Separation membrane for electrochemical device and electrochemical device including said separation membrane

Abstract

According to an embodiment of the present invention, there is provided a separator for an electrochemical device, comprising: a polymer porous support; and an inorganic composite porous layer formed on at least one surface of the porous support, the inorganic composite porous layer comprising a binder polymer and an inorganic filler, the binder polymer comprising a first binder polymer and a second binder polymer, a ratio of the weight of the first binder polymer to the weight of the second binder polymer being 6:4 to 9:1, the first binder polymer being a non-crystalline polymer having a glass transition temperature (Tg) of 180°C or higher, the second binder polymer being a polyvinylidene fluoride-based copolymer comprising a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), and a content of the second repeating unit being 4 to 40 wt% based on a total weight of the polyvinylidene fluoride-based copolymer. According to the present invention, it is possible to provide a separator having improved adhesive strength, a high meltdown temperature, a low shrinkage rate of the separator at high temperatures, and excellent heat resistance and dimensional stability.

Description

[Technical Field]

[0001] The present invention relates to a separator for an electrochemical device and an electrochemical device including the separator.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0011687, filed on January 26, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] Recently, interest in energy storage technology has been growing. As its application fields expand to include mobile phones, camcorders, laptops, and even electric vehicles, research and development efforts in electrochemical devices are becoming increasingly focused. Among these, interest has been focused on the development of secondary batteries, which are energy storage devices that can be charged and discharged based on electrochemical principles. Furthermore, in the development of such batteries, research and development related to new electrode and battery designs has been conducted recently to improve capacity density and specific energy.

[0004] Lithium-ion secondary batteries, in particular, are batteries that can be used repeatedly because lithium ions store and generate electricity by moving back and forth between the positive and negative electrodes. Lithium-ion secondary batteries are characterized by high voltage and energy density, a long cycle life, excellent storage properties, and high output, which has led to a wide range of applications, including portable IT devices, electric vehicle batteries, and energy storage systems (ESS). The widespread use of electric vehicles is a key factor in the growth of secondary batteries and is the main driving force behind the secondary battery market.

[0005] The four main components of such a secondary battery are a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the separator separates the two electrodes (positive and negative electrodes) in the secondary battery to prevent electrical short circuits caused by physical contact, and provides ion conductivity by providing a path through which ions can move between the electrodes via the electrolyte held in micropores.

[0006] Such separation membranes are made of microporous polymer film materials having the above-mentioned functions, and polyolefin separation membranes are particularly widely used. Representative polyolefin separation membranes include polyethylene (PE)-based and polypropylene (PP)-based polymer materials.

[0007] The manufacturing methods for forming such a microporous structure are broadly divided into a dry process based on a stretching process and a wet process based on an extraction process, and dry separation membranes and wet separation membranes are used depending on the desired properties.

[0008] However, when polyolefin-based wet separators are used in secondary batteries, there are concerns that they lack sufficient heat resistance, such as a meltdown that can lead to fires and explosions if the battery temperature rises above the melting point of the polyolefin. To address this issue, technologies have been developed that coat the surface of the separator with inorganic particles and binder polymers. One example of this is the ceramic-coated safety-reinforced separator (SRS), which has been applied to lithium-ion secondary batteries for electric vehicles and has become the standard for heat-resistant separator technology. Wet separators, which are easy to thin, are commonly used to manufacture these separators.

[0009] As a method for producing such a wet separation membrane, a method of coating a dry film with a polymer binder by an immersion phase separation method, which is a nonsolvent-induced phase separation (NIPS) method, has been researched and developed.

[0010] This method has the advantage of being advantageous in terms of resistance due to the thinning of the separator, but it still has disadvantages in terms of dimensional stability due to heat, and there is a problem that microvoids and macrovoids are generated due to a decrease in packing density depending on the composition and process. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a separator for an electrochemical element that has excellent adhesive strength and ensures safety at high temperatures.

[0012] Another object of the present invention is to provide a method for producing a separator for an electrochemical element using an immersion phase separation method, which has excellent adhesive strength and ensures safety at high temperatures.

[0013] It will be readily apparent that other objects and advantages of the present invention can be achieved by the means or methods recited in the claims and combinations thereof. [Means for solving the problem]

[0014] The present inventors have found that the above-mentioned problems can be solved by the following separator for an electrochemical device, an electrochemical device including the separator, and a method for manufacturing the electrochemical device.

[0015] The first embodiment is A separator for an electrochemical element, The separation membrane comprises a polymer porous support and an inorganic composite porous layer formed on at least one surface of the porous support, the inorganic composite porous layer contains a binder polymer and an inorganic filler, the binder polymer includes a first binder polymer and a second binder polymer; The weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), The present invention relates to a separator for an electrochemical device, wherein the content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer.

[0016] The second embodiment is the first embodiment, The separator for an electrochemical device is characterized in that the ratio of the weight of the first binder polymer to the weight of the second binder polymer is 6:4 to 7:3.

[0017] The third embodiment is the first or second embodiment, The separator for an electrochemical device has a content of the second repeating unit of 4 to 15 wt % based on the total weight of the polyvinylidene fluoride copolymer.

[0018] The fourth embodiment is any one of the first to third embodiments, The present invention relates to a separator for electrochemical devices, wherein the inorganic composite porous layer has a porosity of 70% or more.

[0019] The fifth embodiment is any one of the first to fourth embodiments, The present invention relates to a separator for an electrochemical device, wherein the first binder polymer comprises polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyphenylsulfone (PPSU), polyethersulfone (PES), polysulfone (PSU), or two or more of these.

[0020] The sixth embodiment is any one of the first to fifth embodiments, The present invention relates to a separator for an electrochemical device, wherein the inorganic filler is primary particles having an average particle size of 20 nm to 700 nm.

[0021] The seventh embodiment is any one of the first to sixth embodiments, The present invention relates to a separator for an electrochemical element, wherein the inorganic filler comprises alumina (Al2O3), fumed alumina, aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), boehmite (AlOOH), or two or more of these.

[0022] The eighth embodiment is any one of the first to seventh embodiments, The present invention relates to a separator for an electrochemical device, wherein the inorganic composite porous layer further contains 3 parts by weight or less of a dispersant per 100 parts by weight of the inorganic composite porous layer.

[0023] The ninth embodiment is the eighth embodiment, The present invention relates to a separator for an electrochemical element, wherein the dispersant is polyvinylpyrrolidone (PVP).

[0024] A tenth embodiment relates to an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is a separator for an electrochemical device according to any one of the first to ninth embodiments.

[0025] The eleventh embodiment is the tenth embodiment, The electrochemical device is a lithium secondary battery.

[0026] The twelfth embodiment is a method for manufacturing a separator for an electrochemical device according to any one of the first to ninth embodiments, (S1) preparing a polymeric porous support; (S2) applying a slurry containing a binder polymer, an inorganic filler, and a solvent to at least one surface of the polymeric porous support; (S3) immersing the polymeric porous support coated with the slurry in a composition containing a non-solvent and drying the composition to form an inorganic composite porous layer; the binder polymer includes a first binder polymer and a second binder polymer; The weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), The present invention relates to a method for producing a separator for an electrochemical device, wherein the content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer.

[0027] The thirteenth embodiment is the twelfth embodiment, The present invention relates to a method for producing a separator for an electrochemical element, wherein the solvent is an organic solvent.

[0028] The fourteenth embodiment is the twelfth or thirteenth embodiment, The present invention relates to a method for producing a separator for an electrochemical element, wherein the non-solvent comprises water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, isopropyl alcohol, or two or more of these. [Effects of the Invention]

[0029] The separator for an electrochemical device according to an embodiment of the present invention has improved adhesive strength, a high meltdown temperature, and a low separator shrinkage rate at high temperatures, resulting in excellent heat resistance and dimensional stability.

[0030] Therefore, the high temperature stability of a battery manufactured using a separator according to an embodiment of the present invention can be improved.

[0031] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical ideas of the present invention as well as the contents of the invention, and therefore the present invention should not be interpreted as being limited to only the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0032] [Figure 1a] 1 is an SEM image of a cross section of the separation membrane according to Example 1 (magnification: 1000 times). [Figure 1b] 1 is an SEM image of a cross section of the separation membrane according to Example 1 (magnification: 3000 times). [Figure 2a] 1 is an SEM image of a cross section of a separation membrane according to Example 2 (magnification: 1000 times). [Figure 2b] 1 is an SEM image of a cross section of a separation membrane according to Example 2 (magnification: 3000 times). [Figure 3a] 1 is an SEM image of a cross section of a separation membrane according to Example 3 (magnification: 1000 times). [Figure 3b] 1 is an SEM image of a cross section of a separation membrane according to Example 3 (magnification: 3000 times). DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described in detail below. The terms and words used in the specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts that correspond to the technical concept of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0034] Throughout this specification, when a part "comprises" another component, it does not mean excluding the other component, but may further include the other component, unless otherwise specified.

[0035] Furthermore, the term "about" used throughout this specification is used to mean a numerical value or a approximation of a numerical value when given the inherent manufacturing and material tolerances, and is used to prevent unscrupulous infringers from unfairly exploiting the contents of the disclosure in which precise or absolute numerical values ​​are mentioned to aid in the understanding of this application.

[0036] Throughout this specification, the phrase "A and / or B" means "A, B, or both."

[0037] The separator for an electrochemical device according to one embodiment of the present invention comprises: The porous support includes a polymeric porous support and an inorganic composite porous layer formed on at least one surface of the porous support, the inorganic composite porous layer contains a binder polymer and an inorganic filler, the binder polymer includes a first binder polymer and a second binder polymer; The weight ratio of the first binder polymer to the second binder polymer is 6:4 to 8:2; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), The content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer.

[0038] According to an embodiment of the present invention, the polymeric porous support is not limited as long as it has a pore structure, and may be a porous polymer substrate, specifically, a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

[0039] The porous polymer film substrate may be a porous polymer film containing a polyolefin such as polyethylene or polypropylene, and such a polyolefin porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80 to 130°C.

[0040] In this case, the porous polymer film may be formed from a polyolefin polymer such as polyethylene (high density polyethylene, linear low density polyethylene, low density polyethylene, ultra-molecular weight polyethylene), polypropylene, polybutylene, polypentene, or a mixture of two or more of these polymers, or a derivative thereof.

[0041] Representative examples of commercially available polyolefin porous polymer films that can be used as such polymer porous supports include, but are not limited to, wet-type polyethylene systems (Asahi Kasei E-Materials, Toray, SK IEE Technology, Shanghai Energy, Sinoma, Entek), dry-type polypropylene systems (Shenzhen Senior, Cangzhou Mingzhu), and dry-type polypropylene / polyethylene multilayer structures (Polypore, Ube).

[0042] The porous polymer film substrate may be manufactured by molding various polymers such as polyesters in addition to polyolefins into a film. The porous polymer film substrate may be formed into a structure in which two or more film layers are laminated, and each film layer may be formed from the above-mentioned polymers such as polyolefins and polyesters alone or a mixture of two or more of them.

[0043] In addition, the porous polymer film substrate and the porous nonwoven fabric substrate may be formed from a polymer such as polyester (e.g., polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, etc., either alone or in combination.

[0044] The thickness of the polymeric porous support is not particularly limited, but may be 1 μm or more, 3 μm or more, 15 μm or less, or 10 μm or less. When the thickness of the polymeric porous support satisfies this range, the problem of the support acting as a resistance layer can be improved while maintaining mechanical properties.

[0045] The pore size and porosity of the polymeric porous support are not particularly limited, but the porosity may be in the range of 10 to 95%, and the pore size (diameter) may be 0.1 to 50 μm. When the pore size and porosity satisfy these ranges, the problem of acting as a resistance layer can be prevented and mechanical properties can be maintained. In addition, the polymeric porous support may be in the form of a fiber or membrane.

[0046] The inorganic composite porous layer is located on one surface of the polymeric porous support and includes a binder polymer and an inorganic filler.

[0047] The inorganic composite porous layer is one of the constituent layers of the separator, and serves as an isolation layer to prevent short circuits between the positive and negative electrodes, while preventing the polymer porous support from directly contacting lithium metal.

[0048] In the inorganic composite porous layer, inorganic fillers are filled and bound together by the binder polymer while in contact with each other, forming interstitial volumes between the inorganic fillers, which then become void spaces and form pores. That is, the binder polymer adheres the inorganic fillers together to maintain their bound state, for example, the binder polymer connects and fixes the inorganic fillers together. Furthermore, the pores in the inorganic composite porous layer are void spaces formed by the interstitial volumes between the inorganic fillers, which are spaces limited by the inorganic fillers that are substantially in contact with each other in a packed structure (closed packed or densely packed) by the inorganic fillers.

[0049] The inorganic filler serves to form micropores by forming spaces between the inorganic fillers and also serves as a kind of spacer that allows the physical shape to be maintained. Generally, the inorganic filler has the property that its physical properties do not change even at high temperatures of 200°C or higher, so the formed organic / inorganic composite porous film has excellent heat resistance.

[0050] Therefore, in a lithium secondary battery including the separator, even if the polymer porous support ruptures inside the battery under severe conditions due to internal or external factors such as high temperature, overcharging, or external impact, the inorganic composite porous layer can prevent the two electrodes from being completely short-circuited. Even if a short circuit does occur, the expansion of the short-circuited area can be suppressed, thereby improving the safety of the battery.

[0051] In one embodiment of the present invention, the porosity of the inorganic composite porous layer may be 70% or more. Specifically, the porosity of the inorganic composite porous layer may be determined depending on the composition of the inorganic composite porous layer, and may be in the range of 70% to 85% or 75% to 83%. When the porosity of the inorganic composite porous layer satisfies this range, a resistance reduction effect is achieved.

[0052] The thickness of the inorganic composite porous layer may be in the range of 1 μm or more, 3 μm or more, 50 μm or less, 30 μm or less, or 20 μm or less.

[0053] The inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler that can be used in the present invention is a filler that can be used in the range of the operating voltage of the battery to be applied (for example, Li / Li + There are no particular limitations on the inorganic filler, as long as it does not undergo oxidation and / or reduction reactions at a voltage of 0 to 5 V relative to the reference voltage. Examples of such inorganic fillers include alumina (Al2O3), fumed alumina, aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), boehmite (AlOOH), or a mixture of two or more of these. Specifically, alumina (Al2O3) may be used.

[0054] The inorganic filler preferably has an average particle size (D50) of 20 nm to 700 nm to form an inorganic composite porous layer with a uniform thickness and an appropriate porosity. Specifically, it may be in the range of 100 nm to 500 nm. When the inorganic filler has an average particle size (D50) within this range, the dispersion of the inorganic composite porous layer slurry is maintained, making it easy to control the physical properties of the separator. This prevents problems such as a decrease in mechanical properties due to an excessive increase in separator thickness or an internal short circuit during battery charge and discharge due to excessive pore size. In addition, the increased packing density contributes to the thermal shrinkage rate, and a particle size within this range exhibits excellent heat resistance.

[0055] In the present invention, the average particle size (D50) of the inorganic filler is defined as the particle size at 50% of the particle size distribution. In the present invention, the average particle size (D50) of the inorganic filler can be measured by observation using an electron microscope such as a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), or by laser diffraction. When measuring by laser diffraction, more specifically, the inorganic filler is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) at 50% of the particle size distribution measured by the analyzer can then be calculated.

[0056] The inorganic filler may be a primary particle, which is a single particle, or a secondary particle formed from an aggregate of primary particles.

[0057] The content of the inorganic filler is not particularly limited, but may be 50 wt% or more, 60 wt% or more, 95 wt% or less, 97 wt% or less, or 99 wt% or less, based on 100 wt% of the total weight of the inorganic composite porous layer. That is, the weight ratio of the inorganic filler to the binder polymer may be 50:50 or more, 60:40 or more, 70:30 or more, 95:5 or less, 97:3 or less, or 99:1 or less, and may be 50:50 to 99:1, specifically 60:40 to 97:3, and more specifically 70:30 to 95:5. When the content of the inorganic filler satisfies the above range, problems of reduced pore size and porosity in the inorganic composite porous layer due to excessive binder polymer content can be avoided, and problems of reduced adhesion between inorganic materials due to low binder polymer content, resulting in poor peel resistance of the inorganic composite porous layer, can be avoided.

[0058] The binder polymer includes a first binder polymer and a second binder polymer. Preferably, the binder polymer may consist essentially of the first binder polymer and the second binder polymer. Here, the term "substantially" means that although trace amounts of impurities or other components are unavoidably contained in the manufacturing process, the amount of these impurities or other components does not significantly affect the objectives of the present invention.

[0059] The first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher. Specifically, the first binder polymer may be an amorphous polymer having a glass transition temperature (Tg) of 180°C to 350°C. For example, the amorphous binder polymer may be, but is not limited to, polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyphenylsulfone (PPSU), polyethersulfone (PES), polysulfone (PSU), or a mixture of two or more thereof. Specifically, the glass transition temperatures of the amorphous binder polymers are approximately 250 to 340°C for polyimide, approximately 280 to 290°C for polyamideimide, approximately 217°C for polyetherimide, approximately 222°C for polyphenylsulfone, approximately 230°C for polyethersulfone, and approximately 185°C for polysulfone.

[0060] The second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP). Preferably, the second binder polymer is a polyvinylidene fluoride copolymer consisting essentially of the first repeating unit and the second repeating unit.

[0061] The content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer. Specifically, it can be 4 to 15 wt %. If the content of the second repeating unit is less than the above range, the solubility in the solvent is low, making it difficult to control the process, and the phase separation rate is fast, resulting in a decrease in the binding strength within the coating layer. On the other hand, if the content of the second repeating unit is more than the above range, the solubility in the solvent is high, making it difficult to achieve phase separation characteristics. Therefore, it is advantageous for the content of the second repeating unit to satisfy the above range in terms of contributing to the adhesive strength with the electrode.

[0062] In the present invention, the weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1, specifically 6:4 to 7:3.

[0063] When the ratio of the weight of the first binder polymer to the weight of the second binder polymer is within the above range, it is more advantageous in terms of adhesive strength and voltage resistance. For example, when the weight of the first binder polymer is outside the above range, heat resistance and voltage resistance may be deteriorated.

[0064] The inorganic composite porous layer may further contain other additives such as a dispersant and a flame retardant as necessary, in addition to the binder resin and inorganic filler as components of the inorganic composite porous layer.

[0065] According to one embodiment of the present invention, the inorganic composite porous layer may further include 3 parts by weight or less of a dispersant based on 100 parts by weight of the inorganic composite porous layer. In this case, the dispersant may be polyvinylpyrrolidone (PVP). The inclusion of the dispersant increases the hydrophilicity of the first binder polymer, contributing to the dispersibility of the inorganic filler. Furthermore, the bonding strength between the inorganic composite porous layer and the polymeric porous support is increased.

[0066] According to one embodiment of the present invention, 1 is a method for manufacturing a separator for an electrochemical device according to an embodiment of the present invention, (S1) preparing a polymeric porous support; (S2) applying a slurry containing a binder polymer, an inorganic filler, and a solvent to at least one surface of the polymeric porous support; (S3) immersing the polymeric porous support coated with the slurry in a composition containing a non-solvent and drying the composition to form an inorganic composite porous layer; the binder polymer includes a first binder polymer and a second binder polymer; The weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), The content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer, and the method for producing the separator for an electrochemical device is provided.

[0067] When applying the inorganic filler to the inorganic composite porous layer, the slurry can be prepared by dissolving the binder polymer in a solvent (which can be a dispersion medium for the inorganic filler), adding the inorganic filler, and dispersing the resulting mixture. Specifically, in the present invention, the slurry can be prepared by dissolving a binder polymer including a first binder polymer and a second binder polymer in an organic solvent, adding the inorganic filler, and dispersing the resulting mixture. In this case, the inorganic filler can be added in a state crushed to an appropriate size, or the inorganic filler can be added to a binder polymer solution and then crushed and dispersed using a ball mill or the like.

[0068] The solvent may have a solubility index similar to that of the binder polymer and a low boiling point. This facilitates uniform mixing and subsequent solvent removal. The solvent may be an organic solvent. Specifically, the solvent may be one or a mixture of two or more selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, methanol, ethanol, and isopropyl alcohol.

[0069] In this case, the solvent may function as a solvent for dissolving the binder polymer or a dispersion medium for dispersing the binder polymer, depending on the type of the binder polymer to be mixed.

[0070] According to one embodiment of the present invention, methods for coating the slurry onto a polymeric porous support include a pre-metering method and a post-metering method. The pre-metering method is a method in which a coating amount is determined in advance and applied, such as slot die coating and gravure coating. The post-metering method is a method in which a sufficient amount of the coating solution, i.e., the slurry, is applied to the polymeric porous support, and then a predetermined amount is scraped out, such as bar coating. Another method is direct-metering coating, which combines the pre-metering and post-metering methods.

[0071] The slurry can be applied by any of the methods described above, and the polymeric porous support to which the slurry has been applied can be immersed in a composition containing a non-solvent to cause phase separation and form an inorganic composite porous layer.

[0072] According to one embodiment of the present invention, the non-solvent may be an aqueous solvent or a mixture of an aqueous solvent and an oil-based solvent. For example, the non-solvent may include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, isopropyl alcohol, or two or more thereof. Specifically, the non-solvent may be a mixture of water and N-methyl-2-pyrrolidone, or a mixture of water and dimethylacetamide.

[0073] An electrochemical device according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the separator is the separator according to the embodiment of the present invention described above.

[0074] The electrode to be used with the separator of the present invention is not particularly limited, and may be prepared by binding an electrode active material to an electrode current collector by a conventional method well known in the art.

[0075] Non-limiting examples of the positive electrode active material among the electrode active materials include common positive electrode active materials used in the positive electrodes of conventional lithium secondary batteries, and particularly preferred are lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide made by combining these.

[0076] Non-limiting examples of the negative electrode active material include conventional negative electrode active materials used in the negative electrodes of conventional lithium secondary batteries, and particularly preferred are lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbon-based lithium-absorbing materials.

[0077] Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or a combination thereof, and non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or a copper alloy, or a combination thereof.

[0078] The electrolyte used in the electrochemical element according to one embodiment of the present invention is + B - and A + Li + , Na + , K. + or a combination thereof, - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a combination thereof, dissolved or dissociated in an organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or a mixture thereof, but is not limited thereto.

[0079] The electrolyte may be injected at an appropriate stage in the battery manufacturing process depending on the manufacturing process and desired physical properties of the final product, i.e., before battery assembly or at the final stage of battery assembly.

[0080] The present invention also provides a battery module including a battery having an electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, power tools driven by 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, electric golf carts, and power storage systems.

[0081] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0082] [Example] Separation membranes of the examples and comparative examples were prepared in the following manner.

[0083] Example 1 Polyetherimide (PEI, weight-average molecular weight: 128,000) and PVDF-HFP (containing 4.4% HFP-derived repeating units, weight-average molecular weight: 744,000) were dissolved in N-methyl-2-pyrrolidone (NMP) as an organic solvent, and Al2O3 nanoparticles with an average particle size of 20 nm were dispersed as an inorganic filler to prepare a slurry. The weight ratio of PEI:PVDF-HFP was 6:4, and the weight ratio of PEI + PVDF-HFP:inorganic particles was 4:6. The solid content of the slurry was 12%.

[0084] The resulting slurry was applied to both sides of a polyethylene porous support (6.5 μm thick, 37% porosity), then placed in a coagulation bath filled with water for the NIPS process and dried. The porosity of the inorganic composite porous layer after drying was 81.4%.

[0085] <Examples 2 to 4, Comparative Examples 1 and 2> Separation membranes were produced in the same manner as in Example 1, except that the composition of the slurry was changed as shown in Table 1 below.

[0086] <Evaluation of separation membrane properties> The physical properties of the separators prepared in the examples and comparative examples were evaluated by the following methods, and the results are shown in Table 1 below.

[0087] [Table 1]

[0088] (1) Measurement of the meltdown temperature A 10 mm long separator membrane was placed in a thermomechanical analysis (TMA) device (TA Instruments, Q400) and subjected to a temperature increase (5°C / min from 30°C) under a tension of 19.6 mN. As the temperature increased, the length of the sample changed, and the temperature at which the length increased rapidly and the sample broke was measured. Measurements were taken in both the machine direction (MD) and transverse direction (TD), and this was defined as the meltdown temperature.

[0089] (2) Measurement of the porosity of inorganic composite porous layers The porosity of the inorganic composite porous layer was measured using the separators prepared in the Examples and Comparative Examples.

[0090] The porosity was measured by measuring the width / length / thickness of the separator to determine the volume, measuring the weight, and calculating the ratio to the weight when the separator occupied 100% of the volume.

[0091] Porosity (%) = {(actual volume) / (compact volume)} / (actual volume) × 100 Compact volume = loading volume / density Actual volume = thickness of the separation membrane

[0092] (3) Evaluation of heat shrinkage rate A 5 cm x 5 cm cut separator membrane was left in a convection oven at 150°C for 30 minutes, and then the length changes in the machine direction and transverse direction were measured.

[0093] Heat shrinkage rate (%) = {(dimension before shrinkage - dimension after shrinkage) / dimension before shrinkage} x 100

[0094] (4) Evaluation of adhesive strength The active material [natural graphite and artificial graphite (weight ratio 5:5)], conductive material [Super P], and binder [polyvinylidene fluoride (PVDF)] were mixed in a weight ratio of 92:2:6, dispersed in water, and then coated onto copper foil to prepare the negative electrode, which was then cut into a size of 25 mm x 70 mm.

[0095] The separators prepared in the examples and comparative examples were cut to a size of 25 mm x 70 mm. The separator and anode were stacked, sandwiched between 100 μm PET films, and bonded using a flat press. The flat press was heated at 60°C and a pressure of 6.5 MPa for 1 second.

[0096] The end of the bonded separator and negative electrode was attached to a Universal Testing System (UTM, manufactured by Instron), and a force was applied at a 180° angle at a measurement speed of 300 mm / min to measure the force required to separate the negative electrode from the separator bonded to the negative electrode.

Claims

1. A separator for an electrochemical element, the separation membrane is composed of only a polymer porous support and an inorganic composite porous layer formed on at least one surface of the porous support; the inorganic composite porous layer contains a binder polymer and an inorganic filler, the binder polymer includes a first binder polymer and a second binder polymer; the weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, and the amorphous polymer includes polyetherimide (PEI); the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), the content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer; The separator for an electrochemical device has a thickness of 10.5 μm to 12 μm.

2. 2. The separator for an electrochemical device according to claim 1, wherein a weight ratio of the first binder polymer to the second binder polymer is 6:4 to 7:

3.

3. 2. The separator for an electrochemical device according to claim 1, wherein the content of the second repeating unit is 4 to 15 wt % based on the total weight of the polyvinylidene fluoride copolymer.

4. 2. The separator for an electrochemical device according to claim 1, wherein the inorganic composite porous layer has a porosity of 70% or more.

5. 2. The separator for an electrochemical device according to claim 1, wherein the inorganic filler is a primary particle having an average particle size of 20 nm to 700 nm.

6. The inorganic filler is alumina (Al ２ O ３ ), fumed alumina, aluminum hydroxide (Al(OH) ３ ), magnesium hydroxide (Mg(OH) ２ 2. The separator for an electrochemical device according to claim 1, comprising: SiO2 (SiO2), boehmite (AlOOH), or two or more thereof.

7. 2. The separator for an electrochemical device according to claim 1, wherein the inorganic composite porous layer further comprises 3 parts by weight or less of a dispersant based on 100 parts by weight of the inorganic composite porous layer.

8. 8. The separator for an electrochemical element according to claim 7, wherein the dispersant is polyvinylpyrrolidone (PVP).

9. An electrochemical device comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrochemical element, wherein the separator is the separator for electrochemical elements according to claim 1 .

10. 10. The electrochemical device according to claim 9, wherein the electrochemical device is a lithium secondary battery.

11. A method for producing the separator for an electrochemical element according to claim 1, (S1) preparing a polymeric porous support; (S2) applying a slurry containing a binder polymer, an inorganic filler, and a solvent to at least one surface of the polymeric porous support; (S3) immersing the polymeric porous support coated with the slurry in a composition containing a non-solvent and drying the composition to form an inorganic composite porous layer; the binder polymer includes a first binder polymer and a second binder polymer; the weight ratio of the first binder polymer to the second binder polymer is 6:4 to 9:1; the first binder polymer is an amorphous polymer having a glass transition temperature (Tg) of 180°C or higher, and the amorphous polymer includes polyetherimide (PEI); the second binder polymer is a polyvinylidene fluoride copolymer containing a first repeating unit derived from vinylidene fluoride (VDF) and a second repeating unit derived from hexafluoropropylene (HFP), the content of the second repeating unit is 4 to 40 wt % based on the total weight of the polyvinylidene fluoride copolymer; The method for producing a separator for an electrochemical device, wherein the separator has a thickness of 10.5 μm to 12 μm.

12. The method for producing a separator for an electrochemical device according to claim 11 , wherein the solvent is an organic solvent.

13. 12. The method for producing a separator for an electrochemical element according to claim 11, wherein the non-solvent comprises water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, isopropyl alcohol, or two or more thereof.

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