This article focuses on highlights and innovations announced at Tesla Battery Day and the impact on Lithium-ion batteries for EVs.
On Battery Day, Tesla disclosed 5 categories of innovations they’re using to decrease $/kWh in EV batteries by 2025:
- Cell Design
- Cell Factory
- Cell Integration
We will focus on the cell design, new materials, and how the cell is manufactured.
Cell Size: Tesla came up with a new cell design, which they call the 4680. The previous cell design was the 2170. Those numbers of 4680, or 2170, represents the cell size. So the 46 is the diameter in millimeters, and 80 is the height in millimeters. This cell design improves energy by a factor of five, so they have five times the energy, as well as six times the power and 16% longer range. So those are very good numbers. But, we must calculate volume ratio between a 4680 and the 2170. There is about a factor of five increase in volume. We can conclude that at the cell level, the energy density in Wh/L, is actually going to be very similar between the 4680 and the 2170.
However, Tesla's still claims that their range is going to increase by 16%, just with a cell design. This is because of two main factors. First, it is likely the energy density per unit of weight, so Wh/kg, is going to be higher. When you go with a larger cell, especially those types of cells, the actual weight percentage of the packaging is going to be less. So that means that the energy density will go up, and there's going to be less packaging. Second is increased volumetric efficiency, not much at the cell level, but rather at the module level. Instead of having, for example, five 2170 cells connected in parallel, here, you're going to have one larger cell. It is going to gain some energy density at the module and pack level, which can explain the 16% longer range.
Tabless Design: Telsa introduced a tabless design. In a traditional celldesign, there is a tab connected and welded to the top and then the bottom of the cap. The tab also works as a bottleneck for the electron current to be able to go from the electrodes to the outer connection of the cell. If we increase the size of the cell, that one tab is going to be a bigger bottleneck. That is the reason why they came up with this design without tabs. And instead they have is the whole electrode, both anode and cathode, and a section at the top and bottom with exposed foil. The exposed foil is folded, pressed and connected to the top and bottom of the cell. This is a good solution because it allows them to maintain or even improve the power density at the cell level. This is also good for thermal management, they’re able to dissipate heat much better, as they more metal on top and bottom. But this is not a new design, but something that we have seen in lithium ion batteries and also in supercapacitors. If you take a cylindrical ultracapacitor cell cut it in half and to view the cross section, you'll notice that you don't have tabs, but it is a tabless design. This allows for a cell with low impedance, and very good thermal management.
As a summary, all of the design changes listed above will allow Tesla to increase the range, because the cell is larger. At the same time, they also going to be able to decrease the $/kWh by 14%, simply because they have fewer parts in the cell making it easier and more efficient to make the cell. 14% is a huge number, based only on cell design.
Cathode and Anode Materials
Anode: Graphite is the most common form of anode materials. Companies are starting to add high capacity materials such as: silicon, silicon carbon, and silicon oxides. Tesla will focus on silicon because silicon has a much higher capacity than the graphite, but they will not use a nano engineered type of silicon. They are rather going to use silicon in its raw metallurgical form because that is the way to get the lowest $/kWh while also boosting energy density. It is very well known that that's the cheapest form of silicon that you can have in the anode. But this comes with a lot of challenges, one of them being cycle life and expansion of the anode. Tesla stated that they have technology to stabilize the surface of the silicon. Those are made with a polymeric material that is ionically conductive. Additionally, at an electrode level, they will use binders that will allow the silicon to expand without breaking apart.
The interesting point is that they will allow the silicon to expand and design for it. So they will design the cell for expansion. With these innovations, they state that the range will increase by 20%, a huge increase. We can assume that the range increases mostly due to energy density. By rough calculation, that they will need more than 30% of silicon by weight in the anode, and this is quite a large amount. We can expect challenges, for example cycle life. This 30% of silicon anode will improve energy density by 20% if nothing else changes. Despite the fact that they will have such a high loading of silicon anode, they haven't really talked about fast charging. Silicon is well known to be suited for fast charging, because of the way it stores lithium ions. While silicon provides this kind of advantage, the electrode architecture also needs to be designed for that, which may become a bottleneck for them. In conclusion, the anode material is going to bring 20% higher energy density, because they will have at least 30% of silicon, anode. Fast charging will be a challenge.
Cathode: Tesla will not manufacture one cathode material, there is no one-size-fits-all solution. There will be three different chemistries. First, the iron-base cathode, which mostly provides long cycle life and and medium range, because the energy density will be low. However, the will also be the cheapest and very likely, those are going to be the batteries that will go in there $25,000 car.
The second chemistry is nickel manganese. And this is interesting because today, in their current cars, they don't have an NMC type of cathode, rather they have an NCA, and so it seems there will be a shift to NMC. NMC has higher energy density and therefore, that will have longer range at the vehicle level. And finally, they also mentioned a new type of chemistry, which we call the high nickel. And the high nickel is going to be cobalt-free. So this castle will be designed to give the highest capacity and provides a 12% reduction in $/kWh. They also will have access to the to the Nevada lithium sources, which will play a very important role in lowering that $/kWh. They will introduce novel coatings that will allow this cobalt-free cathode to maintain good cycle life while also provide the highest energy density.
The last piece is the cell factory, made up of at least 3 innovations that Tesla presented. First is what they call “powder into film”, which is the dry electrode from Maxwell. Second, they talked about a new way to do the formation of the lithium ion battery cells, likely with the new type of power electronic that is going to be used to charge those batteries that is going to be more efficient and faster. Third, they talked about high speed continuous motion assembly. They’re production line will be very fast. All of these things combined will bring an 18% reduction in dollars per kilowatt hour. This is going to have the biggest impact on the overall cost reduction.
The highlight here is that with a dry electrode, they are able to remove the solvent, as well as the machines use to recover the solvent, from the electrode coating process. The result is a lower investment in factory construction. They discussed that footprint of the factory will smaller. This could allow them to scale faster. But in our opinion, the footprint by itself is not play a major role in $/kWh, but rather the capital expenditures. At Battery Day, Telsa admitted they are having trouble with the manufacturing of the dry electrode, and we will analyze this technology.
The “powder into film” concept is not quite powder into film, because to make this type of electrode, it requires at least three steps. First, there is a step where you take the active material, you mix it, perhaps with some additives, and then you mix it with the binder. This is a particular mixing process with very high energy in which the binder becomes like a like a fiber. The outcome, is a fluffy material that looks like cotton. After this step, the material is milled. There are several rolls that are connected in series. A film is created, and it gets thinner and thinner at each step. There is no aluminum or copper foil. The final step will laminate the active layer to the aluminum or copper foil.
There are limitations to this technology. In order to get to the form of a self-standing active layer, it will require a large amount of binder. In this case, the binder is likely PDF. This translates to lower electrical conductivity at an electrode level, which is a limitation for fast charging. Additionally, the current collector needs to be laminated with the active layer, which means there needs to be an adhesive layer on the current collector. This likely adds layer of inner resistance at the electrode level. So that could also cause an issue in fast charging. The largest drawback may be difficulty scaling in large volume. It is difficult to maintain a uniformity at the electrode level. In addition, this type of electrode is not suited for all lithium ion batteries With this type of technology, you can create an active layer of that cannot be thinner than around 70 microns. It's simply not easy to go even thinner than that because there is no current collector, which means that this could be a solution for energy batteries, but will not be a solution for power batteries where you require lower loadings where the thickness of the material need to be lower.
Neocarbonix by Nanoramic Laboratories
Neocarbonix has very similar savings in terms of $/kWh of a dry electrode, but with the scalability of a wet coating process. We’re able to maintain scalability because Neocarbonix utilizes those machines that are used to make a traditional electrodes. From a technical point of view, the main feature is that Neocarbonix does not contain a PVDF or PTC binder, it is completely binder free. Instead of regular PVDF binder, the electrode has a 3D carbon nanostructure that works as a binder, in that it binds active material particles together and it binds them to the current collector. There are two main mechanisms that provide this. First is the entanglement that we create with this nanocarbon materials. The second is chemical bonds that allow good adhesion to the current collector. There are a lot of advantages to eliminating a material like PVDF or PDF, performance and cost of manufacturing. It is chemistry agnostic, it is compatible with all types of cathode materials or anode materials. Today we focus on NMC type cathodes with high nickel. And on the anode side, we work with high capacity anode such as silicon. The product looks like a regular electrode, which means that it can be used in cylindrical cells, prismatic cells, pouch cells, and so on without issues. It is manufactured with standard roll to roll coating systems.
The first step is slurry preparation, which is very unconventional. Traditionally, there is a train of mixers that prepare the slurry in different stages. Neocarbonix requires only one or two stages, depending on the type of electrode. So in general, you require less of these mixers, resulting in a lower capex for this stage. Next, there is a coating and drying process, which is done with those roll-to-roll coating system with a slot die head, which is a very important step. This step is what defines the throughput, and affects the dollar per kilowatt hour at the cell level. We are able to use those machines, but they can be smaller and operated at a much lower temperature. And the reason is because the solvent is different, it not a conventional NMP solvent. Finally, there is a calendaring process, which is a standard process used to densify the active materials whether it's a cathode or anode material. The main takeaway here is that there is going to be a lower investment for initial capex.
The solvent plays a very important role because the solvent defines the throughput of the electrode. It defines the energy consumption defines the size of the machine. NMP is traditionally used as a cathode solvent, but it is not a very chemically friendly solvent. The biggest issue is that its boiling point is above 200 degrees C, which means it takes a lot of energy in heat and forced air to be able to remove it from the coating. Neocarbonix is PVDF free. We can use other types of solvent which are chemically friendly, like water, or other types of low boiling point solvents with a boiling point below 100C. This makes it very easy to dry. With the same machine, we can have about two times the throughput as conventional PVDF cathode with a shorter oven length and less energy consumption. Instead of keeping the ovens at 130°C, you can keep them at 65°C. Energy consumption plays a huge role in determining $/kWh.
Another aspect that contributes to both improving energy density and lowering the $/kWh is the loading of cathodes, or the amount of effective material that you can coat on the surface of the aluminum foil. From an energy perspective, the thicker the coating, the more active material you have at the cell level. That means, fewer passive components - less aluminum, less copper, less separator, which boosts up the energy density when using the same active materials. There are two reasons why we are able to do this. First, Neocarbonix improves the conductivity of the electrode by about 10 to 100 times higher compared with the conventional PVDF coating. The reason this is important is because you're going to end up with a high energy density cell that still charges and discharges at high rates. Second, it is difficult to obtain those thick coatings with conventional NSP solvent. These more chemically friendly solvents are well suited to maintain thick coatings without having cracks. Cracks are a typical issue that occurs after drying when coating is thick.
High capacity cathode (high loading cathode that yields very high surface capacities) are ideal to be paired with high capacity anode like silicon, silicon oxide, or silicon carbide. And that's also something that Neocarbonix can do. Today we coat those type of electrodes with high loading of silicon material.
The combined benefits of Neocarbonix (lower manufacturing costs provided by faster speeds and decreased energy; lower capex; increased energy provided by higher loading cathodes; high capacity) achieves a cell cost of $80 per kilowatt hour. These cells are optimized for high energy density. In summary, this type of technology fits into the battery into the existing battery ecosystem, as it works with existing materials, equipment, processes. Neocarbonix can be used to make pouch cells, prismatic cell, and cylindrical cells. We can achieve energy density at the cell level that exceeds 350 Wh/kg, at a cost that is lower than $100 per kilowatt hour.
In comparison with the Tesla dry electrode method, Neocarbonix takes the benefits of the coating technology with the benefits of the dry battery electrode. Both Neocarbonix and the dry battery electrode aim to reduce the cost of manufacturing using a smaller footprint. Both processes are more environmentally friendly, using less energy consumption and removing toxic solvents. However, Neocarbonix can maintain the high C-rates because the conductivity of the electrode is higher. Neocarbonix is also easier to recycle, as it's difficult to recycle active materials when you have a large amount of binders. We use standard coating equipment, for easy scalability. Another interesting point is that with same machines, we can make electrodes for power batteries or energy batteries.
Power batteries require thin coatings, while energy batteries require thick coatings with higher loadings. Nanoramic’s Neocarbonix process can reach loadings of 50 mg/cm2, or double the loadings that you see in energy batteries today. Neocarbonix is compatible with high-speed winding systems.