Effects of Non-Solvating Fluorinated Solvents in Localized High-Concentration Electrolytes for Lithium Metal Batteries

Abstract

High-voltage lithium (Li) metal batteries (LMBs) have been revived in recent years due to their high energy density. 1 However, their practical application is still hindered by the poor stability of the Li metal anode (LMA). The electrolyte is critical to the stability of LMA and the performance of LMBs, because the electrolyte formulation and structure determine the properties of the solid electrolyte interphase (SEI) formed on the LMA surface, which acts as a kinetic barrier for the continuous reaction between the LMA and the electrolyte. 2 High-concentration electrolytes (HCEs) and localized high-concentration electrolytes (LHCEs) have been recognized as good alternatives to replace state-of-the-art LiPF6/carbonate electrolytes and overcome the challenges in LMBs. 3 There are three basic components in the LHCEs: conducting salt, solvating solvent and non-solvating solvent (called diluent), forming a unique solvation structure, where highly concentrated salt-solvent clusters are distributed in the diluent. Here we investigated four types of fluorinated solvents in searching for the most suitable diluent for HCEs, including fluorinated ethers, fluorinated carbonate, fluorinated borate or fluorinated orthoformate. Their roles in the electrolyte solvation structures and effects on the electrode/electrolyte interphases will be discussed during the presentation together with battery performance. These systematic investigations and fundamental insights into LHCEs using different fluorinated solvents can guide further design of advanced electrolytes for high-voltage LMBs.