Modelling Li-Ion Cell Thermal Runaway Triggered by an Internal Short Circuit Device Using an Efficiency Factor and Arrhenius Formulations

This paper presents a novel model for analyzing thermal runaway in Li-ion battery cells with an internal short circuit device implanted in the cell. The model is constructed using Arrhenius formulations for representing the self-heating chemical reactions and the State of Charge. The model accounts for a local short-circuit, which is triggered by the device embedded in the cell windings (jelly roll). The short circuit is modeled by calculating the total available electrical energy and adding an efficiency factor for the conversion of electric energy into thermal energy. The efficiency factor also accounts for the energy vented from the cell. The results show good agreement with the experimental data for two cases – a 0D model and a 3D model of a single cell. Introducing the efficiency factor and simplifying the short-circuit modeling by using an Arrhenius formulation reduces the calculation time and the computational complexity, while providing relevant results about the temperature dynamics. It was found that for an 18650 NCA/graphite cell with a 2.4 Ah capacity, 28% of the electrical energy leaves with the effluent. Lithium-ion batteries are gaining more and more popularity in the field of electric energy storage. 1 This trend is followed by an increase in safety, energy density, and cycle life requirements. The in-crease in energy density brought a significant contribution to this trend, but it came with a trade-off concerning safety. 2,3 When operated un-der abusive conditions such as overcharging, over-discharging, object penetrations or even operation under high ambient temperatures, etc., Li-ion batteries can undergo internal short circuits between the current collectors or electrodes, leading to thermal runaway. 3 The reactions with electrolyte inside the cell decompose the battery components, generating a significant amount of heat, which, if not properly man-aged can lead to fires and explosions. 4 To assist the design of thermal management systems in mitigating the effects of thermal runaway, it is important to be able to model thermal runaway and account for the energy contributions in the process. Modeling thermal runaway has been the focus of many researchers, but the authors in Refs. 5,6 brought a substantial contribution to the field. The authors found the activation energies and the enthalpies of the different decomposition reactions for the components in an 18650 LCO (2.6 Ah) Li-ion battery and proposed a model for predicting thermal runaway based on Arrhenius formulations. Papers such as Refs. 7,8 added new decomposition reactions (cathode, electrolyte) and extended the model, from a simplified lumped model to complex 2D and 3D geometries for a single cell. Based on these models, some authors extended the models to simulate the thermal behavior of single battery cells. 9 A comprehensive list of references and studies of modeling safety in Li-ion is given in Ref. 3. The activation energies and the enthalpies found by the authors in Refs. 5, 6 are crucial for predicting the energy released during thermal runaway and are used in this paper. During a thermal runaway, an internal short circuit (ISC) can occur in the cell due to a conducting metal particle, component defects or melting of the separator, causing the adjacent electrodes (the anode and the cathode) to come into contact. Analyzing the ISC is a chal-lenging task being tackled by more and more authors. Some focused on experimental studies on different types of cells, 10–13 but only a few studies have been performed in modeling the ISC.