Solvent-free green synthesis of nonflammable and self-healing polymer film electrolytes for lithium metal batteries

Fire-resistant and self-healing flexible electrolytes are a promising alternative to address thermal runaway in lithium batteries. However, self-healing electrolytes for lithium batteries are not widely used due to their low ionic conductivity, limited self-healing ability, and potential combustion risk. Ionic liquid-based polymer electrolytes are a simple and effective approach to obtaining polymer solid electrolytes with high ionic conductivity, fast self-healing and flame retardant properties. In this work, methyl methacrylate (MMA) and 1-Allyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide (AMIMTFSI) are used as the membrane-forming backbone and also possess ion transport channels. 1-ethyl-3 methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (EMIMTFSI) is added to the membrane to further enhance the ionic conductivity. Due to the existence of ionic liquid units and free ionic liquids in the prepared electrolytes, the fast interaction of ionic bonds confers a faster self-healing ability to the films, and the flame retardancy of the ionic liquids is fully maintained after polymerization. The prepared electrolytes show good flame retardance properties, excellent mechanical properties (tensile rate is ∼ 400%), high thermal decomposition temperature (>260 °C), and can effectively enhance the reliability of lithium metal batteries. When ionic liquids filler mass fraction is 40%, the polymer electrolytes have an ionic conductivity of 1.9 × 10^-4 S cm⁻¹, a decomposition voltage of 4.6 V (vs. Li/Li⁺), and can achieve an initial discharge capacity of 134.9 mAh g⁻¹ with a capacity retention of 96.4% after 90 cycles at 0.1C for LiFePO₄/Li half-cell at 25 °C.