Electric Vehicle Fires – Part2

Why in news?

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

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.

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

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