I wanted to discuss the energy density of the 4680 cells.
Now admittedly a lot of us were surprised when we first heard that the Texas Model Y
only had a range of about 280 miles.
Especially after our expectations after Battery Day.
So much so, that a lot of the community actually thought, that no, this couldn't be 4680 cells,
and some even thought they must be using LFP, myself excluded.
As you recall I ran down all the figures to explain how it was not mathematically possible
to be LFP.
And even made a bet with one of you, to plant 100 trees if I was wrong, whomever that was,
I hope you planted those trees.
4680 And we moved on and eventually discovered
that yes indeed these Texas Model Ys really were using 4680 cells, although they were
the cells from the kato road facility not the Texas 4680 lines.
But I was also admittedly surprised that these vehicles only had a range of 280 miles.
We have also had a lot more information now, such as the quantity of cells confirmed.
Prior to this, other credible people in the industry were speculating that it must be
fewer cells.
These numbers are not simply adding up.
Like I said though, we had enough numbers that we can use to give us more numbers, such
as the total volume of cells in the vehicle.
Now the 2170 battery has about 107 liters of cell.
And the 4680 has 110 liters.
This does however include casing, and although the casing is thicker on the 4680 there is
less casing relative to volume and surface area ratio, due to the cells being larger.
JELLY ROLL Now although the volume of the batteries are
quite similar, that doesn't necessarily mean the actual volume of jelly roll inside the
battery is the same.
At a guess Tesla's 4680 machines are able to wind up the jelly roll more efficiently,
and thus insert more jelly roll per relative to cell volume.
However the thickness of the jelly roll is arbitrary.
However, saying that we had Munro and Associates unravel the jelly roll from the 4680 cell.
And it came to 325 cm.
Whereas the 2170 jelly roll is closer to 81 cm long.
Which would mean that the jelly roll is 4 times longer in the 4680.
The area of a the base of the cell with a diameter of 21 mm compared to 46 mm, is 1384
mm2 compared to 7234 mm2.
So despite the 4680 cell having a diameter larger than 5.2 times as much as much area
for jelly roll, it only has 4 times as much in length.
Of course the jelly roll is also also 10mm more in height for the 4680, so it ends up
being 2600 cm2 in area, compared to the 2170 with 567 cm2 in area.
In other words 4.6 times more jelly roll in area, but 5.5 times more volume in the cell
to fit more jelly roll in.
Like I said this isn't going to give us too much information, as the thickness of the
cathode and anode can differ.
However, The Limiting Factor YouTube channel thinks that the cathode is about 20-25% thicker.
Which would take it to about 5.5 times as much volume.
We can also again validate this with cell weight too.
We know the weight of a 2170 cell is 68g and a 4680 is 355g, which is 5.2 times as much.
I am not sure how much of the cell casing is the weight, but the 2170 has pretty much
twice as much surface area or casing area, relative to volume than the 4680, which was
another genius aspect of the larger cell.
This then makes the cell weight of the 2170 2% more than the 4680.
Therefore I would say that when you factor in the cell casing saving with the 4680, the
actual amount of actual jelly roll would be about the same as a long range Model Y with
2170 cells.
RANGE Ok, that was a really long way to say that
there is pretty much the same amount of jelly roll in the 4680 battery as there is in the
2170 battery.
Yet we still have this huge discrepancy of about 50 miles of range, and this is with
a car that is perhaps 200 lbs lighter.
SILICON So we know there is about as much jelly roll
in the 2170 battery as there is in the 4680 battery.
Remember though the 4680 battery is also smaller in size, meaning it is less limiting when
it comes to the overall design of the vehicle.
It also means the battery weight is more in the center of the vehicle, and thus improving
the polar moment of inertia.
i.e. the car corners and handles better, which Elon actually says will even be noticeable.
As for this discrepancy in range, it really is just too much.
Although again Jordan from The Limiting Factor did have a tear down of the battery done.
And we did notice that despite the anode was using the dry battery electrode process, it
did not contain any silicon.
Silicon is where we can see the biggest opportunity in increasing energy density of a cell.
The fact the 4680 doesn't currently contain any, could be the reason the range of the
4680 isn't as high as much as the 2170 yet.
As there is almost 5% silicon in the anode of the 2170.
It may be that the dry battery electrode process is too difficult to add silicon yet, but don't
go by my word on that at all, I am out of my depth on theories like that.
But bear in mind also, this was an old cell that was torn down, and it was from the kato
road facility not Texas.
In other words we don't know as to what stage the anode is now.
THEORY But this has all lead me to a new theory in
regards to the energy density of the 4680.
Even with no silicon in the 4680 anode, I still think the Model Y should be getting
more than 280 miles of range.
And we are hearing that the energy density of the 4680 is rumored to be around 250 kWh,
which is very close to the 2170 cell, except without silicon.
Which would be amazing, and perhaps the dry battery electrode process is actually improving
energy density, along with thicker electrodes.
Now, it's fairly obvious to us all that in order for a Cybertruck to reach the 500 miles
claimed, yes 500 miles for the tri-motor, thats what they said, then we need a lot more
energy in the battery to reach that.
The previous theory was that Tesla would be using different cathodes, nickel ones for
more energy density, the more manganese for less energy dense, but the difference is not
that noticeable.
I believe now that Tesla might use different levels of silicon in the anode instead.
You see although silicon is fairly abundant and not that costly relative to the extra
range it gets, it does have a major disadvantage.
And if someone can sort this disadvantage out then its potentially worth trillions.
Of course Tesla are already working on mitigating it as much as possible.
The disadvantage is degradation.
The more silicon in a cell, the faster it will degrade.
And now we are seeing 4680 cells that contain no silicon, then perhaps this might be the
different versions offered.
Perhaps for Robotaxis they will contain no silicon.
Therefore they won't degrade, and will likely be capable of hitting a million miles before
too much degradation, even with nickel based cells.
Then for Cybertruck, a consumer product, the one that needs 500 miles of range, it may
have 15% silicon, and perhaps work up to an even higher rate.
And then various level of silicon in between for different cells, for different applications.
They could produce different variants on the different lines even.
LFP If Tesla are not going to make a 4680 LFP
cell, then this might be the cell required for the Robotaxi, a nickel, cobalt manganese
cathode, NCM cathode, with a silicon free anode.
Perhaps still capable of 300 miles a day, depending on the size the Robotaxi is.
Which should be sufficient for a days taxiing.
MORE CELLS Also it was pointed out, that the current
4680 battery does containing padding.
This padding looks like it is expandable, likely enough room for another array of 4680
cells, probably 69 of them.
I also spoke to a structural engineering friend of mine, and he said the structure would probably
still be ok, if an array of cells was also removed.
Therefore Tesla could have batteries with 138 more cells than others, and a lot more
silicon.
Of course although 500 miles of range was mentioned, we aren't entirely sure if that
will be for the first quad or tri motor versions, and may take several years to reach that level
still.
My point is that Tesla are able to offer quite a wide variety of energy capacity in this
4680 battery pack, to serve different applications, and also vary battery degradation too where
necessary.
Remember this is the A architecture, it is meant to be high versatile.
Then again perhaps degradation isn't that big a factor, if the cells can be recycled
at a relatively low cost, especially when compared to the application potential they
can offer.