With the popularity of electric vehicles (EVs) continuing to grow, the steel industry is looking to secure the material's place as the preferred choice for battery enclosures, and thus benefit from the increased steel demand that would follow.
Fastmarkets
December 15, 2020
By Robert England
Steel is competing with aluminium and new non-metal materials used for battery enclosures, including carbon and glass fiber-reinforced polymers.
The battery enclosure is “how you protect the battery module and associated electronics” from crashes and potential fires and possible explosions, according to Hesham Ezzat, a former engineering group manager at General Motors Co who retired in 2015. He pioneered the design of the structure development of the automaker’s EV1 body, the first mass-produced and purpose-designed EV in North America.
“You don’t want the battery pack to deform” if there is a collision, he added.
“In a side full impact, the impact energy must be absorbed inside a fairly small lateral distance. The structure around the modules, the enclosure itself has to be able to mitigate any kind of intrusion and avoid distortion of the battery case and the battery itself,” Ezzat said.
EV automakers also want the battery modules and associated components to be protected from road debris and stones that could be propelled upward and hit the bottom of the battery enclosure.
“Housing is extremely important. Steel can contribute to the overall stiffness and strength,” Ezzat said.
So far, aluminium has been the leading material for battery enclosures, primarily because the metal is the preferred choice of EV pioneer Tesla. For example, the Tesla Model 3 sedan, which has an aluminium battery enclosure, is “by far the most popular electric vehicle,” according to rankings by US News & World Report.
In addition, General Motors will be moving the 2021 Chevrolet Bolt EV to a skateboard design, whereby the battery pack is spread out across the full length and width of the bottom of the vehicle frame, like the four-wheel skate platform. While the battery cover is a composite sheet-molding compound with glass fiber, the new Bolt EV uses an all-steel tray assembly and internal structure, according to General Motors.
Cost effective
The American Iron and Steel Institute (AISI) is collaborating with the auto industry to make the case for steel battery enclosures. The institute cited a string of automakers using steel cages for EV models in recent years: The 2016 Zotye E200 (a Chinese mini-car), the 2017 Chevy Bolt, the 2017 Nissan Leaf SV, the 2018 Nissan Leaf Tekna, the 2019 Nissan Leaf SV Plus and the 2019 Honda Clarity.
Steel offers more stability for the battery cage because it better protects the battery in a crash, AISI automotive program vice president John Catterall said.
“Steel is more resistant than other materials to thermal events,” he said, referring to potential battery overheating, fires and explosions. "This is due to the fact that it is easier to seal battery boxes made of steel than it is for those made of other materials."
Automakers seeking to extend the range of battery EVs to 300 miles and beyond can do that by “lightweighting vehicles to the max,” or by striking a balance between lightweighting and having more batteries capable of greater range at a lower cost, Catterall said.
Further, steel battery enclosures have performance and safety advantages compared with those made of aluminium, he noted.
“With the future increased emphasis on enhanced structural performance of the enclosure itself to maintain the integrity of the batteries and associated components, steel is very well positioned with its exceptional strength to emerge as a more cost- and mass-effective solution," according to Ezzat.
Ezzat said he bases his analysis of competing materials on his experience of having worked with both steel and alumininum. "My thinking is that steel will be a more cost-effective solution, with the broader pallet of strengths and ductility it provides compared to other materials," he said.
