Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries

Abstract

Large-format cells are achieving increasing popularity for Electric Vehicle (EV) applications to maximize volumetric and gravimetric energy densities. These large batteries are often characterized by spatial non-uniformities in temperature and resulting difficulties in maintaining uniform temperature distribution. This poor thermal management is a primary reason for the inefficient performance and safety risks associated with these large format batteries and battery packs. Further, there have been several reported degradation mechanisms which are responsible for the capacity fade within Lithium-ion (Li-ion) batteries over multiple charge/discharge cycles. In particular, the presence of thermal gradients and consequent non-uniformities greatly exacerbates degradation, and poses serious safety risks. Thus, it is imperative to identify and study the degradation mechanisms coupled with the thermal effects by incorporating detailed physics-based models to characterize the cell-level phenomena.This work aims to perform a detailed model-based study on the combined effects of battery degradation and temperature inhomogeneities within large-format Li-ion cells and battery packs. This simultaneous analysis for temperature-dependent degradation will be performed with a state-of-the-art electrochemical model like the classic pseudo-two-dimensional (p2D) model to be able to present a comprehensive analysis of the battery performance parameters. These models will be augmented to include thermal effects and various degradation mechanisms for Solid Electrolyte Interphase (SEI) formation and Lithium plating. The proposed numerical framework will be validated with experimental data for the loss in battery capacity over cycles. In addition, the model development, especially the weak form for model equations and their implementation in a finite-element solver, COMSOL Multiphysics, will be discussed in detail.This study primarily focusses on certain important aspects of temperature-dependent degradation, viz., (a) cell-to-cell temperature variation, (b) operating conditions for current, (c) topology for the cell arrangement within the battery module, and (d) choice of the degradation mechanism. The delineation of the effects of these complex factors on the cell-level signatures will be of significant utility in monitoring and identifying the performance limitations of individual cells, and thereby help maximize the performance of large format cells and battery packs.The ultimate goal is the design of a simple yet efficient numerical model with fast and robust simulations for the analysis of the temperature-dependent degradation of the Li-ion battery packs over a wide range of operating and design conditions. The proposed model will be developed to be computationally feasible for an adoption and implementation in a battery thermal management system.