How does the dry-coating process for battery electrodes differ from wet-coating methods, and what challenges is it addressing?
Wet-coating processes rely on the use of so-called slurries based on solvent (usually N-methyl-2-pyrrolidone or water) coated on current collector foils and then dried for obtaining the electrodes.
While wet-coating is the current industry standard for producing electrodes, it requires a very energy-intensive drying step to evaporate the solvent. To ensure adequate productivity, long oven lines are installed in gigafactories to dry the wet-coated electrodes. In addition, N-methyl pyrrolidone is toxic, so the use of it in the cathode manufacturing process requires special collection and recycling equipment.
Conversely, dry coating processes rely on a well-controlled mixing of the materials constitutive of the electrode in a solid state. This is what we’re developing at Arkema’s dedicated battery dry coating laboratory.
I understand there are different approaches to dry coating. Can you outline some of these, how they work, and what impact they could have on battery production?
Within dry coating, we focus primarily on the calendering and electrodeposition processes. In calendering, hot, cylindrical rollers compress loose, powdery battery components into electrode films before laminating the films onto the current collectors. In the case of electrodeposition, the component mixture must be a fine powder that is deposited onto the current collector before being consolidated in a calendering step.
Calendaring processes are already used in serial production by a few pioneers and are considered more advanced. Electrodeposition is an alternative process whose ramp-up has already started at some equipment manufacturers. Both processes can significantly reduce the manufacturing land footprint and improve sustainability by avoiding energy consumption for drying or use of solvent.
Can dry coating technologies improve the battery’s performance at all? Are there specific advantages when it comes to metrics such as energy density, cycle life, or charging speed?
Dry coating processes are widely recognized for their potential to reduce cell production cost and carbon footprint. They also have a lower space occupancy of the corresponding coating lines (that don’t require long energy consuming drying lines).
It is important to remember that they can also offer technical benefits. The electrode coating itself directly affects electrical conductivity, stability, and overall battery performance. But dry coating has the potential to prevent binder migration, allowing for thicker electrodes with higher energy storage. During cell assembly, these thicker electrodes allow manufacturers to reduce the number of separator and collector layers, which is favorable to increase cell energy density.
Second, the structure of the dry coated electrode differs from their wet-coated counterparts in several aspects. Often, the “tortuosity” of the dry-coated electrodes is lower, which is another way of saying that dry coating enables more uniform electrode structures with better mechanical stability. These uniform structures could be leveraged to improve cell power performance (especially at high C-rates) and, as a result, boost the charging rate.
In addition, dry coating is also regarded as a potential enabler for the manufacturing of components used in all-solid-state batteries. For instance, sulfides that are considered promising solid electrolytes are very sensitive, which makes the identification of suitable solvents for wet coating delicate and difficult work. By eliminating the need for slurries and other wet solvents, dry coating could help solve that issue.
Dry coating eliminates the need for solvent evaporation, which helps reduce the amount of electricity used during battery production. To what extent could this reduce the battery industry’s carbon emissions?
As a materials supplier, we’re probably not in the best position to quantify those items. Moreover, the term “dry coating” refers to a wide range of processes — including calendering, electrostatic deposition, and others — with varying levels of maturity. Most remain in the research and development phase, which can make it difficult to predict the technology’s broader impact. That said, companies across the battery ecosystem generally cite the same rough estimates: up to 15% in cost saving along with up to a 40% reduction in carbon emissions.
By eliminating the need for massive ovens to dry out the wet-coated electrodes, dry coating could also help free up more floor space in gigafactories.
Demand for lithium-ion batteries has been shifting away somewhat from EVs and into backup power and grid-connected energy storage systems (ESS). What’s driving this?
Demand for EVs is still growing at an impressive path, but, indeed, the current biggest growth is on ESS, which may account to almost 30% of the battery production this year. The biggest driver is the massive scale‑up of renewable energy infrastructure such as solar and wind. These energy sources are inherently variable. This creates structural imbalances between supply and demand, which creates pressure on grid stability. It is an excellent business case for electricity storage with the current price of BESS solutions.
Battery ESS solves this by storing excess energy when production is high and releasing it during peak demand or low generation. This “energy shifting” function has become the dominant use case for energy storage, directly enabling higher renewable penetration in electric grids.
Are there any new materials or other battery innovations that you’re looking forward to?
The underlying materials in a battery can have a significant impact on improving its performance, durability, and safety. Arkema has been developing solutions in recent years along these lines, including new polymer-based binder materials.
Very recently, Arkema developed a new solution for the current collector in lithium-ion batteries. This is a thin, highly conductive metal foil that allows the transfer of electrons to lithium ions. Incorporating a primer coating permits increased current conductivity, adhesion with the electrodes, and corrosion resistance. So, they are a must-have for the cathode in lithium-iron-phosphate (LFP) batteries, which are widely used in stationary battery storage. Arkema has developed a class of binders called Incellion Pr to act as a key component of this primer coating, with newer products further increasing its performance.
In the dry process, there is also a requirement for a primer-coated current collector, and Arkema is actively working on developing materials in its Incellion Pr series that can be used for that purpose.