Probing the Solvation Shells of Lithium Ions in Glyme-Based Electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Glymes are key solvents for lithium-battery electrolytes, often mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).
• Quantifying glyme solvation states (free vs. coordinated) in liquid electrolytes is experimentally challenging.
• Understanding solvation structure is crucial for optimizing Li-battery performance and safety.

Purpose of the Study:

• To develop and validate novel vibrational probes for studying glyme solvation in LiTFSI electrolytes.
• To investigate the solvation structure of diglyme and triglyme around Li+ ions.
• To determine the thermodynamic properties and concentration dependence of glyme solvation.

Main Methods:

• Utilized novel amine-based vibrational probes to monitor glyme solvation states.
• Studied electrolytes with salt-to-solvent molar ratios from 1:5 to 1:10.
• Performed complementary molecular dynamics (MD) simulations.

Main Results:

• Vibrational probes demonstrated equilibrium constants near unity, indicating similar solvation behavior to glymes.
• Identified that the first solvation shell of Li+ consists of two partially chelating glyme molecules.
• Observed a lack of significant contact ion pairs and confirmed solvent-separated ion pairs via MD simulations.

Conclusions:

• The developed vibrational probes are effective for studying glyme solvation in LiTFSI electrolytes.
• Even triglyme does not fully coordinate the Li+ cation, with partial chelation observed.
• MD simulations complement experiments but require refinement to fully capture partial solvation structures.