Explained | Why do electric vehicles catch fire?

Is the battery inflicting the issue? What are the protection measures that should be adopted to stop explosions?   

The story thus far: The Union Government has constituted an expert panel to probe the latest sequence of battery explosions in electric vehicles (EVs). Manufacturers like Okinawa and Pure EV have recalled some batches of electrical scooters following fire incidents involving the vehicles. Last Wednesday, an 80-year-old man died at his home in Telangana’s Nizamabad district after the battery of an electric scooter exploded whereas being charged. After the enquiry, the Ministry of Road Transport intends to subject guidelines for EVs, together with assessments for compliance with security norms.

Why is the world poised to transition to electric vehicles?

The rising concern over climate change has led to world efforts to electrify the transportation sector. In parallel, price of Li-ion (Lithium-ion) battery technology has decreased by a staggering order of magnitude within the last decade. The convergence of those two elements has resulted in a novel time in our historical past the place we’re on the cusp of a dramatic transition in the transportation sector, with electric vehicles poised to exchange petrol vehicles.

The world has taken notice of this moment with governments providing incentives to usher in the transition and personal industry ramping up plans for capturing the market. There is a worldwide race rising, with car firms, battery producers, and materials suppliers vying with one another for market share. However, Li-ion batteries are complicated devices requiring a level of sophistication that may takes years to perfect. Hurrying the event of this complicated technology with out cautious safeguards can result in increasing safety incidents, as evidenced recently on Indian roads.

What goes into a Li-ion battery?

Every Li-ion battery consists of three active parts: the anode, sometimes graphite; the cathode, sometimes based on a nickel, cobalt, and manganese-based oxide; and an electrolyte, sometimes 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 aside by a thin separator.

Separators, about 15 microns in thickness — about a fifth of the thickness of the human hair — perform the vital function of preventing the anode and cathode from shorting. Accidental shorting of the electrodes is a recognized cause of fires in Li-ion cells. It is essential that the various layers are assembled with high precision with tight tolerances maintained all through the manufacturing course of. Safety options, similar to thermal switches that flip off if the battery overheats, are added because 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 reinforce safety and improve usable life, achieved by including a number of sensors. Packs are designed to make sure uniform temperature profile with minimal thermal variation throughout operation. Ensuring strong detection, coupled with battery management systems that interpret the info and alter operation primarily based on modifications to the batteries state, stay critically important in enhancing battery efficiency.

Battery packs are integrated into the car in distinctive formfactors relying on the design of the car. The location of the battery ought to shield it from exterior penetration, ensure passenger security whereas speaking into consideration the general weight distribution. Close interplay between car manufacturers and battery manufacturers is important in order that the entire is greater than the sum of the parts.

There are a number of tradeoffs on this complicated ecosystem: engineering greater security typically leads to greater prices and decrease driving range. In this aggressive landscape where companies are vying for market share, a race to the bottom can compromise security.

What causes battery fires?

While Li-ion batteries are complicated, over the past three decades quite a few companies have perfected the art of manufacturing high-quality cells and integrating them into vehicles with minimal security issues. The vitality density of petrol is five hundred times that of a typical Li-ion battery, subsequently security needs to be manageable if strong controls are in place. However, batteries do retailer vitality in a small package and if the vitality is launched in an uncontrolled fashion, the thermal occasion will be significant.

Battery fires, like other fires, happen because of the convergence of three parts of the “fire triangle”: warmth, oxygen, and fuel. If an opposed occasion similar to a brief circuit happens within the battery, the interior temperature can increase because the anode and cathode launch their vitality by the brief. This, in turn, can result in a sequence of reactions from the battery supplies, particularly the cathode, that release heat in an uncontrolled method, together with oxygen.

Such occasions additionally rupture the sealed battery additional exposing the components to outside air and the second a part of the fire triangle, particularly, oxygen. The last element of the triangle is the liquid electrolyte, which is flammable and serves as a fuel. The combination results in catastrophic failure of the battery leading to smoke, warmth, and fire, released instantaneously and explosively.

The set off for such occasions could be a results of inside shorts (like a manufacturing defect that leads to sharp objects penetrating the separator), exterior events (an accident resulting in puncture of the cell and shorting of the electrodes), overcharging the battery which ends up in warmth releasing reactions on the cathode ( by a defective battery management system that doesn’t shut down charging regardless of the battery attaining its designed charge state), or unhealthy thermal design on the module and pack level (by not permitting the battery inside warmth to be launched). Any of those triggers might cascade into a big safety incident.(see graphic).

Explained | Why do electric vehicles catch fire?

Are battery fires inevitable?

Over the previous three decades, Li-ion batteries have proved to be extraordinarily secure, with the business growing controls as security incidents have surfaced. Safety is a should and is a vital consideration that battery and car producers can design for at a number of ranges from the selection of battery materials to designs on the cell, pack, and car stage.

Preventing fires requires breaking the fire triangle. Battery cathodes are a number one reason behind the warmth release. Some cathodes, similar to ones with decrease nickel content or shifting to iron phosphate, can improve security. Tightly controlled manufacturing will stop unintended shorts within the cells, eliminating a number one reason behind fires. Many companies now add a ceramic layer on the separator to mechanically stop shorts. Sensing the state of the battery and integrating this information into sophisticated battery management techniques is a vital side of design. Protecting the cell with strong thermal management is vital, particularly in India where ambient temperatures are excessive. Finally, battery packs should be protected against exterior penetration. Any large-scale manufacturing course of inevitably has a sure percentage of defects; therefore, such steps are wanted to minimise the number of adverse events.

Long time period modifications are additionally underway. Safety stays a priority for Li-ion manufacturers worldwide particularly as cell sizes change into bigger for purposes like solar-connected storage. Companies are growing inside “switches” that flip off parts of the battery that bear thermal occasions to cease them at their inception. Research is now underway to exchange the flammable liquid electrolyte with a strong electrolyte to remove one a part of the fire triangle. An analogous thread of analysis is the event of nonflammable liquid electrolytes. All these modifications promise to take away the specter of battery fires as the roll out of mass electrification takes place.

Engineering security requires dedication from all parts of the battery provide chain and tight integration between car companies and battery companies. Further, regulators play an necessary role, offering the testing and certification wanted to make sure that expertise improvements carry out on the stage that’s promised. Li-ion batteries will not be forgiving of shoddy engineering and approaches that depend on cutting corners. Companies with tightly controlled manufacturing with years of expertise can preserve the variety of adverse security incidents to a minimal. Such batteries possibly dearer, but security shouldn’t be “just another” metric. Rather, guaranteeing security needs to be the priority for manufacturers.

The author is Director of the Argonne Collaborative Center for Energy Storage Science at Argonne National Laboratory, Illinois

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