Separator for lithium ion secondary battery

Abstract

A separator for a lithium ion secondary battery, comprising a microporous film containing: a polyolefin resin (A) as a main component; and a resin solution (B) which is additionally coated on at least one region of the inner surfaces of the micropores of the microporous film to prevent the formation of stress concentration in the microcracks of the micropores so as to improve the puncture strength of the separator by at least 258 gf, the resin solution (B) being different from the polyolefin resin (A), the resin (B) in the resin solution (B) being relatively soft, and the resin (B) in the resin solution (B) being relatively soft. The copolymer is selected from a C4 / C3 alpha-olefin copolymer, a C3 / C4 alpha-olefin copolymer and low-stereoregularity polypropylene; the resin (B) has an elastic modulus of 110 to 520 MPa at 25 DEG C. According to the present invention, it is possible to provide a separator for a lithium ion secondary battery, which exhibits excellent strength, wettability with a non-aqueous electrolyte solution, voltage durability, and cycle characteristics of the lithium ion secondary battery.

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