Abstract
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.
Highlights
Lithium-ion batteries (LIB), initially commercialized by Sony in 1991, are a dominant state-of-the-art energy storage system [1,2], and are still the most promising candidates for storing electrical energy [3,4]
LIB technology provides the best mix of key battery performance metric such as high specific energy, high energy density, high power density, long lifetime, costs, and safety [1], which currently cannot be achieved with any other available technology
The tested aged cells did not show a more harmful failing reaction compared to fresh cells
Summary
Lithium-ion batteries (LIB), initially commercialized by Sony in 1991, are a dominant state-of-the-art energy storage system [1,2], and are still the most promising candidates for storing electrical energy [3,4]. TR has caused most EV fires [8] and is a selfaccelerating exothermic chemical reaction inside the cell, which can be started by a hot spot produced inside the cell (e.g., particle short circuit) or by a heat source outside the cell (e.g., electrical failure) [9,10,11,12]. These possible defects inside or outside the cell causing exothermic reactions challenge the safety for LIB applications. A detailed analysis of possible failures and of TR behavior need to be investigated in detail in order to minimize the risks from failing LIB and to increase safety
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