A Rigid-Flexible Polyinterface Enabling Molecular-Level Dual-Ion Regulation for Ultrastable Lithium Metal Batteries

The unstable lithium metal anode plagued by dendrite growth and parasitic reactions remains a formidable barrier to realizing high-energy-density batteries. While artificial solid-electrolyte interphases offer a protective strategy, most designs are limited to single-ion regulation and fail to orchestrate the complex, dual-ion (Li⁺ and anion) chemistry at the molecular level. Here, we report a rationally designed polymeric artificial interphase of poly-fluorotoluene-triglycoldimercaptan (PFT) featuring rigid fluorinated benzene rings and flexible sulfur-oxygen chains for synergistic dual-ion regulation. The flexible segments enable gradient Li⁺ coordination with differential binding energies, lowering desolvation barrier and facilitating uniform Li⁺ transport, whereas the rigid electron-deficient fluorinated rings trap TFSI^- anions via anion-π interactions. This dual modulation directs the in-situ formation of a robust, LiF-Li₂S-rich inorganic composite SEI, as validated by calculations and spectroscopy. The PFT-based Li anodes exhibit exceptional stability, with symmetric cells operating over 4000 h at 1 mA cm^-2, 1 mAh cm^-2. A high-loading LiFePO₄ full cell retains 80% capacity after 1000 cycles at 5 C, and an NCM811 pouch cell retains 85% capacity after 160 cycles at 0.5 C, demonstrating practical viability. This work establishes a molecular design principle for dual-ion regulation via a polyinterface for high-performance Li metal batteries.