Separator and method for manufacturing the same

Abstract

One aspect of the present invention provides a separator and a method for manufacturing the same, comprising a porous substrate, an electrode adhesive layer provided on one surface of the porous substrate and containing first inorganic particles and a first binder for binding at least a portion of the first inorganic particles together, and a heat-resistant layer provided on the other surface of the porous substrate and containing second inorganic particles and a second binder for binding at least a portion of the second inorganic particles together, wherein the content of the first binder in the electrode adhesive layer is 3 to 20% by weight.

Description

Technical Field

[0001] The present invention relates to a separator and a method for manufacturing the same.

Background Art

[0002] Lithium secondary batteries are widely used as power sources for various electrical products that require miniaturization and weight reduction, such as smartphones, notebook computers, and tablet PCs. With the expansion of their application fields from smart grids to medium and large-sized batteries for electric vehicles, the development of lithium secondary batteries with large capacity, long life, and high stability is required.

[0003] As a means to achieve the above object, a separator with fine pores formed to separate the positive electrode and the negative electrode to prevent internal short circuit and to smoothly move lithium ions in the charge and discharge process. Among them, research and development on a fine porous separator using polyolefin such as polyethylene, which is suitable for forming pores by thermally induced phase separation, is economical, and easily satisfies the physical properties required for the separator, is actively carried out.

[0004] Conventionally, widely used polyolefin-based separators have poor heat resistance and mechanical strength. When exposed at a temperature of 150°C for about one hour, the thermal shrinkage rate is 50 to 90%, resulting in the loss of the function as a separator, and there is a high risk of internal short circuit occurring during an external impact. To compensate for such problems, a technique of coating a heat-resistant layer containing ceramic particles on the surface of the separator has been proposed.

[0005] However, such heat-resistant layers present many technical challenges regarding permeability and conductivity (resistance), which are crucial factors affecting the performance of the separator. Specifically, while forming a heat-resistant layer containing ceramic particles on the surface of a porous substrate improves the heat resistance of the separator, the ceramic particles in the heat-resistant layer clog the pores formed in the porous substrate, reducing the permeability of the separator. Consequently, the ion transfer pathway between the positive and negative electrodes is greatly reduced, resulting in a significant decrease in the charging and discharging performance of the secondary battery. Furthermore, continuous exposure of the heat-resistant layer to the electrolyte inside the battery can cause the ceramic particles to partially and continuously detach from the porous substrate, which can gradually reduce the heat resistance of the separator.

[0006] On the other hand, attempts have been made to improve the adhesion to electrodes and the resulting lifespan characteristics of secondary batteries by further forming an adhesive layer containing an adhesive substance on a polyolefin-based separator or heat-resistant layer to induce adhesion to the electrodes. However, such adhesive layers have the problem of reducing the permeability and conductivity of the separator, and because at least two coating and drying processes are required to form an adhesive layer on the heat-resistant layer, productivity and economic efficiency are reduced.

[0007] In response to this, methods have been proposed to impart a predetermined adhesive strength to the heat-resistant layer by ensuring that the heat-resistant layer contains a certain amount of adhesive substance, or to coat both sides of the separator asymmetrically with an adhesive layer and a heat-resistant layer, respectively. However, in the former case, the amount of ceramic particles in the heat-resistant layer decreases relatively due to the adhesive substance, resulting in a decrease in heat resistance, thus creating a trade-off between adhesive strength and heat resistance. In the latter case, differences in weight, moisture content, drying speed, etc., between the adhesive layer and the heat-resistant layer cause the separator to curl in the longitudinal (MD) and / or transverse (TD) directions, a phenomenon known as curling, which can lead to assembly defects in the battery. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the problems of the prior art described above, and its objective is to provide a separator and a method for manufacturing the same that can achieve and improve a good balance of electrode adhesion, heat resistance, conductivity, and productivity, while also suppressing the curl phenomenon. [Means for solving the problem]

[0009] One aspect of the present invention provides a separator comprising a porous substrate, an electrode adhesive layer provided on one surface of the porous substrate and containing first inorganic particles and a first binder for binding at least a portion of the first inorganic particles together, and a heat-resistant layer provided on the other surface of the porous substrate and containing second inorganic particles and a second binder for binding at least a portion of the second inorganic particles together, wherein the content of the first binder in the electrode adhesive layer is 3 to 20% by weight.

[0010] In one embodiment, the porous substrate may include polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and one selected from the group consisting of two or more combinations or copolymers thereof.

[0011] In one embodiment, the average particle size of the first and second inorganic particles may be 100 to 500 nm, respectively.

[0012] In one embodiment, the first and second inorganic particles may each 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 two or more combinations thereof.

[0013] In one embodiment, the first binder is organic particles containing a water-insoluble polymer, and the second binder may contain a water-soluble polymer.

[0014] In one embodiment, the average particle size of the organic particles may be greater than or equal to the average particle size of the first and second inorganic particles.

[0015] In one embodiment, the average particle size of the organic particles may be 500 to 1,000 nm.

[0016] In one embodiment, the curl height of the separator is 1.5 cm or less, and the curl height may be measured by a method including the following steps (1) and (2).

[0017] (1) A separator having a length (vertical direction, MD) and width (horizontal direction, TD) of 300 mm each is placed on a horizontal reference plane, with the electrode adhesive layer facing the horizontal reference plane; and (2) After 2 hours under conditions of a temperature of 21°C and a humidity of -10°C or lower, the height at which both ends of the separator in the vertical direction (MD) and both ends in the horizontal direction (TD) are separated vertically from the horizontal reference plane is measured and the average value is calculated.

[0018] In one embodiment, the separator can satisfy at least one of the following conditions (i) to (iv).

[0019] (i) Electrode adhesion strength of 5 gf / 25 mm or more, (ii) Resistance of 0.700 Ω or less, (iii) Longitudinal heat shrinkage rate of 4.0% or less at 150°C, and (iv) Transverse heat shrinkage rate of 4.0% or less at 150°C.

[0020] Another aspect of the present invention provides a method for manufacturing a separator, comprising the steps of (a) manufacturing a first coating slurry comprising first inorganic particles and a first binder for binding at least a portion of the first inorganic particles together; (b) manufacturing a second coating slurry comprising second inorganic particles and a second binder for binding at least a portion of the second inorganic particles together; (c) applying the first coating slurry to one surface of a porous substrate and then drying it to form an electrode adhesive layer; and (d) applying the second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer, wherein the content of the first binder in the solid content of the first coating slurry is 3 to 20% by weight, and steps (c) and (d) are performed simultaneously. [Effects of the Invention]

[0021] A separator according to one aspect of the present invention includes a porous substrate, an electrode adhesive layer provided on one surface of the porous substrate and containing first inorganic particles and a first binder that binds at least a portion of the first inorganic particles together, and a heat-resistant layer provided on the other surface of the porous substrate and containing second inorganic particles and a second binder that binds at least a portion of the second inorganic particles together. By adjusting the content of the first binder in the electrode adhesive layer to 3 to 20% by weight, it is possible to achieve and improve a good balance of electrode adhesion, heat resistance, and conductivity, and to effectively suppress the curl phenomenon.

[0022] A method for manufacturing a separator according to another aspect of the present invention can improve the productivity of a double-sided asymmetric coating separator by simultaneously performing the steps of applying a first coating slurry to one surface of the porous substrate and drying it to form an electrode adhesive layer, and applying a second coating slurry to the other surface of the porous substrate and drying it to form a heat-resistant layer.

[0023] The effects of the present invention are not limited to the above-described effects, 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.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 schematically shows a method for measuring the curling phenomenon and curling height of a separator according to an embodiment of the present invention. <000--088>

Modes for Carrying Out the Invention

[0025] Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be realized in various different forms, and therefore, is not limited to the embodiments described herein. In addition, in order to clearly describe the present invention in the drawings, parts not related to the description are omitted, and similar reference numerals are given to similar parts throughout the specification.

[0026] Throughout the specification, when a part is described as being "connected" to another part, this includes not only the case where it is "directly connected", but also the case where it is "indirectly connected" through other members in between. Also, when a part is described as "including" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but can further include other components.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0028] One aspect of the present invention provides a separator including a porous substrate, an electrode adhesive layer provided on one surface of the porous substrate and including first inorganic particles and a first binder that binds at least a part of the first inorganic particles to each other, and a heat-resistant layer provided on the other surface of the porous substrate and including second inorganic particles and a second binder that binds at least a part of the second inorganic particles to each other, wherein the content of the first binder in the electrode adhesive layer is 3 to 20% by weight.

[0029] The porous substrate may contain a large number of pores with substantially uniform average size, and such pores can contribute to improving the resistance characteristics and ionic conductivity of the separator. Furthermore, because it has high mechanical strength despite its high porosity, the separator can be made into a thin film of the required thickness.

[0030] The porosity of the porous substrate may be 30 to 90 volume%, preferably 40 to 80 volume%, and more preferably 40 to 70 volume%. As used herein, "porosity" means the ratio of the volume occupied by pores to the total volume in any porous article. If the porosity of the porous substrate is less than 30 volume%, the air permeability and ionic conductivity may decrease, and if it exceeds 90 volume%, mechanical properties such as tensile strength and puncture strength may decrease.

[0031] The average size of the pores in the porous substrate may be 10 to 100 nm, preferably 20 to 80 nm, and more preferably 30 to 60 nm. If the average size of the pores is less than 10 nm, the air permeability and ionic conductivity may decrease, and if it exceeds 100 nm, mechanical properties such as tensile strength and puncture strength may decrease.

[0032] The thickness of the porous substrate may be 5 to 20 μm, preferably 5 to 15 μm, and more preferably 5 to 12 μm, from the viewpoint of thinning the electrochemical element and increasing its energy density. If the thickness of the porous substrate is less than 5 μm, the mechanical properties may decrease, and if it exceeds 20 μm, the air permeability and ionic conductivity may decrease.

[0033] The porous substrate may contain an electrically insulating polymer resin, and the polymer resin may also contain a thermoplastic resin, taking into consideration the shutdown properties. As used herein, "shutdown properties" means that when the battery overheats and its temperature rises, the polymer resin melts and clogs the pores of the porous substrate, thereby blocking the movement of ions. From this viewpoint, the melting point of the polymer resin or the thermoplastic resin may be 200°C or lower.

[0034] The thermoplastic resin may include, for example, one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and two or more combinations or copolymers thereof. Preferably, it may include at least one of polyethylene and polypropylene, and more preferably, it may include polyethylene, but is not limited thereto.

[0035] The polyethylene may be one selected from the group consisting of ultra-high molecular weight polyethylene (UHMWPE, Mw: 1,000,000 to 7,000,000 g / mol), high molecular weight polyethylene (HMWPE, Mw: 100,000 to 1,000,000 g / mol), high-density polyethylene (HDPE, Mw: 100,000 to 1,000,000 g / mol), low-density polyethylene (LDPE, Mw: 10,000 to 100,000 g / mol), homogeneous linear and linear low-density polyethylene (LLDPE), and two or more combinations thereof. In this specification, the terms "weight-average molecular weight" and "molecular weight distribution" may refer to values ​​measured by gel permeation chromatography (GPC) using polystyrene as a standard sample, according to the methods described in the literature (e.g., Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)).

[0036] For example, the polyethylene has a weight-average molecular weight (M wThe polyethylene may be high-density polyethylene with a weight-average molecular weight of 250,000 to 600,000. If the weight-average molecular weight of the polyethylene exceeds 600,000, the viscosity may increase and processability may decrease. If it is less than 250,000, the viscosity may become excessively low, significantly reducing dispersibility with pore-forming agents, antioxidants, etc., used in the production of porous substrates, and in some cases, phase separation or layer separation may occur.

[0037] The porous substrate is hydrophilized to ensure sufficient wettability of the slurry when coating it with the slurry to form the heat-resistant layer, thereby improving the bonding strength between the porous substrate and the heat-resistant layer. The contact angle of the hydrophilized porous substrate with respect to moisture (H2O) may be 15° or less, and the absolute value of the zeta potential measured as a negative value (-) on the surface of the porous substrate may be 10mV or more, preferably 15mV or more, and more preferably 20mV or more.

[0038] The hydrophilized porous substrate has hydrophilic functional groups, such as -SO3 groups, formed on its surface and the surface of its internal pores, which are hydrophilic. Due to their high affinity with the slurry, which is inherently hydrophilic, the porous substrate can easily bond with the heat-resistant layer, and the bonding strength can be strengthened. As a result, the durability of the separator can be significantly improved, and the loss of hydrophilic groups contained in the porous substrate and / or inorganic particles in the heat-resistant layer can be minimized, thereby improving ionic conductivity and heat resistance.

[0039] The separator may include an electrode adhesive layer provided on one surface of the porous substrate, which includes a first inorganic particle and a first binder that binds the first inorganic particle to each other. The electrode adhesive layer may also include a number of pores formed between the first inorganic particle and / or the first binder, through which fluid and / or ions can pass.

[0040] The content of the first binder in the electrode adhesive layer may be 3 to 20% by weight, preferably 3 to 15% by weight, and relatively, the content of the first inorganic particles may be 80 to 97% by weight, preferably 85 to 97% by weight. If the content of the first binder in the electrode adhesive layer is 3% by weight or less, or if the content of the first inorganic particles exceeds 97% by weight, the electrode adhesive strength may decrease, and if the content of the first binder exceeds 20% by weight, or if the content of the first inorganic particles is less than 80% by weight, not only will the heat resistance decrease, but excessive curling may occur. The curling phenomenon occurs due to differences in weight, moisture content, drying rate, etc., between the electrode adhesive layer and the heat-resistant layer formed on both sides of the porous substrate, i.e., asymmetry. However, if the content of the first inorganic particles is less than 80% by weight, the asymmetry with the content of the second inorganic particles in the heat-resistant layer formed on the opposite side of the electrode adhesive layer becomes more severe, promoting the curling phenomenon and making it more apparent.

[0041] The average particle size of the first inorganic particles may be 100 to 500 nm. The average particle size of the first inorganic particles may be larger than the average size of the pores contained in the porous substrate. If the average particle size of the first inorganic particles is less than or equal to the average size of the pores contained in the porous substrate, the inorganic particles may penetrate into the pores of the porous substrate and close them, thereby significantly reducing the permeability and ionic conductivity of the separator. The average particle size of the first inorganic particles may be 100 to 500 nm, preferably 200 to 400 nm, and more preferably 300 to 400 nm, but is not limited thereto.

[0042] The first inorganic particle may be, for example, one selected from the group consisting of SiO, AlOOH, 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 two or more combinations thereof. Preferably, it may be AlOOH, Mg(OH)2, Al(OH)3, or Al2O3, but is not limited thereto.

[0043] The first binder may be organic particles containing a water-insoluble polymer. As used herein, "water-insoluble polymer" means a polymer that does not dissolve in water and has the property of dispersing and floating in water in the form of fine particles, and is also called latex, emulsion, etc. The water-insoluble polymer may have the form of fine particles as described above in the electrode adhesive layer, and may form and maintain pores together with the first inorganic particles.

[0044] The average particle size of the organic particles may be greater than or equal to the average particle size of the first inorganic particles, and preferably greater than the average particle size of the first inorganic particles. In this case, the average particle size of the organic particles may be 500 to 1,000 nm. If the average particle size of the organic particles is smaller than the average particle size of the first inorganic particles, for example, less than 500 nm, the organic particles may penetrate into the pores of the porous substrate or close the pores formed between the first inorganic particles, significantly reducing the permeability and ionic conductivity of the separator. In particular, if the organic particles close the pores formed between the first inorganic particles, the amount of moisture remaining in the pores of the electrode adhesive layer may decrease, which can exacerbate the asymmetry with the heat-resistant layer in terms of weight, moisture content, drying rate, etc., promoting and further exacerbating the curling phenomenon. Conversely, if the average particle size of the organic particles exceeds 1,000 nm, the surface area of ​​the electrode adhesive layer may decrease, reducing the electrode adhesive strength.

[0045] The water-insoluble polymer may be, but is not limited to, one selected from the group consisting of, for example, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, ethylene vinyl acetate, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, acrylonitrile-styrene copolymer, acrylic rubber, and two or more combinations thereof.

[0046] The separator may include a heat-resistant layer provided on the other side of the porous substrate, which contains a second inorganic particle and a second binder that binds the second inorganic particle together. The heat-resistant layer may also contain a number of pores formed between the second inorganic particles that allow fluids and / or ions to pass through.

[0047] The second inorganic particles may be of the same type and / or quality as the first inorganic particles, and their average particle size may be the same or similar as that of the first inorganic particles. In this case, the type, average particle size, etc., of the second inorganic particles can be determined by referring to what has been stated above regarding the first inorganic particles. On the other hand, the type, properties, morphology, average particle size, etc., of the second inorganic particles may differ from those of the first inorganic particles as necessary.

[0048] The content of the second inorganic particles in the heat-resistant layer may be 60 to 99% by weight. If the content of the second inorganic particles is less than 60% by weight, the desired level of heat resistance cannot be provided, and if it exceeds 99% by weight, the permeability, ionic conductivity, and resistance characteristics of the separator may decrease, the dispersibility of the inorganic particles may decrease, or the workability and processability during slurry coating may decrease.

[0049] The second binder may contain a water-soluble polymer. As used herein, "water-soluble polymer" means a polymer that dissolves in water and is not observed as particles or the like. The water-soluble polymer can not only bind the second inorganic particles together by being melted and fused in the heat-resistant layer, but can also bind the second inorganic particles to the porous substrate.

[0050] The water-soluble polymer may be, but is not limited to, one selected from the group consisting of, for example, polyacrylic acid, polyvinylpyrrolidone, polyvinyl acetate, polyimide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, hydroxyethylcellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, polyvinyl alcohol, polyethylene oxide, polyethylene glycol, acrylonitrile copolymer, and two or more combinations thereof.

[0051] Figure 1 schematically illustrates the curl phenomenon of a separator and a method for measuring the curl height according to one embodiment of the present invention. Referring to Figure 1, the curl height can be measured by a method including the following steps (1) and (2): (1) A separator with a length (vertical direction, MD) and width (horizontal direction, TD) of 300 mm each is placed on a horizontal reference plane, with the electrode adhesive layer facing the horizontal reference plane; and (2) After 2 hours under conditions of a temperature of 21°C and a dew point of -10°C or lower, the height at which both ends of the separator in the vertical direction (MD) and both ends in the horizontal direction (TD) are separated vertically from the horizontal reference plane is measured, and the average value is calculated.

[0052] The curl height of the separator may be 1.5 cm or less, preferably 1.2 cm or less, more preferably 0 to 1.0 cm, and even more preferably 0 to 0.8 cm. If the curl height exceeds 1.5 cm, it may cause defects in the assembly of the battery.

[0053] The separator can satisfy at least one of the following conditions (i) to (iv).

[0054] (i) Electrode adhesion strength of 5 gf / 25 mm or more, preferably 10 to 30 gf / 25 mm, more preferably 15 to 25 gf / 25 mm; (ii) Resistance of 0.700 Ω or less, preferably 0.680 Ω or less, more preferably 0.650 Ω or less; (iii) Longitudinal heat shrinkage rate at 150°C of 4.0% or less, preferably 2.2% or less, more preferably 2.1% or less; and (iv) Transverse heat shrinkage rate at 150°C of 4.0% or less, preferably 1.5% or less, more preferably 1.4% or less.

[0055] Another aspect of the present invention provides a method for manufacturing a separator, comprising the steps of (a) manufacturing a first coating slurry comprising first inorganic particles and a first binder for binding at least a portion of the first inorganic particles together; (b) manufacturing a second coating slurry comprising second inorganic particles and a second binder for binding at least a portion of the second inorganic particles together; (c) applying the first coating slurry to one surface of a porous substrate and then drying it to form an electrode adhesive layer; and (d) applying the second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer, wherein the content of the first binder in the solid content of the first coating slurry is 3 to 20% by weight, and steps (c) and (d) are performed simultaneously.

[0056] In steps (a) and (b) above, the types, properties, forms, and average particle sizes of the first and second inorganic particles and the first and second binders are as described above. The first and second coating slurries may be in which a predetermined solid content is dispersed in a solvent (medium). The solvent may be an oily solvent, an aqueous solvent, or a combination thereof, preferably an aqueous solvent, more preferably water, but is not limited thereto.

[0057] The solid content of the first coating slurry may include the first inorganic particles and the first binder, and the solid content of the second coating slurry may include the second inorganic particles and the second binder. The solid content in the first coating slurry may be 20 to 40% by weight, and the solid content in the second coating slurry may be 10 to 30% by weight, and the first coating slurry may have a higher solid content than the second coating slurry.

[0058] In steps (c) and (d) above, the first and second coating slurries can be simultaneously applied to one and the other surface of the porous substrate, respectively, and then dried to form the electrode adhesive layer on one surface of the porous substrate and the heat-resistant layer on the other surface of the porous substrate. Conventionally, the process of forming the electrode adhesive layer and the heat-resistant layer on one and the other surface of the porous substrate has the problem that it is difficult to improve productivity and economic efficiency because the slurry for forming the electrode adhesive layer is applied and dried, then the slurry for forming the heat-resistant layer is applied and dried, or these steps are reversed and performed continuously or sequentially.

[0059] In response to this, a method has been proposed in which the coating and drying for forming the electrode adhesive layer and the heat-resistant layer are carried out simultaneously on both sides of the porous substrate. However, there are still limitations to improving productivity, such as the need to set different process conditions for both sides due to the differences in composition and properties of the slurry applied to both sides of the porous substrate, i.e., asymmetry.

[0060] The method for manufacturing the separator, by adjusting the composition, properties, and solid content of each slurry during the process of manufacturing the first and second coating slurries, can effectively mitigate the physical properties and / or process asymmetries that may occur in the electrode adhesive layer and the heat-resistant layer, even when the coating and drying processes on both sides of the porous substrate are carried out simultaneously under the same conditions, thereby achieving a good balance of electrode adhesive strength, heat resistance, and conductivity in the manufactured separator.

[0061] The following describes in detail embodiments of the present invention.

[0062] Manufacturing Example 1-1 A first coating slurry was prepared by mixing a solid component containing 85% by weight of boehmite (AlOOH) with an average particle size of 300 nm as inorganic particles and 15% by weight of an acrylic copolymer with an average particle size of 500 nm as an adhesive binder with distilled water in a weight ratio of 30:70 and uniformly dispersing the mixture.

[0063] Manufacturing Examples 1-2 to 1-7 and Comparative Manufacturing Examples 1-1 to 1-2 A first coating slurry was prepared in the same manner as in Production Example 1-1, except that the content of boehmite (AlOOH) and acrylic copolymer in the solid content was changed as shown in Table 1 below.

[0064] Comparative Manufacturing Example 1-3 A first coating slurry was prepared by mixing a solid component containing 85% by weight of boehmite (AlOOH) with an average particle size of 500 nm as inorganic particles and 15% by weight of an acrylic copolymer with an average particle size of 300 nm as an adhesive binder with distilled water in a weight ratio of 30:70 and uniformly dispersing the mixture.

[0065] Manufacturing Example 2-1 A second coating slurry was prepared by mixing a solid component containing 97% by weight of boehmite (AlOOH) with an average particle size of 300 nm as inorganic particles and 3% by weight of acrylonitrile copolymer as an organic binder with distilled water in a weight ratio of 25:75, and uniformly dispersing the mixture.

[0066] [Table 1] (Unit: weight %)

[0067] Example 1 A separator was obtained in which an electrode adhesive layer (derived from the first coating slurry) was formed on one side and a heat-resistant layer (derived from the second coating slurry) was formed on the other side of a 9 μm thick polyethylene porous substrate (air permeability: 90 seconds / 100 ml) simultaneously using a roll-to-roll method to a thickness of 2 μm, and then dried.

[0068] Examples 2-7 and Comparative Examples 1-4 A separator was obtained in the same manner as in Example 1, except that the coating slurry applied to one and the other surfaces of the porous substrate was changed as shown in Table 2 below.

[0069] [Table 2]

[0070] Experimental example The test methods for each physical property measured in this invention are as follows. Unless otherwise specified, measurements were taken at room temperature (25°C). The physical properties of the separators manufactured according to the above examples and comparative examples were measured, and the results are shown in Table 3 below.

[0071] - Electrode adhesion strength (gf / 25mm): After bonding the electrode to the adhesive layer of the separator (180mm in the MD direction x 25mm in the TD direction), it was inserted into an aluminum pouch, and the aluminum pouch was pressed for 30 seconds at 80°C and 1,000 kgf to bond the separator and electrode. Then, the adhesion strength was measured using a Shimadzu UTM while peeling the separator from the electrode.

[0072] -Resistance (Ω): An electrolyte was prepared by dissolving LiPF6 at a concentration of 1.15 molars in a solvent made by mixing ethylene carbonate and ethyl methyl carbonate in a ratio of 30:70 (volume ratio). After impregnating the separator with the electrolyte, a coin cell was fabricated, and the resistance was measured using an EIS (Electrochemical impedance spectroscopy) device.

[0073] - Heat shrinkage rate (%): A separator (200 mm in the MD direction x 200 mm in the TD direction) was placed between sheets of A4 paper and left in an oven at 150°C for 1 hour. After cooling to room temperature, the length of the specimen shrunk in the lateral (TD) and longitudinal (MD) directions was measured, and the heat shrinkage rate was calculated using the following formula.

[0074] Thermal shrinkage rate (%) = (l3 - l4) / l3 × 100

[0075] In the above formula, l3 represents the transverse or longitudinal length of the separator specimen before shrinkage, and l4 represents the transverse or longitudinal length of the separator specimen after shrinkage.

[0076] -Curl height (cm): A separator (300 mm in the MD direction x 300 mm in the TD direction) was placed on a horizontal reference surface with the electrode adhesive layer facing the reference surface and spread out. After 2 hours, the height at which both ends of the separator in the MD direction and both ends in the TD direction were separated from the reference surface by curling was measured (Figure 1), and the average value was calculated as the curl height.

[0077] [Table 3]

[0078] The above-mentioned description of the present invention is illustrative, and a person with ordinary skill in the art to which the invention pertains will understand that it can be readily modified into other specific forms without altering the technical idea or essential features of the invention. Therefore, the above-mentioned embodiments should be understood to be illustrative in all respects and not limiting. For example, each component described in a single form can be implemented in a distributed manner, and similarly, components described as distributed can be implemented in a combined form.

[0079] The scope of the present invention is defined by the claims set forth below, and all modifications or alterations derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention.

Claims

1. Porous substrate and An electrode adhesive layer is provided on one surface of the porous substrate and includes a first inorganic particle and a first binder that binds at least a portion of the first inorganic particle together. A heat-resistant layer is provided on the other side of the porous substrate, and includes a second inorganic particle and a second binder that binds at least a portion of the second inorganic particle together. Includes, A separator wherein the content of the first binder in the electrode adhesive layer is 3 to 20% by weight.

2. The separator according to claim 1, wherein the porous substrate comprises polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and one selected from the group consisting of two or more combinations or copolymers thereof.

3. The separator according to claim 1, wherein the average particle size of the first and second inorganic particles is 100 to 500 nm, each.

4. The first and second inorganic particles are each SiO ２ , AlO(OH), Mg(OH) ２ , Al(OH) ３ , TiO ２ , BaTiO ３ , Li ２ O, LiF, LiOH, Li ３ N, BaO, Na ２ O, Li ２ CO ３ , CaCO ３ , LiAlO ２ , Al ２ O ３ , SiO, SnO, SnO ２ , PbO ２ , ZnO, P ２ O ５ , CuO, MoO, V ２ O ５ , B ２ O ３ , Si ３ N ４ , CeO ２ , Mn ３ O ４ , Sn ２ P ２ O ７ , Sn ２ B ２ O ５ , Sn ２ BPO ６ The separator according to claim 3, comprising one selected from the group consisting of these and combinations of two or more thereof.

5. The first binder is an organic particle containing a water-insoluble polymer, The separator according to claim 3, wherein the second binder comprises a water-soluble polymer.

6. The separator according to claim 5, wherein the average particle size of the organic particles is equal to or greater than the average particle size of the first and second inorganic particles.

7. The separator according to claim 6, wherein the average particle size of the organic particles is 500 to 1,000 nm.

8. The curl height of the separator is 1.5 cm or less. The separator according to claim 1, wherein the curl height is measured by a method comprising the following steps (1) and (2). (1) A separator having a length (vertical direction, MD) and width (horizontal direction, TD) of 300 mm each is placed on a horizontal reference plane, with the electrode adhesive layer facing the horizontal reference plane. (2) After two hours under conditions of a temperature of 21°C and a humidity of -10°C or lower with a dew point, measure the heights at which both ends of the separator in the vertical direction (MD) and both ends in the horizontal direction (TD) are separated vertically from the horizontal reference plane, and calculate the average value.

9. The separator according to claim 8, satisfying at least one of the following conditions (i) to (iv). (i) Electrode adhesion force of 5gf / 25mm or more (ii) Resistance 0.700Ω or less (iii) A thermal shrinkage rate in the vertical direction of 4.0% or less at 150°C, and (iv) Transverse heat shrinkage rate of 4.0% or less at 150°C

10. In the method for manufacturing a separator according to any one of claims 1 to 9, (a) Step of producing a first coating slurry comprising first inorganic particles and a first binder that binds at least a portion of the first inorganic particles together. (b) Step of producing a second coating slurry comprising a second inorganic particle and a second binder that binds at least a portion of the second inorganic particle together. (c) The steps of applying a first coating slurry to one surface of a porous substrate, drying it, and forming an electrode adhesive layer, (d) The process includes the step of applying the second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer, The content of the first binder in the solid content of the first coating slurry is 3 to 20% by weight. A method for manufacturing a separator, wherein steps (c) and (d) are performed simultaneously.

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