Thermal Finite Element Modelling and Prediction of Laser Welded Battery Packs

Battery modules consist of battery cells electrically joined at the terminals by conductive busbars. Laser welds are the most consistent and controllable process to create these connections on a large scale due to their control over power, laser width, speed, wobble, and overlap, and their quality is critical to battery pack performance. Tuning these parameters for an application typically requires weld trials to reach desired weld width, penetration, and strength without overheating the battery cell and weakening the dielectric insulators around the terminals. Poorly welded cells in a module can result in increased electrical resistance, causing greater joule heating and accelerated cell aging, and poorly welded modules can lead to uneven aging and unpredictable performance. To better understand the laser welding process, a modelling approach was developed to predict weld properties to reduce production time, costs, and potential cell damage. The 3D finite element model was calibrated using test data gathered using 1 mm thick aluminum busbars being welded onto 25 mm aluminum terminals with varying laser parameters. A volumetric gaussian heat source was used to characterize the modelled laser. Melting and vaporization in the weld were captured without explicitly modelling them by adjusting the model’s material properties to improve computational efficiency. Each simulation’s predicted melt pool cross section was compared to that of each corresponding weld trial. This modeling approach led to the development of a parametric tool that could quickly predict laser melt pool width and depth which can be used to accelerate laser weld process development.