In lithium metal batteries, sluggish Li⁺ desolvation and anion-dominated ion transport at the separator–electrolyte interface fundamentally limits interfacial kinetics and trigger unstable lithium deposition. Lithium metal batteries suffer from slow interfacial kinetics and unstable lithium deposition, due to poor Li⁺ desolvation and uncontrolled anion transmittance at the separator–electrolyte interface. Here, a sulfonate-functionalized graphene was coated onto a polypropylene (PP) separators to construct an intrinsic anionic electrostatic field layer, which simultaneously regulates ion transport and promotes interfacial desolvation. This negatively charged field not only repels anions but also reshapes the local solvation environment, thereby facilitating Li⁺ desolvation and transport, leading to a high lithium-ion transference number of 0.79. Meanwhile, the negatively charged interface repels polarized solvent molecules and redistributes local electric field lines, weakening Li⁺-solvent charge–dipole interactions and lowering the Li⁺ desolvation energy barrier, thereby accelerating Li⁺ transport kinetics. Benefiting from homogenized Li⁺ flux and facilitated desolvation, the modified separator enables uniform lithium deposition and effectively suppresses dendrite growth, allowing Li symmetric cells to cycle stably for over 1000 h with low polarization. In full cells, Li||NCM622 batteries exhibit excellent high-voltage cycling stability, achieving 82% capacity retention after 1000 cycles, more than doubling that of cells using conventional PP separators. Moreover, Si–C||NCM811 pouch cells retain over 80% capacity after 700 cycles at 1C, demonstrating promising scalability and practical applicability.

The application of solid polymer electrolytes (SPEs) is severely impeded by the insufficient ionic conductivity and low Li⁺ transference numbers (t_Li⁺). Here, we report an iodine-driven strategy to address both the two long-standing issues of SPEs simultaneously. Electronegative iodine-containing groups introduced on polymer chains effectively attract Li⁺ ions, facilitate Li⁺ transport, and promote the dissociation of Li salts. Meanwhile, iodine is also favorable to alleviate the strong O−Li⁺ coordination through a Lewis acid–base interaction, further improving the ionic conductivity and t_Li⁺. As a proof of concept, an iodinated single-ion conducting polymer electrolyte (IPE) demonstrates a high ionic conductivity of 0.93 mS cm⁻¹ and a high t_Li⁺ of 0.86 at 25 °C, which is among the best results ever reported for SPEs. Moreover, symmetric Li/Li cells with IPE achieve a long-term stability over 2600 h through the in-situ formed LiF-rich interphase. As a result, Li−S battery with IPE maintains a high capacity of 623.7 mAh g⁻¹ over 300 cycles with an average Coulombic efficiency of 99%. When matched with intercalation cathode chemistries, Li/IPE/LiFePO₄ and Li/IPE/LiNi_0.8Mn_0.1Co_0.1O₂ solid-state batteries also deliver high-capacity retentions of 95% and 97% at 0.2 C after 120 cycles, respectively.