Polyolefin microporous membrane and separator for lithium ion secondary battery

摘要

A polyolefin microporous membrane that can realize a lithium ion secondary battery having favorable resistance against foreign matters or the like, and high cycle characteristics at a high temperature is provided. The present invention provides a polyolefin microporous membrane having a ratio of tensile strength in a length direction to that in a width direction of 0.75 to 1.25, and a thermal shrinkage rate in the width direction at 120° C. of less than 10%.

主权项

1. A polyolefin microporous membrane having a ratio of tensile strength in a length direction to tensile strength in a width direction of 0.75 to 1.25, and a thermal shrinkage rate in the width direction at 105° C. of less than 1%,
wherein the polyolefin comprises not less than 30% by mass of polyethylene, and wherein the tensile strength in the width direction is not less than 160 MPa.