The mathematical model of 18650 lithium-ion battery in electric vehicles

A mathematical thermal-electrochemical model has been used to predict the temperature and internal electrochemical properties of 18650 lithium-ion battery. This model couples the thermal energy balance equation with the multiphase (solid electrodes, liquid electrolyte and gas phases from the primary reactions) electrochemical equations via the heat generation, where the temperature dependent electrochemical properties, such as active material and the electrolyte concentration, current density and electrode potential of the cell, have been taken into account. Moreover, the positive and negative electrodes made from composite materials are porous and the equation includes the porous theory as well. The equations which are sets of Partial Differential Equations (PDE) in three regions of the battery (positive electrode, negative electrode and separator) are solved using the finite volume method. The results from the model are compared with the experimental results of the battery, and show a quite accurate agreement between them. In addition, high charge current and high discharge current cycles and the European Test Schedule driving cycle which simulates the electric vehicle (EV) operating conditions are applied to the model, and to find the behavior of the internal electrochemical parameters of the battery in EVs.