POLYOLEFIN MICRO-POROUS MEMBRANE AND LITHIUM ION SECONDARY BATTERY SEPARATOR

摘要

Provided is a polyolefin micro-porous membrane that has satisfactory resistance to foreign material and with which it is possible to realize a lithium ion secondary battery with excellent high-temperature cycling characteristics. In the polyolefin micro-porous membrane, the ratio of tensile strength in the length direction to tensile strength in the width direction is 0.75-1.25, and the coefficient of thermal contraction in the width direction at 120°C is less than 10%.