Low moisture absorption coated separator and method for manufacturing same

Abstract

One aspect of the present invention provides a coated separator and a method for manufacturing same, the coated separator comprising: a porous support; and a heat-resistant layer coated on at least one surface of the porous support, wherein the heat-resistant layer includes inorganic particles and a binder, the binder comprises a hydrophilic binder and a hydrophobic binder, the hydrophobic binder is a copolymer comprising a hydrophilic unit and a hydrophobic unit, and the content of the hydrophobic binder in the binder is 25-80 wt%.

Description

Low moisture absorption coating membrane and method for manufacturing the same

[0001] The present invention relates to a low-moisture absorption coated separation membrane and a method for manufacturing the same, and more specifically, to a separation membrane comprising a coating layer capable of imparting low moisture absorption to the separation membrane and a method for manufacturing the same.

[0002] Lithium-ion batteries are widely used as power sources for various electric products requiring miniaturization and lightweight design, such as smartphones, laptops, and tablet PCs. As their application fields expand to include medium and large-sized batteries for smart grids and electric vehicles, there is a demand for the development of lithium-ion batteries with high capacity, long lifespan, and high stability.

[0003] As a means to achieve the above objective, research and development is actively being conducted on separators with formed micropores that separate the anode and cathode to prevent internal short circuits and facilitate the movement of lithium ions during the charging and discharging process; in particular, microporous separators using polyolefins such as polyethylene, which are advantageous for pore formation via thermally induced phase separation, are economical, and easily satisfy the physical properties required for separators.

[0004] However, separators made of polyethylene, which has a low melting point of about 135°C, may undergo shrinkage deformation at high temperatures above the melting point due to heat generation in the battery. If a short circuit occurs due to such deformation, it can cause thermal runaway in the battery, leading to safety issues such as ignition.

[0005] Meanwhile, polyolefin-based separators, which are widely used in the past, have poor heat resistance and mechanical strength, so when exposed to a temperature of 150°C for about 1 hour, a thermal shrinkage rate of 50 to 90% occurs, causing the separator to lose its function, and there is a problem that there is a high possibility of internal short circuits occurring upon external impact.

[0006] To address these issues, a technology has been proposed to coat the surface of a separator with a heat-resistant layer containing ceramic particles and a binder. Ceramic particles can provide heat resistance to the separator, and within the heat-resistant layer, they can be mutually bound by a binder, which in turn fixes and binds the ceramic particles to the surface of the separator. However, this heat-resistant layer leaves significant technical challenges regarding air permeability and conductivity (resistance), which are factors that critically affect the performance of the separator.

[0007] When a heat-resistant layer containing ceramic particles and a binder is formed on the surface of a porous support (or porous substrate), the ceramic particles and binder contained in the heat-resistant layer close the pores formed in the porous support, thereby reducing the air permeability and ion conductivity of the separator. Consequently, the ion transport pathway between the anode and the cathode is significantly reduced, resulting in a problem where the charging and discharging performance of the battery is greatly degraded. In particular, this problem tends to worsen as the relative content of the binder increases.

[0008] Meanwhile, coating compositions for forming such a heat-resistant layer are classified into water-based slurries and non-water-based (oil-based) slurries depending on the properties of the solvent included therein. The water-based slurry has low bonding strength with the porous support, making it easy for the heat-resistant layer to detach, and foreign substances such as dust may be generated during slitting.

[0009] In addition, the above-mentioned aqueous slurry and the heat-resistant layer formed therefrom are inherently hydrophilic and thus absorb moisture from the surrounding atmosphere. The moisture absorbed by the heat-resistant layer can cause various degradations in physical properties, such as a decrease in the adhesion strength of the heat-resistant layer, an increase in resistance, and a decrease in dielectric breakdown voltage, which becomes a direct factor in reducing the electrochemical performance and lifespan of the battery. Although methods such as separate processes, reinforced packaging, or forming a separate moisture barrier layer on the surface of the heat-resistant layer have been proposed to reduce or remove moisture absorbed by the separator, these methods result in reduced productivity and economic efficiency. In particular, forming a separate moisture barrier layer not only reduces air permeability and electrochemical performance but also runs counter to the trend of thinning separators and consequently integrating batteries.

[0010] The present invention aims to solve the problems of the aforementioned prior art. The objective of the present invention is to provide a coating separator capable of maintaining heat resistance while effectively suppressing a decrease in binding strength, an increase in resistance, and a decrease in dielectric breakdown voltage due to moisture absorption, as well as a method for manufacturing the same.

[0011] One aspect of the present invention provides a coating separation membrane comprising a porous support and a heat-resistant layer coated on at least one surface of the porous support, wherein the heat-resistant layer comprises inorganic particles and a binder, wherein the binder comprises a hydrophilic binder and a hydrophobic binder, wherein the hydrophobic binder is a copolymer comprising a hydrophilic unit and a hydrophobic unit, and the content of the hydrophobic binder among the binders is 25 to 80 weight percent.

[0012] In one embodiment, the content of the hydrophobic binder in the heat-resistant layer may be 1.5 to 3.5 weight percent.

[0013] In one embodiment, the inorganic particle may include one selected from the group consisting of SiO2, AlO(OH), Mg(OH)2, Al(OH)3, TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, Li2CO3, CaCO3, LiAlO2, Al2O3, SiO, SnO, SnO2, PbO2, ZnO, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and combinations of two or more of these.

[0014] In one embodiment, the hydrophilic unit may include one selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl alcohol, poly(ethylene glycol) methacrylate, N,N-dimethylacrylamide, sodium acrylate, sodium methacrylate, vinyl sulfone, propylene glycol methacrylate, 2-hydroxypropyl methacrylate, 2-methacryloyloxyethylphosphorylcholine, vinylpyrrolidone, itaconic acid, N-vinylcaprolactam, N,N-dimethylaminoethyl methacrylate, N-isopropylacrylamide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, and combinations of two or more of these.

[0015] In one embodiment, the hydrophobic unit comprises styrene, polystyrene, methyl methacrylate, butyl acrylate, hexyl acrylate, octyl acrylate, isobornyl acrylate, dodecyl methacrylate, isopropyl acrylate, lauryl methacrylate, tetrahydrofuran acrylate, ethyl methacrylate, trimethylsilyl methacrylate, 2-ethylhexyl methacrylate, methoxytrimethylsilyl methacrylate, isobornyl acrylate, cyclohexyl methacrylate, benzyl methacrylate, propyl methacrylate, phenyl methacrylate, isotrimethoxysilyl methacrylate, triethoxysilylpropyl acrylate, methoxysilylpropyl methacrylate, phenyltrimethoxysilane, hexamethyldisiloxane, pentamethyldisiloxane, vinyltrimethoxysilane, vinyltriethoxysilane, trimethoxysilylethyl methacrylate, It may include polydimethylsiloxane methacrylate and one selected from the group consisting of a combination of two or more of these.

[0016] In one embodiment, the moisture content of the coating separator may be 850 ppm or less.

[0017] In one embodiment, the bonding strength between the porous support and the heat-resistant layer may be 80gf / 15mm or more.

[0018] In one embodiment, the resistance of the coating separator may be 0.7Ω or less, and the dielectric breakdown voltage may be 1.85kV or more.

[0019] In one embodiment, the longitudinal (MD) thermal shrinkage rate of the coating separator at 150°C may be 10% or less, and the transverse (TD) thermal shrinkage rate may be 10% or less.

[0020] Another aspect of the present invention provides a method for manufacturing a coating separation membrane comprising: (a) a step of preparing a slurry by mixing an aqueous solvent, inorganic particles, and a binder; and (b) a step of forming a heat-resistant layer by applying the slurry to at least one surface of a porous support and then drying it, wherein the content of the solid component including the inorganic particles and the binder in the slurry is 10 to 50 weight percent.

[0021] A coating separator according to one aspect of the present invention comprises a porous support and a heat-resistant layer coated on at least one surface of the porous support, wherein the heat-resistant layer comprises inorganic particles and a binder, wherein the binder comprises a hydrophilic binder and a hydrophobic binder, and wherein the hydrophobic binder is a copolymer comprising a hydrophilic unit and a hydrophobic unit, and by controlling the content of the hydrophobic binder among the binders to 25 to 80 weight percent, the heat resistance of the coating separator can be maintained, while effectively suppressing a decrease in binding strength, an increase in resistance, and a decrease in dielectric breakdown voltage due to moisture absorption.

[0022] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

[0023] Figure 1 is a scanning electron microscope (SEM) image of the heat-resistant layer of a separator according to an embodiment and a comparative example of the present invention.

[0024] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0025] Throughout the specification, when it is stated that a part is "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0026] One aspect of the present invention provides a coating separation membrane comprising a porous support and a heat-resistant layer coated on at least one surface of the porous support, wherein the heat-resistant layer comprises inorganic particles and a binder, wherein the binder comprises a hydrophilic binder and a hydrophobic binder, wherein the hydrophobic binder is a copolymer comprising a hydrophilic unit and a hydrophobic unit, and the content of the hydrophobic binder among the binders is 25 to 80 weight percent.

[0027] The porous support may include a plurality of pores with substantially uniform average size, and these pores may contribute to improving the resistance characteristics and ion conductivity of the separator. In addition, the separator can be made into a thin film of the required thickness due to its high porosity and high mechanical strength.

[0028] The porous support described above can be configured such that a plurality of pores formed internally have a substantially uniform distribution in terms of average size. This structural uniformity can improve the electrochemical properties of the entire separator by ensuring consistency in the paths through which ions pass through the separator. While passing through a non-uniformly distributed pore structure may result in localized resistance or inefficient formation of conduction paths, the porous support effectively suppresses these problems and is advantageous for reducing the internal resistance of the battery. In particular, when the pores are arranged at regular intervals and shapes, the movement paths of ions are formed predictably and continuously, thereby improving the diffusion rate of ions and consequently improving charge and discharge efficiency.

[0029] The above-described porous support can be designed to maintain excellent mechanical properties while ensuring high porosity as an overall structure, not merely in terms of the number or average size of pores. Generally, material strength tends to decrease as porosity increases; however, the above-described porous support can sufficiently possess mechanical properties, such as tensile strength and puncture strength, through the uniform dispersion of the polymer matrix and the securing of appropriate crystallinity. As a result, the separator is not easily damaged by physical pressure or external impact during the battery assembly process and can maintain a stable structure even in high-temperature environments.

[0030] A porous support possessing both mechanical stability and electrochemical functionality plays an important role in the thinning of separators. By maintaining a thin separator thickness, the ion diffusion distance between electrodes can be shortened, which in turn leads to an improvement in the energy density of the battery. However, as the separator becomes thinner, concerns arise regarding issues such as reduced strength and the occurrence of pinholes; therefore, the performance of a support that maintains mechanical strength within the separator is essential. The porous support provides a foundation to structurally overcome these problems, enabling the thinning of the separator while simultaneously contributing to the advancement of miniaturization and high-integration technologies for the entire battery.

[0031] The porosity of the porous support may be 30 to 90%, preferably 30 to 80%, and more preferably 30 to 70%. As used herein, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume in any porous article. If the porosity of the porous support is less than 30%, air permeability and ion conductivity may be reduced, and if it exceeds 90%, mechanical properties such as tensile strength and puncture strength may be reduced.

[0032] As described above, a porous support designed to maintain a porosity within an appropriate range can ensure a balance between the electrochemical performance and physical stability of the separator. In particular, a structure with a porosity of 30% or more enables smooth diffusion of ions and penetration of electrolytes, thereby improving the ion conductivity of the separator. Furthermore, a continuous pore network formed within the porous structure transmits the flow of ions generated during charging and discharging without resistance, which can contribute to reducing internal battery resistance and improving energy efficiency. On the other hand, if the porosity of the porous support exceeds 90%, the structural integrity is weakened as the pore density within the polymer matrix increases excessively, which may lead to a deterioration in mechanical properties such as tensile strength and puncture strength. Consequently, the separator becomes vulnerable to external physical forces and is susceptible to damage from mechanical stress or thermal expansion that may occur during battery assembly. In particular, if the separator is perforated or torn due to external impact or minute protrusions of internal electrodes, a short circuit may occur between the anode and cathode, potentially causing serious safety issues for the battery. Therefore, the porosity of the above-mentioned porous support needs to be set within a range that does not impair mechanical stability.

[0033] By setting the porous support to a porosity range of 30 to 70%, the above porous support can simultaneously ensure air permeability and ion conductivity, as well as structural durability such as tensile strength and puncture strength. This is advantageous for high-density battery designs requiring thin film separators and can provide sufficient mechanical support even under thin film conditions.

[0034] The average size of the pores included in the porous support may be 20 to 100 nm, preferably 20 to 80 nm, more preferably 30 to 60 nm. If the average size of the pores is less than 20 nm, air permeability and ion conductivity may be reduced, and if it is greater than 100 nm, mechanical properties such as tensile strength and puncture strength may be reduced.

[0035] By controlling the average size of the pores contained in the porous support to the range described above, the separator can maintain overall structural stability while sufficiently securing a free pathway for ion movement. In particular, if the average pore size is 20 nm or larger, the electrolyte can rapidly penetrate into the support to ensure uniform wettability, and ion movement also occurs efficiently without physical barriers. This has a positive effect on improving the initial operating characteristics and output responsiveness of the battery, and can provide performance differentiated from conventional porous structures with poor electrolyte permeability. Furthermore, it is advantageous for suppressing ion concentration gradients and the resulting increase in resistance that may occur during battery operation. On the other hand, if the average pore size exceeds 100 nm, problems may arise with the mechanical integrity of the porous support. Excessively large pores can cause stress concentration within the polymer matrix, posing a risk of easy tearing or damage due to external pressure or thermal expansion. In particular, in thin-film separators, localized vulnerabilities affect overall structural reliability, and durability may be degraded by repeated expansion and contraction cycles that occur during battery use.

[0036] In addition, even if the pores have the same average size, if the pore distribution is widely spread, some areas may have pores that are too small to impede air permeability, or conversely, become too large to weaken strength. The porous support can not only control the average pore size to a preset range but also ensure process stability to narrow the pore distribution width and form a uniform pore structure across the entire area. As a result, the electrolyte is uniformly distributed, enabling stable operation without local overcurrent or concentration deviation at the interface with the electrode, and the performance of the separator can be stably maintained even in high-speed charging and discharging environments.

[0037] The thickness of the porous support may be 1 to 20 μm, preferably 5 to 15 μm, more preferably 5 to 12 μm, in terms of thinning and increasing energy density of the electrochemical device. If the thickness of the porous support is less than 1 μm, mechanical properties may be degraded, and if it exceeds 20 μm, air permeability and ion conductivity may be degraded.

[0038] By adjusting the thickness of the porous support to a preset range, physical stability can be secured while meeting the requirements for miniaturization and high integration of the battery. In particular, a thickness of 5 to 12 μm minimizes the distance between electrodes, thereby simultaneously achieving a reduction in ion diffusion distance and a reduction in internal resistance. Furthermore, as the thickness is reduced, the volume occupied by the separator in the overall cell configuration decreases, thereby securing structural margin to increase the filling rate of the electrode material.

[0039] However, if the thickness becomes less than 1㎛, the porous support may fail to withstand mechanical loads or tensions generated during the manufacturing process. In particular, as the separator becomes thinner, mechanical properties such as tensile strength and puncture strength deteriorate rapidly. This can lead to frequent film damage during the battery assembly stage or cause durability degradation issues during long-term use. Additionally, a non-uniform thickness distribution can cause resistance variations between individual cells of the battery, raising concerns that it may lead to reduced yield and performance reliability in large-area or multi-layer structures. Conversely, if the thickness of the porous support exceeds 20㎛, the ion conductivity and power transfer efficiency of the battery may decrease as the ion migration distance within the separator increases. This induces polarization under high current densities and impairs the operating voltage stability of the battery, which can lead to performance degradation, especially in high-output batteries. Furthermore, a thick separator can delay electrolyte penetration, causing an increase in initial activation time and a decrease in low-temperature performance.

[0040] The porous support may include a polymer resin having electrical insulation properties, and the polymer resin may include a thermoplastic resin considering shutdown characteristics. The term "shutdown characteristic" as used herein means that when a battery overheats and its temperature rises, the polymer resin melts and closes the pores of the porous support, thereby blocking the movement of ions. In this regard, the melting point of the polymer resin or the thermoplastic resin may be 200°C or lower.

[0041] The above thermoplastic resin may include, for example, one selected from the group consisting of polyethylene, polypropylene, polypentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more of these, preferably may include at least one of polyethylene and polypropylene, and more preferably may include polyethylene.

[0042] The above polyethylene may be one selected from the group consisting of ultra-high molecular weight polyethylene (UHMWPE, Mv: 1,000,000–7,000,000 g / mol), high molecular weight polyethylene (HMWPE, Mv: 100,000–1,000,000 g / mol), high-density polyethylene (HDPE, Mv: 100,000–1,000,000 g / mol), low-density polyethylene (LDPE, Mv: 10,000–100,000 g / mol), homogeneous linear and linear low-density polyethylene (LLDPE), and combinations of two or more of these. Here, the viscosity-average molecular weight (Mv) is an average molecular weight calculated based on the viscosity of the polymer solution and can be determined experimentally using the Mark-Houwink equation.

[0043] For example, the polyethylene may be high-density polyethylene with a viscosity-average molecular weight (Mv) of 250,000 to 800,000 g / mol. If the viscosity-average molecular weight of the polyethylene exceeds 800,000 g / mol, the viscosity increases and processability may decrease, and if it is less than 250,000 g / mol, the viscosity becomes excessively low, which drastically reduces dispersibility with pore-forming agents, antioxidants, etc. used when manufacturing porous supports, and in some cases, phase separation or layer separation may occur.

[0044] The above porous support may be a so-called cross-linked porous support having a structure in which at least a portion of the polyethylene is cross-linked by a cross-linking compound. For example, the above cross-linked porous support may include a continuous phase matrix containing polyethylene and silane-modified polyethylene that is cross-linked within the continuous phase matrix and supports the continuous phase matrix. The above silane-modified polyethylene may mean that alkoxyvinylsilane is grafted into the polyethylene chain, and the alkoxyvinylsilane grafted into the polyethylene chain may react with moisture under predetermined conditions to cross-link the polyethylene chains. Since the above cross-linked porous support has a higher meltdown temperature compared to an uncross-linked porous support, the heat resistance of the separator may be significantly improved; however, since the tensile properties of the above porous support may deteriorate due to cross-linking, the content of the silane-modified polyolefin in the above porous support may be controlled to 0.1 to 50 weight%, preferably 0.1 to 30 weight%.

[0045] The above inorganic particles may include one selected from the group consisting of SiO2, AlO(OH), Mg(OH)2, Al(OH)3, TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, Li2CO3, CaCO3, LiAlO2, Al2O3, SiO, SnO, SnO2, PbO2, ZnO, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and combinations of two or more of these, and preferably may include boehmite (AlO(OH)), but is not limited thereto.

[0046] The content of the inorganic particles in the heat-resistant layer may be 50 to 99 weight percent. If the content of the inorganic particles in the heat-resistant layer is less than 50 weight percent, the required level of heat resistance cannot be provided, and if it exceeds 99 weight percent, the dispersibility of the inorganic particles may be reduced, or workability and processability may be reduced.

[0047] The average particle size (D50) of the inorganic particles may be larger than the average size of the pores contained in the porous film. If the average particle size of the inorganic particles is less than or equal to the average size of the pores contained in the porous support, the inorganic particles may penetrate into the interior of the pores of the porous support and close the pores, thereby significantly reducing the air permeability and ion conductivity of the separation membrane. The average particle size of the inorganic particles may be 100 to 1,000 nm, preferably 200 to 800 nm, more preferably 400 to 800 nm, but is not limited thereto.

[0048] The thickness of the heat-resistant layer may be 0.1 to 5 μm. If the thickness of the heat-resistant layer is less than 0.1 μm, it may not be possible to provide the required level of heat resistance, and if it exceeds 5 μm, the separator may become thick, which may hinder the miniaturization and integration of the battery.

[0049] The binder may melt and fuse in the heat-resistant layer to not only bind the inorganic particles together but also bind the inorganic particles to the porous support. The binder may include a hydrophilic binder and a hydrophobic binder, and the hydrophobic binder may be a copolymer comprising a hydrophilic unit and a hydrophobic unit. As used herein, the term "unit" refers to a monomer, oligomer, or polymer constituting the copolymer.

[0050] The hydrophilic unit ensures that the inorganic particles and the binder are uniformly dispersed in the slurry for forming the heat-resistant layer, and the hydrophobic unit can effectively suppress the absorption of moisture from the surrounding atmosphere by the heat-resistant layer in an undried and / or dried state.

[0051] The binder plays a crucial role in simultaneously ensuring the structural stability and environmental durability of the heat-resistant layer. Beyond being a simple binder, the binder acts as a medium to not only bind the inorganic particles together but also to ensure they are stably attached to the surface of the porous support, thereby enhancing the mechanical integrity of the heat-resistant layer. When the binder undergoes a melting and fusion process in the heat-resistant layer, it fills the gaps between the inorganic particles while simultaneously forming a structurally integrated network, which can suppress delamination or cracking. This ensures that the heat-resistant layer remains robust even under mechanical stress or thermal cycling during the battery assembly process.

[0052] The above binder may include both a hydrophilic binder and a hydrophobic binder, and each of these performs a mutually complementary function depending on the characteristics before and after the formation of the heat-resistant layer. During the slurry preparation and application steps, the hydrophilic binder acts to contribute to the uniform dispersion of the inorganic particles and the entire composition and the maintenance of stable viscosity, and after drying, the hydrophobic binder performs a moisture barrier function, thereby ensuring the long-term stability of the heat-resistant layer.

[0053] In particular, the above-mentioned hydrophobic binder is configured in the form of a copolymer, and this copolymer may have a structure containing both hydrophilic and hydrophobic units. Such an amphiphilic copolymer can simultaneously provide dispersion stability in an aqueous slurry and a moisture barrier function after drying within a single molecule, thereby allowing for a multifunctional effect to be expected within a single composition. As a result, moisture resistance and workability can be simultaneously satisfied without the need for a separate moisture barrier or additives.

[0054] The hydrophilic unit is effective in preventing the aggregation of binders and inorganic particles within the aqueous slurry and maintaining the dispersibility and viscosity stability of the slurry. This forms the basis for forming a uniform film thickness during the coating process and ensuring uniformity of physical properties throughout the heat-resistant layer. As the stability of the slurry increases, uncoated areas or film cracks are reduced, and consequently, the yield and quality of the coated separation membrane are improved. Furthermore, such hydrophilic characteristics also act favorably in controlling the interfacial energy between the solid and the solvent, which can contribute slightly to the wettability and adhesion of the porous support.

[0055] On the other hand, the hydrophobic unit serves to effectively block the penetration of external moisture after the heat-resistant layer is dried. This unit is distributed within the polymer chains and inhibits moisture adsorption by lowering the surface free energy, thereby preventing the degradation of electrical properties and mechanical weakening of the heat-resistant layer caused by moisture absorption. In particular, the electrical insulation and binding strength of the heat-resistant layer can be stably maintained even in high-temperature and high-humidity environments or during long-term storage, thus contributing to ensuring the durability and stability of the battery.

[0056] These amphiphilic copolymer-based binders can contribute to improving the long-term stability of the interfacial bonding strength between the heat-resistant layer and the porous support, going beyond simple improvement of physical properties. If the bonding strength is not maintained, the heat-resistant layer may peel off or fine gaps may form due to heat, vibration, shock, etc., which can negatively affect the lifespan and safety of the battery, but the binder can structurally prevent these problems.

[0057] Furthermore, the binder can maintain a flexible molecular structure even in a solid state or exhibit sufficient mechanical flexibility below the glass transition temperature, thereby providing appropriate processability and adaptability for thin-film or multi-layer designs of the heat-resistant layer. As a result, precise coating is possible on surfaces of supports of various shapes, and stable physical properties can be exhibited without a decrease in durability even in a thin-film state.

[0058] Furthermore, the hydrophobic unit can also contribute to preventing unnecessary interactions with the electrolyte component as well as moisture in the external atmosphere. Since the chemical stability as well as the electrical properties of the separator may deteriorate if the binder reacts with the electrolyte or swells unevenly, the chemical inertness and chemical resistance of the binder are important for maintaining actual performance. By providing stability against such external influences, the hydrophobic binder can maintain the reliability of the separator even in high-temperature and high-voltage environments.

[0059] The binder is designed to exhibit excellent compatibility and interfacial bonding with various inorganic particles, thereby significantly improving the freedom of composition selection and process application flexibility of the heat-resistant layer. Based on responsiveness to various conditions such as slurry viscosity control, coating thickness control, and drying speed adjustment, a stable separation membrane can be manufactured without quality variation even under mass production conditions.

[0060] The above hydrophilic unit may include one selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl alcohol, poly(ethylene glycol) methacrylate, N,N-dimethylacrylamide, sodium acrylate, sodium methacrylate, vinyl sulfone, propylene glycol methacrylate, 2-hydroxypropyl methacrylate, 2-methacryloyloxyethylphosphorylcholine, vinylpyrrolidone, itaconic acid, N-vinylcaprolactam, N,N-dimethylaminoethyl methacrylate, N-isopropylacrylamide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, and combinations of two or more of these.

[0061] The above hydrophobic unit is styrene, polystyrene, methyl methacrylate, butyl acrylate, hexyl acrylate, octyl acrylate, isobornyl acrylate, dodecyl methacrylate, isopropyl acrylate, lauryl methacrylate, tetrahydrofuran acrylate, ethyl methacrylate, trimethylsilyl methacrylate, 2-ethylhexyl methacrylate, methoxytrimethylsilyl methacrylate, isobornyl acrylate, cyclohexyl methacrylate, benzyl methacrylate, propyl methacrylate, phenyl methacrylate, isotrimethoxysilyl methacrylate, triethoxysilylpropyl acrylate, methoxysilylpropyl methacrylate, phenyltrimethoxysilane, hexamethyldisiloxane, pentamethyldisiloxane, vinyltrimethoxysilane, vinyltriethoxysilane, trimethoxysilylethyl methacrylate, polydimethylsiloxane It may include methacrylate and one selected from the group consisting of a combination of two or more of these.

[0062] The above hydrophobic unit may be an aromatic monomer, an oligomer or polymer containing it. When the above hydrophobic unit comprises at least one aromatic monomer, the hydrophobic binder is, for example, a styrene-acrylic acid copolymer, a phenyl methacrylate-hydroxyethyl methacrylate copolymer, a benzyl methacrylate-acrylic acid copolymer, a styrene-hydroxyethyl acrylate copolymer, a phenyl methacrylate-acrylamide copolymer, a benzyl acrylate-acrylic acid copolymer, a styrene-N,N-dimethylacrylamide copolymer, a phenyl methacrylate-sodium methacrylate copolymer, a benzyl methacrylate-hydroxyethyl methacrylate copolymer, a styrene-methacrylic acid copolymer, a phenyl methacrylate-sodium acrylate copolymer, a benzyl acrylate-N,N-dimethylacrylamide copolymer, a styrene-poly(ethylene glycol) methacrylate copolymer, and a phenyl It may be one selected from the group consisting of acrylate-hydroxyethyl methacrylate copolymer, benzyl methacrylate-sodium acrylate copolymer, styrene-acrylamide copolymer, phenyl methacrylate-hydroxypropyl methacrylate copolymer, benzyl acrylate-methacrylic acid copolymer, styrene-hydroxyethyl methacrylate copolymer, phenyl acrylate-acrylic acid copolymer, and combinations of two or more of these, and preferably may be a styrene-acrylic acid copolymer, but is not limited thereto.

[0063] In addition, the hydrophobic unit may be a silicon-based monomer, an oligomer or polymer containing the same. When the above hydrophobic unit comprises at least one silicone-based monomer, the hydrophobic binder is a polydimethylsiloxane-acrylic acid copolymer, a trimethoxysilylpropyl methacrylate-hydroxyethyl acrylate copolymer, a methoxysilylpropyl methacrylate-acrylamide copolymer, a polydimethylsiloxane-methacrylic acid copolymer, a pentamethyldisiloxane-acrylic acid copolymer, a triethoxysilylpropyl acrylate-hydroxyethyl methacrylate copolymer, a methoxysilylpropyl acrylate-acrylic acid copolymer, a hexamethyldisiloxane-acrylamide copolymer, a polydimethylsiloxane-methacrylamide copolymer, a trimethoxysilylpropyl acrylate-acrylic acid copolymer, a vinyltrimethoxysilane-hydroxyethyl acrylate copolymer, a hexamethylsiloxane-acrylamide copolymer, It may be one selected from the group consisting of pentamethyldisiloxane-hydroxyethyl methacrylate copolymer, dimethylsiloxane-methacrylic acid copolymer, vinyltriethoxysilane-acrylic acid copolymer, polydimethylsiloxane-acrylamide copolymer, trimethoxysilylethyl methacrylate-acrylic acid copolymer, pentamethyldisiloxane-acrylic acid copolymer, dimethoxysilylpropyl methacrylate-hydroxyethyl acrylate copolymer, triethoxysilylethyl acrylate-methacrylamide copolymer, and combinations of two or more of these, and preferably may be polydimethylsiloxane-acrylic acid copolymer, but is not limited thereto.

[0064] The content of the hydrophobic binder in the above binder may be 25-80 wt%, 30-70 wt%, 40-70 wt%, 50-70 wt%, or 60-70 wt%. If the content of the hydrophobic binder in the above binder is less than 25 wt%, it is difficult to suppress moisture absorption by the separator, and consequently, various physical properties such as a decrease in the binding strength of the heat-resistant layer, an increase in resistance, and a decrease in dielectric breakdown voltage may be caused. If the content of the hydrophobic binder in the above binder exceeds 80 wt%, the content of the hydrophilic binder is relatively reduced, which may result in a decrease in the dispersibility of the inorganic particles or a decrease in workability and processability, causing uncoated areas to occur, and such uncoated areas may have an adverse effect on the heat resistance of the separator.

[0065] Setting the content of the hydrophobic binder among the binders to a range of 25 to 80 weight percent is intended to simultaneously ensure moisture stability of the heat-resistant layer and efficiency of the manufacturing process. By effectively suppressing moisture adsorption of the heat-resistant layer, the hydrophobic binder prevents a decrease in binding strength and insulation properties even in high temperature and / or high humidity environments, thereby ensuring long-term stability of the battery. In particular, when the content of the hydrophobic binder is secured above a certain level, the heat-resistant layer does not react sensitively to contact with moisture in the ambient air, so the physical properties of the heat-resistant layer can be stably maintained even during long-term storage after production or under high temperature conditions. On the other hand, if the content of the hydrophobic binder becomes excessively high, the proportion of the hydrophilic binder decreases relatively, which reduces the dispersibility of inorganic particles in the slurry and may make it difficult to ensure uniformity of coating. Specifically, if the hydrophobic binder is excessive, compatibility with the water-based slurry is reduced, which may lead to deterioration in workability and uneven coating, and as a result, there is a high possibility that partially uncoated areas will be formed in the heat-resistant layer. These uncoated areas impair thermal insulation and insulation functions in high-temperature environments during battery operation, and consequently, may act as a factor that reduces the thermal stability of the separator.

[0066] The content of the hydrophobic binder in the heat-resistant layer may be 1.5 to 3.5 wt%, 2 to 3.5 wt%, or 2.5 to 3.5 wt%. If the content of the hydrophobic binder in the heat-resistant layer is less than 1.5 wt%, it is difficult to suppress moisture absorption by the separator, and consequently, various physical properties such as a decrease in the binding strength of the heat-resistant layer, an increase in resistance, and a decrease in dielectric breakdown voltage may be degraded. If the content of the hydrophobic binder in the heat-resistant layer exceeds 3.5 wt%, the content of the hydrophilic binder is relatively reduced, which may result in a decrease in the dispersibility of the inorganic particles or a decrease in workability and processability, causing uncoated areas to occur, and such uncoated areas may adversely affect the heat resistance of the separator.

[0067] By controlling the content of the hydrophobic binder in the heat-resistant layer to a range of 1.5 to 3.5 weight percent, moisture absorption can be effectively suppressed while simultaneously maintaining the dispersion stability and processing characteristics of the slurry composition. The hydrophobic binder serves to prevent problems such as a decrease in dielectric breakdown voltage and weakening of bonding strength caused by moisture ingress by blocking external moisture penetration into the heat-resistant layer. However, if the content is lowered to less than 1.5 weight percent, the moisture barrier function is not sufficiently exerted throughout the heat-resistant layer, which may accelerate the deterioration of the heat-resistant layer's performance in high-humidity environments or during long-term storage. Conversely, if the content of the hydrophobic binder in the heat-resistant layer exceeds 3.5 weight percent, the dispersion stability of inorganic particles in the slurry may decrease as the proportion of hydrophilic binder within the binder decreases. This leads to viscosity non-uniformity, particle sedimentation, and aggregation during the coating process, increasing the possibility of uncoated areas within the heat-resistant layer and consequently causing coating non-uniformity and a decrease in heat resistance. In particular, since maintaining the workability and processability of the slurry is important for ensuring the continuity and productivity of the membrane manufacturing process, the content of the hydrophobic binder in the heat-resistant layer must be optimized from the perspective of balancing moisture barrier performance and process stability.

[0068] The moisture content of the above-mentioned coating separator may be 850 ppm or less, 800 ppm or less, 750 ppm or less, 700 ppm or less, 650 ppm or less, or 600 ppm or less. If the moisture content of the above-mentioned coating separator exceeds 850 ppm, it may cause various degradations in physical properties, such as a decrease in the bonding strength of the heat-resistant layer, an increase in resistance, and a decrease in dielectric breakdown voltage. The lower limit of the moisture content of the above-mentioned coating separator is not particularly limited, but preferably, it may be 10 ppm or more, 50 ppm or more, or 100 ppm or more.

[0069] If the heat-resistant layer absorbs moisture, the dielectric constant of the heat-resistant layer increases, which may lead to a decrease in dielectric breakdown voltage or induce electrical leakage. Furthermore, moisture is associated with a decrease in the binding strength of the binder, which can weaken the interfacial bonding strength between the heat-resistant layer and the porous support and cause delamination. Such degradation of physical properties can lead to reduced safety during high-temperature operation of the battery; in particular, in high-energy density or high-output cell structures, even minute changes in moisture can significantly affect performance and stability.

[0070] Meanwhile, although there is no specific lower limit for the moisture content of the coating separator, if it is excessively low, shrinkage stress may occur rapidly during the curing process of the binder, or interfacial bonding with inorganic particles may be formed non-uniformly. Accordingly, minimal residual moisture can have a positive effect on the physical dispersion of the binder or stress relief within the heat-resistant layer, and in actual manufacturing processes, a moisture content of 10 to 100 ppm or more can generally be maintained. As such, moisture content is not merely a target for removal, but can act as a precise variable that simultaneously controls the structural stability and electrical properties of the heat-resistant layer.

[0071] The bonding strength of the porous support and the heat-resistant layer may be 80gf / 15mm or more, 90gf / 15mm or more, 100gf / 15mm or more, 110gf / 15mm or more, 120gf / 15mm or more, or 130gf / 15mm or more. The upper limit of the bonding strength of the porous support and the heat-resistant layer is not particularly limited, but preferably may be 300gf / 15mm or less, or 200gf / 15mm or less.

[0072] If the bonding strength between the porous support and the heat-resistant layer is 80 gf / 15 mm or higher, the heat-resistant layer does not detach from the porous support even under heat, mechanical stress, or repeated charge-discharge cycles, thereby ensuring the durability and stability of the battery. Meanwhile, although there is no specific upper limit for this bonding strength, if the bonding strength is excessively high, surface damage to the separator or reduced processability may occur during subsequent processes such as slitting, lamination, and lamination. Furthermore, if the binder content becomes excessively high and the bonding strength becomes excessively strong, it may compromise the flexibility of the heat-resistant layer and increase the possibility of cracks occurring due to stress concentration. Therefore, it is important to set an appropriate range for the bonding strength from the perspective of balancing durability and processability.

[0073] The resistance of the coating separator may be 0.7Ω or less, 0.6Ω or less, 0.55Ω or less, or 0.5Ω or less. If the resistance of the coating separator exceeds 0.7Ω, the ion conductivity, air permeability, and the electrochemical performance of the battery accordingly may be degraded. The lower limit of the resistance of the coating separator is not particularly limited, but preferably may be 0.1Ω or more, or 0.2Ω or more. In addition, the dielectric breakdown voltage of the coating separator may be 1.85kV or more, 1.9kV or more, 1.95kV or more, 2.0kV or more, 2.1kV or more, or 2.2kV or more. When the dielectric breakdown voltage of the coating separator is 1.85kV or more, the low voltage failure rate of the battery can be reduced even if the heat-resistant layer is made into a thin film, and heat resistance at high temperatures and high capacity / high output characteristics can be improved. The upper limit of the dielectric breakdown voltage of the above-mentioned coating separator is not specifically limited, but may be 3.0 kV or less.

[0074] The dielectric breakdown voltage mentioned above is an indicator used to determine whether the separator can function as a stable insulating layer within the battery, and it is related to the electrical reliability of the coated separator. By setting the dielectric breakdown voltage of the coated separator to 1.85 kV or higher, the risk of internal short circuits that may occur during high-voltage charging can be effectively prevented, and the low-voltage failure rate of the battery cell can be reduced. In particular, since electric field concentration is more likely to occur as the thickness of the separator decreases, securing the dielectric breakdown voltage becomes a more critical factor in battery technology where thinning of the separator is carried out in parallel. Furthermore, a higher dielectric breakdown voltage improves the high-temperature heat resistance and high-output operation stability of the battery. This allows for the structural overcoming of problems where the insulation performance of the heat-resistant layer may deteriorate due to changes in the dielectric constant of the electrolyte or softening of the binder in high-temperature environments, and can contribute to reducing the risk of thermal runaway in industrial energy storage systems (ESS) and electric vehicle batteries that operate for long periods. In particular, when the dielectric breakdown voltage of the coating separator is 2.0 kV or higher, the heat-resistant layer can maintain a continuous insulating state without physical damage even with changes in the external environment, thereby ensuring stable operation even during repeated charge and discharge cycles.

[0075] Furthermore, the above-described coating separator has a structure that minimizes the thickness of the heat-resistant layer while increasing the dielectric breakdown voltage. Conventionally, methods of increasing the thickness of the heat-resistant layer were mainly used to secure insulation performance, but this resulted in the entire separator becoming thick, causing problems such as reduced ion conductivity and reduced energy density. On the other hand, according to one embodiment of the present invention, by controlling the composition of inorganic particles and binder, sufficient insulation resistance can be maintained with a thin heat-resistant layer of 5㎛ or less, preferably 3㎛ or less, more preferably 2㎛ or less, while securing high insulation characteristics, thereby providing advantages favorable for high-density cell design and miniaturization of batteries due to thin film formation.

[0076] Meanwhile, although the upper limit of the dielectric breakdown voltage of the above-mentioned coating separator is not specifically restricted, it is generally desirable to manage it within a range of 3.0 kV or less in terms of ensuring manufacturing efficiency and product reliability. If the dielectric breakdown voltage becomes excessively high, the dispersibility of the slurry may be reduced due to an imbalance in the composition of the binder or inorganic particles, or the mechanical flexibility may decrease as the separator becomes rigid. In addition, since higher insulation performance than necessary can lead to adverse effects such as increased manufacturing costs or reduced processability, it is important to secure the dielectric breakdown voltage at an appropriate level by considering the balance between heat resistance, insulation, and processability.

[0077] The longitudinal (MD) thermal shrinkage rate of the above-mentioned coating separator at 150°C may be 10% or less, 8% or less, or 6% or less, and the transverse (TD) thermal shrinkage rate may be 10% or less, 8% or less, or 6% or less. The lower limit of the longitudinal (MD) thermal shrinkage rate and transverse (TD) thermal shrinkage rate of the above-mentioned coating separator is not particularly limited, but preferably may be 0.1% or more.

[0078] Another aspect of the present invention provides a method for manufacturing a coating separation membrane comprising: (a) a step of preparing a slurry by mixing an aqueous solvent, inorganic particles, and a binder; and (b) a step of forming a heat-resistant layer by applying the slurry to at least one surface of a porous support and then drying it, wherein the content of the solid component including the inorganic particles and the binder in the slurry is 10 to 50 weight percent.

[0079] The above-mentioned aqueous solvent may be, for example, one selected from the group consisting of methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, distilled water, and combinations of two or more of these, and preferably may be water, but is not limited thereto. The types, properties, content, effects, etc. of the above-mentioned inorganic particles and the above-mentioned binder are as described above.

[0080] The application of the above slurry may be carried out by one selected from the group consisting of a roll coater, a bar coater, a spray coater, a die coater, a comma coater, and a combination of two or more of these, and preferably by a roll coater and / or a bar coater, but is not limited thereto.

[0081] The content of the solid component including the inorganic particles and the binder in the above slurry may be 10 to 50 weight%, preferably 15 to 45 weight%, and more preferably 20 to 40 weight%. If the content of the solid component in the above slurry is less than 10 weight%, uncoated areas may occur, and such uncoated areas may adversely affect the heat resistance of the separator membrane, and if it exceeds 50 weight%, the dispersibility of the slurry may be reduced, or workability and processability may be reduced.

[0082] The inorganic particles tend to bind and aggregate due to electrostatic attraction. Such aggregation of inorganic particles can impair the uniformity of physical properties on the surface of the separation membrane. Accordingly, the slurry may further include additives to improve the dispersibility of the inorganic particles, such as dispersants and surfactants. In particular, the slurry may include sodium hexametaphosphate ((NaPO3)6) as a dispersant, and the content of sodium hexametaphosphate in the heat-resistant layer may be 0.01 to 1 weight%, preferably 0.01 to 0.5 weight%. The sodium hexametaphosphate is adsorbed onto the edges of the inorganic particles, particularly plate-shaped inorganic particles, and weakens the negative charge on the edges, thereby effectively preventing the aggregation of the inorganic particles. This can improve the storage stability of the slurry for forming the heat-resistant layer and the dispersibility of the inorganic particles within the heat-resistant layer.

[0083] In step (b) above, a heat-resistant layer may be formed by applying the slurry to at least one surface of the porous support and then drying it. The drying refers to a process of applying heat to the slurry applied to at least one surface of the porous support to remove the aqueous solvent and other liquid residues contained in the slurry.

[0084] The heat-resistant layer may be formed on one side of the porous support, and if necessary, may be formed on both sides. The heat-resistant layers formed on both sides of the porous support may have the same thickness, composition, and effect, and in some cases, at least one of these may differ.

[0085] Meanwhile, before applying the slurry to at least one surface of the porous support in step (b) above, the porous support may be plasma treated in the presence of a mixed gas containing sulfur dioxide (SO2) and oxygen (O2).

[0086] By hydrophilizing the surface of the porous support and / or the surface of the internal pores through the above plasma treatment, the bonding strength between both sides of the porous support and the slurry can be improved, and accordingly, the durability of the separation membrane, in particular, long-term durability and heat resistance can be significantly improved.

[0087] Conventionally, a wet process in which the surface of a porous support is immersed in sulfuric acid or the like for a certain period of time to sulfonate it has been mainly used to hydrophilize the surface of the porous support. However, in this case, the wet process is performed separately from the plasma treatment, such as preceding or succeeding the plasma treatment, which makes the process complex and causes a problem of generating a large amount of process waste liquid.

[0088] In this regard, the process gas used in the above plasma treatment includes not only conventional air, oxygen, and / or inert gas but also a certain amount of sulfur dioxide gas. Therefore, functional groups such as -SO3 are generated on the surface of the porous support and the surface of the internal pores through a single dry process called plasma treatment without a wet process such as immersing the porous support in sulfuric acid, i.e., sulfonation, thereby maximizing the hydrophilicity and ion conductivity of the porous support, simplifying the complex conventional process, and is also advantageous in terms of the environment.

[0089] The mixed gas, which is the process gas used in the above plasma treatment, may contain 50 to 90 volume% sulfur dioxide and 10 to 50 volume% oxygen, preferably 60 to 80 volume% sulfur dioxide and 20 to 40 volume% oxygen, more preferably 70 to 80 volume% sulfur dioxide and 20 to 30 volume% oxygen. If the content of sulfur dioxide in the mixed gas is less than 50 volume%, the required level of hydrophilicity for the porous support cannot be achieved, and if it exceeds 90 volume%, the process may become unstable.

[0090] The above plasma treatment can be performed for 0.5 to 90 minutes, preferably 0.5 to 20 minutes. If the above plasma treatment is performed for less than 0.5 minutes, the porous support cannot be hydrophilized and sulfonated to the required level, and if it is performed for more than 90 minutes, the degree of hydrophilization and sulfonation may converge to a certain level, which may reduce process efficiency.

[0091] Hereinafter, embodiments of the present invention will be described in detail.

[0092] Examples and Comparative Examples

[0093] Acrylonitrile copolymer (A), styrene-acrylic acid copolymer (B1), polydimethylsiloxane-acrylic acid copolymer (B2), boehmite (AlO(OH)), dispersant ((NaPO3)6), surfactant, and water were quantified and mixed as shown in Tables 1 to 4 below, and then dispersed using a ball mill to prepare a coating slurry.

[0094] A coating separator was prepared by applying the coating slurry to both sides of a polyethylene porous support (porous film) with a thickness of 9 μm using a bar coater, and then drying it in a hot air oven at a temperature of 80°C for 1 hour to produce a coating separator having a heat-resistant layer with a thickness of 1.5 μm on each side.

[0095] Classification Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5 Water (g) 800 800 800 800 800 Inorganic (g) 190 190 190 190 190 Dispersant (g) 11 1 11 Binder (A) (g) 32 45 6 Binder (B1) (g) 67 54 3 Surfactant (g) 11 1 11 Solid content (g) 20 20 20 20 20 Content of B1 in solids (weight%) 3.0 3.5 2.5 2.0 1.5 Content of B1 in binder (weight%) 66.7 7.8 5.6 4.4 3.3

[0096]

[0097] Classification Comparative Example 1-1 Comparative Example 1-2 Comparative Example 1-3 Comparative Example 1-4 Water (g) 800 800 800 800 Inorganic (g) 190 190 190 190 Dispersant (g) 11 11 Binder (A) (g) 1790 Binder (B1) (g) 8209 Surfactant (g) 11 11 Solid Content (g) 20 20 20 20 B1 Content in Solids (Weight%) 4.0 1.0 0.0 4.5 B1 Content in Binder (Weight%) 88.9 22.2 0.0 100.0

[0098]

[0099] Classification Example 2-1 Example 2-2 Example 2-3 Example 2-4 Example 2-5 Water (g) 800 800 800 800 800 Inorganic material (g) 190 190 190 190 190 Dispersant (g) 11 1 11 Binder (A) (g) 32 45 6 Binder (B2) (g) 67 54 3 Surfactant (g) 11 1 11 Solid content (g) 20 20 20 20 20 B2 content in solids (weight%) 3.0 3.5 2.5 2.0 1.5 B2 content in binder (weight%) 66.7 7.8 5.6 4.4 3.3

[0100]

[0101] Classification Comparative Example 2-1 Comparative Example 2-2 Comparative Example 2-3 Water (g) 800 800 800 Inorganic (g) 190 190 190 Dispersant (g) 111 Binder (A) (g) 170 Binder (B2) (g) 820.9 Surfactant (g) 111 Solid Content (g) 20 20 20 B2 Content in Solids (Weight%) 4.0 1.0 4.5 B2 Content in Binder (Weight%) 88.9 22.2 100.0

[0102]

[0103] Experimental Example

[0104] The physical properties of the coated separators prepared in the examples and comparative examples were measured and evaluated according to the following methods, and the results are shown in Tables 5 to 8 below.

[0105] - Coating performance: The surface of the coated separator specimen was observed using a scanning electron microscope (SEM), and the maximum major axis of the uncoated area where the heat-resistant layer was not formed was evaluated as "High" if it was less than 1 µm, "Medium" if it was 1 to 5 µm, and "Low" if it was greater than 5 µm.

[0106] - Bonding strength (gf / 15mm): After cutting the coated separator to a length of 180mm and a width of 15mm, tape was attached to the surface of the coated separator, and then the interface between the heat-resistant layer and the porous support was peeled at a tensile speed of 0.3m / min using a Shimazu UTM to measure the bonding strength, and the average value of 5 measurements was calculated.

[0107] -Resistance (Ω): A coin cell was manufactured by inserting a coated separator between 1mm thick SUS electrodes. The resistance of the coated separator inserted in the coin cell was measured using EIS (Electrochemical Impedance Spectroscopy) at a frequency of 10 4 ~10 6 The average value was calculated from 5 measurements under conditions of Hz, current 10.0mV, voltage range ±10V, and temperature 25℃.

[0108] - Dielectric breakdown voltage (kV): The voltage (kV) was evaluated as the leakage current value measured at 5mA when the coated separator was placed between the electrodes of a dielectric strength tester (Croma Model 19052) in a dry room (dew point temperature: -60℃) and the applied voltage was increased to 5kV / 10sec.

[0109] - Moisture content (ppm): After cutting the coating membrane to a size of 50 mm x 40 mm, it was left in a dry room for 24 hours, and then measured using a Karl Fischer moisture meter inside the dry room.

[0110] - Thermal shrinkage rate (%): A coated separator specimen with dimensions of 200×200 mm was placed between A4 papers and left in an oven at 150°C for 1 hour, then cooled to room temperature. The shrinkage lengths in the longitudinal (MD) and transverse (TD) directions of the specimen were measured, and the thermal shrinkage rate was calculated using the following formula.

[0111] Thermal shrinkage rate (%) = (13-14) / 13× 100

[0112] In the above formula, l3 is the longitudinal or transverse length of the coated separator specimen before shrinkage, and l4 is the longitudinal or transverse length of the coated separator specimen after shrinkage.

[0113]

[0114] Classification Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5 Coating Properties Adhesion Strength 136 12 195 8983 Resistance 0.49 10.47 80.53 40.55 20.651 Dielectric Breakdown Voltage 1.94 61.96 51.94 21.92 81.885 Moisture Content 62 161 169 874 77 59MD Thermal Shrinkage 273 45TD Thermal Shrinkage 385 66

[0115]

[0116] Classification Comparative Example 1-1 Comparative Example 1-2 Comparative Example 1-3 Comparative Example 1-4 Coating Properties Upper / Lower Adhesion Strength 1 2 9 6 4 6 2 1 10 Resistance 0.5 0 6 0.6 9 5 0.7 7 2 0.5 19 Dielectric Breakdown Voltage 1.9 8 5 1.8 3 5 1.8 2 2 2.0 11 Moisture Content 6 0 2 8 1 3 9 0 0 5 8 9 MD Thermal Shrinkage Rate 1 7 5 2 5 5 TD Thermal Shrinkage Rate 2 0 7 4 6 7

[0117]

[0118] Classification Example 2-1 Example 2-2 Example 2-3 Example 2-4 Example 2-5 Coating Properties Adhesion Strength 1 2 2 1 4 5 1 0 3 8 9 8 6 Resistance 0.4 4 9 0.4 1 3 0.4 9 7 0.5 8 1 0.6 5 9 Dielectric Breakdown Voltage 2.2 2 7 2.3 4 8 2.1 1 6 2.0 2 8 2.0 1 2 Moisture Content 7 1 1 6 3 2 7 2 1 7 8 8 8 4 5 MD Thermal Shrinkage 3 8 5 6 TD Thermal Shrinkage 5 9 6 8 7

[0119]

[0120] Classification Comparative Example 2-1 Comparative Example 2-2 Comparative Example 2-3 Coating Properties Load Bonding Strength 13 27 4 1 1 4 Resistance 0.4 2 5 0.7 1 5 0.4 5 8 Dielectric Breakdown Voltage 2.3 7 1 1.8 4 8 2.4 1 5 Moisture Content 5 7 2 8 6 4 5 1 5 MD Thermal Shrinkage 2 7 6 5 9 TD Thermal Shrinkage 3 3 9 7 5

[0121]

[0122] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0123] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. A porous support and a heat-resistant layer coated on at least one surface of the porous support, and The above heat-resistant layer comprises inorganic particles and a binder, and The above binder includes a hydrophilic binder and a hydrophobic binder, and The above hydrophobic binder is a copolymer comprising hydrophilic units and hydrophobic units, and The content of the hydrophobic binder among the above binders is 25 to 80 weight percent, Coating separator.

2. In Paragraph 1, The content of the hydrophobic binder in the heat-resistant layer is 1.5 to 3.5 weight percent, Coating separator.

3. In Paragraph 1, The above inorganic particles comprise one selected from the group consisting of SiO2, AlO(OH), Mg(OH)2, Al(OH)3, TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, Li2CO3, CaCO3, LiAlO2, Al2O3, SiO, SnO, SnO2, PbO2, ZnO, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and combinations of two or more of these. Coating separator.

4. In Paragraph 1, The above hydrophilic unit comprises one selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl alcohol, poly(ethylene glycol) methacrylate, N,N-dimethylacrylamide, sodium acrylate, sodium methacrylate, vinyl sulfone, propylene glycol methacrylate, 2-hydroxypropyl methacrylate, 2-methacryloyloxyethylphosphorylcholine, vinylpyrrolidone, itaconic acid, N-vinylcaprolactam, N,N-dimethylaminoethyl methacrylate, N-isopropylacrylamide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, and combinations of two or more of these. Coating separator.

5. In Paragraph 1, The above hydrophobic unit is styrene, polystyrene, methyl methacrylate, butyl acrylate, hexyl acrylate, octyl acrylate, isobornyl acrylate, dodecyl methacrylate, isopropyl acrylate, lauryl methacrylate, tetrahydrofuran acrylate, ethyl methacrylate, trimethylsilyl methacrylate, 2-ethylhexyl methacrylate, methoxytrimethylsilyl methacrylate, isobornyl acrylate, cyclohexyl methacrylate, benzyl methacrylate, propyl methacrylate, phenyl methacrylate, isotrimethoxysilyl methacrylate, triethoxysilylpropyl acrylate, methoxysilylpropyl methacrylate, phenyltrimethoxysilane, hexamethyldisiloxane, pentamethyldisiloxane, vinyltrimethoxysilane, vinyltriethoxysilane, trimethoxysilylethyl methacrylate, polydimethylsiloxane Serving with methacrylate and one selected from the group consisting of combinations of two or more of these, Coating separator.

6. In Paragraph 1, The moisture content of the above-mentioned coating separator is 850 ppm or less, Coating separator.

7. In Paragraph 6, The bonding strength of the porous support and the heat-resistant layer is 80gf / 15mm or more, Coating separator.

8. In Paragraph 6, The resistance of the above-mentioned coating separator is 0.7Ω or less, and the dielectric breakdown voltage is 1.85kV or more, Coating separator.

9. In Paragraph 6, The longitudinal (MD) thermal shrinkage rate of the above-mentioned coating separator at 150°C is 10% or less, and the transverse (TD) thermal shrinkage rate is 10% or less, Coating separator.

10. A method for manufacturing a coating separator according to any one of claims 1 to 9, (a) a step of preparing a slurry by mixing an aqueous solvent, inorganic particles, and a binder; and (b) a step of forming a heat-resistant layer by applying the slurry to at least one surface of a porous support and then drying it; comprising, The content of the solid component including the inorganic particles and the binder in the above slurry is 10 to 50 weight percent, Method for manufacturing a coating separator.

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