Multiscale mechanical modeling of lithium-ion battery module

Understanding multi-physics phenomena is crucial for accurately modeling and predicting the behavior of complex systems in engineering. Sometimes, accounting for the coupling across the various scales of the system is also important. In this work, these needs have driven extensive exploration into multi-physics and multiscale modeling with the software COMSOL Multiphysics, especially focusing on the homogenization technique. It is a method used to predict macroscopic properties of heterogeneous materials by analyzing a representative volume element (RVE) that reflects microscale variations. A multiscale approach in a multi-physics domain is then applied to lithium-ion battery pack. Nowadays, lithium-ion batteries (LIBs) are the most widespread energy storage system, covering a large field of applications. In the automotive and working vehicle industry, lithium-ion batteries are a strategic component affecting the design, the cost and the performance of the vehicle. The electrochemical processes which allow the battery to deliver or store electrical energy involve the interaction of lithium ions with the electrode microstructure causing its mechanical deformation, proportional to the concentration of lithium ions in the host material. The electrode microstructure strain results in mechanical degradation, reducing the overall battery's performance, and causes the macroscopic battery deformation. In this thesis, the macroscopic battery deformation originating from the electrode particles strain is analysed with a two-step homogenization process considering the coupling between mechanical, chemical and electrical behaviour. First, the composite electrode (made of active material particles, voids and conductive agents) is modelled with a representative volume element. Secondly, the battery is modelled homogenizing the contribution of the hundreds of composite electrode layers. The output of the model is then validated with experimental measurements quantifying the macroscopic battery deformation during operation. The second contribution of this work focuses on the impact of individual battery deformation on the entire battery pack. Furthermore, the constraint given by the battery pack causes the change of the electrical performance of the battery itself, because of the compression of the microstructure of the electrodes. Then, different design solutions of the battery pack are investigated to optimize the battery performance and lifespan, while keeping a safe battery pack deformation.