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EP-4742413-A1 - COMPOSITE SEPARATOR AND ELECTROCHEMICAL DEVICE INCLUDING THE SAME

EP4742413A1EP 4742413 A1EP4742413 A1EP 4742413A1EP-4742413-A1

Abstract

Provided is a composite separator including: a porous substrate; and a ceramic layer formed on one or both surfaces of the substrate. Specifically, the ceramic layer includes inorganic particles, a binder, and a particulate fusing agent and satisfies the following Equation 1, and the binder is carboxymethyl cellulose having a weight average molecular weight of 180,000 g/mol to 280,000 g/mol. The composite separator according to the present disclosure may secure excellent heat resistance, adhesive strength, and fusion strength with an electrode: 0.9 < T × W 1 + W 2 W 2 × D < 2.4 wherein T, W1, W2, and D are as defined in the specification.

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
20251028

Claims (15)

  1. A composite separator comprising: a porous substrate; and a ceramic layer formed on one or both surfaces of the substrate, wherein the ceramic layer includes inorganic particles, a binder, and a particulate fusing agent and satisfies the following Equation 1, and the binder is carboxymethyl cellulose having a weight average molecular weight of 180,000 g/mol to 280,000 g/mol: 0.9 < T × W 1 + W 2 W 2 × D < 2.4 wherein T is a thickness (µm) of the ceramic layer; W1 is a content (wt%) of the binder to the total weight of the ceramic layer; W2 is a content (wt%) of the particulate fusing agent to the total weight of the ceramic layer; and D is an average particle diameter (µm) of the particulate fusing agent.
  2. The composite separator of claim 1, wherein the particulate fusing agent has an average particle diameter (D50) of 1 µm to 10 µm, preferably 1.5 µm to 10 um; and/or wherein the particulate fusing agent is selected from the group consisting of polyurethane beads, polyurethane acryl beads, epoxy-acryl beads, polystyrene-polybutyl methacrylate-polymethyl methacrylate (PS-PBMA-PMMA), polybutyl methacrylate-polymethyl methacrylate (PBMA-PMMA) polystyrene-polydimethylsiloxane-polybutyl methacrylate (PS-PDMS-PBMA), polystyrene-polydimethylsiloxane-polymethyl methacrylate (PS-PDMS-PMMA), and polydimethylsiloxane-polymethyl methacrylate (PDMS-PMMA).
  3. The composite separator of claim 1 or 2, wherein a total thickness of the ceramic layer is 1 µm to 20 µm.
  4. The composite separator of any one of the preceding claims, wherein the carboxymethyl cellulose has a degree of substitution of 0.6 to 1.2.
  5. The composite separator of any one of the preceding claims, wherein the inorganic particles have an average particle diameter (D50) of 0.01 µm to 1 um, and/or, wherein the inorganic particles are one or two or more selected from 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.
  6. The composite separator of any one of the preceding claims, wherein the inorganic particles are included at 90 to 99 wt% with respect to the total weight of the ceramic layer, and/or wherein the binder is included at 0.1 wt% to 10 wt% with respect to the total weight of the ceramic layer, and/or wherein the particulate fusing agent is included at 0.1 wt% to 10 wt% with respect to the total weight of the ceramic layer.
  7. The composite separator of any one of the preceding claims, wherein the binder and the particulate fusing agent are included at a weight ratio of 5:5 to 8:2.
  8. The composite separator of any one of the preceding claims, wherein the particulate fusing agent has a glass transition temperature (Tg) of 40°C to 80°C.
  9. The composite separator of any one of the preceding claims, 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.
  10. The composite separator of any one of the preceding claims, 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.
  11. An electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator is as defined in any one of claims 1 to 10.
  12. The electrochemical device according to claim 11, wherein the electrochemical device is a lithium battery.
  13. Use of the electrochemical device according to claim 11 or 12 in electric vehicles, battery charging stations, solar power generations and wind power generations.
  14. Use of carboxymethyl cellulose in combination with inorganic particles and a fusing agent for the formation of a ceramic layer formed on one or both surfaces of a porous substrate, optionally to produce a separator, wherein the carboxymethyl cellulose has a weight average molecular weight of 180,000 g/mol to 280,000 g/mol and optionally a degree of substitution of 0.6 to 1.2.
  15. Use of the composite separator according to any one of claims 1 to 10 for storing and transporting in a winding state by suppressing a desorption phenomenon and a blocking phenomenon.

Description

TECHNICAL FIELD The following disclosure relates to a separator and an electrochemical device including the same, as well as to the use of the same in electric vehicles, battery charging stations and solar power and wind power generations, to the use of a combination of binders for a ceramic layer to be disposed on a porous substrate, and to the use of the separator in storing and transporting. 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. In particular, performance required for a separator which plays an important role 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) as well as a binder is introduced onto a porous substrate has been established as an important technology. However, since a conventional composite separator has insufficient adhesion to an electrode, the separator and the electrode are separated during a cell assembly process to cause distortion, deformation, and the other detachment of an electrode assembly and cause short circuit between electrodes, resulting in a safety issue. In order to solve the problem, a method of separately introducing an adhesive layer capable of exhibiting fusion strength with an electrode on an inorganic coating layer has been suggested. However, it is difficult to apply the method to actual commercialization, e.g., due to the necessity of addition of further process steps which results in increasing manufacturing costs, and the added adhesive layer increases internal resistance of a battery and may degrade electrical performance. [Related Art Documents] [Patent Document] KR 10-2573567 B1 (August 29, 2023) SUMMARY An embodiment of the present invention is directed to providing a composite separator in which a particulate fusing agent is introduced to a ceramic layer, which may secure excellent heat resistance, adhesive strength, and fusion strength with electrodes 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 ceramic layer formed on one or both surfaces of the substrate, wherein the ceramic layer includes inorganic particles, a binder, and a particulate fusing agent and satisfies the following Equation 1, and the binder is carboxymethyl cellulose having a weight average molecular weight of 180,000 g/mol to 280,000 g/mol: 0.9<T×W1+W2W2×D<2.4 wherein T is a thickness (µm) of the ceramic layer;W1 is a content (wt%) of the binder to the total weight of the ceramic layer;W2 is a content (wt%) of the particulate fusing agent to the total weight of the ceramic layer; andD is an average particle diameter (µm) of the particulate fusing agent. The average particle diameter D of the particulate fusing agent is defined as the D50 value. The term "particulate" defines that a certain matter, in the present invention e.g. the fusing agent, is present - at least in its initial (original) form - in the form of a particle. The particulate fusing agent may have an average particle diameter (D50) of 1 µm to 10 µm. In a further embodiment, the average particle diameter (D50) of the particulate fusing agent may be 1.0 µm to 10 µm, or 1.5 µm to 10 µm, or 2.0 µm to 10 µm, or 2.5 µm to 10 µm, or 1.5 µm to 7.5 µm, or 1.5 µm to 6.5 µm, or 1.5 µm to 5.5 µm, or 2.0 µm to 5.5 µm, or 2.5 µm to 5.0 µm. In a further embodiment, the D50 of the particulate fusing agent is 2.0 µm to 7.5 µm. In a preferred embodiment, the D50 of the particulate fusion agent is 1.5 µm to 7.5 µm, more preferably 2.0 µm to 7,0 µm, and even more preferably 2.5 µm to 5.5 µm. The particulate fusing agent is selected from the group consisting of polyurethane beads, polyurethane acryl beads, epoxy-acryl beads, polystyrene-polybutyl methacrylate-polymethyl methacrylate (PS-PBMA-PMMA), polybutyl methacrylate-polymethyl methacrylate (PBMA-PMMA) polystyrene-polydimethylsiloxane-polybutyl methacrylate (PS-PDMS-PBMA), polystyrene-polydimethylsiloxane-polymethyl methacrylate (PS-PDMS-PMMA), and polydimethylsiloxane-polymethyl methacrylate (PDMS-PMMA) A total thickness of the ceramic layer may be 1 µm to 20 µm. The carboxymethyl cellulose may have a degree of substitution of 0.6 to 1.2. The inorganic particles may have an average particle diameter (D50) of 0.01 µm to 1 µm. The inorganic particles may be one or two or more selected from boehmite, pseudo-boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC. The inorganic particles may be included at 90 to 99 wt% with respect to the total weight of the ceramic layer. The binder