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Lithium-ion battery (LIB) powered devices, such as laptops, mobile phones and power tools are ubiquitous in our daily lives. Moreover, LIBs are essential for the electrification of vehicles, and play an important role for stationary storage units needed for grid-balancing. The improvement of LIBs, in terms of increasing energy density as well as cycle-life and decreasing costs, is tackled by numerous research groups all over the world. In the last years, research regarding safety aspects has steadily gained more interest. The safety of LIBs can be implemented at different levels, such as material, cell, battery and system level.
The abuse/misuse of an LIB can lead to an internal increase in heat which can trigger a chain of exothermic reactions on cell level. Thus, the cell temperature increases dramatically causing the so-called thermal runaway (TR). This process can lead to flames and/or explosion of the cell. Furthermore, the TR of one cell can initiate the TR of adjacent cells causing the so-called propagation, possibly, leading to the TR of the whole battery.
Herein, we will show the latest result of our safety tests on cell level employing an external heater as TR-trigger. Regarding single cell tests, we will compare different hazardous features during the TR, e.g., cell temperature, occurrence of flames, peak pressure, and toxic gases, depending on the cell format, cell energy and the cathode type. The same cell parameters will be used to discuss the results of the propagation tests. Moreover, the influence of the state of charge (SOC) and the present atmosphere (air vs. N2) as well as the repeatability will be discussed. Overall, the study comprises over 180 tests on cell level.
The findings regarding the TR behaviour can be used to create a hazard-classification scheme of LIBs, e.g., allowing the definition of (cell type specific) conditions for a safe transport. Furthermore, the results can increase the general understanding of the TR mechanism promoting the development of advanced measures to enhance the safety on cell level in the future.
Next to performance features, safety aspects of lithium-ion batteries (LIBs) are a crucial research field. The abuse/misuse of a LIB can trigger a chain of exothermic reactions on cell level. Hence, the cell temperature increases dramatically, causing the so-called thermal runaway (TR). Moreover, the TR of one cell can initiate the TR of adjacent cells leading to a TR-propagation. Due to the risk of a TR, special measures need to be applied while handling, storing, and transporting batteries. According to current transport regulations, all different types of lithium-ion and lithium metal cells/batteries (by means of cell format, cathode chemistry, etc.) require the same transport conditions regardless of the intensity of their reaction during abuse tests. To allow more differentiated transport requirements, the United Nations (UN) Subcommittee Transport of Dangerous Goods created an Informal Working Group (IWG) on the topic of a hazard-based classification of LIBs. BAM is one of nine laboratories working on the development of a respective classification scheme including appendant test protocols.
Herein, we discuss the latest results of our safety tests on commercial LIB-cells employing the test protocols developed in the UN-IWG. Single cell tests are analysed regarding different hazardous features during the TR, e.g., cell temperature, flame occurrence, and gas amount. Next to the general occurrence of a propagation, the propagation speed is analysed by propagation tests. In total, the presented results are gathered from over 200 tests. Next to the classification of the tested cells, the data set obtained is analysed in respect to the cells’ key features, such as cell energy, state of charge and cathode type. Generally, the presented results can increase the overall understanding of the TR-mechanism supporting the design of advanced safety measures on cell level in the future.
Lithium-ion batteries usually consist of numerous individual cells. There is ongoing discussion about enhancing sustainability by considering the replacement of heavily aged or damaged cells. Nevertheless, the planned replacement of individual cells poses significant challenges in ensuring the required reliability and safety of the refurbished device.
Lithium-ion batteries (LIBs) are essential for the electrification of vehicles and play an important role for stationary storage units needed for grid-balancing. Research groups all over the world work on the improvement of LIBs regarding an increase in energy density as well as cycle-life and a decrease in costs. Next to these research topics, a continuously uprising and crucial field is safety features of LIBs, which can be implemented at different levels, such as material, cell, battery and system level.
The abuse/misuse of a LIB can cause an internal release of heat which can trigger a chain of exothermic reactions on cell level. Hence, the cell temperature increases dramatically, causing the so-called thermal runaway (TR), possibly leading to flames and/or explosion of the cell. Moreover, the TR of one cell can initiate the TR of adjacent cells leading to a so-called propagation, possibly, causing the TR of the whole battery. Ideally, easily obtainable key features of a certain cell – such as cathode type, cell format, cell energy and state of charge (SOC) - could allow the prediction of its behaviour under abuse conditions. In the present study, we will discuss the latest result of our safety tests on cell level employing an external heater as TR-trigger. Single cell tests will be analysed regarding different hazardous features during the TR, e.g., cell temperature, occurrence of flames, peak pressure, gas amount and gas composition. Moreover, the possibility of a TR-propagation and the respective propagation speed will be gained from propagation tests utilizing six cells with identical SOC. In total, the study comprises over 200 tests on cell level. The gained data set is analysed in respect to the cell parameters, such as cell format, cell energy, SOC and the cathode type as well as the atmosphere (air vs. N2) present during the test. A special focus is put on the discussion of general conclusions linking cell parameters to TR-effects and propagation behaviour.
The findings regarding common conclusions between key features and TR-effects can enable a rather facile selection process of cells/batteries for certain applications according to specific safety targets. Moreover, it allows to choose cell-specific safety measures, suitable during operation. In further works, the study will be extended to end-of-first life cells yielding important conclusions regarding crucial safety aspects for the implementation of those cells in 2nd-life application. Generally, the presented results can increase the overall understanding of the TR mechanism supporting the design of advanced measures to enhance the safety on cell level in the future.