Automotive manufacturers use a combination of advanced materials and innovative design techniques to reduce the weight of electric vehicles (EVs). Known as lightweighting, the process is crucial in optimizing EV performance, efficiency, and range.
This article discusses why lightweighting EVs is considerably more challenging than minimizing the weight of gasoline-powered vehicles. Additionally, it identifies key mechanical and structural components that require extensive lightweighting, from batteries, electric motors, and thermal management systems to the chassis and vehicle body. The article also explores how new material and design approaches continuously improve EV lightweighting.
Lightweighting: ICE versus EVs
The automotive industry has long prioritized lightweight vehicles, driven by increased fuel efficiency and safety regulations. However, EVs require a specialized design approach to strategically minimize weight while maintaining optimal energy efficiency and performance.
EVs are significantly heavier than gasoline-powered vehicles, primarily because of their lithium-ion (Li-ion) battery traction packs. For example, the GMC Hummer EV SUV (Figure 1) battery pack weighs roughly the same as an entire gasoline-powered Honda Civic. In contrast, the 6,015-to-6,893-pound Ford F-150 Lightning weighs about 50% (3,000 pounds) more than its internal combustion engine (ICE) counterpart. Notably, the popular electric truck can have a 98.0-kWh battery that delivers a 230-mile range (per charge) or a larger 131.0-kWh battery that boosts its maximum range to 320 miles.
Smaller EVs weigh considerably less than GMC’s Hummer or Ford’s F-150 Lightning. For example, the urban-focused 2023 Mini Cooper SE (Figure 2) weighs 3,144 pounds and offers a 114-mile range.
Equipped with a 271-horsepower motor, the 3,565-pound 2023 Tesla Model 3 achieves a range of 272 miles, while the 3,589-pound, 200-horsepower 2023 Chevrolet Bolt EV delivers a 259-mile maximum range. Lastly, the 3,715-pound 2023 Hyundai Kona Electric features a 201-horsepower motor and a 258-mile range, while the 3,509-pound, 147-horsepower 2023 Nissan Leaf S provides a 149-mile range.
Reducing EV battery weight
Advances in battery materials, composition, and structure aim to maximize efficiency, safety, and mileage per charge. More powerful batteries, however, are inevitably bigger and heavier due to the increased energy density required for extended ranges, greater torque, and optimal acceleration and speed. Battery enclosures (Figure 3), which add more weight to an already considerable load, present additional lightweighting challenges.
These enclosures integrate battery management systems (BMS) to regulate energy distribution, heating, and cooling. Moreover, they provide fire protection and shield sensitive battery electronics from vibrations, electromagnetic interference (EMI), and radio frequency interference (RFI).
Although aluminum remains a popular choice for battery enclosures, manufacturers are exploring alternative materials such as fiber-reinforced polymers (FRP), carbon fiber, and composite plastics to minimize weight. These advanced materials provide robust strength-to-weight ratios and can incorporate critical thermal management properties.
Developing more efficient and lighter EV batteries is a priority for many automotive companies and research institutions. For example, Honda is designing a solid-state battery that could potentially weigh 50% less than conventional Li-ion batteries. These lithium-metal batteries incorporate solid rather than liquid electrolytes to provide greater capacity and support faster charging with minimal degradation risks. Smaller solid-state batteries (Figure 4), which can significantly increase the average driving range, are also more resistant to heat damage caused by fast charging.
Additional innovations include Kautex Textron’s Pentatonic battery system, which incorporates thermoplastics and composite metal hybrid materials for improved thermal management, corrosion resistance, and weight reduction. Similarly, a carbon fiber structural battery developed by Chalmers University of Technology contains materials that simultaneously function as electrodes, conductors, and load-bearing components.
Separated by a fiberglass fabric in an electrolyte matrix, the battery includes a carbon fiber negative electrode and a lithium iron phosphate-coated aluminum foil positive electrode. Although the research battery is currently limited to an energy density of 24 watt-hours per kilogram (Wh/kg), future iterations could achieve an energy density of 75 Wh/kg and a stiffness of 75 gigapascals (GPa), providing aluminum comparable strength at a lower weight.
Simplifying EV thermal management systems
Integrating battery thermal management systems (BTMS) with EV air conditioning systems helps eliminate extraneous components and reduce weight. Other lightweight techniques for vehicle-wide thermal management systems include integrating carbon fiber composites and thermoplastics — known for their lightweight properties and high thermal conductivity — into cold plates and coolant hoses.
Additionally, phase-change materials (PCMs), which absorb and release thermal energy during phase transitions, can potentially manage battery temperatures with minimal weight addition.
Lightweighting electric motors
Although electric motors generally weigh less than gas-powered engines, replacing or combining aluminum, copper, and silicon steel with carbon fiber-reinforced polymers and composites can further reduce weight and improve efficiency. Additional lightweighting design techniques for electric motors include:
- Incorporating amorphous metals and combining carbon fiber with traditional metals.
- Replacing circular wire with rectangular flat wire coiled more tightly on the stator lowers shaft weight.
- Using a hybrid rotor shaft made of carbon-reinforced plastic and stainless steel instead of solid metal.
- Redesigning the magnet carrier to weigh less than half a kilogram. Notably, the rotor shaft (Figure 5) accounts for about 30% of the total rotor weight, while the laminated magnet carrier represents approximately 61%.
High-performance plastics in gearboxes and differentials also help lightweight EV drivetrains, as do low-density aluminum alloy calipers and compact hydraulic units in regenerative braking systems.
Optimizing structural elements and materials
EV structural lightweighting involves optimizing materials and manufacturing processes for pedals, seats, chassis, and body. High-strength steel remains popular for its versatility, durability, and integrity in high-volume assembly processes like riveting and welding. Automotive manufacturers also employ aluminum and magnesium alloys to achieve more lightweight designs. These alloys are commonly found in body and chassis components and have high strength, stiffness, and impact resistance.
Carbon fiber-reinforced plastic polymers (CFRPs) and composites also play a major role in lightweighting EVs. These materials, which can be formulated with flame-retardant properties, are used in various components, including battery enclosures and other high-heat areas. Notably, Rivian’s R1S sport utility vehicle (Figure 6) incorporates a combination of aluminum, carbon-fiber composite, and high-strength steel structural components.
Lightweighting manufacturing processes incorporate laser welding, hydraulic forming, hot stamping, and integrated die-casting. Laser welding offers high precision, minimizing thermal deformation in lightweight materials such as aluminum alloys. Hydraulic forming creates compact and lighter components, while hot stamping precisely shapes metal sheets at high temperatures, resulting in thinner, lighter, and more durable components. Integrated die-casting combines multiple parts into a single, lightweight component, eliminating supplemental fasteners and unnecessary assembly.
Summary
EVs are significantly heavier than gasoline-powered vehicles, primarily because of their Li-ion battery traction packs. Lightweighting is a crucial process that helps optimize EV performance, efficiency, and range. Automotive manufacturers use advanced materials and innovative design techniques to reduce the weight of critical components, systems, and structural elements.
References
- The EV Lightweighting Challenge, Assembly Magazine
- Electric vehicles: Can ‘Lightweighting’ Combat Range Anxiety?, BBC
- How Electric Vehicle Light-weighting is Changing the Automotive Industry, Stanley Engineering and Fastening
- High Carbon Steel in EV Manufacturing: Embrace Lightweighting & Multi-Material Design, Three D Metals
- These Are the Lightest EVs You Can Buy Today, Capital One
- The Future of Lightweight, OEM Update
- Electric Vehicle Lightweighting, XDThermal
- Why Lightweight Materials Matter in Electric Vehicle Battery Pack Design, eMotec
- Driving Innovation in Vehicle lightweighting, Plante Moran
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