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 toward metallic Li, the TFDOL-based electrolyte showed oxidation stability up to 5.0 V. Moreover, the inorganic-rich solid electrolyte interphase induced by the weak solvation power of TFDOL along with high oxidation stability enabled a robust cycling stability in a Li|NCM811 full cell (20 μm Li foil, N/P ratio of 2.5).