Welcome back everyone, I'm Jordan Gisighi and this is the limiting factor. After a dry spell for Tesla patents, several Tesla patent application documents came to light in January and February of this year. The first which I'll cover today is titled Elemental Metal and Carbon Mixtures for Energy Storage Devices. What that basically translates to is Tesla's found a way to add highly volatile lithium metal directly to their dry electrode coating process to boost the energy density of their battery cells. Today I'll walk you through the history of the patent application, alternative lithium doping processes, how Tesla's process works and why if they get it working in full-scale production that it may end up being the most commercially viable lithium doping process on the market.
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Let's start with the history of the patent. If we look at the Tesla patent application that was published in February of this year, we can see that in the related US application data, this patent application is actually a continuation of two other patent applications. If we pull up the first application on Google Patents, we can see that Maxwell Technologies filed the original patent application in February of 2017. Then they were granted a patent for that application in October of 2019. Of course, in the interim, Tesla acquired Maxwell Technologies. So as we'd expect, a couple of years after the acquisition, Tesla had the patent assigned under their name in 2021. This for the second patent application, it was filed by Tesla Post-Aquosition in October of 2019 and a patent was granted in December of 2022. The third and final application is the one we see on screen. This is the document that showed up on the radar of the Tesla community and has not yet been granted a patent.
Why is Tesla filing what appears to be redundant patent applications? As with any litigious or bureaucratic process, if you don't get what you want the first time, you work the process if you think you can get a better outcome. So that's what Tesla appears to be doing. In the patent application, Tesla claims they've invented several ways to dope the electrodes with lithium. They've received patent grants for some of those claims, but not all. So they're working with the patent office to amend the wording to get as many of their claims patented as possible.
I won't go through all the claims today in detail and their history because they're 78 and because we don't know which of the claims are most important to Tesla. And that's something that not even Tesla may know at this point if they're still developing the technology. They just want as much freedom to navigate as possible from an intellectual property perspective. The 10,000-foot view is that it appears the patents they've received so far are mostly related to using electrolyte vapor to form a protective SEI layer on elemental lithium. I'll explain how that works later in the video when we get deeper into Tesla's patent application.
So to be clear, what we're looking at today is actually an application for which Tesla's already been granted a patent. It's just that the previous patent applications and patents weren't spotted by the Tesla community. Thanks to the new patent application, they're now on my radar, and I view them as important. Let's look at why, starting with an understanding of what lithium doping is, how it's usually done and how Tesla's process differs.
The first time a battery is charged and discharged, some of the lithium and the electrolyte reacts with the graphite anode to produce what's called a solid electrolyte interface, or SEI. That's a good thing because it protects the graphite anode from degradation. But it's also a bad thing because it choose up lithium and the battery cell that can no longer be used to store energy. I've seen several figures float it around, but typically, for a graphite anode, first cycle losses appear to be around 6 to 7%.
What if you were somehow able to replace the lithium that was lost when creating the SEI? This is what's called lithium doping, and the more technical term for it is pre-lithiation. If we take a typical 2170 battery cell with around 270 watt hours per kilogram of energy density and dope it with lithium to cover the first cycle losses, the energy density would be up to 288 watt hours per kilogram. That's not a massive increase in energy density, but it's certainly significant.
The 6 to 7% increase is only for a graphite anode. What if we used a silicon anode? Silicon can store 10 times more lithium than graphite per unit of weight. However, it expands and contracts by about 300% when it's lithium and de-lithiated. During other degradation mechanisms, that expansion and contraction destroys the SEI layer, which then reforms itself, except thicker. And of course, a thicker SEI choose up more lithium. This is one of several reasons why high-loaded silicon anodes haven't yet been fully commercialized.
How much lithium is lost in the first cycle with a silicon anode? That depends on how much silicon is used. Let's use applied materials pre-lithiation process as an example. According to this slide, with an anode that uses about 30% silicon oxide with graphite, around 20% of a lithium is lost in the first cycle and can be replaced by their pre-lithiation process. In another slide, they go on to say that results in about 20% higher gravimetric and 25% higher volumetric energy density, while being about 2% cheaper than a battery cell with a typical graphite anode. Again, using the 2170 as a benchmark, that would mean around 323 watt-hours per kilogram gravimetric and 900 watt-hours per liter volume metric energy density.
Obviously these things happen incrementally, and I'm not expecting to see silicon loadings of up to 30% with lithium doping and a mass-produced product until the end of the decade. However, when that time comes, whoever has the lowest cost process will have a significant advantage in the market.
Given that note, with the benefits out of the way, let's look at how lithium doping is usually done and then compare that to tezeless process. In a typical battery cell production process, the electrode foils are coated with a wet slurry, which is then dried like paint to form the electrode. Due to the fact that the slurry is a liquid, you can't just add lithium metal powder directly to the coating mixture. Why? Because lithium metal is highly reactive to many solvents, like water. Beyond that, it's even reactive to nitrogen in ambient air, and it quickly reacts to form a lithium nitride layer.
The reaction happens quickly enough that you can watch it in real time here. That is, doping with lithium metal requires either a moisture and nitrogen-free environment, or a way to protect the lithium metal throughout the manufacturing process. There are a number of ways that can be done, but I'm just going to cover one. If you'd like to know the others, check out this Pre-Lithiation Strategies paper by Florian Holchstiga at Al.
The process we're going to cover is called a direct contact process. It starts by coating an electrode foil with a typical wet slurry process, and then drying it to remove all the moisture. Then lithium is placed in direct contact with the electrode, as stabilized lithium metal powder, or SLMP, lithium strips, or a lithium film. This of course has to be done in an environment that's free of moisture and ambient air. For example, in the image on screen, the Pre-Lithiation is occurring in an argon glove box.
SLMP is the most commonly used form of lithium for Pre-Lithiation. It's lithium metal powder that has a shell of lithium carbonate. The benefit of the lithium carbonate shell is that it makes SLMP more robust to ambient air. However, it comes with drawbacks. First, the shell adds a production step, which makes SLMP more expensive than pure lithium metal. Second, the shell contains some dead weight due to the carbonate. Third, SLMP still isn't stable enough to be used in a conventional wet slurry process and reacts with the solvent.
Some researchers have experimented with using solvents that SLMP doesn't react to like polyuein. However, SLMP tends to float in the polyuein, causing dispersion issues, so thus far it's not commercially viable. Regardless, even if it did work, there's another step required for SLMP. The lithium metal particles have to be cracked to expose the lithium. That has to be done in an inert gas environment like argon, or with the electrode soaked in electrolyte.
So really, the only problem that SLMP seems to solve is that it's more stable for shipping and handling. After the lithium metal or SLMP is placed in contact with the graphite, electrolyte is injected and it takes time for the lithium to litheate the graphite.
The visual cue for that is that as the graphite is litheated, it turns yellow. A final complication here is that if there's excess lithium remaining after litheation, it can cause degradation issues, so the doping has to be both even and precise.
Outside of using SLMP, the best solution I've seen so far is to use an ultra-thin film deposition technique after the active anode material is coated to the electrode foil. That appears to be what applied materials is doing. However, that still requires extra manufacturing steps and specialized equipment.
This brings us to the innovations of Tesla's lithium doping patent.
这将引出特斯拉锂掺杂专利的创新。
Starting with some background, as I said earlier, Tesla acquired Maxwell Technologies in 2019. Tesla had an interest in Maxwell because Maxwell had spent over a decade developing the dry battery electrode or DBE technology.
DBE doesn't require the use of any solvents to coat the electrode foils with active material. Instead, the active materials are mixed with a polymer binder which acts like bubble gum to hold the electrode together and stick it to the electrode foil.
You might already see the immediate benefit of DBE for lithium doping. Unlike a wet slurry process that uses a solvent that lithium metal can react to, with a dry process there's no solvent and the lithium metal can be added directly to the coating mixture.
This is what's at the heart of Tesla's lithium doping patent. However, it's of course a little more complicated than that because the elemental lithium still needs protection from ambient nitrogen.
With that in mind, let's take a look at Tesla's patent claims. In the patent they describe several process flows for lithium doping and each of those process flows can have variations at each step.
Given the number of potential options here, let's look at what they have in common and go from there.
考虑到这里有很多潜在选择,让我们先看看它们有什么共同点,然后再做决定。
All of the processes involve using a mill or blender to combine carbon particles with lithium metal. Hydrogen particles can be porous carbon or graphite and the lithium can come in any form from lithium powder to lithium sheets.
Then to further complicate things, the mixing can involve three other variables. First, it can either occur in a dirt gas like argon or electrolyte vapor. Second, the time, temperature and pressure of the mixing can be adjusted. Third, the pre-lithiated mixture can be mixed separately from the dry battery electrode mixture in a two-step process or all the mixing can take place in the same machine.
Given all the options here, there's no way to know which combination turned out the best for Tesla.
在这里所有的选项中,没有办法知道哪种组合对特斯拉来说最好。
With that in mind, I'm going to describe two potential lithium doping pathways that give a feel for the patent and the technology toolkit that Tesla is working with.
考虑到这一点,我将描述两种潜在的锂掺杂途径,以便感受到特斯拉正在使用的专利和技术工具箱。
The first lithium doping pathway uses what the patent calls active carbon. I'm assuming what they're referring to here is the same or similar to the activated carbon that's used in air filters. Activated carbon is basically carbon particles with small cracks in them.
What Tesla suggests is using those cracks to store lithium, which creates a litheated carbon composite material. That composite can then be added to an anode to act as a lithium doping. The question is, how do you get the lithium into the cracks and protect the composite from reacting with ambient air?
The patent explains that one way to do this is to blend the lithium with activated carbon and argon gas at over 180 degrees Celsius. The lithium doesn't react with the argon gas and the lithium melts at 180 degrees Celsius.
The active carbon is robust to those temperatures, so remains in its solid form. As the mixture is blended, the melted lithium metal impacts the activated carbon and then it sucked into the cracks through capillary action.
The result is litheated carbon. Then after the litheated carbon is formed, a polymer can be introduced into the jet mill to form a protective layer over the lithium carbon composite particles.
That protective layer stabilizes the particles so that they don't react with ambient air and can be used as raw material in a dry process.
这个保护层稳定了粒子,使其不会与环境空气发生反应,并可用作干燥工艺的原材料。
The second lithium doping pathway is to use graphite instead of porous active carbon particles. Argonne is again provided as an inert atmosphere, but the gas doesn't necessarily have to be heated this time.
This is because the lithium is simply used to coat the graphite and no capillary action is required. Lithium is a relatively soft metal and the action of the jet mill is enough to adhere the lithium metal to the graphite particles.
Once again, the lithium needs a protective coating so that it doesn't react with the ambient air. This time, instead of using a polymer to create the protective coating, electrolyte vapor is introduced into the mixing chamber.
This causes a protective SEI layer to form over the lithium metal. Interestingly, this not only allows the lithium coated graphite to be used in a dry electrode coating process, but also allows it to be used in a standard wet slurry electrode coating process.
Let's zoom out to look at how the lithium coated graphite and lithium carbon composite particle can be used in the broader electrode coating process.
让我们放大视野来看看锂包覆石墨和锂碳复合颗粒在更广泛的电极涂层过程中如何使用。
Earlier, I said that Tesla's DBE process combines active materials with a polymer binder that acts like bubble gum to hold the electrode together and stick it to the electrode foil. Of course, bubble gum has to be chewed in order to maximize its stickiness, in a sense the same thing happens with the polymer binder.
It starts out as micro particles that are mixed with the active energy storing materials. Then a jet mill is used to stretch the polymer into filaments, which is called fibralization. The fibrelated polymer turns the mixture into a kind of dough that can be run through rollers to form a standing film and then compressed onto an electrode foil.
You may have noticed that Tesla's dry electrode coating process uses a jet mill and the process they use to produce lithiated material also uses a jet mill. Clearly, there's an opportunity here to complete all those operations in the same machine. That's exactly what's being shown in the image on screen from Tesla's patent application. Although a bench scale blender is used in this example, the basic concept is the same.
Figure 8A shows the lithium metal and graphite ready for blending. Figure 8B shows the blended graphite and lithium metal mixture. And Figure 8C shows the mixture after the polymer binder or PTFE has been added. They've left out the step where a polymer coating or electrolyte vapor is added to stabilize the pure lithium metal. Let's add that as Figure 8B1.
After Figure 8C, the lithium-doped mixture would simply be treated the same as Tesla's standard dry coating material. It would be fed into a series of rollers to form the negative electrode. Obviously, there's a lot of complication that's left out here. This wouldn't be carried out in low volume single batches in a fume hood with a full-scale process.
First, in a full-scale process, an industrial-sized jet mill would be used to process larger volumes of materials. Second, rather than single batches, this would have to be turned into a continuous motion process. That means finding a way to generate enough constant throughput with one machine or by switching off between a series of machines.
Then of course, there are the more tactical issues. For example, how to feed lithium metal into the jet mill while keeping it isolated from ambient air. How to control the feeds of argon gas and electrolyte vapor to create consistency across batches, and given that molten aluminum might be used, would that begin to form solid lithium deposits on the walls of the mixing chamber?
These are just wild guesses on my part, so if you have experience with jet mills, please share your thoughts in the comments below. Regardless whether they're correct or not, they're the first and a long list of the type of challenges that need to be addressed to move something from a patent to an actualized production process.
Either way, if Tesla can get this process to work, what their proposing looks like, it would be significantly simpler, faster, and cheaper than anything else on the market. Instead of requiring an extra processing step where the pure lithium is coated on top of the active electrode material, the lithium is simply added to the mix of materials that coat the electrode in the first place.
I'd like to emphasize here that although the basic concept is simple, this would be a hell of an engineering challenge, and I don't think we'll see Tesla doing it anytime soon. This is because they're currently preoccupied with scaling the basic process. However, when they do turn their attention to lithium doping, they have the patents in place to do it without modifying their existing production lines.
In summary, as I've said in the past, if Tesla can get it fully scaled, their DBE process will be far superior to a wet process. Why take dry material, turn it into a slurry, only to dry it again, and then to wet it with electrolyte when it goes into the battery cells. It's the old digging the hole, filling the hole, and redigging the hole analogy.
Now we see another advantage with the dry processing technique and another reason why Tesla bought Maxwell technologies. Maxwell not only had the DBE patents, but also patents for a clever way to do lithium doping, which allows them to place lithium metal directly in, too, the jet mill that's used to create the dough that's used to coat the electrode foils.
If Tesla put their lithium doping process in production, what would the impact be for their 4680 battery cells? With regards to cost, based on this slide by applied materials, the minimum savings look to be around 2% on a dollar per kilowatt hour basis.
But of course the process applied materials is using would require specialized equipment and an extra process step. If I were to guess, I'd say that Tesla would be saving 50% to 100% more than applied materials, which would be 3 to 4% of the cost of a battery cell.
Why not more? Because the cost of a battery anode is already half the cost per unit of weight and twice the energy density of the cathode. Furthermore, there are also a number of other materials in the battery cell like metal foils, electrolyte and separators that dilute the cost savings effect.
That means any improvements to the anode have a minimal impact on cost at the cell level. This is why at battery day, although Tesla teased cheaper anode materials with 20% greater range through higher energy density, the impact on cost was only 5%.
However, bear in mind that batteries are expensive and vehicles use a lot of them. So a cost savings of only 3 to 4% at the cell level would be around $200 per vehicle, which is $200 million for each million vehicles produced.
Furthermore, that doesn't include the fact that a vehicle using battery cells that are doped with silicon and lithium would also be a couple hundred pounds lighter, making them more efficient and reducing structural costs, which brings us to energy density.
First, some caveats. For the next couple of years, Tesla's focus will be on optimizing their battery cells and production system. Chemical approaches for improving energy density are probably further down on their list of priorities.
For example, the generation 2 battery cells that are being produced in Austin will probably see at least a 5% energy density improvement at the cell level alone by making better use of the 4684 factor and removing redundant components. That doesn't include the myriad of improvements that will also be happening with the current overbuilt 4680 pack.
The pack level energy density is just as important as the cell level energy density, and the new pack design will take time to optimize. That is, lithium doping is probably something Tesla won't be doing for a few years, but when they do focus on it and master the process, for a pure graphite anode it would improve energy density by 6 to 7%.
And that's small potatoes compared to what's possible. Tesla teased a 20% range increase at battery day through the use of more silicon and the anode. Let's say that range equates to energy density to keep things simple.
As I've said in past videos, that 20% figure would be difficult to hit without lithium doping. However, with lithium doping and advancements in silicon anode technology in the longer term, 20% might be at the lower end of what's possible.
With that said, let's stick with 20% as a safe figure because I expect to see that by 2026 at the earliest. For a high nickel battery cell, that would mean around 326 watt hours per kilogram. And more importantly, a much faster charging rate because silicon can absorb lithium much quicker than graphite.
For me, where lithium doping is most interesting isn't an ultra high energy density battery cells, but in lower cost LFP battery cells that are easier to scale. In a Tesla Model 3, a lithium doped LFP battery cell in a mature 4680 battery pack architecture would be pushing well over 300 miles of range with no silicon and 350 miles of range with silicon.
对我而言,锂掺杂最有趣的地方不是超高能量密度电池,而是更易于扩展的低成本LFP电池。在Tesla Model 3中,成熟的4680电池组架构中锂掺杂的LFP电池将能够达到超过300英里的续航里程,无硅的情况下续航里程可以达到350英里。
Again, this is years away, but that's where Tesla's headed in the long run if they can capitalize on all the technologies that they have patents for.
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