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

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/LiBF₄ 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 LiFePO₄||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.