Polymer‐Assisted Supercooled Lithium Salts: Nonflammable Single‐Ion Conducting Liquid Electrolytes for Next‐Generation Batteries

ABSTRACT Electrolytes that exhibit both high ionic conductivity and a near‐unity Li + transference number ( t Li ) are essential for next‐generation rechargeable batteries. Here, we present solvent‐free liquid electrolytes based on polymer‐assisted supercooled lithium salts that realize single‐ion conduction under ambient conditions. A trace amount of poly(methyl methacrylate) suppresses crystallization, stabilizing low‐melting Li salts in a deeply supercooled liquid state while retaining t Li ≈ 1. To further enhance ion transport, we employ a dual‐salt strategy, which lowers the glass transition temperature and increases ionic conductivity without compromising the near‐unity t Li . Despite moderate conductivity compared with conventional electrolytes, these supercooled salts suppress concentration overpotentials and support stable cycling in Li/LiCoO 2 cells. The intrinsic adhesive properties of the electrolytes enable the fabrication of binder‐free thick cathodes with high areal capacities, providing a scalable route to high‐energy‐density batteries. Furthermore, the solvent‐free nature of these electrolytes ensures intrinsic nonflammability and promotes the formation of robust inorganic‐rich interphases, indicating their potential applicability to lithium‐metal batteries. This work establishes polymer‐assisted supercooled lithium salts as a new class of nonflammable single‐ion conducting liquid electrolytes, bridging the gap between solid‐state and conventional liquid systems.