Pack Enclosure Materials - Battery Design

A look at battery pack enclosure materials. A number of different materials and construction techniques have been used.

Carbon Fibre

The original Formula E battery pack designed and made by WAE for all of the teams to use has a carbon fibre structural case.

Fabricated Aluminium

The VW ID3 has a fabricated aluminium frame and case that uses a mix of formed aluminium sheets and extrusions. This assembly has been welded together.

The BMW i3 housing is just 19.5kg for the base and 4.5kg for the lid, per a teardown weight breakdown.

Pressed Steel

The Nissan Leaf is a good example of a pressed steel upper and lower pack enclosure.

SMC Lid

The Ford Mach-E has an Sheet Moulding Compound (SMC) lid on the battery enclosure.

The lid of the pack is a composite and based on Munro [1] it is a heavy 14.5kg.

Construction Methods

The material choices above go with a handful of manufacturing routes, and it’s common to combine more than one within the same enclosure:

Stamping / deep-drawing – sheet aluminium or steel is pressed into the tray or cover shape. Suits high production volumes; it’s the route behind both the Nissan Leaf’s pressed-steel tray above and stamped aluminium cover panels elsewhere. Cover panels typically use a softer, highly formable alloy (5182-O is a common choice for stamped aluminium covers) so the sheet can take the draw depth without tearing.
Extrusion + welding – aluminium cross-members and side rails are extruded to a constant profile, then welded, riveted or bonded into a frame, as on the VW ID3 case above. Flexible for low-to-medium production volumes and easy to resize between vehicle platforms without new tooling for the whole tray.
High-pressure die casting, including large single-piece structural gigacastings – molten aluminium alloy is cast into one large structural part, replacing a multi-piece stamped, extruded and welded assembly and cutting weld count at the cost of higher tooling investment. See Pack Frame Giga Casting.
Compression moulding – a composite sheet, such as the Sheet Moulding Compound used on the Mach-E lid above, is pressed and cured into a cover or sub-panel shape. Used where a composite cover replaces a stamped metal one, mainly on non-structural covers rather than the load-bearing tray.
Carbon fibre layup – woven or unidirectional carbon fibre is laid into a mould with resin and cured, as with the Formula E structural case above. Higher cost and lower production volumes than the routes above, so it tends to appear where mass saving outweighs cost, such as motorsport.

Joining between dissimilar materials, or wherever welding isn’t practical, increasingly relies on structural adhesive bonding combined with mechanical fasteners rather than welding alone – useful where a composite or thermoplastic cover meets a metal tray.

References

Ford Mustang Mach-E Battery Exposed!, Munro Live
Aluminum for Electric Vehicle Battery Enclosures: 3003 vs 5052 vs 6061 vs 5182 Selection Guide, Huaxiao Alloy
Lightweight EV Battery Enclosures: Aluminium, Steel, Composites, E-Mobility Engineering