Molecular Dynamics Simulations of SOC-Dependent Elasticity of LixMn2O4 Spinels in Li-Ion Batteries

As has been experimentally observed, stresses due to lithium intercalation, phase transition, and thermal loading can cause local fractures in Li-ion battery active materials. These fractures are one of the main degradation mechanisms in Li-ion batteries. Consequently, predicting the stress level inside of the electrode material is of key importance in designing cells and determining their operation conditions. For lithium manganese oxides, however, the values of Young's modulus that have been reported so far differ widely, resulting in commensurately wide gaps between actual and predicted stress levels. Moreover, little is known about how the Young's modulus changes at different states of charge (SOC). In this study, molecular dynamics (MD) simulations were performed to investigate the Young's moduli of LixMn2O4 as a function of SOC (0 < x < 1). MD simulations show that the Young's moduli vary almost 18% depending on SOC. By decomposing interaction forces between atoms, we analyzed how pair interactions influence the variance. The results suggest that the SOC-dependence of Young's modulus may have an effect on both the stress level inside the particle as well as on Li-ion transport as a result of their mutual coupling to Li-ion diffusivity. (C) 2013 The Electrochemical Society. All rights reserved.