Interfacial Molecular Welding via Passivation‐Triggered Fluoropolymerization: Boosting Li + Conduction and Stabilizing Dual Electrode Interfaces for Solid‐State Lithium Metal Batteries

ABSTRACT Lithium garnet‐reinforced composite polymer electrolytes are particularly promising for high‐voltage solid‐state lithium metal batteries. However, the uncontrollable surface contaminant formation on garnets critically degrades the interfacial contact with the polymer matrix, impedes Li + pathways, and limits the interface compatibility with both the cathode and lithium anode. Here, we exploit this passivation layer to initiate ring‐opening polymerization of fluorine‐containing organics, in situ generating fluorinated oligomers that function as molecular cross‐linkers between garnet fillers and polymer matrix. This precisely engineered interface creates homogeneous, high‐flux Li + migration channels throughout the electrolyte, yielding a high ionic conductivity of 1.43 × 10 −3 S cm −1 . The presence of abundant fluorine synergistically stabilizes electrodes by fostering LiF‐dominated layers on high‐voltage cathodes and Li metal anodes. The cell matching with the LiCoO 2 cathode can stably work for 200 cycles, and the symmetric Li cell can cycle for 1200 h without obvious potential fluctuation. This work presents a waste‐to‐value strategy that is expandable for developing a series of lithium garnet‐enhanced composite electrolytes for high‐voltage lithium‐metal batteries.