No abstract

Automotive manufacturers are currently working to produce commercially-viable electric trucks, driving the need to develop batteries that are higher in energy density and lower in cost. To realize this, cell designers have introduced blended silicon-graphite anodes to combine the high energy density of silicon with the stability and relatively lower mechanical degradation of graphite. As more blended anodes with high lithiation-based volume change are considered, the need to simultaneously account for mechanical and electrochemical phenomena increases. In this study, the focus is to learn how preferential lithiation (caused by differing equilibrium potentials and other intercalation kinetics of the two blended active materials) impact the coupled electrochemical performance and mechanical phenomenon at the electrode and cell scales. To do this, adaptations of previous modeling methods are proposed that treat the active materials as separate particles, representing the mixing of two active materials powders within a slurry. For comparison, the historically-used assumption is shown, where the blended active materials lithiate uniformly. The resulting simulations show that preferential lithiation of the blended materials will have a significant impact on both electrochemical and mechanical phenomena. Discussion is also provided with regard to C-rate, blended electrode composition, and other mechano-electrochemical behavior.

Automotive battery manufacturers are working to improve individual cell and overall pack design by increasing their performance, durability, and range, while reducing cost and active material volume change is one of the more complex aspects that needs to be considered during this process. To improve the balance between cost, stability, performance, and volume change behavior, some cell designers have introduced the use of multiple active materials within the same composite electrode. For example, LiMn2O4 (LMO) and LiNi1/3Co1/3Mn1/3O2 (NMC) active materials are both included in cathodes to benefit from this balance. In anodes, some designers have included both silicon and graphite to maximize gravimetric capacity while maintaining a tolerable degree of volume expansion to prevent damage to the cell and pack structure. While the inclusion of multiple active materials can be used to better tune electrode performance, stability, and volume change for specific applications, the modeling of these electrodes is significantly more complicated. Previously, Albertus et. al developed a model to account for multiple active materials within the same positive electrode.(1) Their model took the concept of a pseudo-two dimensional Li-ion cell model and incorporated multiple pseudo second-dimensions, which correlates to the radial direction of a theoretical active material particle. Therefore, they could account for each active material separately, where previously, an average particle radius, average film resistance, and average equilibrium potential would be assumed for the total electrode. In the study shown here, we build upon this modeling concept by incorporating our previously developed mechano-electrochemical equations to account for active material volume change.(2-5) Figure 1 shows an example of equilibrium potentials for two anode active materials as a function of lithiation fraction. The difference between these equilibrium potentials will dictate the preferential lithiation of the materials, and thus, the rate at which each material undergoes lithiation-based volume change. This allows for the simulation of volume change in diffusion-governed (high rate) or kinetic-governed (low rate) charge and discharge.The relationships between anode/cathode capacity, electrode voltages, and active material volume will be discussed. References P. Albertus, J. Christensen and J. Newman, Journal of The Electrochemical Society, 156, A606 (2009). T. R. Garrick, K. Higa, S.-L. Wu, Y. Dai, X. Huang, V. Srinivasan and J. W. Weidner, Journal of The Electrochemical Society, 164, E3592 (2017). T. R. Garrick, X. Huang, V. Srinivasan and J. W. Weidner, Journal of The Electrochemical Society, 164, E3552 (2017). T. R. Garrick, K. Kanneganti, X. Huang and J. W. Weidner, Journal of The Electrochemical Society, 161, E3297 (2014). D. J. Pereira, J. W. Weidner and T. R. Garrick, Journal of The Electrochemical Society, 166, A1251 (2019). D. J. Pereira, M. A. Fernandez, K. C. Streng, X. X. Hou, X. Gao, J. W. Weidner, and T. R. Garrick, Journal of The Electrochemical Society, 167, 080515 (2020). Figure 1. Equilibrium potential as a function of lithiation fraction for two anode active materials. Figure 1