EXPERIMENTAL RESEARCH OF THE ELEMENTS OF THE TESLA MODEL S POW-ER BATTERY ON THE SUBJECT OF FIRE HAZARD

Abstract

Introduction. The number of electric vehicles on the global car ferry scale continues to grow. This is facilitated by attractive government programmes in countries such as Norway, Germany, Sweden, China, France, etc. Along with the growth  in the number of electric vehicles, the number of fires in such vehicles is also increasing. Therefore, comprehensive research on the fire hazard of electric vehicles and their components is an urgent issue today.
Purpose. The study aims to determine the thermal parameters (ignition temperature, combustion temperature, and heat flux) that describe the combustion processes of electric vehicle power lithium-ion batteries (using the example of TESLA
MODEL S power battery cells), as well as to study the influence of factors on these parameters using the developed fire test methodology. To achieve the declared goal, experimental studies of the effect of an open flame on electric vehicle power lithium-ion batteries were carried out, and the dependencies of the influence of factors on the thermal parameters and combustion characteristics of electric vehicle power lithium-ion batteries were identified and described. 
Material description. For the study, samples were taken from the power battery of the TESLA MODEL S electric vehicle with a capacity of 75 kWh. The sampled battery cells were divided into three groups: with a charge level of 100%, 50%, and
completely discharged. Each group contained nine prototypes. The fire effect on the battery test samples was carried out by a class B model flame. The samples were placed vertically above the model flame: anode up and down, and horizontally. A total of 27 experiments were performed. During the experimental studies, the temperature of the battery prototypes, and the heat flux, as well as photo and video recording were recorded.
Conclusions. Based on the results of full-scale fire tests of the TESLA MODEL S electric vehicle power battery cells according to the developed methodology, it was found that when the cells are placed vertically with the anode down, the vent
hole operates the latest, and when they are placed horizontally, it operates the fastest. In discharged cells, 9-11 seconds after the onset of an irreversible exothermic reaction, the vent is triggered, and burning gases are released, which last 3-5 seconds. The combustion temperature of the vent gases is 700-750 °C. The combustion of such batteries is not accompanied by an explosion. The mass loss of the battery cell was 15-21 %. In all the experiments, regardless of the state of the charge or placement of the battery, an irreversible exothermic reaction occurs when the battery temperature reaches 165-195 °C. As the battery charge increases, the time for the release of burning ventilation gases increases, accompanied by a louder sound, and the time between the completion of ventilation gas release and explosion decreases (which is not the case for discharged batteries). The state of charge has virtually no effect on the combustion temperature of ventilation gases, which is 700-780 °C for different states of battery charge.