Reevaluating the Effect of a LiF-Containing Solid Electrolyte Interphase on Lithium Metal Anodes

Developing high-energy-density lithium metal batteries (LMBs) necessitates robust solid electrolyte interphases (SEIs) capable of enduring prolonged cycling. While lithium fluoride (LiF) is recognized as crucial for lithium metal anode (LMA) protection, the effects of different LiF sources in SEIs remain insufficiently understood. In this study, we systematically introduce single fluorine sources─anion LiF, solvent LiF, and native LiF─into a fluoride-free electrolyte system to elucidate the impact of LiF originating from different sources on the SEI composition and properties. Results reveal that SEI performance depends not only on LiF content but also on coexisting organic components. During deep cycling, solvent-derived LiF-rich SEIs, containing elevated LiF and organics, offer superior LMA protection ability. These SEIs maintain structural integrity during significant volume changes, effectively suppressing dead Li formation and achieving enhanced Coulombic efficiency. This work reexamines LiF's protective mechanisms while advancing SEI chemistry understanding, providing critical insights for developing high-performance LMBs.