Ester Modified Pyrrolidinium Based Ionic Liquids as Electrolyte Component Candidates in Rechargeable Lithium Batteries

Cao X, Roeser S, Rezaeirad B, He X, Streipert B, Winter M, Cekic-Laskovic I

Abstract

Room temperature ionic liquids (RTILs), especially pyrrolidiniumbased RTILs with bis(trifluoromethane-sulfonyl)imide (TFSI)as counterion, are frequently proposed as promising electrolyte componentcandidates thanks to their high thermal as well as high oxidationstability. In order to avoid a resource intensive experimental approach,mainly based on trial and error experiments, a computational screeningmethod for pre-selecting suitable candidate molecules was adopted andthree homologous series compounds were synthesized by modifyingthe cation structure of pyrrolidinium RTILs. The obtained highpurity RTILs: methyl-methylcarboxymethyl pyrrolidinium TFSI(MMMPyrTFSI), methyl-ethylcarboxymethyl pyrrolidinium TFSI(MEMPyrTFSI) and methylpropylcarboxymethyl pyrrolidinium TFSI(MPMPyrTFSI) revealed excellent thermal stabilities higher than300 °C. Furthermore, MMMPyrTFSI and MPMPyrTFSI exhibit highoxidation stability up to 5.4 V vs. Li/Li+. No aluminum corrosion ofcurrent collector was observed at 5 V vs. Li/Li+. In addition to that,these RTILs display a superior salt (LiTFSI) solubility (3.0-3.5 M),compared to the unmodified RTIL 1-butyl-1-methylpyrrolidiniumTFSI (Pyr14TFSI) (1.5-2.0 M) at room temperature. All these propertiesmake novel ester modified RTILs promising and interesting candidatesfor application in rechargeable lithium batteries.