Separator provided with asymmetrical pore structures for an electrochemical cell

19:

• A process for producing a separator for an electrochemical cell comprising
• (A) a flexible perforated support, and
• (B) a porous ceramic material which fills the perforations in the support and is suitable for receiving an ion-conducting electrolyte, wherein the porous ceramic material comprises a first porous layer having an average pore size and at least one second porous layer for contacting with an electrode, the second porous layer having an average pore size which is smaller than the average pore size of the first porous layer the process, comprising the steps of:
• (a) applying a dispersion as a thin layer onto and into a woven and/or nonwoven, the dispersion comprising
• (a1) large ceramic particles whose average particle size provides a pore structure to the layer that is characterized by an average pore diameter, and also
• (a2) ceramic particles having an average primary particle size which is less than the average particle size of the ceramic particles as per (a1),
• (b) solidifying the dispersion at a temperature from 100° C. to 680° C. to form a first layer of porous ceramic material,
• (c) applying a further dispersion to at least one side of the layer of porous ceramic material, the further dispersion comprising:
• (c1) ceramic particles whose particle size provides a pore structure whose average pore size is less than the average pore size of the layer of porous ceramic material that is coated with the dispersion, and
• (c2) optionally ceramic particles having an average primary particle size which is less than the average particle size of the ceramic particles as per (c1),
• (d) solidifying at a temperature from about 100° C. to 680° C. to form a further layer of porous ceramic material and also
• (e) optionally repeating steps (c) and (d) to create
• (e1) on the side of the first porous layer that is opposite the side of the second porous layer,
• (e2) on the second porous layer, and/or
• (e3) on optional interlayers (e1) and/or (e2)
• one or more further porous layers whose average pore sizes are each smaller than the average pore size of the adjacent layer which is in the direction of the first layer and greater than the average pore size of the layer which is in the direction of the electrode assigned this side.