Lithium-Ion-Conducting Electrolytes: From an Ionic Liquid to the Polymer Membrane

Area of Science:

• Electrochemistry
• Materials Science
• Ionic Liquids

Background:

• Ionic liquids (ILs) offer potential as electrolytes in lithium-ion batteries due to their stability and conductivity.
• Developing safe and efficient electrolytes is crucial for advancing battery technology.

Purpose of the Study:

• To design, synthesize, and characterize a novel ionic liquid, PP(24)TFSI, for lithium-ion transport.
• To investigate the electrochemical properties of LiTFSI-PP(24)TFSI mixtures and derived membranes.
• To evaluate the performance of these electrolytes in terms of ionic conductivity and Li-ion transference.

Main Methods:

• Synthesis and characterization of N-butyl-N-ethylpiperidinium bis(trifluoromethane)sulfonimide (PP(24)TFSI) ionic liquid.
• Electrochemical analysis including cyclic voltammetry and electrochemical impedance spectroscopy.
• Preparation and characterization of polymer electrolyte membranes using PVDF-co-HFP matrix.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study ion mobility.

Main Results:

• The LiTFSI-PP(24)TFSI mixture exhibited ionic conductivity of ~10(-4) S cm(-1) and an electrochemical stability window of 1.8-4.5 V.
• Cathodic decomposition formed a passivating layer, enhancing Li/IL interface stability.
• Polymer electrolyte membranes showed similar ionic conductivity to the liquid electrolyte.
• NMR revealed reduced ion mobility upon LiTFSI addition and membrane formation.
• A significant enhancement in the Li transference number was observed in the membrane system.

Conclusions:

• The synthesized PP(24)TFSI ionic liquid, when combined with LiTFSI, forms a promising electrolyte for lithium-ion batteries.
• The formation of a stable passivating layer contributes to the electrochemical stability of the interface.
• The polymer electrolyte membranes maintain good ionic conductivity and exhibit improved Li transference, suggesting suitability for battery applications.