Modeling Diffusion-Induced Stress in Li-Ion Cells with Porous Electrodes

A mathematical model for diffusion-induced stress generation in spherical Li-ion active materials has been incorporated into Dualfoil, a Li-ion cell-sandwich model with porous electrodes. The model is used to examine differences in the electrochemomechanical response of "power" vs "energy" cells at high currents. Porous electrode effects, particularly in "energy-type" cells with thick electrodes, amplify the peak stresses encountered during lithium insertion and extraction and may result in nonuniform decrepitation or disordering through the depth of the electrode. We also elucidate the roles of fragment connectivity, volume expansion factors, nonlinear lattice expansion, and variable solid-state diffusion on diffusion-induced stress, stress-induced diffusion, and the voltage response of dual-intercalation cells with porous electrodes. In conventional electrode materials (with small volume expansion), pressure diffusion plays a limited role in determining the galvanostatic voltage response but becomes important in determining the stress response. Pressure diffusion and nonlinear lattice expansion play an important role in determining both the voltage and stress response in large-volume-expansion materials (e.g., alloys and perhaps graphite at low utilization).