With many recent incidents of electric vehicles (EV) catching fire, particularly two-wheelers, many of us are wondering what is the root cause of such incidents?
We can easily blame the poor cell quality, cell chemistry, hot climate and the poor quality of battery management systems. Here, I doubt. Then why did Telsa or other reputed company’s cars catch fire? They have the best quality EV system, battery cells, and complete control of battery operation. Therefore, we need more understanding of battery cells and their behavior, arrangements, and controls in all types of EVs. There could be many points of failure that needed more thorough investigations.
In the present EV system, battery management systems (BMS) are regarded as critical battery protection systems for safety accidents: known as thermal runaway. The BMS, today, can detect the external surface temperature, voltage, and state of charge (SOC) of a battery cell, and protect the cell/battery pack from overcharge by sending an alarm signal if the battery’s external temperature exceeds the normal range. We need to understand that there is a large difference between the battery’s internal and external temperature due to the poor thermal conduction in a tropical country like us.
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In today’s BMS system, safety mainly relies on a specific gas or smoke detection system and focuses on BMS protection. Specific gases like carbon monoxide (CO) and different hydrocarbons that are consequences of overcharging or overheating are believed to give an effective indicator for safety warning to the battery system.
In technical terms, the above gases arise from the reduction and oxidation of the electrolyte and the degradation of the protective surface film (SEI) at nearly 90 degrees Celsius, when the fire has already occurred and the smoke detector gives rise to an alarm signal the system. Here, the present detection system may not be the best indicator of micro lithium dendrite growth (which is common in graphitic anode cells) until a battery’s internal temperature exceeds 50 degrees Celsius, and until that point, the actual thermal runaway (fire or smoke) may not even have started. In many incidences that have been reported worldwide, the detectors were unable to detect the lithium dendrite growth and prevent battery safety failure, causing recent catastrophic events in many countries.
The important question is what will be the strategy to prevent or understand such events and what could be the early control measures. Many reports suggest that hydrogen gas (H2) was found to be the most sensitive gas and can be detected much earlier than the other gases. Thus, the lithium dendrite growth and thermal accumulation processes inside the battery can be prevented by cutting off the charger at the time when a trace amount of hydrogen gas is detected.
In modern EVs, developing an effective detection method of micron-scale lithium dendrite formation for early safety warning can improve the safety level of lithium-ion battery systems. Unfortunately, in two-wheelers or three-wheelers, this type of detection or BMS will not be a cost-effective solution and we need more unique thinking to prevent such fires here.
The government, along with effective research and development, should give more awareness to the customers, and common people, to increase their confidence level. The EV system is new in our society and needs more knowledge creation, dissemination, and training on how to use it safely.
(The author is a professor at the Department of Energy Science and Engineering, IIT Bombay, and researches lithium-ion batteries)
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