Automotive Engineering - March 2023 - 22

BATTLE
BOX
FOR THE
DuPont's 3-in-1 battery-box concept is a new example of modular design that
consolidates cell cooling, electrical interconnection and structural components.
Its housing is made of the company's heat-resistant Zytel HTN.
In this scenario, Tier 1s are offering both near- and long-range solutions
for OEM evalution. DuPont's 3-in-1 battery-box concept unveiled
in late 2022 is a new example of modular design that consolidates
cell cooling, electrical interconnection, and structural components.
Its housing is made of the company's Zytel HTN, a nylonbased
polyamide capable of resisting high temperatures.
According to Frank Billotto, battery materials business-development
leader in DuPont's Mobility and Materials group, the concept
provides semi-direct cooling (cells are cooled through their tabs) and
easy assembly via electrical interconnections. He said the design enables
batteries with greater energy density, improving vehicle range
and package efficiency.
The " battle for the box " has kicked off a new wave of creativity
among engineers and materials scientists. Roughly 80% of current
EVs have an aluminum battery enclosure, but engineers are quick to
note that the field is wide open for alternatives, based on vehicle
type, duty cycles, volumes, and cost.
" I think we will see more lightweight-steel enclosures in the future,
mainly on smaller, shorter-range vehicles, " offered Dr. Andreas
Asfeth, technical director, North American Automotive at
Constellium, a specialist in aluminum extrusions and sheet. He acknowledged
steel's " strong cost-competitiveness " and said the ferrous
metal's significant weight penalty versus aluminum isn't a huge
issue with small-vehicle batteries.
But in larger, long-range vehicles, " the battery represents the value
of the vehicle. The larger the battery, the more aluminum makes
sense for battery packs, " Asfeth asserted. Bucking that trend is GM's
9000-lb. (4082-kg) Hummer EV, which uses a multi-material battery
enclosure. Tesla also has reduced the amount of aluminum in the battery
enclosure for the Model 3 and Model Y compared to what was
used in its S and X models. And public statements made by the company
regarding the structural battery pack expected to come from
Tesla's Berlin plant indicate the upper and lower covers are steel.
22 March 2023
Each OEM will have its own playbook on EV battery enclosure
design and engineering, said Mario Greco at Novelis.
Aluminum rules - for now
Aluminum battery enclosures typically deliver a weight
savings of 40% compared to an equivalent steel design.
According to Asfeth, the alloys best suited for battery
enclosures are the 6000-series Al-Si-Mg-Cu family -
alloys that are also highly compatible with end-of-life
recycling, he said. The current state-of-the-art solution
for bottom plates is high-strength 6111 alloy in peakaged
temper, which reduces weight by 30% compared
to the benchmark 5754 O-temper alloy, he said.
Looking intensely at vehicle impact requirements,
Constellium is developing a " cost competitive " 4xxxseries
alloy boasting 80-GPa E-modulus and 350-MPa
yield stress, according to Asfeth. The alloy offers potential
for a 40% weight reduction. He added that the 4xxxseries
gauges and widths will be similar to 6000-series
alloy and is compatible with conventional cold forming.
The company also has a 7075 T6 alloy in development.
Asfeth told a Center for Automotive Research
webinar audience that the material offers 500-MPa
yield stress and 70-GPa E-modulus. Potential applications
include battery-pack bottom plates where impact
resistance is key. However, the new alloy requires special
manufacturing processes the added cost of which
might offset the 10% weight savings benefit. Such are
the tradeoffs in battery-box and EV development.
Aluminum's workhorse 6xxx-series alloy is used in two
different advanced extruded alloys that underpin a recent
Constellium dual-frame enclosure prototype. The inner
frame (a second buttress to protect the cells in an impact)
AUTOMOTIVE ENGINEERING
FROM LEFT: DUPONT; LINDSAY BROOKE
Automotive Engineering - March 2023

Table of Contents for the Digital Edition of Automotive Engineering - March 2023
