Truck & Off-Highway Engineering - April 2021 - 10

Material selection for
battery enclosures
Electric-truck enclosures balance demands
Manufacturers of battery-electric commercial trucks have similar requirements for their battery enclosures as do their passenger-vehicle
counterparts. Lightweight construction is very important, but durability and the ability to protect components and occupants in crashes
and the event of a fire are paramount.
The Volvo VNR Electric features an all-metal cab construction, and
the battery enclosure is made from stainless steel. The protection plates
and mounting arrangements are made from casted and steel materials.
" These metals were chosen due to the technical requirements
needed to support the batteries, durability demands, and to provide
protection to cab occupants and vehicle components, " said Brett
Pope, director of electric vehicles, Volvo Trucks North America. " In
the overall development of an electric Class 8 truck, lightweight components are utilized where feasible to maximize payload and to affect
the load distribution on the axles. However, we will not compromise
the safety of our vehicles, so the protection of the occupants of the
cab will always be our top priority. "
Freightliner takes a similar approach with the design of its battery-pack enclosures for the eM2 and eCascadia trucks. " Weight is
always a consideration in trucking, but safety is an even more important factor, " said Alex Voets, Freightliner eMobility sales and product
strategy manager.
Freightliner engineers designed the side-impact protection of the
batteries to distribute the forces along the structure, providing a lightweight structure with maximum safety, Voets said.
Navistar employs a mixed-material approach for its electric-truck
battery enclosures.
" We currently use multiple materials in our battery enclosures -
composites, stamped steel, and aluminum being the most common, "
said Zilai Zhao, director of eMobility Engineering at Navistar. " Safety,

The Volvo VNR Electric's battery
enclosure is made from stainless
steel. The protection plates and
mounting arrangements are made
from casted and steel materials.
weight, durability, cost, dielectric separation, thermal performance, and
manufacturability are all considerations when selecting battery-enclosure materials. Our goal is to balance these considerations while optimizing the design for that particular vehicle's duty cycle. "
Weight is always an important factor when selecting materials,
said Zhao, especially because less weight equals more range, better
acceleration, and more payload. " The challenge is to remove the
weight without compromising the vehicle's durability and performance - all at an acceptable cost, " he said.
Navistar continuously evaluates different materials for use with
battery enclosures. " As electric vehicles continue to grow, the industry
supply base is constantly offering new materials and technologies
with different use cases and advantages depending on the application, " Zhao said.

Ryan Gehm

For parts of the enclosure that are away from the cells,
such as the bottom plate located below the cooling plate,
heat is not a concern. Afseth said he does not see any
issues regarding immersion cooling: " Aluminum alloys of
the 3000, 5000 and 6000 series are very well compatible and completely resistant to common coolant liquids. "

This screenshot from a Hexion video demonstrates phenolic resin's superior fire
resistance compared to aluminum.
that are in direct contact with the cells or other parts of the highvoltage system that gets heated during charging or discharging. " My
main concern would be with alloys like 5182 which has more than 3.5
wt% Mg, as these may over time develop a film of beta-phase precipitates at the grain boundaries which can result in degraded properties, " Afseth explained.
10 April 2021

Justification for the over-cost of aluminum structures
is found in the secondary mass and cost savings tied
to being able to downsize the battery and the powertrain, Afseth stressed. But, as battery costs continue
to drop, the value equation for aluminum may dissipate. In the past decade, battery cost has fallen by
almost a factor of ten, he noted, from about $1,000
kWh in 2010 to below $150 kWh last year. Energy density has almost tripled over this same period, so batteries also weigh much less than before.
" Why we see all the long-range BEVs today using
aluminum is because at the time they were making their
engineering and material choices, this equation was
super simple: You spend a few hundred dollars more on
the body structure and you save thousands of dollars
TRUCK & OFF-HIGHWAY ENGINEERING

FROM TOP: VOLVO TRUCKS NORTH AMERICA; HEXION

Move to multi-materials

Truck & Off-Highway Engineering - April 2021

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