Aluminium 4680 Cell Can Structural Performance

Recent industrial and academic studies have shown that aluminium cell housings can provide several benefits in terms of thermal management and gravimetric energy density in particular^1,2,3. However, as Cell-To-Pack and Cell-To-Chassis approaches arise the battery cell and therefore, the battery cell housing, become part of the structure of the battery electric vehicle contributing with their mechanical properties. The application of high strength materials in the cell housing allows for increased structural contribution and / or wall thickness reduction improving the energy density of the cell.

Within this article, the structural performance of aluminium 4680 cell cans made from two different materials namely Speira ION Cell 3-CB and Speira ION Cell 3-CS will be presented. The cell cans were produced by deep-drawing and wall-ironing featuring a wall-thickness of 0.75 mm. The can bottom features a thickness of 0.9 mm. The deep-drawing and wall-ironing route allows the application of high strength aluminium alloys and hard tempers. Figure 1 displays 4680 cell cans made from Speira ION Cell 3-CS.

The impact of the material grade is revealed in Figure 2 comparing the hardness of a typical battery grade aluminium material as Speira ION Cell 3-CB with the high strength grade Speira ION Cell 3-CS, where the latter provides about 1.8 times higher hardness on average.

While hardness provides a good indication of the mechanical property distribution along the can surface, tensile tests reveal the actual strength level in terms of the yield strength (R_p02) and the tensile strength (R_m). The tensile test results of can samples are displayed in Figure 3. While the moderate strength alloy grade Speira ION Cell 3-CB achieves a yield strength of about 140 MPa within the can bottom and 170 – 180 MPa in the can wall, the high strength material Speira ION Cell 3-CS features a yield strength in the range of 280 MPa in the can bottom and about 300 MPa in the can wall.

This difference in strength translates into significantly higher resistance to plastic deformation of the cell can. Figure 4 displays experimental results of axial compression tests of the 4680 cell can prototypes. While cans made from Speira ION Cell 3-CB exhibit a maximum force of about 10kN (≈ 1000kg), cans made from Speira ION Cell 3-CS require nearly double the force for compression. Here, the maximum force has been about 19kN (≈ 1900kg).

For reference, Table 1 provides curb weight of some EVs. Theoretically, a Tesla Model 3 could be placed on top of one 4680 cell can prototype made from Speira ION Cell 3-CS without surpassing the maximum force.

The resistance against internal pressure can be estimated using Barlow’s and Lame’s equation considering the Tresca yield criterion and the yield strength as onset of plastic deformation:

with

p = pressure
R_i = inner radius
t = wall thickness

Considering a can wall thickness of 0.75 mm for an aluminium version and the lowest yield strength from Figure 3, the maximum internal pressure, which the cell housing can withstand without plastic deformation, can be calculated and is displayed in Table 2. For comparison, an exemplary Ni-plated steel version of the cell with a can wall thickness of 0.55 mm⁸ and a yield strength of 350 MPa⁹ has been considered. In addition, another example with a steel wall thickness of 0.75 mm has been evaluated enabling direct comparison to the aluminium version. Here, it should be noted that assuming higher strength steels would provide higher maximum internal pressure levels.

The investigation of 4680 cell can prototypes made from two different material grades displayed above indicate that an aluminium cell housing can withstand considerable mechanical loads and contribute to the structural strength of an electric vehicle with Cell-To-Pack or Cell-To-Chassis approach, if a suitable high-strength aluminium grade is applied. In addition, the weight of the cell housing can be reduced increasing the gravimetric energy density of the cell. Speira ION Cell 3-CS provides a unique combination of high strength, deep-drawability, weldability as well as electrolyte compatibility and enables high recycled content minimizing the carbon footprint contribution of the cell housing.

References

1. Benefits of aluminium cell housings for cylindrical lithium-ion batteries Speira learn whitepaper (pardot.com)
2. Hendrik Pegel, Dominik Wycisk, Dirk Uwe Sauer, Influence of cell dimensions and housing material on the energy density and fast-charging performance of tabless cylindrical lithium-ion cells, Energy Storage Materials, Volume 60, 2023
3. Gerard Bree, Dan Horstman, Chee Tong John Low, Light-weighting of battery casing for lithium-ion device energy density improvement, Journal of Energy Storage, Volume 68, 2023
4. Dimensions and Weights (tesla.com)
5. Dimensions and Weights (tesla.com)
6. Volkswagen ID.3, Wikipedia
7. ZOE – Dimensions & Specifications, Renault UK
8. Tesla 4680 Cell, BatteryDesign.net
9. DESIGNERS GUIDE, Sigma_Clad

About Speira

Speira is a leading aluminium rolling and recycling company, driven by its purpose to build a circular world that works, and it strives to fully decarbonize its business until 2045. Speira produces one million tons of aluminium rolled products per year. Speira operates eleven manufacturing facilities and one R&D center across Germany and Norway, including various aluminium recycling facilities, its joint venture Alunorf, the world’s largest aluminium rolling mill, and Grevenbroich, the world’s largest rolled aluminium finishing mill. Speira has approximately 5,500 employees. Speira is proud to serve some of the most well-known companies in the global automotive, packaging, printing, engineering, building and construction industries. Speira is headquartered in Grevenbroich, Germany.

Speira is a volume supplier for battery systems to leading global battery manufactures and offers an extensive product portfolio within the brand ION that covers the entire spectrum from battery electrode foils to cell connectors, heat exchangers, and housing materials.

contact: Battery@speira.com