Fluorinated Cyclic Ether Diluent for High-Voltage Lithium Metal Batteries

Although localized high-concentration electrolytes (LHCEs) show promising performance with lithium metal anodes, LHCEs do not necessarily stabilize the interface with state-of-the-art high-voltage cathodes. Here, we report a functional diluent, 2,2-bis(trifluoromethyl)-1,3-dioxolane (BTFMD), to demonstrate LHCEs for high-voltage lithium metal batteries (LMBs), which stabilizes the cathode and anode interfaces simultaneously through distinct mechanisms. The fluorinated cyclic ketal moiety of BTFMD, along with diminished free solvent formation, enables oxidative stability as high as 6.0 V vs Li/Li+. Additionally, BTFMD undergoes self-decomposition to produce lithium fluoride and induces an anion-dominant solvation structure to establish an inorganic-rich solid electrolyte interphase. Incorporation of BTFMD diluent realized a Coulombic efficiency of 99.54% in a Li|Cu cell and 80% capacity retention for Li|LiNi0.8Co0.1Mn0.1O2 full-cells after 570 and 250 cycles, with cutoff voltage levels of 4.3 and 4.4 V, respectively. This study highlights the usefulness of fluorinated diluents and their controlled solvation structures for high-voltage LMBs.