Robust separator which has, on a substrate and in the voids of the substrate, which comprises fibers of an electrically nonconductive material, an electrically nonconductive coating comprising oxide particles which are adhesively bonded to one another and to the substrate by an inorganic adhesive and comprise at least one oxide selected from Al2O3, ZrO2 and SiO2, polymer particles also being present in the ceramic coating in addition to the oxide particles of Al2O3, ZrO2 and/or SiO2. These separators have particularly good handling properties since they are mechanically very stable.