2019 AIChE Annual Meeting

(553e) Activity Coefficients of Salts in Aqueous and Nonaqueous Solvents and in Solvent Mixtures

Authors

Andrew Crothers - Presenter, Lawrence Berkeley National Laboratory,
Clayton Radke, University of California-Berkeley
John Prausnitz, University of California, Berkeley
In chemical technology, we frequently encounter nonaqueous and mixed-solvent electrolytes. For example, lithium-ion batteries and other electrochemical devices. The thermodynamic properties of these electrolytes influences device performance. Based on publications by Bernard and Blum,1 Barthel et al.,2 Simonin et al.,3 and others, this work presents and validates a molecular-thermodynamic model for salt activity coefficients in aqueous and non-aqueous single- and mixed-solvent systems.

The Binding Mean Spherical Approximation (BiMSA) gives electrolyte activity due to long-range electrostatic forces, short-range hard-sphere repulsion, and ion-pair formation. For molalities up to about 2 molar, this theory shows good agreement with measured salt activities in aqueous and non-aqueous solvents using the center-to-center distance of closest approach between oppositely charged ions as the single fitting parameter for each electrolyte system. For mixed-solvent electrolytes, the local solvation environment around the ions dictates short-range interactions. To account for preferential ion solvation in a mixed solvent, the center- to-center distance is obtained from Wang and coworkers’ Dipolar Self-Consistent-Field Theory.4 For a particular salt in a particular solvent mixture at fixed temperature, the model predicts salt activity coefficients using only the fitted single-solvent distance-of-closest approach.

References

  1. Bernard, O.; Blum, L., Binding mean spherical approximation for pairing ions: An exponential approximation and thermodynamics. J. Chem. Phys. 1996, 104 (12), 4746-4754.
  2. Barthel, J.; Krienke, H.; Holovko, M.; Kapko, V.; Protsykevich, I., The application of the associative mean spherical approximation in the theory of nonaqueous electrolyte solutions. Condens. Matter Phys 2000, 3 (3), 23.
  3. Simonin, J.-P.; Bernard, O.; Blum, L., Ionic Solutions in the Binding Mean Spherical Approximation: Thermodynamic Properties of Mixtures of Associating Electrolytes. J. Phys. Chem. B 1999, 103 (4), 699-704.
  4. Nakamura, I.; Shi, A.-C.; Wang, Z.-G., Ion Solvation in Liquid Mixtures: Effects of Solvent Reorganization. Phys. Rev. Lett. 2012, 109 (25), 257802.