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EP-4742407-A1 - COMPOSITE SEPARATOR AND ELECTROCHEMICAL DEVICE INCLUDING THE SAME, AND METHOD FOR PRODUCING THE SAME

EP4742407A1EP 4742407 A1EP4742407 A1EP 4742407A1EP-4742407-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 binder includes polyacrylamide and 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 at a weight ratio of 60 to 90: 40 to 10. 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 binder includes polyacrylamide and carboxymethyl cellulose having a weight average molecular weight of 180,000 g/mol or more and a degree of substitution measured in accordance with ASTM D1439 of 0.6 to 1.2 at a weight ratio of 60 to 90: 40 to 10.
  2. The composite separator of claim 1, wherein the carboxymethyl cellulose has the weight average molecular weight of 180,000 to 1,500,000 g/mol, and/or wherein the carboxymethyl cellulose has the degree of substitution of 0.7 to 1.0.
  3. The composite separator of claim 1 or 2, wherein the polyacrylamide has a weight average molecular weight of 150,000 to 250,000 g/mol.
  4. The composite separator of 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 of any one of claims 1 to 4, wherein the inorganic particles have an average particle diameter (D50) of 0.1 to 1.0 µm, and/or 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 of any one of claims 1 to 5, 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.
  7. The composite separator of any one of claims 1 to 6, 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.
  8. The composite separator of any one of claims 1 to 7, wherein the composite separator has one or both characteristics (i) and/or (ii) : (i) 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; (ii) 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 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 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.
  9. A method for manufacturing a composite separator, the method comprising: applying a composition for forming a ceramic layer including a binder and inorganic particles on one or both surfaces of a porous substrate and drying the composition to form a ceramic layer, wherein the binder includes polyacrylamide and 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 at a weight ratio of 60 to 90: 40 to 10.
  10. The method for manufacturing a composite separator in claim 9, the composition for forming a ceramic layer has a viscosity of 300 to 5,000 mPa·s or 800 to 1500 mPa·s, when the solid mass % thereof is 25 %.
  11. The method for manufacturing a composite separator in claim 9 or 10, the surface of the porous substrate is treated with a corona discharge treatment or a plasma discharge treatment before applying the composition for forming a ceramic layer.
  12. use of carboxymethyl cellulose having a weight average molecular weight of 180,000 to 280,000 g/mol and a degree of substitution of 0.6 to 1.2 in combination with polyacrylamide as a binder together with inorganic particles for the formation of a ceramic layer on one or both surfaces a porous substrate, optionally to produce a separator.
  13. An electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator is according to any one of claims 1 to 8.
  14. The electrochemical device of claim 13, the electrochemical device is a secondary lithium battery.
  15. Use of the electrochemical device according to claim 13 or 14 in electric vehicles, battery charging stations, and solar power generations and wind power generations.

Description

TECHNICAL FIELD The following disclosure relates to a separator, an electrochemical device including the same, and use of the electrochemical device. The present disclosure also relates to a method of manufacturing a composite separator, and to a use of a binder having certain 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 including inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconia (ZrO2), as well as a binder on a porous substrate is introduced 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, since a conventional binder applied to a composite separator does not have sufficient adhesive strength to both the substrate and the inorganic particles, e.g. between the substrate and the ceramic layer; and the inorganic particles among each other, as the thickness of the inorganic particle coating layer, i.e. a ceramic layer, is thinner, mechanical strength and/or heat resistance of the seperator decrease. Though studies for solving the problem are continuing, a binder material having improved heat resistance has somewhat insufficient adhesive strength, or when the adhesive strength of the separator is intended to be improved, properties such as air permeability and interfacial resistance are deteriorated and device performance is degraded. Thus, new binders in the ceramic layer are required for improved heat resistance and adhesive strength of the separator at a small thickness. [Related Art Documents] [Patent Document] Korean Patent Laid-Open Publication No. 10-2015-0071453A 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 by employing a specific binder with the inorganic particles of the ceramic layer. 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 binder includes polyacrylamide and 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 at a weight ratio of 60 to 90: 40 to 10. The carboxymethyl cellulose may have the weight average molecular weight of 180,000 to 1,500,000 g/mol. The carboxymethyl cellulose may have the degree of substitution of 0.7 to 1.0. The polyacrylamide may have a weight average molecular weight of 150,000 to 250,000 g/mol. 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 have an average particle diameter (D50) of 0.1 to 1.0 µm. 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 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. 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. The composite separator according to an exemplary embodiment may have heat shrinkage rates in MD and TD directions which are measured after the composite separator is allowed to stand at 150°C for 60 mi