Exploring different battery tray designs in the automotive industry and three main design concepts have emerged in the design of metallic battery trays:
- Deep-Drawn Sheet Metal Pans
- Extruded aluminum profiles are welded together
- Cast aluminium cases moving to Giga-castings
Building on Posts from Matthias Biegerl [1] and Luca Greco [2].
Deep-Drawn Sheet Metal Pans
This process involves forming the housing with deep-drawn sheet metal pans and sealing it with a lid. The main advantage here is the reduced complexity regarding system tightness. On the downside, there is less flexibility in adapting to different battery sizes compared to extruded profiles, and additionally, the surrounding body structure must absorb the main forces in the event of a crash.
Extruded Aluminium Profiles
These are welded together to form a rigid frame. The advantages of this method include high stiffness/ crash performance, while different profile lengths can accommodate various battery sizes: Impact on costs. However, ensuring a leak-proof system is particularly challenging due to the complexity of the welding and sealing processes.
Cast Aluminium Cases
In the design of smaller battery enclosures, such as those for PHEV vehicles, quite a number are cast aluminium. The tooling for these is a high investment, plus they require post machining of sealing faces and attachment points. However, the result is a highly accurate case that can have a very non-uniform shape.
The 2nd generation of the Rivian R1T has replaced some of the extrusions with a cast aluminium section. Significantly decreasing the part count.
GigaCasting
The emerging trend is a move to gigacasting. This new process is gaining momentum, especially in China. Inspired by Tesla, more manufacturers are adopting the gigacasting method for battery housing production. Guangdong HongTu, for instance, uses a 16,000-ton gigapress to manufacture entire battery housings for Xpeng.
Benefits of Gigacasting: Integration of highly rigid frame structures & simplified sealing concept since the tray is cast as a single piece.
The lower tray for the YE vehicle weighs 51kg and was produced by Guangdong Hongtu using a 12,000 ton press.
Challenges: Requires post-processing to create defined surfaces or threads, and involves enormous investments in machinery and tools to produce the components.
Future
Battery cells as the structure in the cell to pack approach has been taken to the extreme with the CATL Qilin. This pack has a perimeter frame and top and bottom closure panels.
The cooling plates between the cells and the bonding of this all together forms the structure. This overlap of function brings higher risk and reward. This pack achieves a gravimetric energy density of 192.5Wh/kg a significant achievement for a prismatic cell based design.
This brings us to thinking about the overall design and approach.
For all concepts, special attention must be given to the system’s tightness, potential corrosion, and the challenge of integrating as many functions as possible into one tool. The choice of battery housing design is pivotal in achieving optimal performance, safety, and manufacturing efficiency. As the industry evolves, it will be interesting to see which technologies become the standard.
For any sub-system or component in the battery pack we must think in terms of:
- Electrical
- Thermal
- Mechanical
- Control
- Safety
This is no different for battery enclosure design.
References
- Exploring Different Battery Tray Designs in the Automotive Industry, Matthias Biegerl
- Stamped vs Die-Cast Battery Pack, Luca Greco, X
- Battery assembly for the BMW X5 xDrive45e, BMW Group Plant Spartanburg, BMW Press Club
See also: Pack Enclosure, Pack Frame Giga Casting, Pack Enclosure Materials