Welcome back everyone! I’m Jordan Giesige and this is The Limiting Factor.
At Battery Day, Tesla confirmed that they’re using Maxwell’s DBE or Dry Battery Electrode technology
to increase the production speed of lithium ion battery manufacturing by 7 times. However,
they didn’t cover the impact of DBE on their battery at the cell level. In this video,
I’m going to walk you through how DBE works at a microscopic level and why it might be part of the
secret sauce that Elon mentioned at Battery Day. 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 niche topics. Back to DBE.
As a quick refresher, DBE is used to coat active energy storing anode and cathode
materials onto the current collect foils of battery electrodes. It uses a dry process
rather than a wet slurry. DBE has nothing to do with solid state. Solid state batteries are
a type of battery that use a solid electrolyte material, whereas DBE is a manufacturing process.
I predicted Tesla would not only use DBE for their new battery manufacturing lines, but that those
lines would be at least 2-4 times faster than a conventional battery line. How did I know that
DBE would accelerate the manufacturing process by such a large margin? First, I found Maxwell
documentation from 2012 indicating that Maxwell was targeting a pilot production line speed
of 25 meters a minute. Second, I found research indicating that a standard wet slurry production
line is 5 meters minute at pilot scale. Based on this, I assumed that the 5 times
production speed increase at the pilot scale would hold true when the pilot lines were
scaled up to full size commercial lines. I then sandbagged the 5x figure to between
2-4 times speed increase. This is because there was no way to know if Maxwell was working off
the same definition of pilot scale as the research paper. We ended up getting 7 times speed increase.
Why? Probably because Tesla was able to improve on Maxwell’s 2012 technology. This is something
I thought might be possible, but I had no way to verify what I thought was a pipe dream.
In prior videos, based on the same research, I stated that Maxwell DBE
had other potential benefits that went beyond the improved manufacturing speed and we might
see improvements to cell performance. These improvements included lower heat generation,
higher power density, higher energy density, and longer cycle life. None of these benefits
were specifically called out in Tesla’s Battery Day presentation. This may be because DBE forms
part of the secret sauce for Tesla’s 4680 cell. I do think there are other herbs and spices
but we’ll get into those in later videos. Why do I think there’s a secret sauce? As
I mentioned in the introduction, Elon said on stage that there was some secret sauce.
Second, when I was watching the Battery Day presentation, I noticed that the range
numbers didn’t quite match up to the technologies those gains were attributed to. In other words,
they may not have been telling us everything that went into the sausage. By taking a closer look at
DBE technology we might get some answers. Much of the information I’ll be presenting
in this video comes from a doctoral dissertation by Brandon Ludwig.
If you’d like to go a lot deeper than I’m going in this video, I’d recommend checking it out.
To understand the benefits of DBE we first need to take a look at a wet slurry formed electrode at a
microscopic level. A special thanks to Peter Morain of Glacier Design for the animation.
Peter’s a friend of the channel and you can find his details in the description.
The large blue spheres we see here are about the size of red blood cells,
maybe a little larger. This is the typical size of cathode and anode active material particles.
In this case we’ll assume its cathode material. The small black spheres are carbon powder
that’s used to conduct electricity to and from the cathode particles to the foil
current collector. The thin film unevenly coating the cathode particles is binder.
The binder holds the cathode material together like glue and it’s non-conductive.
You might see a problem here. In some places the binder covers parts of the cathode particles
and it’s not actually gluing anything together. The only thing the binder
is doing in this situation is slowing down the flow of ions in and out of the cathode particle,
which reduces ionic conductivity. In other places, the carbon powder is
sandwiched between two particles with little or no binder. This is great for electrical
conductivity. However, without the bonding effect of the binder, the cathode doesn’t hold together
as well as it could and doesn’t stick to the current collector foil as well as it could.
This is called cohesion and adhesion. In summary, a wet slurry coating creates
disorganised and messy electrode coatings that are neither as durable nor as power dense they
could be. Power density refers to how quickly you can get energy out of a battery cell.
Why is the wet slurry coating so messy? During the wet slurry process, NMP, which is a toxic and
flammable solvent, dissolves the binder. When the slurry is dried, the binder comes out of solution
and haphazardly coats all the particles. This is a cathode that’s been formed with a dry
process. How did these clean structures form? During the mixing process, the binder and
carbon particles tend to stick to each other and then stick to the cathode particles.
This forms what looks like a black dough. To get the binder in the dough to bond,
the cathode is run through a heated roller to melt the binder and compress the material together.
This process forms a conductive yet adhesive matrix of point to point connections between
the cathode particles. This matrix maximises the ability of ions to exit
and enter the particles, enhances the electrical pathways between the particles,
and increases the strength of the entire electrode through better cohesion and adhesion.
How much stronger is DBE than an electrode painted with a wet slurry process?
If the same active material mixture is used for a dry process and wet process, and then compared,
the result is that the dry formed electrode is over 50% stronger.
That strength, combined with the additional conductivity gives us a few options:
The first is to change the ratio of active to inactive materials.
A wet slurry electrode is typically 90% cathode active material, 5% binder, and 5% carbon. With
DBE that can be improved to 98% active material, 1% binder, and 1% carbon powder. This would result
in an electrode that’s still more strongly bonded than a wet slurry electrode but has around 9%
greater energy density. However, with only 1% conductive carbon powder, the electrical
conductivity would decrease resulting in higher resistance and heat generation.
The second option is to keep the ratios the same, which would deliver a robust
and highly conductive electrode with no change to energy density. This electrode would have 50%
higher bonding strength and might be well suited to something like a high loaded silicon anode
that requires strong cohesion and adhesion to cope with the 400% expansion rate of the Silicon.
The third option is to find a happy middle ground that optimises
for both energy density and power density. These options are of course not as cut and dry
as I’ve made them out to be. In fact, Tesla may be able to optimise beyond what I’ve stated above
by finding a better, more elastic binder. Ryan Alvarez, who you may remember as the
Battery Day correspondent, found patents indicating that Maxwell was looking to
optimise the binder material. An optimised binder material might increase the margin that Tesla can
play with for energy and power density. For now, we’ll assume that Tesla decided
to take the power density path at the materials level with a standard ratio of active to inactive
materials. This will maximise the durability benefits to cope with a high silicon anode.
Power density, resistance, and heat generation are closely linked, so we’ll discuss them together.
Then, we’ll look at how these factors might affect Tesla’s 4680 battery cell.
One of the primary factors influencing heat generation and power density is resistance.
Resistance is like electrical friction in a battery cell. With greater friction comes greater
amounts of heat generation. Resistance also slows down the chemical reactions within a battery cell.
In other words, when a battery is quickly charged or discharged, it results in a kind
of lag. Energy is being pulled out of the battery cell more quickly than the
battery chemistry can reach equilibrium. This image shows that lag. In this test
the researchers compared a DBE vs a wet slurry chemistry at increasing cycling rates.
Cycling rate simply means how fast a battery is charged or discharged. A 1C rate is a
full charge or discharge in 1 hour. A 2C rate would be 30 minutes and a 3C rate would be 20
minutes. At a 3C rate, DBE performed nearly 20% better than the wet slurry chemistry.
In fact, the DBE at a 3C rate outperformed the wet slurry chemistry at a lower 2C rate by about 5%.
DBE clearly has benefits to charge and discharge rates. However, Tesla can apply those benefits in
several ways. For example, they could use the reduced heat generation, resistance,
and increased power density to instead increase energy density. Let’s look at how that could work.
Batteries can be engineered for power density or energy density by changing the thickness of
the cathode. A thicker cathode stores more energy because there is a higher
ratio of energy storing material to inactive material such as packaging.
However, with a thicker cathode, the electrons and ions have to work their way through more material,
meaning more resistance. Batteries are a closed system and there are almost always trade-off
decisions. In this case, the trade-off is between energy density and power density.
This chart illustrates the impact of cathode thickness on the energy capacity
per square centimetre for an example cathode. A regular cathode is around 56microns thick.
With a thicker 100 micron cathode, the energy capacity of the cathode more than doubles.
However, this chart shows us that with a thicker cathode, the battery quickly loses the ability to
achieve higher charge and discharge rates. As you can see, with a 100 micron cathode thickness at a
20 minute discharge rate, the energy output of the battery cell drops to almost zero.
100 microns would be an extreme jump from the 56 or so microns that Tesla is probably currently at.
Tesla could have found a compromise by picking a cathode thickness that’s slightly thicker
than 56 microns to gain an energy density boost while still maintaining power density
thanks to benefits of DBE. With a small tweak, Tesla could increase energy density by 5%.
It’s worth noting that in my interview with Shirley Meng,
she raised the potential of a thicker cathode. Based on those comments, a thicker cathode
seems like a very real possibility. Would Tesla take the energy density
route or the power density route? My predictions for Battery Day
were based on the assumption that Tesla would balance cost, the maturity of the technology,
energy density, and power density. However, Battery Day made it clear to me that Tesla is
ruthlessly and single-mindedly focused on cost, so long as it doesn’t have a negative impact on the
energy density, power density, and cycle life. DBE can basically provide a free increase to
energy density by increasing the ratio of active materials to inactive materials
such as electrode foils. This reduces costs without negative impacts and trade-off decisions.
However, where would the 5% increase in energy density fit in Tesla’s slide showing how all
their improvements stack? My view is that this improvement fits under the broad heading
of cell design. Cell design is much broader than just form factor. We’ll get into this
more deeply in the next video. It will take some analysis to pull apart that 16% figure.
At the beginning of the video, I mentioned that DBE also increases cycle life. If you’ve
watched previous videos, you’ll remember that Maxwell’s marketing material stated that DBE
could double cycle life. From what I’ve read in the research, DBE does improve cycle life,
but it doesn’t support a doubling. If DBE is used in the same ratio of active to
inactive materials that are used in a wet slurry chemistry, it increases cycle life by up to 50%.
The dissertation by Brandon Ludwig didn’t provide an explanation of why DBE might
improve cycle life. However, I’ll speculate here: • First, the NMP solvent might have a corrosive
effect on the cathode and anode materials. • Second, the additional cycle life could be due
to the increased durability of the dry battery electrode. As a battery cycles, the electrodes
expand and contract. Over time, this places stresses on the cathode and anode materials,
resulting in reduced battery life. • Third, the increased conductivity
of the dry battery electrode might help keep thermal degradation under control.
In summary, Maxwell’s Dry Battery Electrode technology provides several benefits that weren’t
discussed in the Battery Day presentation. Tesla can tweak the ratio of active to inactive material
in two ways: First, at the particle level by adjusting the ratio of binder
and conductive carbon material and second, by increasing or decreasing the thickness
of the electrode active material layer adhered to the foil current collector.
By turning the dials on these ratios, Tesla can manipulate the strength, cycle life,
energy density and power density of their battery cells. So far, we’ve only looked at one aspect
of the new battery. Once all the variables are stacked together, we’ll see that putting
all of this in the Battery Day presentation would have been like eating an elephant in one sitting.
In other words, they simplified the presentation for public consumption. This had the side benefit
of allowing Tesla to focus on the impact of the technology while protecting IP.
I could be totally wrong about DBE being part of Tesla’s secret sauce,
but its significance was definitely underplayed. I’d also speculate that now that Tesla is getting
close to mastering this technology, that the entire battery industry now rushing explore
it and recruit researchers that have worked with it at a lab scale. It’s worth noting
that there’s more than one way to implement DBE. For example, the dissertation referenced in this
video referred to a spray method. I wouldn’t be surprised if other
companies make announcements in the next few years to try and grab some media headlines,
capitalise on hype, and maintain relevancy. We’re seeing a lot of this lately. I don’t
think it was a coincidence that we saw so many battery related announcements in September.
However, I haven’t heard of any other company working with DBE that’s achieved
anything beyond pilot scale, let alone plans for terawatt hours. I expect it will be at
least 5 years before we see any other company deliver what Tesla plans to deliver next year.
The next video will be on Cell Design. We’ll discuss the tabless electrode, the larger form
factor, and we’ll dig deeper into what Tesla may not have been telling us on Battery Day.
If you enjoyed this video, please consider supporting me on Patreon with the link at the end
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A special thanks to Freddie Lewis, Fujio, Robert Valois, Darin J Douma,
Mark Hooker, John Hewling 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.
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