(98c) Construction of Multiphysics System-Level Model of a Lithium-Ion Battery Module and Its Application for Risk Analysis of Battery Energy Storage Systems

Battery energy storage systems (BESSs) consisting of lithium-ion batteries (LIBs) are being increasingly used to supplement the unstable electrical power derived from renewable energy sources. BESSs have to be assessed for risks, including thermal runaway (TR) and thermal runaway propagation (TRP), which occur in LIBs or BESSs because of high energy density. Since a BESS constitutes multiple components, including LIBs, the physical phenomena occurring in BESSs are complex due to the interactions between different components. Therefore, the International Electrotechnical Commission (IEC) stipulated that the risks associated with BESSs are assessed at the component, module, and final system levels. According to the standards published by IEC, interactions between all the subsystems in a BESS must be considered during the assessment of risk scenarios, such as TRP from electrochemical accumulation subsystem(s) to other subsystems or loss of subsystem function related to safety. Thus, risk scenarios must be appropriately assessed not only at the component level but also at the module and final system levels. Some hazards and risk assessments of BESSs have been conducted; however, the comprehensive identification of risk scenarios and the assessment of system-level risks are challenging due to complex system-level interactions in BESSs, which involve multiphysics and dynamic phenomena. Thus, in this study, we focused on multiphysics system-level modeling to model a LIB module and performed simulations of the LIB module using Modelica—an equation-based, object-oriented modeling language that allows the acausal modeling of complex cyber-physical systems. Modelica is used for modeling complex coupled mechanical, electrical, thermal, and control systems. Additionally, the object-oriented feature of Modelica, which enables the processing of the elements of the language as modules, facilitates the establishment of system-level models by assembling and logically connecting individual modules of system components. Some studies have focused on risk analysis/assessment via multiphysics system-level modeling for various systems, such as large space systems or hydrogen dispensing systems. However, the multiphysics system-level model has not been applied to system-level risk analysis/assessment of BESSs. Therefore, in the present study, a multiphysics system-level model of a LIB module is established using Modelica for system-level risk analysis of BESSs. The focus is on TRP to adjacent LIBs, which occurs because of an increase in temperature due to events such as internal short circuits (ISCs), which is a significant system-level risk scenario associated with BESSs. First, we established a multiphysics system-level model of a large-format LIB module using Modelica. Note that TR and TRP in a LIB module are complex due to thermal, electrical, electrochemical, and kinetic interactions between the components. However, in this study, we considered only electrical and thermal interactions for the initial step of the system-level risk assessment of LIB modules and BESSs. Then, we validated the model by comparing the temperature profiles of each LIB in the module under different initial conditions with those reported in the literature. The proposed model can be used to simulate dynamic physical phenomena, including the electrical and thermal behaviors of LIBs. Finally, we applied the multiphysics system-level model of the LIB module to some case studies, such as risk analysis for dynamic quantitative analysis of hazardous scenarios. The results of this study can provide the information for the safety design of LIB modules or BESSs.