Well, side-to-side as in less than 100 microns. The inside of the battery is a very long tape that is rolled up like folded paper. The tape is: 1: Aluminum f

Well, side-to-side as in less than 100 microns. The inside of the battery is a very long tape that is rolled up like folded paper. The tape is: 1: Aluminum foil (about 1/10th as thick as household foil) 2: Cathode material (metal oxides, like NMC or NCA) 3. Separator film (polypropylene + polyethylene, which blocks electrical short circuits but lets li ions through- only ~20 microns thick) 4. Spheroidal graphite anode (mostly artificial, some natural) 5. Copper foil The ions (and some amount of solvent- the solvation sheath!) travel from cathode <-> anode.