As an alternative to that factory, they also come in flavors that use precise temp/humidity environmental control and all steps are performed in actively filtered clean-rooms on fully automated lines with all personal in lint-free gowns.
First the powders with active materials are blended into a slurry with the binder and whatever special sauce additives. This slurry is coated onto the foil with a device not unlike a commercial printing press. Then the foil is dried in a very long oven. The foil next goes through a series of calandar press rollers until the active material coating is at the desired thickness and density (rolling less dense means higher C-rate, more dense means more energy storage). Then the coated foils are die-cut into pouch-sized rectangles with an uncoated piece of foil sticking up that will get welded to it's respective polarity tab (the Aluminum foil becomes the positive tab after being coated in whatever metal oxide cathode material, the copper foil gets coated with various forms of carbon anode material to become the negative tab). The die cut foils have a machine that picks them up one at a time and folds a layer of the long strip of micro-porous separator material between each of the anode and cathode foils until the stack has the correct number of layers. Then this completed stack gets tabs welded onto it (all by automated machine process in a clean room), and goes into a pouch which has 3 edges sealed up. Racks of cells with a single un-sealed edge then go into large vacuum ovens to bake out under hard vacuum for ~24hrs to ensure all humidity and whatever could have gassed has gassed and been purged out the vacuum pump driving the oven. The cells are unloaded from the oven and get a precisely metered dose of electrolyte injected into each pouch, then the pouch is sealed, but leaving a large expansion volume off to the side connected by a small unsealed portion so the gas that evolves during formation has a place to go. Then this cell is connected to a formation machine and undergoes ~24hrs of a pre-formation cycle, then another 24hrs of a formation charge process, then the cell gets cycled with capacity and internal resistance precisely measured. At this point if any spec of the cell is off even a tiny bit, the cell is scrapped because something isn't perfect. If after formation the specs look perfect, then it gets it's final pouch trim to cut off the formation gas expansion pocket and get it's final vacuum heat seal and final pouch foil edges folded neatly (also all automated).
A pouch cell can be made with only some hand tools and lots of labor, but you would never want to use it for something where it matters if it fails.
ATB,
-Luke
