Welcome back everyone, I'm Jordan Geisigee and this is The Limiting Factor.
Last year, Tesla filed a patent application for a method of synthesis of 3R142 dioxazole 5-ones.
The question is, what does that word soup mean and what are the implications of the patent? In short, the patent is for a process to produce a new electrolyte additive more simply and cheaply. But the more important part of the story is that the new electrolyte additive can be used to dramatically increase the cycle life of lithium ion batteries, so much so that the additive appears to be competitive with the electrolyte blends that were used in Jeff Don's groundbreaking million-mile battery.
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Starting with the cover page of the patent, 3R142 dioxazole 5-ones is a mouthful and actually refers to a family of chemicals. To keep it simple, for the rest of the video, I'm going to just refer to one specific chemical within that family called PDO. That's because, as we'll see in a moment, that appears to be the specific chemical that Tesla's most interested in.
Next, the patent applicant is Tesla and the inventors are David Hall, Jeff Don and Torrin Heitz. As you probably know if you've been following my channel, Jeff Don is renowned in the battery field and is Tesla's research partner. So this patent application would have resulted from that partnership. The patent was filed on June 30, 2022 and published on February 2, 2023. Then if we look closer, we can see that there's related US application data. As it turns out, this patent application is a continuation of another that was filed in June of 2019. That patent application received a patent in July of 2022. So why is Tesla filing a patent application if they've already received a patent? From what I can tell, it's because the first patent grant was for the synthesis process, but they also want patents on some of the specific chemical compositions that they've developed with that process. That is, they're in a good position already in terms of patenting, but they're seeking as much patent protection as possible.
Moving along, the title of the patent application states that it's for a method of synthesis. This told me that most of what's going to be in the patent has nothing to do with what the chemical is going to be used for, but rather how to make it. When I skimmed through the document, that assumption was quickly confirmed. Most of the patent application was a mess of chemical compounds and testing parameters. It was pages of data rather than what most of us would consider useful information.
The useful information I did find was in the background information part of the patent. First, PDO is being tested as an electrolyte additive to extend the lifetime of lithium-ion batteries. The way electrolyte additives work is by reacting with other chemicals in the electrolyte solution, like lithium, to form a protective layer on the anode of the battery, but also to a lesser extent the cathode. That protective layer prevents the electrolyte from continuing to react with the electrolyte solution, which would cause the battery to degrade and quickly lose cycle life. That means even a small amount of additive can dramatically increase cycle life. For example, adding 1% PDO to a battery can triple its cycle life, which is less than 2 grams for a battery cell that weighs 1 kilogram.
The second useful piece of information from the patent application was that although the current process is for producing PDO-type compounds result in high purity and high yields, they involve multiple steps that are time-consuming, inefficient, and expensive. But the inventor's proposal in this patent application is a synthesis method for PDO that uses chemicals that are widely available, cheaper, and with a process that involves one step rather than multiple steps. I'm not going to walk you through that process today for two reasons. First, it would involve walking through a recipe with ingredient names that would be unintelligible for most people. Second, it's because the real story for us as consumers or investors is how much PDO could increase the cycle life of batteries and how Don's lab has progressively validated its performance over the past four years. Let's get into that.
After reviewing the patent application, the next thing I did was run searches on PDO, Dioxazalone, and Don, which returned four research papers, three of which we'll look at today. Each of the papers was quite involved and they easily added up to thousands of hours of research. That is, Don's team pursued research on PDO quite aggressively, which they wouldn't have done if it didn't appear to hold some promise.
The first paper we'll cover, titled Dioxazalone and Nitrile Sulfite Electrolyte Additives for Lithium Ion Cells, was by David S. Hall at AL and was published in 2018. It compared three electrolyte additives that were new at the time, MDO, PDO, and BS. The conclusion was that of those three additives, PDO, shown here in purple, offered the greatest improvements to cycle life, especially when combined with other additives. However, the paper only illustrated that PDO is the best of the three new additives, not that it would perform well against the best additives on the market today, such as those used in what's often referred to as Jeff Don's Million Mile Battery Paper, which was published about four years ago. Furthermore, it only tested two standalone concentrations of PDO and three blends, so more research was needed.
我们将要讨论的第一篇论文名为《二氧杂氧醇和Nitrile Sulfite电解质添加剂对锂离子电池的影响》,由AL的David S. Hall发表于2018年。该论文比较了当时新出的三种电解质添加剂:MDO、PDO和BS。结论是在这三种添加剂中,PDO表现最好,特别是当与其他添加剂结合使用时,可以显著改善循环寿命。然而,该论文只证明了PDO是这三种新添加剂中最好的,而并未证明它能否与市场上最好的添加剂相抗衡,例如常被称为Jeff Don的百万英里电池论文中使用的添加剂,该论文发表于大约四年前。此外,该论文只测试了两种独立的PDO浓度和三种混合物,所以还需要进行更多的研究。
The next paper, titled Optimizing PDO as an Electrolyte Additive for Lithium Ion Cells, was by Toren Hines and was published in 2020. This paper tested three standalone concentrations of PDO rather than two, and nine blends rather than three. Let's walk through the results on screen. The lab scale cells they tested used an NMC 622 cathode, which is 60% nickel, 20% cobalt, and 20% manganese, and paired it with a graphite anode.
The cells were charged to 4.3 volts and discharged to 2.8 volts for each charged discharge cycle, and each cell was cycled until it degraded to 90% of its original energy capacity. The cell using no additive hit 90% in 200 cycles. The 2% vinylene carbonate reference cell hit 90% in 400 cycles, and the cell using 1% PDO and 2% DTD, or ethylene sulfate, took 1200 cycles to hit 90% capacity. That is, it performed six times better than the no additive control, and three times better than the vinylene carbonate or VC reference. As a side note, vinylene carbonate was chosen for the reference cell because it's typically the additive used in nickel-based commercial lithium ion battery cells. Again, bear in mind, these percentages are the percentage weight of the electrolyte solution, which is itself a fraction of the total battery weight. So we're talking about nearly insignificant quantities of material for a large effect on battery life.
Next, how does the performance of the battery cells using the PDO additive compare to the additives used in the million-mile battery that Don's lab unveiled about four years ago? Before we get into that, let's start with a quick refresher. In the million-mile battery research paper, Don's lab used single-crystal cathode material, artificial graphite, and several combinations of electrolyte additives that included vinylene carbonate, ethylene sulfate, lithium-difluorophosphate, and fluorine ethylene carbonate. Those materials are well known to maximize battery life, and the purpose of the paper was to show the true potential of lithium-ion batteries if the right materials are used. Notably, no PDO was used. That's because in 2019, when the million-mile battery paper was released, PDO wasn't being used commercially because it was still relatively untested.
Moving along, the million-mile battery paper found that 2% vinylene carbonate with 1% ethylene sulfate and 2% fluorine carbonate with 1% lithium-difluorophosphate yielded the best results. Cells using those electrolyte blends were able to reach well over 3,000 cycles before hitting between 88 and 96% remaining energy capacity. That's as opposed to the PDO paper by Toren Hines, which used polycrystalline cathodes, artificial graphite, and electrolyte combinations that all involved the use of PDO. So obviously what was needed next was an apples-to-apples comparison of the electrolytes used in the million-mile battery paper and the PDO papers. By apples-to-apples comparison, I mean using the same cathodes and anodes under the same cycling conditions, but with different electrolyte blends.
That's exactly what Don's Lab did in 2022 in this paper by Dong Shui Uyang et al, titled the PDO electrolyte additive for NMC 622 and NMC811 lithium-ion cells. They did hundreds of tests of the best electrolyte blends from both the PDO papers and the million-mile battery paper in a broad range of voltages and temperatures.
On screen is just a small portion of the tests that were run. For long-term cycling tests and the top graph of Panel B in Figure 14 is the most representative of real-world conditions. As you can see, the orange, green, and blue lines representing one vinylene carbonate dominant blend and two PDO dominant blends performed best. Of course, the best performing additive did vary with testing conditions.
With all tests considered, the conclusion was that the best performing blends of PDO didn't perform as well as the reference electrolyte blends that were used in the million-mile battery paper for both cycling and high-temperature storage. However, in specific conditions, like the long-term cycling of NMC811 battery cells, a blend of 2% PDO and 1% LFO, or lithium-diflorophosphate, performed well and potentially makes a good candidate for battery cells using high nickel chemistries.
What all this means is that Tesla now has another electrolyte additive in their arsenal. That, in turn, will allow them to use the best electrolyte blend for each use case, whether that be a Model Y, Robotaxi, or grid storage.
As a final note, I still see some areas of opportunity in the PDO research, and I don't think Jeff Don's lab nor Tesla will stop here with PDO. Why do I say that? First, in the final paper from 2022, they used a cathode that was a blend of single and polycrystalline materials, whereas the images from Battery Day indicate that Tesla appears to intend to use polycrystalline cathodes, which might favor using PDO. So, it's one more variable to test.
Second, Tesla and the entire industry intends to use higher percentages of nickel beyond the 60-80% nickel cathodes that are common today. A common theme across the PDO papers, and confirmed in the 2022 paper, was that PDO performs better with high nickel cathodes.
Third, the paper from 2022 found that in some instances, 95% purity PDO actually resulted in better cycle life than 99.8% purity PDO. However, the battery cells they used for the long-term cycling testing of the PDO blends used 99.8% pure PDO rather than 95%. Presumably to eliminate the impurities as a variable. That means there's another variable to test here, because there may be a chemical in the impurities that has a positive impact on cycle life.
If we take all those factors into account, with a full polycrystalline high nickel cathode, we might see even better results than the ones we walk through today.
如果我们考虑到所有这些因素,使用全晶体高镍阳极,我们可能会看到比今天更好的结果。
In summary, Tesla's new patent application, courtesy of Tesla's research partner Jeff Don, is for a manufacturing process for the electrolyte additive PDO. Don's lab has devoted thousands of hours and several years evaluating PDO, and in some cases it appears to be competitive with the reference electrolyte blends that were used for the million-mile battery. If and when these additive blends are used in Tesla's batteries, it should significantly improve their cycle life, possibly to the point where the batteries will outlast the vehicles and grid storage products that they're used in.
For me, the only question that remains is, why hasn't that happened already? The research for the PDO papers was initiated at least five years ago, and for the million-mile battery paper four years ago. I can think of several reasons why Tesla hasn't used these electrolyte additives and their products yet, but it's unclear to me which is the most likely.
First, the mundane and probable answer is that the research is ongoing, and there's more testing needed to validate chemicals like PDO for use in Tesla's products. Bear in mind that Don's lab was still running comparison tests of these chemicals in 2022.
Second, on that note, it could be that the testing is complete and now they're working on an industrialization plan. To bring these chemicals to market, it would take at least two years from planning to production.
Third, the new electrolyte additives could negatively impact the battery cells in ways that aren't apparent from the research we've seen so far, but that Tesla has discovered in their own labs and testing.
Fourth, it could be that Tesla is already dealing with so many variables with the 4680 production ramp that they're waiting until the ramp has hit full stride before they make tweaks to the chemistry.
Fifth, it could be that Tesla is already using these additives, but only for products that the public isn't able to track as closely, like grid storage products, which have a greater need for a high cycle life.
In my view, the first and second reasons are the most likely, and I expect the great work that Don's team has done will eventually make it into Tesla's products. There's no way to know when that could be, but if you're in the battery industry and you have some insights here, let us know in the comments below.
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