Welcome back everyone, I'm Jordan Geisigee, and this is The Limiting Factor. Joe Tegbier recently posted on X that Tesla is trialing asymmetric lamination of their electrodes for their 4680 battery cells, which is expected to contribute to a 10-20% increase in energy density. Normally, I don't cover rumors, but asymmetric lamination appears to be a technology with a lot of potential that, strangely, there's almost no research on. By doing a video on the topic, I'm hoping to draw some experts out of the woodwork for feedback because it almost looks too good to be true.
So today, I'm going to walk you through what I think asymmetric lamination is, how it might improve the energy density of the 4680, and the challenges it faces, like cycle life and manufacturing issues. Before we begin, a special thanks to my Patreon supporters, YouTube members and Twitter subscribers, as well as Rebellionair.com. They specialize in helping investors manage concentrated positions. Rebellionair can help with covered calls, risk management, and creating a money master plan from your financial first principles.
Additionally, for this video, thanks to Billy Wu, Yuka Joravanen, Tom Vaid, and Dr. Yuho Heiska on X, who helped me piece together an understanding of how the electrochemistry of an asymmetric electrode might work. If you're on X, give them a follow.
此外,对于这个视频,我要特别感谢 Billy Wu、Yuka Joravanen、Tom Vaid 和 Dr. Yuho Heiska 在 X 上对我阐释不对称电极的电化学原理方面所给予的帮助。如果你也在X上的话,可以关注一下他们。
Let's start with the source of the asymmetric lamination rumor. Joe Techbier does regular drone flyovers of Giga Austin, where Tesla's 4680 production is located. But more than that, has become a valuable source of intel and analysis on Giga Austin. I highly recommend following Joe on YouTube and X if you're interested in the developments there. But as always, even with trusted sources, information can often get garbled as it passes between people. With that in mind, let's evaluate the rumor.
Joe's post states that Tesla is, quote, trialing asymmetric lamination, with one side of the laminated material thicker than the other. The expectation is this will increase the amount of jelly roll that can fit into the 4680 can. End quote. For those who aren't familiar with the construction of a battery cell, the jelly roll is a roll of several layers of plastic, metal, and active material that's inserted into the cell can, soaked in electrolyte liquid, and then sealed during the manufacturing process. On screen is how one set of layers in the jelly roll look in a cross-sectional microscopic view.
The negative electrode or anode, there's a copper foil that's coated with graphite. There's an inner and outer separator to electrically isolate each set of layers, and for the positive electrode or cathode, there's an aluminum electrode foil that's coated with particles that contain lithium metal oxide. The graphite anode and the lithium metal oxide cathode are the parts of the battery cell that participate in the chemical reactions that store and release energy. That is, they're active materials. And although the rest of the materials like the current collectors do serve a function, they're considered inactive because they don't store or release energy.
So when Joe says that asymmetric lamination will increase the amount of jelly roll that can fit in the 4680 can, what he likely means is increasing the ratio of active to inactive material. An obvious way to do that would be to laminate a thicker coating of cathode and anode material onto the electrode foils. That in turn would increase the energy density of the 4680 by increasing the proportion of energy storing material in the cell can. So why don't battery cell manufacturers, Tesla included, just laminate the active material as thick as possible on both sides of the electrode foil to increase energy density.
Two reasons. First, because with a typical wet coating technique, when the electrode is coated too thick it can cause defects in the electrode. For example, as one viewer, LifeWalk pointed out, the anode can stratify into its component materials during the drying process. As a result, for a single layer lamination, cell manufacturers usually coat the electrode with 50 to 80 microns of active material. However, Tesla doesn't use a wet coating technique. Instead, they use a dry coating process where the active material, polymer binder, and conductive carbon powder are mixed into a kind of dough. And then laminated onto the current collector using heat and pressure.
The dry coating process is able to laminate an ultra thick active material layer of up to 1 millimeter, which is over 10 times thicker than a typical wet coated electrode. In fact, Tesla's already using that advantage to coat their electrodes 50% thicker than the battery cells they purchase from, for example, LG Chem. But going even thicker might create challenges. Let's continue.
The second reason why manufacturers don't laminate the electrode as thick as possible is because although making the active material thicker does increase energy density, it also reduces the charge and discharge rate of a battery cell. Just because a thicker active material layer slows down the flow of ions that occurs between the cathode and anode when the battery cell charges and discharges.
So the choice comes down to thicker anodes that increase energy density versus thinner anodes that offer faster charge and discharge rates. This is where asymmetric lamination could help. Joe states that asymmetric lamination means making one side of the laminated material thicker than the other. If one side of the electrode foil is coated with active material much thicker than usual for increased energy and the other side is coated the same thickness or slightly thinner than usual for increased power, then the battery cell should, overall, have higher energy density while at the same time offering as good as or better charge and discharge rates.
The only catch would be that the thinner electrode facings that offer higher power density would probably only store about 25 to 30 percent of the battery's energy. That means, for example, if you charged a car that had a battery using an asymmetric electrode, the charge rate might be fast for the first 25 to 30 percent of the charge cycle and then slow down after that. But as those who own EVs know, that's already the case for every EV on the market. So asymmetric electrodes might just make that dynamic more pronounced.
What about the claim in Joe's post that asymmetric lamination could contribute to a 10 to 20 percent energy density increase? As far as I can tell, that checks out, but it does require some clarification. First, the 10 to 20 percent increase also includes an upgrade to a higher energy density cathode material that uses more nickel, which would itself probably increase energy density by 3 percent. Second, generally, changes to the design of a battery cell are usually made incrementally. And so, something like a 7 percent energy density increase from asymmetric lamination would be more likely as a starting point. If we add the potential 3 percent from the cathode upgrade, that's about a 10 percent improvement. That is, I'm not expecting an imminent 20 percent energy density improvement, and the best case scenario in my view would be a 10 percent energy density improvement for this year. But that's the best case scenario. I'm not going to start building that into my assumptions and expectations yet. That's because there's been no confirmation that Tesla's actually pursuing asymmetric lamination. And it's a big departure from the way a battery cell is typically manufactured.
So for now, I'm sticking with my view from the Q3 earnings called that the third generation of the 4680 cell will hit at least 280 watt hours per kilogram with improvements to cell design and a better cathode, which is about a 5 percent increase. And that the fourth generation cell could hit at least 300 watt hours per kilogram with the addition of silicon to the anode, which is a 7 percent increase. I'd hope to see the third generation cell this year and the fourth generation cell next year. As usual, I'll be happy if I'm wrong.
If the asymmetric electrode rumor is true, it could both accelerate the increases in energy density and also raise the ceiling for what the 4680 is capable of. But improvements in battery technology often take longer than expected. So for now, I'm going to temper my expectations.
On that note, what could go wrong with asymmetric lamination or cause delays? There are dozens of possibilities, but let's look at the two that I think would most likely be raised in the comments. Cycle life issues and manufacturing challenges.
With regards to cycle life, the argument would be that having electrodes with such a great mismatch in thickness might cause unequal degradation that reduces cycle life. That's because most of the burst charge and discharge rates would be handled by the thinner electrodes. I'll explain why that is in more detail in a moment, but as I said earlier, a simple way to look at it is that the ions move more quickly through and between the thinner electrodes. Those increased charge and discharge rates would mean more electrochemical activity at the thinner electrodes and potentially all the degradation mechanisms that come with that, such as expansion and contraction, greater thermal stress, and more side reactions.
However, from the little information I could find, it looks like the opposite might actually be true and that asymmetric electrodes can increase cycle life. Let's look at one example now from the perspective of mechanical stresses and another example later in the video from an electrochemical perspective.
With regards to mechanical stresses, this paper, titled, Asymmetric Electrode for suppressing swelling and commercial lithium-ion batteries, was shared with me by Pavon Srinivas and Daniel Rogstad of Freyr. The conclusion of the paper was that asymmetric lamination can be used to help direct expansion and contraction pressures within a battery cell as it charges and discharges. That helps reduce delamination and buckling during cycling, which improved the average cycle life of the battery cells that were tested as part of the research.
With that said, the paper only tested a maximum lamination thickness difference of 15%. Comping the thickness of one side of the electrode in a battery cell by 15% would probably only equate to an energy density improvement of at most 3%. That's because the active material on one side of the two double-sided electrodes makes up less than 20% of the weight of the battery cell, and 15% of 20% is 3%. That's a crude guess, but it serves the point. To get close to the 10% or more increase, Joe Tegmeyer shared, the difference in electrode thickness would have to be 50% to 100% or more. That means although the paper doesn't prove asymmetric coatings would improve the cycle life in the case of Tesla's potentially more extreme implementation, it looks promising based on the data we have so far.
The second thing that could go wrong with asymmetric lamination is that it could be difficult to manufacture. Part of the lamination process for Tesla's dry electrode manufacturing technique is calendaring, where the active material is compressed to the correct thickness and therefore porosity by rollers. Typically, when material with asymmetric coating passes through the rollers, each side of the material would be coated evenly and experience equal compression, which is of course the point with a symmetric electrode. If you put an asymmetric electrode through those rollers, it could, for example, cause one side of the coating to be compressed too much or not enough. I can think of a number of solutions to that, like adjusting the temperature of the roller on one side, or slightly changing the coating mixture on one side. But those are just guesses. Whatever the solution, it's an engineering challenge that would take a lot of trial and error to work through and implement on a full-scale production line. As always, I could be wrong here and it could be that asymmetric electrodes can be calendared identically to symmetric anodes and end up with ideal results. But significant changes to a manufacturing process are rarely that fortunate.
Some might point out that Joe did say that Tesla's currently trialing asymmetric lamination. But in my view, that doesn't give us a solid clue on timing because it depends on whether the trials have just begun or whether they've been working the kinks out of the new lamination process on other equipment for months or years. The former could mean we won't see asymmetric electrodes for quite some time, and the latter could mean we see battery cells with asymmetric electrodes this year.
As a final note, some people might be wondering if asymmetric electrodes would cause lithium plating issues or issues with the battery management system or BMS, which is the hardware and software that manages the battery cells. Lithium plating happens when too many lithium ions are shunted to the anode of the battery cell, and rather than entering the anode particles form pure lithium metal over the top of the anode particles. If that happens, it causes the battery cells to degrade more rapidly and can be a safety issue.
That is, the thinking here would be that asymmetric lamination might cause lithium plating by driving uneven reactions throughout the battery cell. Similarly, uneven reactions throughout the battery cell might create challenges for the BMS. Surprisingly, in both cases, it doesn't appear that lithium plating would be more likely, nor would battery management be more difficult. Why is that? Let's take a look. Bear in mind, this is speculation based on chats with several battery scientists. So if you have a different view, let me know in the comments below.
A lithium-ion battery cell that has electrodes coated on each side is actually two cells in one. Looking at the image on screen, the first cell is formed across the inner separator between the outside of the anode on the left and the inside of the cathode on the right. The second battery cell is formed across the outer separator between the outside of the cathode, which spirals inward and puts it across from the inside of the anode on the left. The separators, of course, keep the two cells electrically isolated from each other.
Then, the two electrode foils are joined at the top and bottom of the battery cell to form the positive and negative terminals. That creates a parallel circuit because the two positive foils and the two negative foils are joined.
The implications of that parallel circuit are that when the electrodes are laminated symmetrically, the two cells within the cell charge and discharge at a similar rate, because for the most part they're electrically identical. When the electrodes are laminated asymmetrically, the thinner electrode facings will have lower ionic resistance, which is due to the shorter average distance between the electrodes and because the ions have to travel through less material. That lower resistance means the chemical reactions will occur preferentially on the thinner electrodes and they'll charge and discharge first.
However, when the thinner electrode facings start becoming more fully charged or discharged, the voltage of the thin electrode pathway will increase or decrease as energy is stored or released. That in turn will drive more of the electrical load to the thicker electrode facings that are at a higher or lower voltage. That is, the electrochemical system within the battery cells is effectively self-balancing.
Interestingly, that self-balancing function might also have an unexpected side benefit because the thinner electrode facings would have lower resistance and could absorb and release energy more quickly, they could react more quickly to current loads than the thicker electrode facings. That means in a sense, the thinner electrode facings could act as a filter because they could more easily absorb brief spikes in charge and discharge current, which would smooth the load for the less responsive thicker electrode facing and increase the overall life of the battery cell. This is much the same way that supercapacitors can be used to smooth the load on fuel cells, which extends their life by reducing degradation.
Lastly, as far as the BMS is concerned, with an asymmetric coating the two battery cells within the cell are wired in parallel, which makes them one electronic unit. That means the BMS just sees one battery cell and monitors the voltage as it would with any other battery cell. Meanwhile, the asymmetric electrode self-balanced the entire battery cell through resistance and voltage.
In summary, it's not clear why there's so little research on asymmetric lamination for battery electrodes. It seems like a cheat code for improving the energy density of battery cells while maintaining power density. My best guess is that the wet process that's typically used to manufacture electrodes had limitations on how thick the active material could be coated reliably at high production rates, so making one side of the electrode coating 50 to 100% thicker wasn't explored as well as it could have been. Tesla's dry electrode coating, or lamination process, changes that by allowing for much thicker coatings at high production rates. If that's the case, then the 10 to 20% energy density increase rumor is definitely possible. However, again, I would caution that an innovation like this could take months or years to make it the full-scale production and could have drawbacks that my research didn't tease out. So until we hear more, I'm going to keep my estimates on the conservative side.
With that said, I'm increasingly bullish about the energy density of the 4680 in the long-term. Besides the clear pathway to higher energy density with a higher nickel cathode and higher silicon anode and the asymmetric lamination rumor we covered today, there's also the lithium doping patent I covered last year. As for the latter two, they're much easier to achieve with a dry coating process than with a wet coating process. So although the ramp of the dry coating process has been a challenge for Tesla, it does potentially open the door to the kind of energy densities that were suggested at battery day.
As usual, I'll continue to keep you updated as we learn more. If you enjoyed this video, please consider supporting the channel by using the links in the description. Also consider following me on X. I often use X as a test bed for sharing ideas, and X subscribers like my Patreon supporters generally get access to my videos a week early.
On that note, a special thanks to Phil Roberts and Rov of RCDIY, my YouTube members, X subscribers, and all the other patrons listed in the credits. I appreciate all of your support, and thanks for tuning in.
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