Exploring the dependence of cell aging dynamics on thermal gradient in battery modules: A PDE-based time scale separation approach

摘要

There is an abundance of research dedicated to understanding lithium-ion batteries at the cell-level. However, the cell-level models or estimation algorithms cannot be directly applied to battery modules or packs that are composed of tens to hundreds or thousands of cells. Pack or module-level modeling and estimation must take into consideration the temperature distribution, manufacturing-induced parameter (impedance, capacity) variances, pack topology (electrical interconnections), and thermal interactions between cells. In this work, we motivate the need for pack or module-level modeling by showing that the aging dynamics of a cell is influenced by the adjacent cells it is interacting with, both, electrically and thermally. The characteristic time-scale of the vital dynamics of an interconnected cell, consisting of a high-fidelity coupled electrochemical-thermal-aging model, are studied to reveal a three-time scale behavior. This distinct behavior is explored via singular perturbation theory to derive a reduced-order aging model for an interconnected cell that is shown to depend on the thermal gradient in a serially interconnected module.