Structure-dependent combustion hazards and microscopic reaction pathways of ionic liquids under high-temperature conditions

To uncover the microscopic origins of structure-dependent combustion hazards in ionic liquids (ILs), this study integrates macroscopic thermal analysis (TG-DSC, TG-FTIR, cone calorimetry) with ReaxFF molecular dynamics simulations on 16 ILs categorized into imidazolium, quaternary ammonium, and quaternary phosphonium types. Experimental results show that combustion parameters (e.g., ignition time, heat release rate) are governed by cation frame and anion type. Crucially, ReaxFF simulations reveal that these macroscopic differences stem from distinct microscopic reaction pathways: the high bond energy and steric hindrance of the imidazolium ring lead to a “slow-start, low-peak, long-lasting” risk pattern, while the facile cleavage of C N/C-P bonds in quaternary ammonium/phosphonium ammonium ILs causes a “fast-start, high-peak, short-duration” pattern. This work establishes a direct link from molecular structure to macroscopic fire risk, providing a theoretical basis for intrinsic safety design.