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EP-4742417-A1 - COMPOSITE SEPARATOR AND ELECTROCHEMICAL DEVICE INCLUDING THE SAME

EP4742417A1EP 4742417 A1EP4742417 A1EP 4742417A1EP-4742417-A1

Abstract

Provided is a composite separator including: a porous substrate; and a coating layer which is formed on at least one surface of the substrate and includes organic particles, wherein the coating layer satisfies the following Equation 1, and the composite separator may secure excellent heat resistance, adhesive strength, and fusion strength with an electrode even at a small thickness and prevent a blocking phenomenon: 4 , 000 ≤ A × D 2 / T ≤ 5,500 wherein A, D, and T are as defined in the specification.

Inventors

  • KIM, DONG JAE
  • YUN, CHEOL MIN
  • LEE, SOON BO

Assignees

  • SK Innovation Co., Ltd.
  • SK IE Technology Co., Ltd.

Dates

Publication Date
20260513
Application Date
20251031

Claims (15)

  1. A composite separator comprising: a porous substrate; and a coating layer which is formed on at least one surface of the substrate and includes organic particles, wherein the coating layer satisfies the following Equation 1: 4 , 000 ≤ A × D 2 / T ≤ 5,500 wherein A is the number of the organic particles per unit area (/mm 2 ) on a surface of the coating layer; D is an average particle diameter (µm) of the organic particles observed on the surface of the coating layer; and T is a total thickness (µm) of the coating layer.
  2. The composite separator of claim 1, wherein the average particle diameter (D) of the organic particles on the surface of the coating layer is 1 µm to 10 µm, and/or wherein the organic particles have a glass transition temperature (T g ) of 40°C to 80°C.
  3. The composite separator of claim 1 or 2, wherein the total thickness of the coating layer is 0.1 µm to 20 µm, preferably 1 µm to 10 µm, more preferably 1 µm to 5 um, and even more preferably more than 1 µm and less than 5 µm.
  4. The composite separator of one of claims 1 to 3, wherein the organic particles include one or two or more selected from the group consisting of acryl-based polymers, urethane-based polymers, and fluorine-based polymers.
  5. The composite separator of claim 4, wherein the acryl-based polymer includes a copolymer including an alkyl (meth)acrylatebased monomer polymerization unit; and one or two or more polymerization units selected from a styrene-based monomer polymerization unit, a butadiene-based monomer polymerization unit, and a vinyl-based monomer polymerization unit.
  6. The composite separator of one of claims 1 to 5, wherein the coating layer further includes inorganic particles and a binder, preferably wherein the inorganic particles are included at 96 to 99 wt% with respect to a total weight of the coating layer.
  7. The composite separator of claim 6, wherein the binder and the organic particles are included at a weight ratio of 5:5 to 7:3, and/or wherein the organic particles are included in a range of more than 1 wt% and 2 wt% or less with respect to the total weight of the coating layer.
  8. The composite separator of claim 6 or 7, wherein the inorganic particles have an equivalent spherical diameter (Dv50) of 0.01 µm to 1 µm, preferably wherein the inorganic particles include one or two or more selected from the group consisting of boehmite, pseudo-boehmite, BaSO 4 , CeO 2 , MgO, CaO, ZnO, Al 2 O 3 , SiO 2 , TiO 2 , BaTiO 3 , HfO 2 , SrTiO 3 , SnO 2 , NiO, ZrO 2 , Y 2 O 3 , and SiC.
  9. The composite separator of one of claims 1 to 8, wherein the binder includes one or two or more selected from (meth)acryl-based polymers, fluorine-based polymers, styrene-based polymers, vinyl alcohol-based polymers, vinyl ester-based polymers, vinylpyrrolidone-based polymers, cellulose-based polymers, polyimide-based polymers, polyamide-based polymers, and polyalkylene glycol, preferably wherein the binder includes polyacrylamide and/or carboxymethyl cellulose.
  10. The composite separator of claim 9, wherein the binder includes carboxymethyl cellulose having a weight average molecular weight of 180,000 g/mol or more and a degree of substitution of 0.6 to 1.2.
  11. The composite separator of one of claims 1 to 10, wherein the porous substrate is hydrophilically surface-treated, preferably corona discharge surface-treated.
  12. The composite separator of one of claims 1 to 11, wherein the composite separator has the following anti-blocking performance: [anti-blocking performance] two sheets of the composite separators were placed so that they faced the coating layer, respectively, pressing was performed at a temperature of 25°C and a pressure of 15 kgf/cm 2 for an hour, the separators were peeled off at 180° in accordance with ASTM D903, and it was confirmed whether organic particles and/or inorganic particles were desorbed, through scanning electron microscope (SEM); and 10 random positions were specified, the number of desorbed organic particles and/or inorganic particles per unit area was counted, and as a result of deriving an average value of 10 points, the value was less than 10 -4 /µm 2 , or neither organic particles nor inorganic particles were desorbed.
  13. The composite separator of one of claims 1 to 12, wherein, when the composite separator is subjected to a cardboard test and a degree of foreign matter smeared on a surface of a cardboard is evaluated, a ratio of an area occupied by the smeared foreign matter to an area of the cardboard is 5% or less: [cardboard test] a black cardboard and a rubber pad having a size of 2 cm × 10 cm are sequentially placed on a coating layer of a composite separator specimen having a size of 5 cm × 10 cm, the cardboard is pulled out horizontally at a speed of 0.1 m/s while a force of 10 N is applied to the rubber pad using a pressing device, and a degree of foreign matter smeared on the surface of the cardboard is tested.
  14. A method for manufacturing a composite separator, comprising: applying a composition for forming a coating layer including organic particles on at least one surface of a porous substrate; and drying the composition to form a coating layer, the coating layer being configured to satisfy the following Equation 1: 4 , 000 ≤ A × D 2 / T ≤ 5 , 500 wherein A is the number of the organic particles per unit area (/mm2) on a surface of the coating layer; D is an average particle diameter (µm) of the organic particles observed on the surface of the coating layer; and T is a total thickness (µm) of the coating layer, preferably wherein the drying is performed by drying by warm air, hot air, or low-humidity air, vacuum drying, or irradiation with far infrared rays, and/or electron beam-induced radiation, and/or wherein a drying time is 30 seconds to 500 seconds.
  15. An electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator includes a porous substrate and a coating layer which is formed on at least one surface of the substrate and includes organic particles, and the coating layer satisfies the following Equation 1: 4 , 000 ≤ A × D 2 / T ≤ 5 , 500 wherein A is the number of the organic particles per unit area (/mm 2 ) on a surface of the coating layer; D is an average particle diameter (µm) of the organic particles observed on the surface of the coating layer; and T is a total thickness (µm) of the coating layer.

Description

TECHNICAL FIELD The following disclosure relates to a separator and an electrochemical device including the same. BACKGROUND In recent years, as an electrochemical device has gradually developed a higher capacity and higher output, there is a growing demand for securing heat resistance and safety. In particular, performance required for a separator which acts as a very important factor in securing heat resistance and safety of an electrochemical device is being advanced, and, for example, a composite separator in which an inorganic coating layer including inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconia (ZrO2) and a binder is introduced onto a porous substrate has been established as an important technology. However, since a conventional composite separator often shows insufficient adhesion to an electrode, the separator and the electrode are separated during a cell assembly process which can lead to distortion, deformation, crack or pinhole formation and/or delamination of an electrode assembly and, in turn, may cause short circuits between electrodes, ultimately resulting in a safety issue. To address these issues, a concept based on an introduction of a coating layer including a separate fusing agent, which may exert fusion strength with an electrode, has been suggested. Yet, the fusion effect may not be sufficient and, even if sufficient fusion strength can be implemented, issues related to e.g. a blocking phenomenon, in which the fusing agent and a material in the coating layer are desorbed, may still occur. [Related Art Documents] [Patent Document] (Patent Document 1) KR 10-2573567B1 (August 29, 2023) SUMMARY An embodiment of the present invention is directed to providing a composite separator to which a coating layer including organic particles to implement fusion strength with an electrode is introduced, and the composite separator may secure excellent heat resistance, adhesive strength, and fusion strength with an electrode even at a small thickness and may prevent a blocking phenomenon. Another embodiment of the present invention is directed to providing an electrochemical device employing the composite separator. In one general aspect, a composite separator includes: a porous substrate; and a coating layer which is formed on at least one surface of the substrate and includes organic particles, wherein the coating layer satisfies the following Equation 1: 4,000≤A×D2/T≤5,500 wherein A is the number of the organic particles per unit area (/mm2) on a surface of the coating layer;D is an average particle diameter (µm) of the organic particles observed on the surface of the coating layer; andT is a total thickness (µm) of the coating layer. The average particle diameter (D) of the organic particles on the surface of the coating layer may be 1 µm to 10 µm. The total thickness of the coating layer may be 0.1 µm to 20 µm, preferably 1 µm to 10 µm, more preferably 1 µm to 5 µm, and even more preferably more than 1 µm and less than 5 µm. The organic particles may have a glass transition temperature (Tg) of 40°C to 80°C. The organic particles may include one or two or more selected from the group consisting of acryl-based polymers, urethane-based polymers, and fluorine-based polymers. The acryl-based polymer may include a copolymer including an alkyl (meth)acrylate-based monomer polymerization unit; and one or two or more polymerization units selected from a styrene-based monomer polymerization unit, a butadiene-based monomer polymerization unit, and a vinyl-based monomer polymerization unit. The coating layer may further include inorganic particles and a binder. The inorganic particles may be included at 96 to 99 wt% with respect to the total weight of the coating layer. In this specific content range, increased adhesive strength between the inorganic particles in the coating layer as well as the adhesive strength between the interfaces of the substrate and the coating layer may be achieved, while heat shrinkage may be significantly reduced. The binder and the organic particles may be included at a weight ratio of 5:5 to 7:3. The organic particles may be included at more than 1 wt% and 2 wt% or less with respect to the total weight of the coating layer. A content in this range may lead to improved fusion strength. The inorganic particles may have an equivalent spherical diameter (Dv50) of 0.01 µm to 1 µm. The inorganic particles may include one or two or more selected from the group consisting of boehmite, pseudo-boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC. The binder may be one or two or more selected from (meth)acryl-based polymers, fluorine-based polymers, styrene-based polymers, vinyl alcohol-based polymers, vinyl ester-based polymers, vinylpyrrolidone-based polymers, cellulose-based polymers, polyimide-based polymers, polyamide-based polymers, and polyalkylene glycol. The binder may include polyacrylamide and/or