Ionic liquid electrolyte selection for high voltage supercapacitors in high-temperature applications

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Ionic liquids (ILs) are crucial for advanced energy storage devices like supercapacitors.
• Understanding the physicochemical and transport properties of ILs is key to optimizing electrolyte performance.
• High-temperature operation and high voltage are desirable for next-generation supercapacitors.

Purpose of the Study:

• To evaluate and screen eight hydrophobic ionic liquids for their suitability in high-voltage, high-temperature supercapacitors.
• To correlate the physicochemical properties (density, viscosity, ionic conductivity) with electrochemical performance.
• To identify the most promising IL electrolytes for supercapacitors operating at up to 353.15 K and ≥ 5 V.

Main Methods:

• Systematic analysis of physicochemical properties (density, viscosity, ionic conductivity) of eight selected ILs across a temperature range (278.15–373.15 K).
• Electrochemical characterization using cyclic voltammetry and impedance spectroscopy on supercapacitors assembled with IL electrolytes.
• Evaluation of supercapacitor performance at elevated temperatures (298.15–353.15 K) using multi-walled carbon nanotube electrodes.

Main Results:

• Ionic liquids with the bis(fluorosulfonyl)imide ([FSI]) anion exhibited lower densities and viscosities compared to those with bis(trifluoromethanesulfonyl)imide ([TFSI]).
• [Pyr 1,3][FSI] demonstrated the highest ionic conductivity among the tested ILs.
• Six ILs were identified as suitable for ≥ 5 V supercapacitors at high temperatures, including [Pip 1,3][TFSI] (5.4 V), [Pip 1,3][FSI] (5 V), [N 111,3][TFSI] (5.1 V), [N 111,6][TFSI] (5.2 V), [Pyr 1,102][TFSI] (5.2 V), and [Pyr 1,5][TFSI] (5.2 V).

Conclusions:

• The choice of anion ([FSI] vs. [TFSI]) significantly impacts IL viscosity and conductivity.
• Specific ILs show excellent potential for developing high-performance, high-temperature supercapacitors.
• This research provides valuable insights for selecting optimal ionic liquid electrolytes for demanding energy storage applications.