Separator for electrochemical device and electrochemical device including the same

Abstract

The separator according to the present invention comprises a separator substrate and an inorganic coating layer disposed on at least one surface of the substrate, and a concave pattern portion having a concave pattern is applied only to an end portion of the outer periphery of the separator substrate. The separator according to the present invention is characterized by having the above-mentioned configuration, and can ensure high binding strength between the separator substrate and the inorganic coating layer and exhibit excellent resistance characteristics. In addition, in an electrochemical device including the separator according to the present invention, when the separator is applied to an electrode assembly, the concave pattern portion at the end portion of the outer periphery of the separator is arranged to overlap with a tab portion of the electrode, thereby preventing lithium plating.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2021-0135328, filed on October 12, 2021, and the entire contents disclosed in the specification and drawings of that application are incorporated herein by reference.

[0002] The present invention relates to a separator for an electrochemical device having excellent bonding strength between a porous polymer substrate and a porous inorganic coating layer and excellent electrical resistance characteristics, and an electrochemical device including the separator. [Background technology]

[0003] Secondary batteries, such as lithium-ion secondary batteries, are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras, video cameras, etc. Recently, these batteries have been applied to a wide range of fields, including automobiles, due to their high energy density.

[0004] Lithium secondary batteries have been gaining attention for their advantages of higher operating voltage and significantly greater energy density than conventional batteries using aqueous electrolytes, such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries. However, lithium-ion batteries have drawbacks, such as safety issues such as fire and explosion due to the use of organic electrolytes, and complicated manufacturing processes. While recent lithium-ion polymer batteries have addressed these weaknesses and are considered one of the next-generation batteries, their battery capacity remains relatively low compared to lithium-ion batteries, particularly insufficient discharge capacity at low temperatures. Therefore, improvements in these areas are urgently needed.

[0005] Evaluating the stability and ensuring the safety of such electrochemical elements is extremely important. Regarding the safety characteristics of electrochemical elements, there is a high concern that an explosion could occur if the electrochemical element overheats, causing thermal runaway, or if the separator is penetrated. In particular, polyolefin-based separator substrates commonly used as separators for electrochemical elements exhibit extremely severe thermal shrinkage at temperatures above 100°C due to the material properties and manufacturing process characteristics, including stretching, which can lead to short circuits between the positive and negative electrodes.

[0006] To address these safety concerns in electrochemical devices, separators have been proposed in which a porous inorganic coating layer is formed by coating at least one surface of a porous separator substrate with a mixture of an excess amount of inorganic particles and a binder polymer. However, to fix the inorganic particles in the inorganic coating layer and to ensure interlayer adhesion between the separator and the electrode, a polymer resin is required as a binder. However, increasing the amount of polymer resin improves the binding strength but reduces the interfacial resistance. Conversely, decreasing the amount of polymer resin causes the inorganic particles to detach, reducing durability and preventing adhesion between the separator and the electrode, resulting in increased resistance. For these reasons, there is currently a strong need for a separator that can ensure both resistance and binding strength. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a separator for an electrochemical device that ensures heat resistance stability and durability and has excellent resistance characteristics, and an electrochemical device including the separator. It should be readily understood that the objects and advantages of the present invention can be achieved by the means or methods, or combinations thereof, set forth in the claims. [Means for solving the problem]

[0008] A first aspect of the present invention relates to a separator for an electrochemical element, comprising a separator substrate and an inorganic coating layer formed on a surface of the separator substrate, wherein the separator substrate has a porous structure and comprises a polymer material, the inorganic coating layer comprises inorganic particles and a binder material, and a recessed pattern portion having a predetermined width extending from an end of the periphery to an inner side is formed on the surface of the separator substrate over an entire section or at least a portion of a peripheral section, and the recessed pattern portion has recesses recessed from the surface.

[0009] A second aspect of the present invention is a separator for electrochemical elements according to the first aspect, wherein the recessed pattern portion has recesses formed inward in the thickness direction from one surface of the separator substrate, and the surface roughness (Ra) is 0.8 to 3.2.

[0010] A third aspect of the present invention is a separator for an electrochemical element according to the first or second aspect, wherein the inorganic coating layer has a concave pattern corresponding to the concave pattern portion at a position corresponding to the concave pattern portion, and the concave pattern portion of the separator substrate and the concave pattern of the inorganic coating layer have a shape in which they are interlocked and engaged with each other.

[0011] A fourth aspect of the present invention is the separator for an electrochemical element according to the third aspect, wherein the separator has a uniform overall thickness and has a shape in which the recessed patterns of the inorganic coating layer and the separator substrate interlock with each other at a boundary where the surfaces of the inorganic coating layer and the separator substrate contact each other.

[0012] A fifth aspect of the present invention is the separator for an electrochemical element according to any one of the first to fourth aspects, wherein the area of ​​the recessed pattern portion is 5% to 40% of the area of ​​the separator substrate (100%).

[0013] A sixth aspect of the present invention is a separator for an electrochemical element according to any one of the first to fifth aspects, wherein the recessed pattern portion has a recess formed inwardly in the thickness direction from one surface of the separator substrate, and the planar area of ​​the recessed portion is 20% to 80% of the total area of ​​the recessed pattern portion.

[0014] A seventh aspect of the present invention is a separator for electrochemical elements according to any one of the first to sixth aspects, wherein the area of ​​the recessed pattern portion is 5% to 40% of the area of ​​the separator substrate (100%), the recessed pattern portion is formed as a recess that is recessed inward in the thickness direction from one surface of the separator substrate, and the plane area of ​​the recessed portion is 20% to 80% of the total area of ​​the recessed pattern portion.

[0015] An eighth aspect of the present invention is a separator for an electrochemical element according to any one of the first to seventh aspects, wherein the separator substrate has a planar area of ​​recesses that is 20% to 80% of the total area of ​​the recessed pattern portion, and the recessed pattern portion has a surface roughness (Ra) of 0.8 to 3.2.

[0016] A ninth aspect of the present invention is the separator for an electrochemical element according to any one of the first to eighth aspects, wherein the separator substrate is a porous sheet containing polyolefin.

[0017] A tenth aspect of the present invention is the separator for an electrochemical element according to any one of the first to ninth aspects, wherein the inorganic particles are selected from the group consisting of BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT,0 <x<1,0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3)O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, and TiO2.

[0018] An eleventh aspect of the present invention relates to an electrode assembly, the electrode assembly including a negative electrode, a separator, and a positive electrode, the separator being as described in any one of the first to tenth aspects, the negative electrode including a current collector, an electrode active material layer formed on at least one surface of the current collector, and a negative electrode tab extending from the current collector and protruding to the outside of the negative electrode, and the negative electrode is laminated such that a recessed pattern portion of the separator overlaps with the negative electrode tab entirely or at least partially.

[0019] A twelfth aspect of the present invention is the electrode assembly according to the eleventh aspect, wherein the negative electrode is stacked such that all or at least a part of an end of the electrode active material layer has an inclined surface, and the inclined surface and all or a part of the recessed pattern portion of the separator overlap with each other. [Effects of the Invention]

[0020] The separator according to the present invention includes a separator substrate and an inorganic coating layer disposed on at least one surface of the substrate, with a recessed pattern portion having a recessed pattern applied only to the outer peripheral end portion of the separator substrate. Due to the above-described configuration, the separator according to the present invention can ensure high bonding strength between the separator substrate and the inorganic coating layer and exhibit excellent resistance characteristics. Furthermore, in an electrochemical device including the separator according to the present invention, when the separator is applied to an electrode assembly, the recessed pattern portion on the outer peripheral end portion of the separator is positioned to overlap the tab portion of the electrode, thereby preventing lithium plating. [Brief explanation of the drawings]

[0021] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention to be given later, serve to further understand the technical concept of the present invention, so the present invention should not be interpreted as being limited to only the matters depicted in such drawings. Meanwhile, the shape, size, scale, ratio, etc. of elements in the drawings included in this specification may be exaggerated to emphasize a clearer description.

[0022] [Figure 1] 1 is a schematic diagram illustrating a cross section of a separator according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating a surface of a separator substrate of a separator according to one embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of a prior art electrode assembly. [Figure 4] 1 is a schematic cross-sectional view of an electrode assembly according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described in detail. Prior to this, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts that correspond to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best describe the invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical ideas of the present invention, and therefore, various equivalents and modifications that can be substituted therefor may exist at the time of filing this application.

[0024] Throughout this specification, when a part is described as "comprising" a certain component, this does not mean that other components are excluded, and that other components may also be included, unless otherwise specified.

[0025] Furthermore, terms and phrases such as "about," "substantially," and the like used throughout this specification are used to mean a numerical value or approximation of a numerical value when manufacturing and material tolerances inherent in the stated meaning are given, and are used to prevent unscrupulous infringers from unfairly exploiting the contents of the disclosure in which precise or absolute numerical values ​​are stated to aid in the understanding of the present invention.

[0026] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0027] Certain terminology used in the Detailed Description of the Invention that follows is for ease of description only and is not limiting. The words "right," "left," "top," and "bottom" designate directions in the drawings to which reference is made. The words "inwardly" and "outwardly" designate directions toward or away from the geometric center of the designated device, system, or component thereof, respectively. "Front," "rear," "upward," "downward," and related words and phrases designate locations and orientations in the drawings to which reference is made and are not intended to be limiting. These terms encompass the above-listed words, derivatives thereof, and words of similar import.

[0028] The present invention relates to a separator for an electrochemical device and an electrochemical device including the separator. In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction and is a concept that includes primary batteries and secondary batteries. The secondary batteries are capable of being charged and discharged and include lithium ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc.

[0029] 1. Separator

[0030] 1) Separator structure

[0031] A separator according to the present invention includes a porous separator substrate having a large number of pores and an inorganic coating layer formed on at least one surface of the separator substrate. FIG. 1 is a schematic cross-sectional view of a separator 100 according to one embodiment of the present invention. FIG. 2 is a schematic plan view of a separator substrate 120. The separator substrate 120 has a recessed pattern 120a having a predetermined width disposed on the outer periphery of the edge of at least one surface. The inorganic coating layer 110 is disposed on at least one surface of the separator substrate, preferably covering the entire surface of the separator substrate. The recessed pattern 120a is embedded by the formation of the inorganic coating layer. As a result, a separator coated with an inorganic coating layer has a flat surface, with no pattern corresponding to the recessed pattern visible from the outside of the separator.

[0032] 2) Separator substrate

[0033] The separator substrate is an ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative and positive electrodes, and may be in the form of a sheet with numerous pores formed therein. The pores are interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0034] The material constituting such a separator substrate can be either an organic material or an inorganic material having electrical insulation properties. In particular, from the viewpoint of providing the substrate with a shutdown function, it is preferable to use a thermoplastic resin as the constituent material of the substrate. Here, the shutdown function refers to the function in which, when the temperature of the battery becomes high, the thermoplastic resin dissolves and closes the pores of the separator substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. Thermoplastic resins with a melting point of less than 200°C are preferably used as the thermoplastic resin, and polyolefins are particularly preferred.

[0035] In addition, the separator may further contain at least one polymer resin such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, etc. Examples of the separator substrate include, but are not limited to, nonwoven fabric, porous polymer film, and laminates of two or more of these.

[0036] Specifically, the porous polymer substrate is a porous film and is any one of the following a) to e).

[0037] a) A porous film formed by melting / extruding a polymer resin; b) a multilayer film in which two or more porous films of a) are laminated; c) a nonwoven web produced by accumulating filaments obtained by melting / spinning a polymer resin; d) a multilayer film in which two or more layers of the nonwoven fabric web of b) are laminated; e) A porous composite membrane having a multilayer structure containing two or more of the above a) to d).

[0038] In the present invention, the separator substrate preferably has a thickness of 4 to 15 μm. If the thickness is less than this range, the conductive barrier function is insufficient, whereas if the thickness exceeds this range (i.e., is too thick), the resistance of the separator may increase excessively.

[0039] In one embodiment of the present invention, the weight-average molecular weight of the polyolefin may be in the range of 100,000 to 5,000,000. If the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. On the other hand, if it is more than 5,000,000, the shutdown characteristics may be deteriorated or molding may be difficult. Furthermore, the puncture strength of the separator substrate may be 300 g or more from the viewpoint of improving the production yield rate. The puncture strength of the separator substrate indicates the maximum puncture load (g) measured by a puncture test using a KES-G5 handy compression tester manufactured by Kato Tech Co., Ltd., Japan, under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec.

[0040] In one specific embodiment of the present invention, the separator substrate can be any planar porous polymer substrate used in electrochemical devices, for example, a thin insulating thin film having high ion permeability and mechanical strength, a pore diameter of typically 0.01 μm to 0.10 μm, and a thickness of typically 3 μm to 20 μm or 4 μm to 15 μm. Meanwhile, in one embodiment of the present invention, the porosity of the separator substrate is preferably 30% to 70%.

[0041] In particular, in the present invention, the separator substrate has a recessed pattern 120a having a predetermined width extending from the outermost end to the inside in the outer periphery of its surface. The recessed pattern may be formed on all or part of the periphery. In one embodiment of the present invention, when the separator substrate has a rectangular shape, the recessed pattern may be formed on at least one of the four corners. For example, the recessed pattern may be formed on two opposing corners. Referring to FIGS. 1 and 2, the recessed pattern 120a is schematically shown formed on the outer periphery of the separator substrate 120. In one embodiment of the present invention, the planar area of ​​the recessed pattern may be 5% to 40% of the planar area of ​​the separator substrate. In one embodiment of the present invention, the recessed pattern may be formed by pressing the corresponding portion of the separator substrate with a patterned pressing tool before forming the inorganic coating layer. The formation of the recessed pattern portion as described above increases the surface area of ​​the portion, thereby widening the bonding area with the inorganic coating layer and improving the adhesion between the separator substrate and the inorganic coating layer. Furthermore, the recessed pattern portion exerts an anchoring effect that secures the inorganic coating layer to the separator substrate, thereby enhancing the effect of improving the bonding strength. In this way, by increasing the bonding strength between the separator substrate and the inorganic coating layer at the outer peripheral end portion of the separator, peeling between the separator substrate and the inorganic coating layer can be prevented. Furthermore, because the outer shape of the porous substrate does not change inside the separator, the target porosity and pore diameter as originally designed can be maintained.

[0042] In one embodiment of the present invention, the recessed pattern may be formed using a metal mesh. For example, the recessed pattern may be formed by placing a metal mesh on the surface of the separator substrate where the recessed pattern is to be formed, and then pressing the metal mesh and the separator substrate together. The shape of the recessed pattern formed on the separator substrate is formed to correspond to the shape of the metal mesh used. The metal mesh is not limited to a specific composition or shape, as long as it is possible to transfer the shape corresponding to the metal mesh to the separator substrate by pressing the surface of the separator substrate. For example, a stainless steel (SUS) mesh can be used as the metal mesh. Meanwhile, in the present invention, the recessed pattern may be formed to have recesses 122 recessed inward from the surface of the separator substrate. In one embodiment of the present invention, when forming such a recessed pattern, the surface roughness (Ra) of the separator substrate may be 0.8 to 3.2, preferably 1.0 to 2.0.

[0043] In one embodiment of the present invention, the planar area of ​​the recesses 122 may be 20% to 80%, preferably 30% to 70%, of the total planar area of ​​the recessed pattern portion of the separator substrate. The "planar area of ​​the recesses" refers to the ratio of the total area (area) of the recesses formed on the surface of the recessed pattern portion to the total area (area) of the surface of the recessed pattern portion. The shape of the recesses in the recessed pattern portion is not particularly limited, but is preferably regular in terms of dimensions, size, and arrangement. In other words, when forming the recessed pattern portion, it is preferable that the recesses are uniformly distributed throughout the entire recessed pattern portion without being locally densely packed. Meanwhile, in one embodiment of the present invention, the recessed pattern may have a shape such as a line, a grid, or a dot, but is not limited thereto. In FIG. 2, reference numerals 121 and 120b indicate portions of the separator substrate that are flat and do not have a recessed pattern portion formed thereon.

[0044] Meanwhile, the separator according to the present invention has an inorganic coating layer 110 containing inorganic particles and a binder material formed on at least one surface of the separator substrate. The inorganic coating layer 110 exhibits a porous structure due to pores formed by the interstitial volume between the inorganic particles. The pore size and porosity (pore volume ratio) of the pores can be adjusted according to the particle size and particle size distribution of the particles. This structure enhances resistance to metallic foreign matter present in the electrode and suppresses shrinkage of the polyolefin separator substrate, thereby enhancing the safety of the lithium secondary battery. In this regard, the inorganic coating layer may contain inorganic particles in a ratio of 70 to 99.5 wt %, preferably 80 to 99 wt %, based on 100 wt % of the inorganic coating layer.

[0045] Meanwhile, the inorganic coating layer fills the recesses of the recessed pattern portion, leaving no empty space. Referring to FIG. 1, the shape of the recessed portion of the recessed pattern portion 122 of the separator substrate, filled with the inorganic coating layer, can be seen. As described below, a separator can be manufactured by applying a slurry for forming an inorganic coating layer to the surface of the separator substrate and drying it. The slurry then flows into the recessed portions of the separator substrate, filling the recessed portions. As described above, the separator substrate and the inorganic coating layer are interlocked with each other at the end of the separator through corresponding recessed patterns. Therefore, even if the separator substrate shrinks, the inorganic coating layer secures the end, minimizing distortion of the separator substrate's shape. In FIG. 1, reference numeral 100a denotes the portion of the separator where the separator substrate and the inorganic coating layer interlock with each other through corresponding recessed patterns, and reference numeral 100b denotes the other portion.

[0046] In a specific embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). In particular, when inorganic particles with a high dielectric constant are used as the inorganic particles, they can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0047] For the reasons mentioned above, it is preferable that the inorganic particles include inorganic particles with a high dielectric constant, which has a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles with a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT,0 <x<1,0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, YO3, Al2O3, AlOOH, Al(OH)3, SiC, and TiO2, and the like, and one or more of these may be included.

[0048] In the present invention, the binder material may include an acrylic polymer and / or a PVDF-based polymer. The acrylic polymer may include, for example, a (meth)acrylic polymer. The (meth)acrylic polymer is a monomer containing a (meth)acrylic acid ester. Examples of such monomers include monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate. One or more of these monomers may be included. The PVdF-based polymer may include at least one of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and a copolymerizable monomer, and a mixture thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorine-based monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), among others.In one embodiment of the present invention, the PVDF-based polymer may include one or more selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-chlorofluoroethylene (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene (PVdF-TFE), and polyvinylidene fluoride-trifluoroethylene (PVdF-TrFE).

[0049] In addition, the average particle size of inorganic particles (D 50 ) is not particularly limited, but is preferably in the range of 0.1 μm to 2.5 μm in order to form an inorganic coating layer with a uniform thickness and an appropriate porosity.

[0050] In the inorganic coating layer, the pore diameter may be in the range of 50 nm to 500 nm based on the longest diameter of the pore, but is not limited thereto.

[0051] 2. Separator manufacturing method

[0052] The separator according to the present invention can be produced by a method of forming a recessed pattern by pressing the outer peripheral end portion of the separator substrate with a pressing member (S1), and coating at least one surface of the separator substrate with an inorganic coating layer (S2).

[0053] First, a separator substrate is prepared, and a recessed pattern is formed on the outer peripheral edge of the separator substrate (S1). The recessed pattern may be formed by preparing a pressure member having a recessed pattern formed on its surface and using the pressure member to press down on the outer peripheral edge of the separator substrate. The pressure member having the recessed pattern formed thereon may be, for example, a flat jig or a pressure roller, but is not limited thereto. That is, the pressure member is not particularly limited as long as it can pressurize the surface of a porous polymer sheet to form an irreversible recessed pattern on the surface.

[0054] Next, an inorganic coating layer is coated on the surface of the separator substrate where the recessed pattern portion is formed (S2). First, a binder solution is prepared by dispersing or dissolving a polymer resin, which serves as a binder material, in a solvent. Next, inorganic particles dispersed in a bead mill are added to the binder solution to prepare a slurry for forming the inorganic coating layer. Non-limiting examples of the solvent include one or a mixture of two or more selected from the group consisting of water, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane.

[0055] The method for coating the separator substrate with the slurry may be a conventional coating method known in the art, such as dip coating, die coating, roll coating, comma coating, or a combination thereof. The drying method may be any conventional drying method, such as natural drying or air drying, without any particular limitation.

[0056] 3. An electrode assembly including the separator

[0057] Meanwhile, the present invention provides a secondary battery including the separator, which includes a negative electrode, a positive electrode, and a separator sandwiched between the negative electrode and the positive electrode, and the separator has the above-mentioned characteristics.

[0058] In one embodiment of the present invention, the separator in the electrode assembly may be disposed such that all or at least a portion of the recessed pattern portion faces the tab of the electrode. For example, in a plan view of the electrode assembly, all or a portion of the recessed pattern portion of the separator may be disposed so as to overlap the tab of the electrode. Meanwhile, the tab of the electrode is preferably a tab of the negative electrode.

[0059] FIG. 3 is a schematic cross-sectional view of an electrode assembly according to a conventional embodiment. Referring to FIG. 3, the electrode assembly includes a positive electrode 200, a negative electrode 300, and a separator 100. The positive electrode has a positive electrode active material layer 210 formed on both sides of a positive electrode current collector 220, and the negative electrode has a negative electrode active material layer 310 formed on the surface of a negative electrode current collector 320. In this electrode assembly, the electrode active material layer may have an inclined surface A, rather than a right angle, at its end. Such an inclined surface may be formed intentionally in the electrode design or may be an unavoidable characteristic during the electrode manufacturing process. For example, when an electrode active material layer is formed by applying a fluid electrode slurry to a current collector, the slurry at the end of the electrode may flow down, resulting in an inclined surface at the end that does not maintain a right angle. However, such an inclined surface may prevent the electrode and separator from adhering to each other at their ends, resulting in a gap, which may cause the electrode and separator to separate. In particular, at the end of the negative electrode, such gaps may increase the interfacial resistance between the electrode and the separator, which may lead to more severe lithium plating. Furthermore, if the separator substrate and the inorganic coating layer at the end of the separator are not sufficiently adhered to each other and the adhesive strength is weaker than that between the electrode and the inorganic coating layer, separation between the separator substrate and the inorganic coating layer is likely to occur, which, as described above, may increase the interfacial resistance at the separated portion and result in the occurrence of lithium plating Ld.

[0060] In contrast, the electrode assembly according to the present invention can prevent lithium plating by arranging the recessed pattern portion of the separator, which has improved binding properties, to overlap the inclined surface of the electrode. According to another embodiment of the present invention, the electrode may include a tab 320t extending from the current collector and protruding outside the negative electrode, and the separator and electrode may be stacked such that the recessed pattern portion of the separator overlaps at least the tab or the recessed pattern portion overlaps both the tab and the inclined surface. Meanwhile, in one embodiment of the present invention, the electrode may be a negative electrode, a positive electrode, or both a negative electrode and a positive electrode.

[0061] 4 is a schematic diagram illustrating an electrode assembly according to one embodiment of the present invention. Referring to FIG. 4, a portion 100a of the separator, where the recessed pattern portion of the separator substrate is disposed, is arranged to overlap the tab of the electrode and the inclined surface of the electrode active material layer. The term "overlap" used herein means that the portions appear to overlap in a plan view, but does not necessarily mean that they are in physical contact.

[0062] In the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material is a layered compound such as a lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), a lithium cobalt oxide (LiCoO2), a lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals, and a compound of the general formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7, and oxides of the general formula LiNi 1-x M xNi-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3), and general formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), and LiMn2O4 in which part of the general formula Li is substituted with alkaline earth metal ions, and may contain a mixture of one or more of a disulfide compound and Fe2(MoO4)3.

[0063] In the present invention, the negative electrode includes a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of a negative electrode current collector and the current collector. As the negative electrode active material, the negative electrode includes a lithium metal oxide, carbon such as graphitizable carbon and graphite-based carbon, and Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, and 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides, lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, and may contain a mixture of one or more selected from titanium oxides.

[0064] In one specific embodiment of the present invention, the conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon or metal fiber, metal powder, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more conductive materials thereof. More specifically, the conductive material may be any one selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials thereof.

[0065] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, stainless steel, copper, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can be used.

[0066] As the binder resin, polymers commonly used in electrodes in the art can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of suitable cellulose acetate copolymers include, but are not limited to, cyanoethyl acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0067] The electrode assembly prepared as described above can be placed in a suitable case and an electrolyte injected to manufacture a battery.

[0068] In the present invention, the electrolyte solution is + B - and the like, wherein A + Li + , Na + , K. + or a combination thereof, - PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a combination thereof, dissolved or dissociated in an organic solvent such as, but not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (g-butyrolactone), or a mixture thereof.

[0069] The present invention also provides a battery module including a battery having the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, power tools powered by a battery-like motor, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters, electric golf carts, and energy storage systems.

[0070] The present invention will be described in more detail below with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0071] [Example]

[0072] Separator manufacturing

[0073] A separator substrate (thickness 9 μm, porosity 45%) made of polyethylene was prepared, and a SUS mesh was placed around the outer periphery of two opposing corners. The separator substrate was then pressed using a hot press to prepare a separator substrate with a recessed pattern. The recessed pattern area of ​​the separator was 25%.

[0074] Next, 10 g of carboxymethyl cellulose (SG-L02, manufactured by GL Chem, Korea) and 10 g of acrylic copolymer (CSB 130, manufactured by Toyo Ink Co., Ltd., Japan) were dispersed in 1,500 g of water. 980 g of Al2O3 (AES 11, manufactured by Sumitomo Chemical Co., Ltd., Japan) was then added and dispersed using a ball mill to prepare a slurry for forming an inorganic coating layer. The slurry was then sequentially applied to both sides of the separator substrate using a microgravure method and dried to form an inorganic coating layer. In each example and comparative example, the roughness of the recessed pattern portion and the surface coverage (area of ​​recesses) of the recessed pattern portion were adjusted by adjusting the shape of the SUS mesh and the pressure applied during pressing, as shown in Tables 1 and 2 below.

[0075] [Table 1]

[0076] As can be seen from Table 1 above, when the separator substrate had no distortion and a coverage of 0%, the roughness was low and the peel strength was low, resulting in low adhesion between the electrode and separator. In Comparative Example 2, despite the low coverage and a large recessed pattern area, the peel strength and electrode adhesion were low. In contrast, in Comparative Example 3, despite the small recessed pattern area, the electrochemical performance decreased due to increased resistance in the relevant area. Meanwhile, as the roughness approached 70%, the roughness increased, resulting in improved peel strength and adhesion. However, when the separator was compressed using full pressure without a pattern, the roughness decreased, resulting in decreased peel strength and adhesion. Furthermore, the porosity of the separator substrate decreased, increasing the resistance of the separator after the formation of the inorganic coating layer.

[0077] [Table 2]

[0078] Meanwhile, in Examples 4, 5, and Comparative Examples 4 and 5, the area (%) of the recessed pattern portion of the separator substrate was all 20%, and the surface coverage was also all 40%. As can be seen from Table 2 above, when the coverage was the same, if the roughness under pressure was 1.0 or less, the peel strength and adhesive strength were very low. In contrast, if the roughness was too high, the pores of the separator substrate were blocked, resulting in a significant increase in the separator resistance after the formation of the inorganic coating layer, and local strain reduced the insulation properties.

[0079] Peel Force Test

[0080] The separator samples obtained in each Example or Comparative Example were cut into pieces measuring 80 mm (length) x 15 mm (width) to prepare two test pieces for each. The two test pieces were attached with double-sided tape and then peeled at an angle of 180° at a speed of 300 mm / min at 25°C, and the strength at this time was measured.

[0081] Electrode adhesive strength

[0082] The negative electrode and the separator obtained in each comparative example and example were pressed at 60°C, 6.5 MPa, and 1 second to prepare an electrode adhesion test piece. This was peeled at an angle of 180° at a speed of 300 mm / min at 25°C using a Universal Testing Machine (UTM) manufactured by Intron Co., Ltd. of Japan, and the strength at this time was measured.

[0083] Anode manufacturing

[0084] The negative electrode used in the electrode adhesion evaluation was fabricated as follows. A negative electrode active material slurry was prepared by adding a mixture of 96.3 wt% natural graphite (particle size 20 μm), 1.0 wt% super-p, and 1.5 wt% and 1.2 wt% styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) to N-methyl-2-pyrrolidone (NMP). The resulting negative electrode active material slurry was applied to one side of a copper current collector, dried, and then pressed to fabricate a negative electrode.

[0085] Resistance measurement

[0086] The separators obtained in each example and comparative example were interposed between stainless steel (SUS) to prepare coin cells, and the resistance was measured through electrochemical impedance spectroscopy analysis at 25°C in a scan range of 100,000 Hz to 10,000 Hz using a 1470E cell test system and a frequency response analyzer 1255B manufactured by Japan Solarton Co., Ltd.

[0087] Roughness

[0088] Topographic images were obtained using an NV-2700 optical profiler manufactured by NanoSystems, Korea, and then analyzed using the envelope mode of a white light interferometer (WLI) to measure the average roughness (Ra) value at five locations.

[0089] In the present invention, the roughness (Ra) refers to the average roughness of the centerline, which means the calculated average value of the distance (absolute value) from the centerline to the roughness profile. In the present invention, the centerline can be defined as follows: The centerline is a straight line parallel to the meanline, and is located at a position where the area enclosed by the profile is the same above and below. Meanwhile, the mean line is a line on the roughness profile that has the geometric shape of the measurement surface and is the straight line that minimizes the sum of the squares of the deviations from the profile to the roughness profile.

[0090] Breakdown voltage

[0091] After straining, the breakdown voltage of 30 samples was measured and the average value was used. The breakdown voltage was measured by increasing the voltage from 0 V to 100 V / s, and insulation was determined to have broken down when a current of 0.5 mA or more flowed for 3 seconds or more, and the voltage value at this time was recorded. [Explanation of symbols]

[0092] 100 Separator 110 inorganic coating layer 122 recess 120 Separator substrate 100a: A portion where the separator substrate and the inorganic coating layer are engaged with each other by corresponding concave patterns. 100b Parts other than 110a 121 and 120b: Parts of the separator substrate that do not have a recessed pattern and maintain a flat surface 120a Concave pattern portion 200 positive electrode 210 Cathode active material layer 220 Positive electrode current collector 320t negative electrode tab 300 negative electrode 310 Negative electrode active material layer 320 Negative electrode current collector 400 Separator

Claims

1. The separator includes a separator substrate and an inorganic coating layer formed on a surface of the separator substrate, the separator substrate has a porous structure and contains a polymer material; the inorganic coating layer comprises inorganic particles and a binder material; a recessed pattern portion having a predetermined width extending from an end of the periphery to the inside is formed on the surface of the separator substrate in the entire section or at least a part of the outer periphery, and the recessed pattern portion has recesses recessed from the surface; The recessed pattern portion has a surface roughness (Ra) of 0.8 to 3.2 μm, the inorganic coating layer has a concave pattern corresponding to the concave pattern portion at a position corresponding to the concave pattern portion, and the concave pattern portion of the separator substrate and the concave pattern of the inorganic coating layer are in meshing engagement with each other; a separator for an electrochemical element, wherein the area of ​​the recessed pattern portion is 5% to 40% of the area of ​​the separator substrate (100%), the recessed pattern portion is formed as a recess that is recessed inward in the thickness direction from one surface of the separator substrate, the plane area of ​​the recessed portion is 20% to 80% of the total area of ​​the recessed pattern portion, and the thickness of the separator substrate is 4 μm to 15 μm.

2. 2. The separator for an electrochemical element according to claim 1, wherein the recessed pattern portion has recesses formed therein that are recessed inward in the thickness direction from one surface of the separator substrate.

3. 2. The separator for an electrochemical element according to claim 1, wherein the separator has a uniform overall thickness and has a shape in which the recessed patterns of the inorganic coating layer and the separator substrate are interlocked with each other at a boundary where the surfaces of the inorganic coating layer and the separator substrate are in contact with each other.

4. 2. The separator for electrochemical elements according to claim 1, wherein the recessed pattern portion has a recess formed inward in the thickness direction from one surface of the separator substrate, and the planar area of ​​the recessed portion is 20% to 80% of the total area of ​​the recessed pattern portion.

5. 2. The separator for an electrochemical element according to claim 1, wherein the planar area of ​​the recesses in the separator substrate is 20% to 80% of the total area of ​​the recessed pattern portion.

6. 2. The separator for an electrochemical element according to claim 1, wherein the separator substrate is a porous sheet containing polyolefin.

7. The inorganic particles are BaTiO ３ , Pb(Zr,Ti)O ３ (PZT), Pb １－ｘ La ｘ Zr １－ｙ Ti ｙ O ３ (PLZT, 0<x<1, 0<y<1), Pb(Mg １／３ Nb ２／３ ) O ３ -PbTiO ３ (PMN-PT), hafnia (HfO ２ ), SrTiO ３ , SnO ２ , CeO ２ , MgO, Mg(OH) ２ , NiO, CaO, ZnO, ZrO ２ , SiO ２ , Y ２ O ３ , Al ２ O ３ , AlOOH, Al(OH) ３ , SiC and TiO ２ The separator for an electrochemical element according to claim 1 , comprising at least one selected from the group consisting of:

8. a negative electrode, a separator, and a positive electrode; The separator is according to any one of claims 1 to 7, the negative electrode includes a current collector, an electrode active material layer formed on at least one surface of the current collector, and a negative electrode tab extending from the current collector and protruding to the outside of the negative electrode, The electrode assembly, wherein the recessed pattern portion of the separator is laminated so as to completely or at least partially overlap the negative electrode tab.

9. 9. The electrode assembly according to claim 8, wherein the negative electrode is stacked such that all or at least a portion of an end of an electrode active material layer has an inclined surface, and the inclined surface and all or a portion of the recessed pattern portion of the separator overlap with each other.

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