Welcome back everyone!
I’m Jordan Giesige and this is The Limiting
Factor.
In a patent application made public last week,
Tesla revealed they’ve created a process
for doping their batteries with extra lithium.
Today I’ll explain what doping a battery
with extra lithium does, walk through the
key points of the patent, and if we can expect
to see something like this on Battery Day.
Rechargeable batteries usually lose at least
7-10% of their capacity the first time they’re
charged and discharged.
This is something the consumer never sees
because it happens at the battery factory
as part of a production step called formation.
The reason why the step is called formation
is because this is the step where the solid
electrolyte interphase is formed within the
battery cell.
For the rest of the video, I’ll shorten
the phrase solid electrolyte interphase to
just SEI.
The SEI is a layer that forms over the cathode
and anode as the cathode and anode react with
the electrolyte solution.
After this initial reaction, the SEI protects
the cathode and anode from reacting further
with the electrolyte solution.
This allows the battery to last hundreds or
thousands of cycles.
However, battery cells are a closed system
and the material to build the SEI had to come
from within the battery.
Much of that material is lithium.
When the lithium is used to form the SEI,
it can no longer be used to store energy.
This is what causes the 7-10% first-cycle
loss I mentioned earlier.
This image shows the first cycle loss being
measured.
In the lower left the charging begins at the
green circle at 0 milliamp hours.
If you follow the line up and to the right,
there is a black circle at about 4.1 milliamp
hours where the battery cell is fully charged.
Finally, the cycle finishes with the battery
being fully discharged to .5 milliamp hours
in the red circle.
We’ve just lost .5 of 4.1 milliamps in the
first cycle, which is 12% of the battery capacity
that the battery cell never gets back in this
example.
One way to solve this first cycle capacity
loss is a process called pre-lithiation.
Pre-lithiation means adding enough extra lithium
to make up for the lithium that’s lost when
the SEI is formed.
There are about half a dozen different methods
to pre-lithiate a battery cell, but to my
knowledge none have been commercially successful
yet.
The reasons for this depend on the method,
and that can be covered in another video.
In this patent application, Tesla has chosen
a method that’s broadly referred to as positive
electrode pre-lithiation.
This is a method where cathode material is
doped with excess lithium.
The extra lithium is then dumped into the
cell during the first-cycle and is used to
create the SEI.
After the first cycle, the doped material
has lost it’s extra lithium and then continues
to cycle at a much lower energy capacity.
Let’s dig deeper into the patent.
If you aren’t into detail, I’ll put a
timestamp in the description for the summary.
The patent is titled ‘Active Material for
Electrode and Method of Manufacturing thereof.’
The applicant is Tesla and the inventors are
Sanketh Gowda and Vineet Mehta, who are both
current Tesla employees.
This means the patent has come directly out
of Tesla’s skunkworks rather than from their
research partner, Jeff Dahn.
In paragraph 4, Tesla explains that the patent
is for an active material for the electrode
that can be used as a pre-lithiation source.
They go on to explain that the active material
they are referring to is Lithium Nickel Copper
Oxide.
We’ll call it LNCO for short.
Figure 2 is a high level outline of the process
to make LNCO.
As you can see, it’s relatively simple and
straightforward.
Precursors are the materials that are heated
together to create the LNCO material.
After that, the LNCO material can be milled
down to the correct particle size.
The patent explains two different precursors
recipes can be used to produce LNCO.
These are shown in paragraph 7 and 8 and all
appear to be common bulk materials such as
Lithium Hydroxide, copper oxide, and Nickel
Oxide.
In each of the two recipes, the LNCO material
can be made in any ratio of Nickel to Copper.
For example, 10% Nickel and 90% copper, or
25% copper and 75% Nickel.
The only requirement is that it adds up to
100%.
Paragraphs 10 and 11 explain that the LNCO
material can be mixed with binders, carbon
materials, and other cathode materials like
Nickel Cobalt Aluminum.
Nickel Cobalt Aluminum is also called NCA,
and it’s the material that Tesla currently
uses in their battery cathodes.
Tesla doesn’t say why they would want to
mix the LNCO material with NCA material in
this part of the patent, but I’ll be explaining
this shortly.
Paragraph 56 explains that the LNCO material
could be coated with 1% Alumina by weight.
The patent didn’t explain what this coating
was for and it took me a while to figure this
one out.
Here we can see research suggesting that Alumina
can be used to stabilise pre-lithiation materials
so they are easier to work with in ambient
air.
I’m assuming this is because lithium is
very reactive to moisture and the high lithium
LNCO would react with humidity in the air.
Paragraph 60 advises that Tesla then mixed
up three different samples of the LNCO material
and tested it.
As we covered above, the LNCO material can
be made with different ratios, and so that’s
what Tesla did.
The ratios were 30/70, 50/50, and 70/30 Copper
to Nickel Ratio.
In other words, mostly Copper, half and half
Copper and Nickel, and mostly Nickel.
Tesla then shows that they ran multiple charge
and discharge cycles and plotted these in
figures 5, 6, and 7 which we’ll look at
in a moment.
They advise that the plots showed that as
Nickel increased, the energy capacity of the
material decreased, but it held its cycle
life better.
Let’s take a look at the plots to better
understand that sentence.
As you can see, I’ve marked several items
in red.
The patent application didn’t provide any
information about the diagonal lines that
I’ve marked with red x’s or the numbers
that I’ve put a red strike line through,
so we’ll ignore those for now.
I’ll provide an educated guess on what’s
happening with these in the summary.
What we see in the blue boxes aligns perfectly
with what the patent advises.
I’ll zoom in for a closer look.
As you can see, the lines that look like whiskers
get more squashed and the lines get closer
together as the Nickel increases.
This means that the high nickel material has
a lower energy capacity than the copper but
loses it more slowly as the battery cycles.
Tesla doesn’t explain in the patent whether
this is desirable or not.
In a typical battery cell, it’s best if
the battery retains its cycle life so that
battery lasts longer.
However, if the purpose of this material is
to dump all its lithium in the first cycle,
the remaining cycling ability may not be as
important.
In which case, the high copper material appears
to be the best option.
It doesn’t cycle well, has more energy capacity
which it dumps as lithium in the first cycle.
After running this series of tests, Tesla
goes on create a half battery cell and a full
battery cell using a wet slurry process.
I’ll explain what a half cell is in a moment.
In both tests, Tesla used two different samples.
Both samples included 1% binder and carbon,
for a total of 2% inactive materials.
This makes the maximum amount of active materials
98%, which is what Tesla focuses on here in
the half-cell results.
Sample 1 contained 98% NCA cathode material
and nothing else.
Sample 2 contained 96% NCA cathode material,
but also 2% of the LNCO pre-lithiation material.
A half battery cell is a battery cell that’s
tested in a lab environment and isn’t exposed
to all the reactions it would normally encounter
in an actual battery cell.
The primary purpose of that test in this case
is to verify that the material is meeting
the theoretical expectations.
As you can see, the expected and measured
energy capacity were nearly the same and were
probably within a reasonable margin of human
error.
Note the 4 milliamp hour per gram increase
when the LNCO pre-lithiation material is added.
This explains why Tesla is using a small amount
of the LNCO material mixed with the NCA material.
The LNCO material is so potent that it only
takes a small amount to increase energy capacity.
Finally, here is the full cell battery results
table.
Once again, the battery cell comes out 4mah/g
better off with the LNCO pre-lithiation material
added, both before and after cycling.
For each weight percent of LNCO material added,
it makes up for about 1% of the first cycle
loss.
We’ll come back to this.
Returning to figures 5, 6, and 7.
The figures in the red boxes are the numbers
that had a red strike through them previously
that I advised I’d cover in the summary.
I’ll attempt to explain these now.
These figures show the pre-lithiation material
is between 390 and 430 milliamp hours per
gram.
To put this in perspective, this is nearly
double the energy capacity of a typical high
end cathode material, which is around 200
milliamp hours per gram.
390 to 430 milliamp hours per gram compares
favourably to other materials that have been
researched.
One example is lithium doped nickel oxide
with no copper, which I’ve highlighted in
orange here and refer to as LNO.
The LNO material had a maximum lithiation
capacity of 340 milliamp hours per gram compared
to the Tesla LNCO material which averages
about 412 milliamp hours per gram.
The paragraph also advises that the difference
between the lithium doped state in the first
cycle and the state where the lithium has
been dumped by the LNO is 340 milliamp hours
per gram versus 83 milliamp hours per gram.
It goes on to state that even though the LNO
material had given up its lithium doping in
the first cycle, it still cycled somewhat
after that, but at a lower energy capacity.
I’ve noted the wording in red.
If that information can be applied to the
plots that Tesla provided here, it indicates
that those long diagonal lines that I’ve
now marked in blue are probably the first
cycle.
That would mean the whiskers are the subsequent
discharge and charge cycles after the battery
has given up its lithium.
It’s mostly inactive, but still provides
some benefit, which is much better than being
dead weight.
This leaves us a mystery, and potentially
an error.
My guess is that Tesla meant to swap the numbers
in the two boxes that I’ve connected with
an orange line.
It wouldn’t make sense for the capacity
to leap from 340 milliamp hours with pure
Nickel to 430 milliamp hours with 70% Nickel,
and then start falling again to 417 milliamp
hours and 390 milliamp hours.
Let’s change that, and see how the line
up of samples looks.
In this image, I’ve made the swap and added
100% Nickel as a comparison.
As you can see the energy capacity drops steadily
as Nickel increases.
This would allow all the information we have
from this patent and external research to
line up.
I could be wrong.
If you have a better idea, let me know in
the comments below.
I’ve reached out to one of the inventors
to see if I can get a response.
Tesla’s patent application didn’t advise
which of the LNCO mixtures they used in the
full cell test.
The Nickel content could have been very high
or very low, which would make a big difference
on the amount of LNCO additive that would
be required to eliminate first cycle losses.
Going back to our trusty Pre-Lithiation Strategies
paper, I’ve highlighted in purple that the
researchers found that 5% was enough to compensate
for first cycle losses with a 340 milliamp
hour per gram LNO Nickel material.
If Tesla’s high copper LNCO mixture reaches
at least 430 milliamp hours per gram, Tesla
might be able to completely eliminate first
cycle losses with less than 5% of the LNCO
material added to their cathodes.
This would mean a 7% or greater improvement
in the specific energy capacity of Tesla’s
batteries.
Bear in mind, these samples only went up to
70% copper, it might be possible to incorporate
even more.
Regardless, this would be enough to increase
the specific energy of Tesla’s current batteries
from 247 watt hours per kilogram to 270 watt
hours per kilogram.
How likely is this?
The patent application indicates to me that
the LNCO material is at an intermediate stage
of development.
It’s not a new idea, so it’s not early
state.
However, there was no long term cycling information
provided, so it may not be ready for commercialisation.
The long term cycling data would be needed
to determine if material causes battery degradation
over time.
Maxwell also appears to have a strategy in
mind for first cycle losses.
Their strategy may be very different from
the one we discussed.
However, they also indicate that eliminating
first cycle losses isn’t ready for commercialisation.
As you can see here in their roadmap, they’re
targeting a timeframe around 2027.
Regardless, it should be clear that Tesla
has been incubating multiple technologies
for their in house battery cell.
Battery day is expected to happen soon and
we’ll find out which of these technologies
Tesla has decided to commercialise.
I’ll see you there with a livestream on
the day.
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 John Navarro, Adam Sutton,
Bryce Langlotz, Kaushik Krishna VR, Matt Henderson
and Bradford Ferguson for your generous support
of the channel, and all the other patrons
listed in the credits.
I appreciate all of your support, and thanks
for tuning in.
