Li‐Ion Transfer Mechanism of Gel Polymer Electrolyte with Sole Fluoroethylene Carbonate Solvent

Abstract Although gel polymer electrolytes (GPEs) represent a promising candidate to address the individual limitations of liquid and solid electrolytes, their extensive development is still hindered due to the veiled Li‐ion conduction mechanism. Herein, the related mechanism in GPEs is extensively studied by developing an in situ polymerized GPE comprising fluoroethylene carbonate (FEC) solvent and carbonate ester segments (F‐GPE). Practically, although with high dielectric constant, FEC fails to effectively transport Li ions when acting as the sole solvent. By sharp contrast, F‐GPE demonstrates superior electrochemical performances, and the related Li‐ion transfer mechanism is investigated using molecular dynamics simulations and ⁷Li/⁶Li solid‐state nNMR spectroscopy. The polymer segments are extended with the swelling of FEC, then an electron‐delocalization interface layer is generated between abundant electron‐rich groups of FEC and the polymer ingredients, which works as an electron‐rich “Milky Way” and facilitates the rapid transfer of Li ions by lowering the diffusion barrier dramatically, resulting in a high conductivity of 2.47 × 10⁻⁴ S cm⁻¹ and a small polarization of about 20 mV for Li//Li symmetric cell after 8000 h. Remarkably, FEC provides high flame‐retardancy and makes F‐GPE remains stable under ignition and puncture tests.