Automotive Engineering - March 2023 - 23

BATTERY PACK TRENDS FEATURE
Crush Resiliant Extrusion Alloys
100
90
80
70
60
50
40
30
20
10
Yield
Strength:
330 MPa
Yield Strength:
240 MPa
Yield Strength: 290 MPa
40
35
30
25
20
15
10
5
6063 T6
Reference
(Extrudability) %
Example Battery Enclosure
AL extrusions currently play a major role in the design of EV packs, as show in
this Constellium illustration.
is in strength-optimized 6000 (HSA6 family). The outer
reinforcement, designed as a crumple zone, is a ductile
6000 alloy, HCA6 family. Pack design could shift, however,
if the industry moves to solid-state lithium batteries,
Asfeth noted. " We may see some load-bearing function in
the solid-state battery cells themselves and therefore less
structural demand on the enclosure, " he said.
Molded packs' promise
Suppliers of composites and plastics are undeterred
by aluminum's current dominance in EV battery enclosures.
They're developing new formulations and processes
aimed at matching or exceeding the performance
and cost-competitiveness of the light metal.
" Current battery packs use a lot of metal that is not
optimized. They were designed using existing materials
and technologies, " asserted Dhanendra Nagwanshi, global
automotive leader, EV Batteries and Electricals, at thermoplastic
giant SABIC. He argues that compared to aluminum,
new-generation thermoplastics offer mass savings
of 30% to 50% depending on application. They also
offer equal or better impact performance, lower cost
through simplified assembly and less environmental impact
than aluminum, he claimed. Engineers' interest in
thermoplastic EV battery trays began with GM's 1990
Impact concept car. The EV-1 production car that followed
used a tray made of glass-filled polypropylene (PP).
SABIC's latest innovation aims directly at one of aluminum's
weaknesses - its very high thermal conductivity.
Aluminum begins to melt at approximately 630
deg. C (1166 deg. F); temperatures generated by an
internal thermal runaway can lead to battery fires as
hot as 1100-deg. C (2012-deg. F). Aluminum also burns
outright at high temperature, as evidenced in 1975
AUTOMOTIVE ENGINEERING
Advanced Extrusion Alloy & Design To Provide
Cost Effective Light Weight Solutions
when the U.S. Navy missile cruiser USS Belknap collided with the aircraft
carrier USS John F. Kennedy. The resulting fire effectively melted
much of Belknap's aluminum-intensive superstructure.
Nagwanshi noted SABIC's development of new Stamax FR longglass-fiber
PP with " unique " flame-retardant properties. " When the
material comes in contact with fire, it chars. The char then becomes an
insulating layer, " he said. The company's testing based on the UL2596
standard for battery enclosure materials demonstrated the plastic can
withstand 1000-deg. C (1,832 deg. F) for 30 minutes - " a temperature
threshold where aluminum would be perforating, " he noted. Global
Technical Regulation No. 20 on EV safety (GTR 20), which aims to protect
occupants during thermal runaway for at least five minutes, has
been adopted in China and is coming to Europe and elsewhere.
SABIC currently produces a flame-resistant PP battery-pack cover
used by Honda in the China market. The cover eliminates thermal
blankets, reducing weight by 40% versus a similar metal cover.
Next-generation thermoplastic battery-pack and module prototypes
are in development. Rhode Island-based Tri-Mack Plastics recently
showed lightweight, high-strength enclosures made from just eight
plies of unidirectional carbon-fiber reinforced thermoplastic composite
(TPC) tape, 1 mm (.040-in.) thick. The company's process engineering
manager Ben Lamm noted that the material, combined with Tri-Mack's
manufacturing process, offers new opportunities in part geometry,
parts consolidation and integrated EMI countermeasures.
New twists on proven resin families and compounds are also aimed
at the battery box. Among SABIC's projects is an all-plastic EV battery
tray with integrated cooling channels and crash-protection elements.
It offers up to 12% mass reduction compared with an aluminum
pack, Nagwanshi claimed. Integrated plastic-metal hybrid structures
based on the Stamax FR long glass fiber PP are also in the
works. Testing has demonstrated the structures meet drop-test requirements.
Engineers are encouraged by its ability to absorb " significant "
energy, as would be required in vehicle side-impact tests.
Two more characteristics make thermoplastics competitive with aluminum
for EV battery boxes, Nagwanshi said. One is their anisotropic
March 2023 23
6082 T6
HCA6 HCA6 STEP
Enabled
HCA6 STEP
Enabled
Weight reduction potential (%)
CONSTELLIUM
Automotive Engineering - March 2023

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