Explanation: Do lithium-ion batteries in electric vehicles pose a fire risk?

Aug 23 (Reuters) – General Motors Co (GM.N) has extended the recall of its Chevrolet Bolt electric vehicles over fire risk from pouch-type lithium-ion battery cells manufactured by the South Korean LG. Read more

The recall, the second major involving batteries made by LG Chem’s LG Energy Solution (LGES) battery unit (051910.KS), highlights the challenges battery companies face in making a stable product to power cars electric. Read more

HOW DOES A LITHIUM-ION BATTERY WORK?

Cells come in different shapes and sizes, but most have three key components: the electrodes, the electrolyte, and the separator.

The electrodes store lithium. The electrolyte transports lithium ions between the electrodes. The separator prevents the positive electrode from coming into contact with the negative electrode.

Energy, in the form of electricity, is discharged from the battery cell as lithium ions flow from the negative electrode, or anode, to the positive electrode, or cathode. When the cell charges, these ions flow in the opposite direction from the cathode to the anode.

WHY DO LI-ION BATTERIES PRESENT A FIRE HAZARD?

Lithium-ion batteries, whether used in cars or electronic devices, can catch fire if they have been improperly manufactured or damaged, or if the software that runs the battery is not designed properly.

The main weakness of lithium-ion batteries in electric cars is the use of organic liquid electrolytes, which are volatile and flammable when operated at high temperatures. External force such as an accident can also cause chemicals to leak.

“For electric vehicle fires, it has always been very difficult to identify the exact cause of the fire, as it is extremely difficult to ‘reconstruct’ the fire under the same conditions,” said Kim Pil-soo, professor of automotive engineering at Daelim University.

In addition, authorities, automakers and battery manufacturers often do not disclose the exact safety risk.

WHAT CAUSED THE BOLTS AND KONAS FIRES?

In February, South Korea’s transport ministry said some flaws had been found in some battery cells made at the LGES plant in China and used in Hyundai Motor’s electric cars, including the Kona EV. Hyundai’s recall cost about 1,000 billion won ($ 854 million).

GM said the batteries LG supplied for the Bolt EV and Bolt EUV may have two manufacturing flaws – a torn anode tab and a bent separator – present in the same battery cell, increasing the risk of fire. .

For a factbox on the main battery fires:

ARE SOCKET-TYPE BATTERIES MORE VULNERABLE?

The three types of lithium-ion batteries currently used in electric cars – cylindrical, prismatic, and pocket-type – have basically the same functionality, but each has its advantages and disadvantages.

The cylindrical and prismatic batteries are coated with hard materials. The pocket types use flexible sealed sheets and are protected by thin metal bags.

The technology used in cylindrical batteries is old and gives consistent results. These cells can withstand high internal pressure without deforming. They are also cheaper, which makes them ideal for mass production. But they are heavier and their shape prevents cells from being packed as densely as with other forms of battery. Tesla Inc (TSLA.O) mainly uses cylindrical batteries, some supplied by LGES.

Prismatic batteries are considered to be safer and lighter than cylindrical cells and, because they are rectangular, can be more densely packaged. They optimize space better than cylindrical cells, but are generally more expensive and have a shorter life cycle. They can also swell.

Compared to cylindrical and prismatic cells, pocket-type battery cells allow lighter and thinner cell fabrication, and design flexibility for different capacities and space requirements for different vehicle models. However, they are vulnerable to swelling and are more vulnerable to collisions, posing a greater risk of fire.

GM and Hyundai Motor use pocket battery cells from LG Energy Solution (formerly LG Chem). Volkswagen announced earlier this year that it will be switching from pocket-style airframes made by LG and SK Innovation Co Ltd (096770.KS) to prismatic technology. Read more

ARE THERE OTHER SOLUTIONS?

Companies such as the Chinese company BYD Co (002594.SZ) produce battery cells for electric vehicles that use lithium iron phosphate cathodes, which are less likely to catch fire, but are not able to store as much energy than standard cells that use nickel cobalt manganese cathodes.

Others, including GM, are testing different chemistries such as nickel-cobalt-manganese-aluminum (NCMA) technology, which uses less cobalt, making cells more stable and cheaper.

Chinese battery maker CATL (300750.SZ) last month unveiled a sodium-ion battery that contains no lithium, cobalt, or nickel. Read more

A number of companies, including Toyota Motor Corp (7203.T), are also developing battery cells with solid state electrolytes, which could minimize overheating issues and fire hazards, but could take still three to five years to be marketed.

($ 1 = 1,170.5,800 earned)

Report by Heekyong Yang in Seoul; Written by Sayantani Ghosh; Editing by David Holmes

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