Spatial‐Interfacial Dual Confinement in Phase‐Separated Polymer Electrolytes for Cryogenic Lithium Metal Batteries

ABSTRACT Quasi‐solid‐state polymer electrolytes (QSPEs) hold immense promise for intrinsically safe lithium metal batteries. However, operating QSPEs in sub‐zero environments exposes a critical material design conflict: achieving rapid low‐temperature bulk ion transport typically necessitates highly polar solvents (e.g., DMSO), which conversely trigger parasitic reactions and dendrite growth at the lithium anode. Herein, we propose a hierarchical heterogeneous QSPE via a polymerization‐induced phase separation (PIPS) strategy. The resulting biphasic structure integrates a highly conductive DMSO‐LiTFSI/LiBF ₄ liquid microdomain within a crosslinked fluorinated polymer framework, employing a synergistic “dual‐confinement” mechanism. Spatially, geometric confinement within the polymer scaffold disrupts the long‐range ordering of DMSO, thereby suppressing crystallization and lowering the glass transition temperature of the phase‐separated QSPEs to −100.6°C and −53.8°C. Interfacially, the dual‐salt formulation induces an organic‐inorganic bilayer SEI, completely shielding reactive DMSO from the lithium surface. Consequently, the assembled LiFePO ₄ ||Li full cells demonstrate outstanding rate capability and long‐term cycling stability under rigorous sub‐zero conditions, offering a highly viable structural design paradigm for extreme‐environmental energy storage.