- In May 2022, the Union Government has constituted an expert panel to probe the recent series of battery explosions in Electric Vehicles (EVs).
What are Electric vehicles?
- EVs are vehicles that are either partially or fully powered on electric power.
- While prior EV's used nickel - cadmium batteries beside modern Lithium-ion batteries, that also to be used for mobile.
Why is the world poised to transition to electric vehicles?
- The growing concern over Climate Change has led to global efforts to electrify the transportation sector.
- In parallel, 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 a dramatic transition in the transportation sector, with electric vehicles poised to replace petrol vehicles.
- The world has taken note of this moment with governments providing incentives to usher in the transition and private industry ramping up plans for capturing the market.
- 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 takes 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.
What goes into a Li-ion battery?
- Every Li-ion battery consists of three active components:
(i) The anode, typically graphite.
(ii) The cathode, typically based on a nickel, cobalt, and manganese-based oxide.
(iii) An 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.
- Accidental shorting of the electrodes is a known cause of fires in Li-ion cells.
- It is important that the 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.
What causes battery fires?
- While Li-ion batteries are complex, over the last three decades numerous companies have perfected the art of manufacturing high-quality cells and integrating them into vehicles with minimal safety concerns.
- The energy density of petrol is five hundred times that of a typical Li-ion battery, therefore safety should be manageable if robust controls are in place.
- However, batteries do store energy in a small package and if the energy is released in an uncontrolled fashion, the thermal event can be significant.
- 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 raise as the anode and cathode release their energy through the short.
- This, in turn, can bring to a series of reactions from the battery materials, especially the cathode, that release heat in an uncontrolled manner, along with oxygen.
Are battery fires inevitable?
- Li-ion batteries have proved to be extremely safe, with the industry increasing controls as safety incidents have surfaced.
- 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.
- Many companies now add a ceramic layer on the separator to mechanically prevent shorts.
- Sensing the state of the battery and integrating this data into sophisticated battery management systems is an important aspect of design.
- 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.