Separator and secondary battery including the separator

Abstract

Provided is a separator capable of suppressing an increase in internal resistance and a decrease in a battery performance. A separator having a first layer consisting of a porous polyolefin and an organic antioxidant and a secondary battery including the separator are provided. The first layer has a parameter X, defined by the following equation, equal to or more than 0 and equal to or less than 20, X = 100    MD   tan   δ - TD   tan   δ   MD   tan   δ + TD   tan   δ  2 where MD tan δ and TD tan δ are respectively a loss tangent in a flow direction and a loss tangent in a width direction which are obtained by a viscoelasticity measurement of the first layer at a temperature of 90° C. and a frequency of 10 Hz. A white index of the first layer is equal to or more than 85 and equal to or less than 98.

Dependencies are inferred from the claim text.