A Multiphysics Simulation of the Thermal Runaway in Large-Format Lithium-ion Batteries

Lithium-ion batteries (LIB) have found a wide range of applications in many consumer products in the last 25 years. The United States Navy and Marine Corps have various applications using LIB, and safe battery technologies are critically needed. While many consumer applications typically utilize smaller, high volume cells, military applications can utilize specialty large-format cells in their LIB packs. One of the most important safety considerations for LIB cells is their thermal stability under various abuses such as exposure to heat, nail penetration, external short circuit, crushing, and so on. Several exothermic reactions can occur as the inner cell temperature increases, and if the heat generation is larger than the dissipated heat to the surroundings, this leads to heat accumulation in the cell and acceleration of the chemical reactions, which can then lead to a thermal runaway. Since the behavior of batteries is strongly affected by the interaction of physics on varying length and time scales: a multi-physics and multi-scale model is needed to simulate this process. While many approaches have been reported in literature, they are not directly applicable in large-format LIB cells and the development of multi-scale and multi-physics models are relatively limited and still computationally expensive. For example, in large formatted battery cells, the uniformity of the electrical potential along the current collectors in the cell composites is no longer given. Additionally, due to the inhomogeneity of the distribution of the temperature field with respect to the cell geometry, thermal dynamics must also be taken into account. This study reports the recently developed multi-scale and multi-physics models for simulating the thermal runway inside a lithium-ion battery using COMSOL software. For the electrochemical processes, the porous electrode theory with contributions coming from exothermic side reactions is used to model abuse mechanisms, which could lead to a thermal runaway. For the thermal-mechanical processes, models of thermal abuse reactions that occur at specific elevated temperatures have been simulated. Prior experimental data on a large-scale lithium-ion battery tested at NSWCCD has been used to construct and validate the model with good agreement.