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This is by far the biggest advantage. The electrodes want to expand as you shove lithium ions into them. Left unconstrained, this causes tiny cracks which ruins the electrodes. Silicon anodes are especially bad at this, which is why we still don't have them despite their other wonderful traits.It might be that other advantages of cylindrical cells (such as their mechanical stability against internal swelling) dominate.
What I see and takeaway from this picture of the Tesla battery pack,Note how wasteful cylindrical cell packing is, compared to flat cells. Plus the cooling channels only touch part of the surface of the cylindrical cells:
Note how in that tear-down image the cooling channels are touching maybe 30% of the circumference of each cell. Cylindrical cells also complicate pack design due to their very granular and not easy to pack nature.
Yeah, but small cells are much better thermally than large cells. (Assuming each cell is surrounded with coolant, as it is in Tesla's system.)This is by far the biggest advantage. The electrodes want to expand as you shove lithium ions into them. Left unconstrained, this causes tiny cracks which ruins the electrodes. Silicon anodes are especially bad at this, which is why we still don't have them despite their other wonderful traits.
Cylindrical cells efficiently constrain against expansion. Prismatic cases do so much less efficiently, pouch cells not at all and generally must be externally constrained.
As you point out, cylindrical is not great thermally. More layers = worse thermal performance and the inner part of the cell has a lot of layers for very little active material.
Ahhhhh. The spiral roll process can be made faster more easily than the "stacked sheets" process. Same reason lots of bulk products come in rolls instead of stacks.The inner of core does not have to be the tap for the positive and the outer does not have to be the tap for the negative. The current collectors lay opposite each other the same as the prismatic cell and the taps can be anywhere as designed along the sandwich. There are many youtube videos on how cells can be made.
You can get the idea of which one is faster to create and why Tesla (IMO) is using cylindrical.
I don't see prismatic cells ever compressing tight enough or being created fast enough. Second video. Sure you can speed up that second video's machine but you can also speed up the cylindrical one just the same.
Rimac switched to cylindrical and Rivian may use cylindrical as well.AFAICT Tesla is the only manufacturer to have gone with small cells rather than large cells.
That first video is lab scale equipment. Pouch cell mass production equipment would look more like a newspaper printing press, with multiple layers all joined together before cutting, as at the start of this video. Newspaper presses run at ridiculous speeds.The inner of core does not have to be the tap for the positive and the outer does not have to be the tap for the negative. The current collectors lay opposite each other the same as the prismatic cell and the taps can be anywhere as designed along the sandwich. There are many youtube videos on how cells can be made.
You can get the idea of which one is faster to create and why Tesla (IMO) is using cylindrical.
As others have said. Heating is not an issue for any style if the right amount of cooling is supplied to any cell. Obvious to me because the Model 3 charges faster than anything on the market.
Still there may be an argument for a hybrid type cylindrical cell that has heat sink(s) inserted in the roll so the finished product looks more "eye" shaped or flattened roll. This would give the cell more surface area contact with the cooling plates and suck some heat out of the center through the heat sink(s). (A bit hard to describe the creation method)
There is also no reason a cylindrical cell can't have a heat sink in the middle.
also.... what if there was a way to make the separator a type of heat sink?
I don't see prismatic cells ever compressing tight enough or being created fast enough. Second video. Sure you can speed up that second video's machine but you can also speed up the cylindrical one just the same.
BMW prismaticsThat first video is lab scale equipment. Pouch cell mass production equipment would look more like a newspaper printing press, with multiple layers all joined together before cutting, as at the start of this video. Newspaper presses run at ridiculous speeds.
Geez, so the fastest way to mass-produce prismatics is to produce cylinders and then squash them.BMW prismatics
(suggest 2x speed watch if you do)
a pecision roll in an elongated oval, than a "smoosh flat" with a fair amount of empty space in the middle and the 4 corners
And in the podcast, Elon states Tesla moving to batteries without modules, whatever that means