Welcome back everyone!
I’m Jordan Giesige and this is The Limiting Factor.
This is part nine of the Lithium Mine to Battery Line Series to break down and understand what
was unveiled at Tesla Battery Day.
Like Tesla Silicon, the Tesla Cathode section of Battery Day will take several videos to
fully unpack which I’ll be releasing every two weeks.
This video will cover the nuts and bolts of what was unveiled and Tesla’s surprising
choice to go with a polycrystal cathode rather than a single crystal cathode.
In subsequent videos we’ll do a deep dive on cathode science, the product impact of
the Tesla cathode, the manufacturing process, and the lithium clay + salt extraction process.
Before we begin, a special thanks to my Patreon supporters and YouTube members.
This is the support that gives me the freedom to avoid chasing the algorithm and sponsors,
and I hope will eventually allow me to do this full time.
As always, the links for support are in the description.
Back to the cathode.
Rather than referencing research papers throughout this video, I’ll link my two primary sources
in the description.
Both papers provide a fantastic high-level overview of Nickel Rich Cathodes but vary
in their depth and subject matter.
I recommend starting with the first paper because it’s an easier read.
If you want to go a level deeper, the second paper is more in-depth and a more difficult
read.
Between the two papers, hundreds of other research papers are referenced, some of which
also helped form the opinions in this cathode series.
The first slide that Tesla showed at Battery Day for the Cathode section of the presentation
was titled “What is a Battery Cathode?”
The left panel of the slide states that cathodes are like bookshelves.
While this is true, it’s important to note that what we’re seeing is at the atomic
level.
For the benefit of perspective, if we zoom out by 100,000x, we can see those book shelves
are actually contained in cathode particles.
Those particles are each about the size of a red blood cell and make up the active cathode
layer of a battery, which in itself is about the thickness of a human hair.
Let’s get back to the slide.
There are a few points to clarify about what’s visualised here.
We’ll refer to the Nickel, Cobalt, Manganese, and Aluminum as NCMA for short.
The NCMA is illustrated as crystalline slabs.
It’s illustrated like this for two reasons: The first is to make it easier for the eye
to take in.
The NCMA layer, like the lithium layer, should appear as spheres and it would look like what
we see on screen.
In this structure, it’s more difficult to tell the lithium layer from the NCMA layer
by structure alone.
The second reason is that by illustrating the NCMA as crystalline slabs, it shows that
that the NCMA is locked in place and separate from the lithium.
The lithium is illustrated as spheres to show that it’s not locked in place and is free
to move in and out of the cathode.
The NCMA slabs are not only formed by NCMA atoms, but also oxygen atoms.
The oxygen atoms are the tiny spheres that we see at the edge of the crystalline slabs.
Within the crystalline slabs are the NCMA atoms, which we can barely see here, if at
all.
Let’s look at a more detailed view.
This image uses an aluminum-free cathode, but it’s identical to NCMA for the purposes
of this explanation.
Nickel, Cobalt, and Manganese are all classified as transition metals on the periodic table,
which is why the crystal slab is labelled as ‘TM Slab.’
It stands for transition metal slab.
As you can see, there are Nickel, Cobalt, and Manganese atoms tucked away in the TM
slab.
Cobalt in the transition metal layer has strong bonds with oxygen and is tightly held in place.
A pure nickel transition metal layer doesn’t hold on to the oxygen atoms as tightly as
cobalt.
Those loosely held nickel atoms can drop down into the lithium layer when the battery charges.
When the green lithium spheres move out of the lithium layer and to the anode during
charging, the nickel can drop down and wedge in the vacant spaces left by the lithium.
The technical term for transition metals dropping out of the transition metal slab and mixing
with the lithium layer is called cation mixing.
A cation is just a positive ion such as lithium or nickel.
When Nickel drops into the lithium layer, the cations mix.
When the cations mix, there’s less storage spaces for lithium because the cation mixing
is permanent, and the Nickel is taking up space that could otherwise be filled by energy
storing lithium.
I’ve heard the phrase repeated dozens of times that Cobalt stabilizes the cathode.
My view is that this is a partial explanation of why Cobalt is used in cathodes.
This isn’t something that I’ve seen explicitly stated in research papers, but rather a conclusion
I’ve reached on my own.
There are half a dozen other elements that can be used to dope a cathode that provide
structure besides cobalt.
However, Cobalt has a rare set of characteristics that allows it to both form a strong bookshelf
and store energy.
Cobalt bonds strongly with the crystal structure of the transition metal slab, and also allows
most of the lithium to move in and out of the crystal structure freely.
It still holds on to some lithium, but for the most part the lithium is free to come
and go.
Other elements that can strengthen the bookshelf, like magnesium, hold the crystal structure
strongly, but also grab the lithium ions and don’t allow them to enter and exit the crystal
structure.
This makes the lithium unavailable for charging and discharging and results in a lower energy
density.
Nickel is just the opposite; it barely holds on to the crystal structure and allows lithium
ions to come and go freely.
However, a crystal structure made of pure nickel oxide quickly collapses as the nickel
drops down into the lithium layer during cation mixing.
In other words, yes, cobalt does add structure but it’s a good all-rounder.
Cobalt adds both structure and energy storage.
Based on inferences I’ve made from data in the research, Cobalt provides less structure
than something like magnesium, but more energy density.
On the flip side, it provides less energy density than nickel, but more structure.
If we want to replace cobalt, we need to find the right mix of other elements to replace
cobalt that will provide both the energy density and structure of cobalt.
Before we move on to the chart on the right, it’s worth noting the significance of the
NCMA crystal structure on the left panel.
Tesla’s chemistry is usually referred to as NCA, or just Nickel, Cobalt, and aluminum
with no Manganese.
My view is that NCMA is what they’re actually using or will soon be using, and what we see
on this slide reflects that.
More on this in the next video.
In the right hand panel, three different cathodes are compared.
You may notice that the watt hour per kilogram figures are 4-5 times what you’d expect
from a typical lithium ion battery cell.
This is for two reasons: First, this is just the energy density of the cathode and doesn’t
include the dead weight of the rest of the materials in the battery cell like current
collector foils and separators.
Second, this appears to be theoretical data at 4.2 volts.
Cathodes made of Lithium Nickel Oxide (LNO) and Lithium Cobalt Oxide (LCO) have a theoretical
specific capacity of 275 amp hours per kilogram and are fully charged at 4.2 volts.
When multiplied, the result is 1155 watt hours per kilogram.
I’m not sure if this is how Tesla calculated this chart because they refer to the base
metal rather than LNO and LCO, but 4.2 volts at theoretical capacity looks like a good
approximation.
I’ve remade that chart with real world data extracted from research papers.
This chart takes into account that in reality, Cobalt holds on to more lithium Ions.
I’ve also factored in a more standard voltage of 3.7 volts.
This is because batteries don’t maintain 4.2 volts throughout their discharge cycle.
The voltage drops from 4.2 volts to 3.0 volts and 3.7 volts is a fair midpoint.
As you can see, when we use real world data, Cobalt’s weaknesses are amplified.
What this chart doesn’t take into account is the cycle life of cobalt vs nickel.
An LCO cathode has much greater cycle life than an LNO cathode.
The next slide was an epic surprise for me at Battery Day.
Before Battery Day I droned on quite a bit about single crystal cathodes.
What Tesla is showing us here is a polycrystal cathode, which I did NOT expect.
Polycrystal cathodes are the type of cathode that Tesla currently uses in their batteries.
Let’s do a quick recap of single vs poly crystal cathodes.
What we see on screen is single crystal cathode particles vs polycrystal cathode particles.
Single crystal cathode is made of large, individual, free standing crystals.
Polycrystal cathode is made of spheres that are composed of hundreds or thousands of much
smaller crystals.
The single crystal cathode is inherently stronger because it’s a monolithic slab of crystal
and doesn’t have the thousands of potential fracture points that polycrystal cathode structures
have.
This is important for high nickel, cobalt-free cathodes.
High nickel cathodes expand and contract more during cycling.
This is due to the greater amounts of lithium that leave the nickel crystal structure when
the battery charges.
As we said earlier, Cobalt holds on to more lithium.
This means it shrinks less during discharge.
Before Battery Day, my view was that Single Crystal Cathode was likely what Tesla would
use because it can cope with greater expansion and contraction stresses, and therefore would
be well suited to a high nickel, cobalt free cathode.
I’ve yet to see this fully play out in the research, but from what I’ve seen so far
it’s a promising strategy.
More on this in the next video.
Besides the potential for cobalt-free chemistries, single-crystal cathodes can also operate reliably
at higher voltages and have a longer cycle life.
However, single crystal cathodes are significantly more expensive.
This is because single crystal cathode manufacturing requires two heating cycles, whereas polycrystal
only requires one heating cycle.
Two heating cycles effectively doubles the energy costs for creating single crystal cathode.
The polycrystal approach left me scratching my head because I expected Tesla to bite the
bullet on cost and go for longer cycle life and higher voltage, which would have meant
higher energy density.
However, once again, Tesla left me a bread crumb trail.
There’s a big hint on this slide at the top, which refers to novel coatings and dopants.
After seeing this, I re-read the research paper by Hongyang Li and Jeff Dahn on cobalt-free
cathodes.
As I was reading through the last couple of paragraphs and about to close the document,
I found this passage, and nearly fell out of my chair:
“We are optimistic that with appropriate coatings or low levels of dopants at the surface,
that LiNi1-xMxO2 materials of the type discussed here can be matched or exceeded by materials
without cobalt” Although it’s awkwardly worded, that’s
a clear bingo on coatings and dopants.
Not only that, references for suggested coatings and dopants.
Based on the cathode synthesis notes in this paper, the cathodes that Li and Dahn used
appeared to be polycrystalline.
If that’s correct, then what the paper is suggesting here is that cobalt free polycrystal
cathodes are commercially viable with the right coatings and dopants.
This means that by using a standard polycrystal production process, cobalt-free cathodes could
be produced that have performance that’s equal to or greater than cathodes that contain
cobalt.
This would be exactly what Tesla needs to replace their current cathodes: Cobalt-free,
lower cost due to cheaper materials and a low energy production process, cycle life
equal to or greater than current Tesla cathodes, and slightly greater energy density due to
higher Nickel.
In the next video we’ll do a deep dive into exactly how Tesla can make a Cobalt-free cathode
work.
As with the Cracking the Silicon code video, Tesla had more than one option at their fingertips.
I’ll cut through the noise of those options and give my preferred option.
In the video after that, we’ll discuss the product implications of the Tesla Cathode.
Polycrystal cathodes with coatings and dopants would match or exceed current Tesla cathodes
in terms of cycle life, which is around 2000 cycles.
It’s unlikely that a polycrystal cathode would achieve the 4000+ cycles that a single
crystal cathode is capable of.
This is why I said in the last video that the implications of the Tesla cathode are
more complex and interesting than this slide let on.
Previous to Battery Day, from the feedback I received from researchers and what I saw
confirmed in industry announcements, it looked like single crystal was the way to go for
the Cathode.
As I’ve said earlier in this series, Tesla is ruthlessly and single-mindedly focused
on cost.
Single crystal cathode would have doubled the current cycle life of Tesla batteries,
increased energy density, and allowed for a cobalt-free chemistry.
However, this would come at the cost of a more expensive battery cell due to the increased
energy requirements of single crystal cathode production.
A polycrystal cathode reinforced with coatings and dopants could match Tesla’s current
cycle life, with slightly higher energy density and lower cost while still allowing for a
Cobalt-free chemistry.
Tesla’s slides from Battery Day indicate a 4% range increase, which means around a
3.5% energy density increase.
Tesla also states that the cathode allows for a 12% decrease in cost.
It’s not clear how much of that 12% cost decrease is attributable to the cathode material
itself, and how much is attributable to Tesla’s Cathode manufacturing process.
I doubt that the full 12% is attributable to the cathode material cost, but rather,
I expect most of the cost decrease to be from the cathode manufacturing process.
At the cathode level, cobalt makes up 5% of the cost.
Replacing that with Nickel saves about 3% because Nickel is 1.5 times the energy density
and about half the cost of cobalt.
3% would be a maximum because the some of that cobalt would be replaced with elements
other than high energy density Nickel.
A 3% impact at the Cathode level is only 1% at the pack level, far short of 12%.
As we’ll see in the next video, coatings and dopants might allow for an energy density
increase of the 3.5% Tesla is claiming and could mean that around 3.5% of the 12% cost
reduction is due to increased energy density rather than reduced material cost.
1% for the material and 3.5% for the energy density would result in about 4.5% of the
12% that Tesla is claiming.
Bear in mind, that 4.5% figure is shooting from the hip and might be the maximum, but
it’s about as accurate as we can be with the information Tesla gave us.
Tesla did state that they were able to reduce the cost of the cathode by 15%, but my assumption
is that this is at the cathode material level rather than the cell or pack level.
A 15% reduction at the cathode material level would be a 5.5% cost reduction at the pack
level.
In my view, 5.5% exceeds what’s likely from just a chemistry tweak and could include some
benefits from the cathode production process.
Later in this series, I’ll explain why a 2% cost reduction due to the cathode material
alone is more likely at the pack level.
As I stated above, in the next video we’ll get into the hardcore cathode engineering
that might make Tesla’s durable, polycrystal, higher energy density, cobalt-free cathode
possible.
If you enjoyed this video, please consider supporting me on Patreon with the link at
the end of the video or snag something off the merch shelf below.
I am also active on Twitter and Reddit.
You can find the details of those in the description and I look forward to hearing from you.
A special thanks to Mantas Mikuckas, Alaric Goldkuhl, Ryan Kramer, Gabe Wilson, Patrick
L, Hugh Waller, Ondrej from the TeslaCzech YouTube Channel, Gibson Bathrick, Tim Montague,
and Ron Fradet for your generous support of the channel, my YouTube Members, and all the
other patrons listed in the credits.
I appreciate all your support, and thanks for tuning in.