Structural and Ion Dynamics in Fluorine-Free Oligoether Carboxylate Ionic Liquid-Based Electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Ionic liquids (ILs) are promising for advanced electrolytes.
• Fluorine-free ILs offer potential environmental and cost benefits.
• Understanding ion transport and interactions is key for electrolyte performance.

Purpose of the Study:

• To investigate fluorine-free ionic liquid electrolytes with novel anions.
• To analyze the impact of cation choice and lithium salt doping on IL properties.
• To correlate physicochemical properties with electrochemical performance.

Main Methods:

• Synthesis and characterization of novel ionic liquids.
• Physicochemical property measurements (e.g., glass transition temperature).
• Electrochemical techniques including PFG NMR, 7Li NMR, and ATR-FTIR spectroscopy.

Main Results:

• Weaker cation-anion interactions were observed in tetrabutylphosphonium (P4,4,4,4)+ based ILs compared to tetrabutylammonium (N4,4,4,4)+ based ILs.
• Structural flexibility of the 2-[2-(2-methoxyethoxy)ethoxy]acetate anion (MEEA)- led to low glass transition temperatures.
• Lithium salt doping reduced anion mobility and ionic conductivity due to preferential Li+-carboxylate interactions.

Conclusions:

• The studied ILs serve as a foundation for developing fluorine-free, low glass transition temperature electrolytes.
• Controlling ion-ion interaction strength is critical for optimizing electrolyte design.
• The findings highlight the importance of anion structure in tailoring IL properties for electrochemical applications.