Direct reduction of lithium hexafluorophosphate (LiPF₆) in dimethoxyethane on metallic electrodes yields a pure lithium fluoride (LiF) layer that is passivating to progressive electrolyte reduction, mimicking the beneficial function of an SEI. This layer is shown to be at least as lithium-ion conductive as a similar SEI formed from a commercial electrolyte containing organic carbonates. Electrochemical quartz crystal microbalance results support the stoichiometry of reduction of LiPF₆ to soluble elemental phosphorus and insoluble LiF near the expected thermodynamic potential, well above that of common organic electrolyte components. These results suggest that the LiF component of commercial SEI layers may provide the essential functions of passivation and lithium-ion conduction.