Phenomenological Swelling Model of Battery Module

Sammanfattning

Lithium-ion batteries (LiBs) are the most popular choice in the shift towardselectrification due to their high volumetric energy and power density. An importantaspect to study is the effect of swelling on the mechanical performance of LiBsas it plays an important role in determining the forces in the battery module.During charge/discharge a battery cell swells/shrinks and over the lifetime of thebattery, swelling becomes permanent. The swelling increases with cycling that causesincreasing forces in the module. Excessive pressure generated due to cycling in themodule may electrically short the cells and/or cause mechanical damage to the cells.Compression pads placed between cells in the battery module absorb the swelling. Thematerial properties and size of the compression pads used influence the module forcesat End of Life (EoL).In this study, a 1D phenomenological model is built to predict the swelling forces. Themodel differs from others in literature in a way that the swelling forces are predictedwith cycling rather than State of Charge (SoC) and a stress-strain based constitutivemodel is used rather than a spring model. A process to eliminate the need for multipletests is also proposed in the thesis to predict swelling forces for different compressionpads and preloads.The proposed model is relatively simple and can improve existing battery managementsystems by predicting the swelling and the magnitude of swelling forces for differentcompression pads and preloads during the operational life of the battery.