Predictive Modeling of Transport and Elastic Moduli of Porous Extreme Fast Charging Li-Ion Electrodes

Abstract

Extreme-fast-charging of Li-ion batteries, where the state of charge can be increased by 80% in less than 15 minutes, is increasingly important for electric vehicles. This work demonstrates how simulation can illuminate material- and fabrication-dependent ionic and electronic transport as well as mechanical properties of advanced, fast-charging Li-ion electrodes.Developing high-power Li-ion cells without compromising energy density is a challenge because of volumetric trade-offs between electronic and ionic transport and active material energy storage. Electrode materials and manufacturing steps both affect resulting microstructure and subsequently change transport properties.A multi-phase smoothed particle model was developed within LAMMPS to simulate the drying and calendering manufacturing processes for different electrodes. Generated structures were quantitatively assessed in terms of MacMullin number, electronic conductivity, and Young’s modulus to estimate the contribution of different materials and processing factors. Active material size, shape, stiffness, and orientation were varied.Model results suggest that the size of active particles needs to be taken into careful consideration, as the interaction of active material and binder can affect electrode shrinkage and porosity, ultimately affecting the transport and mechanical properties of the electrode (Figure 1).Spherical and disk shapes (representing typical cathode and anode active material shapes) show unexpected transport properties. These results suggest that the difference between a cathode and an anode is most likely due to the active particle intrinsic conductivity and stiffness.The stiffer the particles are, the more they can handle inter-particle stresses without deformation. On the other hand, distinctive particle orientations (a particle property observed in non-spherical anode active material) are decreased after calendering when the particles seem to align more horizontally, regardless of their original alignment.Careful selection of materials and attention to fabrication process parameters can produce Li-ion electrode microstructures more conducive to extreme-fast-charging.Figure 1. Simulated microstructures after drying (left structure in each pair) and calendering (right structure in each pair) with active particle sizes of: (a) 6 µm, (b) 2-15 µm, and (c) 15 µm. Figure 1