Separation membrane for electrochemical elements and electrochemical elements equipped therewith

Abstract

The present invention provides an electrochemical element that exhibits excellent adhesion between the electrode and the separation membrane even after the electrolyte solution has been injected. [Solution] The present invention relates to a separation membrane for an electrochemical element, comprising a porous polymer substrate and a porous coating layer formed on at least one side surface of the porous polymer substrate, wherein the porous coating layer comprises first binder particles, second binder particles and inorganic particles, the inorganic particles being most abundantly distributed on a first surface facing the porous polymer substrate, the second binder particles being most abundantly distributed on a second surface opposite to the first surface, and the weight per particle of the inorganic particles being greater than the weight per particle of the first binder particles and the second binder particles, respectively.

Description

[Technical Field]

[0001] This invention claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0112886, filed with the Korean Intellectual Property Office on September 6, 2022, and all of its contents are included in this invention. This invention relates to a separation membrane for an electrochemical element with improved dry adhesion and wet adhesion, and an electrochemical element equipped therewith. [Background technology]

[0002] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. Recently, lithium-ion batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, are widely used.

[0003] A lithium secondary battery may include an electrode assembly manufactured from a positive electrode, a negative electrode, and a separator membrane placed between the positive and negative electrodes, the electrode assembly being manufactured in a case with an electrolyte. The separator membrane is placed between the positive and negative electrodes to insulate them, and a porous coating layer containing a polymer binder and inorganic particles may be included on at least one surface of a porous polymer substrate. The inorganic particles can be linked with other inorganic particles by the polymer binder to form an interstitial volume, through which lithium ions can move. In addition to fixing the inorganic particles, the polymer binder can provide adhesion to the porous coating layer, which can then adhere to the porous polymer substrate and the electrodes, respectively.

[0004] A porous coating layer containing a polymer binder and inorganic particles can prevent thermal shrinkage of a porous polymer substrate. The porous coating layer can be formed by applying and drying a slurry containing a polymer binder, inorganic particles, and a solvent on a porous polymer substrate. When the slurry is applied and dried, the solvent volatilizes, allowing the polymer binder and inorganic particles to undergo migration. The migration of the polymer binder and the inorganic particles can be determined by a combination of factors including the physical properties of the polymer binder and the inorganic particles, the physical properties of the slurry, and drying conditions.

[0005] In particular, the physical properties of the polymer binder and the inorganic particles can be the main factors that determine the structure and function of the porous coating layer. For example, by controlling the above factors, the polymer binder can be distributed in the porous coating layer on the opposite surface of the porous polymer substrate, so as to secure the adhesive strength of the separation membrane to the electrode. However, even when the polymer binder is distributed on the surface, if the size of the polymer binder is smaller than that of the inorganic particles, the polymer binder may be sandwiched between the inorganic particles and become unable to move, or the binder may not be distributed to the outermost layer of the porous coating layer, and thus may fail to exhibit sufficient adhesive strength.

[0006] Therefore, studies are being conducted on separation membranes that can prevent a decrease in adhesive strength of separation membranes including a porous coating layer by controlling the physical properties of a polymer binder and inorganic particles. Summary of the Invention Problem to be Solved by the Invention

[0007] An object of the present invention is to provide a separation membrane for an electrochemical device in which binder particles that provide wet adhesive strength are located on the surface of a porous coating layer, and an electrochemical device including the separation membrane that has excellent adhesive strength between an electrode and the separation membrane even after injection of an electrolyte solution. Means for Solving the Problem

[0008] One aspect of the present invention provides a separation membrane for an electrochemical element, comprising a porous polymer substrate and a porous coating layer formed on at least one side of the porous polymer substrate, wherein the porous coating layer comprises first binder particles, second binder particles, and inorganic particles, the inorganic particles being most abundantly distributed on a first surface facing the porous polymer substrate, the second binder particles being most abundantly distributed on a second surface opposite to the first surface, and the weight per particle of the inorganic particles being greater than the weight per particle of the first binder particles and the second binder particles, respectively.

[0009] The weight per particle of the first binder particles may be greater than the weight per particle of the second binder particles. The weight per particle can be determined from the density and diameter (D50) of each particle before manufacturing the slurry for forming the porous coating layer.

[0010] At least one of the first binder particles and the second binder particles may be aqueous binder particles.

[0011] The first binder particles and the inorganic particles are each spherical particles, and the diameter (D50) of the first binder particles may be equal to or greater than the radius of the inorganic particles.

[0012] The second binder particle is a spherical particle, and the diameter (D50) of the second binder particle may be equal to or greater than the radius of the first binder particle.

[0013] The density of the second binder particles may be greater than the density of the first binder particles.

[0014] The first binder particles provide adhesive force between the electrochemical element separation membrane and the electrode when the separation membrane is dry, and the second binder particles provide adhesive force between the electrochemical element separation membrane and the electrode when the separation membrane is impregnated in the electrolyte.

[0015] Said inorganic particles include Li3PO4, 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), Li x Ge y P z S w (0<x<4, 0<y<1, 0<z<1, 0<w<5), Li x N y (0<x<4, 0<y<2), Li x Si y S z (0<x<3, 0<y<2, 0<z<4), Li x P y S z (0<x<3, 0<y<3, 0<z<7), Li7La3Zr2O 12 , BaTiO3, BaSO4, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0<x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, 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 and HBO2, and may be one or more selected from the group consisting of the above.

[0016] Said porous coating layer may comprise a polymer binder including said first binder particles and said second binder particles and said inorganic particles at a weight ratio of 10:90 to 50:50.

[0017] The porous coating layer may contain the first binder particles and the second binder particles in a weight ratio of 1:0.5 to 1:1.5.

[0018] The porous coating layer may have a thickness of 1.5 to 5 μm.

[0019] Another aspect of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane may be a separation membrane for an electrochemical element according to one aspect of the present invention.

[0020] The electrochemical element may be a lithium secondary battery. [Effects of the Invention]

[0021] The separation membrane for electrochemical elements according to the present invention is provided such that inorganic particles, first binder particles, and second binder particles are distributed in order from the surface closest to the porous polymer substrate in the porous coating layer, and the second binder particles provide wet adhesion even after the separation membrane is impregnated with an electrolyte. [Brief explanation of the drawing]

[0022] [Figure 1] This is a conceptual diagram of the separation membrane according to the present invention.

[0023] [Figure 2] This is an SEM image of the surface of the separation membrane in Example 1.

[0024] [Figure 3] This is an SEM image of the surface of the separation membrane in Example 2.

[0025] [Figure 4] This is an SEM image of the surface of the separation membrane in Comparative Example 1.

[0026] [Figure 5] This is an SEM image of the surface of the separation membrane in Comparative Example 5. [Modes for carrying out the invention]

[0027] The following describes in more detail each component of the present invention so that it can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, this is merely an example, and the scope of the present invention is not limited to the following.

[0028] The term "including" as used herein is used to list materials, compositions, apparatus and methods useful for the present invention, and is not limited to such listed examples.

[0029] As used herein, “about” and “substantially” are used to mean a range of numerical values ​​or degrees or similar terms, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting disclosures that refer to precise and absolute numerical values ​​provided to aid in understanding the invention.

[0030] As used herein, "electrochemical element" can mean primary batteries, secondary batteries, supercapacitors, and the like.

[0031] As used herein, "diameter" means D50, which is the diameter that accounts for 50% of the cumulative particle number distribution by diameter, unless otherwise specified.

[0032] As used herein, "radius" refers to the cumulative 50th percentile value from the smallest value, calculated based on the results of measuring the particle size distribution (D50) using a general particle size distribution measurement system. For example, the particle size distribution can be determined by dispersing particles in an aqueous solution, stirring with an ultrasonic dispersion device, and then using laser diffraction or scattering.

[0033] With respect to the term "majority" as used herein, the expression that inorganic particles are abundant in the first surface region facing the porous polymer substrate means that the relative amount of inorganic particles present in the first surface region is greater than that in other regions of the porous coating layer. In other words, inorganic particles are present in the first surface region in the greatest quantity. Similarly, the expression that second binder particles are abundant in the second surface region opposite the first surface region means that the relative amount of second binder particles present in the second surface region is greater than that in other regions of the porous coating layer. In other words, second binder particles are present in the second surface region in the greatest quantity.

[0034] One embodiment of the present invention provides a separation membrane comprising a porous polymer substrate and a porous coating layer formed on at least one side surface of the porous polymer substrate. Specifically, the porous coating layer comprises first binder particles, second binder particles, and inorganic particles, wherein the inorganic particles are most abundantly distributed on the first surface facing the porous polymer substrate, and the second binder particles are most abundantly distributed on the second surface opposite the first surface, and the weight per particle of the inorganic particles is greater than the weight per particle of the first binder particles and the second binder particles, respectively.

[0035] The porous polymer substrate provides pores through which lithium ions can pass, while electrically insulating the positive and negative electrodes to prevent short circuits. The porous polymer substrate can be resistant to the electrolyte of an electrochemical element, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, polymer resins such as polyethylene, polypropylene, polybutene and other polyolefins, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene and copolymers or mixtures thereof. Preferably, the porous polymer substrate contains a polyolefin polymer and may have excellent slurry coatability for forming a porous coating layer, which is advantageous for producing thin separation films.

[0036] 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 contain pores with an average diameter of 0.01 to 10 μm.

[0037] A slurry can be applied to and dried on at least one surface of the porous polymer substrate to form a porous coating layer, as described later. The slurry may further contain a surfactant. The slurry may also contain first binder particles, second binder particles, inorganic particles, a dispersion medium, etc. To improve the impregnation of the slurry into the electrolyte, the porous polymer substrate may be subjected to a surface treatment such as plasma treatment or corona discharge before application of the slurry.

[0038] Examples of surfactants used in the slurry include nonionic surfactants, ionic surfactants, or amphoteric surfactants, and more specifically, the type of substance can be selected from those known in the industry. For example, the surfactant may include dimethyl silicone, aminosilane, acrylicsilane, vinylbenzylsilane, glycidylsilane, mercaptosilane, polydimethylsiloxane, or two or more of these. The surfactant content in the slurry may be 0.5 to 1% of the slurry weight.

[0039] The separation membrane for the electrochemical element may include the porous polymer substrate and a porous coating layer. The porous coating layer may be provided on one or both sides of the porous polymer substrate. The porous coating layer can be formed by applying a slurry to at least one surface of the porous polymer substrate and drying it.

[0040] The porous coating layer may include inorganic particles to improve the mechanical properties and insulating properties of the porous polymer substrate, and a polymer binder to improve the adhesion between the electrode and the separation membrane. The polymer binder includes first binder particles and second binder particles, and the polymer binder provides adhesion between the electrode and the separation membrane, and can bind adjacent inorganic particles together and maintain the bond. The inorganic particles can bind to adjacent inorganic particles to provide an interstitial volume, which is a pore space between the inorganic particles, through which lithium ions can move.

[0041] At least one of the first binder particles and the second binder particles may be aqueous binder particles. The weight-average molecular weight of the aqueous binder particles may be 10,000 to 10,000,000. Preferably, both the first binder particles and the second binder particles may be aqueous binder particles.

[0042] The first binder particles can provide the adhesive force (Dry Adhesion) between the separation membrane and the electrode when the separation membrane is dry. An electrode assembly can be manufactured by laminating the separation membrane and the electrode, and in this case, since there is no electrolyte, the Dry Adhesion between the separation membrane and the electrode is important. The Dry Adhesion, which is the adhesive force of the separation membrane in a dry state, may be 10 gf / 25 mm or more, preferably 10 gf / 25 mm to less than 100 gf / 25 mm, and more preferably 50 gf / 25 mm to less than 100 gf / 25 mm. If the Dry Adhesion exceeds 100 gf / 25 mm, it may hinder electrolyte impregnation into the separation membrane, potentially causing lithium dendrites to precipitate.

[0043] The second binder particles can provide adhesive strength (wet adhesive strength) between the separation membrane and the electrode when the separation membrane is impregnated in the electrolyte. The electrode assembly can be inserted into a pouch or case and the electrolyte can be poured in to manufacture an electrochemical element. In this case, the separation membrane is impregnated in the electrolyte, so the wet adhesive strength between the separation membrane and the electrode is important. The wet adhesive strength, which is the adhesive strength of the separation membrane when impregnated in the electrolyte, may be 1.0 gf / 20 mm or more, more specifically 10 gf / 20 mm or more, and more specifically 7 gf / 20 mm to 20 gf / 20 mm. If the wet adhesive strength is less than 1 gf / 20 mm, the stiffness of the cell will be low, causing assembly problems and bending problems of the separation membrane during the manufacture of the electrode assembly. If it exceeds 20 gf / 20 mm, electrolyte impregnation of the separation membrane may be hindered, potentially causing the deposition of lithium dendrites.

[0044] The first binder particles and the second binder particles may be any particles that provide dry adhesion and wet adhesion, respectively. Preferably, the first binder particles contain an acrylic binder and can provide dry adhesion between the separation membrane and the electrode. For example, the first binder particles may be one or more selected from the group consisting of polymers containing styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate. Preferably, the second binder particles contain a polyvinyl fluoride binder and can provide wet adhesion between the separation membrane and the electrode. For example, the second binder particle may be one or more selected from the group consisting of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trichloroethylene (PVDF-TCE), polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE), and polymers containing polyvinylidene fluoride and acrylate.

[0045] The inorganic particles may form a uniform thickness of the porous coating layer and may not undergo oxidation-reduction reactions within the operating voltage range of the electrochemical element to which they are applied. For example, the inorganic particles may have one or more properties among lithium ion transport capability, piezoelectricity, and flame retardancy.

[0046] Inorganic particles with lithium ion transport capability are those that contain the element lithium but do not store lithium, instead possessing the function of transporting lithium ions. These inorganic particles can transport and move lithium ions through a type of defect present within their particle structure. Therefore, the lithium ion conductivity within the electrochemical element is improved, thereby enhancing the performance of the electrochemical element.

[0047] For example, inorganic particles having lithium ion conductivity include Li3PO4, 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), Li x Ge y P z S w (0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride such as Li3N (Li x N y , 0<x<4, 0<y<2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0<x<3, 0<y<2, 0<z<4), P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z , 0<x<3, 0<y<3, 0<z<7), LLZO systems such as Li7La3Zr2O 12 and may be one or more selected from the group consisting of mixtures of the foregoing, but are not limited thereto.

[0048] Piezoelectric inorganic particles are substances that are insulators at normal pressure but become electrically conductive when a certain pressure is applied due to a change in their internal structure. These inorganic particles can exhibit high dielectric constant characteristics with a dielectric constant of 100 or more, and when stretched or compressed under a certain pressure, they can generate electric charge, causing one side to become positively charged and the other negatively charged, thereby creating a potential difference between the two sides. In the case of such inorganic particles, when an internal short circuit occurs between the positive and negative electrodes due to external impacts such as local crush or nailing, the inorganic particles coated on the separation film not only prevent direct contact between the positive and negative electrodes, but the piezoelectric properties of the inorganic particles also create a potential difference within the particles. This leads to electron transfer between the positive and negative electrodes, i.e., the formation of a minute current flow, which can result in a gentle voltage reduction of the electrochemical element and thereby improve safety.

[0049] For example, piezoelectric inorganic particles include BaTiO3, BaSO4, Pb(Zr,Ti)O3(PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 ) may be one or more selected from the group consisting of O3-PbTiO3 (PMN-PT), HfO2 (hafnia), and mixtures thereof, but is not limited to these.

[0050] Flame-retardant inorganic particles can add flame-retardant properties to separation membranes or prevent a rapid rise in temperature inside electrochemical elements.

[0051] For example, flame-retardant inorganic particles may be one or more selected from the group consisting of 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, but are not limited to these.

[0052] The present invention allows the inorganic particles, the first binder particles, and the second binder particles to be arranged in order in the porous coating layer, starting from the surface closest to the porous polymer substrate, by adjusting the correlation of physical properties between the inorganic particles, the first binder particles, and the second binder particles.

[0053] The inorganic particles may be most abundantly distributed on the first surface of the porous coating layer that faces the porous polymer substrate. For example, 50 to 99.99% by weight of the inorganic particles contained in the porous coating layer may be distributed on the first surface.

[0054] The second binder particles may be most abundantly distributed on the second surface of the porous coating layer, which is opposite to the first surface. For example, 50 to 99.99% by weight of the second binder particles contained in the porous coating layer may be distributed on the second surface. The second binder particles are most abundantly distributed on the second surface, which corresponds to the outermost edge of the separation membrane, and the separation membrane can exhibit excellent adhesion to the electrode when impregnated with the electrolyte.

[0055] The density of the inorganic particles may be greater than the densities of the first binder particles and the second binder particles, respectively. The density of the second binder particles may be even greater than that of the first binder particles. For example, the density of the inorganic particles may be 3 g / cm³. 3 The above is true, and the density of the second binder particles is 1.1-2 g / cm³. 3 The density of the first binder particles is 1.2 g / cm³.3 The following is also acceptable.

[0056] When the slurry is applied to a porous polymer substrate, the inorganic particles can be distributed in the direction of the surface of the porous polymer substrate due to the difference in particle density. The first binder particles and the second binder particles can be laminated on the inorganic particles. For example, as shown in Figure 1, the second binder particles may be laminated on the inorganic particles and the first binder particles may be laminated on the second binder particles, or the first binder particles and the second binder particles may be randomly distributed and laminated on the inorganic particles.

[0057] The weight per particle of the inorganic particles may be greater than the weight per particle of the first binder particles and the second binder particles, respectively. The weight per particle of the first binder particles may be greater than that of the second binder particles. When forming the porous coating layer, the heaviest inorganic particles are distributed on the first surface facing the porous polymer substrate, and the lightest second binder particles can move to the surface of the porous coating layer faster than the first binders.

[0058] The first binder particles and the inorganic particles are each spherical particles, and the diameter of the first binder particles may be equal to or greater than the radius of the inorganic particles. For example, the radius of the inorganic particles may be 250 nm to 2500 nm, and the diameter of the first binder particles may be equal to or greater than the radius of the inorganic particles. If the radius of the inorganic particles is less than 250 nm, an additional polymer binder is required for bonding between the inorganic particles, which is disadvantageous in terms of electrical resistance. If the radius of the inorganic particles exceeds 2500 nm, the uniformity of the surface of the coating layer will be low, and particles protruding after coating may damage the separation film and electrodes during lamination, potentially causing a short circuit. If the diameter of the first binder particles is smaller than the radius of the inorganic particles, the first binder particles will be sandwiched between the inorganic particles, making it impossible to ensure sufficient dry adhesion. Preferably, the diameter of the first binder particles may be larger than the radius of the inorganic particles.

[0059] The second binder particles are spherical particles, and the diameter of the second binder particles may be equal to or greater than the radius of the first binder particles. When the slurry is dried, the dispersion medium contained in the slurry evaporates, which can induce the movement of the first and second binder particles. The movement speed of the second binder particles, which are lighter per particle, may be faster than that of the first binder particles. The second binder particles can move past the first binder particles to the opposite side of the porous polymer substrate, and after moving, since the diameter of the second binder particles is greater than the radius of the first binder particles, they can not move any further in the direction of the porous polymer substrate. If the diameter of the second binder particles is smaller than the radius of the first binder particles, the second binder particles will be sandwiched between the first binder particles, and sufficient wet adhesion cannot be ensured. Preferably, the diameter of the second binder particles may be larger than the radius of the first binder particles.

[0060] In the porous coating layer formed by the evaporation of the dispersion medium, a concentration gradient of second binder particles, first binder particles, and inorganic particles may be formed in the direction from the outermost part of the porous coating layer toward the porous polymer substrate.

[0061] The second binder particles may be most abundantly distributed on the second surface of the porous coating layer (the region opposite to the region facing the porous polymer substrate) and least abundantly distributed on the surface region facing the porous polymer substrate (the first surface).

[0062] The first binder particles may be most abundantly distributed in the region between the second surface of the porous coating layer and the first surface facing the porous polymer substrate.

[0063] The inorganic particles may be most abundantly distributed on the first surface facing the porous polymer substrate and least abundantly distributed on the second surface of the porous coating layer.

[0064] The second surface of the porous coating layer is distributed with both second and first binder particles, although the amount of second binder particles may be greater than the amount of first binder particles. For example, 10 to 50% by weight of the first binder particles contained in the porous coating layer may be distributed on the second surface. The first binder particles distributed on the second surface of the porous coating layer provide dry adhesion, while the second binder particles distributed on the second surface of the porous coating layer provide wet adhesion.

[0065] The porous coating layer may contain a polymer binder containing the first binder particles and the second binder particles and the inorganic particles in a weight ratio of 10:90 to 50:50. If the polymer binder is contained in a quantity 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 separation membrane may not be ensured. If the polymer binder content exceeds the above range, there is a problem that the cell resistance becomes too high.

[0066] The porous coating layer may contain the first binder particles and the second binder particles in a weight ratio of 1:0.5 to 1:1.5. If the amount of the second binder particles is less than the aforementioned range, adhesion between the electrode and the separation membrane cannot be maintained when impregnated in the electrolyte. If the amount of the second binder particles exceeds the aforementioned range, the second binder particles are not sufficiently distributed on the surface of the porous coating layer (for example, the second surface), and adhesion between the electrode and the separation membrane cannot be maintained when impregnated in the electrolyte.

[0067] The thickness of the porous coating layer may be between 1.5 μm and 5 μm. If the thickness of the porous coating layer is less than 1.5 μm, the wet adhesion strength decreases sharply, and a problem occurs in which the electrode and the separation membrane separate when the electrolyte is injected. Even if the thickness of the porous coating layer exceeds 5 μm, the adhesion strength between the separation membrane and the electrode does not increase significantly.

[0068] The porous coating layer may further contain a dispersant to further improve the dispersibility of inorganic particles. The dispersant functions to maintain a uniform dispersion state of inorganic particles within the polymer binder during slurry production. For example, the dispersant may be 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. If the slurry contains a dispersant, the porous coating layer may contain the dispersant in an amount of 5% by weight or less.

[0069] Another embodiment of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, a separation membrane disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the separation membrane is a separation membrane for an electrochemical element according to the above-described embodiment.

[0070] The positive electrode and the negative electrode may be formed by coating at least one surface of the current collector with an active material and drying it. The current collector can be made of a material that is conductive without inducing a chemical change in the electrochemical element. For example, the positive electrode current collector may be made of 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 to these. For example, the negative electrode current collector may be made of 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 to these. The current collector may be in various forms such as a thin metal sheet, film, foil, net, porous material, or foam.

[0071] For example, the positive electrode active material is lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2); chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), 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 as O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented as 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 in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, etc. may be included, but are not limited to these.

[0072] The negative electrode active material is carbon such as non-graphitizable carbon and graphite-based carbon; Lix 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, Group 2, and Group 3 elements of the periodic table, and halogens; 0<x≦1; 1≦y≦3; 1≦z≦8) and other metal composite oxides; lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, and Bi₂O₅ and other metal oxides; conductive polymers such as polyacetylene; may also include, but is not limited to, Li-Co-Ni-based materials and the like.

[0073] The electrolyte solution may be a lithium salt-containing non-aqueous electrolyte solution. The electrolyte solution consists of an electrolytic solution and a lithium salt, and as the electrolytic solution, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. may be used.

[0074] As the non-aqueous organic solvent, for example, non-protic 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate may be used.

[0075] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerization agents containing ionic dissociation groups may be used.

[0076] As the inorganic solid electrolyte, for example, lithium nitrides, halides, sulfates such as Li3N, LiI, Li5NI2, Li3NLiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2 may be used.

[0077] The lithium salts mentioned above are substances that are easily soluble in the non-aqueous electrolyte, such as LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc. may also be used.

[0078] The electrochemical element can be manufactured by inserting a positive electrode, a negative electrode, a separation membrane, 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 element may be cylindrical, prismatic, coin-type, or pouch-type lithium secondary battery.

[0079] The lithium secondary battery may be packed or modularized as a unit cell and used in small devices such as computers, mobile phones, and power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric motorcycles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and medium to large devices such as power storage systems.

[0080] The present invention will be described in more detail below with reference to specific examples and experimental cases. The following examples and experimental cases are for illustrative purposes only and do not limit the present invention to the following examples and experimental cases.

[0081] Examples 1 and 2

[0082] Slurry preparation

[0083] At room temperature, distilled water has the density (g / cm³) shown in Table 1 below. 3 ), diameter (nm) and weight per particle (×10 -14 After adding inorganic particles having g) and a dispersant, an inorganic dispersion was prepared by bead milling (adding the same amount of 0.7 μm zirconia beads as the inorganic particles and milling for 2 hours using a paint shaker). The prepared inorganic dispersion was then subjected to the density (g / cm³) shown in Table 1 below. 3 ), diameter (nm) and weight per particle (×10 -14A polymeric binder containing (g) was added. At this time, the polymeric binder consisted of first binder particles and second binder particles added in the weight ratios shown in Table 1, and a surfactant was added to improve wettability with the substrate. A styrene-butadiene copolymer was used as the first binder, PVdF-butyl acrylate was used as the second binder, and dimethyl silicone (0.5% by weight of the slurry) was used as the surfactant. The mixture was stirred at 10 rpm for 10 minutes to produce a slurry in which the binder particles and inorganic particles were dispersed.

[0084] Preparation of porous polymer substrates

[0085] A polyethylene film (PE) with a thickness of 9 μm was used as the porous polymer substrate.

[0086] Manufacturing of separation membranes

[0087] A slurry was coated onto both sides of a polyethylene film using a doctor blade, and then dried using a hot air blower to form porous coating layers with each coating having a thickness of 2.5 μm, thereby producing a separation membrane with an overall thickness of approximately 14 μm.

[0088] Comparative Examples 1-5

[0089] The separation membranes were manufactured in the same manner as in Examples 1 and 2, except that the inorganic particles and polymer binder with the density, diameter, and weight per particle listed in Table 1 below were used during slurry preparation. Comparative Examples 1 to 3 used only the first binder particles as the polymer binder.

[0090] Experimental Example 1: Confirmation of the adhesive strength of the separation membrane.

[0091] The dry and wet adhesion strengths of the separation films used in Examples 1 and 2 and Comparative Examples 1 to 5 were confirmed and are shown in Table 1 below.

[0092] Dry adhesive strength

[0093] A 2cm x 6cm separation membrane was laminated onto one surface of a 2.5cm x 6cm negative electrode, and pressurized at 6.5MPa for 1 second at 60°C. Then, using a UTM (Universal Test Machine, Instron), the negative electrode was fixed, and the separation membrane was peeled off at a speed of 300mm / min in a 180° direction. The peel strength (gf / 25mm) was measured.

[0094] Wet adhesive strength

[0095] A separation membrane of the same size was laminated onto one side of a 2cm x 6cm positive electrode. After pressurizing it at 6.5MPa for 1 second at 60°C, it was inserted into a pouch, 1.0g of electrolyte (EC / EMC 3:7 with LiPF61.0M) was poured in, and it was left at room temperature for one day.

[0096] The laminate of the positive electrode and the separation membrane was removed from the pouch, pressurized at 70°C and a pressure of 5 kgf for 5 minutes, and then left at room temperature for 1 hour. After that, the positive electrode was fixed using a UTM, and the separation membrane was peeled off at a speed of 200 mm / min in a 90° direction, and the peel strength (gf / 20 mm) was measured.

[0097] [Table 1]

[0098] Experimental Example 2. Confirmation of the surface state of the separation membrane.

[0099] The surfaces of the separation membranes from Examples 1 and 2 and Comparative Examples 1 and 5 were observed by SEM and are shown in Figures 2 to 5, respectively. In the comparative examples, it was confirmed that the binder particles were trapped in the spaces between the inorganic particles, and the binder could not be properly distributed on the surface.

[0100] In Comparative Example 4, the second binder particles had a higher density than the first binder particles, and it was not possible to distribute the second binder particles on the surface of the first binder particles (the surface of the separation membrane).

[0101] In Comparative Example 5, the diameter of the second binder particles was too small, causing them to be sandwiched between the first binder particles (or inorganic particles), making it impossible to distribute the second binder particles on the first binder particles.

[0102] Therefore, in Comparative Example 4 and Comparative Example 5, the wet adhesive strength was relatively low, at 2 gf / 20 mm and 3 gf / 20 mm, respectively.

[0103] Figure 4 relating to Comparative Example 1 shows that some of the first binder particles, which have a smaller diameter than the inorganic particles, are distributed on the inorganic particles, and some of the first binder particles are sandwiched between the inorganic particles.

[0104] Figure 5, relating to Comparative Example 5, shows that the first and second binder particles are distributed on the inorganic particles, and the inorganic particles are not observed. Furthermore, it shows that the diameter of the second binder particles is too small, causing them to be sandwiched between the first binder particles. Figure 5 shows that the second binder particles are not well distributed on the separation membrane.

Claims

1. The material comprises a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate. The porous coating layer is It comprises a first binder particle, a second binder particle, and an inorganic particle, The inorganic particles are most abundantly distributed on the first surface facing the porous polymer substrate, and the second binder particles are most abundantly distributed on the second surface opposite the first surface. The first binder particles are most abundantly distributed in the region between the second surface of the porous coating layer and the first surface facing the porous polymer substrate in a separation membrane for an electrochemical element.

2. The weight per particle of the first binder particle is greater than the weight per particle of the second binder particle. The separation membrane for an electrochemical element according to claim 1, wherein the weight per particle of the inorganic particles is greater than the weight per particle of the first binder particles and the second binder particles, respectively.

3. The separation membrane for an electrochemical element according to claim 1, wherein at least one of the first binder particles and the second binder particles is an aqueous binder particle.

4. The first binder particle and the inorganic particle are each spherical particles, The separation membrane for an electrochemical element according to claim 1, wherein the diameter (D50) of the first binder particles is equal to or greater than the radius of the inorganic particles.

5. The aforementioned second binder particle is a spherical particle, The separation membrane for an electrochemical element according to claim 4, wherein the diameter (D50) of the second binder particles is equal to or greater than the radius of the first binder particles.

6. The separation membrane for an electrochemical element according to claim 5, wherein the density of the second binder particles is equal to or greater than the density of the first binder particles.

7. The first binder particles provide adhesion between the electrochemical element separation membrane and the electrode in the dry state of the electrochemical element separation membrane. The electrochemical element separation membrane according to claim 1, wherein the second binder particles provide adhesive force between the electrochemical element separation membrane and the electrode when the separation membrane for the electrochemical element is impregnated in the electrolyte.

8. The inorganic particles are Li ３ 2O ４ 、 ｘ Ti ｙ (2O ４ ) ３ (0<8<2、0<y<3),L- ｘ Al ｙ Ti ｚ (2O ４ ) ３ (0<x<2、0<y<1、0<z<3), L- ｘ Lạ ｙ TiO ３ (0<8<2、0<y<3),L- ｘ Ge ｙ P ｚ S ｗ (0<x<4、0<y<1、0<z<1、0<w<5), L. ｘ N ｙ (0<8<4、0<y<2), L- ｘ Si ｙ S ｚ (0<x<3、0<y<2、0<z<4), L. ｘ P ｙ S ｚ (0<x<3、0<y<3、0<z<7), L- ７ Lạ ３ Zr ２ O １２ 、BTT9O ３ 、BBO ４ 、Pb(Zr,Ti)O ３ (PZT), Pb １－ｘ Lạ ｘ Zr １－ｙ Ti ｙ O ３ (>^ZT、0<x<1、0<y<1), Pb(Mg １／３ Nb ２／３ )O ３ -PbTiO ３ (PMN-PT), HfO ２ 、Sb ２ O ３ 、Sb ２ O ４ 、Sb ２ O ５ 、SrTiO ３ 、SnO ２ 、CeO ２ 、MgO、Mg(OH) ２ , NiO, CaO, ZnO, Zn ２ SnO ４ ZnSnO ３ , ZnSn(OH) ６ , ZrO ２ , Y ２ O ３ SiO ２ Al ２ O ３ , AlOOH, Al(OH) ３ SiC, TiO ２ , H ３ BO ３ and HBO ２ A separation membrane for an electrochemical element according to claim 1, which is one or more selected from the group consisting of the following.

9. The porous coating layer is A separation membrane for an electrochemical element according to claim 1, comprising a polymer binder containing the first binder particles and the second binder particles and the inorganic particles in a weight ratio of 10:90 to 50:

50.

10. The porous coating layer is A separation membrane for an electrochemical element according to claim 1, comprising the first binder particles and the second binder particles in a weight ratio of 1:0.5 to 1:1.

5.

11. The porous coating layer is A separation membrane for an electrochemical element according to claim 1, having a thickness of 1.5 to 5 μm.

12. An electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, The separation membrane is an electrochemical element according to any one of claims 1 to 11.

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