Thermal modelling of second-life repurposed EV battery pack.

Lithium-ion batteries, retired from their first life in automotive field, can still retain 70% - 80% of their original capacity. Consequently, they could be repurposed for less demanding energy storage applications, delaying or eliminating the need for new systems. However, identifying suitable second-life applications is challenging and uncertain, as lithium-ion batteries passed through their first life, do not show the same thermal behaviour and heat production of a new battery, posing safety risks if not properly managed. This thesis focuses on high-fidelity evaluation of the thermal performance of a PHEV’s battery in second-life scenarios, using limited cell information and minimal experimental data. The evaluation employs a coupled electrochemical-thermal modeling approach. The first model, developed and optimized using PyBaMM software, accurately represents cell behavior and, thanks to a lumped thermal submodel, can evaluate the heat generated under a wide range of operating conditions. The second model, based on the battery’s CAD design and implemented in the SimScale environment, assesses the thermal behaviour of the battery under various boundary conditions. These models are interdependent, as the thermal model requires heat production data estimated by the PyBaMM model, which in turn depends on the battery temperature data provided by the thermal model. Once validated by means of experimental data, the complete model is used to simulate duty cycles and boundary conditions of second life scenarios, accurately selected for the battery protagonist of this study. The implemented approach allows the evaluation of battery’s suitability and safety under the new operating conditions. The scope and execution of this thesis are exceptionally ambitious due to its multidisciplinary nature and innovative approach. Moreover, it has proven to be remarkably effective in addressing multiple facets of battery performance and safety. The integrated models have demonstrated optimal fidelity with the experimental tests, achieving exceptional average accuracy and enabling representative simulations for the selected second-life applications. The final results have shown the suitability and safety of the battery module in all the new operating scenarios.