Separator substrate, manufacturing method thereof, and separator including same

Abstract

The present invention relates to a separator substrate, a separator, an electrode assembly, and an electrochemical device, and the separator substrate according to one embodiment of the present invention has a surface roughness (Sa) within a predetermined range, thereby maintaining good adhesive strength of the separator and reducing the amount of impregnation of the slurry during the formation of a porous coating layer, thereby improving the resistance characteristics of the separator.

Description

[Technical Field]

[0001] The present invention relates to a separator substrate, a manufacturing method thereof, and a separator including the same. More particularly, the present invention relates to a separator having improved adhesive strength and electrical resistance, and an electrode assembly and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0095298, filed on July 21, 2023, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] Lithium secondary batteries are manufactured by inserting an electrode assembly (composed of a positive electrode, a separator, and a negative electrode) into a battery case, injecting an electrolyte, and sealing the battery. Separators for lithium secondary batteries typically use polyolefin-based porous substrates. To address the issue of short circuits between the positive and negative electrodes due to the thermal shrinkage of polyolefin-based porous substrates, separators have been developed that improve the strength and heat resistance of the separator by forming a coating layer made of a mixture of inorganic particles and a binder polymer on the surface of the porous substrate. Examples of such separators include safety-reinforced separators (SRS) and ceramic-coated separators (CCS).

[0004] In SRS or CCS, inorganic particles in the coating layer act as a spacer that can maintain the physical shape of the separator, preventing the porous substrate from shrinking when exposed to high temperatures and preventing direct contact between the positive and negative electrodes. This makes it possible to manufacture an electrode assembly by bonding the positive and negative electrodes together with a separator having porous coating layers on both sides sandwiched between them.

[0005] However, there is a problem that the resistance increases when a part of the slurry solution for forming the porous coating layer is impregnated into the porous polymer substrate. Recently, there has been a gradual increase in the need for batteries with high-speed charging and high-power characteristics, and in conjunction with this, research efforts on reducing the resistance of batteries have been continuously conducted. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide a separator that can solve the above-mentioned problems, and an electrode assembly and an electrochemical device including the separator.

[0007] Specifically, the present invention aims to provide a separator substrate for reducing the resistance of a separator, which is one of the components of an electrochemical element, for example, a lithium secondary battery, in order to reduce the resistance of the battery; a method for producing the same; a separator using the same; and an electrochemical element including the same.

[0008] In particular, the present invention aims to provide a separator substrate having improved surface properties, and a manufacturing method thereof, that can reduce the degree of impregnation of a slurry for forming a porous coating layer when forming the porous coating layer on the separator substrate, thereby reducing an increase in the resistance of the separator. [Means for solving the problem]

[0009] To solve the above problems, According to one aspect of the present invention, there is provided a separator substrate having the following embodiments.

[0010] The separator substrate according to the first embodiment comprises: The porous polymer substrate has a surface roughness value (Sa) of 30 nm to 80 nm on at least one surface.

[0011] According to the second embodiment, in the first embodiment, The surface roughness value (Sa) of both surfaces of the porous polymer substrate may be 30 nm to 70 nm.

[0012] According to another aspect of the present invention, there is provided a separator having the following embodiment.

[0013] The separator according to the third embodiment comprises: a separator substrate according to the first or second embodiment; and a porous coating layer formed on at least one of the surfaces having a surface roughness value (Sa) of 30 nm to 80 nm, the porous coating layer including inorganic particles and a binder polymer.

[0014] According to the fourth embodiment, in the third embodiment, The adhesive strength between the separator substrate and the porous coating layer may be 30 gf / 15 mm or more.

[0015] According to the fifth embodiment, in the third or fourth embodiment, The adhesive strength between the separator substrate and the porous coating layer may be 30 gf / 15 mm to 140 gf / 15 mm.

[0016] According to the sixth embodiment, in any one of the third to fifth embodiments, The separator may have an electrical resistance of 1 Ω or less.

[0017] According to the seventh embodiment, in any one of the third to sixth embodiments, The separator may have an electrical resistance of 0.9 Ω or less.

[0018] According to the eighth embodiment, in any one of the third to seventh embodiments, The average particle size (D 50 ) can be 100 nm or more.

[0019] According to yet another aspect of the present invention, there is provided an electrode assembly according to the following embodiment.

[0020] The electrode assembly according to the ninth embodiment comprises: a separator according to any one of the third to eighth embodiments; a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0021] According to the tenth embodiment, in the ninth embodiment, The electrode assembly may have a resistance of 1 Ω or less.

[0022] According to the eleventh embodiment, in the ninth or tenth embodiment, The electrode assembly may have a resistance of 0.9 Ω or less.

[0023] According to yet another aspect of the present invention, there is provided an electrochemical device according to the following embodiment.

[0024] The electrochemical device according to the twelfth embodiment comprises: The electrode assembly according to any one of the ninth to eleventh embodiments is housed in a case.

[0025] According to yet another aspect of the present invention, there is provided a method for producing a separator substrate according to the following embodiment.

[0026] The method for producing a separator substrate according to the thirteenth embodiment includes the steps of: S1) extruding a polymer slurry to obtain a polymer sheet; S2) heat-setting the obtained polymer sheet; Including, The heat setting in step S2 is carried out under a temperature condition of 119°C to 132°C. [Effects of the Invention]

[0027] The separator substrate according to one embodiment of the present invention has an improved surface roughness value (Sa), which has the effect of improving the degree of impregnation of the slurry for forming a porous coating layer when the coating layer is formed on the surface.

[0028] Therefore, a separator using this material can exhibit advantages such as improved adhesive strength and resistance characteristics compared to conventional separators that have a porous coating layer formed thereon to provide heat resistance and adhesiveness.

[0029] From this, an electrochemical element using the separator not only has heat resistance but also low electrical resistance, and therefore has the advantage of excellent high-output characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in detail below.

[0031] Throughout this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0032] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0033] Certain terminology used in the following detailed description is for ease of description only and is not intended to limit the invention. Additionally, directional words such as up, down, left, right, front, rear, inside, outside, etc., refer to directions in the drawings to which reference is made or to directions toward or away from the geometric center of the specified device, system, and components thereof, respectively.

[0034] According to one aspect of the present invention, there is provided a separator substrate which is a porous polymer substrate, and at least one surface of which has a roughness value (Sa) of 30 nm to 80 nm.

[0035] Separator substrate and manufacturing method thereof According to one aspect of the present invention, there is provided a separator substrate which is a porous polymer substrate, and at least one surface of which has a roughness value (Sa) of 30 nm to 80 nm.

[0036] To explain this, first, one feature of the method for producing a separator substrate according to one embodiment of the present invention will be described.

[0037] A method for producing a separator substrate according to one aspect of the present invention includes the steps of: S1) extruding a polymer slurry to obtain a polymer sheet; S2) heat-setting the obtained polymer sheet.

[0038] At this time, according to one aspect of the present invention, the heat setting in step S2 is performed under a temperature condition of 119°C to 132°C.

[0039] In one embodiment of the present invention, the heat setting may be performed to forcibly grip the polymer sheet to remove residual stress in the sheet, but the scope of the present invention is not limited thereto.

[0040] Conventionally, when manufacturing a porous polymer substrate as a separator substrate, a polymer slurry is extruded to obtain a polymer sheet, and the obtained polymer sheet is heat-set at a high temperature. The inventors of the present invention discovered that the heat-setting of the polymer sheet causes crystallization of the surface of the polymer sheet, resulting in a wide variety of surface characteristics. By setting the heat-setting temperature within a specific temperature range, a separator substrate having a surface roughness (Sa) of 30 nm to 80 nm was obtained due to the crystallization of the surface of the separator substrate.

[0041] In one embodiment of the present invention, the heat setting in step S2 is performed at a temperature of 119°C to 132°C, and more specifically, at a temperature of 120°C to 131°C or 121°C to 130°C. When the heat setting temperature is within the above range, a surface roughness value (Sa) of 30 nm to 80 nm can be achieved. If the temperature is too high, the surface roughness of the separator substrate may increase, resulting in an increase in the resistance of the separator. If the temperature is too low, the surface roughness of the separator substrate may be low, resulting in poor adhesion strength between the separator substrate and the porous coating layer. However, the present invention is not limited thereto.

[0042] In one embodiment of the present invention, heat may be applied during the heat setting while the film is uniaxially stretched in the machine direction (MD) or transverse direction (TD), or while the film is biaxially stretched in the machine direction (MD) and transverse direction (TD), but the present invention is not limited thereto.

[0043] In this specification, the "machine direction" refers to the direction parallel to the running direction of the steps [extrusion → molding → stretching...] in the manufacturing process of the separator substrate. The machine direction can be confirmed using the orientation direction of the polymer fibers of the separator substrate, and the direction parallel to the orientation direction of the fibers is the machine direction. Accordingly, the "transverse direction" refers to the direction perpendicular to the machine direction. The transverse direction can also be confirmed by the direction perpendicular to the orientation direction of the polymer fibers of the separator substrate.

[0044] According to one embodiment of the present invention, the method for manufacturing the separator substrate may further include, after the extrusion in step S1), steps S1-2) forming the extrudate into a sheet, S1-3) stretching the formed sheet, and S1-4) extracting the diluent from the stretched sheet. In this case, step S2) may be performed to heat-set the sheet from which the diluent has been extracted.

[0045] First, the extrusion in step S1) will be described in detail.

[0046] In one embodiment of the present invention, step S1) may be a step of melt-extruding and processing a polymer resin as a raw material of the separator substrate to obtain a porous polymer sheet.

[0047] In one embodiment of the present invention, the polymer resin may be any resin that can be used as a raw material for manufacturing a separator substrate. The polymer resin may include resins such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or a mixture of two or more thereof. The polyolefin resin refers to a polymer of an olefin, typically used in separator substrates, polymerized as a monomer. For example, the polyolefin resin may be, but is not limited to, polyethylene, polypropylene, polybutylene, polypentene, polyhexene, polyoctene, a homopolymer of a monomer selected from ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene, a copolymer of two or more thereof, or a mixture thereof.

[0048] In one embodiment of the present invention, the porous polymer substrate may be a polyolefin substrate.

[0049] In one embodiment of the present invention, the porous polymer substrate may be a polyethylene substrate.

[0050] In one embodiment of the present invention, a common diluent can be used to extrude the polymer resin into an extruder, such as liquid or solid paraffin oil, wax, soybean oil, or the like, which are commonly used in the manufacture of separators.

[0051] In one embodiment of the present invention, the melting and extrusion may be performed using a conventional single-screw extruder or a twin-screw extruder, but is not limited thereto. In one embodiment of the present invention, the mixture of the diluent and the polymer resin may be introduced into an extruder, and then mixed while melting the polymer resin at a high temperature to obtain a molten composition.

[0052] Next, S1-2) the molten composition can be formed into a sheet.

[0053] In one embodiment of the present invention, the molten composition may be extruded using a die of an extruder, such as a T-die, and then formed into a sheet using a conventional casting method or calendering method using a method such as water cooling or air cooling. In one embodiment of the present invention, the molten composition may be formed into a sheet by pressing the molten composition between a pair of casting rolls in a cooling device equipped with the casting rolls.

[0054] In this case, since the polymer sheet is generally extruded at a high temperature, for example, 150°C to 300°C, the polymer sheet extruded through the extrusion section has a high surface temperature, for example, 130°C to 200°C, immediately after extrusion, and is cooled while in contact with the casting roll while maintaining such a surface temperature. Generally, the surface temperature of the casting roll can be 20°C to 45°C, 25°C to 45°C, 35°C to 45°C, or 25°C.

[0055] Next, S1-3) a step of stretching the sheet formed into a sheet shape may be carried out.

[0056] In one embodiment of the present invention, the stretching may include secondary stretching of the polymeric sheet in the same or different directions, for example, independently stretching the polymeric sheet in a direction parallel to the machine direction (MD) and / or the transverse direction (TD).

[0057] In one embodiment of the present invention, the stretching can be performed by, for example, sequential or simultaneous stretching using a roll system or a tenter system.

[0058] In one embodiment of the present invention, the stretching may be performed at a stretch ratio of, for example, 3 times or more, 5 times to 12 times, or 6 times to 7 times. When the stretch ratio satisfies the above numerical range, advantageous effects are achieved in terms of thickness uniformity of the separator substrate to be manufactured and balance of physical properties between the machine direction and the cross direction, but the present invention is not limited thereto.

[0059] In one embodiment of the present invention, S1-4) after the stretching, the diluent may be extracted from the stretched sheet to form pores.

[0060] In one embodiment of the present invention, the diluent may be extracted using an organic solvent, such as methyl ethyl ketone, methylene chloride, hexane, or a mixture of two or more thereof, which has high extraction efficiency and quick drying, but the present invention is not limited thereto.

[0061] In one embodiment of the present invention, the temperature at which the extraction is carried out is not particularly limited as long as it is within a range that does not change the surface roughness value of the porous substrate to be formed.

[0062] In one embodiment of the present invention, step S2) may involve heat fixing the porous polymer sheet in which the diluent is extracted and pores are formed as described above.

[0063] According to one embodiment of the present invention, there can be provided a separator substrate in which the surface roughness value (Sa) of both surfaces of the porous polymer substrate is 30 nm to 70 nm.

[0064] According to one embodiment of the present invention, the surface roughness value (Sa) of at least one surface of the porous polymer substrate may be 35 nm to 70 nm.

[0065] According to one embodiment of the present invention, when the surface roughness value (Sa) of at least one surface of the porous polymer substrate is within the above-mentioned range, advantageous effects are obtained in terms of reducing an increase in the resistance of the separator during the formation of the porous coating layer and ensuring appropriate adhesive strength between the separator substrate and the porous coating layer, but the effects of the present invention are not limited thereto.

[0066] Meanwhile, in addition to measuring the Sa value, other methods for measuring the surface roughness of a separator substrate include methods that indicate two-dimensional surface roughness, such as Ra (center line average), Rmax (maximum peak-to-valley roughness height), Rz (ten-point height), and Rg (root mean square, RMS). However, Ra, Rmax, Rz, and Rg only measure the two-dimensional (linear) roughness of the surface, and these values ​​alone cannot determine the surface roughness profile. That is, even if at least one of Ra, Rmax, Rz, and Rg is the same for two different surfaces, the three-dimensional roughness profile may differ. This may result in different amounts of impregnation of the slurry used to form the porous coating layer, making it difficult to determine whether the resistance characteristics have improved. In consideration of this issue, the present invention defines the surface roughness value of a separator substrate using Sa.

[0067] In one embodiment of the present invention, the surface roughness value (Sa) can be measured by performing surface analysis of the porous polymer substrate using atomic force microscopy (AFM). For example, a 30 μm × 30 μm sample of the porous polymer substrate to be measured for surface roughness is obtained, and the surface characteristics of both sides are measured. In this case, the surface roughness value (Sa) is measured by analyzing the average height difference of the surface over the entire region based on the average height plane.

[0068] The porous polymer substrate will be exemplified below, but is not limited to the components described below.

[0069] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein, which is a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the anode and cathode. The pores are interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0070] In one embodiment of the present invention, the porous polymer substrate may be a porous polymer film containing a thermoplastic resin, which provides a shutdown function. Here, the shutdown function refers to the function of preventing thermal runaway of the battery by blocking ion migration when the temperature of the battery rises by dissolving the thermoplastic resin and blocking the pores of the porous polymer substrate.

[0071] In one embodiment of the present invention, the thickness of the porous polymer substrate is not particularly limited as long as it satisfies the above-mentioned range based on the overall thickness of the separator, and may be, for example, 5 to 300 μm, specifically, 5 to 100 μm, 5 to 50 μm, 5 to 20 μm, 5 to 15 μm, or 9 to 12 μm.

[0072] In one embodiment of the present invention, the "thickness" of the porous polymer substrate can be measured by a known method for measuring the thickness of each component of a separator. For example, the thickness of the porous polymer substrate can be measured using a known thickness measuring device, such as a commercially available thickness measuring device (VL-50S-B, manufactured by Mitutoyo Corporation, Japan).

[0073] Separator According to one aspect of the present invention, there is provided a separator including the above-described porous polymer substrate as a separator substrate, and a porous coating layer formed on at least one surface of the separator substrate, the porous coating layer including inorganic particles and a binder polymer, wherein the porous coating layer may be formed on at least one surface of the separator substrate having a surface roughness value (Sa) of 30 nm to 80 nm.

[0074] According to another aspect of the present invention, there is provided a separator including the above-described porous polymer substrate as a separator substrate, and a porous coating layer formed on at least one surface of the separator substrate, the porous coating layer including inorganic particles and a binder polymer, wherein the porous coating layer is formed on at least one surface of the separator substrate having a surface roughness value (Sa) of 30 nm to 80 nm.

[0075] The porous coating layer contains a large amount of inorganic particles and a binder polymer that binds them together to improve the safety of the separator. The inorganic particles improve the heat resistance of the separator, and the binder polymer provides adhesion to the surface of the separator. If the surface of the separator substrate on which the porous coating layer is formed is flat, poor adhesion strength at the interface between the separator substrate and the porous coating layer may occur. However, if the surface of the separator substrate is excessively rough, the pores of the separator substrate may be impregnated with a large amount of slurry for forming the coating layer. This may cause the inorganic particles and / or binder polymer to penetrate the pores of the separator substrate and / or the surface of the separator substrate, resulting in an increase in the resistance of the separator. As a result, a separator having a porous coating layer formed on a separator substrate according to one aspect of the present invention can exhibit a characteristic that a certain level of surface roughness is achieved, preventing impregnation of inorganic particles and / or binder polymers onto the surface, thereby improving the phenomenon of increased resistance.

[0076] In one embodiment of the present invention, the separator may have a feature that the adhesive strength between the porous coating layer and a separator substrate surface having a surface roughness value (Sa) of 30 nm to 80 nm, specifically 30 nm to 70 nm, is 30 gf / 15 mm or more. For example, the adhesive strength between the porous coating layer and a separator substrate surface having a surface roughness value (Sa) within the above range may be 30 gf / 15 mm to 140 gf / 15 mm, 30 gf / 15 mm to 120 gf / 15 mm, 30 gf / 15 mm to 100 gf / 15 mm, 30 gf / 15 mm to 85 gf / 15 mm, or 32 gf / 15 mm to 81 gf / 15 mm. When the adhesive strength between the separator substrate and the porous coating layer of the separator is within the above range, advantageous effects are achieved in terms of improving the manufacturing process performance of an electrode assembly using the separator and improving the stability of the separator.

[0077] The adhesive strength of the separator can be measured, for example, by the following method. The separator to be measured for adhesive strength is sampled to a width of 15 mm and attached to a glass slide using 18 mm double-sided tape (manufactured by 3M) so that the surface to be measured for adhesive strength is in contact with the glass. Then, the peel strength between the separator substrate and the porous coating layer is measured using a universal testing machine (manufactured by Instron) under conditions of 180° and 300 mm / min.

[0078] In one embodiment of the present invention, the separator may have an electrical resistance of 1 Ω or less. When the surface roughness value (Sa) of the separator substrate is within the above range, the degree of impregnation of the slurry for forming a porous coating layer on the separator substrate is improved, thereby reducing the amount of slurry impregnated into the interface between the separator substrate and the porous coating layer, thereby reducing the amount of inorganic particles and / or binder polymer that penetrates into the separator substrate, thereby exhibiting the advantage of mitigating an increase in separator resistance.

[0079] According to one embodiment of the present invention, the separator may have an electrical resistance of 0.9Ω or less. Specifically, the separator may have an electrical resistance of 0.5Ω to 0.9Ω, 0.6Ω to 0.85Ω, or 0.63Ω to 0.82Ω.

[0080] The resistance of the separator can be measured, for example, using electrochemical impedance spectroscopy (EIS). Specifically, a separator to be measured for resistance is punched out to a diameter of 19 mm to prepare a CR2016-type coin cell. A positive electrode can be prepared by applying a solution of an active material (NCMA), a binder polymer (PVDF), and a conductive material (CNT) in a solvent (NMP) at a weight ratio of 97:1:2 to an aluminum foil, drying the solution, and punching out to a diameter of 12 mm. A negative electrode can be prepared by applying a solution of an active material (graphite), a binder polymer (SBR), and a conductive material (Super P) in distilled water at a weight ratio of 95:0.5:4.5 to a copper current collector, drying the solution, and punching out to a diameter of 12 mm. After laminating the positive electrode / separator / negative electrode in this order, the resultant is immersed in an electrolyte solution consisting of 1M LiPF6, ethyl carbonate (EC) and ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC) to assemble a coin cell.

[0081] For the measurement by the EIS method, for example, a Solartron analytical EIS device manufactured by Solartron Analytical can be used, and the resistance value can be measured under the condition of a frequency of 100,000 Hz to 10,000 Hz.

[0082] The structure of the porous coating layer will be described below by way of example, but the structure of the porous coating layer is not limited thereto.

[0083] In one embodiment of the present invention, the porous coating layer may include inorganic particles and a binder polymer, and all or at least a portion of the surfaces of the inorganic particles may be coated with the binder polymer. In this case, the inorganic particles may be bound by the binder polymer at surfaces and / or points.

[0084] For example, the inorganic particles and binder resin in the porous coating layer may be contained in a weight ratio of 99:1 to 1:99. Specifically, the inorganic particles and binder resin in the porous coating layer may be contained in a weight ratio of 95:5 to 5:95, 90:10 to 10:90, 80:20 to 10:90, 70:30 to 10:90, 60:40 to 10:90, 50:50 to 10:90, 40:60 to 15:85, 60:40 to 15:85, 70:30 to 20:80, or 20:80. The porous coating layer has a large number of micropores therein, and these micropores are interconnected, providing the structural characteristic of a porous layer that allows gas or liquid to pass from one surface to the other.

[0085] In one embodiment of the present invention, the porous coating layer may have a porous structure due to pores formed by interstitial volume between inorganic particles. The pore size and porosity (pore volume ratio) of the pores may be controlled depending on the particle size and particle size distribution. This structure enhances resistance to metallic foreign matter present in the electrode and suppresses shrinkage of the porous polymer substrate, thereby enhancing the safety of the electrochemical device.

[0086] In one embodiment of the present invention, the porous coating layer includes a plurality of nodes including the inorganic particles and a binder polymer covering at least a portion of the surface of the inorganic particles, and one or more filaments formed in a thread-like shape from the binder polymer at the nodes, the filaments having node connection portions extending from the nodes to connect to other nodes, and the node connection portions may have a structure in which a plurality of filaments derived from the binder polymer cross each other to form a three-dimensional network structure.

[0087] In one embodiment of the present invention, as described above, the porous coating layer may be formed using a manufacturing method for a safety reinforced separator (SRS), a ceramic coated separator (CCS), or other known manufacturing methods, but is not limited thereto.

[0088] In one embodiment of the present invention, the inorganic particles can be used without any particular limitation as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention can be used within the operating voltage range (e.g., Li / Li) of the applied electrochemical device. + There are no particular limitations on the inorganic particles as long as they do not undergo oxidation and / or reduction reactions at a voltage of 0 to 5 V relative to the reference voltage. Non-limiting examples of such inorganic particles 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, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, and one or more of these may be included.

[0089] In one embodiment of the present invention, the average particle size (D 50 Specifically, the average particle size (D 50 The average particle size of the inorganic particles may be 100 nm to 1 μm, or 100 nm to 500 nm. When the average particle size of the inorganic particles is within the above range, an advantageous effect is exhibited in terms of suppressing an increase in the resistance of the separator, but the present invention is not limited thereto.

[0090] The particle size of the inorganic particles can be measured by a known particle size measurement method, for example, using a particle size analyzer (PSA) manufactured by Malvern Instruments. 50 ) means the particle size at 50% of the cumulative particle number distribution according to particle size, and can be measured using a known laser diffraction method. In this case, the laser diffraction particle size distribution measuring device that can be used is, for example, Microtrac (registered trademark) S3500 manufactured by Microtrac Corporation.

[0091] In one embodiment of the present invention, the binder polymer may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin) and / or an acrylic binder. In one embodiment of the present invention, the PVdF-based resin 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. The acrylic binder may include, for example, polyacrylic acid (PA), polyacrylonitrile (PAN), polyacrylamide (PAA), or a (meth)acrylic polymer, or a mixture of two or more of these, but the present invention is not limited thereto. The (meth)acrylic polymer refers to a polymer containing a (meth)acrylic acid ester as a monomer. Such monomers may include, for example, 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, tetradecyl (meth)acrylate, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the binder polymer may also include, but is not limited to, an oil-based binder, a water-based binder, or a mixture thereof that can be used in a porous coating layer.

[0093] In one embodiment of the present invention, the thickness of the porous coating layer is not particularly limited as long as it satisfies the above-mentioned ratio range relative to the overall thickness of the separator, and may be, for example, 0.5 to 50 μm, specifically 0.5 to 10 μm, 0.5 to 5 μm, or 1.5 to 3 μm.

[0094] electrode assembly According to yet another aspect of the present invention, there is provided an electrode assembly including the separator described above, and a positive electrode and a negative electrode formed on both sides of the separator, respectively.

[0095] As described above, one feature of the separator according to one aspect of the present invention is that it has improved resistance characteristics and thus realizes low resistance, and therefore, one feature of an electrode assembly using the separator is that it has low resistance and therefore high output characteristics.

[0096] In one embodiment of the present invention, the electrode assembly may have a resistance of 1 Ω or less.

[0097] In one embodiment of the present invention, the resistance of the electrode assembly may be 0.9Ω or less. Specifically, the resistance of the electrode assembly may be 0.5Ω to 1Ω, 0.5Ω to 0.9Ω, 0.5Ω to 0.8Ω, 0.5Ω to 0.7Ω, or 0.52Ω to 0.62Ω.

[0098] In one embodiment of the present invention, the resistance of the electrode assembly may be measured by the following method.

[0099] The separator is sandwiched between two electrodes, one on each side, and pressed together to prepare an electrode assembly with a theoretical capacity of 50 mAh. CC / CV charging at 4.2 V and 2.5 mA cutoff and CC discharging at 2.5 V and 50 mA are then repeated three times. The fully charged cell is then set to 50% SOC and discharged at 250 mA for 30 seconds. The voltage drop at 50% SOC is recorded, and the DC resistance is calculated using Ohm's law (R = V / I). The compositions of the positive electrode, negative electrode, and electrolyte described above in the section on measuring the separator resistance can be used.

[0100] In one embodiment of the present invention, when a separator using the separator substrate is used, it not only has excellent adhesive strength with the positive and negative electrodes but also reduces the resistance of the electrode assembly, thereby providing an electrochemical device with high output characteristics.

[0101] The configuration of the electrodes will be described below by way of example, but the present invention is not limited thereto.

[0102] In one embodiment of the present invention, the positive electrode and the negative electrode may each be formed by coating an electrode active material on a current collector, and the size and shape thereof are not particularly limited.

[0103] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, a lithium transition metal oxide, a lithium metal iron phosphate, a lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, or two or more of these. Specifically, the positive electrode active material may include, but is not limited to, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these. Specifically, the positive electrode active material may include, but is not limited to, a layered compound such as lithium cobalt oxide (LiCoO) or lithium nickel oxide (LiNiO), or a compound substituted with one or more transition metals; a compound represented by the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x O2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (wherein M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1); lithium metal phosphate oxide LiMPO4 (wherein M is Fe, Co, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-xO2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1); Oxide in which part of lithium nickel-manganese-cobalt oxide is substituted with aluminum, Li a [Ni b Co c Mn d Al e 1-f M1 f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1); Oxide in which part of lithium nickel-manganese-cobalt oxide is substituted with other transition metals, Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), disulfide compound; Examples include, but are not limited to, Fe2(MoO4)3.

[0104] In one embodiment of the present invention, the negative electrode active material may be, for example, lithium metal or a lithium alloy, soft carbon, hard carbon, natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, petroleum or coal tar pitch-derived cokes, silicon (Si)-based compounds (M-SiOx (M=Li, Mg, Ca, Al, or Ti, 0≦x<2)), or a mixture of two or more of these, but is not limited thereto.

[0105] Electrochemical elements According to yet another aspect of the present invention, there may be provided an electrochemical device in which the above-described electrode assembly is housed in a case.

[0106] In one embodiment of the present invention, the electrochemical device may be a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium ion secondary battery.

[0107] In one embodiment of the present invention, the case may be a commonly used battery case and is not particularly limited in shape depending on the intended use of the battery. For example, the case may be cylindrical, rectangular, pouch-like, or coin-like using a can.

[0108] Once the electrode assembly is completed, it can be housed in a case and sealed in a conventional manner to manufacture an electrochemical device, which may be, for example, a lithium secondary battery.

[0109] The present invention will be described in more detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not necessarily limited to these examples.

[0110] [Separator substrate manufacturing] A porous polymer substrate was prepared by the following method.

[0111] A polyethylene polymer with a molecular weight of 600,000 (g / mol) and an antioxidant were mixed in an extruder, melted at 200°C, extruded through a T-die, and cooled on a stainless steel casting roll with a surface temperature of 25°C. The polymer sheet was then formed into a sheet to obtain a polymer sheet. The polymer sheet passing through the casting roll was stretched in the MD (stretch ratio: 7x, stretch temperature: 115°C) and the TD (stretch ratio: 6x, stretch temperature: 125°C) using a tenter-type sequential stretching machine placed downstream of the casting roll. The diluent was then extracted using methylene chloride. The resulting polymer sheet was then heat-set under the temperature conditions listed in Table 1 below to obtain a porous polymer substrate. Heat-setting was performed while the polymer sheet was held in both the MD and TD directions. The resulting porous polymer substrate had a thickness of 9 μm and a porosity of 45 vol%.

[0112] [Table 1]

[0113] [Separator manufacturing] Separators were manufactured by using the porous polymer substrates of Comparative Example 1, Comparative Example 2, and Examples 1 to 3 prepared above as separator substrates, and forming porous coating layers on both sides of the separator substrates by the following method.

[0114] Fabrication of porous coating layer A slurry for inorganic coating was prepared by mixing a PVDF-HFP binder (Mw: 500,000 g / mol, HFP: 15 wt%) and inorganic particles (Al2O3) in a weight ratio of 80:20 in an appropriate solvent. The slurry for inorganic coating prepared above was applied to the entire surface of the porous substrate by dip coating and then dried using a humidified phase separation method to form a porous coating layer with a thickness of 3 μm on each of the upper and lower surfaces of the porous substrate prepared above.

[0115] This produced a separator with an overall thickness of 15 μm.

[0116] [Manufacturing of electrode assemblies] The separators prepared above were used as separators, and negative and positive electrodes were prepared as follows and attached to one side of the separators, respectively, to prepare electrode assemblies.

[0117] Anode manufacturing An active material (graphite), a binder polymer (SBR), and a conductive material (Super P) were mixed in distilled water in a weight ratio of 95:0.5:4.5 to prepare a composition for forming a negative electrode.

[0118] The negative electrode composition was applied to one side of a copper current collector and dried to prepare a negative electrode. The loading of the negative electrode was 5.3 mAh / cm. 2 It was.

[0119] Cathode manufacturing An active material (NCMA), a binder polymer (PVDF), and a conductive material (CNT) were mixed in a solvent (NMP) at a weight ratio of 97:1:2 to prepare a composition for forming a positive electrode.

[0120] The positive electrode composition was applied to one side of an aluminum current collector and dried to prepare a positive electrode. The loading of the positive electrode was 4.949 mAh / cm 2 It was.

[0121] Assembling the electrode assembly With the separators prepared as described above still sandwiched between them, the positive electrode was placed on one side and the negative electrode on the other side, and then the electrodes were rolled under conditions of 90°C, 4 MPa, and 1 s, and dried to obtain an electrode assembly with a theoretical capacity of 50 mAh.

[0122] [Evaluation of physical properties] The separator substrate, separator, and electrode assembly were prepared in the above order and their physical properties were evaluated by the following methods. The results are shown in Table 2 below.

[0123] As the adhesive strength of the separator in Table 2 below, the adhesive strength between the surface where the surface roughness value was measured and the porous coating layer was measured.

[0124] Measurement of the surface roughness value (Sa) of the separator substrate The surface of the porous polymer substrate was analyzed using atomic force microscopy (AFM) to obtain a height map of the surface. The roughness value (Sa) was measured by analyzing the difference in the average height of the surface over the entire area based on the average height plane.

[0125] The roughness measurements were performed on both sides of the separator substrate.

[0126] Separator adhesive strength measurement The separator was sampled to a width of 15 mm and attached to a glass slide using 18 mm double-sided tape (manufactured by 3M Co.) so that the surface to be measured for adhesive strength was in contact with the glass.Then, the peel strength between the separator substrate and the porous coating layer was measured using a universal testing machine (manufactured by Instron Co.) under conditions of 180° and 300 mm / min.

[0127] The adhesive strength was measured on both sides of the separator.

[0128] Measuring the separator resistance A CR2016 type coin cell was manufactured by the following method, and the resistance of the separator was measured by the EIS method.

[0129] The separator to be measured was prepared by punching out a separator of 19Φ. The electrodes produced during the manufacture of the electrode assembly were punched out to 12Φ for the positive and negative electrodes, respectively, and then the positive electrode / separator / negative electrode were stacked in this order in a CR2016-type coin cell case. An electrolyte solution composed of 1M LiPF6, ethyl carbonate (EC), ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC) was poured into the case, and the cap was closed to prepare a coin cell.

[0130] Measurement by the EIS method was carried out using a Solartron analytical EIS device manufactured by Solartron Analytical, and the resistance value was measured under the condition of a frequency of 100,000 to 10,000 Hz.

[0131] Measuring the resistance of the electrode assembly The electrode assembly prepared for measuring the separator resistance was measured for resistance in the following manner.

[0132] CC / CV charging under the cutoff condition of 4.2V, 2.5mA and CC discharging at 2.5V, 50mA were repeated three times. After this, the fully charged cell was set to SOC 50% and discharged at a current of 250mA for 30 seconds. The voltage drop at SOC 50% was recorded and the DC resistance was calculated using R = V / I (Ohm's law).

[0133] [Table 2]

[0134] As can be clearly seen from Tables 1 and 2 above, the porous polymer substrate, which is a separator substrate and obtained by heat setting at temperatures between 119°C and 132°C, exhibits a surface roughness value (Sa) of 30nm to 70nm, which indicates that it has low resistance while maintaining an appropriate level of adhesive strength. Furthermore, it was confirmed that the resistance of an electrode assembly using this can be significantly improved.

[0135] In contrast, the porous polymer substrates obtained by heat setting at temperatures outside the above range as separator substrates were confirmed to have surface roughness values ​​(Sa) outside of 30 nm to 70 nm. In particular, in the case of Comparative Example 1, where the surface roughness value (Sa) was less than 30 nm, the separator exhibited low resistance but poor adhesive strength, while in the case of Comparative Example 2, where the surface roughness value (Sa) exceeded 70 nm, not only did the adhesive strength appear to be extremely high, but the separator also exhibited poor physical properties in terms of resistance, and the resistance of the electrode assembly using the same was measured to be extremely high.

Claims

1. A separator substrate which is a porous polymer substrate, at least one surface of which has a surface roughness value (Sa) of 30 nm to 80 nm.

2. The separator substrate according to claim 1, wherein the surface roughness value (Sa) of both surfaces of the porous polymer substrate is 30 nm to 70 nm.

3. The separator substrate according to claim 1 ; a porous coating layer formed on at least one of the surfaces having a surface roughness value (Sa) of 30 nm to 80 nm, the porous coating layer including inorganic particles and a binder polymer; Including, separator.

4. The separator according to claim 3 , wherein the adhesive strength between the separator substrate and the porous coating layer is 30 gf / 15 mm or more.

5. 5. The separator according to claim 4, wherein the adhesive strength between the separator substrate and the porous coating layer is 30 gf / 15 mm to 140 gf / 15 mm.

6. The separator according to claim 3 , wherein the separator has an electrical resistance of 1Ω or less.

7. The separator according to claim 6, wherein the separator has an electrical resistance of 0.9 Ω or less.

8. The average particle size (D ５０ 4. The separator according to claim 3, wherein the average particle size is 100 nm or more.

9. The separator according to any one of claims 3 to 8; a positive electrode and a negative electrode formed on both sides of the separator, respectively; An electrode assembly comprising:

10. 10. The electrode assembly according to claim 9, wherein the resistance of the electrode assembly is 1 ohm or less.

11. The electrode assembly according to claim 10, wherein the resistance of the electrode assembly is 0.9 Ω or less.

12. An electrochemical device comprising the electrode assembly according to claim 9 housed in a case.

13. S1) extruding a polymer slurry to obtain a polymer sheet; S2) heat-setting the obtained polymer sheet; Including, The heat fixation in step S2 is carried out under a temperature condition of 119°C to 132°C. A method for manufacturing a separator substrate.

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