SEPARATOR HAVING POROSITY DIFFERENCE ACCORDING TO THICKNESS DIRECTION AND MANUFACTURING METHOD THEREFOR

Disclosed is a separator for a secondary battery comprising a polyolefin and a separator body having a porous structure, wherein the separator body is configured to be in a form having a difference in porosity along a thickness direction, and it is possible to improve the problem of imbalance in ionic conductivity caused by differences in thickness and electrical conductivity between a positive electrode and a negative electrode.