Science and Tech

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

·       Manufacturers such as Okinawa and Pure EV have recalled some batches of electric scooters after their vehicles caught fire.

What goes into a Li-ion battery?

·       lithium-ion battery cell consists of the following: Cathode: the positive terminal of the battery – generally graphite Separator: a thin permeable polymer or similar that separates the cathode and anode Electrolyte: generally, a salt of lithium in an inorganic solvent.

·       Battery manufacturing could be a complicated operation involving forming sheets of the anode and cathode and assembling them into a sandwich structure held apart by a thin separator.

·       Separators, regarding fifteen 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.

What causes battery fires?

·       Li-ion batteries are complex.

·       The energy density of petrol is five hundred times that of a typical Li-ion battery, 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 a short circuit occurs in the battery, the inner temperature will raise because the anode and cathode release their energy through the short.

·       This, in turn, can lead to a series of reactions from the battery materials.

·       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 a catastrophic failure of the battery resulting in smoke, heat, and fire, released instantaneously and explosively.

·       The trigger for such events may be a results of internal shorts (like a manufacturing defect that results in sharp objects penetrating the separator), external events (an accident resulting in 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), or bad thermal design at the module and pack level (by not allowing the battery internal heat to be released).

·       Preventing fires requires breaking the fire triangle. Battery cathodes are a leading reason for the heat release.
Some cathodes, such as ones with lower nickel content or moving to iron phosphate, will increase safety.