Reasons for recent incidents of catching fire by Electric vehicles

• The Union Government has constituted an expert panel to probe the recent series of battery explosions in electric vehicles (EVs).
• After the enquiry, the Ministry of Road Transport intends to issue guidelines for EVs, including tests for compliance with safety norms.

Transition to electric vehicles worldwide

• The growing concern over climate change has led to global efforts to electrify the transportation sector.
• In parallel, the cost of Li-ion (Lithium-ion) battery technology has decreased by a staggering order of magnitude in the last decade.
• The convergence of these two factors has resulted in a dramatic transition in the transportation sector, with electric vehicles poised to replace petrol vehicles.
• There is a worldwide race emerging, with vehicle companies, battery manufacturers, and material suppliers vying with each other for market share.
• However, Li-ion batteries are complex devices requiring a level of sophistication that can take years to perfect.
• Hurrying the development of this complex technology without careful safeguards can lead to increasing safety incidents, as evidenced recently on Indian roads.

Li-ion battery

• Every Li-ion battery consists of three active components:
  • Anode: typically graphite;
  • Cathode: typically based on a nickel, cobalt, and manganese-based oxide;
  • Electrolyte: typically a salt of lithium in an inorganic solvent.
• Battery manufacturing is a complex operation involving forming sheets of the anode and cathode and assembling them into a sandwich structure held apart by a thin separator.
• Separators, about 15 microns in thickness-about a fifth of the thickness of the human hair -perform the critical function of preventing the anode and cathode from shorting.
• Accidental shorting of the electrodes is a known cause of fires in Li-ion cells.
• Various layers are assembled with high precision with tight tolerances maintained throughout the manufacturing process.
• Safety features, such as thermal switches that turn off if the battery overheats, are added as the sandwich is packaged into a battery cell.
• Battery cells are assembled into modules and then further assembled into packs.
• Li-ion batteries require tight control on the state of charge and the temperature of operation to enhance safety and increase usable life, achieved by adding multiple sensors.
• Packs are designed to ensure a uniform temperature profile with minimal thermal variation during operation.
• Battery packs are integrated into the vehicle in unique form factors depending on the design of the vehicle.
• The location of the battery should protect it from external penetration, ensure passenger safety while taking into consideration the overall weight distribution.
• Close interaction between vehicle manufacturers and battery manufacturers is essential so that the whole is greater than the sum of the parts.
• There are multiple tradeoffs in this complex ecosystem: engineering higher safety often results in higher costs and lower driving range.

Factors causing battery fires

• Battery fires, like other fires, occur due to the convergence of three parts of the “fire triangle”: heat, oxygen, and fuel.
• If an adverse event such as a short circuit occurs in the battery, the internal temperature can rise as the anode and cathode release their energy through the short circuit.
• This, in turn, can lead to a series of reactions from the battery materials, especially the cathode, that release heat in an uncontrolled manner, along with oxygen.
• Such events also rupture the sealed battery further exposing the components to outside air and the second part of the fire triangle, namely, oxygen.
• The final component of the triangle is the liquid electrolyte, which is flammable and serves as a fuel.
• The combination leads to catastrophic failure of the battery resulting in smoke, heat, and fire, released instantaneously and explosively.

Trigger of such events

• internal shorts (like a manufacturing defect that results in sharp objects penetrating the separator),
• external events (an accident leading to puncture of the cell and shorting of the electrodes), * overcharging the battery which leads to heat releasing reactions on the cathode (by a faulty battery management system that does not shut down charging despite the battery achieving its designed charge state),
• bad thermal design at the module and pack level (by not allowing the battery internal heat to be released).

Measures to prevent battery fires

• Preventing fires requires breaking the fire triangle.
• Battery cathodes are a leading cause of the heat release.
• Some cathodes, such as ones with lower nickel content or moving to iron phosphate, can increase safety.
• Tightly controlled manufacturing will prevent accidental shorts in the cells, eliminating a leading cause of fires
• Protecting the cell with robust thermal management is critical, especially in India where ambient temperatures are high.
• Finally, battery packs need to be protected from external penetration.
• Any large-scale manufacturing process inevitably has a certain percentage of defects; therefore, such steps are needed to minimise the number of adverse events.

Conclusion

• Engineering safety requires commitment from all parts of the battery supply chain and tight integration between vehicle companies and battery companies.
• Further, regulators play an important role, providing the testing and certification needed to ensure that technology innovations perform at the level that is promised.
• Companies with tightly controlled manufacturing with years of experience can maintain the number of adverse safety incidents to a minimum.
• Ensuring safety of EV users should be the priority for manufacturers.

Exam Track

Prelims Takeaway

• Li ion Battery components

Mains Track

Q. In the wake of recent events of EV battery explosion. Discuss about the reasons leading to such incidents and steps to reduce them.