Thermal runaway mechanism of LiFePO4 battery electrolytes: a molecular dynamics and density functional theory simulation study

Abstract

LiFePO₄ (LFP) batteries are widely used in power and energy storage applications due to their high safety, but their large-scale applications are still constrained by the thermal runaway problem, and the mechanism of electrolyte thermal stability has yet to be elucidated. To deeply understand the behavior of LFP battery electrolytes during thermal runaway, this study uses a commercial mixed-solvent electrolyte system as the research object and adopts the method of combining molecular dynamics (MD) and density functional theory (DFT) to systematically analyse ionic migration, solvation structures, and degradation pathways. Calculation results show that in the undegraded stage of the electrolyte, temperature increase has a dual effect on the migration behavior of ions, where the molecular thermal motion and the dynamics of the solvation shell synergistically enhance the diffusion rate of ions. In the thermal degradation stage, the degradation rate of solvent molecules generally shows a three-stage characteristic of “rise-fall-rise”, in which EC is the first to decompose and dominates the initial degradation due to the concentration of electrostatic potential and the high ring strain. In addition, the thermal degradation behavior of each solvent is significantly different due to the molecular structure, the catalytic effect of PF₅, and the coupling of bond dissociation energies.