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Electric Vehicle Fires – Part2

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May 02, 2022

Why in news?

The Union Government has constituted an expert panel to probe the recent series of battery explosions in electric vehicles (EVs).

What are EVs?

  • EVs are vehicles that are either partially or fully powered on electric power.
  • While some EVs used lead acid or nickel metal hydride batteries, the standard for modern battery electric vehicles is now considered to be lithium ion batteries.
  • But, the recent incidents of fire involving electric two-wheelers (ETWs) have raised concerns over quality and safety of these vehicles.

To know more about EV fires, click here

What goes into a 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
  • The sheets of the anode and cathode are assembled into a sandwich structure held apart by a thin separator (about 15 microns in thickness) to prevent shorting.
  • Accidental shorting of the electrodes is a known cause of fires in Li-ion cells.
  • Safety features, such as thermal switches that turn off if the battery overheats, are added into a battery cell.
  • Battery cells are assembled into modules and then further assembled into packs that are designed to ensure uniform temperature profile with minimal thermal variation during operation.

What causes battery fires?

  • Battery fires occur due to the convergence of three parts of the “fire triangle” - heat, oxygen, and fuel.
  • Heat- If an adverse event such as a short circuit occurs in the battery, the internal temperature can raise as the anode and cathode release their energy in an uncontrolled manner, along with oxygen.
  • Oxygen- Such events also rupture the sealed battery further exposing the components to the second part of the fire triangle, namely, oxygen.
  • Fuel- The final component of the triangle is the liquid electrolyte, which is flammable and serves as a fuel.
  • Trigger for battery fires
    • Internal shorts - manufacturing defect that results in sharp objects penetrating the separator
    • External events
      • puncture of the cell and shorting of the electrodes
      • overcharging the battery
      • faulty battery management system
      • bad thermal design at the module and pack level

ev-fires

Are battery fires inevitable?

  • Battery Cathodes- Since battery cathodes are a leading cause of the heat release, the one with lower nickel content or moving to iron phosphate can increase safety.
  • Manufacturing- Tightly controlled manufacturing will prevent accidental shorts in the cells, eliminating a leading cause of fires.
  • Adding a ceramic layer on the separator mechanically prevents shorts.
  • Design-Sensing the state of the battery and integrating this data into sophisticated battery management systems is important.
  • Protecting the cell with robust thermal management is critical, especially in India where ambient temperatures are high.
  • Battery packs need to be protected from external penetration.
  • Current developments- Companies are developing internal switches that turn off parts of the battery that undergo thermal events to stop them at their inception.
  • Research is underway to replace the flammable liquid electrolyte with a solid electrolyte and nonflammable liquid electrolytes to eliminate one part of the fire triangle.
  • Role of regulators- Regulators play an important role, providing the testing and certification needed to ensure that technology innovations perform at the level that is promised.

 

References

  1. https://www.thehindu.com/business/Industry/explained-why-are-electric-vehicles-catching-fire/article65369737.ece?homepage=true
  2. https://www.twi-global.com/technical-knowledge/faqs/what-is-an-ev
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