The present invention relates to a separator including: (a) a porous substrate; and (b) an inorganic composite layer formed on one surface or both surfaces of the porous substrate, and including one or more inorganic particles and one or more one-dimensional inorganic materials, wherein the dimensions of the one or more inorganic particles and the one or more one-dimensional inorganic materials are different, wherein the one or more one-dimensional inorganic materials include inorganic nanowire(s) and/or inorganic nanofiber(s), wherein the one or more inorganic particles may be bound to each other, or the inorganic composite layer may be anchored and adhered to the porous substrate, by the one or more one-dimensional inorganic materials, and the inorganic composite layer does not include a polymer-based organic binder.