Fluorinated\nCyclic Ether Diluent for High-Voltage\nLithium Metal Batteries

Abstract

Although localized high-concentration electrolytes (LHCEs)\nshow\npromising performance with lithium metal anodes, LHCEs do not necessarily\nstabilize the interface with state-of-the-art high-voltage cathodes.\nHere, we report a functional diluent, 2,2-bis(trifluoromethyl)-1,3-dioxolane\n(BTFMD), to demonstrate LHCEs for high-voltage lithium metal batteries\n(LMBs), which stabilizes the cathode and anode interfaces simultaneously\nthrough distinct mechanisms. The fluorinated cyclic ketal moiety of\nBTFMD, along with diminished free solvent formation, enables oxidative\nstability as high as 6.0 V vs Li/Li⁺. Additionally, BTFMD\nundergoes self-decomposition to produce lithium fluoride and induces\nan anion-dominant solvation structure to establish an inorganic-rich\nsolid electrolyte interphase. Incorporation of BTFMD diluent realized\na Coulombic efficiency of 99.54% in a Li|Cu cell and 80% capacity\nretention for Li|LiNi_0.8Co_0.1Mn_0.1O₂ full-cells after 570 and 250 cycles, with cutoff voltage\nlevels of 4.3 and 4.4 V, respectively. This study highlights the\nusefulness of fluorinated diluents and their controlled solvation\nstructures for high-voltage LMBs.