Lithium cation conducting TDI anion-based ionic liquids.

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Current electrolytes often pose safety risks due to flammability and the potential release of hazardous substances like hydrogen fluoride at elevated temperatures.
• The development of safer, high-performance electrolytes is crucial for advancing energy storage technologies such as lithium-ion batteries.

Purpose of the Study:

• To synthesize and characterize a new class of ionic liquids (ILs) utilizing the TDI (4,5-dicyano-2-(trifluoromethyl)imidazolium) anion for potential use in electrolytes.
• To evaluate the electrochemical properties, thermal stability, and safety aspects of these novel IL-based electrolytes.

Main Methods:

• Synthesis of EMImTDI, PMImTDI, and BMImTDI ionic liquids featuring the TDI anion and varying alkyl chains.
• Thermal stability analysis using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA).
• Electrochemical characterization including ionic conductivity, lithium cation transference number, viscosity, and electrochemical stability window measurements after lithium salt addition.

Main Results:

• Synthesized ILs demonstrated high thermal stability, with no decomposition observed up to 250 °C.
• The TDI anion, with its C-F bonds, is less prone to fluorine or hydrogen fluoride emission compared to P-F bonds found in LiPF6.
• Electrolytes formed by adding LiTDI salt to the ILs exhibited excellent ionic conductivity (> 3 mS cm⁻¹ at room temperature), a transference number > 0.1, low viscosity, and a broad electrochemical stability window.

Conclusions:

• The novel TDI-based ionic liquids offer a safer, non-flammable alternative to conventional electrolytes.
• These ILs possess favorable electrochemical properties, including high ionic conductivity and thermal stability, making them suitable for advanced energy storage applications.
• The reduced propensity for hazardous gas emission enhances the overall safety profile for both application and environmental impact.