Pyrrolidinium Ionic Liquid Electrolyte with Bis(trifluoromethylsulfonyl)imide and Bis(fluorosulfonyl)imide Anions: Lithium Solvation and Mobility, and Performance in Lithium Metal–Lithium Iron Phosphate Batteries (original) (raw)

A mixture of n-methyl-n-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [PYR13][TFSI] and npropyl-n-methylpyrrolidinium bis(fluorosulfonyl)imide, [PYR13][FSI] ionic liquids (ILs) is investigated for lithium−metal batteries. Specifically, the relation among conductivity, solvation structure, and Li + mobility is investigated in a Li/IL/IL type ternary mixture. Li + anion coordination numbers with both [TFSI] and [FSI] in the ternary mixtures are derived from Raman analysis. The Li + transference number was measured by a combination of potentiostatic polarization and electrochemical impedance spectroscopy (EIS) techniques. The electrochemical stability and transport property of the developed ternary mixture were confirmed with Li−Li symmetrical and Li−LiFePO 4 cells. The ternary system exhibited improved rate capability compared to binary parent electrolytes as well as the state-of-the art carbonate-based electrolyte at −20°C, and slightly better cycling stability at 25°C. This study demonstrates the flexibility in tailoring physical properties and the Li + solvation environment by ternary Li/ IL/IL mixtures for enhanced battery performance.