Patent ID: 8168332

Claim:
A separator, comprising: (A) a porous substrate having a plurality of pores; and (B) a porous coating layer formed on at least one surface of the porous substrate to have a thickness of 0.01 to 20 μm and made of a mixture of a plurality of inorganic particles with a particle size of 0.001 to 10 μm and a binder polymer, wherein a weight ratio of the inorganic particles to the binder polymer is 50:50 to 99:1, wherein the binder polymer comprises: (i) polyvinylidene fluoride-co-hexafluoropropylene which is a first polyvinylidene fluoride-based copolymer having solubility of 25 weight % or more with respect to acetone at 35° C.; (ii) polyvinylidene fluoride-co-chlorotrifluoroethylene which is a second polyvinylidene fluoride-based copolymer having solubility of 10 weight % or less with respect to acetone at 35° C.; and (iii) a polymer having a cyano group; and wherein, based on the entire weight of the porous coating layer, the content of the first polyvinylidene fluoride-based copolymer is 5 to 30 weight %, the content of the second polyvinylidene fluoride-based copolymer is 1 to 10 weight %, and the content of the polymer having a cyano group is 0.1 to 5 weight %, respectively.