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Tesla's Model 3 2170 cells=same energy desity as 18650's

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Sure, I don't disagree with that. The speculation I am offering is that the larger form-factor would be joined by a more advanced, improved cooling system, perhaps because the cell-size allows for better cooling to run between or around the cells. What kind of cooling that may be, I have no opinion. I just think it would make more sense for Tesla to have optimized the new cell-size for more optimal packing, than to have developed a new cell-size that would allow less optimal packing...

We shall see. :)
 
Sure, I don't disagree with that. The speculation I am offering is that the larger form-factor would be joined by a more advanced, improved cooling system, perhaps because the cell-size allows for better cooling to run between or around the cells. What kind of cooling that may be, I have no opinion. I just think it would make more sense for Tesla to have optimized the new cell-size for more optimal packing, than to have developed a new cell-size that would allow less optimal packing...

We shall see. :)

Tesla has a patent out there for heatpipe cooling with single sided contacts and flexible circuit board connectors with fusible necks in the circuit.

That approach would presumably allow tighter packing, with heating/cooling either only from the bottom of the cell, or from the bottom plus heat pipes running up the packing gaps between the cells, while also being about the same thickness (no safety gaps on the bottom, but a new heat pipe layer.)

Pack thickness doesn't seem critical - they could easily engineer a new version that extended a quarter inch further downward with no real impact to the car if that seems necessary/useful, and the extra height of the 2170 cells means ~8% more kWh for the same cross section and packing density.
 
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Exactly. A slightly thinker pack could house a lot more energy capacity.
Audi I believe doesn't place batteries under the feet of occupants, make their seat more comfortable for a given seat height working with a given roof height. One could make packs thicker under the rear seat, like a doucle stack, to gain that volume back and then some,
I see so many ways a Model S/X like car could have vastly more battery capacity from unused spaces, but with bad energy density at the cell level, it's always going to be heavy. Perhaps there are lighter ways to package 100kWh than Tesla's? At least those packs are pretty bullet proof.

I'm someone who likes progress. I hope the calcs will prove incorrect and Tesla did manage a good bit higher density all while cutting costs. In 5 years, what have they brought in terms of density inprovements? The silicone anode ones introduced for the 90 pack require slower (if frequent) DC charging, or they degrade too quickly.
 
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On a volumetric energy density basis compared to 18650's in the 100D

I've checked my math numerous times and I can't find an error. If the numbers are right it'd really not earth shaking news since the whole idea of the 2170's is to lower costs. If correct it possibly implies that Tesla Panasonic just repackaged the existing 18650 cell into a new form factor and there is no "secret sauce" in the new 2170's.

The key to the calcs is the usable energy in the EPA report.
http://www.teslarati.com/wp-content/uploads/2017/09/Tesla-Model-3-EPA-CSI-HTSLV00.0L13.pdf

usable energy for 2170's in Model 3 is 78.3 kwh in the new model 3 long range pack
Tesla Model 3 actually has 334 miles of range according to EPA data
It actually is there more than once in the report on pages 6 and 7 at the bottom of the page it says:

"Manufacturer Test Comments Internal Test results for MY2017 Model 3 Long Range. Range determined by using SAE J1634 Multi-cycle test procedure. END-SOC 78270 wh."

also it says:

"Integrated Amp-hours 222.81
Average System Voltage 351"

multiplying those 2 numbers = 78273 watt hours

Therefore usable energy= 78.3 kwh

number of cells in big model 3 battery=4416
Tesla Model 3: Exclusive first look at Tesla’s new battery pack architecture

therefor usable energy per cell is 78.3/4416=.0177 kwh per cell

model S 100D pack has 8256 cells and 98.4 kwh usable energy
Teardown of new 100 kWh Tesla battery pack reveals new cooling system and 102 kWh capacity

therefore usable energy in one 18650 cell=.01192 kwh/cell

Therefore increase in usable energy in one 2170 cell is 48% greater than the 18650 (.01192/.0177)

Volume in 2170 cell is 47% greater than the volume in the 18650 (simple volume calc for 18X65 vs 21X70 cells)

so energy went up 48%
volume went up 47%

basically the same within 1%

Do these numbers make sense? Can you guys find any holes in this analysis or math errors??

Thanks,
George

Hi George

You are absolutely correct with your calculations! However the one thing you did not consider is that the specific energy or kWh/kg increases not the kWh/l or energy density.
Your conclusion is correct considering that the core materials must be the same.
However consider the fact that when you increase the volume and reduce the amount of surface (which I believe is made of stainless steel) you reduce significantly the weight of the cell, hence you reduce the total energy density.
The volume being r^2*pi*h with respect to the surface (2*r^2*pi+2*r*pi*h). It is a simple geometric optimization. All you do is make the derivative dS/dr=0 which yields (assuming the Volume is a constant C) r=cuberoot(C/2*pi), you find the minimum surface for maximum volume thus minimizing weight of the covering for the amount of battery content. However what is interesting to observe is that they did not change the h/r ratio at all. Ideally they would increase the radius to improve even further the specific energy. (for ex in the 1860 cell the ideal radius would be 13.4mm) but I suppose that this would be very impractical. Nonetheless by increasing the Volume, the surface still decreases with respect to the Volume, thus reducing the weight per battery capacity.
for the 1860 cell the S/V=0.256 and for the 21/70=0.219!! That is where they reduce weight.
But if they were really focused on weight reduction the ideal radius would be ~15.7mm for the 21700 cell with a height of 31.4mm which is about double of what they have. This yields S/V=0.191!!! This would be a huge improvement in weight! However I think that this h/r ration is more linked to costs. Although using this ideal ratio would reduce covering material significantly.
 
Are the 18650's used then steel sleeve?

Also note that the P3D has an output of around 300kW. So far, that's at best 4C.
Charging though is on the high side, similar to the fastest S/X at 1.5C.

Reports from drivers is that the power output doesn't seem to drop nearly as much due to heating of motors and battery. It could be that the 2170's have significantly lower internal resistance. When used in S/X, these might actually charge at 2+C without problem?
 
Are the 18650's used then steel sleeve?

Also note that the P3D has an output of around 300kW. So far, that's at best 4C.
Charging though is on the high side, similar to the fastest S/X at 1.5C.

Reports from drivers is that the power output doesn't seem to drop nearly as much due to heating of motors and battery. It could be that the 2170's have significantly lower internal resistance. When used in S/X, these might actually charge at 2+C without problem?

Difference is also available in the permanent magnet motors vs. the induction motors of the S/X.
Papers and studies exist, such as this one. http://www.iieta.org/sites/default/files/Journals/IJHT/30.1_12.pdf