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