Targeted Functionalization of Cyclic Ether Solvents for Controlled Reactivity in High-Voltage Lithium Metal Batteries

Understanding the degradation pathways and reactivity of electrolytes is the key to address the shortcomings of conventional electrolytes and to develop new electrolytes for high voltage lithium metal batteries (LMBs). Accordingly, while 1,3-dioxolane (DOL) exhibits desired features such as good compatibility with Li metal, low viscosity and high ionic conductivity, it suffers from poor oxidation stability mainly from its ring-opening polymerization. In an effort to control the reactivity of DOL by tuning its electronic properties, we introduced methyl and trifluoromethyl groups to the ethyl moiety of DOL and developed 4-methyl-1,3-dioxolane (MDOL) and 4-(trifluoromethyl)-1,3-dioxolane (TFDOL) as solvents, respectively. Whereas the MDOL-based electrolyte exhibited serious side reactions towards metallic Li, TFDOL-based one showed oxidation stability up to 5.0 V. Moreover, the inorganic-rich SEI induced by weak solvation power of TFDOL along with high oxidation stability enabled a robust cycling stability in Li|NCM811 full cell (20 µm Li foil, N/P ratio of 2.5).