The model defines and solves the current and material balances in the lithium-ion battery. The intercalation of lithium inside the particles in the positive electrode is solved using a fourth independent variable r for the particle radius (x, y, and t are the other three). The reaction kinetics and the intercalation are coupled to the material and current balances at the surface of the particles. The model equations are found in the Battery Design Module User’s Guide. The model was originally formulated for 1D simulations by Nobel Laureate John Newman and his co-workers at the University of California at Berkeley. The model is popularly known as pseudo-2D model (or P2D model) in the literature.