Fluorine-Induced Anion Anchoring in Novel Polymer Electrolytes for High-Performance Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are pivotal for safer, high-energy-density lithium metal batteries but remain constrained by the intrinsic limitations of ionic transport within the polymer matrix. Conventional polyethylene oxide (PEO) electrolytes typically exhibit low lithium transference numbers ( t Li+ ) and narrow electrochemical stability windows (< 3.8 V), severely hindering their integration with high-voltage cathodes and limiting overall rate capability. Here, we describe a fluorine-induced anion anchoring strategy enabling PEO-based copolymer electrolytes with regulated anion-Li solvation via rational molecular design. By integrating monofluoromethylene (CHF) and difluoromethylene (CF 2 ) units into the polymer backbone, the continuous polarized C-H bonds serve as effective binding sites. These sites immobilize anions to promote salt dissociation and reconfigure the solvation environment. This synergistic modulation facilitates a distinct transition from the traditional cation-trapped solvation structure to an anion-anchored solvation motif. Furthermore, the fluorinated backbone imparts superior oxidative stability, ensuring compatibility with high-voltage cathodes. Consequently, symmetric Li||Li cycling demonstrates stable operation for over 1000 hours. This performance is attributed to the CHF/CF 2 motifs, which promote the in-situ formation of a robust, LiF-rich solid electrolyte interphase (SEI). This stable interface effectively suppresses lithium dendrite growth and reduces interfacial resistance. This work offers a critical molecular-level design strategy by simultaneously introducing fluorination and specific anion-binding sites within a single structural motif. Figure 1