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Lithium ion batteries (LIBs) are omnipresent in our daily lives. LIBs power our laptops and mobile phones, are the energy storage of choice for the electrification of vehicles, and play a vital role in the layout of the storage devices needed for the balancing of the grid.
Research groups all over the world work on the improvement of LIBs, e.g., an increase in energy density and cycle-life as well as a decrease in costs. In recent years, investigations concerning the LIB’s safety continuously gain importance, especially, pushed by incidents with electric vehicles. They are multiple levels at which safety measures can be implemented, i.e., material, cell, battery and system level. Accordingly, the behaviour of LIBs under abuse/misuse conditions are often investigated on those levels.
Here, we focus on the safety on cell level. Generally, the abuse/misuse leads to an increase in heat in the cell at worst triggering a chain of exothermic reactions. Hence, the cell’s temperature rapidly increases leading to the so-called thermal runaway (TR) possibly accompanied by flames and/or explosion of the cell. Herein, different hazardous features during the TR of different commercial cells are analysed such as temperature, flames, projectiles and toxic gases. In order to gain further insights on the parameters influencing the TR, different type of initiation modes, e.g., external heating, overcharging, nail penetration and external short circuiting are utilized. Moreover, the state of charges (SOCs) are varied to differ the amount of electrical energy present in the cells.
Next to the characteristic of the TR of a single cell, the investigation of the propagation of the TR from one cell to another is an important parameter, as a battery is usually composed of multiple cells. Due to the close packaging of the single cells, the TR of one cell is often able to initiate the TR of the surrounding cells, finally, causing the TR of the whole battery. Herein, the propagation ability is studied depending on the cell type and SOC. Finally, the results will be used to formulate (cell specific) conditions for a safe transport of LIBs. Moreover, the gained knowledge can support the development of advanced measures to increase the safety on cell level in the future.
Im Zusammenhang mit den Untersuchungen zu den Möglichkeiten von gekühlten Transporten von Lithiumbatterien werden unterschiedliche Zerstörungsmethoden vorgestellt und diskutiert. Insbesondere wird dabei das neu entwickelte Nageltool und die vorläufigen Untersuchungen für den Einfluss von Ultratiefkühlung auf unbeschädigte Lithiumbatterien vorgestellt.
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.
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.