| 摘要 |
PROBLEM TO BE SOLVED: To obtain a finely porous polyolefin-based membrane having an elongated cycle life without damaging a battery-assembling property and useful as separators for lithium ion secondary batteries which can stably be used for a long period, by forming a membrane structure having a specific average pore diameter and a specified average surface pore diameter. SOLUTION: This finely porous polyolefin-based membrane has an average pore diameter of 0.01-0.2μm and an average pore diameter of 0.5-2μm on at least one of the surfaces. The finely porous polyolefin-based membrane preferably has a penetration strength of >=600 g, a porosity of 30-70% and a thickness of 10-80μm. The finely porous polyolefin-based membrane is preferably obtained, for example, by melting and kneading a composition comprising a polyolefin and a plasticizer, extruding the kneaded product, cooling and solidifying the formed sheet-like product, once orienting the sheet-like product in at least one axial direction, extracting the plasticizer to form a membrane layer A, once orienting the membrane layer A in one direction to form a membrane layer B, and then laminating the membrane layer A to the membrane layer B to form the laminate structure. |
