Ionic liquid electrolytes for lithium batteries: Synthesis, electrochemical, and cytotoxicity studies

We have synthesized and determined the electrochemical and thermal stabilities of a series of 1-methyl-3-alkoxyalkyl and 1-methyl-3-fluoroalkyl imidazolium and the corresponding pyrrolidinium-based ionic liquids and estimated the cytotoxicities of representative ionic liquids. The pyrrolidinium-TFSI based ionic liquids have wide electrochemical stability (>5.7–6.2 V vs. Li/Li+) but show limited thermal stabilities and lithium cell discharge characteristics, as compared to those that are imidazolium-based (4.8–5.1 V vs. Li/Li+). The fluoroalkyl-derived ionic liquids typically have superior thermal stability (Td > 350 °C) as compared to the alkoxyalkyl-substituted analogues. In all these cases, TFSI− anion-based ionic liquids are thermally and electrochemically more stable than the BF4− anion-based analogues. We have also shown that the imidazolium-based ionic liquids are relatively nontoxic and their EC50 values are comparable to their corresponding lithium salts.

► Ionic liquids are evaluated as potential electrolytes for Li/CFx primary batteries.
► High discharge capacities and wide electrochemical windows are demonstrated.
► The studied ionic liquid electrolytes are relatively nontoxic to human health.