Tunable Fluorinated Polyether-Based Solid Electrolytes

Polymer electrolytes, owing to their low cost, ease of processing, low mass density, and nonvolatility, are promising candidates for making solid-state lithium batteries (LBs). Among them, fluorinated polymer electrolytes can effectively promote the formation of LiF-rich solid electrolyte interphases, thereby enhancing the long-term stability of the LBs. However, fundamental research on the electrochemical properties of fluorinated polyether electrolytes with lithium salts remains limited. In this study, a series of random copolyethers (PFTs, composition ratios = 0.5–2) were synthesized via cationic ring-opening copolymerization using 2,2,3,3-tetrafluoropropoxy-1,2-epoxypropane and tetrahydrofuran as monomers. These PFTs were blended with 5 wt % lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to form fluorinated polyether electrolytes. At 30 °C, the ionic conductivity of the PFT-based electrolytes reached 1.3 × 10–5 S·cm–1, with a lithium-ion transference number as high as 0.75 and an electrochemical stability window (ESW) of up to 5.7 V. Increasing the fluorine content (from PFT12 to PFT21) in PFT enhances both the ESW and lithium-ion transference number, while excessive fluorine content (PFT21) reduced the ionic conductivity. This study provides fundamental guidance for developing fluorinated polyether electrolytes with an excellent overall performance.