Lithium-ion batteries (LIBs) are gaining importance in the automotive sector because of the potential of electric vehicles (EVs) to reduce greenhouse gas emissions and air pollution. However, there are serious hazards resulting from failing battery cells leading to exothermic chemical reactions inside the cell, called thermal runaway (TR). Literature of quantifying the failing behavior of modern automotive high capacity cells is rare and focusing on single hazard categories such as heat generation. Thus, the aim of this study is to quantify several hazard relevant parameters of a failing currently used battery cell extracted from a modern mass-produced EV: the temperature response of the cell, the maximum reached cell surface temperature, the amount of produced vent gas, the gas venting rate, the composition of the produced gases including electrolyte vapor and the size and composition of the produced particles at TR. For this purpose, overtemperature experiments with fresh 41 Ah automotive lithium NMC/LMO—graphite pouch cells at different state-of-charge (SOC) 100%, 30% and 0% are performed. The results are valuable for firefighters, battery pack designers, cell recyclers, cell transportation and all who deal with batteries.

Safety for automotive lithium-ion battery (LIB) applications is of crucial importance, especially for electric vehicle applications using batteries with high capacity and high energy density. In case of a defect inside or outside the cell, serious safety risks are possible including extensive heat generation, toxic and flammable gas generation, and consequently fire and explosion. New regulations (GB 38031-2020) require a warning for passengers at least five minutes before serious incidents. This regulation can hardly be fulfilled with state-of-the-art battery monitoring. In this study, gases produced during battery failure before and during a thermal runaway (TR) are investigated in detail and the use of different gas sensors as early detectors of battery incidents is tested and proposed. The response of several commercially available gas sensors is tested in four battery failure cases: unwanted electrolysis of voltage carrying parts, electrolyte vapor, first venting of the cell and the TR. The experiments show that battery failure detection with gas sensors is possible but depends highly on the failure case. The chosen gas sensor can detect H₂ produced by unwanted electrolysis and electrolyte vapor and gases produced by degassing of state-of-the-art LIBs. The results may contribute significantly to failure detection and improvement of battery safety.

Lithium-ion batteries (LIBs) are a dominant state-of-the-art energy storage system and have importance in the automotive sector. Still, LIBs suffer from aging effects and serious hazards from failing batteries are possible. These failures can lead to exothermic chemical reactions inside the cell, ending up in thermal runaway (TR). TR has caused most electric vehicle (EV) fires. Since statistically most accidents with EVs happen after about one year of vehicle usage, in particular, the failing behavior of aged cells needs to be investigated. Little information is available in open literature about the influence of aging paths on the failing behavior and especially on the degassing behavior of large automotive LIBs. Therefore, this study investigates the influence of three different aging paths (cyclic at −10 °C and at 45 °C and calendric at 60 °C) on the thermal behavior, the vent gas emission, and the vent gas composition. The results show a clear effect of aging on the failing behavior. The aged cells showed a less violent failing reaction, reduced maximal temperatures, lower amount of produced gas, significantly lower amount of CO in the vent gas, and lower mass loss than fresh cells in the same overtemperature experiments. The results are valuable for the scientific and industrial community dealing with LIBs.