Mesoscopic Inhomogeneities in Concentrated Electrolytes.

Area of Science:

• Physical Chemistry
• Materials Science
• Theoretical Chemistry

Background:

• Recent experiments show unexpectedly large periods in the disjoining pressure decay for water-in-salt electrolytes.
• The behavior of lithium bis(trifluoromethylsulfonyl)-imide (LiTFSI) electrolytes presents a challenge to existing theoretical models.

Purpose of the Study:

• To develop a mesoscopic theory explaining the oscillatory decay of disjoining pressure in water-in-salt electrolytes.
• To elucidate the role of ion-ion interactions and solvent effects in electrolyte structure.

Main Methods:

• Developed a mesoscopic theory combining density functional and field-theoretic methods.
• Assumed spherical ions with differing diameters and implicit solvent, incorporating short-range attractions between like-charged ions.
• Calculated correlation functions to analyze mesoscopic inhomogeneities.

Main Results:

• Identified conditions for mesoscopic inhomogeneities: attractive short-range and repulsive long-range interactions between like ions.
• Adjusted the model's attractive potential to match experimental data for water-in-LiTFSI.
• Achieved semiquantitative agreement with experimental data for both the period and decay rate of correlations.

Conclusions:

• The developed theory successfully explains the experimental observations in water-in-salt electrolytes.
• Mesoscopic inhomogeneities are crucial for understanding the electrolyte's disjoining pressure.
• The decay length of correlations shows a near-linear dependence on the ion volume fraction.