Is Dry Coating the Next Best Thing to Happen to the Battery Industry?
With better and more efficient production methods for energy storage increasingly in demand, batteries are becoming more important as we head toward a more electrified world.
Electrode coating is one of the main steps in the manufacturing process of lithium-ion batteries where the active material is coated on top of the metal foil. The active material in charge of energy density and capacity chemically reacts to produce energy as the cell discharges before returning to its original state when charging.
The main and exclusive way of coating electrodes was through wet coating. However, industry players are increasingly trying to move towards dry coating. Companies including LG, Samsung, CATL, Ford, GM, Volkswagen and of course, Tesla are all making efforts to develop dry coating, announcing the upcoming trend. As they realise the potential of this technique and face the challenges that come with it, what will the future of electrode coating hold?
Wet Coating Vs Dry Coating
The conventional process of coating electrodes, also referred to as wet coating, involves mixing various electrode powders with water or a solvent to create a slurry, which is then coated onto metal foil to create an electrode. For the coated foils to be a smooth and uniform layer, they are then squeezed through huge rollers in a process known as calendering. The coated electrodes must then be dried in huge ovens for them to become solid before the solvent is removed.
The new process, dry coating, skips the more liquid and drying phases and instead, the powder is mixed with a binder that acts as a glue, and then is coated onto the electrodes. Pressure is then applied to the mixture that allows it to stick to the foil. By applying this pressure, the binder is released meaning that only the powder remains on the electrodes.
Dry Coating Benefits
Though dry coating electrodes can be considered to be a more complex process, it enables a reduction in costs, is a more environmentally-friendly option and requires less time to complete.
By avoiding a more liquid form, the dry coating process consists of less steps and therefore less machinery to purchase and to maintain. This reduces the amount of factory space needed to make the electrodes to 1/10 of the original size in addition to decreasing the required energy that goes into battery production by the same amount. Combined, these reductions lead to the battery’s cost being cut by around 10%.
A More Environmentally-Friendly Process
Not only does dry coating reduce costs but by cutting the amount of machines needed, less energy is required throughout the process. Furthermore, although dry processes may use heated rollers, reducing the amount of steps such as eliminating drying time, which can take 12–24 hours to completely dry, lowers the electricity consumption and costs. Indeed, approximately 39% of the energy consumption in the production of lithium-ion batteries is associated with overall drying processes, where the electrode drying step accounts for around half of that.
A secondary benefit is decreasing the amount of chemicals used in the battery production process. This in turn leads to less waste generation.
The process of dry coating comes with the allowance to skip certain steps such as the solvent one and just go from dry mix to coating. By reducing the amount of steps in producing the dry mixture and applying it, less time is needed for the overall process. This amounts to a higher capacity with less costs and less energy used.
Credit: Waldemar Brandt, Unsplash
The Challenges of Dry Coating
As with any works of improvement, challenges can arise in practice. From unexpected results to investments, this can lead to unexpected revisions and delays.
As previously discussed, for the coating to be usable, it must be a smooth and uniform layer. Similarly to wet coating, dry coated foils are also squeezed through huge rollers but this must be done with more calendering pressure due to the consistency of the dry version. In Tesla’s case, the mixture was unexpectedly denting the calender rollers, which according to Elon Musk is an engineering problem and is solvable. However, it still requires a substantial amount of trials and error for it to be commercially ready.
In the event that the coating is not uniform, it will cause hotspots in the battery which will make the battery heat up unnecessarily. This will lead to localized battery degradation, potential short circuits and even battery failure. The correct active material adhesion must be maintained and the quantity of binder optimized as these all affect battery performance. Therefore, the dry mix must be uniform, with the materials evenly distributed and with the same concentration in all areas.
Finding a new efficient technique requires significant investment in machinery and their revisions to get the sought-after results. For Tesla, they bought the dry coating process by acquiring its developer, Maxwell Technologies, in an all-stock deal in 2019 as part of their scaling and manufacturing improvements, before selling the company this year. He also estimates that in Tesla’s case, they will be on machine revision 5 or 6 before large scale production using dry coating can go ahead. Additionally, whilst Elon 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. Could this be down to how much investment is required to optimize the process?
Credit: Kumpan Electric, Unsplash
3D Architecture Allows the Use of the Drying Process
In the case of 2D foils where the coating is layered, it suffers from a lack of mechanical stability and there is a risk for the layers to separate. Indeed, in the case of Maxwell Technologies’ patent, they sometimes etch or roughen the surface of the current collector to prevent dry ink movement on the surface to improve adhesion. With Addionics 3D Electrodes, this process would be compatible and can be included in the production line.
By using 3D electrodes, the powder from the dry coating can really get into the structure as the dry coating process integrates the active material inside the metal framework, allowing it to be more stable. The metal scaffold acts as a binder, and a less expensive version and smaller amount of it is needed. This allows the battery to have better mechanical stability. Additionally, thick electrodes are often the target of dry coating, which is one of Addionics’ big advantages, especially while matching the capacity of emerging high energy chemistries.
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