Aromatic heterocyclic anion based ionic liquids and electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Organic Chemistry

Background:

• Ionic materials are crucial for energy storage devices.
• Developing novel electrolytes with tunable properties is essential for improving device performance.
• Fluorine-free ionic compounds offer potential environmental and cost benefits.

Purpose of the Study:

• To synthesize and characterize new fluorine-free ionic materials based on pyridine and pyrazine anions.
• To investigate the impact of anion structure on material properties, including phase behavior and ion-ion interactions.
• To evaluate the potential of these materials as electrolytes for energy storage applications.

Main Methods:

• Synthesis of five new ionic materials with a common phosphonium cation and heterocyclic anions.
• Differential scanning calorimetry (DSC) to determine melting points and phase transitions.
• Electrochemical impedance spectroscopy (EIS) to measure ionic conductivity.
• Computational modeling to understand ion-ion interactions and diffusion.

Main Results:

• Two room temperature ionic liquids (RTILs), one semi-solid, and two organic ionic plastic crystals (OIPCs) were obtained.
• OIPCs exhibited plastic crystalline phases, solid-solid transitions, and melt phases.
• Ion-ion interactions and ionic conductivity were strongly influenced by the anion's nitrogen atom position and electronic structure.
• Anion diffusion was faster than cation diffusion in RTILs but slowed in Li+-containing electrolytes due to strong electrostatic interactions.

Conclusions:

• Structural tuning of aromatic anions significantly affects ion-ion interactions and material properties.
• The synthesized ionic materials demonstrate promising characteristics for use as solid and liquid electrolytes.
• These findings contribute to the development of advanced electrolytes for next-generation energy storage devices.