Automotive Engineering - September 2021 - 24

ADVANCED MATERIALS FEATURE
New
composites
target EV
applications
For EV battery pack
applications, composites
are vying with metals to offer
engineers improved packaging,
thermal management and lighter
weight.
L
ightweighting solutions that are financially viable, reliable and
sustainable for conventionally-powered vehicles are arguably
even more important for electric vehicles (EVs). Range anxiety
remains a major concern of many consumers and must be addressed
if EVs are to have a significant impact on the industry and
the environment. With current battery chemistries, extending the
range of EVs requires more cells to be added, increasing curb weight.
For example, the compact Chevrolet Bolt EV's 65-kWh battery pack
weighs nearly half a ton - which is almost one-third the car's curb
weight. More extreme is the 2022 GMC Hummer EV full-size pickup:
its 200-kWh pack, engineered to deliver more than 350 miles (563
km) of driving range, is estimated to weigh in excess of 2,000 lb.
(907 kg). The truck itself weighs more than 9,000 lb. (4,082 kg).
The EV battery mass/vehicle range reality is forcing engineers to
look for mass savings in other areas. Material selection plays a vital
role in EV design, and the right material can be used to reduce the
overall weight while still maintaining strength and integrity.
Intelligent structural core designs used in combination with lightweight
materials provide the strength and rigidity necessary to allow
OEMs to move away from traditional steel components.
Composites have been somewhat overlooked due to high manufacturing
costs and slow cycle times. But recent advances have
streamlined the manufacturing process to make high-volume composites
a realistic alternative for EVs. Thermoset and thermoplastic
composites have the potential to offset the weight of large battery
packs and electric propulsion systems. They also can aid in battery
thermal management, providing high-voltage insulation and allowing
for more intelligent designs to further reduce parasitic weight. They
also present opportunities to reduce noise, vibration and harshness
(NVH) in many applications.
24 September 2021
No longer a low-volume play,
the latest composite materials
offer EV developers new options
for lightweighting, thermal
management and structures.
by Andrew Dugmore
Mass and heat challenges
The introduction of larger battery systems brings an
unavoidable vehicle-mass increase. Battery weight,
and how it is distributed in the vehicle, can affect performance
parameters such as energy consumption,
acceleration dynamics and handling. EVs tend to
house their batteries low, ideally beneath the cabin
floor and evenly distributed longitudinally and transversely.
However, unlike traditional vehicles with internal
combustion engines and fuel tanks, the weight of
the battery in an EV is never diminished - if a bus
starts its day with a 1-ton battery pack, it will end its
day with a 1-ton pack. This may offer some benefits in
terms of vehicle dynamics, but it is a challenge for
driving range.
Increased weight isn't the only issue. Lithium-ion (Liion)
batteries are leading the way in EV development,
but there are a number of " stress factors " that significantly
impact the performance and capacity of these
batteries over time, many of which are exacerbated by
increasing battery capacity or the number of cells.
Extreme temperatures, which can either be a result of
environmental conditions or localized heat exchange
during battery operation, have a profound effect on
charge/discharge rate and battery performance. For
example, charging in very low temperatures causes metallic
lithium to form spikes around the anode, slowing
the current. Temperature extremes also lead to the expansion
and contraction of metallic components such
AUTOMOTIVE ENGINEERING
TRB LIGHTWEIGHT STRUCTURES
Automotive Engineering - September 2021

Table of Contents for the Digital Edition of Automotive Engineering - September 2021
