Ionic Liquid Electrolytes for Safer Lithium Batteries: I. Investigation Around Optimal Formulation

In this paper we report on the investigation of ionic liquid-based electrolytes with enhanced characteristics. In particular, we have studied ternary mixtures based on the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and two ionic liquids sharing the same cation (N-methyl-N-propyl pyrrolidinium, PYR13), but different anions, bis(trifluoromethanesulfonyl)imide (TFSI) and bis(fluorosulfonyl)imide (FSI). The LiTFSI-PYR13TFSI-PYR13FSI mixtures exhibit better ion transport properties (about 10-3 S cm-1 at -20 °C) with respect to similar ionic liquid electrolytes till reported in literature. An electrochemical stability window of 5 V is observed in carbon working electrodes.