Fluorinated Aromatic Diluent for High‐Performance Lithium Metal Batteries

: In lithium metal batteries, electrolytes containing high-concentration salts have demonstrated promising cyclability, but their practicality with respect to the cost of materials is yet to be warranted. Here we report a fluorinated aromatic compound, namely 1,2-difluorobenzene, for use as a diluent solvent in the electrolyte to realize the "high-concentration effect". The low lowest unoccupied molecular orbital (LUMO) level, weak binding affinity for lithium ions, and high fluorine-donating power of 1,2-difluorobenzene jointly give rise to the high-concentration effect at a bulk salt concentration near 2 M while modifying the composition of the solid-electrolyte-interphase (SEI) layer to be rich in lithium fluoride (LiF). The employment of triple salts to prevent corrosion of the aluminum current collector further improves cycling performance. This study offers a design principle on how to achieve the local high-concentration effect at reasonably low bulk concentrations of salts.