## Article
### Large-Scale Fire Tests of Battery Electric Vehicle (BEV): Slovak Case Study
They also interpret the mechanism of the thermal runway with the subsequent promotion and method of extinguishing them, with an overview of already published studies. The Electrochemical Safety Research Institute [22] lists thermal runaway as one of the main risks associated with lithium-ion batteries. It is a phenomenon in which the lithium-ion cell enters an uncontrollable self-heating state [22]. Thermal runaway is the worst safety issues of BEVs [23; 24]. Figure 1 shows the origin of thermal runaway in EV traction batteries, including electrolyte side reactions, the cathode, anode, and interfacial reactions at the electrode surface and Li plating. These side reactions are triggered by mechanical, thermal, and electrical damage (the term misuse is also often used). Breakdown of the separator and evolution of oxygen from the cathode side are the main causes of thermal runaway in batteries (as shown by the solid line in Figure 1--d). There are five types of causes of this phenomenon called \"thermal runaway\", which are shown in Figure 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{4}{c}{**Membrane Composition of the Separator**} \\ \cline{2-5}  & **PE** & **PP** & **PP/PE/PP** & **PVDF** & **PE/PVDF** \\ \hline Temperature of thermal degradation (\({}^{\circ}\)C) & 130–133 & 156–163 & 134–135 & \\ \hline Melting point (\({}^{\circ}\)C) & 139 & 162 & 165 & \\ \hline Thickness (\(\upmu\)m) & 20 & & & 25–26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Switch-off temperatures and melting temperatures of various polyethylene (PE), polypropylene (PP), and three-layer hybrid PP/PE/PP membranes [1; 19]. They are as follows:  
1. The first type is the uncontrolled generation of internal heat, which causes the re-lease of oxygen from the cathode material, leading to numerous side reactions [13; 25]. 2. In the second type, separator defects (due to heat-induced shrinkage or mechanical damage) create short circuits in the battery and rapid discharge of the energy stored in it [26], accompanied by unwanted chemical chain reactions and the release of enormous amounts of heat. 3. The third type is electrical abuse [27]. Electrolyte decomposition occurs at the cathode interface, especially at a high state of charge (SOC). This leads to the accumulation of heat and the subsequent release of oxygen from the cathode and damage to the separator. 4. The fourth type consists of electrochemical side reactions caused by local thermal abuse. If the heat generated during normal LIB operations cannot be dissipated quickly enough, the separator at that specific location will shrink or crack [28; 29]. 5. The fifth type occurs when the battery is mechanically damaged, resulting in a short circuit and/or air infiltration into the battery [30]. The main causes of battery safety accidents among these five categories are short circuits due to separator damage, and electrical and mechanical misuse [31]. Several studies have been devoted to the research of thermal runaway from the point of view of its causes [32; 33; 34; 35; 36; 37; 38]. Furthermore, [PERSON] et al. [39] did a series of fire tests on BEV cars and batteries that were equipped with multiple thermocouples, voltage sensors, heat flow meters, smoke detectors, and gas sampling lines to UL 2580 [40] (minimum 590 \({}^{\circ}\)C, in 5 min, burning for 20 min, no explosions). BEV car fire tests are in the spotlight [41] due to the current increase in the number of mentioned vehicles on the road. [PERSON] et al. [42] conducted experimental investigations during the safety project: fire tests with battery cells; fire tests with battery modules; and fire tests with BEVs, including a survey of firefighting procedures. Heat release and production of (toxic) substances were evaluated in a series of fire tests. [PERSON] et al. [43] studied and addressed vehicle fires caused by lithium-ion batteries with thermal runaway.