LiBr‐Rich SEI for Stabilizing Lithium Metal Batteries

The practical applicability of lithium‐metal batteries (LMBs) is severely hindered by uncontrollable lithium dendrite growth, interfacial instability, poor reversibility, and the formation of an unstable solid‐electrolyte interphase (SEI) on lithium‐metal anodes. Constructing a robust, uniform, and ionically conductive SEI is therefore critical to enable stable Li cycling. Herein, we report the in‐situ formation of LiBr‐rich SEI layer through modification of the separator surface, which effectively regulates Li deposition behavior. Owing to its low Li + diffusion barrier, high lithium adsorption capability, and ability to form a thin and compact interfacial layer, the LiBr‐derived SEI facilitates homogeneous ion flux, suppresses dendritic growth, and mitigates dead Li formation. Symmetric Li||Li cells demonstrate excellent rate performance even under high current densities. Post‐cycling and computational studies reveal formation of LiBr‐rich SEI layer with suppressed electrolyte decomposition, while the NMR data confirm suppressed HF evolution. Furthermore, GITT, Tafel slope, transference number, and activation‐energy analyses substantiate the accelerated Li + diffusion and improved charge‐transfer kinetics endowed by the LiBr‐rich SEI. Full‐cell configurations using LiMn 0 . 6 Fe 0 . 4 PO 4 , Li||LMFP full‐cell and Li||Cu systems further demonstrate the substantial improvement in electrochemical performance, highlighting the potential of LiBr‐rich SEI layer as an effective interfacial engineering strategy for high‐energy, long‐life lithium metal batteries (LMBs).