Separator having difference in porosity along thickness direction and manufacturing method thereof

1 . A separator for a secondary battery, comprising:

a separator body having a porous structure, wherein the separator body consists of a polyolefin,

wherein the separator body has a difference in porosity along a thickness direction,

wherein the separator further comprises a first coating layer on a first surface of the separator body and a second coating layer on a second surface of the separator body, and

wherein the first coating layer and the second coating layer are formed by coating the separator body.

2 . The separator for the secondary battery according to claim 1 , wherein the separator body does not have an interface in which the difference in porosity occurs, and wherein the porosity continuously changes.

3 . The separator for the secondary battery according to claim 1 , wherein the separator body comprises at least one of a portion in which a porosity increases along the thickness direction and a portion in which a porosity decreases along the thickness direction.

4 . The separator for the secondary battery according to claim 1 , wherein the separator body has a maximum porosity at a center of the thickness direction of the separator body.

5 . The separator for the secondary battery according to claim 1 , wherein a hardness of the first coating layer and a hardness of the second coating layer are different from each other.

6 . The separator for the secondary battery according to claim 1 , wherein

the first coating layer comprises a first inorganic material having a first hardness and a first binder, and

the second coating layer comprises a second inorganic material having a second hardness and a second binder,

wherein the first inorganic material and the second inorganic material have the same hardness and are present in different amount ratios, or have different hardnesses regardless of a amount ratio.

7 . A method of manufacturing the separator for the secondary battery according to claim 1 , the method comprising:

1) Preparing the separator body having the porous structure comprising the polyolefin;

2) Forming the first coating layer on the first surface of the separator body of step 1) and forming the second coating layer on the second surface of the separator body of step 1); and

3) pressing the separator of step 2).

8 . The method according to claim 7 , wherein a hardness of the first coating layer and a hardness of the second coating layer are different from each other.

9 . The method according to claim 7 , wherein a compression ratio of a first surface side of the separator body and a compression ratio of a second surface side of the separator body are different.

10 . The method according to claim 7 , wherein

the first coating layer comprises a first inorganic material and a first binder, and

the second coating layer comprises a second inorganic material and a second binder,

wherein a rolling strength of the first coating layer and the second coating layer is dependent on a type and amounts of the first inorganic material, the second inorganic material, the first binder, and the second binder.

11 . The method according to claim 7 , wherein, in step 3), the same pressure is applied from an outside of the first coating layer and the second coating layer toward the separator body.

12 . An electrode assembly having a stacked structure in which the separator according to claim 1 is interposed between a positive electrode and a negative electrode,

wherein, between the positive electrode and the negative electrode, an electrode having a first ionic conductivity is disposed in a direction having a first porosity in the separator, and an electrode having a second ionic conductivity lower than the first ionic conductivity is disposed in a direction having a second porosity higher than the first porosity in the separator.

13 . A separator for a secondary battery, comprising:

a separator body having a porous structure, extending from a first surface of the separator body to a second surface of the separator body opposite to the first surface in a thickness direction, wherein the separator body consists of a polyolefin,

wherein the porous structure has a difference in porosity along the thickness direction,

wherein the separator further comprises a first coating layer on the first surface of the separator body and a second coating layer on the second surface of the separator body,

wherein the separator has a difference in porosity between a first surface side and a second surface side of the separator body, and

wherein the first coating layer and the second coating layer are formed by coating the separator body.