Search Results (3)

One of the major concerns for battery electric vehicles (BEVs) is the occurrence of thermal runaway (TR), usually of a single cell, and its propagation to adjacent cells in a battery pack. To guarantee sufficient safety for the vehicle occupants, the TR mechanisms must be known and predictable. In this work, we compare thermal runaway scenarios using different initiation protocols (heat–wait–seek, constant heating, nail penetration) and battery chemistries (nickel manganese cobalt oxide, NMC; lithium iron phosphate, LFP; and sodium-ion batteries, SIB) with the cells in a fully charged state. Our goal is to specifically trigger a variety of different possible TR scenarios (internal failure, external hotspot, mechanical damage) with different types of chemistries to obtain reliable data that are subsequently employed for modeling and prediction of the phenomenon. The safety of the tested cells depending on their chemistry can be summarized as LFP > SIB >> NMC. The data of the TR experiments were used as the basis for high-fidelity modeling and predicting of TR phenomena in 3D. The models simulated reaction rates, represented by the typically employed Arrhenius approach. The effects of the investigated TR triggering methods and cell chemistries were represented with sufficient accuracy, enabling the application of the models for the simulation of thermal propagation in battery packs. Full article

In this experimental investigation, we studied the safety and thermal runaway behavior of commercial lithium-ion batteries of type 21700. The different cathode materials NMC, NCA and LFP were compared, as well as high power and high energy cells. After characterization of all relevant components of the batteries to assure comparability, two abuse methods were applied: thermal abuse by the heat-wait-seek test and mechanical abuse by nail penetration, both in an accelerating rate calorimeter. Several critical temperatures and temperature rates, as well as exothermal data, were determined. Furthermore, the grade of destruction, mass loss and, for the thermal abuse scenario, activation energy and enthalpy, were calculated for critical points. It was found that NMC cells reacted first, but NCA cells went into thermal runaway a little earlier than NMC cells. LFP cells reacted, as expected, more slowly and at significantly higher temperatures, making the cell chemistry considerably safer. For mechanical abuse, no thermal runaway was observed for LFP cells, as well as at state of charge (SOC) zero for the other chemistries tested. For thermal abuse, at SOC 0 and SOC 30 for LFP cells and at SOC 0 for the other cell chemistries, no thermal runaway occurred until 350 °C. In this study, the experimental data are provided for further simulation approaches and system safety design. Full article

Commercial coin cells with LiNi_0.6Mn_0.2Co_0.2O₂ positive electrode material were investigated using an accelerating rate calorimeter and a Tian-Calvet calorimeter. After cycling and charging to the selected states of charge (SOCs), the cells were studied under thermal abuse conditions using the heat-wait-seek (HWS) method with the heating step of 5 K and a threshold for self-heating detection of 0.02 K/min. The onset temperature and the rate of the temperature rise, i.e., the self-heating rate for thermal runaway events, were determined. The morphology of the positive electrode, negative electrode and the separator of fresh and tested cells were compared and investigated with scanning electron microscopy (SEM). Furthermore, the microstructure and the chemical compositions of the individual components were investigated by X-ray diffraction (XRD) and inductively coupled plasma with optical emission spectrometry (ICP-OES), respectively. In the Tian-Calvet calorimeter, the coin cells with the selected SOCs and the individual components (positive electrode, negative electrode and separator) were heated up with a constant heating rate of 0.1 °C/min (ramp heating mode). Simultaneously, the heat flow signals were recorded to analyze the heat generation. The combination of the three different methods—the HWS method using the ES-ARC, ramp heating mode on both cells and the individual components using the Tian-Calvet calorimeter—together with a post-mortem analysis, give us a complete picture of the processes leading to thermal runaway. Full article