Ternary Potassium Single Cation Ionic Liquids Explored by Bayesian Optimization.

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Potassium single cation ionic liquids (SCILs) offer a safer alternative to flammable organic solvents in electrolytes.
• Current research is limited to binary SCILs due to the high cost of determining eutectic compositions in multinary systems.

Purpose of the Study:

• To efficiently identify a ternary eutectic composition for potassium SCILs.
• To expand the operating temperature range of SCIL electrolytes.
• To investigate the impact of specific anion combinations on SCIL properties.

Main Methods:

• Utilized Bayesian optimization for efficient identification of ternary eutectic composition.
• Synthesized and characterized the ternary SCIL: KFSI$_{0.31}$TFSI$_{0.25}$TFA$_{0.44}$.

Main Results:

• Successfully identified a ternary eutectic composition, KFSI$_{0.31}$TFSI$_{0.25}$TFA$_{0.44}$, with a melting point of approximately 43 °C.
• The ternary SCIL demonstrated stability, maintaining a supercooled liquid state for over 3 months at room temperature.
• Introduction of the strong Lewis base TFA$^-$ led to increased cation-anion Coulombic interactions, resulting in lower conductivity compared to binary SCILs.

Conclusions:

• Bayesian optimization enables efficient discovery of multinary SCILs with improved thermal properties.
• The developed ternary SCIL offers an expanded operating temperature range, enhancing safety.
• Balancing Coulombic interactions is crucial for optimizing conductivity in SCIL electrolytes.