abstract |
According to the present invention, there is provided a polyolefin microporous membrane suitable for uniformly installing the thickness of the porous layer, and a battery separator suitable for increasing the capacity of a battery in which the thickness of the porous layer is uniformly formed on the polyolefin microporous membrane. A battery separator having a polyolefin microporous membrane having a fluctuation range of F25 value in the longitudinal direction of 1 MPa or less, a fluorine-based resin and inorganic particles on at least one surface thereof, and a porous layer having an average thickness T (ave) of 1 to 5 µm. (Here, the F25 value represents the value obtained by dividing the load value when the test piece is stretched by 25% using a tensile tester by the cross-sectional area of the test piece.) |