Conventional processes for manufacturing battery electrodes use toxic solvents and require a lot of space and energy. In contrast, DRYtraec — a new dry-coating process developed by the Fraunhofer Institute for Material and Beam Technology (IWS; Dresden, Germany; www.iws.fraunhofer.de) — uses no solvents, is environmentally friendly, cost effective and can be used on a large scale.
Battery electrodes normally consist of a metal foil with a thin coating, which contains the active components that are responsible for storing energy. “The conventional coating process uses a wet chemical method that applies what is known as slurry,” explains Benjamin Schumm, group manager for Chemical Coating Technologies at IWS. The active material, conductive carbon and binders are dispersed in a solvent to make a kind of paste, which is initially applied to the metal foil to form a wet coating. “Extremely large machines with very long drying tracks are needed to ensure that the solvent will evaporate afterward,” he continues. “With DRYtraec, we can design this process more efficiently.”
DRYtraec uses similar raw materials as in the slurry process, but instead of a solvent, a special binder is used. These materials form a dry mixture that is fed into a calender gap — the space between two rollers rotating in opposite directions. The crucial detail is that one of the rollers must be turning faster than the other. This induces a shear force that ensures that the binder forms thread-like networks (fibrils). The process is designed so that both sides of the film can be coated simultaneously. The resulting coil then is cut to the required size. The process not only eliminated the need for solvent, but also the final, energy- and time-intensive drying step.
The first prototype DRYtraec systems were commissioned as part of the DryProTex funding project, which demonstrated that it is possible to manufacture electrodes continuously, regardless of the type of battery. Discussions are currently underway with several automobile and cell manufacturers to plan the construction of a number of pilot systems.