Thermal Degradation Mechanisms of the Solid Electrolyte Interphase on Graphite: Insights from ReaxFF Molecular Dynamics Simulations

ReaxFF molecular dynamics simulations were used to examine the thermal degradation of the solid electrolyte interphase (SEI) at a graphite/electrolyte interface in lithium-ion batteries. Above 450 K, the initially stratified SEI, comprising an inorganic inner layer and an organic outer layer, progressively transforms into a disordered and porous mixed phase. Heating accelerates electrolyte decomposition, broadens the product speciation, promotes CO2 and HF evolution, and destabilizes the interface. The dominant bond-breaking sequence is C–O cleavage, followed by Li–O and P–F cleavage. These events are coupled in a degradation network rather than occurring independently. The results provide atomistic insight into thermally driven SEI failure and identify design targets for thermally robust battery interfaces.