The housings of high-voltage storage systems in battery electric vehicles must meet various requirements. Safety-related aspects include high impact resistance and the ability to absorb energy during crashes or provide protection against short circuits. The material must also be heat-resistant and flame-retardant. Efficient heat dissipation is also essential. Nevertheless, the sensitive cells must be protected from excessive cooling at low temperatures. Stones or road salt must not damage the housing. Additionally, it should fit precisely into the vehicle's underbody structure, contribute to the stiffness of the body, and increase the vehicle's range with low weight. Aluminum foam meets the requirements to fulfill all these demands.
At the Battery Show North America in early October in Detroit, Fraunhofer IWU and automotive supplier Amsted Automotive presented an integrally constructed battery housing with aluminum foam sandwiches. This is a special material structure consisting of two solid aluminum sheets enclosing an inner core of aluminum foam. A cooling structure or a thermal storage medium (PCM, Phase Change Material) can be incorporated into these sandwiches if needed.
Fraunhofer IWU succeeded in integrating PCM into closed-cell aluminum foam. PCM can absorb or release very large amounts of thermal energy while changing their state (solid or liquid) – without significantly changing their own temperature. They are therefore particularly well-suited for efficient thermal management in lithium-ion batteries.
The demonstrator presented in Detroit shows a wide range of possible series solutions. Depending on prioritized properties, pure AAS (precisely: aluminum-aluminum foam sandwiches), AAS with infiltrated PCM, AAS with cooling structure, or AAS with cooling structure and PCM can be implemented.
In order for battery housings made of aluminum foam to gain traction in large-scale vehicles in the future, researchers led by Dr. Thomas Hipke and Dr. Rico Schmerler are now increasingly focusing on economic viability. An important factor for future production costs is the raw material. Hipke: 'We are increasingly relying on recycled material for the production of aluminum foam. This is not only significantly more cost-effective but also reduces the CO2 footprint considerably.'
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