To aid in Si electrode design and account for dynamic particle expansion/contraction, the standard pseudo-2D battery model is reformulated to account for finite-strain chemo-mechanics. This model explores the trade-offs between initial electrode porosity, electrode thickness, rate-capability, and external pressure. Additionally, the model implements simplified SEI growth dynamics to explore how SEI growth effects should be accounted for in electrode design.
The Figure illustrates polarization responses for a 1C charge for a Si/NMC532 cell. The different colors indicate different initial anode porosities. As shown in Figure a, the low initial porosity cases results in significant polarization, but additional gains after 50% initial porosity are significantly diminished. These results are shown for an external pressure of 15 psi. Figure b illustrates the cell thickness as a function of time. As illustrated, the lower porosity case starts at a shorter initial thickness. For all cases, the cell thickness increases as Si lithiates/expands. Figure c illustrates the anode porosity at the cut-off voltage as a function of anode thickness. As shown, the lower initial porosity case has significant pore-closure on the right-side at the separator interface. The higher initial porosity cases have increased anode lengths because the Si utilization is improved due to the reduced pore-closer effects. The graphic illustrates the main features of the reformulated pseudo-2D battery model.