Locking Active Li Metal through Localized Redistribution of Fluoride Enabling Stable Li‐Metal Batteries

Abstract The creation of fluorinated interphase has emerged as an effective strategy for improving Li‐metal anodes for rechargeable high‐energy batteries. In contrast to the introduction of fluorine‐containing species through widely adopted electrolyte engineering, a Li‐metal composite design is reported in which LiF can locally redistribute on the Li‐metal surface in liquid electrolytes via a dissolution–reprecipitation mechanism, and enable the formation of a high‐fluorine‐content solid electrolyte interphase (SEI). For validation, a Li/Li 22 Sn 5 /LiF ternary composite is investigated, where the as‐formed LiF‐rich SEI locks the active Li metal from corrosive electrolyte. The Li/Li 22 Sn 5 /LiF anode displays an impressive average Coulombic efficiency (ACE, ≈99.2%) at 1 mA cm −2 and 1 mAh cm −2 in a carbonate electrolyte and a remarkable cycling life of over 1600 h at 1 mA cm −2 and 2 mAh cm −2 . Applied to a LiCoO 2 full cell with a high cathode areal capacity of 4.0 mAh cm −2 , a high capacity retention of ≈91.1% is realized for 100 cycles at 0.5 C between 2.8 to 4.5 V with a low negative/positive (N/P) ratio of 2:1. This design is conceptually different from the design employing the widely used fluorine‐containing electrolyte additive and provides an alternative approach to realize reliable Li‐metal batteries.