LITHIUM SECONDARY BATTERY INCLUDING Si-BASED ANODE ACTIVE MATERIAL

A lithium secondary battery comprising;

• an anode comprising a Si-based anode active material,
• a cathode, and
• a separator interposed between the anode and the cathode, the separator comprising a separator substrate comprising a polyolefin resin having a polydispersity index (PDI) of 2.5 to 4.2,
• wherein the separator substrate has a plurality of pores,
• and
• the plurality of pores have an average pore size of 20 to 40 nm and a maximum pore size of 50 nm or less and
• wherein the separator substrate has:
• a strain of 25% or less when a tensile stress of 15 MPa is applied at 60° C. for 60 seconds and
• a recovery time of 200 seconds or less to reach a recovery rate of 70% when a tensile stress of 2 MPa is applied at 70° C. for 180 seconds and then removed.