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EP-4738594-A2 - LITHIUM SECONDARY BATTERY COMPRISING SI-BASED NEGATIVE ELECTRODE ACTIVE MATERIAL

EP4738594A2EP 4738594 A2EP4738594 A2EP 4738594A2EP-4738594-A2

Abstract

Provided is a lithium secondary battery with reduced Hi-pot defects and improved capacity retention rate. According to one aspect of the present disclosure, there is provided a lithium secondary battery including an anode, a cathode, and a separator interposed between the anode and the cathode, in which the anode includes a Si-based anode active material, the separator includes a separator substrate having a plurality of pores and including a polyolefin resin, the polyolefin resin has a polydispersity index (PDI) of 2.5 to 4.2, an average pore size of 20 to 40 nm, and a maximum pore size of 50 nm or less.

Inventors

  • BAE, Kyeong Hui
  • LEE, SO YEONG
  • JEONG, SO MI
  • BAE, WON SIK

Assignees

  • LG Energy Solution, Ltd.

Dates

Publication Date
20260506
Application Date
20230331

Claims (11)

  1. A lithium secondary battery comprising an anode, a cathode, and a separator interposed between the anode and the cathode, wherein the anode comprises a Si-based anode active material, the separator comprises a separator substrate having a plurality of pores and comprising a polyolefin resin, the polyolefin resin has a polydispersity index (PDI) of 2.5 to 4.2, wherein the PDI = (weight average molecular weight)/(number average molecular weight) and is measured as described in the description, and the pores have an average pore size of 20 to 40 nm and a maximum pore size of 50 nm or less, measured as described in the description.
  2. The lithium secondary battery according to claim 1, wherein the polyolefin resin has a PDI of 2.5 to 4.0, measured as described in the description, the pores have an average pore size of 20 to 39 nm and a maximum pore size of 48 nm or less, measured as described in the description, and the separator substrate has a strain of 23% or less when a tensile stress of 15 MPa is applied at 60°C for 60 seconds and a recovery time of 190 seconds or less until reaching a recovery rate of 70% when a tensile stress of 2 MPa is applied at 70°C for 180 seconds and then removed, wherein the strain and the recovery time are measured as described in the description.
  3. The lithium secondary battery according to claim 1, wherein the polyolefin resin has a PDI of 2.6 to 3.9, measured as described in the description, the pores have an average pore size of 21 to 38 nm and a maximum pore size of 46 nm or less, measured as described in the description, and the separator substrate has a strain of 21% or less when a tensile stress of 15 MPa is applied at 60°C for 60 seconds and a recovery time of 180 seconds or less until reaching a recovery rate of 70% when a tensile stress of 2 MPa is applied at 70°C for 180 seconds and then removed, wherein the strain and the recovery time are measured as described in the description.
  4. The lithium secondary battery according to claim 3, wherein the pores have an average pore size of 22.2 to 36.1 nm, measured as described in the description, and the separator substrate has a strain of 20.1% or less when a tensile stress of 15 MPa is applied at 60°C for 60 seconds and a recovery time of 178 seconds or less until reaching a recovery rate of 70% when a tensile stress of 2 MPa is applied at 70°C for 180 seconds and then removed, wherein the strain and the recovery time are measured as described in the description.
  5. The lithium secondary battery according to claim 1, wherein the polyolefin resin has a weight average molecular weight of 500,000 to 1,500,000 g/mol, measured as described in the description.
  6. The lithium secondary battery according to claim 1, wherein the separator substrate comprises a core portion made of a mixture of polyethylene and polypropylene and a polyethylene skin portion provided on each of both surfaces of the core portion.
  7. The lithium secondary battery according to claim 1, wherein the separator further comprises an organic/inorganic composite coating layer on at least one surface of the separator substrate, and the organic/inorganic composite coating layer comprises a crystalline binder and an amorphous binder.
  8. The lithium secondary battery according to claim 7, wherein the lithium secondary battery further includes an electrolyte, wherein the crystalline binder and the amorphous binder each independently have a concentration gradient in a thickness direction of the organic/inorganic composite coating layer.
  9. The lithium secondary battery according to claim 7, wherein the organic/inorganic composite coating layer comprises a first portion adjacent to the separator substrate and a second portion opposite to the first portion, and the concentration of the crystalline binder in the second portion is higher than the concentration of the crystalline binder in the first portion.
  10. The lithium secondary battery according to claim 1, wherein the Si-based anode active material includes at least one type selected from the group consisting of Si, SiO, and Si alloys.
  11. The lithium secondary battery according to claim 1, wherein the anode further comprises graphite.

Description

Technical Field The present disclosure claims the benefit of the filing date of Korean Patent Application No. 10-2022-0072073 filed with the Korean Patent Office on June 14, 2022, the entire contents of which are incorporated herein by reference. The present disclosure relates to a lithium secondary battery including a Si-based anode active material as an anode active material. Background Art As a separator for a lithium secondary battery, a film based on a polymer resin such as polyolefin and having a plurality of pores is used. Typically, an electrode assembly is manufactured through a lamination process in which a separator and an electrode are bonded by application of heat and pressure. The higher the heat and pressure applied to the separator, the higher the bonding force between the electrode and the separator. Recently, for the purpose of improving productivity, adhesion is secured by increasing application pressure because time of heat application to the separator is shortened as the process speeds up. However, the increase of application pressure may cause the electrode assembly to be deformed. During the lamination process, the thickness of the polymer film substrate is significantly reduced and the damage to the pores increases, resulting in a decrease in the performance of a battery as well as a decrease in the dielectric breakdown voltage of the separator, resulting in increased Hi-pot defects and reduced capacity retention rates (CRR) . Particularly, when a Si-based anode active material such as Si, SiO, or Si alloy is used as an anode active material of a lithium secondary battery, the volume expansion of the anode is large, and thus the internal pressure of cells increases, resulting in intensified compression deformation of the separator. In addition, the Si-based anode active materials have a greater granularity, roughness, and hardness than graphite anode active materials, thereby causing local damage to the separator while lamination of the anode active material and the separator is performed. Therefore, when an Si-based anode active material is used, it is necessary to develop a separator having improved compression resistance. Disclosure Technical Problem An objective of the present disclosure is to provide a lithium secondary battery including a Si-based anode active material, the lithium secondary battery having reduced Hi-pot defects and an improved capacity retention rate. It will be readily apparent that the objectives and advantages of the present disclosure can be achieved by means or methods and combinations thereof recited in the claims. Technical Solution According to a first aspect of the present disclosure, there is provided a lithium secondary battery including an anode, a cathode, and a separator interposed between the anode and the cathode, in which the anode includes a Si-based anode active material, the separator includes a separator substrate having a plurality of pores and including a polyolefin resin, the polyolefin resin has a polydispersity index (PDI) of 2.5 to 4.2, an average pore size of 20 to 40 nm, and a maximum pore size of 50 nm or less. According to a second aspect of the present disclosure, there is provided a lithium secondary battery including an anode, a cathode, and a separator interposed between the anode and the cathode, in which the anode includes a Si-based anode active material,the separator includes a separator having a plurality of pores and including a polyolefin resin,the polyolefin resin has a polydispersity index (PDI) of 2.5 to 4.2,the pores have an average pore size of 20 to 40 nm and a maximum pore size of 50 nm or less, andthe separator substrate has characteristics in whicha strain thereof is 25% or less when a tensile stress of 15 MPa is applied thereto at 60°C for 60 seconds andit takes 200 seconds until reaching a recovery rate of 70% after a tensile stress of 2 MPa is applied at 70°C for 180 seconds and then removed. According to a third aspect of the present disclosure, there is provided a lithium secondary battery, in the first or second aspect,the polyolefin resin has a polydispersity index (PDI) of 2.5 to 4.0,the pores have an average pore size of 20 to 39 nm and a maximum pore size of 48 nm or less, andthe separator has characteristics in whicha strain thereof is 23% or less when a tensile stress of 15 MPa is applied thereto at 60°C for 60 seconds andit takes 190 seconds or less until reaching a recovery rate of 70% after a tensile stress of 2 MPa is applied at 70°C for 180 seconds and then removed. A fourth aspect of the present disclosure provides a lithium secondary battery, in the third aspect,the polyolefin resin has a polydispersity index (PDI) of 2.6 to 3.9,the pores have an average pore size of 21 to 38 nm and a maximum pore size of 46 nm or less, andthe separator has characteristics in whicha strain thereof is 21% or less when a tensile stress of 15 MPa is applied thereto at 60°C for 60 seconds andit takes 180 seconds