(40a) Session Keynote: Ionic Liquid Electrolytes for Electrochemical Energy Storage

Ionic Liquids (ILs) are liquid salts that have emerged as ‘designer solvents’ over the last twenty years due to their highly tunable chemical structure. Remarkable physical properties such as high thermal and electrochemical stability, non-flammability, and negligible volatility render ILs ideal electrolytes in electrochemical systems such as batteries and supercapacitors. Rate-capability and long-term cyclability of rechargeable batteries such as lithium-ion and sodium-ion batteries depend on many factors including the stability of the solid-electrolyte interface and ion conduction efficiency. As stand-alone electrolytes ILs are poor ion conductors because of their high viscosity, preferential ion interactions and ion aggregates that induce high-energy barriers for conduction. An increase in temperature often offsets some of the challenges associated with ion conduction. We have showed that a sodium-ion battery operating at 60 ËšC with ionic liquid electrolyte, Na[FSI] / [PYR13][FSI] (1-propyl-methylpyrrolidinium bis(fluorosulfonyl)imide), achieves superior performance in terms of capacity and cyclability, compared to organic carbonate-electrolytes at a current density of 100 mA/cm². Similarly, long-term cyclability with Li[TFSI] / [PYR13][TFSI] ([TFSI] is bis(trifluoromethylsulfonyl)imide) at 25 ËšC is achievable in Li-Li symmetrical cells, however at lower current densities (e.g., 0.1 mA/cm²). In order to improve rates at which battery can discharge, while maintaining cyclability, we designed binary IL-IL mixtures as electrolytes with improved conductivities. Since ILs are variable in chemical makeup and in terms of stability against a metal such as the lithium metal, we investigated the solid-electrolyte interface to determine a pre-treatment strategy for the use of lithium metal as an electrode with IL electrolytes. A perspective on IL electrolytes for energy storage devices will be delivered in this presentation. Our most recent findings on the application of binary IL-IL mixtures in lithium batteries and the characteristics of the lithium-IL interfaces determined by Electrochemical Impedance Spectroscopy and X-ray Photoelectron Spectroscopy will be presented.