Re: [EVDL] tesla battery fog

Wed, 23 Sep 2020 10:14:10 -0700

Yes, I think you're right about what they meant: 16% improvement at the pack level, and 5x increase at the cell level, though that's kind of irrelevant. I don't think there's any change in the percent of wasted space based on cell size (I'm guessing, I didn't do any math). So, I presume the 16% comes from less packaging. 

Peri
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------ Original Message ------
From: "Haudy Kazemi" <kaze0...@umn.edu>
To: "Peri Hartman" <pe...@kotatko.com>; "Electric Vehicle Discussion List" <ev@lists.evdl.org> 
Sent: 23-Sep-20 9:58:42 AM
Subject: Re: [EVDL] tesla battery fog
Each cell is bigger, so more energy can be stored in each cell, but pack space in vehicle remains the same, so number of cells goes down. Some manufacturers have been use large prismatic cell formats from the start. Bigger cells don't directly give increased range. Assuming other factors are equal, more active cell material in a pack gives more range.
Effectively, Tesla is migrating from laptop type small format cylindrical cells (18650 in MS and MX) to larger format cells (21700 in Model 3/Y) to even larger 46800s (guessing for Roadster 2.0, Semi, Cybertruck).
Fewer, larger, cells can allow for better space utilization efficiency as less volume is used for cases and dead space between cells. Cooling capacity may suffer.
Range improves as a result of better space utilization efficiency, lower weight from more efficient packing, and also cell energy density improvements.
On Wed, Sep 23, 2020, 09:28 Peri Hartman via EV <ev@lists.evdl.org> wrote: 
Lots of news today on tesla's battery day. Here's one excerpt from
wired:
https://www.wired.com/story/where-was-the-battery-at-teslas-battery-day/
Based on the digital mockups shown at the event, the new 4680 cell is a lot different from the lithium-ion cells currently used in Teslas... The diameter of the cylindrical cell is twice as wide, and it is 14 percent 
longer than the largest batteries [tesla uses]. Altogether, that makes
its volume about six times greater... the larger form factor alone was
enough to boost the energy by five times, the power by six times, and
the range of a car using these batteries by 16 percent.

Also some talk about removing cathode and anode tabs:

But these tabs hobble the performance of the cells and make them more
difficult to produce. Manufacturers must use a specialized welding
technique to connect them to the foil current collectors, which results 
in wasted time and material. Even worse, the tabs reduce the battery’s
efficiency, because electric current must travel the full length of the 
electrode to reach each tab. ...the company laser-patterned existing
foil current collectors so that they can have dozens of connections to
the electrode materials. The result is a current collector that Baglino 
described as a “shingled spiral” that looks a bit like a curled-up,
copper-plated armadillo. “The distance the electron has to travel is
much less,” Musk said.

And some talk about using silicone instead of graphite to increase
energy density by 20-40%. Apparently, that isn't "new" news. Tesla
claims to have a new way to incorporate silicon that doesn't expand over 
time. Also eliminate cobalt.

--------

So, I guess the "tabless" statement is the main takeaway - a more
efficient cell with basically the same chemistry. The first statement is 
confusing to me: how can you have 5 times the energy but only gain 16%
in range ? It could be that the form factor, itself, increases the range by 16% and the other numbers relate to the increases from all the other 
changes taken together.

Wall street apparently expected more from all the hype over the last
several months. But, all in all, if Tesla can build what it announce, it 
does sound pretty significant. While Tesla typically misses its
deadlines, it typically doesn't fail on meeting its goals.

Peri



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