Deep Eutectic Interaction Induced Lithium Salt Dissociation for Inorganic‐Rich Solid Electrolyte Interphase in All‐Solid‐State Batteries

All‐solid‐state lithium (Li) metal batteries incorporating solid polymer electrolytes (SPEs) have emerged as promising candidates for next‐generation energy storage technologies due to their theoretically superior energy density and inherent safety. However, due to the limited dissociation of Li salts in SPEs, the native solid electrolyte interphase (SEI) typically manifests insufficient inorganic constituents, leading to sluggish and heterogeneous Li‐ion transport kinetics. Herein, the dissociation of Li salts is significantly enhanced by deep eutectic interaction between 1,3‐dimethylurea (DMU) molecules and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), which constructs a Li2S and LiF‐rich SEI. The resultant SEI demonstrates remarkably enhanced Li‐ion transport kinetics and stability, enabling an impressive performance of 2900 h in symmetrical cells. Moreover, the all‐solid‐state LiFePO4 | Li cells benefiting from the Li2S and LiF‐rich SEI maintain 80% capacity retention over 700 cycles and demonstrate a high specific capacity of 91 mA h g−1 after 1000 cycles at a high rate of 1.0 C. This study provides a simple and accessible method to enhance the dissociation of Li salt by deep eutectic interactions, which assists in constructing an inorganic‐rich SEI and achieves performance improvement of all‐solid‐state Li metal batteries.