## 3 Experimental Section
This was the biggest difference between the actual conducted test against the specification mentioned in the FreedomCAR test manual, i.e., a data recording period of 4 h [8]. The reaction of the cells was evaluated using EUCAR hazard levels [8], as it is the common classification of Li-Ion cells under abnormal operating conditions for evaluating the overcharging behavior [8]. The behavior of Li-Ion cells in abuse tests is subdivided into a total of eight hazard levels [8]. While the activation of the CID can be assigned to hazard level 2 and the blowing-off gases can be assigned to level 3 or 4, depending on the escaped mass of the electrolyte [8]. Figure 5: Test setup. V\({}_{1}\)–V\({}_{4}\) represent voltage sources for supplying the measuring devices. An ignition of the escaping gases or of the individual cell itself is classified in level 5, a mechanical rupture of the housing in level 6, and an explosion of the cell finally in hazard level 7. The latter behavior represents the most dangerous state of the single cell in the context of an overload test [8]. For further deeper analyses with IBM SPSS V29.0.0(software used for statistical analysis of the recorded data), three color levels regarding the safety behavior of a cell are defined. Hazard levels 0 to 3 are defined as safety status green, while level 4 is yellow and levels 5 to 7 are red. Yellow and red are unsafe conditions. Moreover, for the binary logistic regression, it was necessary to have only two conditions, i.e., safe, and unsafe. To evaluate the results thoroughly, ten tests per cell, along with different voltage levels (120 V, 400 V and 800 V), were performed. The reason for such voltage levels is because the majority of available EVs are within these levels. A comparison was made between the higher voltage levels and the double nominal voltage taken from the FreedomCar overcharge test to check whether the hazard is directly proportional to the voltage, i.e., increasing the voltage increases the hazard as well. Before the tests, all cells (see Table 2) were brought to 100% SOC. For this purpose, the cells were charged in the laboratory using cell cycling devices until the cells reached their final charging voltage. Fully charged cells were then brought to the test site for abuse tests. The FreedomCar overcharge test defines that the current should be set at 32 A [8] for EV tests. However, if the tests are performed at less than pack level, the current must be scaled down [8]. Therefore, for this test series, the current level (refer to Table 3) for each type of cell was selected according to the manufacturer cell datasheet. For the NCA and the NMC cell, the current was set to 4 A. This was limited by the maximum current of the Gwinstek PSW 800-4.32 power supply. Both cells can handle potentially higher continuous currents. In the case of the maximum continuous charge, the current was 1.5 A, according to the datasheet. The cell was charged until the CID interrupted the charge flow or the test was terminated. Each test in the series was carried out for 30 min, regardless of how the cell performed, i.e., irrespective of whether the cell had a thermal runaway or not. During the statistical evaluation of data by SPSS software, the focus was on the safety of the cells, based on the binary expression \"safe\" or \"unsafe\", which were defined for the target variable in the context of this statistical investigation. There are various statistical models to explain a target variable (here the expression \"safe\" or \"unsafe\") by several other variables and to safeguard the relationship against random fluctuations. The most used model is regression analysis, in which the coefficients of a functional relationship (including linear, quadratic, cubic, or exponential) between the independent and dependent variables are estimated from the data and their significance is verified. Due to the discrete nature of the dependent variables, the evaluation was carried out using so-called binary logistic regression.