchange of Proton‐Conducting Ionomers and Polyelectrolytes

“…The combination of relatively low total conductivity and low alkaline ion transference number is expected to lead to significant concentration polarization effects (formation of salt concentration gradients) even at moderate alkaline ion currents. [9] Especially for high drain applications, such as high power batteries, electrolytes with a high single ion (Li + , Na + ) conductivity may therefore help to reduce polarization effects within the electrolyte. This has been stimulating many attempts towards true single alkaline ion conductors, but in most cases either the transference number remained clearly below unity [10,11] or the conductivity was reduced to a non acceptable level.…”

Determination of individual contributions to the ionic conduction in liquid electrolytes: Case study of LiTf/PEGDME-150

“…In that case, the total Li + transport is found to be the sum of the free Li ion conductivity and indirect transport (σ − s/(σ − + s)) enabled by counter motion of ion pair and anion as shown in Fig. 1b [27]. Here there are no indications of triple ions as they are typically portrayed by an additional conductivity increase at high c salt .…”

“…However, there is an indication for presence of dimers and their conductivity equivalent (concentration × diffusivity × F 2 /RT) is denoted as s′. After repeating the analysis in [27] by including dimers, it can be shown that in the equation forσ DC , s is now replaced by s + 4 s′, while in the equations for σ Li Tr and σ F Tr , s is replaced by s + 2 s′ (see Table 2). Deconvoluted individual transport coefficients of all species are given in Fig.…”

“…Using the concept of conservative ensembles [26] allows for deconvolution of effective conductivity, into transport contributions from free ions and ion pairs even when higher-order aggregates are present [27,28]. The fast internal reaction equilibria give rise to important corrections in the build-up of stoichiometric gradients.…”