Explainer: Are lithium-ion batteries in EVs a fire hazard?

General Motors Co has expanded the recall of its Chevrolet Bolt electric vehicles due to the risk of fire


Reuters August 24, 2021

General Motors Co has expanded the recall of its Chevrolet Bolt electric vehicles due to the risk of fire from pouch-type lithium-ion battery cells made by LG of South Korea.

LG Chem Battery Unit The second major battery recall, made by LG Energy Solutions (LGES), underscores the challenges facing battery firms in creating a stable product to power electric cars.

How does a lithium-ion battery work?

Cells come in a variety of shapes and sizes, but most consist of three major elements: an electrode, an electrolyte, and a separator.

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

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Energy, in the form of electricity, is released from the battery cell when lithium ions flow from the negative electrode, or anode, to the positive electrode, or cathode. When the cell is charging, those ions flow from the cathode to the anode in the opposite direction.

Why are Li-ion batteries a fire hazard?

Lithium-ion batteries, whether used in cars or electronic equipment, can catch fire if they are improperly manufactured or damaged, or if the software that operates the battery is not designed correctly.

The major 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. An external force such as an accident can also cause a chemical leak.

“For EV fires, it has always been very difficult to pinpoint the exact root cause of a fire, as it is extremely difficult to ‘re-enforce’ a fire event under similar conditions,” said Professor of Automotive Engineering, Kim Pil-soo. Delim University.

Also executives, car makers and battery makers often don’t disclose what the exact safety risk is.

What causes bolts and cones to fire?

In February, South Korea’s Ministry of Transport said some defects had been found in some battery cells manufactured at the LGES China factory and used in Hyundai Motor’s electric cars, including the Kona EV. Hyundai’s recall cost approximately 1 trillion won ($854 million).

GM said LG-supplied batteries for the Bolt EV and Bolt EUV may have had two manufacturing defects — a cracked anode tab and folded separator — present in the same battery cell, which would have increased the risk of fire. Is.

For Factbox on Big Battery Fire:

Are pouch-type batteries more vulnerable?

All three types of lithium-ion batteries currently used in electric cars – cylindrical, prismatic and pouch-type – are basically similar in functionality, but each has pros and cons.

Cylindrical and prismatic batteries are housed in hard materials. Pouch-types use sealed flexible foil 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 inexpensive, making them ideal for mass production. But they are heavy and their size prevents the cells from being packed as tightly as in other battery forms. Tesla Inc mostly uses cylindrical batteries, some supplied by LGES.

Prismatic batteries are considered safer and lighter than cylindrical cells and, because they are rectangular, they can be packed more densely. They adapt to space better than cylindrical cells, but are usually more expensive and have a shorter life cycle. They can even flower.

Compared to cylindrical and prismatic cells, pouch-type battery cells allow for lighter and thinner cell construction, and design flexibility for different capacities and space requirements for different vehicle models. However, they are sensitive to inflammation, and are more vulnerable in accidents, posing a greater risk of fire.

GM and Hyundai Motor use pouch battery cells from LG Energy Solutions (formerly LG Chem). Volkswagen said earlier this year it would move from pouch-style cells made by LG and SK Innovation Co, Ltd to prismatic technology.

Are there other solutions?

Companies such as China’s BYD Co produce EV battery cells that use lithium iron phosphate cathodes, which are less prone to fire, but not able to store as much energy as standard cells which use a nickel cobalt manganese cathode.

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

Chinese battery maker CATL last month unveiled a sodium-ion battery that doesn’t contain lithium, cobalt or nickel.

Several companies, including Toyota Motor Corp are also developing battery cells with solid-state electrolytes, which can reduce overheating issues and fire risks, but could take three to five years to commercialize.

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