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, 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 finelong-term cycling performance in full cells, maintaining 93.2% capacity retention after 150 cycles at 0.1C with LiFePO4 (LFP) cathodes. The electrolyte also proved compatible with high-nickel LiNixCoyMn1-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, safe solid-state batteries.