The video shows a rendering of a reconstruction (obtained by focused ion beam tomography) of the microscopic structure of a glass fiber separator. Such a separator is often used in research in lab-scale lithium-ion cells. The task of the separator is to spatially separate the anode from the cathode to avoid a short-circuit between them. Additionally, it serves as a reservoir (like a sponge) for the liquid electrolyte, filling the porosity and providing ionic transport paths between the two electrodes.The purpose of this video is to demonstrate the high porosity of this kind of separator, which also leads to a low tortuosity (a measure of how twisty the transport paths are).