A conventional lithium-ion battery cell is a lot like a jelly roll. A strip of metal is slathered with a slurry containing solvents and the materials that actually store the electrical charge. Then it has to be dried before the whole thing is rolled up tighter than seven sisters in a size six swimsuit and stuffed into a metal external shell. That drying process takes time and uses rather a lot of energy. Good but not great, in other words.
Fraunhofer Institute says it has developed a better way. In a press release, Benjamin Schumm of Frauhofer says in normal battery production, “Extremely large machines with very long drying tracks are needed to ensure that the solvent will evaporate afterward. With DRYtraec, we can design this process more efficiently.” [Note: we first wrote about this in 2019. Getting from the lab to commercial production is a slow, torturous process.]
The new coating process uses raw materials similar to those used in the traditional slurry process, except the dry-coating technology works without solvents, using a special binder instead. Together, according to Green Car Congress, the materials form a dry mixture that is fed into a calender gap — a gap between two rollers rotating in opposite directions. The crucial detail is that one of the rollers must be turning faster than the other. That induces a shear force which makes sure the binder forms thread-like networks known as fibrils. “Imagine it as a spider’s web that mechanically embeds the particles,” Schumm says.
The pressure and motion combine to form a fine film on the faster rotating roller. The film is then transferred in a second calender gap onto a current collector foil which allows both sides to be coated simultaneously without significant additional work. In the final step, the resulting coil is cut to the required size and the individual parts are stacked as appropriate in order to produce the finished battery cell.
DRYtraec has a clear ecological and economic advantages over existing battery electrode coating processes, Fraunhofer says. Removing toxic solvents and long, energy-intensive drying machines from the process benefits the environment. The new process also accelerates production and requires only one-third the space of a conventional solution. The result is lower manufacturing costs.
The range of possible uses for the new technology is not limited to a particular cell chemistry. It can be used on lithium-ion cells as well as lithium sulfur or sodium ion cells. Frauhofer is even looking ahead to solid state batteries, which will be increasingly important in the future. The materials used in solid state batteries cannot tolerate wet chemical processing, which makes the DRYtraec process ideal for making them as well.
Frauhofer says it is already in discussions with several automobile and battery cell manufacturers which are planning to construct pilot systems. Further research is being conducted to determine if the DRYtraec process can be used to lower energy costs and production times for the entire battery cell manufacturing process.
Sometimes, you can learn more from the comments to an article than from the article itself. Here is one posted to the Green Car Congress story by someone with the user name gryf. “Tesla may be involved with this as well. Saueressig Engineering is said to have developed this together with Fraunhofer IWS (their specialty is roller equipment). Saueressig Engineering plans to establish a facility in San Antonio, about 80 miles from Gigafactory Texas. Combined with the 4680 cell design, this process would significantly reduce battery cost. Also, Samsung SDI has completed creating the first sample cells of Tesla’s 4680 battery (Samsung is another partner in this research).”
We don’t know the source of gryf’s information, but it is mighty interesting. The march of progress toward less expensive battery cells is picking up speed and is fascinating to watch. They say there are three kinds of people in the world — those who make things happen, those who watch things happen, and those who wonder what happened. Pretty soon, anti-EV people will find themselves in that last group and will be shocked — SHOCKED! — to find there are so many electric cars on the road.