Separator and secondary battery including the separator
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 M D tan δ - T D tan δ M D tan δ + T D 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.
1. A separator comprising:
a first layer consisting of a porous polyolefin, having a parameter X equal to or more than 0 and equal to or less than 20 and a white index equal to or more than 85 and equal to or less than 98,
wherein the parameter X is defined by the following equation:
X
=
100
M
D
tan
δ
-
T
D
tan
δ
M
D
tan
δ
+
T
D
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.
2. The separator according to claim 1 ,
wherein the parameter X is equal to or more than 2 and equal to or less than 20.
3. The separator according to claim 1 ,
wherein the white index is equal to or more than 85 and equal to or less than 95.
4. The separator according to claim 1 , further comprising a porous layer over the first layer.
5. The separator according to claim 1 , further comprising a pair of porous layers sandwiching the first layer.
6. A secondary battery comprising the separator according to claim 1 .