(Invited) Electrochemical Properties of Ionic Liquids Containing Aprotic Heterocyclic Anions (AHA ILs) and Their Mixtures with Lithium Salts

We have previously studied a series of room temperature ionic liquids (RTILs) based on 1-ethyl-3-methylimidazolium ([emim]+) and tetra-alkylphosphonium ([P222n]+) cations with different aprotic heterocyclic anions (AHAs). It has been found that many of the AHA ILs exhibit very good conductivity for their viscosities. The results provide insight into the design of ILs with enhanced dynamics that may be suitable for electrolyte applications (1, 2). Lithium salts based on the bis(trifluoromethylsulfonyl)imide ([TFSI]-), bis(fluorosulfonyl)imide ([FSI]-) and tetrafluoroborate ([BF4]-) anions have been extensively studied in lithium salt/IL mixtures for such applications (3-18). Here we will further explore how the addition of lithium AHA salts, compared to the popular [TFSI]-, [FSI]- and [BF4]--based ones, affects the transport properties of the RTILs in order to evaluate the feasibility of using these AHA ILs for lithium-ion battery applications. In particular, we investigate the viscosity and ionic conductivity, as well as anion, cation and lithium diffusivity, as measured by Pulse-Gradient-Spin-Echo NMR spectroscopy.