Separator for electrochemical devices and method for manufacturing the same

Abstract

The separator according to the present disclosure not only has excellent adhesion to the electrode, but also ensures sufficient porosity, thereby exhibiting excellent electrical resistance and ion conductivity characteristics. Furthermore, the time taken for the lamination process during the electrode assembly manufacturing can be reduced, thereby achieving high processing efficiency in battery manufacturing.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2023-0194080, filed on December 28, 2023. This disclosure relates to separators for electrochemical devices, such as lithium-ion secondary batteries. Background Technology

[0002] Non-aqueous secondary batteries, such as lithium-ion batteries, are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras, and camcorders. Furthermore, in recent years, due to their high energy density, their application in automobiles and other fields is also being considered.

[0003] In currently manufactured lithium-ion batteries, porous polymer substrates, such as polyolefin-based polymer resins, are used as separator substrates to prevent short circuits between the positive and negative electrodes. However, these polymer substrates have the problem of shrinking or melting at high temperatures, exhibiting low heat resistance. Therefore, when the battery temperature rises to a high level due to internal or external stimuli, the separator may shrink or melt, increasing the likelihood of the positive and negative electrodes coming into contact with each other, leading to a short circuit. Consequently, electrical energy may be released rapidly, potentially causing the battery to explode or catch fire.

[0004] Therefore, to address these issues, methods are widely used to improve heat resistance by forming a porous filler layer containing a mixture of inorganic particles and binder resin on at least one surface of a polymer substrate. However, the heat-resistant layer needs sufficient porosity to ensure ion transport pathways and electrolyte impregnation. The pores in the heat-resistant layer originate from the interstitial volume between the inorganic particles. As the binder resin content increases, the interstitial volume becomes blocked by the binder resin, making it difficult to ensure sufficient porosity. On the other hand, when the binder resin content is insufficient, the electrodes and separators cannot adhere tightly to each other, and the electrodes and separators may separate during battery manufacturing or operation.

[0005] Meanwhile, electrode assemblies are typically manufactured via a continuous roll-to-roll process, and in this paper, a lamination process is performed to press the laminated electrodes and spacers together (applying hot pressing as needed). To achieve the desired level of electrode-spacer bonding strength, sufficient lamination process time needs to be ensured; however, this may lead to reduced productivity, such as reduced production speed.

[0006] Therefore, in separators for electrochemical devices, continuous research and development are needed to ensure sufficient porosity and adhesion (between the electrode and the separator) as well as processing efficiency. Summary of the Invention

[0007] Technical issues

[0008] This disclosure aims to provide a separator capable of ensuring high adhesion to the electrodes and improving battery production efficiency. Furthermore, this disclosure aims to provide an electrochemical device including said separator. It will be readily apparent that other objects and advantages of this disclosure can be achieved by the means or methods set forth in the claims, or combinations thereof.

[0009] Technical solution

[0010] A first aspect of this disclosure relates to a separator for an electrochemical device, the separator comprising: a porous polymer substrate; and an inorganic coating covering one or both surfaces of the porous polymer substrate.

[0011] The inorganic coating comprises a plurality of adhesive polymer columns, each having a predetermined volume, and the polymer columns are made of a polymer material and are non-porous.

[0012] At least a portion of the polymer column is exposed on the surface of the inorganic coating, and another portion is in contact with the surface of the porous substrate.

[0013] At least one of the polymer columns is spaced apart from the other polymer column by a predetermined distance.

[0014] The spaces between the polymer columns are filled with inorganic particles, and

[0015] The polymer column has a storage modulus (G') of 100 Pa or greater and 3,500 Pa or less at room temperature and a solubility of 15% to 70% in THF, and the solubility is determined according to Equation 1 below.

[0016] [Equation 1]

[0017] Solubility (%) = {(Weight measured before impregnation - Weight measured after impregnation) / (Weight measured before impregnation)} × 100

[0018] In the foregoing aspects of this disclosure, the first compression ratio obtained by the first compression of the separator under compression conditions of 2.0 MPa to 4.0 MPa and 55°C to 65°C can be 20% to 25%.

[0019] The first compression ratio is the value calculated using the following Equation 2, and refers to the compression ratio of the separator before contact with the electrolyte (dry compression ratio), and

[0020] The height (T) of the inorganic coating after compression under the above conditions c ) is 1.1×T i <T c <1.5×T i Furthermore, the protruding height of the polymer column after compression can be 1 μm or greater.

[0021] [Equation 2]

[0022] First compression ratio (%) = {(Initial thickness before first compression - Thickness after first compression) / (Thickness before first compression)} × 100

[0023] In any of the foregoing aspects of this disclosure, the second compression ratio obtained by the second compression of the separator under the pressing conditions of 0.5 MPa to 1.5 MPa and 35°C to 85°C may be 30% or greater. The second compression ratio is calculated by the following Equation 3 and refers to the compression ratio (wet compression ratio) obtained in the state where the separator is pressed under the aforementioned conditions after the first compression has been immersed in an electrolyte for 5 minutes or longer and then the electrolyte on the surface has been removed.

[0024] The thickness of the inorganic coating after the second compression (T) c ) is 1.0×T i <T c ≤1.1×T i ,as well as

[0025] After the second compression, the protruding thickness of the polymer column can be 1 μm or less.

[0026] [Equation 3]

[0027] Second compression ratio (%) = {(Initial thickness before second compression - Thickness after second compression) / (Thickness before second compression)} × 100

[0028] In any of the foregoing aspects of this disclosure, the D of the polymer column 50 D can be inorganic particles 50 At least twice as much.

[0029] In any of the foregoing aspects of this disclosure, the inorganic coating may comprise polymer columnar particles in an amount ranging from 10% to 50% of 100% by volume, based on 100% by volume of inorganic particles.

[0030] In any of the foregoing aspects of this disclosure, the thickness (T) of the inorganic particle portion i ) can be a polymer columnar structure D 50 85% or less.

[0031] In any of the foregoing aspects of this disclosure, the D of the polymer column 10 D 50 30% or more, and D of polymer columnar materials 90 D 50 200% or less.

[0032] In any of the foregoing aspects of this disclosure, based on a top view of the separator, the area occupied by the polymer columnar body may be 10% to 50% relative to 100% of the area of ​​the inorganic coating surface.

[0033] In any of the foregoing aspects of this disclosure, the cross-sectional area (b) of at least one of the polymer columns included in the inorganic coating, observed in a section at the upper 5% of the inorganic coating from the uppermost part toward its lower part, may be greater than the cross-sectional area (a) of the polymer column observed in a section at the lower 5% of the inorganic coating from the lowermost part toward its surface portion.

[0034] In any of the foregoing aspects of this disclosure, in the cross-section of the polymer column observed in the vertical section of the inorganic coating, the lower diameter (a) of at least one of the polymer columns included in the inorganic coating is smaller than the upper diameter (b) of the polymer column, and the ratio of diameter (b) to diameter (a) can be from 2 to 20.

[0035] In any of the foregoing aspects of this disclosure, the inorganic coating may have a porous structure formed by the interstitial volume between inorganic particles.

[0036] One embodiment of this disclosure relates to an electrochemical device that includes a separator for an electrochemical device according to any of the foregoing aspects.

[0037] One embodiment of this disclosure relates to a method for manufacturing a separator for an electrochemical device according to any of the foregoing aspects, the method comprising: preparing a laminate comprising at least one positive electrode, at least one separator and at least one negative electrode, wherein the positive electrode, the negative electrode and the separator between the positive electrode and the negative electrode are laminated at least once;

[0038] The laminate is pressed at a temperature of 55°C to 65°C with a strength of 3.0 MPa to 4.0 MPa to prepare a first electrode assembly;

[0039] The first electrode assembly is immersed in an electrolyte; and

[0040] A pressure of 0.5 MPa to 1.5 MPa is applied to the impregnated first electrode assembly.

[0041] In any of the manufacturing methods according to the foregoing aspects of this disclosure, pressure is applied to the impregnated first electrode assembly to bring the separator into close contact with the positive electrode and / or the separator with the negative electrode, and the pressure can be applied at a temperature of 35°C to 45°C.

[0042] In any of the manufacturing methods according to the foregoing aspects of this disclosure, impregnating the first electrode assembly with an electrolyte includes storing the first electrode assembly in a battery case, and may also involve aging after impregnation and before applying pressure.

[0043] In this disclosure, each of the above embodiments can be implemented independently. Alternatively, two or more of the above embodiments can be implemented in combination.

[0044] Beneficial effects

[0045] The separator according to this disclosure not only exhibits excellent adhesion to the electrodes but also ensures sufficient porosity, thereby demonstrating excellent electrical and ionic conductivity characteristics. Furthermore, the time spent on the lamination process can be reduced during electrode assembly manufacturing, thus achieving high processing efficiency in battery manufacturing. Attached Figure Description

[0046] The accompanying drawings illustrate preferred embodiments of this disclosure and are intended to provide a better understanding of the technical concept of this disclosure in conjunction with the foregoing description of the invention. Therefore, this disclosure should not be construed as limited to the content described in these drawings. Furthermore, for clarity, the shapes, dimensions, scales, or proportions of elements in the drawings included in this specification may be enlarged.

[0047] Figure 1 This is a diagram schematically illustrating one embodiment of the separators in this disclosure.

[0048] Figure 2 An SEM image of the surface of the inorganic coating of the separator manufactured in Example 1 is shown.

[0049] Figure 3 An SEM image of the surface of the inorganic coating of the separator manufactured in Example 1 after the first compression is shown.

[0050] Figure 4 SEM images of the surface of the inorganic coating of the separator manufactured in Comparative Example 2 are shown.

[0051] Figure 5 SEM images of the surface of the inorganic coating of the separator manufactured in Comparative Example 2 after the first compression are shown. Detailed Implementation

[0052] The present disclosure will be described in detail below. Prior to this, the terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, but rather should be interpreted as corresponding to the technical concept of the present disclosure based on the principle that the inventors can appropriately define the concepts of the terms in order to describe their own invention in the best possible way. Therefore, the embodiments described in this specification and the constructions shown in the accompanying drawings are merely one of the most preferred embodiments of the present disclosure and do not fully represent the technical concept of the present disclosure. It should be understood that various equivalents and modifications may exist at the time of submission.

[0053] Throughout this specification, unless otherwise stated to the contrary, a description in which a part “includes” a component means that it may also include other components, and does not exclude other components.

[0054] Furthermore, terms such as “about” or “substantially” used throughout this specification, when there are inherent manufacturing and material tolerances in the meanings mentioned, are used to indicate values ​​or close to those values, and are intended to prevent unethical infringers from unfairly exploiting the disclosure of precise or absolute values ​​presented to aid in understanding this application.

[0055] Throughout this specification, the description of "A and / or B" means "A or B or both".

[0056] Throughout this specification, particle size D 50 This refers to the particle size at the 50th percentile point in the cumulative particle count distribution based on particle size. In other words, D 50 This refers to the particle size at the 50% point of the cumulative particle count distribution based on particle size. Furthermore, D... 10 This refers to the particle size at the 10% point in the cumulative particle count distribution based on particle size, and D. 90 This refers to the particle size at the 90th percentile point in the cumulative particle count distribution based on particle size. Particle size can be measured using laser diffraction. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the differences in the diffraction patterns based on particle size as the particles pass through the laser beam. 10 D 50 and D 90 The particle size can be measured by calculating the particle size at the 10%, 50%, and 90% points of the cumulative particle count distribution based on particle size in the analyzer.

[0057] The specific terminology used in the following detailed description of the invention is merely for convenience and is not intended to be limiting. Terms such as “left,” “right,” “up,” and “down” may indicate directions in the referenced figures and should not be limiting. Terms such as “inward” and “outward” respectively indicate directions toward or away from the geometric center of the designated device, system, and its components. Terms such as “front,” “back,” “up,” and “down,” as well as related words and phrases, indicate positions and orientations in the referenced figures and should not be limiting. Such terms include the words listed above, their derivatives, and words with similar meanings.

[0058] In this disclosure, the glass transition temperature (Tg) can be measured by a DSC curve obtained by differential scanning calorimetry (DSC) at a heating rate of 10 °C / min.

[0059] This disclosure relates to separators for electrochemical devices and electrochemical devices including the same. In this disclosure, an electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and includes the concepts of primary batteries and secondary batteries. Secondary batteries are rechargeable and encompass concepts such as lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries.

[0060] Separator

[0061] In one embodiment of this disclosure, the separator includes a porous substrate 10 and an inorganic coating 20 formed on at least one or both side surfaces of the porous substrate. Figure 1 This is a schematic cross-section of a separator in this disclosure, in which inorganic particles 200 and polymer columnar bodies 100 are disposed. Figure 1 Specifically, the form of the separator before compression (pressing) during the manufacturing process is shown, where the polymer columnar parts protrude beyond the inorganic particle filling portion. Compression can refer to the artificial application of external force during the battery assembly process.

[0062] The total thickness of the spacer can be from 5.0 μm to 30 μm, and the thickness can be appropriately adjusted within the above range. For example, the total thickness can be 25.0 μm or less, 20.0 μm or less, 15.0 μm or less, 12.0 μm or less, or 10.0 μm or less. In one embodiment of this disclosure, the spacer can be introduced during the manufacture of the electrode assembly and, after being flattened by a pressing process such as lamination, can have a thickness of 15.0 μm or less, 14.0 μm or less, 13.0 μm or less, 12.0 μm or less, 11.0 μm or less, or 10.0 μm or less. Furthermore, the porosity of the spacer can be from about 25 vol% to 80 vol%. The porosity can be appropriately adjusted within the above range. For example, the porosity can be 30 vol% or more, 35 vol% or more, 40 vol% or more, 50 vol% or more, or 55 vol% or more. Alternatively, the porosity can be 70% by volume or less, 65% by volume or less, 60% by volume or less, or 55% by volume or less. Meanwhile, the permeability of the separator can be in the range of approximately 50 seconds / 100 cc or more and approximately 250 seconds / 100 cc or less. The permeability can be appropriately adjusted within the above range. For example, the permeability can be 60 seconds / 100 cc or more, 70 seconds / 100 cc or more, 100 seconds / 100 cc or more, 120 seconds / 100 cc or more, or 150 seconds / 100 cc or more. Alternatively, the porosity can be 220 seconds / 100 cc or less, 200 seconds / 100 cc or less, or 180 seconds / 100 cc or less.

[0063] In one embodiment of this disclosure, the thickness of the separator can be determined by cutting a cross-section of the separator sample, observing the cross-section using SEM, and taking the thickness at the thickest point as the thickness of the separator. Alternatively, the thickness can be measured at two or more arbitrary points, and the average of these measurements can be taken as the thickness of the separator. When the thickness is measured at four or more points, the lowest and / or highest values ​​can be excluded, and the average of the remaining values ​​can be taken.

[0064] In one embodiment of this disclosure, porosity can be calculated by determining the density (apparent density) of the test object, such as a separator, and the net density of the test object based on the composition ratio of the materials contained in the test object and the density of each component, and then calculating the difference between the apparent density and the net density. For example, porosity can be calculated using the following Equation 4.

[0065] [Equation 4]

[0066] Porosity (volume %) = {1 - (apparent density / net density)} × 100

[0067] Meanwhile, the apparent density in the above equation can be calculated by the following equation 5.

[0068] [Equation 5]

[0069] Apparent density (g / cm³) 3 = {Weight of the object to be measured [g] / (Thickness of the object to be measured [cm] × Area of ​​the object to be measured [cm²])} 2 ])}

[0070] Alternatively, porosity or pore size can be measured using the BELSORP (BET device) of BEL JAPAN Co., Ltd. with an adsorbed gas such as nitrogen, or by methods such as mercury porosimetry or capillary flow porosimetry.

[0071] As used in this specification, the term "permeability" refers to the time required for 100 cc of air to pass through an object whose permeability is to be measured (e.g., a separator or porous substrate), and can be expressed in seconds per 100 cc. It is interchangeable with transmittance and is typically expressed as a Gurley value, etc. In one specific embodiment of this disclosure, permeability can be measured according to JISP 8117. Furthermore, the air transmittance P1 measured for an object of thickness T1 can be converted to the transmittance P2 corresponding to an object thickness of 20 μm using the equation P2 = (P1 × 20) / T1.

[0072] Porous substrate

[0073] A porous substrate, acting as a porous ion conduction barrier that allows ions to pass through while simultaneously blocking the electrical contact between the negative and positive electrodes, refers to a substrate in which multiple pores are formed. These pores are interconnected, allowing gas or liquid to flow from one side surface of the substrate to another.

[0074] As the material constituting such a porous substrate, organic or inorganic materials with electrical insulating properties can be used. In particular, thermoplastic resins are preferred as the material constituting the substrate in order to provide a shut-off function. Here, the shut-off function refers to the function that, when the battery temperature rises, the thermoplastic resin melts and closes the pores of the porous substrate to prevent ion migration, thereby preventing thermal runaway of the battery. Thermoplastic resins with a melting point below 200°C are suitable, and polyolefins are particularly preferred.

[0075] In addition, it may contain at least one of the following polymer resins: for example, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, or polyvinyl naphthalene. The porous substrate may be a nonwoven fabric, a porous polymer membrane, or a laminate of two or more thereof, but is not particularly limited thereto.

[0076] Specifically, the porous polymer substrate is any one of the following a) to e).

[0077] a) A porous membrane formed by melting / extruding a polymer resin.

[0078] b) Multilayer membranes formed by laminating two or more porous membranes from a)

[0079] c) Nonwoven webs prepared by laying filaments obtained by melting / spinning polymer resin.

[0080] d) Multilayer films formed by laminating two or more layers of nonwoven webs from b), and

[0081] e) A porous composite membrane having a multilayer structure including two or more of a) to d).

[0082] In this disclosure, the thickness of the porous substrate can be in the range of 3 μm to 12 μm or 5 μm to 12 μm. When the thickness does not reach the above values, the conductive barrier is not functional enough; conversely, when the thickness exceeds the above range (i.e., too thick), the resistance of the separator may increase excessively.

[0083] In one embodiment of this disclosure, the weight-average molecular weight of the polyolefin can be from 100,000 to 5,000,000. For example, the molecular weight (Mw) can be 200,000 or greater, 500,000 or greater, 700,000 or greater, or 1,000,000 or greater. Alternatively, the molecular weight can be 4,000,000 or less, 3,000,000 or less, 2,500,000 or less, 2,000,000 or less, or 1,500,000 or less. The unit for molecular weight (Mw) can be g / mol. When the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. Furthermore, when the weight-average molecular weight is greater than 5,000,000, the shut-off properties may deteriorate, or molding may become difficult. Additionally, in terms of improving manufacturing yield, the puncture strength of the porous substrate can be 300 gf or greater. The puncture strength of the porous substrate is represented by the maximum puncture load (gf) measured by puncture testing using a Kato tech KES-G5 portable compression tester under conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / s.

[0084] In one specific embodiment of this disclosure, any planar porous polymer substrate for electrochemical devices can be used as the porous polymer substrate. For example, an insulating film with high ion permeability and mechanical strength, a pore size typically from 10 nm to 200 nm, and a thickness typically from 2 μm to 12 μm can be used. Meanwhile, the porous substrate can have a porosity of 20 vol% to 60 vol% or 30 vol% to 60 vol% and a pore size of 10 nm to 200 nm; however, the porosity and pore size are not particularly limited thereto.

[0085] Inorganic coating

[0086] In this disclosure, the separator comprises an inorganic coating formed on one side surface of a porous substrate. The inorganic coating comprises a plurality of polymer columnar structures and a plurality of inorganic particles.

[0087] In one specific embodiment of this disclosure, the inorganic coating may contain inorganic particles in an amount ranging from about 50% to 95% and from about 70% to 90% by weight, relative to 100% by weight of the inorganic coating. Furthermore, polymer columnar particles may be contained in an amount ranging from 10% to 40% by weight, preferably from 20% to 35% by weight, relative to 100 parts by weight of the inorganic particles.

[0088] When the content of polymer columns in the inorganic coating is low, it is difficult to ensure the desired level of adhesion. However, when polymer columns are included in amounts exceeding the above range, the Gurley value and / or porosity of the separator may decrease, which is undesirable.

[0089] Meanwhile, in the planar image of the inorganic coating, the total area of ​​the polymer columnar body can be 10% to 80%, preferably 10% to 50%, based on the total area of ​​the inorganic coating. The total area of ​​the polymer columnar body can correspond to the area before compression, the area after compression, or the area before and after compression.

[0090] In inorganic coatings, two or more of the polymer columns may aggregate to form clusters, or individual polymer columns may be spaced apart from each other at predetermined intervals. In one embodiment of this disclosure, the aggregated polymer columns that form clusters comprise 30% or less, preferably 20% or less, and more preferably 10% or less, relative to 100% of the total polymer columns. Excessive aggregation of the polymer columns can lead to non-uniform resistance in the separators. Therefore, for improving resistance uniformity, the aggregated polymer columns preferably comprise 10% or less relative to 100% of the total polymer columns.

[0091] In one embodiment of this disclosure, the polymer columns are preferably spaced apart from other polymer columns at a predetermined distance without direct contact, and are distributed in an island pattern in the inorganic coating.

[0092] In one embodiment of this disclosure, when the separator is not artificially pressed after manufacturing, one or more of the polymer columns may protrude above the inorganic particle filling portion. In other words, one or more of the polymer columns may protrude from the surface of the inorganic particle filling portion. A plurality of polymer columns are embedded in the inorganic coating such that they are exposed or protrude beyond the surface of the inorganic coating, and some of the polymer columns may have a protrusion height T greater than 1 μm. p For example, T p The diameter can be greater than 1 μm and 10 μm or smaller, and for example, 7 μm or smaller, 5 μm or smaller, or 3 μm or smaller. Furthermore, some of the polymer columnar structures exposed on or protruding from the inorganic coating surface can contact the porous substrate. In this document, "polymer columnar structure protruding beyond the inorganic coating surface" refers to the height T of the polymer columnar structure within the inorganic coating. c Greater than the height T of the inorganic particle filling part i This results in a height greater than that of the inorganic particle filling portion.

[0093] In one embodiment of this disclosure, the average pore size of the inorganic coating can be from 20 nm to 1,000 nm. In one embodiment of this disclosure, the pore size of the inorganic particle filling portion can be measured. Within the above range, the average pore size of the inorganic coating can be 800 nm or less, or 500 nm or less, and independently or jointly with it, can be 20 nm or greater, 50 nm or greater, or 100 nm or greater. For example, the average pore size of the inorganic coating can be from 20 nm to 800 nm. The pore size can be calculated using shape analysis from SEM images. When the pore size is smaller than the above range, the pores may become clogged due to the expansion of the binder resin in the coating, and when the pore size exceeds the above range, there are problems such as difficulty in using it as an insulating layer and deterioration of self-discharge characteristics after manufacturing a secondary battery.

[0094] In one embodiment of this disclosure, the porosity of the inorganic coating (porosity in the state comprising polymer columnar structures) is preferably 30 vol% to 80 vol%. The porosity can be appropriately adjusted within the above range. For example, the porosity can be 35 vol% or more, 40 vol% or more, or 45 vol% or more. Alternatively, the porosity can be 75 vol% or less, 70 vol% or less, or 65 vol% or less. A porosity of 30% or more is advantageous in terms of lithium-ion permeability, and when the porosity is 80% or less, the surface opening ratio is not too high, which is suitable for ensuring adhesion between the spacer and the electrode.

[0095] Polymeric column

[0096] Relative to 100% by weight of polymer columns, the polymer columns may contain polymer resin in amounts of 90% by weight or more, 95% by weight or more, or 99% by weight or more. Preferably, the polymer columns may be formed from polymer resin. Furthermore, the polymer columns have adhesive properties and can adhere to battery materials adjacent to the polymer columns, such as inorganic particles or porous substrates.

[0097] In this disclosure, the polymer column may not have open cell pores in its body. Preferably, the polymer column does not have open cell pores, so that fluids such as gases or fluids do not flow through the polymer column body.

[0098] As described above, at least a portion of one or more of the polymer columns is exposed or protrudes from the surface of the inorganic coating, while another portion may be in contact with the surface of the porous substrate.

[0099] In one embodiment of this disclosure, the polymer columnar structure D 10 It can be D50 30% or more, and its D 90 It can be D 50 200% or less. Together with or independently of this, the D of the polymer columnar material... 50 D can be inorganic particles 50 At least twice as much.

[0100] In one embodiment of this disclosure, the polymer columnar structure D 50 It can be from about 2.5 μm to 7.5 μm or from 3.0 μm to 7.0 μm, and preferably, the D 50 The diameter can be in the range of 3.5 μm to 6.5 μm or 4.0 μm to 6.0 μm. The D-type polymer column... 50 This reflects the state before the separator is pressed, and preferably before the slurry is prepared.

[0101] Furthermore, in this disclosure, to prevent flattening due to compression during the first compression period, the storage modulus (G') of the polymer column at room temperature is preferably 100 Pa or greater and 3,500 Pa or less. For example, within the above range, the storage modulus can be 500 Pa or greater, 700 Pa or greater, 1,000 Pa or greater, 1,200 Pa or greater, 1,500 Pa or greater, or 2,000 Pa or greater. Preferably, the storage modulus can be related to the material forming the polymer column. In one embodiment of this disclosure, the room temperature can be in the range of 20°C to 25°C. In one embodiment of this disclosure, the storage modulus of the polymer column at high temperatures (50°C to 80°C or 60°C to 80°C) can be in the range of 0.1 Pa to 100 Pa. For example, within the above range, the energy storage modulus at high temperatures can be 0.5 Pa or greater, 1.0 Pa or greater, 2.0 Pa or greater, 5.0 Pa or greater, 10.0 Pa or greater, or 50 Pa or greater.

[0102] Furthermore, more preferably, when measured using a dynamic mechanical analyzer (DMA; ARES-G2, TA Instrument), the polymer column can have at least one tan δ peak in the range of 45°C to 80°C.

[0103] In one embodiment of this disclosure, the storage modulus and tan δ peak can be measured using a rheological analyzer (Dynamic Mechanical Analyzer (DMA), ARES-G2, TA Instrument). In one specific embodiment, the storage modulus can be determined by performing a temperature scan test at a temperature range of -60°C to 80°C and a frequency of 1.0 rad / s. Furthermore, the tan δ peak can be determined by calculating the ratio of the loss modulus to the storage modulus from the moduli measured above (storage modulus and loss modulus). Additionally, with such a DMA, the slope between the storage modulus (G') at 45°C and the storage modulus (G') at 70°C can be measured.

[0104] In this respect, the first compression ratio obtained by the separator of this disclosure through a first compression under pressing conditions of 3.0 MPa to 4.0 MPa and 55°C to 65°C can be 25% or less, 20% or less, 15% or less, or 10% or less. Meanwhile, the first compression ratio can be 5% or more, or 10% or more. For example, the first compression ratio can be 15% to 25%, or 20% to 25%. The first compression ratio is a value calculated by the following Equation 2, and refers to the compression ratio (dry compression ratio) when the separator is first compressed after manufacturing and before contact with the electrolyte.

[0105] [Equation 2]

[0106] First compression ratio (%) = {(Initial thickness before first compression - Thickness after first compression) / (Thickness before first compression)} × 100

[0107] After the first compression under the above conditions, the height T of the inorganic coating c 1.1×T i <T c <1.5×T i Specifically, after the first compression, the protrusion height of the polymer column is greater than 1 μm, and the protrusion height does not flatten to 1 μm or less.

[0108] The first compression condition is typically based on the lamination process conditions of the electrodes and spacers used to manufacture the electrode assembly. According to such a compression ratio, the electrodes and spacers do not come into complete contact with each other during the lamination process, thus creating a gap, which can serve as an electrolyte impregnation path through which the electrolyte flows into the electrode assembly when it is impregnated with the electrolyte. Simultaneously, when the compression ratio is within the aforementioned range, the spacers can achieve the adhesion required for the manufacturing process, such as manufacturing the electrode assembly and storing it before electrolyte impregnation. For example, in manufacturing the electrode assembly via a continuous roll-to-roll process, sufficient adhesion to prevent the electrodes and spacers from bending can be ensured.

[0109] In one embodiment of this disclosure, the second compression ratio of the separator obtained by second compression under pressure conditions of 0.5 MPa to 1.5 MPa and 35°C to 85°C can be 30% or greater. The temperature during this compression can be appropriately adjusted within the above range according to the applied pressure range. The temperature during this compression can be, for example, 75°C or lower, 65°C or lower, 55°C or lower, or 45°C or lower. The second compression ratio can be calculated using the following Equation 3. In one embodiment of this disclosure, the second compression ratio can be the compression ratio (wet compression ratio) obtained after the separator has been immersed in an electrolyte for 5 minutes or longer after the first compression and then the electrolyte on the surface has been removed, wherein the separator is compressed under the above conditions. In one embodiment of this disclosure, the electrolyte that can be applied when measuring the second compression ratio can refer to all the descriptions of electrolytes below.

[0110] [Equation 3]

[0111] Second compression ratio (%) = {(Initial thickness before first compression - Thickness after second compression) / (Initial thickness before first compression)} × 100

[0112] After the second compression under the above conditions, the thickness T of the inorganic coating... c 1.0×T i <T≤1.1×T i Furthermore, after the second compression, the separator can flatten, resulting in a protruding polymer column thickness of 1 μm or less. This property enhances the adhesion between the electrode and the separator during battery manufacturing and ensures tight contact between them, preventing separation. In other words, the polymer column exhibits further softening properties after being impregnated with the electrolyte. Moreover, the deformation of the polymer column can be achieved under milder conditions than in dry compression. Simultaneously, the compression time during the first and second compressions can be controlled within the range of 1 to 60 seconds.

[0113] In this specification, the term "flattening" refers to the thickness T of the inorganic particle-filled portion. i With respect to the height T of the polymer column c The deviation between them is 1 μm or less. In one embodiment of the disclosure, the height of the polymer column can be based on the polymer column with the largest height. (See reference...) Figure 1 T c This refers to the total height of the inorganic coating (on one side), and is based on the highest point of the inorganic coating from the surface of the porous substrate. In this disclosure, T... cThis can maximize the height of the polymer columnar structure. Meanwhile, in this disclosure, T... p Based on the highest part of the inorganic coating starting from the inorganic particle filling part.

[0114] In other words, when the separator according to this disclosure is used in battery manufacturing, it is preferable that, after laminating the electrodes and the separator, the thickness of the inorganic particle filling portion is less than the D of the polymer columnar structure. 50 .

[0115] Furthermore, compared to before pressing, the flattened polymer columnar structure observed in the planar plot can have a larger area. In this paper, the major axis length of the polymer columnar structure observed in the planar plot after flattening is preferably D of the polymer columnar structure before flattening. 50 10 times or less.

[0116] In one embodiment of this disclosure, in order to ensure the desired second compression ratio, the material forming the polymer column preferably has a solubility of 15% to 70% in an organic solvent or electrolyte and / or an electrolyte absorption rate of 30% or greater.

[0117] In one specific embodiment of this disclosure, the polymer columnar material, after being dissolved in THF (tetrahydrofuran) for 1 to 48 hours, can have a solubility of 15% to 70%, preferably 20% to 60%, and more preferably 25% or greater and 50% or less (by weight). When the solubility is within the corresponding range, the electrolyte is readily absorbed during the second compression, while preventing an increase in resistance in the battery due to binder dissolution, thereby ensuring the compression ratio. In this disclosure, the solubility can be calculated using the following Equation 5.

[0118] [Equation 5]

[0119] Solubility (%) = {(Weight measured before impregnation - Weight measured after impregnation) / (Weight measured before impregnation)} × 100

[0120] Meanwhile, the electrolyte absorption rate can be calculated using the following equation 6.

[0121] [Equation 6]

[0122] Electrolyte absorption rate (%) = {(Total weight of polymer columns after electrolyte impregnation - Weight of polymer columns before electrolyte impregnation) / (Weight of polymer columns before electrolyte impregnation)} × 100

[0123] Furthermore, when the above characteristics are met, it can prevent the polymer columnar material from dissolving and losing its adhesiveness after being injected with the electrolyte, or it can prevent the resistance of the lithium secondary battery from increasing due to the increased viscosity of the electrolyte caused by the dissolved components.

[0124] The electrolyte absorption rate is calculated as follows: a polymer column of predetermined size is immersed in the electrolyte for several minutes to one hour, for example, 5 minutes; it is then removed, the electrolyte residue on the surface is removed, and the weight is measured. As an electrolyte, for example, a 1 M LiPF6 electrolyte in ethylene carbonate / ethyl methyl carbonate (EC / EMC, volume ratio 30:70) can be used; however, the electrolyte is not limited to this, and those used as electrolytes for lithium-ion secondary batteries can be used without restriction.

[0125] However, after the polymer columns are injected with electrolyte, they may dissolve and lose their adhesiveness, or the viscosity of the electrolyte may increase due to the dissolved components, leading to an increased risk of resistance in the lithium secondary battery. Therefore, it is necessary to properly adjust the solubility in the electrolyte as described above by cross-linking the surface of the material forming the polymer columns.

[0126] Furthermore, in this disclosure, pressing can be performed within a range of seconds to minutes. For example, pressing can be performed within 60 seconds or 30 seconds. Since the separator according to this disclosure can be flattened in a short period of time, processing efficiency can be improved.

[0127] In one embodiment of this disclosure, the polymer column having the above-described properties preferably comprises a material that is non-reactive in lithium-ion batteries and provides bonding strength between the separator and the electrode. Taking these aspects into consideration, the polymer column may contain acrylic polymers in amounts such as 10% or more, 30% or more, 50% or more, 70% or more, or 90% or more, relative to 100% by weight. In this disclosure, the polymer column may comprise acrylic polymers. For example, acrylic polymers may comprise at least one repeating unit from the following: acrylates based on acrylates, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. However, acrylic polymers are not limited to these. Furthermore, in one specific embodiment, at least one hydrogen atom in the unit may be replaced by an additional substituent. In one embodiment of this disclosure, the acrylic polymer may contain the repeating unit described above in amounts of 30% or more, 50% or more, 70% or more, or 90% or more, relative to 100% by weight of the acrylic polymer.

[0128] Furthermore, in one embodiment of this disclosure, the weight-average molecular weight of the acrylic polymer can be from about 20,000 to 800,000. In one embodiment of this disclosure, the cross-sectional area (b) of at least one of the polymer columns observed in a section at the upper 5% of the inorganic coating from the uppermost portion downwards can be greater than the cross-sectional area (a) of the polymer column observed in a section at the lower 5% of the inorganic coating from the lowermost portion towards the surface portion. This characteristic of the polymer columns can correspond to the polymer columns protruding from the surface of the inorganic coating and / or flattening by compression. Preferably, this characteristic can be defined as the polymer columns after protrusion and subsequent flattening.

[0129] Together with or independently of this, in a cross-section of the polymer column observed in a vertical section of the inorganic coating, the lower diameter (a) of at least one of the polymer columns may be smaller than the upper diameter (b). In one embodiment, the ratio of the upper diameter (b) to the lower diameter (a) may be greater than 1 and less than 20, 1.2 to 20, 1.5 to 20, or 2 to 20. This characteristic of the polymer column may correspond to the polymer column protruding from the surface of the inorganic coating and / or being flattened by pressing. Preferably, this characteristic can be determined in the form of the polymer column after flattening. In one embodiment of this disclosure, the upper diameter refers to the diameter measured at 5% of the uppermost point of the polymer column towards the lower part, and the lower diameter refers to the diameter measured at 5% of the lowermost point of the polymer column towards the upper part.

[0130] In one embodiment of this disclosure, the height of the polymer column, the diameter of the polymer column, and / or its cross-sectional dimensions can be calculated from SEM images of the horizontal or vertical cross-section of the separator. Figure 2 An SEM image of the surface of the separator according to Embodiment 1 of this disclosure is shown, in which the dimensions of each component can be identified. As another method of using the SEM image, the SEM image is divided into gray levels, and the area corresponding to a specific gray level corresponding to the polymer column can be measured. A gray level refers to the brightness of multiple pixels contained in the SEM image. For example, in an SEM image with 256 gray levels of 0 to 255, the brightness can be in the range of 0 to 255. In a specific embodiment of this disclosure, the gray level of the polymer column can be in the range of 10 to 50, and the gray level of the inorganic particles can be in the range of 160 to 220. Therefore, in an SEM image of any cross-section of the separator, the region of the polymer column can be defined and defined by pixels with gray levels of 10 to 50, and its length and area can be calculated. In this disclosure, cross-sectional SEM images of the electrode can be obtained by energy-dispersive X-ray spectroscopy (EDS) mapping of the components on the cross-section of the electrode obtained by argon (Ar) ion milling using an EDS detector of a scanning electron microscope (SEM) apparatus, followed by image processing.

[0131] In another specific embodiment of this disclosure, the diameter or area of ​​the polymer column can be calculated by three-dimensional modeling of the separator and / or inorganic coating, thereby obtaining an arbitrary cross-section.

[0132] Inorganic particle-filled portion

[0133] In the inorganic coating of the separator, the spaces between the polymer columns can be filled with inorganic particles. In this specification, the portion filled with inorganic particles is referred to as the "inorganic particle-filled portion." The inorganic particle-filled portion may also contain a binder resin to ensure bonding strength between the inorganic particles and between the inorganic particles and the porous substrate. The inorganic particle-filled portion has pores created by interstitial volumes (spaces formed between adjacent inorganic particles). The inorganic coating can have a porous structure with a predetermined porosity due to these pores, thereby allowing gas or liquid to flow from one side surface to another. The inorganic particles and polymer columns can be bonded to each other due to adhesive properties or via a binder resin.

[0134] In one embodiment of this disclosure, the thickness T of the inorganic particle filling portion i This can be the D of the polymer column before the separator is flattened. 50 85% or less. For example, thickness T i It can range from 5% to 40%. In one specific implementation, T i The thickness can range from 1.0 μm to 5 μm, and can be appropriately adjusted within this range. T can be, for example, 4 μm or less, 3 μm or less, or 2 μm or less. i The thickness can preferably be 1.0 μm or greater, and within the above-mentioned numerical range, it exhibits excellent adhesion to the electrodes, thus improving the cell strength of the battery. Meanwhile, a thickness of 5.0 μm or less is advantageous in terms of battery cycle characteristics and resistance characteristics. When the inorganic coating is disposed on both surfaces of the porous substrate, the thickness of the inorganic particle-filled portion refers to the value measured for the inorganic coating disposed on either surface.

[0135] In one embodiment of this disclosure, the height (thickness, T) of the inorganic particle filling portion i The thickness can be determined by cutting a cross-section of the separator specimen, observing the cross-section using SEM, and then measuring the thickness at two or more arbitrary points in the area where no polymer columnar structure is present, taking the average of these measurements as the height. When measuring the thickness at four or more points, the lowest and / or highest values ​​can be excluded, and the average of the remaining values ​​can be taken.

[0136] Meanwhile, in one embodiment of the present disclosure, as the inorganic particle-filled portion approaches the polymer column, the height of the inorganic particle-filled portion may tend to increase. For the surrounding area of the polymer column, this trend may be more obvious. In other words, outside the surrounding area, the height of the inorganic particle-filled portion may gradually increase from any point of the inorganic particle-filled portion towards the polymer column, and this height may increase relatively sharply from the boundary of the surrounding area towards the polymer column. In one embodiment of the present disclosure, the surrounding area may refer to a portion having a width of about 2 μm from the boundary between the inorganic particle-filled portion and the polymer column towards the inorganic particle-filled portion.

[0137] Inorganic particles

[0138] In a specific embodiment of the present disclosure, the inorganic particles are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles that can be used in the present disclosure are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the electrochemical device in which they are used (e.g., 0 V to 5 V based on Li / Li+). In particular, using inorganic particles with a high dielectric constant as the inorganic particles helps to increase the degree of dissociation of electrolyte salts such as lithium salts in the electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0139] For the above reasons, the inorganic particles preferably include high-dielectric inorganic particles having a dielectric constant of 5 or greater, and preferably 10 or greater. Non-limiting examples of inorganic particles having a dielectric constant of 5 or greater include BaTiO3, Pb(Zr,Ti)O3 (PZT), b 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), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2 or a mixture thereof.

[0140] In addition, as the inorganic particles, inorganic particles having lithium ion transfer ability can be used, that is, inorganic particles containing lithium element but not storing lithium but having the function of transporting lithium ions. Non-limiting examples of inorganic particles having lithium ion transfer ability include glass based on (LiAlTiP) x O y (0 < x < 4, 0 < y < 13), such as lithium phosphate (Li3PO4); lithium titanium phosphate (Lix Ti y (PO4)3, where 0 < x < 2 and 0 < y < 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, where 0 < x < 2, 0 < y < 1, and 0 < z < 3) or 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5; lithium germanium thiophosphate (Li x Ge y P z S w , where 0 < x < 4, 0 < y < 1, 0 < z < 1, and 0 < w < 5), such as lithium lanthanum titanate (Li x La y TiO3, where 0 < x < 2 and 0 < y < 3) or Li 3.25 Ge 0.25 P 0.75 S4; lithium nitride (Li x N y , where 0 < x < 4 and 0 < y < 2), such as Li3N; glass based on SiS2 (Li x Si y S z , where 0 < x < 3, 0 < y < 2, and 0 < z < 4), such as Li3PO4 - Li2S - SiS2; glass based on P2S5 (Li x P y S z , where 0 < x < 3, 0 < y < 3, and 0 < z < 7), such as LiI - Li2S - P2S5; or a mixture thereof.

[0141] In addition, the average particle size of the inorganic particles is not particularly limited, but it can be preferably in the range of 0.1 μm to 1.5 μm to form a coating with a uniform thickness and appropriate porosity. When the average particle size is less than 0.1 μm, the dispersibility may decrease, and when the average particle size is greater than 1.5 μm, the thickness of the formed coating may increase. According to a non - restrictive embodiment of the present disclosure, the diameter (D 50 ) of the inorganic particles can be appropriately adjusted within the range of 0.1 μm to 1.5 μm, and for example, it can be within the range of 200 nm to 1 μm.

[0142] Binder resin

[0143] In addition, as described above, the inorganic coating can also contain a binder resin to supplement the bonding strength. Relative to 100% by weight of the inorganic coating, the binder resin can be included in an amount of about 10% by weight or less, 5% by weight, 1% by weight or less, or 0.5% by weight or less.

[0144] In one embodiment of this disclosure, the adhesive resin may comprise a PVdF-based polymer resin. The PVdF-based polymer resin may include at least one of the following: a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and monomers thereto, and mixtures thereof. In one embodiment of this disclosure, examples of said monomers may include fluorinated monomers, chlorine-based monomers, etc. Non-limiting examples of fluorinated monomers may 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-m-dioxane); perfluoro(2,2-dimethyl-1,3-m-dioxane) (PDD); and so on, and may include one or more of them.

[0145] Together with or independently of this, the adhesive resin may also comprise a (meth)acrylate polymer resin. The (meth)acrylate polymer comprises (meth)acrylates as monomers, and non-limiting examples may include the following (meth)acrylate polymers comprising the following monomers: butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, or tetradecyl (meth)acrylate.

[0146] Furthermore, in one embodiment of this disclosure, the inorganic coating may also contain additives, such as dispersants and / or thickeners, in an amount ranging from 1% to 3% by weight relative to 100% by weight of the inorganic coating. In one embodiment of this disclosure, one or more of the following may be suitably selected and used as additives: polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and cyanoethylene polyvinyl alcohol.

[0147] Method for manufacturing a separator

[0148] Next, a method for manufacturing the separators of this disclosure will be described. However, the following description relates to one embodiment of manufacturing the separators of this disclosure, and the method is not particularly limited thereto.

[0149] Specifically, inorganic particles are first introduced into a suitable solvent to prepare a mixture. Then, polymer particles for polymer columns are introduced into the mixture to prepare a slurry for the inorganic coating. The slurry is then applied to a porous substrate and dried.

[0150] In one embodiment of this disclosure, when the inorganic coating also comprises a binder resin, a polymer solution is prepared by dissolving the binder resin in a solvent. Inorganic particles and polymer particles for polymer columns can then be introduced sequentially or simultaneously into the polymer solution to prepare a slurry for the inorganic coating. The binder resin is preferably a water-soluble binder resin.

[0151] The obtained separators are then dried to integrally form an inorganic coating on the porous substrate. In this study, to prevent deformation of the polymer columnar material, the drying temperature of the separators is preferably set to a temperature no more than 20°C higher than the observed glass transition temperature of the polymer columnar material.

[0152] When preparing the slurry, water or an aqueous solvent containing water can be used as the solvent. Furthermore, when there are limitations in terms of drying speed and temperature, methanol, ethanol, isopropanol, etc., which have lower boiling points than water, can be used as a co-solvent.

[0153] The slurry can be applied using existing coating methods such as Mayer bars, slot die coaters, reverse roll coaters, or gravure coaters. Simultaneously, drying can be performed using general methods for solvent removal. Examples of drying methods include natural drying, forced-air drying, warm or hot air drying, high-temperature drying, convection drying, etc., however, the drying methods are not limited to these.

[0154] In addition to the manufacturing methods described above, any manufacturing method capable of realizing the above-mentioned separator structure can be applied without restriction.

[0155] This disclosure also provides a secondary battery including the aforementioned separator. The battery includes: a negative electrode; a positive electrode; and a separator located between the negative and positive electrodes, and the separator is provided with the aforementioned characteristics.

[0156] In this disclosure, the positive electrode comprises a positive current collector and a positive active material layer comprising a positive active material, a conductor, and a binder resin on at least one side surface of the current collector. The positive active material may include one or a mixture of two or more of the following: layered compounds, such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium manganese oxides, such as those with the chemical formula Li...1+x Mn 2-x O4 (where x is from 0 to 0.33), LiMnO3, LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5 or Cu2V2O7; represented by 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) of Ni-site type lithium nickel oxide; represented by the chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn) of lithium manganese composite oxide; LiMn2O4 in which some Li in the chemical formula is replaced by alkaline earth metal ions; disulfide compounds; and Fe2(MoO4)3.

[0157] In the present disclosure, the negative electrode is provided with a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductor, and a binder resin on at least one side surface of the current collector. The negative electrode may contain, as the negative electrode active material, one or a mixture of two or more selected from the following: lithium metal oxides; carbon such as non-graphitizable carbon or graphite-based carbon; metal composite oxides such as Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1) and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2 or Group 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); 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 titanium oxide.

[0158] In one specific embodiment of this disclosure, the conductor may be, for example, selected from any of the following: graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. More specifically, the conductor may be selected from one of the following: natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lampblack, thermal cracking black, Tenca black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0159] There are no particular restrictions on the current collector, as long as it has high conductivity and will not cause chemical changes to the corresponding battery. For example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used.

[0160] As the binder resin, polymers commonly used in electrodes in the art can be used. Non-limiting examples of such binder resins may include, but are not limited to, polyvinylidene fluoride-copolyhexafluoropropylene, polyvinylidene fluoride-copolytrichloroethylene, polymethyl methacrylate, ethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-copolyvinyl acetate, polyethylene oxide, polyarylates, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc.

[0161] Manufacture of a battery

[0162] The method for manufacturing a battery disclosed herein is characterized by performing a first compression (dry compression) during the manufacture of the electrode assembly or before impregnation with an electrolyte, and then performing a second compression after impregnating the electrode assembly with an electrolyte and softening the polymer column with the electrolyte.

[0163] First, a laminate comprising at least one positive electrode, at least one spacer, and at least one negative electrode is prepared. The laminate is formed by laminating the positive electrode, negative electrode, and spacer therebetween at least once. The components constituting the laminate, such as the electrodes and spacers, are not in close contact with each other but are simply stacked. The laminate is then pressed at a temperature of 55°C to 65°C and a strength of 3.0 MPa to 4.0 MPa to prepare a first electrode assembly. Here, the polymer columns in the spacer are not completely flattened. Because the polymer columns are not completely flattened before being impregnated with the electrolyte as described above, and because a certain distance is maintained between the spacer and the electrode, the electrolyte can advantageously flow into the first electrode assembly. In other words, it has the advantage of ensuring a flow path for the electrolyte.

[0164] Next, the first electrode assembly is immersed in the electrolyte, followed by a second compression. The second compression includes applying a pressure of 0.5 MPa to 1.5 MPa to the immersed first electrode assembly. The pressure is applied to the immersed first electrode assembly to ensure close contact between the separator and the positive electrode and / or the separator and the negative electrode, and preferably this pressure is applied at a temperature of 35°C to 85°C. After the electrode assembly is sufficiently immersed in the electrolyte, the second compression is performed to ensure close contact between the electrode and the separator as described above. Therefore, it has the advantage of improved wettability of the electrode assembly. Simultaneously, the step of immersing the first electrode assembly in the electrolyte includes storing the first electrode assembly in a battery case, and an aging step may also be performed after immersion and before applying pressure. Aging can preferably be performed in the range of 20°C to 75°C.

[0165] In this disclosure, the electrolyte comprises a liquid having a component such as A + B - (where A) + Including alkali metal cations such as Li + Na + or K + or combinations thereof, ions, and B - Including anions such as PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - Or C(CF2SO2)3 -An electrolyte is obtained by dissolving or dissociating a salt of an ion (or a combination thereof) in an organic solvent, said organic solvent including propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone (g-butyrolactone), ester-based compounds, or mixtures selected from one or more of these, however, the electrolyte is not limited thereto.

[0166] Furthermore, in one specific embodiment of this disclosure, the organic solvent may comprise an ester-based compound. The ester-based compound may preferably be included in an amount of 30% or more, 50% or more, 60% or more, or 65% or more, relative to 100% by weight of the organic solvent.

[0167] In one specific embodiment of this disclosure, the ester-based compound may include at least one selected from: isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0168] Furthermore, this disclosure 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 this device may include: power tools that operate by receiving power from an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheeled bicycles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; systems for energy storage; and so on, but are not limited thereto.

[0169] The present disclosure will be described in detail below with reference to embodiments in order to specifically describe the present disclosure. However, embodiments based on the present disclosure may be modified in various other forms, and the scope of the present disclosure should not be construed as limited to the embodiments described below. Embodiments of the present disclosure are provided to describe the present disclosure more fully to those skilled in the art.

[0170] Example

[0171] Measurement of the thickness of the separator

[0172] In the examples and comparative examples, the thickness of the separator was determined by cutting a cross-section of the separator sample, observing the cross-section using SEM, and then taking the thickness at the thickest point as the thickness of the separator. The thickness of the separator was measured after the first and second compressions to calculate the compression ratio, and the results are summarized in Table 2. Simultaneously, the thickness of the inorganic particle filling portion was determined as the average of the values ​​measured at three arbitrary points.

[0173] Measurement of storage modulus of polymer columnar materials

[0174] Samples with dimensions of 40 mm × 60 mm were prepared using the polymer material to be used as polymer columns in the comparative examples and embodiments. The thickness of the samples was 1 mm. The storage modulus of the samples was measured. The storage modulus was measured using a rheological analyzer (Dynamic Mechanical Analyzer (DMA), ARES-G2, TA Instrument). The storage modulus was determined by performing temperature scan tests at a temperature condition of -60°C to 80°C and a frequency of 1.0 rad / s. The results are summarized in Table 1 below. In addition, the storage modulus and loss modulus were determined during the measurement, and the tan δ peak was determined from them.

[0175] Measurement of the solubility of polymer columnar materials

[0176] A 0.3 g sample was prepared using the polymer material to be used as the polymer column in each comparative example and embodiment. The sample was placed on an 80 mesh sieve and dissolved in THF (tetrahydrofuran) for 24 hours, after which the weight of the remaining residue was compared with the initial weight. Solubility was calculated based on Equation 1 below. The results are summarized in Table 1 below.

[0177] [Equation 1]

[0178] Solubility (%) = {(Weight measured before impregnation - Weight measured after impregnation) / (Weight measured before impregnation)} × 100

[0179] [Table 1]

[0180]

[0181] Example 1

[0182] Inorganic particles (Al2O3, D) 50An acrylic emulsion (Toyo Corporation, CSB-130) and carboxymethyl cellulose (Daicel Corporation, Daicel 1220), approximately 0.6 μm thick, used as a binder resin, and were introduced into a solution of water and ethanol (95:5) at a ratio of 96:2:2, and dispersed using a bead mill to obtain a mixture. Acrylic polymer A100 was introduced into the mixture, and the resulting product was stirred to obtain a dispersion slurry. The mixed polymer columns had a solubility of 25% and a storage modulus of 1,245 Pa at room temperature. The concentration of solids in the dispersion slurry was 30% by weight. In the mixture, the content of polymer particles used for the polymer columns was approximately 20 parts by weight relative to 100 parts by weight of inorganic particles. The dispersion slurry was applied to a porous substrate (Senior SW807I, 7 μm thick) using a microgravure coating method and dried at 80°C to obtain separators. Furthermore, the opposite surface was coated and dried in the same manner to obtain a double-sided coated separator. In the separator, based on a porous substrate on one side, the loading of the inorganic coating (one side) was 6.2 g / m². 2 .

[0183] The obtained separator was then compressed for 20 seconds using a hot press at 2.5 MPa and 60°C to determine the compression ratio of the separator. Figure 3 SEM images of the surface of the separator obtained after the first compression are shown. Referring to these images, it is determined that polymer columns are exposed on the inorganic coating surface, and that multiple polymer columns are spaced apart at predetermined distances and distributed in an island-like pattern. Furthermore, it is determined that the protruding portions of the polymer columns are not flattened.

[0184] Next, an electrolyte was prepared by mixing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 7:3 and adding 1 M LiPF6. The separator after the first compression was immersed in the electrolyte and allowed to stand for approximately 5 minutes. Afterward, the immersed separator was removed, and the remaining electrolyte was dried. The resulting separator was then subjected to a second compression using a hot press at 1.0 MPa and 60°C for 20 seconds, and the compression ratio of the separator was determined. Referring to Table 2 below, the thickness of the separator after the second compression was 10.1 μm, indicating a thickness reduction of 30% or more compared to the initial thickness of the separator before compression.

[0185] Comparative Example 1

[0186] Inorganic particles (Al2O3, D) 50An acrylic emulsion (Toyo Corporation, CSB-130) and carboxymethyl cellulose (Daicel Corporation, Daicel 1220), approximately 0.6 μm in diameter, serving as a binder resin, were introduced into a solution of water and ethanol (95:5) at a ratio of 96:2:2, and dispersed using a bead mill to obtain a mixture. An acrylic polymer (A24, D...) was then introduced into the mixture. 50 The mixture was stirred to obtain a dispersion slurry (4.22 μm thick). The concentration of solids in the dispersion slurry was 30% by weight. In the mixture, the content of polymer particles for the polymer columns was approximately 20 parts by weight relative to 100 parts by weight of inorganic particles. The dispersion slurry was applied to a porous substrate (Senior SW807I, 7 μm thick) using a microgravure coating method and dried at 80°C to obtain a separator. Furthermore, the opposite surface was coated and dried in the same manner to obtain a double-sided coated separator. In the separator, the loading of the inorganic coating (one side) was 6.1 g / m² based on one side of the porous substrate. 2 .

[0187] The obtained separator was then compressed for 20 seconds using a hot press at 2.5 MPa and 60°C to determine the compression ratio of the separator. Figure 5 SEM images of the surface of the separator obtained after the first compression are shown. Referring to these images, it is determined that polymer columns are exposed on the inorganic coating surface, and that multiple polymer columns are spaced apart at predetermined distances and distributed in an island-like pattern. Furthermore, it is determined that all protrusions within the polymer columns are flattened.

[0188] Next, the second compression ratio was determined in the same manner as in Example 1. Although the second compression ratio was 30% or greater, the thickness had already been significantly reduced in the first compression, and it was determined that the amount of reduction by the second compression after the first compression was not significant.

[0189] Comparative Example 2

[0190] Inorganic particles (Al2O3, D) 50 An acrylic emulsion (Toyo Corporation, CSB-130) and carboxymethyl cellulose (Daicel Corporation, Daicel 1220), approximately 0.6 μm thick, serving as a binder resin, were introduced into a solution of water and ethanol (95:5) at a ratio of 96:2:2, and dispersed using a bead mill to obtain a mixture. An acrylic polymer (A25, D...) was then introduced into the mixture. 50The mixture was stirred to obtain a dispersion slurry (3.92 μm thick). The concentration of solids in the dispersion slurry was 30% by weight. In the mixture, the content of polymer particles for the polymer columns was approximately 20 parts by weight relative to 100 parts by weight of inorganic particles. The dispersion slurry was applied to a porous substrate (Senior SW807I, 7 μm thick) using a microgravure coating method and dried at 80°C to obtain a separator. Furthermore, the opposite surface was coated and dried in the same manner to obtain a double-sided coated separator. In the separator, the loading of the inorganic coating (one side) was 6.4 g / m² based on one side of the porous substrate. 2 .

[0191] The obtained separators were then compressed for 20 seconds using a hot press at 2.5 MPa and 60°C to perform a first compression, and the compression ratio of the separators was determined. Furthermore, as a result of surface observation, it was determined that polymer columns were exposed on the inorganic coating surface, and that multiple polymer columns were spaced at predetermined distances and distributed in an island-like pattern. Additionally, it was determined that all protrusions within the polymer columns were flattened.

[0192] Next, the second compression ratio was determined in the same manner as in Example 1. Although the second compression ratio was 30% or greater, as in Comparative Example 1, the thickness had already been significantly reduced in the first compression, and it was determined that the amount of reduction by the second compression after the first compression was not significant.

[0193] Comparative Example 3

[0194] Inorganic particles (Al2O3, D) 50 An acrylic emulsion (Toyo Corporation, CSB-130) and carboxymethyl cellulose (Daicel Corporation, Daicel 1220), approximately 0.6 μm thick, serving as an adhesive resin, and water and ethanol (95:5) were introduced at a ratio of 96:2:2, and the mixture was stirred to obtain a mixture. The mixture was applied to a porous substrate (Senior SW807I, 7 μm thick) using a microgravure coating method and dried at 80°C. Simultaneously, the obtained separator was subjected to a first compression for 20 seconds at 2.5 MPa and 60°C using a hot press to flatten the surface. Next, a second compression ratio was determined in the same manner as in Example 1. It was determined that Comparative Example 3 had a significantly lower compression ratio obtained by the first and second compressions compared to Example 1.

[0195] [Table 2]

[0196]

[0197] Manufacturing of the positive electrode

[0198] A positive electrode active material slurry was prepared by adding LiCoO2 (as the positive electrode active material), carbon black (as the conductor), and polyvinylidene fluoride (PVdF) (as the binder) to the solvent N-methylpyrrolidone (NMP) in a weight ratio of 96:2:2. The positive electrode active material slurry was coated onto a sheet-like aluminum current collector and dried to achieve a final positive electrode loading of 3.8 mAh / cm³. 2 The positive electrode active material layer.

[0199] Manufacturing of negative electrode

[0200] A negative electrode slurry was formed by mixing artificial graphite as the negative electrode active material, carbon black as the conductor, carboxymethyl cellulose as the dispersant, and styrene-butadiene emulsion as the binder in a weight ratio of 96:0.5:1.5:2.0, and then adding the mixture to water as a solvent. The negative electrode slurry was then used at a concentration of 4.0 mAh / cm³. 2 The loading amount is coated onto a copper current collector and dried to manufacture a negative electrode in which a layer of negative electrode active material is formed.

[0201] Evaluation of the adhesion (dry adhesion) between the negative electrode and the separator

[0202] The separator samples obtained in each embodiment and comparative example were cut into dimensions of 100 mm (length) × 25 mm (width) to prepare individual specimens. Each specimen was laminated with a negative electrode and then hot-pressed at 60°C for 20 seconds to obtain a first electrode assembly (dry adhesion force was measured). The laminate was fixed to an adhesive strength measuring device (LLOYD Instrument, LF plus), and the separator portion was peeled off at a rate of 25 mm / min at a 180° angle at 25°C, and the corresponding strength was measured.

[0203] Referring to Table 2, the separator in Comparative Example 3 did not adhere to the electrode. Meanwhile, Example 1 ensured adhesive strength comparable to the separator in the Comparative Example while having a lower compression ratio for the same pressing time. Therefore, the separator according to this disclosure exhibits excellent adhesion and ensures the electrolyte impregnation path, thus providing advantages in processability.

[0204] Determination of Li plating after battery assembly

[0205] First, the positive and negative electrodes were prepared as described above, and the separators of each embodiment and comparative example were inserted between them to prepare a laminate. Then, the laminate was pressed at 60°C and a pressure of 2.5 MPa to prepare a first electrode assembly. Next, the first electrode assembly was inserted into a battery case, an electrolyte was injected, and the case was sealed. It was allowed to stand for approximately 5 minutes. Then, the resulting battery was activated at approximately 40°C under a pressure of 1.0 MPa and a charge rate of 0.5 C until a State of Charge (SOC) of 65 was achieved. An electrolyte was obtained using a mixture of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 7:3, with 1 M LiPF6 added. After activation, the battery was subjected to 10 consecutive charge and discharge cycles at a charge rate of 1.0 C and a discharge rate of 1.0 C. Then, the battery was disassembled at an SOC of 80, and the deposition level on the negative electrode surface was determined.

[0206] Measurement of molecular weight

[0207] Molecular weight (weight-average molecular weight / number-average molecular weight) was measured by gel permeation chromatography (GPC). An Agilent Technologies PL GPC220 was used, and the measurement conditions are as follows.

[0208] - Column (Manufacturer, Model): 2×TSKgel SupermultiporeHZ-M+TSKgel SuperHZ-2500

[0209] - Eluent: THF

[0210] - Temperature: 40℃

[0211] - Flow rate: 1.0 mL / min

[0212] - Injection volume and sample concentration: 30 μL, and 1 mg / mL to 10 mg / mL

[0213] - Standard material: Polystyrene

[0214] - Detector: RI

[0215] Measurement of glass transition temperature

[0216] The glass transition temperature (Tg) was measured using a differential scanning calorimeter (DSC, TA Instrument). Each obtained sample (10 mg to 15 mg) was cooled from ambient temperature to -30 °C and then heated to 200 °C at a rate of 10 °C / min. The samples were then cooled to -30 °C and reheated at 10 °C / min while the glass transition temperature was measured.

[0217] [Figure Labels]

[0218] 10 Porous Substrates

[0219] 20 Inorganic Coating

[0220] 100 polymer columnar bodies

[0221] 200 inorganic particles

[0222] T s Thickness of the separator

[0223] T p The protrusion height of the polymer column

[0224] T i The height of the inorganic particle filling section, T c Height of inorganic coating

Claims

1. A separator for an electrochemical device, the separator comprising: Porous polymer substrate; and An inorganic coating covering one or both surfaces of the porous polymer substrate. The inorganic coating comprises a plurality of adhesive polymer columns, each having a predetermined volume, and the polymer columns are made of a polymer material and are non-porous. At least a portion of the polymer columnar structure is exposed on the surface of the inorganic coating, and another portion is in contact with the surface of the porous substrate. At least one of the polymer columns is spaced apart from the other polymer column by a predetermined distance. The spaces between the polymer columns are filled with inorganic particles. The polymer column has a storage modulus (G') of 100 Pa or greater and 3,500 Pa or less at room temperature. The polymer columnar material has a solubility of 15% to 70% in THF, and The solubility is determined according to the following Equation 1: [Equation 1] Solubility (%) = {(Weight measured before impregnation - Weight measured after impregnation) / (Weight measured before impregnation)} × 100.

2. The separator according to claim 1, wherein the first compression ratio obtained by the first compression of the separator under compression conditions of 2.0 MPa to 4.0 MPa and 55°C to 65°C is 20% to 25%. The first compression ratio is a value calculated using the following Equation 2, and refers to the compression ratio of the separator before contact with the electrolyte (dry compression ratio), and The height (T) of the inorganic coating after compression under the above conditions c ) is 1.1×T i <T<1.5×T i And the protruding height of the polymer column after the compression is 1 μm or greater: [Equation 2] First compression ratio (%) = {(Initial thickness before first compression - Thickness after first compression) / (Initial thickness before first compression)} × 100.

3. The separator according to claim 2, wherein the second compression ratio obtained by the second compression of the separator under compression conditions of 0.5 MPa to 1.5 MPa and 35°C to 85°C is 30% or greater. The second compression ratio is calculated by the following Equation 3, and refers to the compression ratio (wet compression ratio) obtained after the first compression, in which the separator is immersed in the electrolyte for 5 minutes or longer and then the electrolyte on the surface is removed, and the separator is pressed under the above conditions. After the second compression, the thickness (T) of the inorganic coating is 1.0 × T. i <T c ≤1.1×T i ,as well as After the second compression, the protruding thickness of the polymer column is 1 μm or less: [Equation 3] Second compression ratio (%) = {(Initial thickness before first compression - Thickness after second compression) / (Initial thickness before first compression)} × 100.

4. The separator according to claim 1, wherein the D of the polymer columnar body 50 D of the inorganic particles 50 At least twice as much.

5. The separator according to claim 1, wherein the inorganic coating comprises the polymer columnar body in an amount of 10% to 50% by volume, based on 100% by volume of the inorganic particles.

6. The separator according to claim 1, wherein the thickness (T) of the inorganic particle portion is... i ) is the D of the polymer column. 50 85% or less.

7. The separator according to claim 1, wherein the D of the polymer columnar body 10 D 50 30% or more, and the D of the polymer column 90 D 50 200% or less.

8. The separator according to claim 1, wherein, based on a top view of the separator, the area occupied by the polymer column is 10% to 50% relative to 100% of the surface area of ​​the inorganic coating.

9. The separator according to claim 1, wherein the cross-sectional area (b) of at least one of the polymer columns included in the inorganic coating, observed in a section at 5% of the upper portion of the inorganic coating toward its lower portion, is greater than the cross-sectional area (a) of the polymer column observed in a section at 5% of the lower portion of the inorganic coating toward its surface portion.

10. The separator according to claim 1, wherein in the cross-section of the polymer column observed in the vertical section of the inorganic coating, the lower diameter (a) of at least one of the polymer columns included in the inorganic coating is smaller than the upper diameter (b) of the polymer column, and the ratio of the diameter (b) to the diameter (a) is 2 to 20.

11. The separator according to claim 1, wherein the inorganic coating has a porous structure formed by the interstitial volume between the inorganic particles.

12. An electrochemical device comprising the separator according to claim 1.

13. A method for manufacturing a battery, the method comprising: Prepare a laminate comprising at least one positive electrode, at least one separator and at least one negative electrode, wherein the positive electrode, the negative electrode and the separator between the positive electrode and the negative electrode are laminated at least once; The laminate is pressed at a temperature of 55°C to 65°C with a strength of 3.0 MPa to 4.0 MPa to prepare a first electrode assembly; The first electrode assembly is immersed in electrolyte; as well as A pressure of 0.5 MPa to 1.5 MPa is applied to the impregnated first electrode assembly. The separator described therein is the separator according to claim 1.

14. The method of claim 13, wherein pressure is applied to the impregnated first electrode assembly to bring the separator into close contact with the positive electrode and / or the separator with the negative electrode, and the pressure is applied at a temperature of 35°C to 45°C.

15. The method of claim 13, wherein immersing the first electrode assembly in the electrolyte comprises storing the first electrode assembly in a battery case and aging it after the immersion and before applying the pressure.

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