Heterogeneous Aging in a Multi-cell Lithium-ion Battery System Driven by Manufacturing-induced Variability in Electrode Microstructure: A Physics-Based Simulation Study

Abstract

Heterogeneous aging of lithium-ion battery cells within a battery pack is a major challenge that limits the pack’s overall performance, safety, and life. Variations in cell degradation rates lead to nonuniform charge/discharge behavior among cells in a pack, accelerated aging in some cells turning them into “weak links”, and reducing energy throughput at the pack level. While previous studies have investigated uneven aging driven by differences in capacity or resistance, limited attention has been given to the root causes of these variations, particularly those arising from manufacturing-induced differences in the electrode microstructure. This study addresses this gap by investigating the effects of variations in active material particle size, a key design parameter of a porous electrode, on the aging behavior of battery cells connected in series and parallel. Using an electrochemical battery model, the aging behavior of individual cells and the pack as a whole is investigated for three electrical configurations (i.e., 1S4P, 4S1P, and 2S2P) at select C-rates and voltage windows. Results indicate that cells with smaller particle radii degrade faster despite having a thinner SEI layer at the end of life, and a minor variation of even 1 µm in the active material particle size can lead to significant uneven capacity fade across cells and accelerated aging of the pack, particularly at low C-rates. These findings highlight the critical impact that variability in the microstructure has on pack-level aging and provide insights into effective cell and pack manufacturing.