Insight into the Effect of Ionic Liquid-Based Additives at the Solid Electrolyte Interphase for Lithium Metal Batteries

We have investigated the effect of ionic liquids (ILs) additives in 1 M LiTFSI in 1,3-dioxolane (DOL)/dimethyl ether (DME) (1:1, v/v) on the solid electrolyte interphase (SEI) using a combined theoretical and experimental method for next-generation Li metal batteries. Among all investigated cations of ILs including imidazolium (IMI + ), pyrrolidinium (PYR + ), and piperidinium (PIP + ) cations, we have observed that the presence of IMI + provides relatively larger decomposed products of the TFSI anion on the Li metal surface when compared with saturated-ring type cation ILs including PYR + - and PIP + -ILs due to its high electron affinity (EA). Furthermore, the reactive molecular dynamics results show that the SEI layer of the system using the ILs with saturated rings is significantly thin when compared to that of the ILs with aromatic-ring, which is desired for fast Li-ion diffusivity through the SEI. This finding may lead to an ideal design of electrolyte system for future Li-metal batteries.