Method for manufacturing a separator for electrochemical devices

Abstract

The present invention relates to a method for manufacturing a separator for an electrochemical device, the method comprising: (S1) preparing a coating slurry including a polymer binder, inorganic particles, and a dispersion medium; (S2) heating at least one surface of a porous substrate; and (S3) applying the coating slurry prepared in (S1) to at least one surface of the porous substrate heated in (S2) to form a porous coating layer, the porous coating layer including a region in which the polymer binder is formed into a film on at least a portion of a surface in contact with the porous substrate.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0100284, filed with the Korean Intellectual Property Office on August 11, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a separator for an electrochemical device and a separator for an electrochemical device manufactured by the method. [Background technology]

[0003] Electrochemical elements convert chemical energy into electrical energy using electrochemical reactions, and in recent years, lithium secondary batteries have become widely used because of their high energy density, high voltage, long cycle life, and applicability in a variety of fields.

[0004] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The electrode assembly may be housed in a case together with an electrolyte. The separator may include a porous coating layer including a polymer binder and inorganic particles on at least one surface of a porous substrate. The inorganic particles may be connected to other inorganic particles by the polymer binder to form interstitial volumes, through which lithium ions can move. In addition to fixing the inorganic particles, the polymer binder may also provide adhesive strength to the porous coating layer, which may then adhere to the porous substrate and the electrode.

[0005] Previously, porous coating layers were formed using slurries containing an oil-based dispersion medium and an oil-based polymer binder dispersed in the oil-based dispersion medium, ensuring excellent adhesion to the porous substrate and electrodes. However, porous coating layers formed using such slurries had problems with poor wet adhesion when the separator was immersed in an electrolyte due to difficulty in controlling the distribution of the polymer binder and inorganic particles. Recently, wet adhesion was improved by using an aqueous dispersion medium and an aqueous polymer binder dispersed in the dispersion medium in the slurry used to form the porous coating layer, but this resulted in poor adhesion to the porous substrate and electrodes. To address this issue, methods such as stacking electrode assemblies or applying higher temperatures and pressures during the pressurization of stacked electrode assemblies were introduced. However, these methods resulted in problems such as poor air permeability and ionic conductivity of the separator and damage to the porous substrate.

[0006] Therefore, research is being conducted into methods for manufacturing separators that can improve the adhesive strength of the porous coating layer to the electrode and the porous substrate while maintaining the advantages of the porous coating layer containing an aqueous polymer binder and the physical properties of the separator. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a method for manufacturing a separator for an electrochemical device, in which a porous coating layer containing a polymer binder and inorganic particles has excellent adhesive strength to a porous substrate and an electrode. [Means for solving the problem]

[0008] One aspect of the present invention provides a method for manufacturing a separator for an electrochemical device, comprising: (S1) preparing a coating slurry containing a polymer binder, inorganic particles, and a dispersion medium; (S2) heating at least one surface of a porous substrate; and (S3) applying the coating slurry prepared in (S1) to at least one surface of the porous substrate heated in (S2) to form a porous coating layer, wherein the porous coating layer includes a region in which the polymer binder is formed into a film on at least a portion of a surface that contacts the porous substrate.

[0009] In the step (S1), the coating slurry is heated to a temperature higher than room temperature (25° C.) and heated to a glass transition temperature (T g ) lower than the temperature (T S ) can be produced.

[0010] In the step (S2), the porous substrate is heated to a melting point (T m ) can be heated to less than

[0011] In the step (S2), the porous substrate is heated to a temperature above the glass transition temperature (T g ) higher temperature (T P ) can be heated.

[0012] The method for producing a separator for an electrochemical device can satisfy the following formula (1):

[0013] Formula (1) T P -T g ≧T g -T S

[0014] The area where the polymer binder is filmed may be 25% by weight to 50% by weight based on the total weight of the porous coating layer.

[0015] The porous coating layer may have a thickness of 1 μm to 20 μm.

[0016] The step (S2) may heat only one or more of an area extending a predetermined thickness from the edge of the one surface, a checkerboard area formed on the one surface, and a pattern area in which the same shape is repeatedly formed on the one surface.

[0017] In the method for manufacturing a separator for an electrochemical device, the step (S3) may include drying the porous substrate coated with the coating slurry at a temperature of 50° C. to 70° C. for 5 to 10 minutes.

[0018] In the method for manufacturing a separator for an electrochemical device, the step (S3) may involve repeating the drying step five or more times.

[0019] In the method for manufacturing a separator for an electrochemical device, the polymer binder may be one or more particulate polymer binders selected from the group consisting of an acrylic polymer, a fluorine-based polymer, and a hybrid polymer of an acrylic polymer and a fluorine-based polymer.

[0020] In the method for manufacturing a separator for an electrochemical device, the fluoropolymer may be a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and another polymerizable monomer, or a mixture of two or more of these.

[0021] In the method for manufacturing a separator for an electrochemical device, the particulate polymer binder may have an average particle size (D50) of 100 nm to 700 nm, and the inorganic particles may have an average particle size (D50) of 300 nm to 700 nm.

[0022] In the method for manufacturing a separator for an electrochemical device, the polymer binder may include an acrylic polymer, a fluorine-based polymer, and a hybrid polymer of an acrylic polymer and a fluorine-based polymer.

[0023] Another aspect of the present invention provides a separator for an electrochemical device, produced by the method for producing a separator for an electrochemical device according to the above aspect.

[0024] Another aspect of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator for an electrochemical device according to the above aspect.

[0025] The electrochemical device may be a lithium secondary battery. [Effects of the Invention]

[0026] The separator for an electrochemical device according to the present invention includes a region in which a polymer binder is filmed in a porous coating layer, and the filmed region is formed on a surface of the porous coating layer that contacts the porous substrate, thereby providing improved peel strength compared to conventional separators.

[0027] The separator for an electrochemical device according to the present invention has 25 to 50 wt % of the total weight of the porous coating layer formed into a film, thereby providing improved electrode adhesion compared to conventional separators. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a conceptual diagram illustrating a process for manufacturing a separator for an electrochemical device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, each configuration of the present invention will be described in more detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0030] As used herein, the term "comprising" is used to list materials, compositions, devices, and methods useful in the present invention, and is not limited to the listed examples.

[0031] As used herein, "about" and "substantially" mean a numerical value or range of degree or approximation thereof, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly using disclosures in which precise or absolute numerical values ​​are provided to aid in the understanding of the invention.

[0032] As used herein, "electrochemical device" can refer to a primary battery, a secondary battery, a supercapacitor, and the like.

[0033] As used herein, unless otherwise specified, "particle size" refers to D50, which is the particle size corresponding to 50% in the cumulative distribution of particle numbers by particle size.

[0034] As used herein, the term "filmed region" refers to a region formed when the polymer binder contained in the porous coating layer is exposed to temperatures above its glass transition temperature, is unable to maintain its original shape, and is physically or chemically connected to one or more adjacent polymer binders.

[0035] One embodiment of the present invention provides a method for manufacturing a separator for an electrochemical device, comprising: (S1) preparing a coating slurry containing a polymer binder, inorganic particles, and a dispersion medium; (S2) heating at least one surface of a porous substrate; and (S3) applying the coating slurry prepared in (S1) to at least one surface of the porous substrate heated in (S2) to form a porous coating layer. The porous coating layer formed on the prepared separator for an electrochemical device includes a region in which the polymer binder is filmed on at least a portion of the surface that contacts the porous substrate.

[0036] Step (S3) is performed after steps (S1) and (S2), but the order of steps (S1) and (S2) is not specified. For example, after preparing the coating slurry in step (S1), the porous substrate can be heated in step (S2), or vice versa. Also, preparing the coating slurry in step (S1) and heating the porous substrate in step (S2) can be performed simultaneously.

[0037] Step (S1) is a step of preparing a coating slurry including a polymer binder, inorganic particles, and a dispersion medium. The coating slurry may include an aqueous dispersion medium, a polymer binder dispersed in the aqueous dispersion medium, and inorganic particles.

[0038] The aqueous dispersion medium may be at least one selected from the group consisting of water and alcohols having 1 to 5 carbon atoms. For example, the aqueous dispersion medium may be a mixture of water and isopropyl alcohol. The polymer binder may maintain a particle shape in the aqueous dispersion medium, and the particle shape may be, but is not limited to, spherical. The aqueous dispersion medium may evaporate during or after the coating slurry is applied to at least one surface of the heated porous substrate in step (S3).

[0039] The polymer binder may be at least one particulate polymer binder selected from the group consisting of an acrylic polymer, a fluorine-based polymer, and a hybrid polymer of an acrylic polymer and a fluorine-based polymer.

[0040] The average particle size (D50) of the particulate polymer binder can be 100 nm to 700 nm. During the formation of the porous coating layer, the polymer binder can migrate in the opposite direction of the porous substrate using the evaporation of the aqueous dispersion medium as a driving force, and can be distributed on the surface of the porous coating layer to provide adhesion to the electrode.

[0041] If the average particle size of the particulate polymer binder is greater than 700 nm, the movement of the polymer binder is hindered, resulting in poor adhesion to the electrode. A polymer binder with a large average particle size will remain near the surface of the porous substrate for a long time during step (S3). The porous coating layer formed in step (S3) may have a film-like region exceeding 50 wt % based on the total weight of the porous coating layer. This results in increased separator permeability and electrical resistance, and although the peel strength is high, the electrode adhesion is low, making it difficult to ensure the structural stability of the electrochemical device.

[0042] If the average particle size of the particulate polymer binder is less than 100 nm, the polymer binder is densely layered, resulting in a sharp decrease in the air permeability and ionic conductivity of the separator. Polymer binders with small average particle sizes actively move in the opposite direction of the porous substrate in step (S3). The porous coating layer formed in step (S3) has a film area of ​​less than 25 wt % based on the total weight of the porous coating layer, making it difficult to ensure the peel strength of the porous coating layer.

[0043] The acrylic polymer can provide the porous coating layer with dry adhesion. Dry adhesion can refer to the adhesion between the porous coating layer and the porous substrate when the separator is not impregnated with an electrolyte, and the adhesion between the porous coating layer and the adjacent electrode. The average particle size (D50) of the acrylic polymer can be 400 nm to 700 nm.

[0044] The acrylic polymer may be at least one selected from the group consisting of (co)polymers containing alkyl (meth)acrylate repeating units having 1 to 18 carbon atoms, copolymers of butyl acrylate and ethylhexyl acrylate, copolymers of butyl acrylate and styrene, copolymers of methyl methacrylate and ethylhexyl acrylate, polyacrylonitrile, and polycyanoacrylate, but is not limited thereto. For example, the acrylic polymer may further include a particulate polymer such as acrylonitrile-butadiene-styrene rubber or acrylonitrile-butadiene rubber. Preferably, the acrylic polymer may be a copolymer of methyl methacrylate and ethylhexyl acrylate.

[0045] The fluoropolymer and the hybrid polymer of the acrylic polymer and the fluoropolymer can provide wet adhesion to the porous coating layer. Wet adhesion refers to the adhesion between the porous coating layer and the porous substrate when the separator is impregnated with an electrolyte solution, and the adhesion between the porous coating layer and the adjacent electrode. The average particle size (D50) of the fluoropolymer may be 100 nm to 500 nm.

[0046] The fluoropolymer may be a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and another polymerizable monomer, or a mixture of two or more thereof. The vinylidene fluoride and another polymerizable monomer may be at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene, and vinyl fluoride, but is not limited thereto. Preferably, the fluoropolymer may be a copolymer of vinylidene fluoride and hexafluoropropylene. The content of vinylidene fluoride and another polymerizable monomer in the fluoropolymer may be 1 wt% to 40 wt% based on the total weight of the fluoropolymer.

[0047] In the hybrid polymer of an acrylic polymer and a fluorine-based polymer, the acrylic polymer and the fluorine-based polymer may be the same as those described above. The content of the acrylic polymer in the hybrid polymer may be 20 wt% to 40 wt% based on the total weight of the hybrid polymer. Preferably, the hybrid polymer may contain the acrylic polymer and the fluorine-based polymer in a weight ratio of 3:7.

[0048] Preferably, the polymer binder can include an acrylic polymer, a fluorine-based polymer, and a hybrid polymer of an acrylic polymer and a fluorine-based polymer. For example, the polymer binder can provide excellent dry adhesion and wet adhesion, including both a copolymer of methyl methacrylate and ethylhexyl acrylate, a copolymer of vinylidene fluoride and hexafluoropropylene, and a hybrid polymer thereof.

[0049] The polymer binder has a glass transition temperature (T g), the particulate form cannot be maintained and may be converted into a film form. g ) may refer to the lowest glass transition temperature of the amorphous polymer binders included in the polymer binder.

[0050] For example, when the polymer binder contains an acrylic polymer and a fluorine-based polymer, the glass transition temperature (T g ) may be the glass transition temperature of the acrylic polymer. At temperatures above the glass transition temperature of the amorphous acrylic polymer, the acrylic polymer cannot maintain its particle shape and can form a film-like region. The crystalline fluoropolymer has a melting point relatively higher than the glass transition temperature of the acrylic polymer and can maintain its particle shape below the melting point.

[0051] For example, when the polymer binder contains multiple acrylic polymers, the glass transition temperature (T g ) may be the glass transition temperature of an acrylic polymer having a relatively low glass transition temperature.

[0052] Preferably, the polymer binder may include an acrylic polymer or a hybrid polymer of an acrylic polymer and a fluorine-based polymer. The glass transition temperature (Tg) of the polymer binder may be higher than room temperature (25°C).

[0053] The inorganic particles may be inorganic nanoparticles having an average particle size (D50) of 300 nm to 700 nm, preferably 300 nm to 500 nm. The inorganic particles can be linked and fixed to adjacent inorganic particles by a binder polymer, and the interstitial volume between the inorganic particles can form pores in the porous coating layer. When the average particle size of the inorganic particles is within the above range, uniform pores can be formed in the separator. A separator with more uniform pores facilitates the movement of lithium ions and increases the impregnation rate of the electrolyte, contributing to improved battery performance.

[0054] The inorganic particles can form a uniform thickness of the porous coating layer and may not undergo a redox reaction within the operating voltage range of the applied electrochemical device. For example, the inorganic particles can have one or more of the properties of lithium ion conductivity, piezoelectricity, and flame retardancy.

[0055] The inorganic particles having lithium ion conductivity mean that they contain lithium element but do not store lithium and have the function of moving lithium ions. The inorganic particles having lithium ion conductivity can transmit and move lithium ions due to a kind of defect existing in the particle structure. Therefore, the lithium ion conductivity in the electrochemical device is improved, and thereby the performance of the electrochemical device can be improved.

[0056] For example, the inorganic particles having lithium ion conductivity can be one or more selected from the group consisting of Li3PO4, LixTiy(PO4)3 (0 < x < 2, 0 < y < 3), LixAlyTiz(PO4)3 (0 < x < 2, 0 < y < 1, 0 < z < 3), LixLayTiO3 (0 < x < 2, 0 < y < 3), LixGeyPzSw (0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitrides such as Li3N (LixNy, 0 < x < 4, 0 < y < 2), SiS2-based glasses such as Li3PO4-Li2S-SiS2 (LixSiySz, 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glasses such as LiI-Li2S-P2S5 (LixPySz, 0 < x < 3, 0 < y < 3, 0 < z < 7), LLZO-based such as Li7La3Zr2O 12 etc., and mixtures thereof, but are not limited thereto.

[0057] Piezoelectric inorganic particles refer to materials that are non-conductors at normal pressure but conduct electricity when a certain amount of pressure is applied due to a change in their internal structure. These inorganic particles can exhibit high dielectric constants (dielectric constants of 100 or more). When tensioned or compressed with a certain amount of pressure, they generate charges, with one side positively charged and the other side negatively charged, creating a potential difference between the two sides. When an internal short circuit occurs between the positive and negative electrodes due to an external impact such as a local crush or a nail, the inorganic particles coated on the separator not only prevent direct contact between the positive and negative electrodes, but also prevent direct contact between the positive and negative electrodes due to the piezoelectricity of the inorganic particles. This generates a potential difference within the particles, which allows electrons to move between the positive and negative electrodes, i.e., a minute current to flow, resulting in a gradual voltage decrease in the electrochemical device and improved safety.

[0058] For example, inorganic particles with piezoelectric properties include BaTiO3, BaSO4, Pb(Zr,Ti)O3 (PZT), (0 <x<1,0<y<1),Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), HfO2 (hafnia), and mixtures thereof, but is not limited thereto.

[0059] The flame-retardant inorganic particles can impart flame-retardant properties to the separator and prevent a sudden rise in temperature inside the electrochemical device.

[0060] For example, the flame-retardant inorganic particles can be at least one selected from the group consisting of, but not limited to, Sb2O3, Sb2O4, Sb2O5, SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, SiO2, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, H3BO3, HBO2, and mixtures thereof.

[0061] The coating slurry may contain 10 to 30 wt % of solids including a polymer binder and inorganic particles based on the total weight. The porous coating layer formed by the coating slurry may contain the polymer binder and inorganic particles in a weight ratio of 1:9 to 9:1, preferably 3:7 to 7:3.

[0062] In the step (S1), the coating slurry is heated to a temperature higher than room temperature (25° C.) and heated to a glass transition temperature (T g ) lower than the temperature (T S For example, a polymer binder and inorganic particles are added to an aqueous dispersion medium and stirred to prepare a coating slurry in which the polymer binder and inorganic particles are uniformly dispersed, and then the temperature (T S The polymer binder contained in the coating slurry can maintain a particulate state, and when the coating slurry is applied to a porous substrate to form a porous coating layer in step (S3) described below, at least a portion of the polymer binder forms a film-like region.

[0063] In the step (S2), at least one surface of the porous substrate is heated to a temperature (T g ) higher than the glass transition temperature (T g ) of the polymer binder. P ) is heated.

[0064] The porous substrate can electrically insulate the positive and negative electrodes, preventing short circuits due to electrode contact, while providing a path for lithium ion migration. For example, the porous substrate can be, but is not limited to, a polymer film or nonwoven fabric containing at least one polymer resin selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous substrate can be, but is not limited to, a single-layer polymer film or nonwoven fabric, and can be composed of multiple layers.

[0065] The thickness of the porous substrate may be 3 μm to 50 μm. If the thickness of the porous substrate is less than 3 μm, the mechanical properties of the resulting separator may be reduced, and the separator may be easily damaged. The pore size of the porous substrate may be 0.01 μm to 50 μm, and the porosity may be 10 vol% to 90 vol%, but is not limited thereto.

[0066] In the step (S2), at least one surface of the porous substrate is heated using a heater or the like, and the melting point (T m For example, if the porous substrate is polyethylene (melting point: about 107°C), step (S2) can be performed by heating both surfaces of the porous substrate to a temperature of about 40°C to 60°C (T g ) and is approximately 107°C (T m ) is lower than the temperature (T P ) can be heated.

[0067] Step (S2) may involve heating only a portion of at least one surface of the porous substrate. In this case, the region where the polymer binder is formed into a film by applying the coating slurry in step (S3), described below, can be controlled to prevent excessive film formation and a decrease in the air permeability and ionic conductivity of the porous coating layer. For example, step (S2) may involve heating only one or more of the following regions: a region extending a predetermined thickness from the edge of the surface; a checkerboard region formed on the surface; or a pattern region where the same shape is repeatedly formed on the surface. The pattern region may include, but is not limited to, a circle, ellipse, polygonal shape such as a triangle or square, or a linear or irregular shape such as a dotted line or solid line.

[0068] In step (S3), the coating slurry prepared in step (S1) is applied to at least one surface of the porous substrate heated in step (S2) to form a porous coating layer.

[0069] The coating slurry may be applied to the porous substrate by one or more methods selected from the group consisting of, but not limited to, dip coating, die coating, bar coating, roll coating, and comma coating.

[0070] The coating slurry is heated to a temperature above the glass transition temperature (T g ) higher temperature (T P ), heat is conducted while in contact with the surface of the porous substrate heated to the glass transition temperature (T g) or higher. At least a portion of the polymer binder contained in the coating slurry is unable to hold the particles together, forming a film-like region in the porous coating layer. The film-like region improves the adhesive strength between the porous coating layer and the porous substrate, and the adhesive strength can be expressed as peel strength. A separator for an electrochemical device including a porous coating layer having a film-like region formed thereon may have a peel strength of about 50 gf / 20 mm to 80 gf / 20 mm. If the peel strength of the separator is lower than 50 gf / 20 mm, the separator may be damaged during the manufacture of an electrode assembly and the use of an electrochemical device.

[0071] The glass transition temperature (T g ), the coating slurry is heated at a relatively low temperature (T S ), and the porous substrate is heated to a relatively high temperature (T P ), and if these temperatures satisfy the following formula (1), a peel strength falling within the above range can be obtained.

[0072] Formula (1) T P -T g ≧T g -T S

[0073] For example, the porous substrate may be formed at a temperature higher than the glass transition temperature (T g ) at temperatures 10℃ to 30℃ higher (T P ), and the coating slurry is heated to the glass transition temperature (T g ) at a temperature 5℃ to 10℃ lower than S ) of the polymeric binder. g ) at temperatures 10℃ to 20℃ higher (T P ) can be heated.

[0074] The porous coating layer formed in step (S3) may have a film region of 25 wt % to 50 wt % based on the total weight of the porous coating layer. When thermal energy of the porous substrate is conducted to the porous coating layer, a portion of the thermal energy is released to the outside of the separator and lost, so the film region may be formed only partially in the thickness direction of the porous coating layer.

[0075] Step (S3) may include drying the porous substrate coated with the coating slurry at a temperature of 50°C to 70°C for 5 to 10 minutes. A portion of the dispersion medium contained in the coating slurry remains after coating on the porous substrate and can be removed by the drying step. Preferably, step (S3) may involve repeating the drying step five or more times.

[0076] In step (S3), a portion of the polymer binder contained in the coating slurry forms a film on the surface that contacts the porous substrate, while another portion migrates in the opposite direction from the surface that contacts the porous substrate. The polymer binder migrates toward the surface of the porous coating layer during the coating and drying steps of the coating slurry. In this embodiment, the porous substrate is heated to the aforementioned temperature TP, or the coating slurry prepared at the aforementioned temperature TS is applied to a porous substrate heated to the aforementioned temperature TP, thereby making the migration of the polymer easier than before.

[0077] After the porous coating layer is formed, it may comprise a film-like region of 25 to 50 wt %, based on the total weight of the porous coating layer, in a region of 50% or less of its thickness from the surface facing the porous substrate. Preferably, the porous coating layer may comprise a film-like region of 30 to 50 wt %, based on the total weight of the porous coating layer, in a region of 50% or less from the surface facing the porous substrate. The porous coating layer contains a relatively small amount of polymer binder on the surface facing the porous substrate, but the polymer binder is in the form of a film to provide adhesion to the porous substrate, while the surface facing the porous substrate contains a relatively large amount of particulate polymer binder, ensuring adhesion to the electrode. A separator for an electrochemical device having such a polymer binder distribution may have an electrode adhesion of approximately 70 gf / 20 mm to 90 gf / 20 mm. If the adhesive strength of the separator to the electrode is less than 70 gf / 20 mm, it is not possible to manufacture an electrode assembly by adhering the electrode and separator together.

[0078] The thickness of the porous coating layer may be 1 μm to 20 μm, and preferably, the thickness of the porous coating layer may be 2 μm to 10 μm.

[0079] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings, and the same description as the previous embodiment will be used as the description of the embodiment.

[0080] FIG. 1 is a conceptual diagram showing a process for producing a separator 1 for an electrochemical element according to one embodiment of the present invention using a separation membrane production apparatus 100. As shown in FIG.

[0081] Referring to FIG. 1, a separation membrane manufacturing apparatus 100 may include a porous substrate supply roll 110 , a heater 120 , a slurry supply unit 130 , a drying oven 140 and a take-up roll 150 .

[0082] The porous substrate 10 is provided in a wound state around a porous substrate supply roll 110, and can be supplied to the separation membrane production apparatus 100 in the form of a sheet.

[0083] The porous substrate 10 is supplied to a heater 120 capable of heating at least one side. The heater 120 forms a heating zone on at least a portion of the target surface of the porous substrate 10 and can heat the heating zone to a predetermined temperature TP. The heated porous substrate 10 is supplied to a slurry supply unit 130.

[0084] The slurry supply unit 130 may include a slurry storage unit 131, a slurry heating unit 132, a coating slurry 133 stored in the slurry storage unit 131, and a slurry application unit 134. The slurry storage unit 131 provides a space for storing the coating slurry 133, but is not limited thereto. A polymer binder, inorganic particles, and a dispersion medium may be supplied to the slurry storage unit 131 and stirred to form the coating slurry 133, and the slurry heating unit 132 heats the coating slurry 133 to a predetermined temperature (T S The heated coating slurry 133 can be applied to at least one surface of the porous substrate 10 through a slurry application unit 134. The slurry application unit 134 can be a die, a bar, a roll, or the like depending on the coating method. The porous substrate coated with the coating slurry is supplied to a drying oven 140.

[0085] The drying oven 140 may dry the porous substrate coated with the coating slurry at a predetermined temperature for a predetermined time to form a porous coating layer. The drying oven 140 may repeat the drying step two or more times under the same or different conditions, and preferably repeat the drying step five or more times. The manufactured separator 1 is supplied to a take-up roll 150.

[0086] Another embodiment of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the separator being manufactured according to the above-described embodiment. For example, the electrochemical device may be a lithium secondary battery including a positive electrode that provides lithium ions.

[0087] The positive electrode and the negative electrode may each be formed by applying an active material to at least one surface of a current collector and then drying the applied active material. The current collector may be a material that is conductive and does not cause chemical changes in the electrochemical device. For example, the positive electrode current collector may be, but is not limited to, aluminum, nickel, titanium, calcined carbon, stainless steel, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. For example, the negative electrode current collector may be, but is not limited to, copper, nickel, titanium, calcined carbon, or stainless steel. For example, the negative electrode current collector may be, but is not limited to, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The current collector may be in various forms, such as a thin metal plate, film, foil, net, porous material, or foam.

[0088] For example, the positive electrode active material is lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2). 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; Lithium copper oxide (Li2CuO2); Vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; 1-xNi-site type lithium nickel oxide represented by MxO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3). Lithium manganese composite oxide represented by the chemical formula LiMn2-xMxO2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn). LiMn2O4 in which part of Li in the formula is substituted with alkaline earth metal ions; disulfide compounds; it can include, but is not limited to, Fe2(MoO4)3, etc.

[0089] as The negative electrode active material can include, but is not limited to, carbon such as graphitized carbon and graphite-based carbon: LixFe2O3 (0 ≦ x ≦ 1), LixWO2 (0 ≦ x ≦ 1), SnxMe1-xMe‘yOz (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc.

[0090] The electrolyte can be a non-aqueous electrolyte containing a lithium salt. The electrolyte consists of an electrolyte and a lithium salt, and as the electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. can be used. [[ID=X]]

[0091] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0092] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyeditation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing ionic dissociative groups.

[0093] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiNLiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0094] The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte, and examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2) chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate lithium, imide, etc. can be used.

[0095] The electrochemical device may be manufactured by inserting a positive electrode, a negative electrode, a separator, and an electrolyte into a case or a pouch and sealing the case or pouch. The shape of the case or pouch is not limited. For example, the electrochemical device may be a cylindrical, prismatic, coin-shaped, or pouch-shaped lithium secondary battery.

[0096] The lithium secondary battery unit cells can be used in small devices such as computers, mobile phones, and power tools packed or modularized as well as power tools powered by a battery motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric bicycles, electric two-wheeled vehicles including electric scooters; electric golf carts; and medium- to large-sized devices such as power storage systems.

[0097] The present invention will be described in more detail below with reference to specific examples and experimental examples. The following examples and experimental examples are provided to illustrate the present invention, and the present invention is not limited to the following examples and experimental examples.

[0098] Example 1 Coating slurry preparation

[0099] Water and isopropyl alcohol were mixed at room temperature (25°C) in a 95:5 weight ratio to prepare 100 mL of aqueous dispersion medium. 11.7 g of acrylic polymer binder (Styrene-acrylic, particle size: 350 nm - 400 nm, Tg: 40°C), 8.2 g of fluorine-based polymer binder (PVDF-HFP, particle size: 250 nm, Tg: -40°C), and 27.615 g of inorganic particles (Al2O3, particle size: 400 nm) were added to the aqueous dispersion medium and stirred for 60 minutes using a shaker to produce a coating slurry in which the polymer binder and inorganic particles were dispersed. The coating slurry was then heated to 35°C.

[0100] Preparation of porous substrate

[0101] The porous substrate was a polyethylene film measuring 20 cm x 30 cm and 9 μm thick (MI: 0.2 g / 10 min, Tm: 135°C, porosity: 45%, average pore size: 45 nm). The polyethylene film was placed in an oven and heated to a surface temperature of 50°C on both sides.

[0102] Separation membrane manufacturing

[0103] The coating slurry heated at 35°C was coated on both sides of a polyethylene film heated at 50°C using a bar coater to form porous coating layers each having a thickness of 2 µm.

[0104] The polyethylene film with the porous coating layer formed thereon was dried by applying low-temperature airflow five times to prepare a separator membrane with a total thickness of 13 μm.

[0105] Comparative Example 1 A separator was prepared in the same manner as in Example 1, except that the coating slurry and the porous substrate were not heated.

[0106] Comparative Example 2 A separator was prepared in the same manner as in Example 1, except that the coating slurry was not heated.

[0107] Comparative Example 3 A separator was prepared in the same manner as in Example 1, except that the porous substrate was not heated.

[0108] Comparative Example 4 A separator was prepared in the same manner as in Example 1, except that the coating slurry was heated to 45°C.

[0109] Comparative Example 5 A separator was manufactured in the same manner as in Example 1, except that the particle size of the acrylic polymer binder and the fluorine polymer binder was 50 nm or more and less than 100 nm.

[0110] Comparative Example 6 A separator was manufactured in the same manner as in Example 1, except that the particle sizes of the acrylic polymer binder and the fluorine polymer binder were each 750 nm to 1000 nm.

[0111] Experimental example 1. Checking the distribution of filmed areas Tape peeling tests were repeatedly performed on the entire surface of the separators of the Examples and Comparative Examples to confirm the distribution of film-formed regions in the porous coating layer. Of the polymer binders contained in the porous coating layer, those that were in the form of a film were not removed by the tape peeling test, and only the polymer binders that remained in a particulate form were able to adhere to the tape.

[0112] Each separation membrane sample was prepared in a size of 5 cm x 5 cm, and the initial weight (L ini Tape (3M) was attached to one side of the separation membrane sample, and the end of the tape was peeled off three times at a speed of 300 mm / min in a direction 180° to the adhesive direction using a Universal Testing Machine (UTM, Instron). p ) was measured.

[0113] Weight of the separation membrane after peeling the tape three times (L p ) to fabric weight (L b ) minus the weight of the filmed area in the porous coating layer, L p -L b ) to the weight of the porous coating layer (L ini -L b The film formation rate was calculated as a percentage of the total film thickness (film formation rate, %) and is shown in Table 1 below.

[0114] [Table 1]

[0115] Experimental example 2: Confirmation of the physical properties of the separation membrane The air permeability of the separators of the Examples and Comparative Examples, the adhesive strength (peel strength) between the porous substrate and the porous coating layer in the separator, and the adhesive strength (lami strength) between the separator and the electrode were measured and are shown in Table 2 below.

[0116] Air permeability measurement The air permeability was measured using a Gurley densometer (Gurley, 4110N) by measuring the air permeability of a 100cc tube with a diameter of 28.6mm and an area of ​​645mm. 2 The time required for the solution to permeate the separation membrane was measured.

[0117] Peel strength measurement Each separation membrane was sampled in a width of 20 mm and attached to a slide glass using 18 mm of double-sided tape (3M) to prepare a test sample.

[0118] The slide glass was peeled off from the separation membrane in a direction 180° to the adhesive direction at a speed of 300 mm / min using the UTM, and the peel strength was measured.

[0119] Measurement of electrode-separator adhesion The negative electrode active material (natural graphite and artificial graphite in a weight ratio of 5:5), conductive material (Super P), and binder (polyvinylidene fluoride (PVdF)) were mixed in a weight ratio of 92:2:6, dispersed in water, and then coated on copper foil to prepare the negative electrode.

[0120] The separators of the Examples and Comparative Examples and the negative electrode were each sampled to a width of 20 mm, and then stacked together, and pressed at 60° C. and 6.5 MPa for 1 second to prepare a sample for electrode adhesion test.

[0121] The electrode adhesive strength of the separator was measured by peeling the cathode from the separator in a direction 180° to the adhesive direction at a speed of 300 mm / min using a UTM.

[0122] [Table 2] [Explanation of symbols]

[0123] 1: Separation membrane for electrochemical element 10: Porous substrate 100: Separation membrane manufacturing apparatus 110: Porous substrate supply roll 120: heater 130: slurry supply unit 131: Slurry storage section 132: Slurry heating section 133: Coating slurry 134: Slurry application section 140: Drying oven 150: Winding roll

Claims

1. (S1) preparing a coating slurry containing a polymer binder, inorganic particles, and a dispersion medium at a temperature (Ts) higher than room temperature (25°C) and lower than the glass transition temperature (Tg) of the polymer binder; (S2) heating at least one surface of the porous substrate to a temperature (T p ) higher than the glass transition temperature (T g ) of the polymer binder; (S3) applying the coating slurry prepared in step (S1) to at least one surface of the porous substrate heated in step (S2) to form a porous coating layer; The porous coating layer comprises: the polymer binder is formed into a film on at least a portion of the surface that contacts the porous substrate; The method for manufacturing a separator for an electrochemical device, wherein the polymer binder has an average particle size (D50) of 100 nm to 700 nm.

2. The method for producing a separator for an electrochemical element according to claim 1, which satisfies the following formula (1): Formula (1) T Ｐ -T ｇ ≧T ｇ -T Ｓ

3. The step (S2) is The porous substrate is heated to a temperature of 1000.degree. C. for 1 hour at a melting point (T.sub. ｍ 2. The method for producing a separator for an electrochemical element according to claim 1, wherein the temperature is lower than 1000° C.

4. The region where the polymer binder is formed into a film is 2. The method for manufacturing a separator for an electrochemical device according to claim 1, wherein the porous coating layer has a weight ratio of 25 to 50% by weight based on the total weight of the porous coating layer.

5. 2. The method of claim 1, wherein the porous coating layer has a thickness of 1 μm to 20 μm.

6. The step (S2) is 2. The method for manufacturing a separator for electrochemical devices according to claim 1, wherein only one or more of a region extending a predetermined thickness from an edge of the one surface, a checkerboard region formed on the one surface, and a pattern region in which the same shape is repeatedly formed on the one surface are heated.

7. The step (S3) is 10. The method of claim 1, further comprising drying the porous substrate coated with the coating slurry at a temperature of 50 to 70° C. for 5 to 10 minutes.

8. The step (S3) is 8. The method for manufacturing a separator for an electrochemical device according to claim 7, wherein the drying step is repeated five or more times.

9. The polymer binder is 2. The method for producing a separator for an electrochemical element according to claim 1, wherein the particulate polymer binder is at least one selected from the group consisting of an acrylic polymer, a fluorine-based polymer, and a hybrid polymer of an acrylic polymer and a fluorine-based polymer.

10. The fluorine-based polymer is 10. The method for producing a separator for an electrochemical element according to claim 9, wherein the separator is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and another polymerizable monomer, or a mixture of two or more of these.

11. The method for producing a separator for an electrochemical element according to claim 9, wherein the inorganic particles have an average particle size (D50) of 300 nm to 700 nm.

12. The polymer binder is The method for producing a separator for an electrochemical device according to claim 9, wherein the separator comprises an acrylic polymer, a fluorine-based polymer, or a hybrid polymer of an acrylic polymer and a fluorine-based polymer.

13. A porous substrate; a porous coating layer provided on at least one surface of the porous substrate; the porous coating layer includes a polymer binder and inorganic particles, and includes a region in which the polymer binder is filmed on at least a portion of a surface that contacts the porous substrate; The separator for an electrochemical device, wherein the area where the polymer binder is formed into a film is 25 wt % to 50 wt % of the total weight of the porous coating layer.

14. An electrochemical device comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrochemical device, wherein the separation membrane is the separation membrane according to claim 13 .

15. 15. The electrochemical device according to claim 14, wherein the electrochemical device is a lithium secondary battery.

Images