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.