Battery is 25% more dense than Tesla

Cosmacelf

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So says the Rivian battery VP according to this Engadget article.

They get 25% more volumetric density by stacking cells on top of each other separated by a cold plate. Note this is battery pack density, not individual cell volumetric density. Also of interest is that they have a dedicated heating/cooling system for the battery pack. They imply that the three cooling loops of drivetrain, cabin and battery are independent. Presumably that means a single compressor and chiller, but three glycol loops running through it.

Also, the entire battery is encased in an aluminum casting.
 

lookmtb

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Fascinating. a quick quote from the article:

"These packs are individually wrapped in a non-metallic lightweight material and the cells within are bonded together using structural adhesives, "so that it's strong, but it's lightweight in the directions that we need it," Farquahr explained."

This makes me wonder what the orientation of the cells are. What he's saying seems to imply that the cooling solution is only between the two layers and not in between individual cells like in a tesla. This thing doesn't need to be some track monster with continuous high output so they likely can get by with a little less cooling.

Also from the article it does indeed sound like the cooling systems are fully independent. even down to the chillers or air conditioning-like systems.

Can't wait to see more details!
 

Cosmacelf

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Oh wow, I just realized mods can edit other people’s posts. I can now fix those annoying typo spelling mistakes :)

Since the cells are made like a Swiss roll, cooling just one end actually works. Ideally, you’d have three cold plates, so you could cool both ends, but that isn’t actually possible since you need electrical connections. Cooling the sides isn’t as useful since it is hard to extract heat when going through all the layers.

Btw, this implies that one of the cell layers is upside down with electrical connection on the bottom of the pack. Some interesting structural engineering going on there.
 

Cosmacelf

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Continuing on, the Rivian battery cooling system looks good. It is similar to what the Chevy Bolt uses. The Bolt also has a cold plate on the bottom the cells.

Tesla and Rivian use cylindrical cells, which look like this:

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Unrolled (below), the cell is a multilayer sandwich of a cathode current collector (aluminum sheet), the cathode sheet itself (a complex mixture of nickel, cobalt, etc.), a polymer separator, a graphite sheet for the anode, and a copper sheet for the anode current collector.

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Luckily for heat transfer, everything is in close proximity to metal sheets (copper and aluminum) which transfer heat very well. If you look at the Tesla Model S/X cooling design (they did it better for Model 3), here is what it looks like looking at the tops of the cylindrical cell:

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So the coolant only touches the outside of one side of the cell. Translating that into the unrolled cell picture above, only one side (say the left side) of the 36 inch long sheet is cooled, the rest of the sheet has to transfer the heat 36" along the metals. Even worse, in the module, the glycol starts off cool at the top, but by the time it reaches the bottom, it is fairly warm and isn't cooling the bottom cells as well as the top cells in the above diagram (they fixed this issue in the Model 3 as well).

Rivian, OTOH, has a cool plate that touches each cell at the bottom of the cell. Translating this to the unrolled cell picture above, the cell is cooled along the entire 36" of the cell and heat only has to move 2.7" inches from the top of the sheet to the bottom. I don't think we know exactly how the glycol moves across the battery module, but you would think they would have a manifold and cool along the short dimension of the module to minimize cross module cooling issues.

Anyways, bottom line, looks like the overall battery cooling architecture is robust and should work well.
 
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