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

• Published in: Advanced materials (Weinheim) 2023-07, Vol.35 (28), p.e2300998-n/a
• Main Authors: Sun, Qifang, Wang, Su, Ma, Yue, Song, Dawei, Zhang, Hongzhou, Shi, Xixi, Zhang, Na, Zhang, Lianqi
• Format: Article
• Language: English
• Subjects: Carbonates; Diffusion barriers; Electrolytes; fluoroethylene carbonate; gel polymer electrolytes; Gels; high safety; Lithium; Li‐ion transfer mechanism; Molecular dynamics; Molten salt electrolytes; Polymers; Segments; Solid electrolytes; Solvents; stable interfaces; Vinyl Compounds
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202300998

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. A gel polymer electrolyte is in situ solidified with fluoroethylene carbonate and ester monomers to investigate the Li‐ion transfer mechanism. Therein, an electron‐delocalization interface layer between the solvent and the polymer matrix is formed. With lower ion‐diffusion barrier, the electron‐rich “Milky Way” is expected as a novel ion‐transfer path, facilitating Li‐ion migration.