Electro-thermal Modeling of Lithium-ion Batteries

The development and implementation of Lithium-ion (Li-ion) batteries, particularly in applications, requires substantial diagnostic and practical modeling efforts to fully understand the thermal characteristics in the batteries across various operating conditions. Thermal modeling prompts the understanding of the battery thermal behavior beyond what is possible from experiments and it provides a basis for exploring thermal management strategies for batteries in hybrid electric vehicles (HEVs) and electric vehicles (EVs). These models should be sufficiently robust and computationally effective to be favorable for real time applications. The objective of this research is to develop a complete range of modeling approaches, from full numerical to analytical models, as a fast simulation tool for predicting the temperature distribution inside the pouch-type batteries. In the first part of the study, a series of analytical models is proposed to describe distributions of potential and current density in the electrodes along with the temperature field in Li-ion batteries during standard galvanostatic processes. First, a three-dimensional analytical solution is developed for temperature profile inside the Li-ion batteries. The solution is used to describe the special and temporal temperature evolution inside a pouch-type Li-ion cell subjected to the convective cooling at its surfaces. The results are successfully verified with the result of an independent numerical simulation. The solution is also adapted to study the thermal behavior of the prismatic and cylindrical-type nickel metal hydride battery (NiMH) batteries during fast charging processes, which demonstrated the versatility of the model. Afterward, to resolve the interplay of electrical and thermal processes on the heat generation and thermal processes, a closed-form model is developed for the electrical field inside the battery electrodes. The solution is coupled to the transient thermal model through the heat source term (Joulean heat). The results of the proposed multi-physic are validated through comparison with the experimental and numerical studies for standard constant current discharge tests. The model results show that the maximum temperature in the battery arises at the vicinity of the tabs, where the ohmic heat is established as a result of the convergence/divergence of the current streamlines. In the second part of the study, an equivalent circuit model (ECM) is developed to simulate the current-voltage characteristics of the battery during transiently changing load profiles. The ECM that is calibrated by a set of characterization tests collected over a wide range of temperature, then coupled with a numerical electro-thermal model. The validated ECM-based model is capable of predicting the time variation of the surface temperature, voltage, and state of charge (SOC) of the battery during different driving cycles and environmentaltemperatures.