Composite Battery Enclosure for High-Performance Electric Vehicles

This project develops a lightweight battery enclosure for EVs using composite materials, aiming to reduce vehicle weight while meeting the standards required from sheet steel. Targeting luxury performance vehicles that prioritize performance over cost, the design employs an Epoxy/Carbon Fiber laminate, which is significantly lighter than sheet steel. The design process utilized Ashby’s methods for material selection, with an emphasis on stiffness and strength per unit mass. ANSYS FEA was employed to optimize design choices and confirm adequate stiffness and crashworthiness. A quasi-isotropic layup was selected to create a balanced laminate capable of handling complex loading scenarios in a battery enclosure. Manufacturing methods to optimize cost and post-processing for corrosivity and electrical insulation were considered, recommending a polyurethane coating. Results demonstrate significant weight savings, up to 80%, and compliance with crash and standard use conditions; however high material costs restrict immediate adoption to the performance EV market. The design process reveals a trade-off between performance and manufacturing costs, but scalability and affordability are expected to improve with advancements in manufacturing technology, positioning this innovative enclosure as a promising solution for enhanced EV performance with potential for broader adoption.

Electric vehicles (EVs) are increasingly prominent in the high-performance segment, with models like the Porsche Taycan, Rimac Nevera, Tesla Model S, and Lucid Air Sapphire pushing the boundaries of speed, handling, and range. A critical component in these vehicles is the battery enclosure, which safeguards the battery pack, ensures safety, and often contributes to structural integrity. Traditionally, enclosures are made from steel or aluminum; materials that, while robust, add significant weight and are susceptible to corrosion in harsh environments, such as salted roads in cold, humid regions.

For daily-use vehicles, sheet metal enclosures work great as they are easy to manufacture, cheap, and highly scalable. However, its weight limits its suitability for performance EVs. A perfect example of this fact is that 85% of Formula 1 car’s volume is composites, specifically carbon fiber. With EV technology improving rapidly, along with the increasing demand, there is high motivation for producing an electric super car[1] where every kilogram of mass saved influences the acceleration, cornering ability, and top speed of a vehicle.

[1]Supercar: a street-legal sports car with race track-like power, speed, and handling (Wikipedia)

Proposed Solution

This project proposes a fiber-reinforced composite battery enclosure doubling as the vehicle’s underbody for high-performance EVs. The design prioritizes weight reduction, crash safety, and structural integration. Only the platter was designed for this project as it’s the important part for stiffness and structural integrity and carries the entirety of the load.

Rationale

Reducing weight enhances acceleration, handling, and range—critical for performance EVs. Composites like CFRP offer exceptional mechanical properties, corrosion resistance, and electrical insulation. Targeting the luxury market justifies higher costs, leveraging the premium buyers are willing to pay (e.g., $200K+ supercars).

Design

The enclosure will feature (refer to figure 1):

• Cross members for structural rigidity.
• Curved edges to prevent stress concentration
• Dimensions 2.52m(L) x 1.7m(W) x 0.21m(h) were determined based on an average sampling of wheelbase length and width of Sedans

Underbody Integration

By serving as the underbody, the enclosure simplifies design and manufacturing, getting rid of the necessity for an additional underbody component. This also further reduces the net mass of the vehicle

To compare to the objectives defined initially, the Epoxy/Carbon Fiber:

Objectives:

• Reduced enclosure weight by 80%, surpassing the 20% goal.
• Exceeded the 50% cost premium limit significantly (1300%).

Constraints

• Met the shock requirement per SAE J2464.
• Had small deformation (7.4mm).
• Had a first natural frequency of 82Hz (>40Hz).
• Is  insulating and corrosion resistant with the application of coating.

Tests that still need to be performed include penetration tests, physical tests for acceleration and force, drop tests, and fatigue life tests. Furthermore, after coating is applied (e.g. Polyurethane), the electrical and corrosive properties must be verified through fuse tests and corrosion tests.

From a mechanical property standpoint, it is a superior alternative the sheet metal. However, from a manufacturing perspective, with current costs and technology, the price premium and production difficulty are likely not worth it for a sport or performance vehicle that will rarely, if at all, be used in a track setting.

Until either CFRP costs decrease or metal matrix composites (MMC)[1] that are cheaper and easier to manufacture in large quantities are discovered, it is likely that Epoxy/Carbon fiber will be used in race settings, such as F1 cars, or super cars that are priced at $500,000 or more.
   

[1] A group of materials that use metals as their matrix, which often have very high material costs. Promising experimental MMCs include magnesium matrix, boron fiber reinforced, and zinc matrix, titanium carbide particulate reinforced.