Imidazolium-Based Ionic Liquid High Decomposition Potential Electrolytes for Lithium-Oxygen Batteries

Abstract

Ionic liquids, because of the low volatility, high ionic conductivity, wide electrochemical window and other advantages are attracted to researchers. In this work, the ionic liquid 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C2M2IM][TFSI]) was chosen for investigating in Li-O2 batteries. The electrolyte with different proportion of ionic liquids have been explored, and it was found that the electrolyte with a content of 3% had the highest ion transference number of lithium and ionic conductivity. Because the proton of C(2) on Ethylmethyl imidazolium bis(trifluoromethanesulfonyl-imide) ([EMI][TFSI]) is replaced with an alkyl group that can hinder the strong reducibility of the three protons especially the proton of C(2) on imidazolium ring. LSV test confirms the decomposition potential of 3%-[C2M2IM][TFSI]-base electrolyte is increased from 4.1V to 5V compared with the base electrolyte, that means the alkyl groups substituted imidazolium ionic liquid can act together with TEGDME and LiTFSI to protect electrolyte from early decomposition. And the cycle performance of Li-O2 batteries with a small amount (˂ 10%) of [C2M2IM][TFSI] added are truly extended.

Keywords: Ionic liquid, high decomposition potential, ionic conductivity, transference number, Li-O2 batteries.