Molecular Dynamics Study of Fracture Behavior of LiMn2O4 in Li-Ion Batteries

Fracture represents one of key degradation mechanisms in Li-ion batteries over repeating cycles, because it causes the loss of electric contact and increases the surface areas exposed to the electrolyte. To address this issue, considerable efforts have been made to develop mechanical models. In this study, the fracture toughness of LiMn2O4 was calculated by molecular dynamics (MD) simulations. For these calculations, the stress response of LMO materials was obtained upon tensile loading. The MD simulations showed that the fracture stress decreased and plastic behavior increased at the atomic scale as Li concentrations decreased. The decomposition of the stress response revealed that the Mn4+–O2− pair interaction dominated the decline in the fracture stress. In addition, hopping of Li ions to empty sites at low Li concentrations initiated amorphization, enhancing the plastic behavior. From the simulations, the fracture toughness of LiMn2O4 was calculated as about 1.4 MPam1/2 and that of Li05Mn2O4 as about 1.6 MPam1/2. The values calculated for fracture toughness can serve as useful input for the continuum model of fracture analysis in Li-ion batteries to guide operating conditions and engineering design of electrode materials.