The Influence of Structure on the Electrochemical and Thermal Response of Li-Ion Battery Electrodes

Advancement of lithium-ion batteries for transportation applications requires addressing two key challenges: increasing energy density and providing fast charging capabilities. The first of these challenges can be met using thicker electrodes. However, the implementation of thick electrodes inherently presents a trade-off with respect to fast charging. As the thickness is increased, transport limitations reduce the ability of the battery to meet aggressive charge conditions. At the particle scale, interactions between solid diffusion and reaction kinetics influence the effective storage of lithium. At the electrode scale, diffusion limitations can lead to local variations in salt concentrations and electric potential. These short-range and long-range effects can combine to influence local current and heat generation. In the present work, a pseudo-2D lithium-ion battery model is applied to understand how active material particle size, porosity, and electrode thickness impact local field variables, current, heat generation, and cell capacity within a single-cell stack. The model was built assuming that the active particles are representative spherical particles. The governing equations and boundary conditions were set following the common Newman model. Cell response under varied combinations of charge and discharge cycling is assessed for rates of 1 C and 5 C. Aggressive charge and discharge conditions lead to locally elevated C-rates and attendant increases in local heat generation. These variations can be impacted in part by tailoring electrode structures. To this end, results for parametric studies of active material particle size, porosity, and electrode thickness are presented and discussed.