With global demand for batteries expected to increase from 185 GWh in 2020 to over 2000 GWh by 2030, finding more efficient production methods is a growing focus for the industry.
One of the main steps in the battery manufacturing process is the coating of active material on top of the metal foil to create the electrode. This active material is where electrochemical reactions occur, allowing the electrode to store and then release energy when the cell discharges. Traditionally, the electrode material is mixed with water or an organic solvent to form a liquid slurry that is applied to the top of the metal foil. After the coating, the electrodes are dried and pressed. The pressing process, also known as calendering, decreases the electrode’s porosity, which leads to an increase in energy density due to a smaller volume, as well as improvements in adhesion and coating uniformity. The drying process is costly and both energy and time-intensive, taking some electrodes 12–24 hours to become completely dry. Moreover, the organic solvents used for the slurry preparation, which are usually hazardous, must be recovered and re-distilled for the next usage.
Obviously, the process of “wet coating” poses a disadvantage when market demands are necessitating the rapid and economical scale-up of battery production, so it’s no wonder that leading companies such as LG, Samsung, CATL, Ford, GM, Volkswagen and Tesla are all making efforts to develop “dry coating”, pointing to a growing trend. As the industry realizes the potential of this technique and works to overcome the challenges that come along with it, will dry coating electrodes usher in next-generation batteries?
The benefits of dry coating
The new process, referred to as dry coating, eliminates the conventional drying phase. A powder is mixed with a specific polymeric binder that acts as a glue, and then is applied onto the metal foil. Pressure and temperature changes are then applied to the mixture that allows it to adhere to the foil.
Although dry coating electrodes often involve a more complex process, it enables a reduction in cost and fabrication time, while being a more environmentally-friendly option. Let’s take a closer look at the benefits.
By avoiding using solvents, the dry coating process requires fewer preparation steps and equipment, lowering overall capital and operational expenses. With less heavy equipment involved in dry coating, it is possible to manufacture electrodes using one-tenth of the usual factory footprint. This also reduces the energy required for battery production. Furthermore, the faster process of dry coating leads to a higher manufacturing output while reducing costs and energy consumption. Specifically, these advantages may result in the battery’s cost being cut by at least 10%.
Approximately 39% of the energy consumption in the production of lithium-ion batteries is associated with overall drying processes, whereby the electrode drying step accounts for about a half of that consumption. Although dry processes may still use heated rollers, the elimination of drying and solvent recovery steps significantly lowers electricity consumption and costs. A secondary benefit is environmental, as there is no need to use the aforementioned hazardous solvents.
As with any improvement efforts, challenges can arise with the dry coating process such as uniformity issues and complications around large scale production. As mentioned, for the dry coating mixture to be usable, it must be uniform across the large areas of the battery electrodes. Similar to wet coating, dry coated foils are also calendered, but with higher pressure and temperature. In Tesla’s case, the mixture unexpectedly dented the expensive calender rollers, which according to Elon Musk, is a rather solvable engineering problem. However, this still requires a substantial amount of trial and error for it to be commercially ready.
In the event that the coating is not uniform, it may cause the formation of so-called hot spots in the battery electrodes, leading to battery degradation, potential short circuits and even catastrophic battery failure. To maintain battery performance, it’s critical to ensure active material adhesion to the foils with a minimal amount of binder used. Therefore, the dry mix must be uniform even before the coating, with the materials evenly distributed in the mix volume.
Finding a new efficient technique requires significant investment in battery fabrication equipment and their modifications to achieve the sought-after results. Tesla uses the dry coating process developed by Maxwell Technologies, which was acquired by Tesla in an all-stock deal in 2019 as part of their scaling and manufacturing improvements. Elon Musk estimates that in Tesla’s case, the company will be revising machinery five or six times before large scale production using dry coating can go ahead. Additionally, while Musk initially announced that dry coating would be huge news for the industry, it was then downplayed two years later, and is still not commercially available. The delays we’ve seen around dry coating adoption may be due to large investments that are still required to optimize the process.
Can 3D electrode architecture solve the challenges of dry coating?
Traditionally, all batteries have a two-dimensional electrode structure composed of a flat metal foil coated with active chemical materials. In contrast, newly advanced 3D electrodes use a porous metal structure with the active chemical material embedded inside during the coating process.
In the case of 2D foils where the coating is layered, the batteries may suffer from a lack of mechanical stability, which poses a risk of delamination for battery electrodes. Indeed, in the case of Maxwell Technologies’ patent, the surface of the current collector is sometimes roughened to prevent dry ink sliding on the surface and to improve adhesion. With 3D Electrodes, this process can be even more efficient and incorporated in the production line.
By using 3D electrodes, the active material powder can be more easily infiltrated into the metal framework simultaneously from both sides, allowing it to be more uniform. This enables better mechanical stability and adhesion of battery 3D electrodes. Furthermore, the dry coating process with 3D electrodes is compatible with the fabrication process using foils and can be carried out on the same production line.
Accelerating the electrification trend in industries ranging from electric vehicles to distributed energy storage is critical to meeting widespread decarbonization goals in order to mitigate the impacts of climate change. The battery industry needs to use all of the tools at its disposal to improve the performance, cost and scale-up of next generation batteries, and the dry coating of electrodes shows significant promise for supporting these efforts. It’s not only about the development of more advanced battery chemistries – it is also about improvements in electrode design including 3D electrodes that can facilitate new fabrication methods such as dry coating. Only when we focus on the intricacies of battery development can we expedite the energy transition that the future of society depends on.