Welcome back everyone!
I’m Jordan Giesige and this is The Limiting
Factor.
Those who follow Tesla closely will be aware
of Tesla’s alleged acquisition of a company
called SilLion.
In this video I’m going to explain what
SilLion’s technology is and my literal moon-shot
idea for where this technology might end up.
Before we begin, a special thanks to Bradford
Ferguson of Halter Ferguson Financial and
the Patreon supporters listed in the credits.
It’s the support on Patreon that keeps me
grinding away on interesting, niche topics.
Back to SiILion.
First, it’s worth noting that we’ve received
no confirmation of whether Tesla has acquired
SiILion and it’s also worth noting that
SiILion may have other technologies than the
one I’m going to lay out below.
The information in this video is derived from
two sources.
This first is a SilLion PDF that was removed
from the internet shortly after I downloaded
it.
The second is a 2017 patent application by
SilLion.
This image was provided in the SilLion PDF.
At the bottom of the image is a key that describes
what each part of the image is.
Si stands for Silicon, which is typically
an anode material.
This lets us know that SilLion’s product
most likely has to do with a high Silicon
anode.
What’s cPAN?
I did a search on this acronym through research
websites and found that PAN stands for Polyacrylonitrile.
Polyacrylonitrile is a common industrial material
and it’s used to make carbon fiber.
However, the c remained a mystery to me for
several months.
The patent application points out that the
c stands for cyclised.
Cyclised means that the Polyacrylonitrile
has been heated to stabilise its structure.
This stabilisation also results in the Polyacrylonitrile
becoming more conductive, which is a requirement
for anode material.
However, we’re getting ahead of ourselves.
Let’s dive into the patent application.
Daniela Molina Piper and Tyler Evans of SilLion
were listed as the inventors of this patent
application.
Daniela is the President and Chief Operating
Officer and Tyler is the Chief Technology
Officer of SilLion.
I’ll refer to Daniela and Tyler as the inventors
for the rest of this video.
The patent application was originally lodged
with an international patent body on 13 October
2017 to stake a claim and begin the search
for any competing applications.
The inventors begin by laying out basic facts
about silicon in anodes.
For example, it has ten times the capacity
of standard graphite anode material.
However, that extra energy density comes at
a cost.
When a conventional graphite anode is charged
up in a lithium ion battery, empty spaces
in the graphite structure are filled by the
lithium ions.
This means graphite only expands by 10-13%
during cycling.
With silicon, there are no empty spaces and
the lithium actually bonds directly to the
silicon causing the structure to expand and
contract by up to 300% during charge and discharge.
This causes the silicon to tear itself apart.
During this process, the SEI layer is also
destroyed.
SEI stands for Solid Electrolyte Interphase.
The SEI layer is a protective layer that forms
on the cathode and anode particles.
It’s created by the electrolyte reacting
with the anode and cathode.
Much of the material used to create the SEI
layer is from lithium in the electrolyte solution.
If that SEI layer is left alone, it consumes
very little of the battery’s lithium reserves.
If the SEI layer is destroyed every time the
battery cycles, it uses up the lithium in
the electrolyte solution, which reduces the
battery’s cycle life.
Cycle life refers to the number of times a
battery can be charged and discharged.
That’s where SilLion’s cPAN, or cyclised
polyacrylonitrile comes in.
As the image here shows, the cPAN, shown in
blue, is used to coat the silicon particle.
The silicon particle is shown changing from
light grey, to black, and back to grey is
it cycles.
When the lithium enters the new particle and
fuses with the silicon, the silicon still
expands and cracks, but the cPAN holds the
shattered particle together.
The inventors referred to this as self-contained
fragmentisation.
During this first cycle, the protective SEI
layer forms over the cPAN, shown in yellow.
The cPAN takes all the mechanical stress and
the SEI layer remains mostly undisturbed.
Because of this, the SEI layer doesn’t need
to completely re-form itself each cycle.
And, because it doesn’t need to re-form
itself, it doesn’t use up lithium from the
electrolyte solution.
Let’s take a look at how this cPAN coating
would be manufactured.
The researchers start by saying that they
believe they’ve created the first drop-in
high loaded silicon anode product.
In other words, a conventional wet slurry
manufacturing process and equipment could
be used, rather than requiring new manufacturing
equipment.
The wet slurry method starts with mixing,
where dry powders are mixed with liquid solvent.
The formula for conventional lithium ion batteries
is 90% graphite powder, 5% carbon powder and
5% binder powders.
The graphite is the active material that stores
lithium ions, the conductive carbon allows
electricity to move to and from the graphite
more easily, and the binder holds the electrode
together.
Those powders are then mixed with the liquid
solvent to create a slurry.
The cPAN electrode still starts with a dry
powder.
However, the recipe is Silicon powder, rather
than graphite, along with carbon powder and
polyacrylonitrile powder.
The inventors state that several different
ratios can be successfully used for the powder
mixture.
They called out one ratio to use as an example.
That ratio was 30% silicon powder, 55% carbon
powder, and 15% polyacrylonitrile.
Once again, the powders were mixed with liquid
solvent to create a slurry.
The result is the image shown on screen, where
the polyacrylonitrile has formed a uniform
3-5 nanometer coating.
The inventors didn’t specify in the wording
of the patent application whether the carbon
particles are in in the core with the silicon,
or in the shell with the polyacrylonitrile.
Now that we have a wet slurry mixture, the
next step is to apply that slurry to a copper
foil to make an electrode.
Earlier, I mentioned that conventional graphite
anode only expands 10-13%.
Because the graphite anode expands very little,
it isn’t difficult to keep the anode attached
to the smooth copper foil backing as the anode
expands and contracts.
This works out well for conventional lithium
ion batteries because smooth copper foil adds
less weight to the battery.
Foil is only as strong as its thinnest point.
Rough copper foil is heavier because it needs
to maintain a minimum thickness for strength,
but it’s also thicker in some areas to create
a rough surface.
The SilLion cPAN anode is applied to a rough
copper foil because the silicon expands by
up to 300% when it combines with lithium.
Unless the cPAN anode is strongly attached
to the copper foil, it will peel away from
the copper foil.
A rough surface helps the anode stick to the
foil like a rough road helps your tires get
traction.
Although the rough anode is heavier, the energy
density of the silicon will more than make
up for the space and weight.
The inventors note that their battery also
required a higher negative to positive ratio,
or n/p ratio than a conventional lithium ion
battery.
A higher n/p ratio means that the anode has
greater energy storage capacity than the cathode.
Typically, the ratio is around 1.1 in a conventional
lithium ion battery.
Why are anodes manufactured with excess energy
capacity compared to cathodes?
There are several reasons, but one reason
is that if the n/p ratio is below one, then
the anode can’t store all the lithium ions
that arrive from the cathode.
The ions then plate directly to the surface
of the anode particles rather than being stored
neatly between the graphite layers.
This is dangerous and can lead to the battery
shorting out, causing an explosion.
The n/p ratio of the SilLion battery was much
higher.
For example, in the 30% Silicon recipe mentioned
earlier, the n/p ratio was 1.3.
In the first cycle, the silicon core is pulverised.
This pulverisation causes a loss of energy
capacity in the anode.
The inventors make up for this pulverised
silicon by increasing the capacity of the
anode, which raises the n/p ratio.
The n/p ratio is controlled by adjusting the
coating thickness in the wet slurry process.
The slurry containing silicon, carbon powder,
and polyacrylonitrile is coated to the copper
anode foil.
After the wet slurry is applied, the next
step is for the electrode foil to be dried.
After the electrode is dried, it’s calendared.
This means that the electrode is run though
rollers that compress the electrode material.
This makes the surface of the anode material
flat.
It also brings the anode material to the correct
porosity.
What’s porosity?
Now that all the solvent has evaporated, it’s
left gaps between the particles in the anode
material.
Those gaps are called porosity.
Some porosity is needed to allow the anode
to access the lithium ions in the electrolyte
solution.
However, too much porosity reduces energy
density.
With the silicon anode, porosity needs to
be very high to allow for expansion and contraction.
If there’s not enough porosity to allow
for expansion and contraction, the anode will
separate from the foil backing.
The porosity of a conventional lithium ion
battery anode is 30-40%.
The porosity of the SilLion cPAN anode would
need to be 50-70% to allow for expansion and
contraction.
The next step in a conventional lithium ion
battery production process is to dry the electrode
rolls at 60-150 Celsius under vacuum or with
inert gas such as Nitrogen or Argon.
This removes any remaining solvent.
The SilLion process is the same, except the
rolls of electrode are heated to 600 Celsius.
This is where the magic happens.
Polyacrylonitrile reorganises itself when
exposed to heat in a process called cyclisation.
Cyclisation can be remembered by thinking
of the molecule cycling through different
forms as its heated.
The first cyclisation stage is called stabilisation
and occurs around 300 Celsius.
The inventors carried out the stabilisation
stage under vacuum.
Stabilisation means that instead of melting,
the Polyacrylonitrile molecules oxidise, or
lose electrons, and crosslink with other molecules.
In other words, the Polyacrylonitrile molecules
join together to form stronger, larger molecules
that are more stable in high heat.
These larger molecules also serve as a conductive
matrix that allows the anode to give and take
electrons from the copper foil.
This is why cyclised polyacrylonitrile, or
cPAN was chosen over any other polymer.
Many other polymers need to be treated with
additional chemicals to transform their structure
and conductivity, whereas polyacrylonitrile
just needs to be exposed to heat.
After stabilisation, the second cyclisation
stage occurs at 600 Celsius.
This is called carbonisation, and further
improves conductivity and strength.
Carbonisation was done under vacuum with argon
gas because at temperatures above 100 Celsius
the copper foil of the electrode would have
reacted with oxygen in the air and damaged
the electrode rolls.
At higher levels of heat, the chains become
larger and more conductive.
However, they also become more brittle, so
the maximum temperature the inventors experimented
with was 1000 Celsius.
Our high Silicon anode is now complete.
The inventors included this image in the patent
application.
Luckily, the SiIlion pdf also contained this
image, which more legible.
What this is telling us that a full battery
cell using SilLion’s technology can last
450 cycles before it’s considered end of
life.
The industry typically considers 80% remaining
capacity as end of life.
By conventional lithium ion battery standards,
450 cycles is a poor showing.
This would worsen as the percentage of silicon
in the anode is increased.
This chart doesn’t tell us how much energy
the battery can store.
However, I spoke to a battery researcher and
asked what type of energy density this battery
might be capable of if it had an average voltage
of 3.8 Volts.
I chose 3.8 volts because this is likely the
average voltage we’ll be seeing in the near
future from conventional lithium ion batteries.
The result was roughly 278 watt hours per
kilogram.
This is compared to 390 watt hours per kilogram
that the researchers promise in their marketing
material.
Why so low?
The high porosity, thicker current collector,
and a high n/p ratio cancels out many of the
gains provided by a high silicon anode.
However, the cell still has several more gears.
First gear.
The example cell in the research paper was
only 30-35% Silicon in the anode.
SilLion is claiming up to 80% Silicon in the
Anode, which would put the 278 watt hours
per kilogram up to 293 watt hours per kilogram.
Why did such a huge leap in silicon only increase
the energy density by 15 watt hours per kilogram?
N/p ratio.
At 80% silicon, the n/p ratio needs to be
1.8 in order to make up for the silicon that
pulverises itself in the first cycle.
The anode would be about 45% dead weight after
pulverisation.
Second gear.
The patent application mentioned that the
researchers are considering the use of lithium
doping.
Check out my video on lithium doping if you’d
like to know more about this.
In that video I noted that lithium doping
is likely still many years away, so this seems
less likely.
If they got it to work, it would add about
5-10% to the energy density.
If we split the difference and applied a 7.5%
energy density increase, this would bring
the energy density of the cell up to 315 watt
hours per kilogram.
The inventors mentioned several other potential
technologies.
However, I have the feeling that this was
patent talk, and they were just covering their
bases to protect their intellectual property.
Why would Tesla acquire a company like this?
450 cycles is an order of magnitude less cycle
life than we expect on battery day.
315 watt hours per kilogram is high, but this
would be stretching what is likely and is
nothing write home about.
This brings us to three additional gears,
which are speculation on my part.
Third gear.
Maxwell dry battery electrode technology,
also known as DBE, could allow for silicon
loadings beyond 30-35% while maintaining or
increasing the cycle life.
The whitepaper on DBE stated that it allows
for better cohesion and adhesion.
Cohesion is the tendency for particles to
stick to each other and adhesion is the tendency
of the particles to stick to the copper foil.
In other words, the sticky factor.
With a higher sticky factor, a smooth copper
foil might be used along with less binder
material.
This would increase energy density by removing
dead weight.
DBE technology also reduces the need for solvents
that are required in the wet slurry process.
Those solvents are corrosive to batteries
and reduce battery life.
The only reason they are used is because they
were the only solution the industry had for
high volume manufacturing until the invention
of DBE.
The lack of this corrosion during the manufacturing
process means DBE might extend cycle life
by reducing corrosion.
There’s no way to know how much improvement
DBE would provide to cycle life and energy
density, because it would all be trade secret.
In fact, it may have just been marketing hype.
However, we still have two more gears.
These two gears would provide definite benefits.
Fourth gear.
By using different sizes and shapes of silicon
particles, the amount of pulverisation could
be reduced.
Elon hinted to the importance of this on Twitter
a few days ago.
If the pulverisation could be reduced, the
n/p ratio could be reduced.
This means that the anode would be carrying
less dead weight.
It could provide dramatic gains to energy
density that wouldn’t require farfetched
lithium doping and would also improve cycle
life.
Once again, this would be trade secret.
The benefits would be definite, but we wouldn’t
know the magnitude of progress Tesla has made
here.
I’d cap the energy density at around 350
watt hours per kilogram to be conservative.
With the right engineering and secret sauce,
we might see a bit more, but not the 390 watt
hours per kilogram that SiILion claimed.
This is because electrolyte SiILion used in
their patent application was heavier than
a typical liquid electrolyte.
This brings us to the fifth and final gear:
The SilLion battery cell uses what’s called
an imide based electrolyte.
Some imide based electrolytes are more resistant
to flammability, operate better at higher
temperatures, and have a low vapor pressure.
The drawback is that imide based electrolytes
cost 100X more than a typical electrolyte.
This is because they are not currently produced
at scale.
Let’s dig a little deeper.
Tesla’s current NCA battery cells operate
best close to temperatures that humans feel
comfortable at.
They become flammable at temperatures above
150 Celsius.
Imide based batteries operate comfortably
at temperatures that would boil water, and
can be stable up to 250 Celsius.
Vapor pressure in the simplest terms, measures
how readily a liquid evaporates at a given
temperature and pressure.
High temperatures and lower pressures increase
the vapour pressure, meaning the liquid evaporates
more readily.
The liquid electrolytes in conventional lithium
ion batteries have a higher vapour pressure
than imide based electrolytes.
This matters because in extreme environments
with high temperatures or lower pressures,
the electrolyte in conventional lithium ion
batteries would evaporate rapidly.
Depending on the cell architecture, this would
cause the cell to either dry out, swell, or
burst.
In most earth based applications, Tesla battery
cells are safe.
However, there are two holdings in Elon’s
portfolio that would be willing to pay more
for batteries that are safer and more stable
in extreme environments: SpaceX and The Boring
Company.
SpaceX would be willing to pay a premium for
battery cells like this for three reasons:
1) Space is hard, flammable batteries make
it harder.
NASA is also interested in Imide type liquid
electrolytes because of their greater safety.
A safer battery may also mean less shielding
material and lower weight.
2) The batteries would be operating at low
pressures or in a vacuum, which may make vapour
pressure a concern.
3) Operating in a vacuum also means that there’s
no atmosphere to radiate battery heat to,
which means the battery thermal management
system is more important.
Higher thermal tolerance means a lighter weight
cooling system.
This could save millions in launch costs over
time.
In other words, if Tesla can develop a battery
that works better in a vacuum with higher
heat tolerance, and safety, it has a compounding
effect on weight because less packaging and
a lighter thermal management system is required.
If that battery cell also has a much higher
energy density than a typical battery cell,
SpaceX might be able to reduce the weight
of battery packs for extra-terrestrial exploration
by 50% or even more.
What about The Boring Company?
Tunnels are a confined space.
Any heat that’s generated, which is a huge
amount with a boring machine, is trapped in
the tunnel.
So, a battery that actually works better at
high temperatures is ideal.
Finally, any fire that breaks out can quickly
suffocate anyone working in the tunnel.
Elon puts a high value on human life and safety
is usually his first priority.
As I said at the beginning of the video, this
is a moon-shoot idea.
There are many missing pieces.
However, based on what I found in this patent
application the battery cells SiIlion is working
on would be high performance speciality cells
perfect for extraplanetary use cases and niche
uses cases like tunnel boring.
In summary, despite the high cost and shorter
battery life, the SiILion battery cells would
easily pay for themselves in launch cost savings.
And even more importantly, the cost of the
battery pales in comparison to the cost of
human life, whether that’s in space or underground.
SiILion may also be working on other forms
of high loaded silicon anodes for Tesla battery
cells that will go into vehicles, but that’s
not indicated by anything I’ve found in
this patent application.
Elon did state on twitter that Carbon-Silicon
anodes are one of the key elements to a battery,
but Carbon-Silicon is already in Tesla battery
cells.
They’re mostly carbon with a dash of silicon.
Just enough silicon to help energy density,
but not enough to cause volume expansion problems.
Something certainly seems to be going on with
Tesla near Broomfield, Colorado where SiIlion
located.
Tesla is hiring battery engineers that have
experience with battery prototyping and silicon
anodes.
This indicates to me that that Tesla is rapidly
iterating in a skunkworks type operation similar
to Neuralink or SpaceX at Boca Chica.
That is, they’re likely designing a manufacturing
system along with the battery.
As stated in previous videos, high loaded
silicon anodes may be 4-5 years away.
If Tesla starts a skunkworks to tackle high
silicon anodes, whether for spaceships or
vehicles, they might have a viable cell within
a couple of years, but that timeframe would
be a stretch.
I’d love to be wrong here and see a SiIlion
battery sooner.
Besides the timeframes I’ve suggested, there
is another reason why I don’t think SiILion
tech will be part of what’s revealed at
battery day.
Tesla’s R&D line, called TERA, is at Tesla’s
Kato road facility along with a prototype
Roadrunner line which is currently being built.
If there is another prototyping line a thousand
miles away, it’s probably working on something
different.
Whether that something different is a specialty
cell for SpaceX or a technology that will
eventually go into Tesla’s vehicles, it
appears to be high silicon, which means higher
energy densities.
Let me know in the comments below what your
thoughts are, especially if you have a passion
for space technologies and know something
about the types of batteries that’ll be
needed for off-planet exploration.
In the next video, I’ll be releasing a final
video on Tesla Battery Day.
This will be a wrap up of the original series
along with updates based on what we’ve learned
in the past 5 months.
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A special thanks to Stephen Wilson Barker,
Toomas Mardi, and Joel Brown for your generous
support of the channel, and all the other
patrons listed in the credits.
I appreciate all your support, and thanks
for tuning in.
