Welcome back everyone!
I’m Jordan Giesige and this is The Limiting Factor.
In a Patent published last week, Tesla revealed they’ve created a process for a single crystal
cathode material made of Nickel Cobalt and Aluminum.
Today, I’ll explain what a single crystal cathode is, walk you through the patent step
by step, and how the patent fits with my predictions for Battery Day.
Along the way, we’ll cover some key pieces of information that I haven’t seen discussed
elsewhere.
Let’s get right into it.
Most cathode materials are polycrystalline.
This means that the crystals that make up the cathode are actually many crystals that
have fused together.
The image on screen is a polycrystalline structure.
I’ve outlined in green one crystal and you can see that it’s fused to the other crystals
around it at the crystal border, forming a solid mass.
If we zoom in to take a closer look at one of these borders, shown by the red line, we
can also see that the atoms in the crystal structure form perfect rows.
The blue arrows show that these rows are pointing in different directions at either side of
the crystal border.
As a lithium ion battery charges and discharges, lithium ions enter and exit the space between
those rows of atoms, which causes individual crystals to expand and contract.
This creates stresses at the crystal borders because the crystal structure is aligned in
different directions and therefore expands and contracts in different directions.
Over time, the polycrystalline structure tears itself apart at the seams, the crystal disintegrates,
and the battery fails.
Large single crystals don’t run into this problem because the rows of atoms are facing
the same direction in every part of the crystal.
Even better, with the right coatings and additives, they can last for thousands of cycles.
We’ll get back to that.
Let’s take a look at the first page of the patent.
The title of the patent is ‘Method for Synthesizing Nickel-Cobalt-Aluminum Electrodes.’
I’ll refer to Nickel Cobalt Aluminum by its abbreviation, NCA.
However, the method is what’s important here rather than the specific materials.
When we get deeper into the patent, it will become clear why.
The patent was filed by Tesla Motors Canada and the inventors are listed as Jeff Dahn,
Hongyang Li and Jing Li.
Jeff Dahn is located in Canada and he’s Tesla’s exclusive research partner.
The other inventor names will be familiar if you watched the last video.
Hongyang Li was also leading work on a Cobalt free battery with Jing Li and the work was
overseen by Jeff Dahn.
As we’ll see, this patent leaves room for a Cobalt free battery.
In the fourth paragraph of the patent, Tesla describes the standard method for making a
polycrystalline NCA material and the standard method for making a single crystal NMC material.
NMC stands for Nickel Manganese Cobalt.
Tesla describes these methods because they will be showing how their method is different,
and therefore can be patented.
Tesla explains that the standard method for making a battery cathode involves a process
called lithiation.
Lithiation is the process of making crystals that contain lithium by heating lithium with
NCA or NMC materials at specific ratios.
For the rest of the patent, when Tesla refers to the ratio of Lithium to NCA or NMC, they
simply refer to the NCA and NMC as other metals.
Tesla states that the in standard lithiation process for NCA, the lithium to other metal
ratio of is 1.02.
In other words, 2% more lithium is used than NCA.
The 2% extra is added because some of the lithium burns off when heated.
They go on to say that the single crystal NMC process uses a lithium to other metal
ratio of 1.2 instead of 1.02 or 20% instead of 2%.
In paragraph 5, Tesla lays out the problem that the patent will be solving.
High temperatures are needed to create large crystals for a single crystal cathode material.
However, high temperatures also cause the excess lithium to start reacting with the
other metals, which results in low purity material.
Reducing the lithium to other metal ratio improves the purity, but then the material
does hold much lithium and the battery wouldn’t store much energy.
In paragraph 8, Tesla summarises their solution, which is a two-step process: Step 1 is to
start with a mixture that has a low lithium to other metal ratio, and heat it at very
high temperatures.
This allows large crystals to form without excess lithium reacting to the other metals.
Step 2 is to reheat the material from Step 1.
However, this time at lower temperature with high lithium to other metal ratio.
Viola – you now have a cathode material with large single crystals that’s high lithium
and very pure.
In the next paragraph, Tesla explains that there are three variables to get this right
in each step: Temperature, cooking time, and the ratio of lithium to other metals.
They advise that this patent will show the effects of changing those variables.
Paragraph 14 states that this process could be used with a range of other metals, such
as Aluminum, Nickel, Cobalt, Manganese and Magnesium.
It’s worth noting that these are the same metals that Hongyang Li, Jeff Dahn, and Jing
Li tested in their paper outlining a cobalt free battery.
Pay close attention to the last sentence, which states that this process could be applied
to a cathode that is strictly Nickel and Aluminum, and no Cobalt.
That’s the Cobalt Free chemistry I targeted in the last video.
From here, Tesla begins to explain the visuals included with the patent application.
I’ve modified the images to make it clear what each is describing.
Let’s walk through the important ones in detail.
If you aren’t a details person, then feel free to jump straight to the summary.
I’ll put time a time stamp in the comments.
Figure 2 shows the results of Step 1 of Tesla’s 2 step process.
These are scanning electron microscope images.
This is the step where Tesla advised that they would use high temperatures and a low
lithium to other metal ratio.
The temperature ranges from 850-950 Celsius and the ratio ranges from .8 to .975 Lithium
to other metal ratio.
As you might recall, step 1 involves high temperatures to grow large crystals and a
low lithium to other metal ratio to avoid impurities.
Each image you see here is the result of a different combination of temperature and ratio.
I’ve marked four of the samples with coloured dots.
These will show in the top of the next figure.
Figure 3 shows the four samples that I marked with coloured dots in the last slide.
Below that, you can see that Tesla provides 8 more samples.
These samples are the result of step 2 of the process.
The four selected samples from the last slide were reheated to 735 Celsius at two different
lithium to other metal ratios.
4 samples at two different lithium to other metal ratios results in the 8 additional samples
we see here.
Again, Step 2 involves low temperatures because the crystals don’t need to grow any larger,
but high lithium to infuse extra lithium into the crystal structure.
In the next figure, you’ll see these images replaced with charts.
At the top of the figure you’ll again see the red, orange, green, and blue marker dots
for the step one materials.
The red and orange boxes will instead be replaced with a 1.01 and 1.02 in red and orange lettering.
The 1.01 and 1.02 are the two lithium to other metal ratios that were used in Step 2.
This is figure 5.
It took me a few hours to get my head around this.
I’ll break it down piece by piece.
What we’re seeing is x-ray diffraction patterns for the 12 samples in the last slide.
The first step to understanding this slide is to understand what x-ray diffraction is.
When you shine a light through a crystal, you’ll often see a band of rainbow caused
by the light bouncing through the crystal structure.
When an X-ray passes through a crystal, it does something similar.
But, instead of a rainbow band, you get an x-ray plot.
And instead of different colours, you get different intensities of x-rays scattered
around the x-ray plot.
X-ray diffraction captures those places where the x-rays are intense and spits out graphs
like you see here.
Each peak you see is a spot were the x-rays where intense.
The degrees are the degree of angle from the x-ray source.
Over time, scientists have worked out what each peak tells us about the crystal structure.
In this set of graphs, Jeff Dahn and his team have chopped up the x-ray diffraction graphs
into pieces.
They’ve kept the pieces that show the information that is important.
They’ve also zoomed in and out where helpful.
Let’s start with the top half and find out if our crystals have plenty of Lithium in
them.
We’re zoomed in very close here, to about 1 degree of the x-ray plot.
If you follow the black line up from the red arrows, you’ll see a bump on the left side
of the peak, like a little tumour.
This bump tells scientists that the crystal structure is short on Lithium.
If you follow the line up from the green arrows, you’ll notice that the black line is a little
bit further to the right than on the red arrow.
You’ll also notice that there is a nice smooth curve on the left side of the peak.
This tells is us that the crystal structure is topped up with Lithium.
The red and green boxes also indicate how much lithium is in the material.
Notice that the peaks in the red boxes are giving us what looks like a middle finger
or knuckles.
This tells us that the crystal structure is short on lithium.
The green boxes show split peaks, which indicates plenty of lithium in the crystal structure.
We can throw out the samples on the left hand side of the screen and take a closer look
at the samples on the right hand side of the screen.
The ones on the left don’t have enough lithium and the ones on the right do.
These graphs are zoomed out and are showing 15 degrees instead of 1 degree.
Any peaks in this section of the x-ray plot would indicate impurities.
The samples that only went through the 1st step of the 2 step process have a small peak
which I’ve circled in red, and the materials that went through both steps have smaller
peaks which I’ve circled in green.
The smaller peaks or no peaks mean the sample has a low amount of impurities.
I’ve marked the high lithium, low impurity samples on the right hand side of the screen
with a blue box.
In the next slide, Dahn and his team apply math to the information in these graphs to
find out more about the crystal structure.
If you’re curious about the math, you can look up the Rietveld Method on Wikipedia.
These graphs tell us how much Nickel is in the Lithium layer of the cathode material
samples.
Understanding why that’s important requires some background.
The structure of this NCA cathode material is layered in sheets.
The sheets are made of Nickel, Cobalt, and Aluminum.
In between those sheets is where the lithium ions hang out.
Any Nickel in the lithium layer takes up space that could be filled with lithium and blocks
the lithium from entering and exiting the sheets.
This of course means that the lower the percentage of Nickel in the Lithium layer, the better.
The bar charts are showing us that the samples that only went through step 1 have a lot of
Nickel in the Lithium layer.
All the samples that were heated a second time have very little Nickel in the Lithium
layer, around 2% or less.
I’ve marked in green the best candidate.
Which is around 1% Nickel in the lithium layer.
This is an excellent result and suspect it would increase the energy density of the material
by a small amount as well as extend battery life.
There are 2 more figures worth discussing, and we’ll cover those off in a moment to
wrap things up.
The rest of the patent document was lots of legal speak to make sure that Tesla has every
base covered and states Tesla intends to use this method for a wide range of material combinations.
This patent touches on several points made in the last video of my Battery Day series.
Let’s check how my predictions are going: I advised in the last video that Tesla would
move to a 4.3 volt chemistry if the battery management system allows.
Here is Fig. 7 from the patent, which indicates the single crystal cathode is good for 4.3
volts.
This will translate into an 8.3% improvement in battery cell specific energy density, which
could be applied to battery pack profit margin or range improvements.
One of our viewers pointed out that Tesla’s Battery Management System is capable of 5.0
volts, and the lead looks promising.
A 5 volt limit would make sense because battery chemistries top out at 5 volts.
It would be common sense future proofing.
Next, I speculated that Tesla would unveil a million mile battery.
The patent doesn’t verify that, but it does show 2 things that support a million mile
battery.
First, figure 8 from the patent shows the phase transitions covered in the last video.
For this video, you don’t need to know what dq/dv is, only the size of the number.
In this patent, the dq/dv ratio maxes out around 400.
A chemistry that degrades quickly would have a dq/dv number in the thousands, as shown
in the examples here from the last video.
Second, figure 9 from the patent shows how the single crystal cathode performs against
polycrystalline cathode materials.
Figure A shows that the polycrystalline starts with a higher energy capacity, but then quickly
drops to the same capacity as the single crystal.
If this chart kept going, the polycrystalline battery would die first.
Figure B adjusts for the energy capacity difference and shows that the single crystal clearly
degrades more slowly.
The titanium coating I suggested wasn’t covered in this patent.
Briefly, Jeff’s team has also been working on a titanium coating for single crystal cathodes
that extend battery life even more than single crystal alone.
If Tesla and Dalhousie patented the coating as well, then Tesla could fully manufacture
the single crystal coated cathode in house.
One new piece of information I didn’t cover in my last video is that Jeff Dahn is likely
in the process of patenting an alternative to a battery additive called Lithium Difluorphosphate.
Lithium difluorophosphate is the most effective additive on the market for extending battery
cycle life.
Lithium difluorophosphate is expensive because one company holds the patent and it’s extremely
effective at extending battery life.
However, Jeff Dahn discovered old research describing how to make Sodium Difluoro Phosphate,
and he found that it’s just as effective as Lithium Difluoro Phosphate at extending
battery life.
I expect Tesla has filed a patent for this and they will be making this in house as well.
In the last video, I said the battery unveiled at battery investor day would be Cobalt free,
with 95% Nickel and 5% aluminum.
This patent clearly states that this process could be used for a cathode that was strictly
Nickel and Aluminum.
This might allow for an additional 2.5% increase in specific energy.
There is no guarantee that Tesla will use this single crystal patent or cover it at
Battery Day, however, this patent definitely improves the likelihood.
If this is covered at Battery Day, it will be part be part of the broader set of improvements
we just discussed.
Many of these improvements go hand in hand and would result a specific energy at the
cell level of up to 300wh per kilogram at the cell level and below $100/kwh at the pack
level if there are also pack improvements.
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