- May 1, 2022
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Subject: Science and Tech
Context- The Union government has constituted an expert panel to probe the recent series of battery explosions in electric 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 – typically based on a nickel, cobalt, and manganese-based oxide;
- Anode: the negative terminal of the battery – typically graphite
- Separator: a thin permeable polymer or similar that separates the cathode and anode
- 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.
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 internal temperature can raise as 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 can be a result of
- 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), 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 cause of the heat release.
- Some cathodes, such as ones with lower nickel content or moving to iron phosphate, can increase safety.