The present invention relates to flexible ceramic membranes which, depending on embodiment, are useful as separators for batteries, especially lithium batteries, and also a process for their production.Ceramic or hybridic membranes have the disadvantage that, whatever the level of flexibility already achieved, they tend to crumble off the ceramic coating on bending. This is prevented by the present membranes, which comprise, on and in a polymeric nonwoven, a solidified ceramic coating which is constructed from two fractions of metal oxide particles of different size and which adheres to the polymeric nonwoven through a network constructed by two different adhesion promoters.