Abstract: A crosslinked structure-containing polyolefin porous substrate is provided. The crosslinked structure-containing polyolefin porous substrate has a crosslinked structure including polymer chains interconnected directly with one another, wherein the polyolefin porous substrate includes, in a height direction extending from one surface to the other surface, a first region contacted with the one surface and a second region extended from an outside of the first region toward the other surface. Polyolefin contained in the first region and polyolefin contained in the second region have a difference in crosslinking degree of 10% or more. A method for manufacturing the crosslinked structure-containing polyolefin porous substrate is also provided. Even though the separator including the crosslinked structure-containing polyolefin porous substrate has a crosslinked structure, it shows a low shutdown temperature and a high meltdown temperature.

Abstract: A separator for a lithium secondary battery, a method of making the same, and a lithium secondary battery including the same is disclosed herein. In some embodiments, a separator for a lithium secondary battery including a porous polyolefin substrate having a tan(?) of 0.3 or less. The tan(?) is determined by Formula 1 at a temperature of 230° C. and an angular frequency of 0.1 rad/s: tan(?)=G?/G???[Formula 1] wherein G? is a storage modulus of the polyolefin and G? is a loss modulus of the polyolefin. The separator has a low viscosity but high elasticity at high temperature, maintains strength at high temperature, and has resistance against external force at high temperature. A lithium secondary battery including the separator has improved safety.

Abstract: Disclosed are a crosslinked separator for a lithium secondary battery which comprises a crosslinked polyolefin porous substrate including a plurality of fibrils and pores formed by the fibrils entangled with one another, wherein polyolefin chains forming the fibrils are crosslinked directly with one another; and shows a change in tensile strength of 20% or less in the machine direction, as compared to a non-crosslinked separator including a polyolefin porous substrate before crosslinking, and a method for manufacturing the same. The crosslinked separator for a lithium secondary battery has excellent thermal safety, while not adversely affecting the other physical properties.