Decoupled Ion Transport via Triadic Molecular Synergy in Flame-Retardant Quasi-Solid Electrolytes for Safe Lithium Metal Batteries

Abstract

Ionic liquids (IL)-based quasi-solid polymer electrolytes (QSPEs) hold promise for safe lithium metal batteries owing to their tunable electrochemical properties and processability. However, traditional design strategy has ignored the interdependencies among “component-function-interface”, leading to compromised practical applications hindered by sluggish lithium-ion transport kinetics and safety concerns. Herein, a triadic molecular synergy paradigm is proposed to decouple lithium-ion conduction mechanisms in flame-retardant QSPEs. Pentaerythritol tetraacrylate-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) provides the structural framework, while the IL (1-butyl-3-methylimidazole bis (trifluoromethylsulfonyl) imide, BmimTFSI) as a plasticizer softens the polymer chains by weakening the intermolecular forces to provide an additional ion-transport pathway while imparting flame-retardant properties. Additionally, the highly electronegative fluorine atoms of the additive (2-(perfluorohexyl)ethyl methacrylate, PFMA) promote LiTFSI dissociation through electron cloud migration, simultaneously immobilizing TFSI⁻ anions and suppressing cationic competition through strong PFMA−Bmim⁺ coordination. As a proof-of-concept, this synergistic design achieves a high lithium-ion transference number (0.72), forms a stable lithium fluoride-dominated interphases, and enhances battery safety via a condensed-phase flame-retardant mechanism. Experimental validation demonstrates that the designed quasi-solid electrolyte significantly enhances cycling stability in Li symmetric cells, Li||LiFePO₄ and Li||LiNi_0.8Co_0.1Mn_0.1O₂ cells. The proposed molecular engineering strategy establishes a paradigm for developing high-performance QSPEs in lithium metal batteries.