Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[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

[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.

[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.

[Alan Stewart]

And they could have made the no ribbon improvement to the 18650 or 21700 cells.

I think the removal of the cooling ribbon is made possible by the tabless design. In addition to reducing resistance it conducts heat from the interior of the cell to the end caps, so cooling via top and bottom plates becomes effective. As I said earlier it seems like the tabless design could be applied to other (cylindrical) cell formats such as 18650 and 2170 to give the same benefits as it does to the 4680 format.

[Crissa]

How are they cells compressed?

In between the cooling rails?

So the cells will be "packed tightly with cooling rails atop or below". Mounted in "something that itself is rigid". That sounds like regular standard batterypacks, i.e. loose cells in structural container.

Yes and no.  Tesla is trying to get approval for a safety medium which is also rigid.  So right now the box itself is the structure, but they want something which is laminated together where the cylinders are part of the structure instead of contained in it.  I don't know if that means they're countervailing forces or just glued in place; but their anti-fire resin itself is supposed to be rigid structure.  Which is wholly unlike how Zero or Energica cells are potted.

I still call phooey on the claims of 5-6 times improvement, simply because they're not comparing same size cells.

Per cell, which is how fast they come out of the factory, their numbers hold.  But yes, that's nearly all from just 'being bigger'.  But no one could make bigger cylindrical cells and have them perform as well until now.

Bigger cells means they can make more battery capacity in the same per-unit time.  Bigger cells means they can try their 'structural medium'.  Dry cells means smaller factory, so they can fit more production lines in the same place.  Bigger, in their case, is better.  And the tabless allows that to happen.

-Crissa

[Richard230]

The cells used in my 2008 Electric Motorsport GPR-S were made by Hi Power (not exactly the right name for that company  ) and were about the size and shape of a home Webster Dictionary. Their claim to fame were that they couldn't handle power draws of over about 50 amps very well and when used to power an electric motorcycle sometime tended to expand like a balloon and vent gas at inopportune moments.    I suspect they were designed more for storing electricity to power decorative lights on Asian buses than they were for EV motivation. 

[Crissa]

There's also how fast the cells can be manufactured, how cheap it is to manufacture, how much resources it takes, etc.

That's why Tesla went with cylindrical cells:  They are cheap and fast to manufacture.  But manufacturing machines can only run so fast, so at that point, to speed up you need more factory or bigger cells to have more capacity.

Bigger cells were not reliable in cylinders because of the tabs.  Hense the new design.

-Crissa

[T.S. Zarathustra]

Congratulations on 2000 posts Crissa.

Here is a nice youtube video at the EEV blog about the 4680 cell. A guy who actually knows a little bit about electronics and is mildly impressed.

Edit. Real explanations instead of marketing lies speech. If I'd found this video in the beginning I would have linked to it. It would have saved me few posts. 

[Richard230]

That certainly was an interesting video, Zarathustra. Thanks for posting it.  My feeling has always been the the real advantage for Tesla by using the cylindrical cells is the ease of quickly manufacturing millions of them using robotic machines, compared with manufacturing pouch cells. Any other advantages are just gravy.    When you are planning to sell millions of electric vehicles a year, money becomes a big deal, especially when government subsidies are shrinking and in their case, disappearing.