Functionalized Organic Lithium Salt Enables Flexible Solid‐State Electrolytes With Dual‐Ion Channels for Safe Li Metal Batteries

Solid electrolytes, developed to address the safety hazards of liquid electrolytes, still face some issues, such as low ionic conductivity, non‐flame retardancy, and poor compatibility with electrodes. Herein, an organic ionic liquid lithium salt (named PQ‐Li) with good intrinsic conductivity and flame retardancy was synthesized, and a flexible and homogeneous all‐solid “polymer in salt” electrolyte, composed of 73.15 wt% PQ–Li and 26.85 wt% poly(ethylene oxide) (PEO), referred to as PQSE, was prepared. This preparation strategy, based on a dual‐functional lithium salt, endows PQSE with great electrochemical performance (e.g., an ionic conductivity of 0.11 mS m −1 at 30°C, and an electrochemical stability window of 5.1 V), excellent flame retardancy, and good compatibility with Li electrodes considering the absent short circuits and lithium dendrites. The sound charge/discharge performance of Li|PQSE|LiFePO 4 cells (e.g., a discharge capacity of 150.6 mAh g −1 at 0.1 C, Coulombic efficiency beyond 99%, and repeatable power‐supply processes for light‐emitting diode bulbs) exactly results from the formation of a stable solid–electrolyte interface film with a favorable bilayer architecture. Through molecular dynamic simulation and two‐dimensional correlation Raman technique, a dual‐channel Li + conduction mechanism in PQSE under an electric field has been proposed, with the dominant mode relying on the hopping of Li + in ionic aggregates/bridges, and the auxiliary mode relying on the random movement of PEO segments coordinating with Li + . The developed PQSE provides a trade‐off of safety, electrochemical properties, and processibility of electrolytes and represents a promising avenue in solid‐state lithium battery technologies.