Thermal Aging of Anions in Ionic Liquids containing Lithium Salts by IC/ESI-MS

• Thermal aging investigation of TFSI- and FSI- based ionic liquids and their mixtures with Li salts.
• PYR13FSI shows thermal decomposition when mixed with LiPF6 and LiClO4.
• PYR13TFSI does not show any decomposition products with the electrolyte salts.
• LiPF6 dissolved in ionic liquids suffers of thermal aging as in conventional Li-ion battery electrolytes.

The stability of 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI) and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) ionic liquids at elevated temperatures (60 °C) is investigated by ion chromatography. Additionally, the influence of the electrolyte salts, lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium perchlorate (LiClO4), on the decomposition of both the ionic liquids was analysed over a long term stability study. It has been found out that TFSI has a much higher thermal stability than FSI. The addition of LiTFSI did not show any effect on the aging of both ionic liquid anions. However, PYR13FSI degraded when mixed with the electrolyte salts LiPF6 and LiClO4, while PYR13TFSI did not. Finally, LiPF6 forms the same hydrolysis products in the investigated ionic liquids as in the commonly used electrolytes based on organic solvents in lithium-ion batteries.