Effect of the Ion, Solvent, and Thermal Interaction Coefficients on Battery Voltage

Abstract

In order to increase the adoption of batteries for sustainable transport and energy storage, improved charging and discharging capabilities of lithium-ion batteries are necessary. To achieve this, accurate data that describe the internal state of the cells are essential. Several models have been derived, and transport coefficients have been reported for use in these models. We report for the first time a complete set of transport coefficients to model the concentration and temperature polarization in a lithium-ion battery ternary electrolyte, allowing us to test common assumptions. We include effects due to gradients in chemical potentials and in temperature. We find that the voltage contributions due to salt and solvent polarization are of the same order of magnitude as the ohmic loss and must be taken into account for more accurate modeling and understanding of battery performance. We report new Soret and Seebeck coefficients and find thermal polarization to be significant in cases relevant to battery research. The analysis is suitable for electrochemical systems, in general.

In Situ Observation of Thermally Activated and Localized Li Leaching from Lithiated Graphite

“…Therefore, the electrochemical potential of a symmetric cell is typically measured under non-isothermal conditions where the temperature at one electrode is varied while the other is held at a constant temperature. Under the assumption that there are negligible contributions from the Seebeck effect (i.e., electrochemical potential induced by a temperature gradient within an electrode) and Soret effect (i.e., temperature-dependent ion/molecule transport in the electrolyte) (eq ), α can be approximated from the slope of the measured electrochemical potential at different temperatures. ∂ E Gr ∂ T = ∂ E eq ∂ T + ∂ E Seebeck ∂ T + ∂ E Soret ∂ T ; ⁣ ∂ E Seebeck ∂ T + ∂ E Soret ∂ T < < ∂ E eq ∂ T It is important to clarify that the Seebeck effect here refers to the electrochemical potential induced by a temperature gradient within a single electrode, whereas some work has defined the Seebeck effect in an electrochemical cell differently. , …”

“…In contrast, for a non-uniform temperature distribution on an electrode, regions with a relatively high temperature would be expected to have a higher potential than the relatively low temperature regions if lithium were to remain uniformly distributed across the electrode. However, the electrode is presumed to be electronically well-connected and the Seebeck (∼20 μV/K) , and Soret effects are relatively small, thus the spatial variation in the potential across the electrode is believed to be minimal. It is therefore proposed that Li must redistribute within the graphite electrode to maintain a uniform potential across the electrode while conserving the total amount of intercalated Li.…”