SEPARATOR FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING SAME

The present invention relates to a rechargeable battery comprising a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive electrode active material selected from a lithium cobalt oxide, a lithium nickel cobalt manganese oxide, a lithium nickel cobalt aluminum oxide, or a combination thereof, wherein the separator including: a porous substrate; and a coating layer on at least one surface of the porous substrate. The porous substrate essentially consists of polyolefin and the thickness of the porous substrate is about 5 μm to about 15 μm. The coating layer faces the positive electrode and includes a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide, a second structural unit derived from (meth)acrylonitrile, and a third structural unit derived from (meth)acrylamido sulfonic acid, (meth)acrylamido sulfonic acid salt, or a combination thereof. The heat shrinkage rate in traverse direction of the separator is less than 5%.