In Situ Construction of LiF/Li₃N/Li_xGa Hybrid SEI to Boost Long‐Lifespan Succinonitrile‐Based Solid‐State Lithium Metal Batteries

Abstract Succinonitrile (SN)‐based in situ polymerized solid‐state electrolytes (SIPSSEs) for lithium batteries have attracted considerable attention due to their high ionic conductivity, wide electrochemical stability window (ESW), and potential for large‐scale applications. Despite these advantages, the polar cyano groups in SN molecules lead to significant interfacial problems upon direct contact with metallic lithium (Li), including unstable solid electrolyte interface (SEI) and the growth of Li dendrites, which impede the further application of SIPSSEs to solid‐state lithium metal batteries (SSLMBs). To address these challenges, here a GaF 3 ‐modified SIPSSE (GSNE) is developed by incorporating GaF 3 and fluoroethylene carbonate to passivate metallic Li and employing ethoxylated trimethylolpropane triacrylate to anchor SN molecules. As a result of this strategic electrolyte component design, GSNE achieves an ionic conductivity of 1.3 × 10 −3 S cm −1 at 30 °C as well as wide ESW up to 4.6 V. Additionally, a LiF/Li 3 N/Li x Ga hybrid SEI is formed on the metallic Li surface through an in situ alloying reaction. This hybrid SEI demonstrates superior interfacial stability and fast Li⁺ transport kinetics, as confirmed by various advanced characterization techniques and theoretical calculations. Consequently, LiFePO 4 /GSNE/Li cells exhibit excellent rate performance and cycling stability. This work provides new insights into the designing of long‐lifespan SIPSSEs‐based SSLMBs.