Stability and structure of the aqueous LiTFSI-LiCl interface.

Area of Science:

• Physical Chemistry
• Materials Science
• Electrochemistry

Background:

• Aqueous solutions of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium chloride (LiCl) can form stable liquid-liquid biphasic systems at high salt concentrations.
• Understanding the molecular mechanisms governing interfacial structure and stability is crucial for designing advanced electrolytes.

Purpose of the Study:

• To investigate the driving forces behind liquid-liquid interface formation in concentrated electrolyte solutions.
• To correlate interfacial molecular structure with thermodynamic stability using molecular dynamics simulations and experimental analysis.

Main Methods:

• Molecular dynamics simulations were employed to model interfacial behavior.
• Experimental analysis was conducted to validate simulation findings.
• Thermodynamic properties such as surface tension and interfacial thickness were analyzed.

Main Results:

• At the liquid-vapor interface, TFSI- anions act as surfactants, reducing surface tension and increasing interfacial thickness.
• In biphasic LiTFSI-LiCl systems, increasing salt concentration enhances interfacial stability, indicated by rising surface tension and reduced interfacial thickness.
• Anion adsorption/desorption influences water-water hydrogen bonding, interfacial structure, and cation diffusion, leading to opposing effects on interfacial stability.

Conclusions:

• The liquid-liquid separation in these systems is primarily driven by the 'salting out' effect of LiCl.
• The observed phenomena are linked to the complex interplay between ionic concentration, anion behavior, and water structure at interfaces.