Investigation of the Effect of Electrode Design and Material Parameters on the Homogeneity of Reaction Current Density Distribution in Hybrid Anodes Using Continuum Scale Modeling

Abstract

Li-ion batteries that have both high-energy density and high-power density are necessary for achieving widespread adoption of electric vehicles. One approach to achieve these properties simultaneously is to employ the hybrid electrode design where two or more active materials are uniformly mixed to fabricate the composite electrodes. Such a design can enable one to exploit the advantages of all the active materials while overcoming their limitations. For instance, it is known that graphite anodes (with loading > 3mAh/cm2) exhibit high energy density, but they suffer from poor rate performance due to high inhomogeneity of reaction current density distribution. On the other hand, hard carbon anodes exhibit high power density, but have low energy density due to the high open circuit voltage (OCV) and low initial coulombic efficiency of hard carbon. However, when the two active materials are combined in equal proportions (in mass fraction), the resulting hybrid anode has been reported to exhibit both high energy and power densities 1. In the hybrid anode, the hard carbon reduced inhomogeneity of the reaction current density distribution, while the graphite component provided the high energy density. However, it is not fully understood what causes the observed improvement in the rate performance of the energy-dense hybrid anodes. There are several factors that influence the homogeneity of the reaction current density within a hybrid anode. These factors can be broadly categorized into two categories. First, factors related to electrode design that such as electrode thickness, porosity, and volume fractions of the active materials. Second, factors related to material properties such as OCV, solid state diffusivity, electrolyte diffusivity and conductivity, exchange current density, and average particle size. In this study, we investigate the effect of each of these parameters on the homogeneity of the reaction current density distribution both qualitatively and quantitatively using continuum-scale modeling. Our results offer new insights for designing and potentially optimizing hybrid electrodes. In addition to our modeling results, we will also discuss a fully-automated method of parameterizing the continuum-scale model.Reference: K. Chen et al., Adv. Energy Mater., 11, 2003336 (2021) https://onlinelibrary.wiley.com/doi/10.1002/aenm.202003336.