Halogen‐Induced Anion‐Rich Solvation Structure Enables High Li ⁺ Transference Number of Gel Polymer Electrolyte for Durable Lithium Metal Batteries

ABSTRACT Gel polymer electrolytes (GPEs) show great promise for lithium metal batteries (LMBs), yet achieving a durable Li anode remains challenging due to the instability of the solid electrolyte interphase (SEI) layer. Regulating the Li ⁺ solvation structure is a critical approach to construct an effective SEI layer on the Li anode. In this work, a nanofiber membrane with polyethylenimine‐iodine (PEI‐I)/PAN complex core and polyacrylonitrile/polyvinylidene fluoride‐co‐hexafluoropropylene (PAN/PVDF‐HFP) polymer sheath (P‐I/P@P/P) is elaborately designed and prepared via the electrospinning method. The synergistic effect between the three‐dimensional matrix and the slowly released PEI‐I additive not only suppresses the combustion property of traditional GPEs, but also promotes the lithium‐ion desolvation and the generation of inorganic SEI layer on Li anode. As demonstrated, the optimized P‐I/P@P/P GPE delivers a high Li ⁺ transference number of 0.88, high ionic conductivity of 2.34 mS cm ⁻¹ , and heterogeneous SEI composition of Li ₃ N/Li ₂ CO ₃ /LiF. The corresponding Li||Li cell achieves stable voltage polarization for 1000 h at 5 mA cm ⁻² , and the Li||Cu cell displays a high Coulombic efficiency of 97.84%. Satisfyingly, the targeted Li||LiFePO ₄ battery exhibits an impressive capacity retention ratio of 97% after 3000 cycles. These findings offer a design paradigm for functional GPEs to drive the implementation of high‐energy‐density LMBs in practical scenarios.