High load Operation of Lithium-Ion Batteries – Modeling Study on a LiFePO ₄ Graphite Cell

Modeling of lithium iron phosphate electrodes calls for appropriate extensions of established model approaches. An electrochemical pseudo two-dimensional and a single-particle model are enhanced to address the phase separating behavior of this material with a variable solid state diffusion model. A particle size distribution model tackles the heterogeneity of the electrode microstructure. Both models are embedded in a framework to describe multi-layer electrode designs featuring segregated material properties. The models are parameterized following literature replicating a good match with measured discharge curves at low, medium and high currents. A simplified version of the rigorous model shows the effort of reparameterization, the computational advantage of model order reduction techniques, the model accuracy and application scope. The impact of the electrode morphology is investigated using the full model by simulating variants of porosity and particle size distribution in single and bi-layered electrodes. The simulations reveal porosity changes, and electrode layering plays a minor role as solid diffusion in lithium iron phosphate particles dominates the cell behavior. This is underlined by results from varied particle size distributions that strongly influence the predicted cell capacity.