Future Tesla Batteries

Cosmacelf · Oct 24, 2015

I've always been struck by how Panasonic hasn't been able to sign up any other EV manufacturer to use their cells. LG seems the company that is signing up everyone else.

One big difference is that Panasonic makes small cells, while the others all make those large pouch cells favored by the rest of the car industry.

I wonder if the real reason Tesla allowed others to use their patents was pressure from Panasonic. Tesla had patents on the battery pack itself which might have been preventing others from using Panasonic's cells.

techmaven · Oct 24, 2015

Cosmacelf said:
I've always been struck by how Panasonic hasn't been able to sign up any other EV manufacturer to use their cells. LG seems the company that is signing up everyone else.

One big difference is that Panasonic makes small cells, while the others all make those large pouch cells favored by the rest of the car industry.

I wonder if the real reason Tesla allowed others to use their patents was pressure from Panasonic. Tesla had patents on the battery pack itself which might have been preventing others from using Panasonic's cells.

Well... there's a lot wrong with your statements. First, Panasonic sells cells to a variety of auto manufacturers including Audi. The R8 e-tron uses Panasonic's cells for instance. The Volkswagen E-Golf and A3 uses a Panasonic supplied battery. Panasonic also supplies batteries for the Prius Plug-in Hybrid. Further, Panasonic supplies small cylindrical, pouch, and prismatic form factor cells to a variety of markets.

Cosmacelf · Oct 24, 2015

Ah, I stand corrected. I didn't know any of that.

shokunin · Oct 25, 2015

Model 3 said:
I guess you meant TM3?
Probably correct. But if you look at the original plans for the GF, it would produce 50GWh of battery packs, of witch 35GWh would come from cells produced at the GF and 15GWh from current Panasonic factories. From my understanding of this plan the 35GWh produced at the GF was for the cars, and the 15GWh from Panasonic elsewhere was for stationary batteries. Maybe just for exactly this reason. But on the other hand, plans may have changed since then...

I think JB mentioned a revised cell size (20750 is a guess) to get the increased density needed. The current asia factories are not equipped to deal with this new size and the current 18650 cells would be used for the stationary packs.

wdolson · Oct 25, 2015

shokunin said:
I think JB mentioned a revised cell size (20750 is a guess) to get the increased density needed. The current asia factories are not equipped to deal with this new size and the current 18650 cells would be used for the stationary packs.

With the introduction of Tesla Energy, they created a new market niche for batteries that don't have to be to the same tolerances as car batteries. I agree they will probably continue to use the smaller batteries for stationary systems and use larger batteries in the cars.

It also opens up a place for used car batteries. When battery packs for cars need to be retired, they can be repurposed into stationary battery arrays. If a 85KWh pack has degraded to 60 KWh, that isn't good for transportation, but it's still useful in a stationary application. They could sell a cheaper edition of the Power Wall with used batteries instead of new and people would buy it. Considering a higher percentage of Tesla fans are green than the general population, it would probably be quite popular, just like the CPO program opened the door to Tesla ownership to the less well heeled who wanted a Model S.

Model 3 · Oct 26, 2015

shokunin said:
I think JB mentioned a revised cell size (20750 is a guess) to get the increased density needed. The current asia factories are not equipped to deal with this new size and the current 18650 cells would be used for the stationary packs.

From what I have read/seen/heard is that it was mentioned that Tesla/Elon/JB thinks that the ideal cells for their car would still be in the same cylinder form as they are, but a bit lager both in height and width. Someone has calculated that what they was talking about would be around 20750.

What was - as far as I know - not said was "This is the form factor that we will produce at the GF" or "This is the form factor that we will use in our cars". That is just an informed speculation. But it's probably right. Building a new factory for their battery cells, it would not cost any more to produce the most ideal form factor for their use then some standard form factor.

Ingineer · Oct 26, 2015

I would think they would go with a larger diameter cell but keep the height the same to keep them compatible with existing pack sizes on the S/X. If not, then they likely require a thicker pack. Although only 10mm thicker if it's indeed a 20750.

JRP3 · Oct 26, 2015

10% taller and 10% wider, which is I believe what they said, would be a 20720.

Yonki · Oct 26, 2015

Ingineer said:
I would think they would go with a larger diameter cell but keep the height the same to keep them compatible with existing pack sizes on the S/X. If not, then they likely require a thicker pack. Although only 10mm thicker if it's indeed a 20750.

Are we sure the existing pack form factor couldn't accommodate batteries 10mm taller?

scaesare · Oct 26, 2015

Yonki said:
Are we sure the existing pack form factor couldn't accommodate batteries 10mm taller?

I've actually heard it said somewhere way back when in an early teardown thread that there was some space at the bottom of the pack... so perhaps so.

Ingineer · Oct 26, 2015

I think the space at the bottom is a buffer zone. This insures small dents in the bottom housing doesn't contact the cells or bus bars.

10mm isn't much though, so maybe there's room.

scaesare · Oct 27, 2015

Ingineer said:
I think the space at the bottom is a buffer zone. This insures small dents in the bottom housing doesn't contact the cells or bus bars.

10mm isn't much though, so maybe there's room.

That thought occurred to me as well... so I don't know if they allowed for both. If I recall the person estimated it as "1/4 inch", but I don't know if that was just eyeballing it. If that's an actual measurement, then it's not even sufficient for the taller cells we are talking about, much less also allowing for buffer space.

JRP3 · Oct 27, 2015

The height difference should be less than 10mm, could be closer to 5 if they slightly round down the 10% longer figure and make the cell a 20700 instead of a 20720. My guess is they will make it short enough to fit into S/X packs, because to not do so would seem...insane?

Troy · Oct 27, 2015

This is what Tesla said:

26:09 JB Straubel: We're also customizing the cell shape and size to further improve the cost efficiency of the cell and our packaging efficiency.
26:22 Elon Musk: Right. We've done a lot of modeling trying to figure out what's the optimal cell size. And it's really not much. It's not a lot different from where we are right now but we're sort of in the roughly 10% more diameter, maybe 10% more height. But then the cubic function effectively ends up being just from a geometry standpoint probably a third more energy for the cell or maybe 30%. And then the actual energy density per unit mass increases.
Source: Tesla Conference Call, July 2014

Here are different cell dimensions Tesla could chose:

Current cells:
Dimensions: 18mm*65mm
Volume= 16,540 mm^3
Cells needed: 7104

20720 cells:
Dimensions: 20mm*72mm
Volume= 22,619 mm^3
Volume difference= 22,619/16,540-1= 36.7%
Cells needed: 5196

20700 cells:
Dimensions: 20mm*70mm
Volume= 21,991 mm^3
Volume difference= 21,991/16,540-1= 33.0%
Cells needed: 5342

20690 cells:
Dimensions: 20mm*69mm
Volume= 21,676 mm^3
Volume difference= 21,676/16,540-1= 31.1%
Cells needed: 5418

Even if the new cells are only 4 mm taller, they would still have 31.1% more volume. Therefore I think 4 mm taller is more likely. I would say maximum 5mm.

scaesare · Oct 27, 2015

Troy said:
This is what Tesla said:

26:09 JB Straubel: We're also customizing the cell shape and size to further improve the cost efficiency of the cell and our packaging efficiency.
26:22 Elon Musk: Right. We've done a lot of modeling trying to figure out what's the optimal cell size. And it's really not much. It's not a lot different from where we are right now but we're sort of in the roughly 10% more diameter, maybe 10% more height. But then the cubic function effectively ends up being just from a geometry standpoint probably a third more energy for the cell or maybe 30%. And then the actual energy density per unit mass increases.
Source: Tesla Conference Call, July 2014

Here are different cell dimensions Tesla could chose:

Current cells:
Dimensions: 18mm*65mm
Volume= 16,540 mm^3
Cells needed: 7104

20720 cells:
Dimensions: 20mm*72mm
Volume= 22,619 mm^3
Volume difference= 22,619/16,540-1= 36.7%
Cells needed: 5196

20700 cells:
Dimensions: 20mm*70mm
Volume= 21,991 mm^3
Volume difference= 21,991/16,540-1= 33.0%
Cells needed: 5342

20690 cells:
Dimensions: 20mm*69mm
Volume= 21,676 mm^3
Volume difference= 21,676/16,540-1= 31.1%
Cells needed: 5418

Even if the new cells are only 4 mm taller, they would still have 31.1% more volume. Therefore I think 4 mm taller is more likely. I would say maximum 5mm.

Duh...one of the earlier posts referred to 10mm taller, rather than 10% and I didn't catch the mistake.

Allow me to correct my earlier post and suggest that even if the ~1/4" dead-space estimate in the bottom of the pack casing is correct, that's 6.5mm, which might allow the taller cells to indeed fit.

Thanks for that.

aronth5 · Oct 27, 2015

Many automatically assumed that when Elon says the Model 3 will be approximately 20% smaller than the Model S the battery pack is also 20% smaller.
With the taller cells that wouldn't be the case which is encouraging.

ecarfan · Oct 27, 2015

And if true that is encouraging news for those looking forward to the next version of the Roadster. I want that vehicle to be small, significantly smaller than the Model 3, and I've wondered how Tesla will fit a high capacity battery in the floor of the car.

wdolson · Oct 27, 2015

aronth5 said:
Many automatically assumed that when Elon says the Model 3 will be approximately 20% smaller than the Model S the battery pack is also 20% smaller.
With the taller cells that wouldn't be the case which is encouraging.

They have also said the base version will have 200 mile real world range. That would indicate the battery pack is smaller. The Model 3 will almost certainly be lighter, and targeting a 200 mile range, various people have made estimates of the weight and size of battery pack needed. It puts the pack for the base model around 55KWh.

roblab · Nov 3, 2015

aronth5 said:
Many automatically assumed that when Elon says the Model 3 will be approximately 20% smaller than the Model S the battery pack is also 20% smaller.
With the taller cells that wouldn't be the case which is encouraging.

I have always thought that "20% smaller" meant 20% shorter height and width, and 20% narrower. That would change the overall weight:

A cube with dimensions 10 x 10 x 10 gives a volume of 1000.

A cube with dimensions 8 x 8 x 8 gives a volume of 512

Or about half.

So the battery could be considerably smaller than "20%" of a full size battery.

Yeah, I know it's not a cube, or a sphere (also about half), but it is not 80% of full size. Sure: maybe a Honda Fit type. Here again, that's about 2500 lb, compared to nearly 5000 for Model S.

See?

wdolson · Nov 3, 2015

roblab said:
I have always thought that "20% smaller" meant 20% shorter height and width, and 20% narrower. That would change the overall weight:

A cube with dimensions 10 x 10 x 10 gives a volume of 1000.

A cube with dimensions 8 x 8 x 8 gives a volume of 512

Or about half.

So the battery could be considerably smaller than "20%" of a full size battery.

Yeah, I know it's not a cube, or a sphere (also about half), but it is not 80% of full size. Sure: maybe a Honda Fit type. Here again, that's about 2500 lb, compared to nearly 5000 for Model S.

See?

I'm pretty sure they mean 20% volume not 20% smaller in all dimensions. If you shrink the wheelbase of the Model S by 20%, you get down to the wheelbase of some of the smaller cars on the road. On the other hand Elon Musk has also commented the Model 3 will be about the same size as the BMW 3 Series, which is about 20% smaller in volume than the Model S. Tesla is aiming for the middle of the market for the Model 3 and that's the platform most midisize and compact sedans are built on.

Midsize includes cars like the Chevy Malibu, Ford Fusion, and I believe the BMW 5 Series. Compact sedans include the BMW 3 Series and the Subaru Impreza. Cars smaller than the compact sedans start getting into specialty cars and cars aimed at first time car buyers. There are already BEVs in that size niche and I don't think Tesla wants to compete with those cars.

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