Date:4 giu 2025A new video by Jordan Giesige on The Limiting Factor YouTube channel offers a clear and insightful explanation of how single wall carbon nanotubes (SWCNTs) enable unique advantages in lithium-ion batteries, particularly in silicon-rich anodes.
The video highlights key performance improvements already validated in numerous scientific studies. It also explains why, despite their higher cost compared to multiwall carbon nanotubes (MWCNTs) or carbon black, use of single wall CNTs can ultimately lead to cost reductions by enhancing battery performance and efficiency.
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Welcome back everyone! I’m Jordan Giesige and this is The Limiting Factor. Carbon nanotubes can be used in lithium-ion batteries to unlock higher energy densities and faster charge rates. The question is, will such a difficult-to-manufacture and expensive material ever actually be used in mass-produced lithium-ion batteries?
Much to my surprise, it’s already happening, and for me, it’s rewriting the script on one of the technologies that Tesla teased at Battery Day.
Before we begin, a special thanks to my Patreon supporters, YouTube Members, and Twitter subscribers as well as Rebellionaire.com. They specialize in helping investors manage concentrated positions. Rebellionaire can help with covered calls, risk management, and creating a money master plan from your financial first principles.
Let's start by looking at the roles that carbon nanotubes can play in a lithium-ion battery.
Nanotubes can play in lithium-ion batteries. When the electrode foils of a lithium-ion battery are coated at the factory, the coating is made of a powder mixture that contains three ingredients: the active material particles, which make up about 95% of the powder or more, and about 5% additives.
The two additives are carbon black, which improves the electrical conductivity of the electrode, and polymers that help hold the electrode film together and stick to the electrode foil.
Carbon nanotubes help with both binding and conductivity because they're orders of magnitude more conductive than carbon black powder and, due to their stretchy, string-like nature, they can help hold the electrode film together. That is, carbon nanotubes can be used as a replacement or in conjunction with existing additives to increase the performance of lithium-ion batteries.
That's backed up by a paper from Jeff Dahn's lab, which is Tesla's research partner, titled Optimization of Si-containing and SiO-based Anodes with Single-Walled Carbon Nanotubes for High Energy Density Applications. The conclusion of the paper says:
"The strong positive effect of carbon nanotubes is undeniable even when used in small amounts. The use of CNTs in SiO/Gr composite electrodes in an amount of only 0.2% allowed the use of any binder to enable good capacity retention over 100 cycles. Although not inexpensive, the addition of these CNTs allow the use of simple binders that favor slurry processing to reduce cost... This data shows that overall electrical connectivity of the anode through the use of SWCNT is an important part of maintaining anode capacity in high volume expansion active material."
Translation: Although carbon nanotubes are expensive, they're potent and can be used in tiny amounts in standard processes and with simple binders, which may make them commercially viable.
Furthermore, carbon nanotubes could be very useful for anodes that use high loadings of silicon. Higher loadings of silicon are the next likely step for increasing the energy density of lithium-ion battery cells, but due to the fact that silicon expands by several hundred percent when the battery charges, it causes the electrode to disintegrate.
Currently, the loading of elemental silicon in lithium-ion battery cells is limited to about 4% by weight, but increasing that to 20%, for example, could increase the energy density of lithium-ion battery cells by 20%.
The research that Jeff Dahn's lab has done on nanotubes, and the fact that they're Tesla's research partner, made me rethink my initial analysis from my Battery Day series.
In Tesla's Battery Day presentation, they said they would use a highly elastic binder to help deal with the expansion issues from silicon. At that time, I concluded that Tesla might use polyrotaxanes, or self-healing polymers for the binder.
Now that I've researched carbon nanotubes, they seem like the better choice. That's because carbon nanotubes can be used at less than 1% of the electrode by mass versus the 5% that would be necessary with polyrotaxanes. That 5% of additional material would mean about a 2–3% energy density penalty, which would negate some of the positive energy density benefits of using silicon.
Furthermore, the availability of carbon nanotubes has increased greatly in the past 5 years since Battery Day. In 2020, there wasn't yet a large-scale supplier of the type of carbon nanotubes that Tesla would need, but that has now changed.
With all that background on nanotubes in place, let's get more specific on factors like performance, cost, and scalability.
With regards to performance, it's important to start by teasing out the specific type of carbon nanotubes that I'm referring to in this video, which are single wall carbon nanotubes.
Single wall nanotubes have, as the name indicates, a single wall, and multi-wall nanotubes have several layers of walls.
As far as I'm aware, OCSiAl has the best publicly available slides and information on carbon nanotubes, so I'll be using several of their slides today. To be clear, OCSiAl hasn't sponsored this video. The only sponsor I have and have ever had is Rebellionaire.
As you can see on screen, single wall carbon nanotubes have a clean and long structure. That's as opposed to multi-wall carbon nanotubes, which have a structure that's gnarled and tangled.
Single wall carbon nanotubes are more difficult to manufacture, but it's worth it. As the paper from Jeff Dahn's lab points out, they're highly flexible, have strong adhesion, and show huge tensile strength. By comparison, multi-wall carbon nanotubes are less expensive, but are often very stiff and short with much less adhesion strength.
The takeaway here is that single wall carbon nanotubes are far more potent as an additive and can do things that multi-wall carbon nanotubes simply can't.
For example, due to their conductivity, flexibility, adhesion, strength, and length, single wall carbon nanotubes are uniquely able to loop through the electrode film, providing both a conductive electrical network and reinforcing it against expansion and contraction forces.
As this image from the Dahn research paper shows, for a 92% silicon anode, with no carbon nanotubes, after 100 cycles, the test cells have about 150 milliamp-hours per gram of capacity remaining. With 0.25% single wall carbon nanotubes by mass, there's about 1000 milliamp-hours per gram of capacity remaining after 100 cycles. And at 0.5% by mass, degradation remains relatively flat and is minimized after 100 cycles, with 1300 milliamp-hours per gram of capacity remaining. Adding more nanotubes to 0.75% had minimal further beneficial impact.
What this means is that single wall carbon nanotubes could unlock higher loadings of silicon in the anode to increase energy density. But, to be clear, as Tesla showed at Battery Day, other technologies will also be required as well, such as a polymer coating on the silicon to keep it from reacting with the electrolyte.
What about electrodes that don't use silicon — would using single wall carbon nanotubes provide any benefits? Yes, in three ways.
First, due to their higher conductivity, single wall carbon nanotubes lower the resistance of lithium-ion battery cells. That reduces heat generation, allowing the battery to charge and discharge more quickly without increasing thermal strain and therefore causing degradation. That effect wouldn't be dramatic because most of the resistance in a battery cell is from the ionic resistance, but the improved electronic conductivity from carbon nanotubes might be good for a 10% improvement in charging speed.
Second, due to the strength and flexibility of carbon nanotubes, the electrodes can be made thicker without cracking. Thicker electrodes mean higher energy density battery cells because it increases the ratio of active to inactive material. Again, the impact wouldn't be huge, but 5–10% higher energy density wouldn't be unreasonable.
Third, by replacing the 2–3% carbon black that's used in conventional electrodes with a fraction of a percent of nanotubes, the dead weight that's removed could increase the energy density of the battery cells by around 1% or so.
That is, there would be benefits to using single wall carbon nanotubes in conventional battery chemistries, but most of the benefit of nanotubes would come from unlocking the potential of higher silicon battery cells, with up to 20% greater energy density over time.
Let’s move on to cost. OCSiAl provided cost reference figures, which are shown on screen. They claim that battery-grade carbon black costs $7/kg and 1–3% by mass is needed in the electrode; multi-wall carbon nanotubes cost $50/kg and 0.6–1% is needed; and for their single wall carbon nanotubes, the price is about $1,000/kg at volume, with only around 0.05% needed in the electrode depending on the application.
Why does OCSiAl suggest 0.05% single wall carbon nanotubes by mass, when Jeff Dahn’s research showed that 0.5% was needed? It’s because Dahn’s tests were run on anodes with a 92% silicon loading, which is extreme. For a more reasonable 10% silicon loading, only about 0.05% nanotubes are needed. In other words, roughly an order of magnitude less silicon requires an order of magnitude less nanotube material.
As a side note, I checked OCSiAl’s cost figures using Grok DeepSearch, and all of them came up higher, even for carbon black. My assumption is that OCSiAl is using information that’s more up-to-date than what the AI had access to.Since these industries are scaling fast, it’s expected that the prices being quoted to bulk customers are dropping year by year. But if you have better cost figures, let me know in the comments below.
With that in mind, even though there is potential for bias, I’m going to consider OCSiAl’s figures realistic—but take them with a grain of salt.
Moving along, whether the application is for conventional lithium-ion battery chemistries or high-silicon anodes, OCSiAl indicates that single wall carbon nanotubes add about $1 per kilowatt-hour. That compares to about 20 cents for carbon black and 60 cents for multi-wall carbon nanotubes. In other words, it’s not cost prohibitive. In fact, if single wall carbon nanotubes enable high-energy-density, high-silicon anodes, the reduced battery pack weight could actually save money.
For example, if the battery pack in the Tesla Semi is roughly 900 kWh, carbon nanotubes would add about $720 to the cost of the pack. But if the nanotubes enabled a 10% energy density increase through higher silicon loadings, that would cut about 529 kilograms of mass from the battery pack. Over the Semi’s million-mile lifespan, that’s half a tonne of additional cargo per trip,
or half a tonne less mass causing wear on tires and the powertrain. In the case of Tesla’s premium vehicles, like the Model S or Cybertruck, it could allow for 10% more range at a cost of about $70–86 on a 100–123 kWh battery pack. This could also apply to versions of the Model 3 and Y. However, for mid- to low-cost vehicles, the extra spend may not be worth it-especially for commercial use cases that are cost sensitive but not mass sensitive, like the Cybercab.
Next, what about scaling? I found a number of companies that are producing single wall carbon nanotubes at gram to kilogram scales, but no other company besides OCSiAl seems to be producing them at the scale of tens of tons per year or more. In 2024, they completed a production facility with 60 tonnes of annual production capacity. That is, they have a full-scale commercial production facility that's already operational. Beyond that, they have plans for 240 tonnes of annual production capacity by 2026 and 1,000 tons of annual production capacity by 2030 with continued scaling from there.
The question is, how many EVs is that enough for? According to this slide from OCSiAl, which I double-checked the math on, the average EV uses about 3–4 kg of carbon black, and that could be replaced with about 100 g, or 0.1 kilograms, of single wall carbon nanotubes. That means 1 million vehicles require about 100,000 kilograms, or 100 tons.
So OCSiAl currently has nanotube production capacity for about 600,000 vehicles per year, with plans for 2.4 million vehicles of production capacity by 2026, and 10 million vehicles by 2030. That is, they already have plenty of capacity in place for one medium-sized EV maker and plans for enough production capacity to supply several large EV makers like Tesla. And, I don’t doubt that in the coming years other companies will follow suit to build a broader-based and more competitive single wall carbon nanotube supply chain.
This brings us to the last question of the video. Will Tesla use single wall carbon nanotubes? As I've shown in the past, spider silk-like threads can be seen in the anode in Tesla's 4680 cells. However, that's been confirmed through chemical analysis by UC San Diego to be the PTFE, or Teflon, that's used in Tesla's dry coating process.
PTFE is flexible and has some strength as a binder, but it's an electrical insulator. The ideal material for binding a high-silicon anode would be much stronger, flexible, and electrically conductive like carbon nanotubes. However, PTFE can't be replaced with carbon nanotubes because it's necessary for the dry electrode coating process. It turns the electrode powder into a kind of dough that can be laminated onto the electrode foils.
So, if the PTFE can't be replaced, could Tesla still add carbon nanotubes to the powder mixture to provide additional binding capacity and electrical conductivity? According to Tesla's patents for the dry coating process, yes.
Does this mean Tesla will use single wall carbon nanotubes in their batteries in the future? I'm not sure, but in my view, so far, they're the best candidate yet for the filaments that Tesla showed in their silicon anode illustration at Battery Day.
The sticking point for me is that Tesla doesn't like to be reliant on single-source third-party supply because it creates supply chain risks. Additionally, it's likely that Tesla doesn't want to be in a situation where the supplier is wagging the dog.
The only solutions I see to that are for Tesla to vertically integrate into carbon nanotubes, wait for the nanotube supply chain to expand, or buy a controlling share in a nanotube manufacturer. They could also become the primary customer of OCSiAl with huge material supply agreements like Tesla at one time did with Panasonic, but that could be risky.
With that said, those risks could be mitigated if Tesla had employees embedded and working with the team at OCSiAl.
As a final note, I did double-check with people in the industry about whether carbon nanotubes are currently being used in lithium-ion batteries, and they are. That is, carbon nanotubes are no longer a future technology, but an off-the-shelf technology. That's particularly true with multi-wall carbon nanotubes, which are already being produced in the tens of thousands of tons per year.
In summary, single wall carbon nanotubes are here and already used in lithium-ion batteries. For conventional battery chemistries, they provide more of an incremental rather than revolutionary improvement, with lower resistance for slightly faster charging speeds, thicker electrodes that could lead to 5–10% more energy density, and a reduction in dead weight in the battery that could increase energy density by around 1% or so.
However, where single wall carbon nanotubes appear to be uniquely useful is for future battery chemistries that use higher silicon loadings, which could provide a base for the next 20% of energy density increases that we'll see in mass-produced automotive EV battery cells in the next 5–10 years.
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