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[Crissa]

The test factory in Fremont is running, yes.

But they plan to build full-size ones at their other facilities once they have the kinks knocked out.

Basically, Fremont is where they put pilot programs, learn how to lay things out, while the other facilities is where they multiply it.  Fremont is closest to a port and other tech facilities, so while some may be optimized for other things, Silicon Valley is optimized for development.  All the things are there.

They also said they were already testing cars with the batteries in them.

-Crissa

[T.S. Zarathustra]

So it's a test factory (still). 

I do find it funny how people treat batteries from trashed Tesla cars as some sort of treasures. Not realizing they are actually nothing more than used Panasonic (and in some cases, in the newest cars, LG or CATL) cells.

According to this https://www.theverge.com/2020/9/22/21449238/. "Tesla’s new cell manufacturing system is “close to working” at the pilot plant level." "The company’s 2170 cells, which are currently used in Model 3 and Model Y vehicles, are produced by Panasonic"

I do find it sad when Tesla talk about their new 4680 (46mm diameter, 80mm length) cells as huge step forward, having 5 times the energy of their old cells, 6 times the power, neglecting to mention they take much more space than the 18650 (18mm diameter, 650mm length) cells. I calculate them as taking 8 times the space.  I'm sure someone will double check it and let me know if I'm wrong. 

[Crissa]

(46*80)/21*70=2.5 not 8.

The new cells are also more space efficient, with how they go into the car; they require less adhesive, less insulation, and are more structural.  So they will be able to fit more cell mass into the same space.

-Crissa

[T.S. Zarathustra]

Thank you Crissa.
Volume of a cylinder is Pi x R² x H. So for 4680 cell it is Pi×23²×80 = 42320 x Pi = 132952 mm3, and for 18650 cell it is Pi×8²×65 = 4160 x Pi = 13069 mm3. I used this website for the calculations https://www.calculator.net/volume-calculator.html?
The ratio can be done in many ways but without grabbing a calculator it is easiest if you half 132952, then you get 66476, if you half that again (1/4) you get 33238, if you half that again (1/8) you get 16619. So 1/8 of the 4680 cell is a bit bigger volume than 18650 cell.
But I did go to the website again and divided 13069 into 132952. It said said 13069 would go 10.17 times into 132952.
So it was slightly worse than I thought after the quick calculations I did in my head. Tesla gets 5-6 times the energy out of 10 times the volume. Now, this math must be wrong somewhere. Why would they start making much bigger cells if they only get half the power out of the volume? Partial answer to that could be simply fewer cells in a pack. That makes the BMS simpler and cheaper. Maybe they'd get better cooling but the bigger cell has proportionally smaller surface area, so physics would argue that the cells would need more cooling.
Another interesting theory is that they are going to switch to similar chemistry to what the A123 battery manufacturer used. It has higher cycle count than the standard Lithium Ion with Cobalt. It doesn't have Cobalt which is the most expensive part of the battery. They need more of the other materials, but the cost of extra materials will be offset by only using miniscule amounts of the most expensive material. But the A123 chemistry only has half the power density of Lithium Ion cells.
I guess the future will show us what is actually going on. Hindsight is 2020. 

[Crissa]

I don't know where you get your volume numbers.

(3.14*((46/2)^2)*80)/(3.14*((21/2)^2)*70)=5.5

The ratio doesn't change from cubic to cylinder here; I forgot the third dimension but that doesn't make it tenfold.

The actual 'cell' is a flat sheet, anyhow, so the change isn't really cubic.

-Crissa

[T.S. Zarathustra]

I see the problem. You are comparing the 4680 cell with the 21700 cell. I am comparing the 4680 cell with the 18650 cell. Now which cells was Tesla comparing?
The 4680 cell is 132952 mm3 in volume.
The 21700 cell is 24245 mm3 in volume.
The 18650 cell is 13069 mm3 in volume.
The cells are cylindrical in shape, not cubed.

PS. I used this website for volume calculations https://www.calculator.net/volume-calculator.html?

[princec]

Probably not directly volume-related by capacity... is cell power not a function of the area of the rolled up sheet of electrolytic material inside?
Anyway, nvm all that... the more pressing concern is if anyone else will ever get to use these batteries in any other vehicles.

Cas

[Richard230]

Probably not directly volume-related by capacity... is cell power not a function of the area of the rolled up sheet of electrolytic material inside?
Anyway, nvm all that... the more pressing concern is if anyone else will ever get to use these batteries in any other vehicles.

Cas

If you were Tesla, manufacturing your own batteries in several very expensive factories around the world because you needed every battery you could make to power your cars and trucks, would you sell your batteries to any other competitor, or to a motorcycle or some other power-sports company? I don't think I would. 

[princec]

Well, absolutely not

Cas

[NEW2elec]

An EV news video said LG Chem teased it will be announcing a very similar cell in the very near future.

I found it interesting because Damon had mentioned their cells would be Korean.

This is my own theory based on a few puzzle pieces.  We'll see.

[Crissa]

Probably not directly volume-related by capacity... is cell power not a function of the area of the rolled up sheet of electrolytic material inside?

Yes.  The sheet does have a height, so volume does have an impact, but yes.

The tabless means there's no choke point at the edge of the end of the sheet, which frees the cylinder from it's size constraint.  So the whole sheets gets to be used.

And I'm not sure why I wouldn't compare the cells Tesla is using now vs the cells they will be using.

-Crissa

[Alan Stewart]

I see the problem. You are comparing the 4680 cell with the 21700 cell. I am comparing the 4680 cell with the 18650 cell. Now which cells was Tesla comparing?
The 4680 cell is 132952 mm3 in volume.
The 21700 cell is 24245 mm3 in volume.
The 18650 cell is 13069 mm3 in volume.
The cells are cylindrical in shape, not cubed.

PS. I used this website for volume calculations https://www.calculator.net/volume-calculator.html?

But you got it wrong. In your first message you use 8 as the radius of an 18650. Half of 18 is 9, not 8.

9 x 9 x 65 x PI = ~16540 mm3

I think the other two calculations are correct.

The primary purpose of the larger cells is to drive down manufacturing costs. Fewer cells means fewer parts, fewer manufacturing and assembly operations, and fewer potential failure points.

The new form factor also may make the use of the cells as structural components more tenable. The aspect ratio between cell diameter and height is more favorable from a structural perspective. Is the wall thickness the same? I don’t know.

Despite all the online speculation otherwise, when Tesla introduced the 2170 format Elon said the primary driver was cost. It’s likely the same for the 4680.

The tabless design makes the larger cell practical, solving cooling and charge/discharge rate issues with a traditional single tab in such a large cell. It might also benefit the smaller form factors.

Regardless of the cells, it’s the pack as a whole that matters. Certainly eliminating the cooling ribbon used by the 18650 and 2170 packs will improve the horizontal density of the Tesla battery pack.

[T.S. Zarathustra]

Thank you Alan.
Good points. It's amazing how much 1 mm changes. 

132952/24545=5,5. Volume of 21700 cell goes 5,5 times into 4860 cell. Since Tesla claims 5-6 times better cell that sounds about right. But it's more or less the same energy for the same volume. There is probably small weight savings, just in the casing materials.
I doubt the cells will become structural, that would require relatively larger wall thickness, adding weight to the cells, and taking up precious space that could be used to store energy. If you are taking the same amount of energy out of the same volume it should heat up the same. With the bigger cell having less surface area for cooling it would heat up more, especially in the core.
While there are fewer potential failure points, each failure is likely to have more effect. Cell that goes into thermal runaway is burning with 5,5 times the energy release. Harder to put out, and 5,5 times the material lost. But that sort of failures probably does not happen much in modern cell factory.

132952/16540=8. Volume of 18650 goes 8 times into 4860. 18650 is, as far as I know, still used in the older Tesla car designs. Tesla X for example. 

[Crissa]

Having less wasted space will make the cells more structural, especially as they're compressed.  Right now they use big I-beams and the cells will instead be packed tightly with cooling rails atop or below them.  All that means they can mount them in something that itself is rigid instead of gooey or soft like the material they use now.

Basically, no ribbons, plus rigid mounting medium, means no I-beams, which means even more space saved.

And Tesla is looking at sheathing them in even less material!  Denser means more structural.  The cylinders already expanded less than pouches!

-Crissa

[Sklith]

If you are taking the same amount of energy out of the same volume it should heat up the same. With the bigger cell having less surface area for cooling it would heat up more, especially in the core.

Not necessarily since the tabless design of the new cells will have lower internal resistance. This is how they're claiming much faster charging speeds.