POLYOLEFIN SEPARATOR FOR AN ELECTROCHEMICAL DEVICE AND ELECTROCHEMICAL DEVICE INCLUDING SAME

A polyolefin separator for an electrochemical device, the separator having a plurality of pores having an average pore size of 20 nm to 40 nm and a maximum pore size of 50 nm or less and including a polyolefin resin having a polydispersity index (PDI) of in a range of 2.5 to 4.2. The polyolefin separator may have a strain rate of 25% or less as measured when a tensile stress is applied at 60° C. at 15 MPa for 60 seconds, and the polyolefin separator may have a recovery time of 200 seconds or less to reach a recovery rate of 70% as measured after removing a tensile stress applied at 70° C. at 2 MPa for 180 seconds.