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

Abstract

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||LiFePO 4 and Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells. The proposed molecular engineering strategy establishes a paradigm for developing high‐performance QSPEs in lithium metal batteries.