Low Solvating Power of Acetonitrile Facilitates Ion Conduction: A Solvation-Conductivity Riddle

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Acetonitrile (AN) and propylene carbonate (PC) are common electrolyte solvents.
• High ionic conductivity in LiTFSI AN solutions is not fully understood.
• Understanding solvent behavior is crucial for advanced energy storage.

Purpose of the Study:

• Investigate solution species and ion conduction in LiTFSI AN and PC solutions.
• Determine the factors contributing to the high conductivity of AN-based electrolytes.
• Challenge conventional understanding of solvent properties for electrolytes.

Main Methods:

• Raman spectroscopy to analyze solution species.
• Dielectric relaxation spectroscopy to study ion dynamics.
• Comparison of 0.1 M and 3.0 M LiTFSI concentrations in AN and PC.

Main Results:

• LiTFSI AN solutions have more free solvent than LiTFSI PC solutions.
• Lower viscosity in LiTFSI AN facilitates higher ion conduction.
• AN's lower Li-solvation power is compensated by TFSI anions loosely bound to Li ions, ensuring comparable salt dissociation.

Conclusions:

• High solvent solvating power is not essential for high electrolyte conductivity.
• Abundant free solvent and specific ion-ion interactions are key to high conductivity.
• This research opens new avenues for designing optimal solvents for high-power energy storage devices.