Fluorinated DOL-based copolymer electrolytes enabling wide electrochemical window and stabilized interphases for lithium batteries

Abstract

Solid polymer electrolytes for lithium batteries face critical challenges including low ionic conductivity, unstable interphases and narrow electrochemical window. To overcome these limitations, we developed an in situ polymerized fluorinated polyether electrolyte via LiPF₆-initiated ring-opening copolymerization of 1,3-dioxolane (DOL) and glycidyl 2,2,2-trifluoroethyl ether (GTE) monomers. Our molecular design incorporates pendant fluorinated moieties, leveraging their high electronegativity to enable multifunctional properties. This fluorination strategy simultaneously enhances Li⁺ dissociation, achieving a high ionic conductivity of 7.3 × 10⁻⁴ S cm⁻¹, and fosters the formation of stable, ion-conductive yet electron-insulating interphases rich in LiF on both electrodes. The robust C–F and M–F bonds confer exceptional non-flammability with ignition resistance exceeding 10 seconds and thermal stability above 300 °C. Consequently, the electrolyte exhibits an ultra-wide electrochemical stability window surpassing 5.9 V and an ultralow Li⁺ migration activation energy of 0.22 eV. The PDOL/GTE-IL electrolyte significantly enhances interfacial stability, evidenced by Li‖Li symmetric cells operating steadily for over 650 hours with minimal overpotential at 0.05 mA cm⁻², far exceeding the PDOL-IL control which failed after 450 hours. The electrolyte also enables superior rate capability (154.8 mAh g⁻¹ at 0.1C with 91.5% capacity recovery) and good long-term cycling performance in full cells, exhibiting 93.2% capacity retention after 150 cycles at 0.1C with LiFePO₄ (LFP) cathodes. The electrolyte also proved compatible with high-nickel LiNi_xCo_yMn_1−x−yO₂ (NCM) cathodes, enabling, for instance, a sustained capacity of 180 mAh g⁻¹ after 100 cycles at a 1C rate with the NCM622 cathode. This molecular engineering approach establishes a scalable platform for high-performance and safe solid-state batteries.