ANALYSIS OF FIRE DANGER OF ELECTRIC VEHICLES ACCORDING TO THERMAL STABILITY OF POWERFUL LITHIUM BATTERY

Abstract

Formulation of the problem. The world's car fleet numbers more than 1 billion units and is projected to grow to 2.5 billion in 50 years. The fleet includes vehicles with internal combustion engines (ICE), as well as those vehicles that use alternative energy sources. The development of the latter is due to the depletion of oil and gas reserves, the colossal amount of exhaust emissions from vehicles equipped with internal combustion engines, as well as strict environmental standards imposed on internal combustion engines. The main air pollutants in the exhaust gases of internal combustion engines are CO2, NOx, CO, and NOx. This greatly worsens the environmental situation. This trend has led to the rapid development of electric vehicles. The rapid increase in the number of electric vehicles leads to an increase in the dangers that accompany them. One of such dangers is their fire danger.
The purpose of this work is to identify and classify the factors influencing the fire hazard of electric vehicles, to create a basis for its improvement.
Description of the material. Even though in modern electric vehicles, there is a control system (BSM) of the power battery (charge/discharge control (SOC), control of capacity (SOH) and temperature (SOT) of the battery), the use of fuses and safety vents for digestion Excess pressure from the battery cell causes malfunctions that cause an irreversible exothermic reaction, which ends in fire or even explosion. Control and management of the temperature of the power battery is a determining factor that directly ensures the safety of the electric vehicle as a whole. The main causes of irreversible exothermic reaction of power batteries include violations of operating rules. Violations of the rules of operation include battery recharging, mechanical damage, including as a result of an accident, and overload of the power plant of the electric vehicle, which leads to leakage of overload currents through the conductors. Violations of operating rules lead to overheating of the battery, which initiates an irreversible exothermic reaction with subsequent ignition or explosion. Mechanical damage leads to a short circuit of the battery, which also initiates an irreversible exothermic reaction. Already at a temperature of 80 ˚C in the power battery may be irreversible thermal processes and at 130 ˚C melting of the separator, which leads to a short circuit (CC) of the battery. When the battery is fully charged, the temperature generated by one cell of the battery in the event of a short circuit can reach 700 ˚C and more. Of all the types of batteries used in modern electric vehicles, the NCA poses the greatest fire hazard (at the same time, the NCA has the best performance in terms of specific energy capacity). It is followed by a more fireproof lithium-ion battery, the cathode of which is based on lithium cobalt oxide (LCO), followed by a lithium-ion battery, the cathode of which is based on lithium-nickel-cobalt oxide manganese (NMC) and lithium-ion battery, the cathode of which is based on lithium-manganese oxide (LMO) The most dangerous is the lithium-ion battery whose cathode is based on lithium-iron-phosphate oxide (LFP).
Results. Based on the results of analytical research, the factors influencing the fire hazard of EV have been identified and classified. These are design, operational and service factors. Structural factors: type of power battery, battery capacity, availability of safety systems, control and monitoring of the power battery and protection of the battery from mechanical damage. Operational factors: age of the electric vehicle and condition of the SOC. Service factors: non-compliance or violation of maintenance rules, use of non-standard factory devices. In the event of exothermic reactions with the battery, flammable and toxic gases are released (with subsequent combustion or explosion), including hydrogen, methane, ethane, carbon monoxide, carbon dioxide and others. The battery of an electric car in an exothermic reaction can create a lethal concentration of CO in the interior of the electric car in a few seconds. Power battery is the greatest danger, the weight of which can be 200-600 kg for a car. As soon as 80 ° C is reached, exothermic reactions can occur in lithium-ion batteries, which cause a sharp rise in battery temperature with subsequent ignition and/or explosion.