On-Line Gas Detection During the Thermal Runaway of Li-Ion Cells by ARC-MS

Li-ion batteries are used for energy storage in a variety of applications such as smartphones, laptop computers, power tools, stationary energy storage, unmanned aerial vehicles (UAV), light electric vehicles (LEV), as well as electric cars (EV, HEV, PHEV). Besides costs, high energy density, and fast-charging capability, a high safety level is one of the most important properties during the whole life of a battery.<br/>For Li-ion cells, safety relevant incidents can happen due to abusive conditions. Such conditions are tested in the lab, for example by nail penetration, overcharge, or overheating experiments. Especially, at elevated temperatures exothermic reactions can occur, generating substantial heat and gas in the cells. If the heat transfer from the cell to the surrounding is insufficient, the rate of the undesired chemical reactions inside the cell accelerate which can lead to venting and thermal runaway.<br/>In this study, we coupled accelerating rate calorimetry (ARC) with on-line mass spectrometry (MS), resulting in a new method (ARC-MS). ARC-MS allows measuring the thermal properties of the cell under quasi-adiabatic conditions with simultaneous analysis of the emitted gases after venting [1]. Additionally, data from gas and audio sensors as well as resistance and voltage are recorded at the same time.<br/>This method is applied to different commercial Li-ion cells at different state-of-charge (SOC) and state-of-health (SOH) for overheating as well as overcharging to gain insights into the safety critical mechanisms. It turns out that safety of aged cells depends not only on the value of the SOH. Moreover, safety also depends on the aging mechanism as determined by Post-Mortem analysis [2] and in case of Li plating on the rest time between the end of cycling and the start of the ARC test [3]. Cells with Li deposition on the anode and overcharged cells show an early onset of self-heating. The organic solvent signals are predominant at the time of cell venting whereas the C₂H₄, CO₂, and POF₃ signals are more common at cell explosion.<br/>Due to electrolyte decomposition by anodic and cathodic exothermic reactions, the amount of the detected species by MS are depending on the chemical composition and history of the cell, e.g. SOC, aging mechanism, and overcharging.<br/><b>References</b><br/>[1] A.A. Abd-El-Latif, P. Sichler, M. Kasper, T. Waldmann, M. Wohlfahrt-Mehrens, Batteries & Supercaps 4 (2021) 1135–1144. https://doi.org/10.1002/batt.202100023.<br/>[2] T. Waldmann, J.B. Quinn, K. Richter, M. Kasper, A. Tost, A. Klein, M. Wohlfahrt-Mehrens, J. Electrochem. Soc.164 (2017) A3154-A3162. https://doi.org/10.1149/2.0961713jes<br/>[3] T. Waldmann, M. Wohlfahrt-Mehrens, Electrochim. Acta 230 (2017) 454-460. http://dx.doi.org/10.1016/j.electacta.2017.02.036<br/><b>Acknowledgment</b><br/>Funding of the AnaLiBa project (03XP0347C) by the German Federal Ministry of Education and Research (BMBF) and the TEESMAT project (n° 814106) (http://www.teesmat.eu) by European Community's Horizon 2020 Framework are gratefully acknowledged.