Interactions and Transport in Highly Concentrated LiTFSI-based Electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Highly concentrated electrolytes (HCEs) are promising for advanced lithium-ion batteries (LIBs).
• Understanding ion transport limitations in HCEs is critical for improving battery performance and safety.
• Key properties influencing ion transport include viscosity, ionic conductivity, ionicity, and transport numbers.

Purpose of the Study:

• To investigate the factors controlling and limiting ion transport in HCEs.
• To correlate electrolyte properties with rate capability in LIB cells.
• To evaluate the impact of solvent polarity and salt concentration on electrolyte performance.

Main Methods:

• Systematic study of viscosity, ionic conductivity, ionicity, and transport numbers.
• Preparation of nine model electrolytes using LiTFSI salt at varying concentrations (1:2, 1:4, 1:16) and solvents (MTBE, THF, PC).
• Performance evaluation in Li-ion battery (LIB) cells.

Main Results:

• Low polarity solvents like MTBE lead to ion pairing, limiting ionic conductivity despite low viscosity.
• In less concentrated electrolytes (1:16), decreasing ionic diffusivity with increasing temperature indicates aggregation.
• Despite aggregation, ionic conductivity and LIB performance improved in some cases with increased concentration.
• Both low ionic conductivity and high viscosity were identified as primary limitations for HCEs in LIBs.

Conclusions:

• Ion pairing and high viscosity are significant barriers to ion transport in HCEs for LIBs.
• No apparent compensating mechanisms were found to overcome these limitations.
• Further research is needed to design HCEs with improved ion transport properties for enhanced LIB performance.