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EP-4742408-A1 - COMPOSITE SEPARATOR AND ELECTROCHEMICAL DEVICE INCLUDING THE SAME, AND MANUFACTURING METHOD OF SAID COMPOSITE SEPARATOR

EP4742408A1EP 4742408 A1EP4742408 A1EP 4742408A1EP-4742408-A1

Abstract

Provided is a composite separator including: a porous substrate; and a ceramic layer which is formed on one or both surfaces of the substrate and includes inorganic particles and a binder, wherein the inorganic particles have an average particle diameter (D50) of 0.20 µm to 0.40 µm and have a ratio (A/B) between an area (A) of a small particle diameter side and an area (B) of a large particle diameter side of 1.05 or more based on a maximum peak in a particle size distribution diagram of the inorganic particles. The composite separator may satisfy all of excellent mechanical and thermal stability and excellent ion conduction properties.

Inventors

  • YUN, CHEOL MIN
  • KIM, DONG JAE
  • OH, EUN JI
  • JUNG, HEE JOON

Assignees

  • SK IE Technology Co., Ltd.

Dates

Publication Date
20260513
Application Date
20251022

Claims (15)

  1. A composite separator comprising: a porous substrate; and a ceramic layer which is formed on one or both surfaces of the substrate and includes inorganic particles and a binder, wherein the inorganic particles have an average particle diameter (D50), measured via laser diffraction, of 0.20 µm to 0.40 µm and have a ratio (A/B) between an area (A) of a small particle diameter side and an area (B) of a large particle diameter side of 1.05 or more based on a maximum peak in a particle size distribution diagram of the inorganic particles.
  2. The composite separator according to claim 1, wherein the inorganic particles have a (D95-D50)/D50 value of 1.8 to 2.5 in the particle size distribution diagram.
  3. The composite separator according to claim 1 or 2, wherein the ratio (A/B) between the area (A) of the small particle diameter side and the area (B) of the large particle diameter is 1.05 to 1.3 based on the maximum peak in the particle size distribution diagram of the inorganic particles.
  4. The composite separator according to any one of claims 1 to 3, wherein 0.1 to 10 parts by weight of the binder is included with respect to 100 parts by weight of the inorganic particles.
  5. The composite separator according to any one of claims 1 to 4, wherein the inorganic particles are one or two or more selected from 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.
  6. The composite separator according to any one of claims 1 to 5, wherein the binder is one or two or more selected from (meth)acryl-based polymers, fluorine-based polymers, styrene-based polymers, vinylalcohol-based polymers, vinylester-based polymers, vinylpyrrolidone-based polymers, cellulose-based polymers, polyimide-based polymers, polyamide-based polymers, polyalkylene glycol, copolymers thereof, and heteropolymer blends thereof, preferably wherein the binder includes polyacrylamide, carboxymethyl cellulose, or a combination thereof.
  7. The composite separator according to claim 6 , wherein the binder includes carboxymethyl cellulose having a weight average molecular weight of 180,000 or more and a degree of substitution of 0.6 to 1.2.
  8. The composite separator according to any one of claims 1 to 7, wherein the porous substrate comprises at least one polar functional group introduced through hydrophilic surface treatment, optionally wherein the at least one polar functional group is selected from any one or more of a carboxyl group, an aldehyde group, a hydroxyl group, a carbonyl group, an amino group, preferably wherein the hydrophilic surface treatment is a corona discharge treatment or a plasma discharge treatment, or a combination thereof.
  9. The composite separator according to any one of claims 1 to 8, wherein a coating density of the ceramic layer is 1.2 to 1.8 g/cm 3 , and/or wherein a total thickness of the ceramic layer is 0.5 µm to 10 µm, preferably more than 0.5 µm and less than 5 µm, and more preferably more than 0.5 µm and less than 3 µm.
  10. The composite separator according to any one of claims 1 to 9, wherein a thickness of the composite separator is 1 to 100 µm.
  11. The composite separator according to any one of claims 1 to 10, 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 the 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 ceramic 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 for a distance of 60 mm 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.
  12. The composite separator according to any one of claims 1 to 11, wherein the composite separator has heat shrinkage rates in the machine direction (MD) and the transverse direction (TD), which are measured after the composite separator is allowed to stand at 150°C for 60 minutes, of both 4% or less.
  13. A method for manufacturing a composite separator, comprising: applying a coating slurry containing inorganic particles and a binder on one or both surfaces of a porous substrate; drying of the applied coating slurry, wherein the inorganic particles have an average particle diameter (D50), measured via laser diffraction, of 0.2 µm to 0.4 µm and satisfy a ratio (A/B) between an area (A) of a small particle diameter side and an area (B) of a large particle diameter side of 1.05 or more based on a maximum peak in a particle size distribution diagram of the inorganic particles.
  14. Use of inorganic particles, which have an average particle diameter (D50), measured via laser diffraction, of 0.20 µm to 0.40 µm and which have a ratio (A/B) between an area (A) of a small particle diameter side and an area (B) of a large particle diameter side of 1.05 or more based on a maximum peak in a particle size distribution diagram of the inorganic particles, in the formation of a ceramic layer optionally with a binder, on one or both surfaces a porous substrate, optionally to produce a separator.
  15. An electrochemical device comprising a positive electrode, a negative electrode, and the composite separator of any one of claims 1 to 12, optionally wherein the electrochemical device is a secondary lithium battery, and/or wherein the electrochemical device is used in electric vehicles, battery charging stations, and solar power generations and wind power generations.

Description

TECHNICAL FIELD The present disclosure relates to a composite separator and an electrochemical device including the same. The present disclosure further relates to a method of manufacturing a composite separator, and to a use of inorganic particles having certain size characteristics in a ceramic layer to be disposed on a porous substrate. BACKGROUND In recent years, as an electrochemical device gradually has a higher capacity and higher output, there is a growing demand for securing heat resistance and safety, and in particular, to this end, the required performance for a separator acting as a very important element is being advanced. For example, as a method for securing heat resistance and safety of a separator, a composite separator to which a coating layer is introduced that includes inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconia (ZrO2), as well as a binder on a porous substrate has been established as an important technology. Recently, research is conducted aiming for thinning of the separator for the high capacity and high output characteristics of an electrochemical device. Yet, it is difficult to achieve sufficient heat resistance for the thickness range of the thinned inorganic particle coating layer and when heat resistance is intended to be improved, adhesive strength and/or air permeability is deteriorated. [Related Art] [Patent Document] KR 10-2023-0144943 A (October 17, 2023) SUMMARY An embodiment of the present invention is directed to providing a composite separator including: a porous substrate; and a ceramic layer which is formed on one or both surfaces of the porous substrate and has pores formed between inorganic particles which are connected and fixed by a binder, wherein the composite separator has both excellent heat resistance and adhesive strength. Surprisingly, this can be achieved even though the thickness of the ceramic layer in the separator is thin, as disclosed herein. Another embodiment of the present invention is directed to providing an electrochemical device having excellent battery performance and safety by employing the composite separator. In one general aspect, a composite separator includes: a porous substrate; and a ceramic layer which is formed on one or both surfaces of the substrate and includes inorganic particles and a binder, wherein the inorganic particles have an average particle diameter (D50) of 0.20 µm to 0.40 µm and have a ratio (A/B) between an area (A) of a small particle diameter side and an area (B) of a large particle diameter side of 1.05 or more based on a maximum peak in a particle size distribution diagram of the inorganic particles. The inorganic particles may satisfy a (D95-D50)/D50 value of 1.8 to 2.5 in the particle size distribution diagram. The ratio (A/B) between the area (A) of the small particle diameter side and the area (B) of the large particle diameter may satisfy 1.05 to 1.3 based on the maximum peak in the particle size distribution diagram of the inorganic particles. The composite separator according to an exemplary embodiment may include 0.1 to 10 parts by weight of the binder with respect to 100 parts by weight of the inorganic particles. The inorganic particles may be one or two or more selected from 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, vinylalcohol-based polymers, vinylester-based polymers, vinylpyrrolidone-based polymers, cellulose-based polymers, polyimide-based polymers, polyamide-based polymers, polyalkylene glycol, copolymers thereof, and heteropolymer blends thereof. The binder may include polyacrylamide, carboxymethyl cellulose, or a combination thereof. The binder may include carboxymethyl cellulose having a weight average molecular weight of 180,000 or more and a degree of substitution of 0.6 to 1.2. The porous substrate may be hydrophilically surface-treated. Specifically, the porous substrate may comprise at least one polar functional group introduced through hydrophilic surface treatment, the polar functional group being selected from any one or more of a carboxyl group, an aldehyde group, a hydroxyl group, a carbonyl group, an amino group. The hydrophilic surface treatment may preferably be a corona discharge treatment or a plasma discharge treatment, or a combination thereof. A coating density of the ceramic layer may be 1.2 to 1.8 g/cm3. The total thickness of the ceramic layer may be 0.5 µm to 10 µm. Preferably, the total thickness of the ceramic layer may be more than 0.5 µm and less than 5 µm. More preferably, the total thickness of the ceramic layer may be more than 0.5 µm and less than 3 µm. A thickness of the composite separator according to an exemplary embodiment may be 1 to 100 µm. When the composite separator according to an exemplary embodiment is subjected to a cardboard test