Material parameters affecting Li plating in Si/graphite composite electrodes

Abstract

Silicon is a frequently used active material in the negative electrode of lithium-ion batteries which provides significant improvements in the energy density. Due to large volume changes during cycling, it is typically mixed with graphite. Understanding the interactions of composite materials during battery operation is key to optimizing battery performance and predicting aging phenomena. Even though lithium plating is a critical degradation process, which influences both lifetime and safety, a systematic analysis of electrochemical material parameters affecting plating in composite electrodes is missing. Therefore, a parameter study is performed using 3D microstructure-resolved simulations. We investigate the influence of critical material parameters such as open-circuit potential, electronic conductivity, chemical diffusion coefficient, and exchange current density in simple and interpretable model geometries. The simulations reveal the importance of chemical diffusion and exchange current density, as well as their ratio, in predicting plating. Finally, we apply the set of material parameters to a complex electrode geometry reconstructed from FIB/SEM tomography data of commercial anode material. The analysis shows that preferential plating on the electrode surface dominates all other factors.