Tesla Cylindrical vs Prismatic: Is It Really a Simple Choice?

These days, because of recent Tesla issues, many people say things like “using cylindrical cells was a mistake” or “Tesla had no choice but to use them.” That might have been true long ago when prismatic and pouch cells were not widely available. But even today, choosing a cell type is far from a simple decision.

In battery pack design, there is always a trade-off. Safety, energy density, manufacturing complexity, and cost are all interconnected, and the outcome depends on which factor is given the highest priority .That is why system engineering exists as a specialized discipline.

If we focus only on the clear advantages and disadvantages of cylindrical cells, they can be summarized as follows:

• Advantage: Relatively safer during collision or thermal runaway propagation

• Disadvantage: Lower energy density and more complex pack manufacturing process

In the end, it depends on what matters most among safety, capacity, and manufacturing simplicity. Different engineers will naturally have different answers. What would you consider the most important?

Personally, if I had sufficient technical capability and quality control, I would still choose cylindrical cells today. Battery fires are not just product defects. They can destroy a company’s reputation and business itself.

Think of the Sony VAIO laptop or the Samsung Galaxy incidents. Sony eventually had to sell its battery division, and Samsung lost a significant share of the market after the fire issue. This is why some companies still put safety at the top of their design priorities.

This may also explain why Rivian, Lucid, and Rimac continue to use cylindrical cells even though they do not offer many advantages other than safety. BMW is also developing its next-generation battery packs based on cylindrical cells.

As for Tesla, some might wonder why it uses both cylindrical and prismatic cells. If it were my design decision, I would use cylindrical cells with NCA or NCM chemistry for high capacity models that require strong power performance, even though they are slightly more prone to thermal runaway. For lower capacity models, I would use LFP prismatic cells, which are more thermally stable. This approach allows a balanced consideration of safety, capacity, and power.

Below is a comparison of CATL’s NCM811 and LFP cells during thermal runaway testing.

Schöberl, J., Ank, M., Schreiber, M., Wassiliadis, N. & Lienkamp, M. Thermal runaway propagation in automotive lithium-ion batteries with NMC-811 and LFP cathodes: Safety requirements and impact on system integration. eTransportation 19, 100305 (2024).