Development of Representative Microstructure Model to Investigate the Electro-chemo-mechanical Response of Lithium-Ion Batteries

Summary:

Due to the increasing market share of Battery Electric vehicles (BEVs), the importance of electrochemical energy storage systems is continuously increasing. Due to their high energy density, Lithium-Ion Batteries (LIBs) are currently the most important energy storage system for BEVs.
The electrode microstructure in LIBs has a substantial impact on their electrochemical performance. Therefore, optimization of morphology with respect to functionality plays a major role in LIBs development. Furthermore, in most state-of-the-art active materials in LIBs, Li insertion into and de-insertion from the host materials induce volume changes during battery cycling resulting in significant stress formation. Particularly in high-capacity electrode materials, intensive deformation and resulting stresses might exceed the threshold value. Consequently, the existing bonds and the integrity in the electrode structure degrades, leading to a loss of electrical contacts in local areas and thus to a reduced performance of LIBs.
CAE-based modeling links early conceptual designs and optimization with manufacturing as an alternative for time-consuming and expensive tomography techniques. Computational modeling of electrode morphologies allows virtual testing of material, transport properties, and overall LIBs performance. This modeling approach is intrinsically non-destructive, and its primary goal is to reflect the constrained environment in realistic electrode microstructures. Furthermore, to improve our understanding of the highly interactive electro-chemo-mechanical physics in LIBs, the corresponding partial differential equations (PDEs) are solved in the relevant domains of the developed morphology.
Recently, the Institute for Combustion Engines of RWTH Aachen University and FEV Europe GmbH have developed a Multiphysics Microstructural Resolved Model. The proposed model contains mathematically generated 3D and 2D virtual morphologies representing the real electrodes in LIB cells. In this regard, a novel numerical methodology by utilization of spherical harmonics functions has been introduced to construct 3D microstructure. Furthermore, the 2D virtual morphology is developed by the application of the random Gaussian function. The 2D model is employed to investigate the electro-chemo-mechanical behavior of LIBs. To obtain the electrode microstructure transport properties e.g. tortuosity, Laplace’s equation on such 2D virtual morphology is solved. Eventually, the calculated stress in the active material particles and other components, e.g., binder and separator, is studied to identify the most susceptible regions to crack initiation or delamination. Thus, the model outcome can be further hired to optimize the influencing geometrical parameters and battery operating conditions to prevent mechanical degradation in the LIB.