Thermal decomposition behavior and thermal stability of dimethyl carbonate-based electrolyte systems: A reactive molecular dynamics study

To elucidate the microscopic mechanism of thermal runaway in lithium-ion battery electrolytes and to optimize high-safety electrolyte formulations, four electrolyte systems containing a pure dimethyl carbonate (DMC) system, a dimethyl carbonate-ethylene carbonate (DMC-EC) mixed system, a dimethyl carbonate-fluoroethylene carbonate (DMC-FEC) mixed system, and a dimethyl carbonate-ethylene carbonate-fluoroethylene carbonate (DMC-EC-FEC) mixed system were constructed and different amounts (0%, 5%, and 10%) of lithium hexafluorophosphate (LiPF 6 ) were introduced into each system. ReaxFF MD simulations were performed to examine the thermal decomposition behavior, radical evolution, and product formation characteristics of each system under heating conditions (from 298 to 2500 K), thereby clarifying the regulatory mechanisms of solvent composition and lithium salt content on electrolyte thermal runaway. The results show that the pure DMC system exhibits the highest oxygen consumption and CO 2 production, indicating the most violent oxidation reactions. EC and FEC can significantly inhibit the severe oxidation of DMC, reduce the oxygen consumption rate and CO 2 generation, and enhance the thermal stability of the system. LiPF 6 exerts a concentration-dependent dual regulatory effect on thermal runaway, especially in the pure DMC system, it accelerates oxygen consumption via its decomposition product PF 5 , which catalyzes oxidation reactions, whereas in mixed systems containing EC or FEC, LiPF 6 exhibits an inhibitory effect, further improving the thermal stability of the system. The decomposition sequence of the carbonate solvents shows that FEC and EC decompose preferentially over DMC, with DMC being the latest decomposing component in all systems. These findings offer a theoretical foundation for designing high-safety electrolytes in lithium-ion batteries.