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‐Li 2 S‐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 LiFePO 4 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.