Elucidating Kinetic-Mediated Polymerization Behavior for In Situ Formation of Fluorine-Containing Gel Polymer...

Fluorinated gel polymer electrolytes (FGPEs) prepared via in situ polymerization are expected to expedite the large-scale application of lithium metal batteries (LMBs) by enabling stable LiF-rich solid electrolyte interphases (SEIs) and good compatibility with high-voltage cathodes. However, the electron-withdrawing nature of fluorine units retards polymerization kinetics of such monomers, resulting in GPEs with compromised mechanical performance and cycling durability. Herein, a design principle for in situ formation of fluorinated copolymers is proposed to regulate the polymerization kinetics of trifluoroethyl methacrylate (TFEMA)-typed monomers. Such strategy yields relatively uniform polymer chains with moderate molecular weights, which are subsequently crosslinked to form a robust fluorinated-nitrogenated copolymer network (FNPE). The tailored polymer matrix integrates the capabilities to form a LiF-containing SEI promoted by fluorinated segments, enhanced mechanical robustness, and a Li₃N-rich interphase contributed by the N-isopropylacrylamide (NIPAM) domains. Consequently, the FNPE achieves NCM811(6.8 mg cm^-2, 1.2 mAh cm^-2)//Li full cells with high capacity retention (> 80%, 225 cycles), and applicable in wide temperature range (-15 to 60°C) and pouch cell configuration (40 µm Li). Through experimental and multiscale modeling investigations, this work elucidates the intrinsic kinetic challenge for in situ formed FGPEs and provides a new design principle of copolymer-type electrolytes for durable LMBs.