Separator with long-term stability for an electrochemical cell

A porous separator for an electrochemical cell, comprising:

• (A) a flexible perforated support,
• (B) a first porous ceramic material coated as a first layer directly on the flexible perforated support and which fills the perforations in the flexible perforated support, and which
• (i) has a pore structure having an average pore size, and
• (ii) comprise an ion-conducting electrolyte,
• (C) a second layer covering the surface of the first layer of the first porous ceramic material wherein the second layer comprises fine particles of a second material, wherein the average particle size of the fine particles is in the range from 0.5 to 30% of the average pore size of the first porous ceramic material and at least a portion of the pores of the first porous ceramic material are filled with the fine particles of the second material, wherein the second material is at least one selected from the group consisting of Li2CO3, and LixAlyTiz(PO4)3 wherein 1≦x≦2, 0≦y≦1 and 1≦z≦2.