Studies on fluorinated ether co-solvents for lithium-metal batteries

Abstract

Lithium (Li)-metal batteries (LMBs) have been developed for next-generation energy storage with higher energy density than the current lithium-ion batteries. However, interfacial reactions at Li surface are complicated and significantly depend on electrolyte solutions. Ether-based electrolyte solutions showed good battery performance owing to their high reductive potential (< 0.5 V vs. Li/Li+) and chemical stability against the metallic Li. Nonetheless, the low oxidative potential (< 4 V vs. Li/Li+) of ether-based electrolyte solution was not applicable to the high-voltage cathode. In this study, we used fluorinated ether cosolvent by mixing 1,2-diethoxyethane (DEE) and fluorinated 1,4-dimethoxylbutane (FDMB). The inductive effect of fluorine in FDMB significantly raised the oxidative potential up. the addition of DEE that had stronger Li+ solvation ability improved the ionic conductivity. The ionic conductivities and voltage polarizations of symmetric Li cells were improved with increasing DEE concentrations with less resistive SEI layer. The oxidative potentials shift more positively as higher FDMB amounts when both Al and carbon electrode was used. As the result, DEE/FDMB 1:6 co-solvent electrolyte showed superior full-cell cyclability with $LiFePO_4$ cathode.