Long‐Life Lithium Metal Batteries Enabled by In Situ Solidified Polyphosphoester‐Based Electrolyte

The practical application of lithium metal batteries (LMBs) is hindered by the imbalanced periodic oscillatory distribution of cations/anions in liquid electrolytes (LEs) and thus the formed mechanically vulnerable solid electrolyte interphase (SEI), which collectively exacerbate lithium (Li) dendrite formation and degrade electrochemical stability. To overcome these issues, a polyphosphoester electrolyte (PPUM-PE) is designed through a dual-ion regulation strategy. The ‒NH‒ moieties in PPUM polymer effectively anchor anions, while its P═O/C═O functional groups reconstruct Li⁺ solvation architecture, collectively enabling an exceptional Li⁺ transference number (0.82) and improved reductive stability of the solvation sheath. A bilayer SEI layer formed on Li anodes-composed of an outer lithium-containing alkyl phosphate polymer and an inner LiF-enriched inorganic phase-exhibits high Young's modulus, effectively suppressing Li dendrite propagation and continuous electrolyte decomposition. Impressively, the as-assembled LMBs employing LiFePO₄ cathodes retain 91.28% capacity retention after 1000 cycles at 1C. The electrolyte also demonstrates good compatibility with high-voltage cathodes (LiCoO₂, LiNi_0.8Co_0.1Mn_0.1O₂) and substantially improves battery thermal safety. This dual-ion synergistic regulation provides a scalable pathway toward high-energy-density LMBs.