Separator including coating layer of inorganic and organic mixture, and battery including the same

Disclosed herein is a polyolefin porous separator including a polyolefin porous base film, and a coating layer formed on one or both sides of the base film, wherein the coating layer includes inorganic particles, and the inorganic particles include first inorganic particles having an average particle size ranging from 150 nm to 600 nm, and second inorganic particles having an average particle size ranging from 5 nm to 90 nm, and the separator has a thermal conductivity of 0.3 W/mk or more.