Abstract
Commercial coin cells with LiNi0.6Mn0.2Co0.2O2 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.
Highlights
In the field of electric vehicles (EVs), as well as electric devices, Li-ion batteries (LIBs) are increasingly being adopted as mobile electric suppliers, due to their high capacity, long cycle life and high energy density [1,2,3]
The thermal failure of a commercial 18,650 battery with a NMC622 cathode was analyzed by accelerating rate calorimetry (ARC) [20], while the morphological changes due to the thermal runaway were investigated by applying X-ray computed tomography (CT)
During the measurements on fully charged coin cells, which are shown in Figure 3, maximum temperatures during thermal runaway exceeded 450 °C, which corresponds to the level above which the ARC starts to actively cool down by pressurized air
Summary
In the field of electric vehicles (EVs), as well as electric devices, Li-ion batteries (LIBs) are increasingly being adopted as mobile electric suppliers, due to their high capacity, long cycle life and high energy density [1,2,3]. Ma et al [16] applied accelerating rate calorimetry (ARC) to investigate the impact of different electrolyte additives on the electrode/electrolyte reactivity in NMCgraphite cells. This investigation was further extended by Huang et al [17] with ARC measurements, who demonstrated the influence of the upper cut-off potential and the sample morphology on the thermal stability of NMC compounds. The thermal behavior during thermal runaway events of commercial coin cells with positive electrode material LiNi0.6Mn0.2Co0.2O2 (NMC 622) were investigated by an accelerating rate calorimeter (ES-ARC, Thermal Hazard Technology, Bletchley, United Kingdom) [22,23] and a Tian-Calvet calorimeter (C80, Setaram Instruments, Lyon, France) [24]. The chemical composition of the pristine materials was determined by inductively coupled plasma with optical emission spectrometry (ICPOES) and the crystal structure as well as the morphology of the samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively
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