A separator for an electrochemical device and an electrochemical device comprising the same

Abstract

The present invention relates to a separator comprising a porous polymer substrate; and an inorganic particle containing a metal element and a polymer binder, and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the polymer binder comprises (a) a fluorine-based polymer; and (b) an acrylic polymer, a hybrid polymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof, wherein a concentration gradient of the metal element and carbon exists in the thickness direction of the porous coating layer, and the porous coating layer has a low rate of change in thickness before and after electrolyte impregnation, so that detachment is prevented even after electrolyte impregnation.

Description

Technology Field

[0001] The present invention relates to a separator for an electrochemical device with improved wet adhesion by reducing the rate of change in coating layer thickness due to an electrolyte, and an electrochemical device equipped with the same. Background Technology

[0002] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions; recently, lithium-ion batteries, which offer high energy density and voltage, long cycle life, and applicability to various fields, are widely used.

[0003] A lithium secondary battery may include an electrode assembly manufactured with a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and the electrode assembly may be manufactured by housing it in a case together with an electrolyte. The separator is disposed between the positive and negative electrodes to insulate the electrodes and may include a porous coating layer comprising a polymer binder and inorganic particles on at least one surface of a porous polymer substrate. The inorganic particles may be connected to other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions may move through the interstitial volume. In addition to fixing the inorganic particles, the polymer binder may impart adhesion to the porous coating layer, and the porous coating layer may be adhered to the porous polymer substrate and the electrode, respectively.

[0004] Fluorinated polymers such as polyvinylidene fluoride (PVdF) can be used as polymer binders due to their excellent dielectric strength and mechanical strength, and polymer binders containing fluorinated polymers can provide dielectric strength to porous coating layers. Although fluorinated polymers provide adhesion to the separator and thus to the electrode, problems have arisen where the porous coating layer collapses or detaches during the process of manufacturing electrochemical devices by injecting an electrolyte, which is a non-aqueous organic solvent, as the polymer dissolves in the electrolyte, leading to a decrease in adhesion. Accordingly, development is underway for separators that maintain the thickness and adhesion of the porous coating layer even in a wet state when impregnated with the electrolyte. The problem to be solved

[0005] The present invention aims to provide a separator for an electrochemical device comprising a polymer binder including a fluorine-based polymer and an acrylic-based polymer, which maintains the thickness of the porous coating layer even after the injection of an electrolyte and has excellent wet adhesion, and an electrochemical device including the same. means of solving the problem

[0006] One aspect of the present invention provides a separator for an electrochemical device comprising a porous polymer substrate and a polymer binder containing inorganic particles containing a metal element and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein a concentration gradient of the metal element and carbon exists in the thickness direction of the porous coating layer and the separator has a value of 15% or less according to the following formula (1).

[0007] Equation (1)

[0008] | {(Δt - Δt bare ) / Δt bare} × 100 (%) |

[0009] Among the foods,

[0010] Δt is the difference value (Δt = t2- t1) between the time (t1) required for the carbon content curve and the metal content curve among the elemental content curves resulting from ion beam etching to intersect for the first time and the time (t2) required for the second time to intersect, in the separator impregnated and dried in the electrolyte of the electrochemical device.

[0011] Δt bare is the time (t) required for the carbon content curve and the metal content curve among the elemental content curves to first intersect according to ion beam etching in the above-mentioned membrane. 1,bare ) and the time required to intersect for the second time (t 2,bare The difference value between ) (Δt bare = t 2,bare - t 1,bare )am.

[0012] The above polymer binder may include (a) a fluorine-based polymer, and (b) an acrylic polymer, a hybrid polymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof.

[0013] The porous polymer substrate comprises a polyolefin-based polymer, and the carbon content included in the porous substrate may be greater than the metal content.

[0014] The above fluorine-based polymer may include one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0015] The above acrylic polymer may include one or more selected from the group consisting of polyacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, and methyl methacrylate.

[0016] The thickness of the porous coating layer may be 1 to 30 μm.

[0017] The above separation membrane may have a value of 10% or less according to the above formula (1).

[0018] The above ion beam etching can be performed in monatomic mode at a voltage of 1.0 to 2.5 keV.

[0019] Another aspect of the present invention provides an electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein the separator may be a separator for an electrochemical device according to one aspect of the present invention.

[0020] The above electrochemical device may be a lithium secondary battery. Effects of the invention

[0021] The separator for an electrochemical device according to the present invention includes both a fluorine-based polymer and an acrylic-based polymer as polymer binders in the porous coating layer, thereby preventing a decrease in the thickness of the porous coating layer even after the separator is impregnated with an electrolyte, providing wet adhesion, and preventing detachment. Brief explanation of the drawing

[0022] Figure 1 is a graph showing the atomic percent of the porous coating layer according to the ion beam etching time of the separator immediately after manufacturing the separator of one embodiment. Figure 2 is a graph showing the elemental content of a porous coating layer according to the ion beam etching time of a separator membrane of one embodiment after impregnating the separator membrane in an electrolyte. Figure 3 is a graph showing the elemental content of a porous coating layer according to the ion beam etching time of the separator after manufacturing an electrochemical device with a separator of one embodiment. Figure 4 is a graph showing the elemental content of the porous coating layer according to the ion beam etching time of the separator membrane immediately after manufacturing the separator membrane of the comparative example. Figure 5 is a graph showing the elemental content of the porous coating layer according to the ion beam etching time of the separator of the comparative example after impregnating the separator with an electrolyte. Figure 6 is a graph showing the elemental content of the porous coating layer according to the ion beam etching time of the separator after manufacturing an electrochemical device with the separator of the comparative example. Specific details for implementing the invention

[0023] Hereinafter, each component of the present invention is described in more detail so that a person skilled in the art to which the present invention pertains can easily implement it; however, this is merely an example, and the scope of the rights of the present invention is not limited by the following.

[0024] The term “comprising” as used herein is used when listing materials, compositions, devices, and methods useful for the present invention, and is not limited to the examples listed.

[0025] As used herein, "about" and "substantially" are used to mean a range of numerical values ​​or degrees or approximations thereof, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from unfairly exploiting the disclosure in which precise or absolute figures provided to aid in understanding the invention are mentioned.

[0026] As used in this specification, "electrochemical device" may refer to a primary battery, a secondary battery, a supercapacitor, etc.

[0027] As used in this specification, "detachment of separator" may encompass the detachment of the separator and the electrode, the folding of the separator, and the detachment of the porous polymer substrate and the porous coating layer of the separator in an electrode assembly including a separator.

[0029] One embodiment of the present invention comprises a porous polymer substrate and an inorganic particle containing a metal element and a polymer binder, and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the polymer binder comprises (a) a fluorine-based polymer and (b) an acrylic polymer, a hybrid polymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof, and there is a concentration gradient of the metal element and carbon in the thickness direction of the porous coating layer, and the porous coating layer comprises a first layer facing the porous polymer substrate and containing the metal element in an amount equal to or greater than the carbon, and a second layer disposed on the first layer and containing the carbon in an amount greater than the metal element.

[0030] The porous polymer substrate electrically insulates the anode and cathode to prevent short circuits, while providing pores through which lithium ions can pass. The porous polymer substrate may be resistant to the electrolyte of an electrochemical device, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, polymer resins such as polyolefins including polyethylene, polypropylene, and polybutene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof.

[0031] Preferably, the porous polymer substrate comprises a polyolefin-based polymer, which has excellent slurry applicability for forming a porous coating layer and may be advantageous for manufacturing a thin-thickness separation membrane. The porous polymer substrate may have a carbon content greater than the metal element content, and the metal element may be the same as that contained in the inorganic particles.

[0032] The thickness of the porous polymer substrate may be 1 to 100 μm, preferably 1 to 30 μm, and more preferably 15 to 30 μm. The porous polymer substrate may include pores with an average diameter of 0.01 to 10 μm.

[0033] A slurry may be applied and dried on at least one surface of the porous polymer substrate to form a porous coating layer to be described later. The slurry may include a polymer binder, inorganic particles, a dispersion medium, a dispersant, etc. Before applying the slurry, a surface treatment such as plasma treatment or corona discharge may be performed on the porous polymer substrate to improve impregnation with an electrolyte.

[0034] The separator for the electrochemical device described above may include the porous polymer substrate and the porous coating layer. The porous coating layer may be provided on one or both sides of the porous polymer substrate. A porous coating layer may be formed by applying and drying a slurry on at least one side of the porous polymer substrate.

[0035] The porous coating layer may include inorganic particles to improve the mechanical properties and insulation of the porous polymer substrate, and a polymer binder to improve the adhesion between the electrode and the separator. The polymer binder may include (a) a fluorine-based polymer, and (b) an acrylic polymer, a hybrid polymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof. The polymer binder provides adhesion between the electrode and the separator, while simultaneously binding adjacent inorganic particles and maintaining said binding. The inorganic particles can bind with adjacent inorganic particles to provide an interstitial volume, which is a void between the inorganic particles, and lithium ions can move through said interstitial volume.

[0036] The above (a) fluorine-based polymer can provide adhesion (dry adhesion) between the separator and the electrode in a dry state where the separator is not impregnated with an electrolyte. An electrode assembly can be manufactured by laminating the separator and the electrode, and in this case, since there is no electrolyte, the dry adhesion between the separator and the electrode is important. The dry adhesion, which is the adhesion of the separator in a dry state, may be 10 gf / 25 mm or more, preferably 10 gf / 25 mm to 150 gf / 25 mm, and more preferably 50 gf / 25 mm to 100 gf / 25 mm. If the dry adhesion exceeds 150 gf / 25 mm, lithium dendrites may precipitate as the impregnation of the electrolyte into the separator is hindered.

[0037] The above fluorine-based polymer may include one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0038] The above (b) acrylic polymer, a copolymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof can provide adhesion (wet adhesion) between the separator and the electrode when the separator is impregnated with the electrolyte. The above (b) polymer binder does not dissolve in the electrolyte or maintains its original shape, so that adhesion can be maintained even after the separator is impregnated with the electrolyte. An electrochemical device can be manufactured by inserting the electrode assembly into a pouch or case and injecting the electrolyte, and in this case, the wet adhesion between the separator and the electrode is important as the separator is impregnated with the electrolyte. The wet adhesion, which is the adhesion of the separator when impregnated with the electrolyte, may be 1.0 gf / 20 mm or more, specifically 10 gf / 20 mm or more, and even more specifically 7 gf / 20 mm to 25 gf / 20 mm. If the wet adhesion falls outside the above range, detachment of the separator occurs.

[0039] The above acrylic polymer may include one or more selected from the group consisting of polyacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, and methyl methacrylate.

[0040] The copolymer of the acrylic polymer and the fluorine polymer described above may be a blend of one or more of the aforementioned acrylic polymer and fluorine polymer, respectively.

[0041] The weight-average molecular weight of the polymer binder may be 10,000 to 10,000,000. Preferably, the polymer binder may be included in the porous coating layer in the form of particles.

[0042] The above-mentioned inorganic particles may contain metal elements, such that they uniformly form the thickness of the porous coating layer and do not undergo redox reactions within the operating voltage range of the applied electrochemical device. The metal elements may include alkali metals, alkaline earth metals, and transition metals. For example, the above-mentioned inorganic particles may possess one or more properties among lithium ion transfer capability, piezoelectricity, and flame retardancy.

[0043] Inorganic particles capable of lithium ion transport refer to particles that contain lithium elements but do not store lithium, instead possessing the function of transporting lithium ions. These lithium ion transporting inorganic particles can transport and move lithium ions due to a type of defect existing within their particle structure. Consequently, the lithium ion conductivity within the electrochemical device is enhanced, thereby enabling improvements in the device's performance.

[0044] For example, inorganic particles capable of transporting lithium ions are Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li x La y TiO3(0 <x<2, 0<y<3), Li7La3Zr2O 12 It may be one or more selected from the group consisting of LLZO series such as and mixtures thereof, but is not limited thereto.

[0045] Piezoelectric inorganic particles refer to materials that are insulators at atmospheric pressure but possess the property of conducting electricity due to changes in their internal structure when a certain pressure is applied. The inorganic particles can exhibit high dielectric constant characteristics with a dielectric constant of 100 or more, and when subjected to tension or compression by applying a certain pressure, electric charge is generated, causing one side to become positively charged and the opposite side to become negatively charged, thereby enabling the function of generating a potential difference between the two sides. In the event of an internal short circuit between the anode and cathode caused by external impacts such as a local crush or a nail, the inorganic particles coated on the separator prevent direct contact between the anode and cathode. Furthermore, due to the piezoelectricity of the inorganic particles, a potential difference is generated within the particles, which leads to electron movement between the anode and cathode—that is, a flow of minute current—thereby enabling a gradual reduction in the voltage of the electrochemical device and consequently improving safety.

[0046] For example, piezoelectric inorganic particles include BaTiO3, BaSO4, Pb(Zr,Ti)O3(PZT), Pb1-xLaxZr1-yTiyO3 (PLZT)(0 <x<1, 0<y<1), Pb(Mg1 / 3Nb2 / 3)O3-PbTiO3 (PMN-PT), HfO2 (하프니아) 및 이들의 혼합물로 이루어진 군으로부터 선택된 하나 이상일 수 있으나, 이에 한정되는 것은 아니다.

[0047] Inorganic particles with flame retardant properties can add flame retardant characteristics to the separator or prevent the temperature inside the electrochemical device from rising rapidly.

[0048] For example, flame-retardant inorganic particles may be one or more selected from the group consisting of SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, Al2O3, AlOOH, Al(OH)3, TiO2, and mixtures thereof, but are not limited thereto.

[0049] The porous coating layer can be divided into a first layer facing a porous polymer substrate and a second layer formed on the first layer during the process of forming through the application and drying of a slurry. Even when the polymer binder and inorganic particles are uniformly dispersed in the slurry, some of the polymer binder and dispersant may move toward the surface of the porous coating layer during the application and drying process.

[0050] The porous coating layer may have a concentration gradient of metal elements and carbon in the thickness direction. The porous coating layer may have different element concentration gradients in the first layer and the second layer. Both the first layer and the second layer may contain a polymer binder and inorganic particles, and the first layer may further contain impurities, etc., in addition to the polymer binder and inorganic particles. The first layer may have a relatively high content of inorganic particles containing metal elements, and the first layer may contain the metal element in an amount equal to or greater than that of carbon. The second layer may have a relatively high content of polymer binder, and the second layer may contain carbon in an amount greater than that of the metal element.

[0051] The first layer and the second layer of the porous coating layer may each have a unique elemental concentration gradient. For example, the first layer may have equal or greater content of metal elements and carbon on the surface facing the porous polymer substrate and on the surface facing the second layer. The first layer may contain more metal elements than carbon between the surface facing the porous polymer substrate and the surface facing the second layer, based on the thickness direction. For example, the second layer may contain more carbon than metal elements, and based on the thickness direction, the carbon content may be lowest on the surface facing the first layer and highest on the surface of the porous coating layer as the opposite surface.

[0052] The porous coating layer may contain the polymer binder and the inorganic particles in a weight ratio of 10:90 to 50:50. If the polymer binder is contained in an amount less than the above range, the porous coating layer may peel off from the porous polymer substrate or sufficient adhesion between the electrode and the separator may not be secured, and if the content of the polymer binder exceeds the above range, there is a problem that the resistance of the cell becomes too high.

[0053] The porous coating layer may contain the above (a) fluorine-based polymer and the above (b) acrylic polymer, a copolymer of an acrylic polymer and a fluorine-based polymer, or a mixture thereof in a weight ratio of 90:10 to 10:90. If the polymer of (b) is included in an amount outside the above range, adhesion between the electrode and the separator cannot be maintained while impregnated in the electrolyte.

[0054] The thickness of the porous coating layer may be 1 to 30 μm. If the thickness of the porous coating layer is less than 1 μm, the wet adhesion force decreases rapidly, causing a problem where the electrode and the separator detach during electrolyte injection. Even if the thickness of the porous coating layer exceeds 30 μm, the adhesion force between the separator and the electrode does not increase significantly. Preferably, the thickness of the porous coating layer may be 2 to 10 μm, and more preferably, the thickness of the porous coating layer may be 2 to 5 μm.

[0055] The porous coating layer may further include a dispersant to further improve the dispersibility of inorganic particles. The dispersant functions to maintain a uniformly dispersed state of inorganic particles within a polymer binder during slurry preparation. For example, the dispersant may include one or more selected from oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. When the slurry contains a dispersant, the porous coating layer may contain the dispersant in an amount of 5% by weight or less.

[0056] The separator for an electrochemical device according to the above embodiment may have a value of 15% or less according to the following formula (1):

[0057] Equation (1)

[0058] | {(Δt - Δt bare ) / Δt bare} × 100 (%) |

[0059] Among the foods,

[0060] Δt is the difference value (Δt = t2- t1) between the time (t1) required for the first layer to be exposed by ion beam etching and the time (t2) required for the porous polymer substrate to be exposed in the separator impregnated and dried in the electrolyte of the electrochemical device, and

[0061] Δt bareis the time (t) required for the first layer to be exposed according to ion beam etching in the separator. 1,bare ) and the time required for the porous polymer substrate to be exposed (t 2,bare The difference value between ) (Δt bare = t 2,bare - t 1,bare )am.

[0062] The above separator is manufactured and ion beam etched before impregnating it with the electrolyte to Δt bare can be calculated, and the Δt value can be calculated by impregnating the separator in the electrolyte, drying it, and then ion beam etching. 1,bare and t1 is the time required to perform ion beam etching starting from the second layer, which is the surface of the separator, so that the first layer is exposed after the second layer is etched. When the content of elements contained in the separator is quantified while ion beam etching the separator, the above t 1,bare and t1 may represent the time required until the carbon content curve and the metal element content curve first intersect. 2,bare and t2 is the time required for the porous polymer substrate to be exposed after the first layer is etched, by continuing ion beam etching from immediately after the first layer is exposed. When the content of elements contained in the separator is quantified while ion beam etching the separator, the above t 2,bare and t2 may represent the time required until the carbon content curve and the metal element content curve intersect for the second time.

[0063] The above ion beam etching is not limited in type as long as it can be used to etch a porous coating layer and analyze the content of elements contained in the porous coating layer. For example, the above ion beam etching may be included in an XPS instrument to quantify the content of the coating material according to the etching time using argon cations and provide a depth profile of the element content according to the depth of the porous coating layer, and may be performed in monatomic mode under conditions of a voltage of 1.0 to 2.5 keV, a raster size of 0.1 to 1 mm, and an etching rate of 5 to 5.5 nm / s based on Ta2O5.

[0064] Whether the separator membrane detaches can be confirmed by comparing the change in thickness of the separator membrane before and after impregnation with the electrolyte. If the change in thickness exceeds a predetermined range, it can be evaluated that the separator membrane detaches because the wet adhesion strength within the aforementioned range is not maintained. For example, if the value according to Equation (1) exceeds 15%, it can be evaluated that the separator membrane detaches. When it exceeds 15%, folding of the separator membrane due to a decrease in wet adhesion strength resulting from the detachment of the separator membrane may be observed. A separator membrane with a value according to Equation (1) of 15% or less has a low rate of change in thickness of the porous coating layer before and after impregnation with the electrolyte, and the shape and function of the porous coating layer may be maintained even if some of the polymer binder contained in the porous coating layer dissolves in the electrolyte. Preferably, the value according to Equation (1) of the separator membrane according to the above embodiment may be 10% or less.

[0065] Alternatively, whether detachment of the separator occurs can be determined by the rate of change in separator weight before and after electrolyte impregnation. The change in separator weight may be due to the change in weight of the porous coating layer before and after electrolyte impregnation, and if the thickness of the porous coating layer decreases as it is impregnated with the electrolyte, it may fail to maintain adhesion, leading to detachment. For example, by measuring the weight of the separator before and after electrolyte impregnation to determine the rate of weight loss, separators with a rate of weight loss of 8% or more may cause defects, such as detachment, because the shape and function of the porous coating layer are not maintained.

[0067] Another embodiment of the present invention provides an electrochemical device comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte, wherein the separator is a separator for an electrochemical device according to the above-described embodiment.

[0068] The anode and the cathode may each have an active material coated and dried on at least one surface of a current collector. The current collector may be made of a material that is conductive without causing chemical changes in the electrochemical device. For example, the current collector for the anode may be aluminum, nickel, titanium, calcined carbon, stainless steel; or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the current collector for the cathode may be copper, nickel, titanium, calcined carbon, stainless steel; or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. The current collector may be in various forms such as a metal sheet, film, foil, net, porous body, foam, etc.

[0069] For example, the positive electrode active material is lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); chemical formula Li 1+x Mn 2-x O 4　(where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01–0.3); chemical formula LiMn 2-x M x Lithium manganese complex oxides represented by O2 (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 the Li of the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, etc., may be included but are not limited thereto.

[0070] The negative electrode active material is carbon such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5 등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료 등을 포함할 수 있으나, 이에 한정되는 것은 아니다.

[0071] The above electrolyte may be a non-aqueous electrolyte containing a lithium salt. The above electrolyte consists of an electrolyte and a lithium salt, and the above electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0072] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0073] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0074] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5NI2, Li3NLiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0075] The above lithium salt is a substance that dissolves well in the above-mentioned non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, imide, etc. may be used.

[0076] The above electrochemical device can be manufactured by inserting a positive electrode, a negative electrode, a separator, and an electrolyte into a case or pouch and sealing it. The shape of the case or pouch is not limited. For example, the electrochemical device may be a cylindrical, prismatic, coin-type, or pouch-type lithium secondary battery.

[0077] The above lithium secondary battery can be used as a unit cell in packs or modules for small devices such as computers, mobile phones, and power tools, and power tools that move by receiving power from an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and medium to large devices such as power storage systems.

[0079] The present invention will be explained in more detail below through specific embodiments and experimental examples. The following embodiments and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following embodiments and experimental examples.

[0080] Examples

[0081] Preparation of slurry

[0082] Alumina (Sumitomo, AES11) with an average particle size (D50) of 500 nm was used as the inorganic material, and a fluorine-based water-dispersible emulsion (Arkema, Aquatec9530, 30 wt% solid content) and an acrylic-based water-dispersible emulsion (LGC, SA22, 30 wt% solid content) were used as polymer binders, and carboxymethylcellulose (GL Chem, SG-L02) was mixed in the order of 79:18:2:1 to prepare a slurry.

[0083] Preparation of porous polymer substrate

[0084] A polyethylene film with a thickness of 9 μm (SEM corp, SV-9) was used as the porous polymer substrate.

[0085] Manufacturing of separation membranes

[0086] Using a bar coater, the above-mentioned slurry for coating the separator was coated on both sides of a polyethylene film to a thickness of 3 μm each and dried to produce a separator with a total thickness of 15 μm.

[0087] Comparative example

[0088] A separation membrane was prepared in the same manner as in the example, except that a fluorine-based water-dispersible emulsion was used as the polymer binder, and a slurry was prepared by mixing an inorganic material, a polymer binder, and carboxymethylcellulose in a ratio of 79:20:1.

[0090] Experimental Example 1 and Comparative Experimental Example 1. Confirmation of the rate of change in thickness of the porous coating layer before and after electrolyte impregnation

[0091] Experimental Example 1

[0092] Figure 1 shows the elemental content (Atomic percent, %) according to etching time (Etching time, s) by performing ion beam etching using argon cations (voltage 2 keV, raster size 0.5 mm, etching rate 5.46 nm / s based on Ta2O5) on the surface of the separator prepared in the example, and XPS analysis (X-ray: Monochromatic Al Kα, 1486.6 eV, X-ray spot size: 100 μm) at 500-second intervals.

[0093] In Figure 1, t is the time taken to reach the point where the carbon content curve and the aluminum content curve first intersect. 1,bare , the time to reach the second intersection point is t 2,bare It was denoted as, and the time difference value (Δt bare = t 2,bare - t 1,bare ) was calculated and shown in Table 1 below.

[0094] Experimental Example 1-1

[0095] The separator prepared in the example was completely immersed in an electrolyte containing 1.0 M LiPF6 and composed of an EC:EMC weight ratio of 3:7, left for 12 hours, and then air-dried. Ion beam etching and XPS analysis were performed using the dried separator in the same manner as in Experimental Example 1, and the elemental content according to etching time is shown in Figure 2.

[0096] In Figure 2, the time taken to reach the first intersection point of the carbon content curve and the aluminum content curve is denoted as t1, and the time taken to reach the second intersection point is denoted as t2. The time difference (Δt = t2 - t1) and the rate of change in the thickness of the porous coating layer ({(Δt - Δt bare ) / Δt bare The values ​​were calculated and shown in Table 1 below.

[0097] Experimental Example 1-2

[0098] An electrode assembly sample was prepared by placing the separator prepared in the example between an anode coated with an anode composite containing nickel, cobalt, and manganese on an aluminum foil and a cathode coated with a cathode composite containing graphite on a copper foil, and applying pressure under conditions of 60°C, 6.5 MPa, and 1 second.

[0099] The electrode assembly sample was placed in an aluminum pouch, an electrolyte containing 1.0 M LiPF6 and composed of an EC:EMC weight ratio of 3:7 was injected and sealed, and stored at 70°C for 7 days. Afterward, the pouch and electrode assembly were disassembled, and the obtained separator was dried and ion beam etching and XPS analysis were performed in the same manner as in Experimental Example 1. The elemental content according to etching time is shown in Figure 3.

[0100] In Fig. 3, the time taken to reach the first intersection point of the carbon content curve and the aluminum content curve is denoted as t1, and the time taken to reach the second intersection point is denoted as t2. The time difference (Δt = t2 - t1) and the rate of change in the thickness of the porous coating layer ({(Δt - Δt bare ) / Δt bare The values ​​were calculated and shown in Table 1 below.

[0101] Comparative Experiment Example 1

[0102] Except for using the separation membrane prepared in the comparative example, the elemental content according to etching time was determined in the same manner as in Experimental Example 1 and is shown in Fig. 4.

[0103] In Fig. 4, the time to reach the point where the carbon content curve and the aluminum content curve first intersect is t. 1,bare , the time to reach the second intersection point is t 2,bare It was denoted as, and the time difference value (Δt bare = t 2,bare - t 1,bare ) was calculated and shown in Table 1 below.

[0104] Comparative Experiment Example 1-1

[0105] Except for using the separation membrane prepared in the comparative example, the elemental content according to etching time was determined in the same manner as in Experimental Example 1-1 and is shown in Fig. 5.

[0106] In Fig. 5, the time taken to reach the first intersection point of the carbon content curve and the aluminum content curve is denoted as t1, and the time taken to reach the second intersection point is denoted as t2. The time difference (Δt = t2 - t1) and the rate of change in the thickness of the porous coating layer ({(Δt - Δt bare ) / Δt bare The values ​​were calculated and shown in Table 1 below.

[0107] Comparative Experiment Example 1-2

[0108] Except for using the separation membrane prepared in the comparative example, the elemental content according to etching time was determined in the same manner as in Experimental Example 1-2 and is shown in Fig. 6.

[0109] In Fig. 6, the time taken to reach the first intersection point of the carbon content curve and the aluminum content curve is denoted as t1, and the time taken to reach the second intersection point is denoted as t2. The time difference (Δt = t2 - t1) and the rate of change in the thickness of the porous coating layer ({(Δt - Δt bare ) / Δt bare The values ​​were calculated and shown in Table 1 below.

[0110] Experimental Example 1 Experimental Example 1-1 Experimental Example 1-2 Time difference value Δt bare 4200 Δt 4000 Δt 4200 Rate of change in thickness of porous coating layer - -4.8% 0% Comparative Experiment Example 1 Comparative Experiment Example 1-1 Comparative Experiment Example 1-2 Time difference value Δt bare 4600 Δt 3600 Δt 3800 Rate of change in thickness of porous coating layer - -22% -17%

[0112] Experimental Example 2 and Comparative Experimental Example 2. Confirmation of whether the separator detaches before and after electrolyte impregnation

[0113] Experimental Example 2-1

[0114] In Experimental Example 1-1, the weight of the separator before and after electrolyte impregnation was measured to determine the weight loss rate ({(W 함침전 -W 함침후 ) / W 함침전The weight change rate was measured and shown in Table 2 below. If the weight change rate was 8% or more, it was evaluated as defective due to the detachment of the porous coating layer.

[0115] Experimental Example 2-2

[0116] In Experimental Example 1-2, since an electrode assembly was manufactured, the bonding state between the separator and the electrode before separating the electrode assembly sample and whether folding of the separator occurred after separating the electrode assembly sample were visually checked, and the results are shown in Table 2 below.

[0117] Comparative Experiment Example 2-1

[0118] In Experimental Example 1-1, the weight of the separator before and after electrolyte impregnation was measured, and the weight change rate ({(W 함침전 -W 함침후) / W 함침전 The weight change rate was measured and shown in Table 2 below. If the weight change rate was 8% or more, it was evaluated as defective due to the detachment of the porous coating layer.

[0119] Comparative Experiment Example 2-2

[0120] The bonding state of the separator and the electrode before separating the electrode assembly sample of Experimental Example 1-2 and whether folding of the separator occurred after separating the electrode assembly sample were visually checked, and the results are shown in Table 2 below.

[0121] Membrane detachment evaluation Experimental Example 2-1 Experimental Example 2-2 Comparative Experiment Example 2-1 Comparative Experiment Example 2-2 Porous layer delamination evaluation (weight loss) Good (1.1%) - Defective (10.5%) - Visual assessment of membrane detachment - Good (no folding or detachment) - Defect (part of the separator detaches from the electrode before separation of the electrode assembly, and separator folding is also observed in some samples)

Claims

Claim 1 A separator for an electrochemical device comprising: a porous polymer substrate; and a polymer binder containing carbon and inorganic particles containing a metal element, wherein the separator comprises a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer faces the porous polymer substrate and comprises a first layer containing the metal element in an amount equal to or greater than that of the carbon, and a second layer disposed on the first layer and containing the carbon in an amount greater than that of the metal element, wherein the polymer binder comprises a fluorine-based water-dispersible emulsion and an acrylic-based water-dispersible emulsion, and the separator has a value according to the following formula (1) of 15% or less: Formula (1) | {(Δt - Δt bare ) / Δt bare In the equation} × 100 (%) |, Δt is the difference value (Δt = t2 - t1) between the time (t1) required for the carbon content curve and the metal content curve among the elemental content curves resulting from ion beam etching to intersect for the first time and the time (t2) required for the second time to intersect, in the separator impregnated with and dried in the electrolyte of the electrochemical device, and Δt bare is the time (t) required for the carbon content curve and the metal content curve among the elemental content curves to first intersect according to ion beam etching in the above-mentioned membrane. 1,bare ) and the time required to intersect for the second time (t 2,bare The difference value between ) (Δt bare = t 2,bare - t 1,bare ) and the above ion beam etching is performed on the surface of the separator with argon cations in a monatomic mode at a voltage of 1.0 to 2.5 keV, and the elemental content is the elemental content (at%) confirmed by XPS analysis according to the ion beam etching time. Claim 2 delete Claim 3 A separator for an electrochemical device according to claim 1, wherein the porous polymer substrate comprises a polyolefin-based polymer, and the carbon content contained in the porous substrate is greater than the metal content. Claim 4 A separator for an electrochemical device according to claim 1, wherein the fluorine-based polymer comprises one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE). Claim 5 A separator for an electrochemical device according to claim 1, wherein the acrylic polymer comprises one or more selected from the group consisting of polyacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, and methyl methacrylate. Claim 6 A separator for an electrochemical device according to claim 1, wherein the thickness of the porous coating layer is 1 to 30 μm. Claim 7 In claim 1, the separator is a separator for an electrochemical device having a value of 10% or less according to the formula (1). Claim 8 delete Claim 9 An electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein the separator is a separator for an electrochemical device according to any one of claims 1 and 3 to 7.

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