Separator for electrochemical device, and method for manufacturing same

Abstract

The present invention provides a separator for an electrochemical device, comprising: a porous polymer substrate; and an inorganic coating layer for covering one surface or both surfaces of the porous polymer substrate, wherein: the inorganic coating layer includes a plurality of adhesive polymer columns having a predetermined volume; the polymer columns are made of a polymer material and have no pores; at least some parts of the polymer columns are exposed to the surface of the inorganic coating layer while other parts thereof are in contact with the surface of the porous polymer substrate; at least one polymer column is spaced a predetermined distance apart from another polymer column; the space between the polymer columns is filled with inorganic particles; and, on the basis of the top view of the separator, the area occupied by the surface area of the polymer column exposed to the surface of the inorganic coating layer is 10% to 80% with respect to 100% of the surface area of the inorganic coating layer.

Description

Separator for electrochemical devices and method for manufacturing the same

[0001] The present invention relates to a separator for electrochemical devices such as lithium ion secondary batteries.

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2023-0194145, filed with the Korean Intellectual Property Office on December 28, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Non-aqueous secondary batteries, such as lithium-ion secondary batteries, are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras, and camcorders. Furthermore, due to their high energy density, these batteries are also being considered for use in automobiles.

[0005] Lithium secondary batteries currently in production use porous polymer substrates, such as polyolefin polymer resins, as separator substrates to prevent short circuits between the positive and negative electrodes. However, these polymer substrates have low heat resistance due to shrinkage or melting at high temperatures. Therefore, when the battery is exposed to internal or external stimuli, the separator shrinks or melts, increasing the likelihood of the positive and negative electrodes contacting each other and causing a short circuit. This can lead to a rapid release of electrical energy, potentially leading to battery explosion or ignition.

[0006] Accordingly, in order to solve the above problems, a method of improving heat resistance by forming a porous heat-resistant layer on at least one side of a polymer substrate, in which inorganic particles and a binder resin are mixed, is widely used. However, the heat-resistant layer must have sufficient porosity in terms of securing an ion transport path and electrolyte impregnation. The pores of the heat-resistant layer originate from the interstitial volume between the inorganic particles. However, if the content of the binder resin is high, the interstitial volume is blocked by the binder resin, making it difficult to secure sufficient porosity. On the other hand, if the content of the binder resin is insufficient, the electrode and the separator may not be closely adhered, resulting in separation between the electrode and the separator during the battery manufacturing process or battery operation.

[0007] Meanwhile, electrode assemblies are typically manufactured using a roll-to-roll continuous process, during which a lamination process is performed to pressurize the stacked electrodes and separator. To ensure the desired level of electrode-separator bonding, sufficient lamination time must be secured, but this can lead to reduced productivity, such as reduced production speed.

[0008] Accordingly, continuous research and development is required to secure sufficient porosity and electrode-separator adhesion in electrochemical device separators and to improve process efficiency.

[0009]

[0010] The present invention aims to provide a separator that can ensure high adhesion to electrodes and improve battery production efficiency. Furthermore, the present invention aims to provide an electrochemical device comprising the separator. It will be readily apparent that other objectives and advantages of the present invention can be achieved by the means or methods described in the claims, and combinations thereof.

[0011]

[0012] One aspect of the present invention relates to a separator for an electrochemical device, wherein the separator comprises a porous polymer substrate and an inorganic coating layer covering one surface or both surfaces of the porous polymer substrate, wherein the inorganic coating layer comprises a plurality of adhesive polymer columns having a predetermined volume, wherein the polymer columns are made of a polymer material and do not have pores, at least a portion of the polymer columns is exposed to the surface of the inorganic coating layer and another portion is in contact with the surface of the porous polymer substrate, at least one polymer column is spaced apart from another polymer column by a predetermined distance, and a space between the polymer columns is filled with inorganic particles, and the surface area of ​​the polymer columns exposed to the surface of the inorganic coating layer is 10% to 80% of the surface area of ​​the inorganic coating layer based on a top view of the separator, and the zeta potential of the polymer columns in a dispersed state is -20 mV or less at room temperature.

[0013] In the above-described aspect of the present invention, when the separation membrane is pressurized for 1 second to 60 seconds under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C, the average sphericity of the polymer column according to the following formula 1 may be 0.5 or more and 1.0 or less.

[0014] [Formula 1]

[0015] Sphericity of polymer column = (short axis / long axis)

[0016] At this time, the sphericity of the polymer column is a value calculated by obtaining a planar image (top view) by photographing the surface of the inorganic coating layer obtained when the separation membrane is pressurized under the pressure and temperature conditions using a scanning electron microscope (SEM), obtaining the average length of the long axis of the polymer column particles from the planar image, and obtaining the average length of the short axis of the polymer column particles.

[0017] In any one of the aforementioned aspects of the present invention, when the separation membrane is pressurized for 1 second to 60 seconds under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C, the ratio of the homopolymer column of the following formula 2 may be 80% or more, and the homopolymer column may be a polymer column of the following formula 1 having a sphericity of 0.9 or more.

[0018] [Formula 1]

[0019] Sphericity of polymer column = (short axis / long axis)

[0020] [Formula 2]

[0021] Proportion of homopolymer columns (%) = Number of homopolymer columns / Number of total polymer columns x 100

[0022] At this time, the number of polymer columns is determined by photographing the surface of the inorganic surface layer obtained when the membrane is pressurized under the above pressure and temperature conditions using a scanning electron microscope (SEM) to obtain a planar image (top view) of the membrane, and a polymer column distinguished by inorganic particles regardless of shape in the planar image is defined as one polymer column.

[0023] In any one of the aforementioned aspects of the present invention, when the separation membrane is pressurized for 1 second to 60 seconds under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C, the ratio of dumbbell-shaped polymer columns is 20% or less, and the dumbbell-shaped polymer columns may be two or more single polymer columns overlapping each other.

[0024] The present invention relates to a method for measuring the average diameter (D) of the polymer column based on a planar image (top view) of the separation membrane in any one of the aforementioned aspects. 50 ) may be 2 ㎛ or more and 20 ㎛ or less.

[0025] In any one of the aforementioned aspects of the present invention, the content of the polymer column in the separation membrane may be 5 to 40 parts by weight based on 100 parts by weight of the inorganic particles.

[0026] The present invention relates to any one of the aforementioned aspects, wherein D of the polymer column 10 D of the above polymer column 50 30% or more of the D of the polymer column 50 D of the above polymer column 50 It may be less than 200% of .

[0027] In any one of the aforementioned aspects, the present invention has a thickness of the inorganic particle filling portion made of inorganic particles filled between the polymer columns equal to D of the polymer columns. 50 It may be less than 85% of .

[0028] In any one of the aforementioned aspects, the present invention may be such that the surface area of ​​the polymer column exposed to the surface of the inorganic coating layer may be 10% to 45% of the surface area of ​​the inorganic coating layer relative to 100% of the surface area of ​​the inorganic coating layer based on a planar image (top view) of the separation membrane.

[0029] In any one of the aforementioned aspects of the present invention, the inorganic coating layer may have a pore structure due to interstitial volume between inorganic particles.

[0030] In addition, the present invention provides an electrochemical device including a separator for an electrochemical device according to any one of the aforementioned aspects.

[0031] In the present invention, each of the above embodiments may be implemented independently. Alternatively, two or more of the above embodiments may be implemented in combination.

[0032]

[0033] The separator according to the present invention not only exhibits excellent adhesion to electrodes but also secures sufficient porosity, resulting in superior resistance characteristics. Furthermore, it can shorten the lamination process time during electrode assembly manufacturing, thereby achieving high process efficiency in battery manufacturing.

[0034]

[0035] The drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further enhance the understanding of the technical spirit of the present invention. Therefore, the present invention is not limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0036] Figure 1 is a schematic diagram showing one embodiment of the separation membrane of the present invention.

[0037] Figure 2 schematically illustrates one embodiment of a dumbbell-shaped polymer column.

[0038] Figures 3a and 3b are SEM images of the surface of the inorganic coating layer of the membrane manufactured in Example 1 after compression.

[0039] Figure 3c is a vertical cross-section SEM image of the membrane manufactured in Example 1 before compression.

[0040] Figure 3d is a vertical cross-section SEM image of the membrane manufactured in Example 1 after compression.

[0041] Figures 4a and 4b are SEM images of the surface of the inorganic coating layer of the separation membrane manufactured in Example 3 after compression.

[0042] Figure 5 is an SEM image of the surface of the inorganic coating layer after compression of the separation membrane manufactured in Comparative Example 3.

[0043] Figures 6a and 6b are SEM images for measuring the ratio of the lower diameter and the upper diameter of the polymer column before and after pressurization of the separation membrane manufactured in Example 1.

[0044]

[0045] Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her invention. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical spirit of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0046]

[0047] Justice

[0048] Throughout this specification, when it is said that a part "includes" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0049] In addition, the terms "about", "substantially", etc. used throughout this specification are used in the sense of numerical values ​​or near numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention exact or absolute values ​​to aid understanding of this specification.

[0050] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0051] D in the original specification 50 D means the particle size at the 50% point of the cumulative distribution of the number of particles (or polymer columns) according to particle size. That is, D 50 refers to the particle size at the 50% point of the cumulative distribution of the number of particles (or polymer columns) according to particle size. In addition, D 10 D means the particle size at the 10% point of the cumulative distribution of the number of particles (or polymer columns) according to particle size. 90 It means the particle diameter at the 90% point of the cumulative distribution of the number of particles (or polymer columns) according to particle diameter. The particle diameter can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle (or polymer column) size when the particles pass through the laser beam. By calculating the particle (or polymer column) diameter at the points where it becomes 10%, 50% and 90% of the cumulative distribution of the number of particles (or polymer columns) according to particle diameter in the measuring device, respectively, D 10 , D 50 and D 90 can be measured.

[0052] Certain terminology used in the following detailed description of the invention is for convenience only and is not limiting. The words "left," "right," "upper," and "lower" may indicate directions in the drawings to which reference is made and should not be limiting. The words "inwardly" and "outwardly" indicate directions toward or away from the geometric center of the designated device, system, and its components, respectively. The words "front," "rear," "upper," and "lower," and related words and phrases indicate positions and orientations in the drawings to which reference is made and should not be limiting. These terms include the words listed above, their derivatives, and words of similar import.

[0053] In the present invention, the glass transition temperature (Tg) can be measured through a DSC curve derived from a temperature increase analysis at 10°C / min using a differential scanning calorimeter (DSC).

[0054]

[0055] The present invention relates to a separator for an electrochemical device and an electrochemical device comprising the same. In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept that includes a primary battery and a secondary battery. The secondary battery is a concept that encompasses lithium-ion batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc., and is capable of charging and discharging.

[0056] A separator for an electrochemical device according to the present invention (hereinafter also referred to as a “separator”) comprises a porous polymer substrate including a plurality of pores and an inorganic coating layer formed on at least one surface of the porous polymer substrate.

[0057]

[0058] <Separator>

[0059] The present invention provides a separator for an electrochemical device.

[0060] Figure 1 is a schematic diagram showing a cross-section of a separation membrane of the present invention, and particularly shows the state of the separation membrane before compression.

[0061] In one embodiment of the present invention, the separation membrane includes a porous polymer substrate (10) and an inorganic coating layer (20) formed on at least one side or both sides of the porous polymer substrate (10). The inorganic coating layer (20) includes a plurality of adhesive polymer columns (columns, 100) of a predetermined volume, and includes an inorganic particle filling portion including inorganic particles (200) filled between the polymer columns (100).

[0062] The separator may have a total thickness of 5.0 ㎛ to 30 ㎛ and may be appropriately adjusted within the above range. For example, the thickness may be 25.0 ㎛ or less, 20.0 ㎛ or less, 15.0 ㎛ or less, 12.0 ㎛ or less, or 10.0 ㎛ or less. In one embodiment of the present invention, the separator may be introduced during the manufacture of an electrode assembly and, after a pressurizing process such as lamination is performed to flatten the separator, the thickness may be 15.0 ㎛ or less, 14.0 ㎛ or less, 13.0 ㎛ or less, 12.0 ㎛ or less, 11.0 ㎛ or less, or 10.0 ㎛ or less. In addition, the separator may have a porosity of about 30 vol% to 80 vol%. The porosity may be appropriately adjusted within the above-mentioned range. For example, the porosity may be 30 vol% or more, or 35 vol% or more, or 40 vol% or more, or 50 vol% or more, or 55 vol% or more. Alternatively, the porosity may be 70 vol% or less, or 65 vol% or less, or 60 vol% or less, or 55 vol% or less. Meanwhile, the separation membrane may exhibit a permeability in a range of about 50 sec / 100cc or more and about 250 sec / 100cc or less. The permeability may be appropriately controlled within the above-mentioned range. For example, the permeability may be 60 sec / 100cc or more, or 70 sec / 100cc or more, or 100 sec / 100cc or more, or 120 sec / 100cc or more, or 150 sec / 100cc or more. Alternatively, the porosity may be 220 sec / 100cc or less, or 200 sec / 100cc or less, or 180 sec / 100cc or less.

[0063] In one embodiment of the present invention, the thickness (T) of the separation membrane s ) is a cross-section of a membrane specimen, observed through SEM, and the thickness of the thickest point is measured as the thickness of the membrane (T s) can be used. Or, the thickness of multiple points (more than two points) can be measured and the average value can be used as the thickness of the membrane (T s ) can be used. If the thickness of four or more points is measured, the lowest and / or highest values ​​can be excluded and the average of the remaining values ​​can be taken. When measuring the thickness of the membrane by the average, it is appropriate to measure it based on the polymer column in addition to the inorganic particle filling portion.

[0064]

[0065] In addition, in one embodiment of the present invention, the height (T) of the polymer column c ) can be obtained by cutting a cross-section of a membrane specimen and observing it through SEM, and then taking the value of the highest part of the polymer column.

[0066] In addition, in one embodiment of the present invention, the protrusion height (T) of the polymer column p ) can be obtained by cutting a cross-section of a membrane specimen and observing it through SEM, and then taking the value of the part where the gap between the inorganic particle filling part and the polymer column is the largest.

[0067] In one embodiment of the present invention, the porosity can be calculated by calculating the true density of the measurement object from the density (apparent density) of the measurement object such as a membrane, the composition ratio of materials included in the measurement object, and the density of each component, and calculating the porosity from the difference between the apparent density and the true density. For example, the porosity can be calculated by [Equation 3] below.

[0068] [Formula 3]

[0069] Porosity (vol%) = {1-(apparent density / true density)} × 100

[0070] Meanwhile, the apparent density in the above equation can be calculated from [Equation 4] below.

[0071] [Formula 4]

[0072] Apparent density (g / cm)3 ) = {Weight of the measurement object [g] / (Thickness of the measurement object [cm] × Area of ​​the measurement object [cm 2 ])}

[0073] Alternatively, the porosity or pore size can be measured using an adsorbent gas such as nitrogen using BELSORP (BET equipment) from BEL JAPAN, or by a method such as mercury intrusion porosimetry or capillary flow porosimetry.

[0074] The term 'permeability' used in this specification means the time it takes for 100 cc of air to permeate a permeability measurement target such as a membrane or a porous polymer substrate, and the unit thereof can be second / 100 cc, can be used interchangeably with permeability, and is typically expressed as a Gurely value, etc. In a specific embodiment of the present invention, the permeability can be measured in accordance with JIS P8117. In addition, the air permeability P1 measured in an object having a thickness T1 can be converted into the permeability P2 when the thickness of the object is 20 ㎛ by the formula: P2 = (P1 × 20) / T1.

[0075] In one embodiment of the present invention, the separation membrane may have a compressibility of the thickness of the separation membrane of 25% or more and 95% or less under pressurized conditions of 0.5 MPa to 20 MPa or 1.5 MPa to 4.0 MPa, 20°C to 85°C or 45°C to 65°C. Preferably, the compressibility may be 75% or less, or 60% or less, or 50% or less, or 40% or less within the above range. The compressibility may be calculated by the following [formula].

[0076] [Formula]: Compression ratio (%) = {(Initial thickness of the membrane before compression - Thickness of the membrane after compression) / (Initial thickness of the membrane before compression)} x 100.

[0077]

[0078] In one embodiment of the present invention, the initial thickness of the separator before compression refers to the thickness in a state where no artificial pressurization is performed after manufacturing the separator. The compression ratio and the difference in thickness before and after compression refer to the difference in thickness when compressed in a state where no artificial pressurization is performed after manufacturing the separator, and the ratio of the thickness before and after compression. The thickness of the separator is measured based on the thickest part of the separator before and after compression.

[0079] In one embodiment of the present invention, the separation membrane may have a thickness difference of 4 µm or more before and after compression when pressurized under pressurized conditions of 0.5 MPa to 20 MPa or 1.5 MPa to 4.0 MPa, 20°C to 85°C or 45°C to 65°C. Meanwhile, the thickness of the separation membrane after compression may be 5 µm to 20 µm.

[0080] In one embodiment of the present invention, the separation membrane has a height (T) of the polymer column after compression when pressurized under pressurized conditions of 1.5 MPa to 4.0 MPa and 45°C to 65°C. c ) may be equal to or greater than the thickness of the inorganic particle filling portion, and may be 1.1 times or less than, or less than 1.1 times the thickness of the inorganic particle filling portion. In a specific embodiment, the T c may be 1.07 times or less, or 1.05 times or less, of the thickness of the inorganic particle filling portion. In addition, the protrusion height (T) of the polymer column in the inorganic coating layer after compression p ) may be 1㎛ or less, or less than 1㎛.

[0081]

[0082] The above membrane may have one or more polymer columns higher than the height of the inorganic particle filling portion when not artificially pressurized after manufacture, i.e., may protrude from the surface of the inorganic particle filling portion.

[0083] The above compressibility may be primarily due to deformation (compression) of the polymer column as described below.

[0084] Meanwhile, in one embodiment of the present invention, the height (T) of the inorganic particle filling portion i ) can be obtained by cutting a cross-section of a membrane specimen, observing it through an SEM, and then measuring the thickness of two or more arbitrary points in an area where no polymer column is located, and taking the average value as the height. If the thickness of four or more points is measured, the lowest and / or highest values ​​can be excluded, and the average value of the remaining values ​​can be taken.

[0085] In one embodiment of the present invention, the height (T) of the polymer column c ) can be obtained by cutting a cross-section of a membrane specimen and observing it through SEM, and then taking the value of the highest part of the polymer column.

[0086] In one embodiment of the present invention, the protrusion height (T) of the polymer column p ) can be obtained by cutting a cross-section of a membrane specimen and observing it through SEM, and then taking the value of the part where the gap between the inorganic particle filling part and the polymer column is the largest.

[0087]

[0088] <Porous polymer substrate>

[0089] The above porous polymer substrate refers to a substrate having multiple pores formed therein as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the cathode and the anode. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0090] The material constituting this porous polymer substrate can be any organic or inorganic material with electrical insulation properties. In particular, from the perspective of imparting a shutdown function to the substrate, it is preferable to use a thermoplastic resin as the substrate material. Here, the shutdown function refers to the function of preventing thermal runaway of the battery by blocking the movement of ions by melting the thermoplastic resin and closing the pores of the porous substrate when the battery temperature rises. Suitable thermoplastic resins include those with a melting point below 200°C, and polyolefins are particularly preferred.

[0091] In addition, at least one of polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene may be further included. The porous polymer substrate may be, but is not particularly limited to, a nonwoven fabric, a porous polymer film, or a laminate of two or more thereof.

[0092]

[0093] Specifically, the porous polymer substrate is one of the following a) to e).

[0094] a) A porous film formed by melting / extruding a polymer resin,

[0095] b) A multilayer film in which two or more layers of the porous film of a) above are laminated,

[0096] c) A nonwoven web manufactured by accumulating filaments obtained by melting / spinning a polymer resin.

[0097] d) A multilayer film in which two or more layers of the nonwoven web of the above b) are laminated,

[0098] e) A porous composite membrane having a multilayer structure comprising two or more of the above a) to d).

[0099]

[0100] In the present invention, the porous polymer substrate may have a thickness ranging from 3 μm to 12 μm or from 5 μm to 12 μm. If the thickness falls short of the above values, the conductive barrier function is insufficient, whereas if the thickness exceeds the above range (i.e., is too thick), the resistance of the separator may excessively increase.

[0101] In one embodiment of the present invention, the weight average molecular weight (Mw) of the polyolefin may be 100,000 to 5,000,000. For example, the molecular weight (Mw) may be 200,000 or more, or 500,000 or more, or 700,000 or more, or 1,000,000 or more. Alternatively, the molecular weight may be 4,000,000 or less, or 3,000,000 or less, or 2,500,000 or less, or 2,000,000 or less, or 1,500,000 or less. The unit of the molecular weight (Mw) may be g / mol. If the weight average molecular weight is less than 100,000, it may be difficult to secure sufficient mechanical properties. In addition, if it exceeds 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult. In addition, the puncture strength of the porous polymer substrate may be 300 gf or more from the viewpoint of improving the manufacturing yield. The puncture strength of a porous substrate refers to the maximum puncture load (gf) measured by performing a puncture test using a Kato tech KES-G5 handy compression tester under conditions of a needle tip radius of 0.5 mm and a puncture speed of 4 mm / sec.

[0102] At this time, the weight average molecular weight can be measured through gel permeation chromatography (GPC). For example, the gel permeation chromatography analysis device may be PL GPC220 from Agilent Technologies, and the measurement conditions may be as follows, for example.

[0103] - Column (maker, model no.): 2 x TSKgel SupermultiporeHZ-M + TSKgel SuperHZ-2500

[0104] - Eleunt: THF

[0105] - Temperature: 40℃

[0106] - Flow rate: 1.0 mL / min

[0107] - Injection volume, sample concentration: 30 ㎕, 1~10 mg / mL

[0108] - Standard: Polystyrene

[0109] - Detector: RI

[0110] In a specific embodiment of the present invention, the porous polymer substrate may be any planar porous polymer substrate used in an electrochemical device, and for example, an insulating thin film having high ion permeability and mechanical strength, a pore diameter of generally 10 nm to 200 nm, and a thickness of generally 5 ㎛ to 12 ㎛ may be used.

[0111] In one embodiment of the present invention, the porous polymer substrate may have a porosity of 20 vol% to 80 vol% or 30 vol% to 60 vol%. Meanwhile, the average pore size of the porous polymer substrate may be 10 nm to 200 nm when measured using a capillary flow porometer.

[0112]

[0113] <Weapon coating layer>

[0114] In the present invention, the separation membrane comprises an inorganic coating layer formed on one surface of the porous polymer substrate. The inorganic coating layer comprises a plurality of polymer columns and a plurality of inorganic particles. The space between the polymer columns is filled with inorganic particles, which is referred to as an inorganic particle filling portion.

[0115] In a specific embodiment of the present invention, the inorganic particles in the inorganic coating layer may be included in an amount of about 50 to 95 wt%, preferably about 70 to 90 wt%, relative to 100 wt% of the inorganic coating layer. In addition, the polymer column may be included in an amount of 5 to 40 wt%, preferably 10 to 35 wt% or 20 to 30 wt%, relative to 100 wt% of the inorganic particles.

[0116] If the content of the polymer column is low, it is difficult to secure the desired level of adhesiveness, but if it is included in an excessive amount exceeding the above range, the Gurley value and / or porosity of the membrane may be lowered, which is not desirable. Meanwhile, under the conditions of a given pressure, temperature, and time, the total area of ​​the polymer column in the planar image of the inorganic coating layer before pressurization may be 10% to 80%, 10% to 50%, 10% to 45%, or 10% to 40% of the surface area of ​​the inorganic coating layer by 100%. The total area of ​​the polymer column may be before compression, after compression, or both before and after compression.

[0117]

[0118] In the above-described inorganic coating layer, the polymer columns may be clustered in two or more polymer columns, or the individual polymer columns may be spaced apart from each other by a predetermined distance. In one embodiment of the present invention, at least one polymer column may be spaced apart from another polymer column by a predetermined distance, and this is also referred to herein as a "single polymer column."

[0119]

[0120] In one embodiment of the present invention, when the separation membrane is pressurized under conditions of a pressure of 0.5 MPa to 20 MPa, 1 Mpa to 10 MPa, or 2 MPa to 8 MPa and a temperature of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C, the average sphericity of the polymer column may be 0.5 or more and 1.0 or less, 0.6 or more and 0.9 or less, or 0.7 or more and 0.8 or less.

[0121] At this time, the sphericity of the polymer can be derived by the following equation 1.

[0122] [Formula 1]

[0123] Sphericity of polymer column = (short axis / long axis)

[0124] At this time, the sphericity of the polymer column is a value calculated by obtaining a planar image (top view) by photographing the surface of the inorganic coating layer obtained when the separation membrane is pressurized under the pressure and temperature conditions using a scanning electron microscope (SEM), obtaining the average length of the long axis of the polymer column particles from the planar image, and obtaining the average length of the short axis of the polymer column particles.

[0125]

[0126] In one embodiment of the present invention, the height, diameter, and / or cross-sectional size of the polymer column can be calculated from an SEM image of a horizontal or vertical cross-section of the membrane. FIG. 3c shows an SEM image of a cross-section of the membrane of Example 1 of the present invention before compression, and FIG. 3d shows an SEM image of a cross-section of the membrane of Example 1 of the present invention after compression, which allows for confirmation of the dimensions of each component. Another method of utilizing the SEM image is to divide the SEM image into gray levels and measure an area corresponding to a specific gray level corresponding to the polymer column. The gray level refers to a brightness value for a plurality of pixels included in the SEM image. For example, in an SEM image of 256 gray levels with steps of 0 to 255, the brightness value range can be a value of 0 to 255. In a specific embodiment of the present invention, the polymer column can have a gray level of 10 to 50, and the inorganic particles can have a gray level of 160 to 220. Accordingly, the region of the polymer column can be set and defined from pixels having 10 to 50 gray levels in the SEM image of an arbitrary cross-section of the membrane, and its length and area can be calculated. In the present invention, the cross-section SEM image of the membrane can be obtained by performing EDS mapping of the components using an energy dispersive X-ray spectroscopy (EDS) detector of a scanning electron microscope (SEM) equipment on a cross-section of the membrane obtained by argon ion milling, and then performing image processing.

[0127] In another specific embodiment of the present invention, the diameter or the size of the short axis or long axis of the polymer column can be calculated by three-dimensionally modeling a pressurized separation membrane and / or inorganic coating layer under predetermined conditions, for example, a pressure of 0.5 MPa to 20 MPa, 1 MPa to 10 MPa, or 2 MPa to 8 MPa and a temperature of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C, and then obtaining an arbitrary cross-section therefrom.

[0128] In one embodiment of the present invention, when the separation membrane is pressurized under conditions of a pressure of 0.5 MPa to 20 MPa, 1 Mpa to 10 MPa, or 2 MPa to 8 MPa and a temperature of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C, the ratio of the homopolymer column of the following formula 2 may be 70% or more, 75% or more, 80% or more, or 85% or more. When the ratio of the homopolymer column is less than the lower limit, the polymer columns may excessively form clusters, causing non-uniformity of resistance in the separation membrane, which may result in excessively high resistance.

[0129] [Formula 2]

[0130] Proportion of homopolymer columns (%) = Number of homopolymer columns / Number of total polymer columns x 100

[0131] At this time, the number of polymer columns is determined by photographing the surface of the inorganic surface layer obtained when the membrane is pressurized under the above pressure and temperature conditions using a scanning electron microscope (SEM) to obtain a planar image (top view) of the membrane, and a polymer column distinguished by inorganic particles regardless of shape in the planar image is defined as one polymer column. At this time, the planar image may be measured by magnifying an area of, for example, 200 ㎛ x 150 ㎛ by 500 times.

[0132] Meanwhile, in the present invention, the pressurization may be performed for a period ranging from several seconds to several minutes. For example, it may be within 60 seconds or within 30 seconds. Since the separation membrane according to the present invention can be flattened in a short period of time, process efficiency can be improved.

[0133]

[0134] In one embodiment of the present invention, preferably, the polymer columns are distributed in a sea-like manner in the inorganic coating layer at a predetermined interval without being in direct contact with other polymer columns.

[0135] At this time, the homopolymer column may be a polymer column having a sphericity of 0.8 or more or 0.9 or more of the following formula 1, and the value that serves as a standard for the sphericity of the polymer column that is determined to be a homopolymer column may be appropriately selected depending on the resolution of the scanning electron microscope (SEM) used.

[0136] Meanwhile, when two or more of the above homopolymer columns, preferably two of them, are overlapped in a pressurized separation membrane, it is called a dumbbell-shaped polymer column. In one embodiment of the present invention, the proportion of the dumbbell-shaped polymer columns may be 20% or less, 15% or less, or 10% or less based on the total number of polymer columns. When the proportion of the dumbbell-shaped polymer columns exceeds the upper limit, the polymer columns may excessively form clusters, causing non-uniformity of resistance in the separation membrane, which may result in excessively high resistance.

[0137] In one embodiment of the present invention, when the separation membrane is pressurized under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C for 1 second to 60 seconds, the ratio of dumbbell-shaped polymer columns may be 20% or less, 15% or less, or 10% or less.

[0138] In one embodiment of the present invention, the shape in which two homopolymer columns overlap each other may be, for example, as shown in FIG. 2. The homopolymer columns may simply be in contact, or the homopolymer columns may overlap each other by a length of 3 μm or less, and the average overlap length (o) may be 2 μm or less, or 1 μm. When the overlap length satisfies the above-described range, the dumbbell-shaped polymer columns may not excessively protrude above the surface of the inorganic coating layer, thereby ensuring a stable structure.

[0139] At this time, the overlap length (o) can be obtained through simple image processing from a planar image of the membrane. For example, in the dumbbell-shaped polymer columns illustrated in FIG. 2, the centers of gravity (C1, C2) of each overlapping homopolymer column are found, the diameters (r1, r2) of the homopolymer columns are obtained, and then the distance between each center of gravity (d) is subtracted from the sum of the diameters of the homopolymer columns (r1 + r2).

[0140] In one embodiment of the present invention, when observing a pressurized membrane, the average diameter (D) of the polymer column is based on a planar image (top view) of the membrane. 50 ) may be 2 ㎛ or more and 20 ㎛ or less, 2.5 ㎛ or more and 15 ㎛ or less, or 3 ㎛ or more and 10 ㎛ or less. The pressurizing conditions may be, for example, a pressure of 0.5 MPa to 20 MPa, 1 Mpa to 10 MPa, or 2 MPa to 8 MPa and a temperature of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C.

[0141] In the above inorganic coating layer, a plurality of polymer columns are embedded so as to be exposed or protrude outside the surface of the inorganic coating layer, and the protrusion height (T) of some of the polymer columns p ) can exceed 1 ㎛ before pressurization. For example, T pmay be greater than 1 ㎛ and less than or equal to 10 ㎛, for example, less than or equal to 7 ㎛, or less than or equal to 5 ㎛, or less than or equal to 3 ㎛. In addition, some of the polymer columns exposed to or protruding from the surface of the inorganic coating layer may be in contact with the porous substrate. Here, the protrusion of the polymer columns outside the surface of the inorganic coating layer means that the inorganic particle filling portion (T) of the inorganic coating layer i ) compared to the height of the polymer column (T c ) means that it has a higher height than the inorganic particle filling part.

[0142]

[0143] In one embodiment of the present invention, the average pore size of the inorganic coating layer may be 20 nm to 1,000 nm. In one embodiment of the present invention, the pore size may be measured for the inorganic particle filling portion. Within the above range, the average pore size of the inorganic coating layer may be 800 nm or less, or 500 nm or less, and independently or together may be 20 nm or more, 50 nm or more, or 100 nm or more. For example, the average pore size of the inorganic coating layer may be 20 nm to 800 nm. The pore size may be calculated from shape analysis using an SEM image. If the pore size is smaller than the above range, the pores are likely to be blocked due to expansion of the binder resin in the coating layer, and if the pore size is outside the above range, it is difficult to function as an insulating film, and there is a problem that the self-discharge characteristics deteriorate after manufacturing a secondary battery.

[0144]

[0145] In one embodiment of the present invention, the porosity of the inorganic coating layer (porosity in a state where the polymer columns are included) may be 30 vol% to 80 vol%. The porosity may be appropriately controlled within the above range. For example, the porosity may be 35 vol% or more, or 40 vol% or more, or 45 vol% or more. Alternatively, the porosity may be 75 vol% or less, or 70 vol% or less, or 65 vol% or less. If the porosity is 30 vol% or more, it is advantageous in terms of lithium ion permeability, and if the porosity is 80 vol% or less, the surface opening ratio is not too high, which is suitable for securing adhesion between the separator and the electrode.

[0146]

[0147] Polymer column

[0148] The polymer column may contain at least 90 wt% of the polymer resin relative to 100 wt% of the polymer column. Preferably, the polymer column may be formed of the polymer resin. In addition, the polymer column has adhesive properties, and may adhere to a battery material adjacent to the polymer column, such as an inorganic particle or a porous polymer substrate.

[0149] In the present invention, the polymer column may not have open cell-type pores in its body. It is preferable that the polymer column does not have open cell-type pores, so that a fluid such as a gas or liquid does not flow through the polymer column body.

[0150] As described above, at least a portion of one or more of the polymer columns may be exposed or protruding outside the surface of the inorganic coating layer, and another portion thereof may be in contact with the surface of the porous substrate.

[0151] In one embodiment of the present invention, D of the polymer column 10 D of the above polymer column 5030% or more of the D of the polymer column 90 D of the above polymer column 50 may be less than 200% of the D of the polymer column, together with or independently of this. 50 D of silver inorganic particles 50 may be twice or greater than that of the polymer column. At this time, the D of the polymer column 10 , D 50 , D 90 may be the size measured before being contained in the membrane and pressurized, respectively.

[0152] In one embodiment of the present invention, D of the polymer column 50 silver It may be about 2.5 to 7.5 ㎛ or 3.0 ㎛ to 7.0 ㎛, preferably D 50 This may have a range of 3.5㎛ to 6.5㎛. D of the polymer column 50 It reflects the state before the membrane is pressurized, preferably before slurry preparation.

[0153]

[0154] In the present invention, the polymer column may have a storage modulus (G') at room temperature of 1,000 Pa or more and 3,500 Pa or less in terms of flattening by pressurization. For example, within the above range, the storage modulus may be 1,000 Pa or more, 1,500 Pa or more, and the storage modulus may be 3,000 Pa or less or 2,000 Pa or less. For example, the storage modulus may be 1,000 Pa to 3,000 Pa. Preferably, the storage modulus may be for a material forming the polymer column. At this time, the room temperature may be about 18°C ​​to 25°C.

[0155] In addition, the polymer column has a ratio of the storage modulus at 60°C to the storage modulus at room temperature (Modulus (60°C) / Modulus (room temperature)) in consideration of the temperature application situation in the actual battery assembly process, which is greater than 0 and less than or equal to 0.01. For example, it may be less than 0.01. In one embodiment of the present invention, the polymer column may have a storage modulus at a high temperature (55°C to 80°C or 60°C to 80°C) in the range of 0.05 Pa to 50 Pa. For example, the storage modulus may be the storage modulus at 60°C. Typically, the temperature of the lamination process for bonding the electrode and the separator in the electrode assembly manufacturing process is controlled to about 60°C to 80°C. At this time, the lower the storage modulus, the more the polymer column is pressed and the more the separator can be flattened. In addition, at room temperature, preferably, the higher the storage modulus, the more sufficient bonding force with the electrode can be secured.

[0156] Together with or independently of this, the polymer column may have at least one tan δ peak in the range of 45°C to 80°C, 45°C to 75°C, or 45°C to 70°C when measured with a Dynamic Mechanical Analyzer (DMA; ARES-G2, TA Instrument) device. When the above range is satisfied, the polymer column is deformed in the lamination process of bonding the separator and the electrode, so that the electrode and the separator come into close contact and a desired level of electrode-separator adhesion can be secured.

[0157] In one embodiment of the present invention, the storage modulus and tan δ peak can be measured using a rheological property measuring equipment (Dynamic Mechanical Analyzer (DMA), ARES-G2, TA Instrument). In a specific embodiment, the storage modulus can be confirmed by performing a temperature sweep test under temperature conditions of -60°C to 80°C and a frequency of 1.0 rad / s. In addition, the tan δ peak can be calculated by calculating the ratio of the loss modulus to the storage modulus from the measured elastic moduli (storage modulus and loss modulus). In addition, the storage modulus (G') at 45°C and the slope of the storage modulus (G') at 60°C to 70°C can be measured through the DMA.

[0158]

[0159] The polymer columns may be at least partially exposed to the surface of the inorganic coating layer and the other portions may be in contact with the surface of the porous polymer substrate. Here, the polymer columns being exposed or protruding outside the surface of the inorganic coating layer means the height (T) of the inorganic particle filling portion of the inorganic coating layer. i ) means that the height of the polymer column is higher than that of the inorganic particle filling section.

[0160]

[0161] Meanwhile, in one embodiment of the present invention, the one or more polymer columns may protrude a predetermined height outside the surface of the inorganic coating layer. At this time, when pressurized with a pressure of 0.5 MPa or more and 20.0 MPa or less, the protruding portion may be flattened, so that the thickness of the inorganic coating layer may become uniform. The pressure may be appropriately adjusted within the above range, for example, 2.0 MPa to 8.0 MPa, or 4 MPa or less. When the applied pressure is low, the temperature may be adjusted to increase the processability. For example, when pressurized with a force of 4 MPa or less, the temperature may be adjusted within the above-mentioned range. In addition, the protruding height (T) of the polymer columns after compression under the above conditions p ) can be 1㎛ or less, or less than 1㎛. That is, the height difference between the inorganic particle filling portion and the polymer column is reduced, so that the separation membrane is flattened. Referring to FIG. 1, in the present invention, the T c refers to the total height of the inorganic coating layer (one side), and is based on the highest part of the inorganic coating layer in the porous substrate. In the present invention, the T c may be the height of the highest protruding polymer column. Here, the fact that the polymer column protrudes outside the surface of the inorganic coating layer means that the height of the polymer column is higher than the height of the inorganic particle filling portion among the inorganic coating layers, and thus has a higher height than the inorganic particle filling portion.

[0162]

[0163] In one embodiment of the present invention, the separator may have one or more polymer columns higher than the height of the inorganic particle filling portion when not artificially pressurized after manufacture. They may protrude from the surface of the inorganic particle filling portion. In one embodiment of the present invention, the polymer columns may be flattened to the thickness of the inorganic particle filling portion when pressurized with a force of 0.5 MPa to 20.0 MPa, which is advantageous in strengthening the adhesion between the electrode and the separator during manufacture of the electrode assembly and preventing a gap between the electrode and the separator. That is, under conditions for lamination of the electrode and the separator, i.e., hot press conditions, the polymer columns may exhibit softening properties.

[0164] Meanwhile, in the present invention, the pressurization may be performed for a period ranging from several seconds to several minutes. For example, it may be within 60 seconds or within 30 seconds. Since the separation membrane according to the present invention can be flattened in a short period of time, process efficiency can be improved.

[0165]

[0166] Meanwhile, in the present specification, the flattening may mean that the thickness of the inorganic particle filling portion and the height of the polymer column are the same or the deviation between the height of the inorganic particle filling portion and the main polymer column is 1 ㎛ or less or less than 1 ㎛, preferably less than 0.5 ㎛, and more preferably less than 0.3 ㎛. In one embodiment of the present invention, the height of the polymer column may be based on the one having the highest height among the polymer columns. That is, when the separator according to the present invention is applied to battery manufacturing, the thickness of the inorganic coating layer after lamination of the electrode and the separator is less than the thickness of the polymer column D. 50 Smaller is preferable.

[0167]

[0168] Meanwhile, the flattened polymer column may have a larger planar surface area than before pressurization. In this case, the planar major axis length of the polymer column after flattening is D of the polymer column before flattening. 50 It is desirable that it be less than 10 times.

[0169] In one embodiment of the present invention, when the polymer column protrudes outside the inorganic coating layer, the thickness (T) of the inorganic coating layer i ) is the D of the polymer column 50 It may be less than 85% of the total.

[0170] Meanwhile, in one embodiment of the present invention, when the surface of the separator is measured from a top view using SEM, the area of ​​the polymer columns exposed to the surface of the inorganic coating layer relative to 100% of the surface area of ​​the inorganic coating layer based on a planar image (top view) of the separator may be 10% to 80%, 10% to 50%, 10% to 45%, or 10% to 40%. The total area of ​​the polymer columns may correspond to before or after compression, or both before and after compression. At this time, the separator may be pressurized under conditions of a pressure of 0.5 MPa to 20 MPa, 1 Mpa to 10 MPa, or 2 MPa to 8 MPa and a temperature of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C. When the surface area of ​​the polymer column exposed to the surface of the above-described inorganic coating layer satisfies the above-described range, the adhesion of the separation membrane, the Gurley value and / or the porosity of the separation membrane may be excellent.

[0171]

[0172] Meanwhile, in a specific embodiment of the present invention, the polymer column may have a zeta potential of -20 mV or less, more preferably -25 mV or less, at room temperature when dispersed in a specific solvent. When the zeta potential of the polymer column satisfies the above range, it is preferable in that it improves the dispersibility of the polymer column when forming an inorganic coating layer, prevents overlapping between particles, and maintains long-term storage properties because the polymer column particles do not precipitate. In particular, since the dispersion of particles is very vulnerable near the isoelectric point where the zeta potential becomes 0, the absolute value of the zeta potential must be increased by adjusting the pH, etc.

[0173] In one embodiment of the present invention, the zeta potential can be measured by dispersing a polymer column in water or alcohol and then using electrophoresis (ELS). For example, a sample solution can be prepared by adding 0.1 g or more of the polymer column to 10 ml or more of the solvent, and then measured using the analysis method of ISO13099-2.

[0174]

[0175] In one embodiment of the present invention, one or more polymer columns may have a cross-sectional area (a) of the polymer column ascertained in a cross-section at the lower 5% from the bottom of the inorganic coating layer toward the surface, and a cross-sectional area (b) of the polymer column ascertained in a cross-section at the upper 5% from the top of the inorganic coating layer toward the bottom, wherein the area (a) is greater than the area (a). This characteristic of the polymer column may apply when the polymer column protrudes from the surface of the inorganic coating layer and / or is flattened by pressurization. Preferably, the characteristic may be confirmed in the shape of the polymer column after it is flattened after protrusion.

[0176]

[0177] Together with or independently of this, one or more polymer columns may have a diameter (a) of the lower portion of the polymer column that is shorter than a diameter (b) of the upper portion of the column in a cross-section of the polymer column as seen in the vertical cross-section of the inorganic coating layer. In one embodiment, the ratio of the upper diameter (b) to the lower diameter (a) may be greater than 1 and less than or equal to 20, or from 1.2 to 20, or from 1.5 to 20, or from 2 to 20. This characteristic of the polymer column may apply when the polymer column protrudes from the surface of the inorganic coating layer and / or is flattened by pressurization. Preferably, the characteristic may be found in the shape of the polymer column after being flattened. In one embodiment of the present invention, the upper diameter refers to the diameter at the upper 5% point from the top of the polymer column toward the bottom, and the lower diameter refers to the diameter at the lower 5% point from the bottommost portion of the polymer column toward the top.

[0178]

[0179] <Material of polymer column>

[0180] In one embodiment of the present invention, the polymer column preferably includes a material having the above-described characteristics, being non-reactive within a lithium secondary battery, and capable of imparting bonding strength between a separator and an electrode. Considering these aspects, in the present invention, the polymer column may include an acrylic polymer. The polymer column may include, for example, 10 wt% or more, 30 wt% or more, 50 wt% or more, 70 wt% or more, or 90 wt% or more of the acrylic polymer relative to 100 wt% of the polymer column. In one embodiment of the present invention, the acrylic polymer is an acrylate series, that is, for example, acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexylacrylate, heptylacrylate, octylacrylate, 2-ethylhexylacrylate, nonylacrylate, decylacrylate, lauryl acrylate, n-tetradecylacrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, It may include repeating units derived from one or more selected monomers from among octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. However, it is not limited thereto. Meanwhile, in a specific embodiment, one or more hydrogens in the unit may be substituted with another substituent. In one embodiment of the present invention, the acrylic polymer may include the above-described repeating units in an amount of 30 wt% or more, 50 wt% or more, 70 wt% or more, or 90 wt% or more, based on 100 wt% of the acrylic polymer.

[0181] In one embodiment of the present invention, the weight average molecular weight of the polymer column may be from 20,000 to 800,000. In a more specific embodiment, the weight average molecular weight of the acrylic polymer may be from 20,000 to 800,000.

[0182]

[0183] However, there is a concern that the polymer column may dissolve and lose adhesiveness after the liquid electrolyte is injected, or that the viscosity of the liquid electrolyte may increase due to the dissolved components, thereby increasing the resistance of the lithium secondary battery. Therefore, it is desirable to have an appropriate solubility as described below. For example, the solubility in organic solvents or electrolytes can be reduced by cross-linking the surface of the material forming the polymer column.

[0184] In one embodiment of the present invention, the polymer column may have a dissolved amount (weight) of 55% or less, preferably 35% or less, more preferably 25% or less, even more preferably 22% or less, and most preferably 20% or less after being dissolved in THF (Tetrahydrofuran) for 1 to 48 hours. When manufacturing a battery, there is a concern that the polymer column may dissolve after injecting the liquid electrolyte and lose adhesiveness, or that the viscosity of the liquid electrolyte may increase due to the dissolved components, thereby increasing the resistance of the lithium secondary battery. Therefore, it is preferable to have an appropriate solubility as described above. For example, the solubility in an organic solvent or electrolyte can be lowered by crosslinking the surface of the material forming the polymer column.

[0185]

[0186] Meanwhile, in order to satisfy the zeta potential of the polymer column described above when preparing a slurry for forming an inorganic coating layer, the slurry for forming an inorganic coating layer may further include additives such as a wetting agent and / or a dispersing agent. In a non-limiting embodiment, the additive may be included in an amount of 0.1 to 10.0 parts by weight, preferably 0.1 to 5.0 parts by weight, based on 100 parts by weight of the polymer column. Such a wetting agent acts as a surface-active substance to improve the wettability of a solid, and the dispersing agent plays a role in preventing particle agglomeration by various mechanisms (electrostatic effect, steric effect).

[0187] In one embodiment of the present invention, the additive may be selected from, but is not limited to, one or more appropriate ones selected from polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and cyanoethylene polyvinyl alcohol.

[0188]

[0189] <Inorganic particle filling part>

[0190] The space between the polymer columns in the inorganic coating layer of the above-described separation membrane may be filled with inorganic particles. In the present specification, the portion filled with inorganic particles is referred to as an “inorganic particle filling portion.” The inorganic particle filling portion may further include a binder resin to secure adhesion between the inorganic particles and between the inorganic particles and the porous polymer substrate. The inorganic particle filling portion has pores resulting from an interstitial volume formed between adjacent inorganic particles. Due to the pores, the inorganic coating layer may have a porous structure having a predetermined porosity, and gas or liquid may pass from one side to the other side. The inorganic particles and the polymer columns may be bonded by the adhesive properties of the polymer columns or may be bonded via a binder resin.

[0191] In one embodiment of the present invention, before flattening the separation membrane, the thickness (T) of the inorganic particle filling portion i ) is the D of the polymer column 50 It can be less than 85% of the total. For example, it can range from 5% to 40%.

[0192] The thickness of the above inorganic particle filling part (T i ) may be 1.0 ㎛ to 5.0 ㎛, and is preferred. The thickness may preferably be 1.0 ㎛ or more, and may be appropriately adjusted within the above range. The T i For example, it may be 4 ㎛ or less, 3 ㎛ or less, or 2 ㎛ or less. The above T iThe thickness is preferably 1.0 ㎛ or more, and within the above numerical range, the adhesion with the electrode is excellent, and as a result, the cell strength of the battery is increased. On the other hand, if the thickness is 5.0 ㎛ or less, it is advantageous in terms of cycle characteristics and resistance characteristics of the battery. When the inorganic coating layer is disposed on both sides of the porous substrate, the thickness of the inorganic particle filling portion refers to a value measured for the inorganic coating layer disposed on either side.

[0193] In one embodiment of the present invention, the height (thickness) of the inorganic particle filling portion may be determined by cutting a cross-section of a membrane specimen, observing it through an SEM, and then measuring the thickness of two or more arbitrary points in an area where no polymer column is located, and taking the average value thereof as the height. For example, for an area of ​​50 ㎛ x 50 ㎛, the thickness may be measured at 2 to 10 points, and then taking the average value thereof. Alternatively, in the case of a cross-section, the thickness may be measured at 2 to 10 points over a length of 50 ㎛ or less, and then taking the average value thereof. If the thickness of four or more points is measured, the lowest and / or highest values ​​may be excluded, and the average value of the remaining values ​​may be taken.

[0194] Meanwhile, in one embodiment of the present invention, the height of the inorganic particle-filled portion may tend to increase as it gets closer to the polymer column in the inorganic particle-filled portion. This tendency may be more noticeable with respect to the periphery of the polymer column. That is, the height of the outer portion of the periphery may gradually increase from any point of the inorganic particle-filled portion toward the polymer column, and may relatively rapidly increase as it goes from the boundary of the periphery toward the polymer column. In one embodiment of the present invention, the periphery may mean a portion having a width of about 2 μm from the boundary between the inorganic particle-filled portion and the polymer column toward the inorganic particle-filled portion.

[0195]

[0196] <Inorganic particles>

[0197] In a specific embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are those that can operate within the operating voltage range of the applied electrochemical device (e.g., Li / Li). + There are no particular limitations as long as no oxidation and / or reduction reaction occurs at a voltage of 0 to 5 V as a standard. In particular, when using inorganic particles with a high dielectric constant as inorganic particles, it can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0198] For the reasons mentioned above, it is preferable that the inorganic particles include high-k inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC and TiO2 or mixtures thereof.

[0199] In addition, as the inorganic particles, inorganic particles having lithium ion transfer capability, i.e., inorganic particles containing lithium element but having the function of transferring lithium ions without storing lithium, can be used. Non-limiting examples of inorganic particles having lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (LixTiy(PO4)3, 0 < x <2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Aly Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li2O-9Al2O3-38TiO2-39P2O5, etc. (LiAlTiP) x O y Series Glass (0) <x < 4, 0 < y < 13), 리튬란탄티타네이트(Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li 3 N ), etc. x N y , 0 < x <4, 0 < y < 2), SiS2 series glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 글래스(glass) (Li x P y S z , 0 < x < 3, 0< y < 3, 0 < z < 7) or mixtures thereof.

[0200] In addition, the average particle diameter of the inorganic particles (D 50 ) has no special limitations, but in order to form a coating layer of uniform thickness and have an appropriate porosity, it is preferably in the range of 0.1 ㎛ to 1.5 ㎛, or 200 nm to 1 ㎛. If it is less than 0.1 ㎛, dispersibility may be reduced, and if it exceeds 1.5 ㎛, the thickness of the formed coating layer may increase.

[0201]

[0202] Binder resin

[0203] Additionally, as described above, the inorganic coating layer may further include a binder resin to enhance the bonding strength. In the inorganic coating layer, the inorganic particles and the binder resin may be included in a weight ratio of 70:30 to 99.9:0.1 or 70:30 to 99:1.

[0204] In one embodiment of the present invention, the binder resin may include a PVdF-based polymer resin. The PVdF-based polymer resin may include at least one of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of a monomer copolymerizable with vinylidene fluoride, and a mixture thereof. In one embodiment of the present invention, the monomer may include, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and more than one of these may be included.

[0205] Together with or independently of this, a (meth)acrylic polymer resin may further be included as a binder resin. The above (meth)acrylic polymer contains a repeating unit derived from a (meth)acrylic acid ester as a monomer, and non-limiting examples thereof include 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 (meth)acrylic polymer containing a repeating unit derived from two or more monomers thereof.

[0206]

[0207] In one embodiment of the present invention, the inorganic coating layer may further include an additive such as a dispersant and / or a thickener in a range of 1 wt% to 3 wt% based on 100 wt% of the inorganic coating layer. In one embodiment of the present invention, the additive may be selected from the group consisting of polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and cyanoethylene polyvinyl alcohol. The above additives can help the zeta potential of the polymer column meet the desired range as described above.

[0208]

[0209] <Method for manufacturing a separation membrane>

[0210] Next, a method for manufacturing the membrane of the present invention will be described. However, the following description is for one embodiment of manufacturing the present invention and is not particularly limited thereto.

[0211] Specifically, first, a binder resin is dissolved in a solvent to prepare a polymer solution. Then, inorganic particles are added to an appropriate solvent to the polymer solution to prepare a mixture. Then, polymer particles for a polymer column are added to the mixture to prepare a slurry for an inorganic coating layer. Next, the slurry is applied onto a porous polymer substrate and dried. After the drying, a pressurizing process is additionally performed. The pressurization may be performed under pressure conditions of 0.5 MPa to 20 MPa, 1 MPa to 10 MPa, or 2 MPa to 8 MPa and temperature conditions of 20°C to 85°C, 25°C to 80°C, or 25°C to 70°C.

[0212] Meanwhile, in one embodiment of the present invention, as described above, a predetermined amount of additive may be further included in the slurry. Thereafter, by drying the obtained membrane, an inorganic coating layer can be integrally formed on the porous polymer substrate. Any drying method that can remove the solvent and obtain an inorganic coating layer can be applied and is not limited to a particular method. For example, the drying method may be applied in a method such as natural drying, air drying, cold air drying, hot air drying, convection drying, or high-temperature drying, but is not limited thereto. At this time, the drying temperature of the membrane is preferably set to a temperature of 20°C or lower than the glass transition temperature (Tg) of the polymer column material in order to prevent deformation of the polymer column.

[0213] In the preparation of the above slurry, water or an aqueous solvent containing water may be used as the solvent. In addition, when there are limitations on drying speed and temperature, methanol, ethanol, isopropyl alcohol, etc., which have a lower boiling point than water, may be used as a co-solvent.

[0214] The above slurry can be applied using conventional coating methods such as a Meyer bar, die coater, reverse roll coater, or gravure coater.

[0215] In addition, the separation membrane of the present invention can also be manufactured by a method in which the inorganic coating layer and the porous polymer substrate are manufactured separately, these sheets are overlapped and combined, and then composited by thermal compression or an adhesive. As a method for obtaining the inorganic coating layer as an independent sheet, a method in which the slurry is applied onto a peeling sheet, an inorganic coating layer is formed by the above-described method, and only the inorganic coating layer is peeled off, etc.

[0216] Meanwhile, in addition to the above-described manufacturing method, any manufacturing method that can achieve the above-described membrane structure can be applied without limitation.

[0217]

[0218] Lithium secondary battery

[0219] The present invention provides an electrochemical device comprising the separator for the electrochemical device. Specifically, the present invention provides a lithium secondary battery comprising the separator. The secondary battery comprises a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is a low-resistance separator having the characteristics described above.

[0220]

[0221] In the present invention, the positive electrode has a positive electrode current collector and a positive electrode active material layer including a positive electrode active material, a conductive material, and a binder resin on at least one surface of the positive electrode current collector. The positive electrode active material is a layered compound such as lithium manganese oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x A lithium manganese composite oxide represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a portion of Li in the chemical formula is replaced by an alkaline earth metal ion; a disulfide compound; or a mixture of two or more of Fe2(MoO4)3.

[0222]

[0223] In the present invention, the negative electrode has a negative electrode current collector and a negative electrode active material layer including a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The negative electrode includes carbon such as lithium metal oxide, non-graphitizable carbon, and graphite carbon as the negative electrode active material; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물 중 선택된 1종 또는 2종 이상의 혼합물을 포함할 수 있다.

[0224]

[0225] In a specific embodiment of the present invention, the conductive material may be, for example, one selected from the group consisting of graphite, carbon black, carbon fibers or metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more conductive materials thereof. More specifically, the conductive material may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials thereof.

[0226]

[0227] The above-mentioned current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used.

[0228]

[0229] As the above binder resin, a polymer commonly used in electrodes in the art can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples thereof include, but are not limited to, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0230]

[0231] The electrode assembly prepared as above can be placed in an appropriate case and an electrolyte can be injected to manufacture a battery.

[0232]

[0233] In the present invention, the electrolyte is A + B - As a salt with the same structure as A + is Li + , Na + , K + B containing an ion composed of an alkali metal cation or a combination thereof; - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - Salts containing anions such as or combinations thereof are dissolved or dissociated in organic solvents 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), gamma butyrolactone (g-butyrolactone), ester compounds, and mixtures of one or more selected from these, but are not limited thereto.

[0234]

[0235] Meanwhile, in a specific embodiment of the present invention, the organic solvent may include an ester compound. Preferably, the ester compound may be at least 30 wt%, at least 50 wt%, at least 60 wt%, or at least 65 wt% relative to 100 wt% of the organic solvent.

[0236] In a specific embodiment of the present invention, the ester compound may include at least one selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methylpropionate, ethylpropionate, propylpropionate, butylpropionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0237]

[0238] In addition, the present invention provides a battery module including a battery including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool that is powered by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0239]

[0240] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0241] [Example]

[0242] <Example 1>

[0243] Inorganic particles (Al2O3, D 50About 0.6㎛), acrylic emulsion (Toyo, CSB-130) as a binder resin, carboxyl methyl cellulose (Daicel, Daicel1220) as a dispersant resin were added to a water:ethanol 95:5 solution at a ratio of 96:2:2, and a dispersion process using a bead mill was performed to obtain a mixture. Acrylic polymer A15a (D) was added to the mixture as polymer particles for a polymer column. 50 3.84㎛, zeta potential -41.0mV) was added and stirred to obtain a dispersion slurry. The concentration of the solid content in the dispersion slurry was 30 wt%. The content of polymer particles for polymer columns in the mixture was about 10 parts by weight per 100 parts by weight of inorganic particles. The dispersion slurry was applied to a porous polymer substrate (Toray B09PJ1, thickness 9㎛) by a microgravure coating method and dried at a temperature of 80℃ to obtain a separator. In addition, the opposite side was coated and dried in the same manner to obtain a double-coated separator. Thereafter, the separator was wrapped with a release-treated PET film and pressurized at a pressure of 6.5 MPa and a temperature of 60℃ for about 1 second. At this time, the loading amount of the inorganic coating layer in the separator was 12.1 g / m in total for double-coating. 2 It was.

[0244]

[0245] <Example 2>

[0246] In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the content of polymer particles for the polymer column was changed to about 15 parts by weight relative to 100 parts by weight of inorganic particles.

[0247]

[0248] <Example 3>

[0249] In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the content of polymer particles for the polymer column was changed to about 20 parts by weight relative to 100 parts by weight of inorganic particles.

[0250]

[0251] <Comparative Example 1>

[0252] Inorganic particles (Al2O3, D 50 (About 0.6㎛), acrylic emulsion (Toyo, CSB-130) as binder resin, carboxyl methyl cellulose (Daicel, Daicel1220) were added in a 96:2:2 ratio to a 95:5 water:ethanol solution and stirred to obtain a mixture. The mixture was applied to a porous polymer substrate (Toray, B09PJ1) by microgravure coating and dried at a temperature of 80°C.

[0253]

[0254] <Comparative Example 2>

[0255] In Example 1, the polymer particles for the polymer column are HES40(D) ​​from Hansol Chemical Co., Ltd. 50 A separation membrane was manufactured in the same manner as in Example 1, except that the particle size (1.21 ㎛, solubility 36%, zeta potential -19.0 mV) was changed to about 1.21 ㎛, solubility 36%, and zeta potential -19.0 mV) and the content of polymer particles for the polymer column was changed to about 20 parts by weight per 100 parts by weight of inorganic particles. At this time, the method for measuring the zeta potential is described later in the experimental example.

[0256]

[0257] <Comparative Example 3>

[0258] In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the content of polymer particles for the polymer column was changed to about 45 parts by weight based on 100 parts by weight of inorganic particles, and the pH of the slurry for forming an inorganic coating layer was adjusted to 9.4 to change the zeta potential of the polymer column to -18.2 mV. At this time, the method for measuring the zeta potential is described later in the experimental examples.

[0259]

[0260] [Experimental Example]

[0261] <Experimental Example 1: Solubility, storage modulus, D of polymer particles for polymer columns50 , Tg measurement>

[0262] Solubility measurement

[0263] In each example and comparative example, the polymer material to be used as the polymer column was dried at 60°C to prepare a 0.3 g sample. The sample was placed in an 80-mesh mesh sieve and dissolved in THF (Tetrahydrofuran) for 24 hours. The residual weight was compared to the initial weight. The solubility was calculated based on Equation 5 below. This is summarized and presented in Table 1 below.

[0264] [Formula 5]

[0265] Solubility (%) = {(Weight measured before immersion - Weight measured after immersion) / (Weight measured before immersion)} x 100

[0266]

[0267] Storage modulus measurement

[0268] In each example and comparative example, a 40 cm x 60 cm sample was prepared using a polymer material to be used as a polymer column. The thickness of the sample was 1 mm. The elastic modulus was measured for the sample. The storage modulus was measured using a rheological property measuring equipment (Dynamic Mechanical Analyzer (DMA), ARES-G2, TA Instrument). The storage modulus was confirmed by conducting a temperature sweep test at a temperature condition of -60°C to 80°C and a frequency of 1.0 rad / s. In addition, the storage modulus and loss modulus were confirmed in the measurement, and through this, the tan δ peak was confirmed.

[0269]

[0270] Tg measurement

[0271] The glass transition temperature (Tg) of the polymer material to be used as the polymer column in each example and comparative example was measured using a DSC device (TA instrument, DSC 2920).

[0272] Specifically, the glass transition temperature Tg was measured by cooling 10 mg to 15 mg of each sample from ambient temperature to -30°C and then heating to 200°C at 10°C / min. Thereafter, the sample was cooled to -30°C and then reheated at 10°C / min.

[0273]

[0274] Zeta potential measurement

[0275] In each example and comparative example, the polymer material to be used as the polymer column was dispersed in water and measured using electrophoresis (ELS). Specifically, a sample solution was prepared by adding 0.1 g of the polymer material to be used as the polymer column to 10 ml of water, and then measured using the analysis method of ISO 13099-2.

[0276]

[0277] Solubility (%)D 50 (㎛)Storage modulus (Pa, 25℃)Storage modulus (Pa, 60 o C) Storage modulus (60℃) G' / G' Storage modulus (room temperature) tan δ peak (℃, 45℃ to 80℃) Tg (℃) Zeta potential (mV) Acrylic polymer A15a 19% 3.841,38151.10.03669.959.3-41.0

[0278] <Experimental Example 2: Membrane Thickness Measurement>

[0279] In Examples 1 to 3 and Comparative Examples 1 to 3, the thickness of the separator was determined by cutting a cross-section of the separator sample and observing it through SEM, and the thickness of the thickest point was used as the thickness of the separator, and this is shown in Table 2.

[0280]

[0281] <Experimental Example 3: Measurement of the Surface Area of ​​a Polymer Column>

[0282] The surface of the membrane manufactured in each example was obtained by obtaining a top view SEM image, and the gray level of the polymer column and the gray level of the inorganic particle were distinguished in the obtained image, and the ratio of the surface area of ​​the polymer column exposed to the surface of the inorganic coating layer to 100% of the surface area of ​​the inorganic coating layer was calculated and shown in Table 2. Specifically, the SEM image of the surface of the membrane of Example 1 is shown in FIGS. 3a and 3b (pictures showing the gray level of the polymer column), and the SEM image of the surface of the membrane of Example 3 is shown in FIGS. 4a and 4b (pictures showing the gray level of the polymer column). In addition, the SEM image of the compressed surface of the membrane manufactured in Comparative Example 3 is shown in FIG. 5.

[0283]

[0284] <Experimental Example 4: Evaluation of dry adhesion between cathode and separator>

[0285] Manufacturing of anodes and cathodes

[0286] A slurry of positive electrode active material was prepared by adding LiCoO2 as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder to N-methylpyrrolidone (NMP) as a solvent at a weight ratio of 96:2:2. The positive electrode active material slurry was coated on a sheet-shaped aluminum current collector and dried to obtain a final positive electrode loading of 3.8 mAh / cm. 2 The polarity was prepared to make this happen.

[0287] Artificial graphite as a negative active material, carbon black as a conductive agent, carboxymethyl cellulose as a dispersant, and styrene butadiene emulsion as a binder were mixed in a weight ratio of 96:0.5:1.5:2.0, respectively, and added to water as a solvent to prepare a negative electrode slurry. The negative electrode slurry was prepared at a capacity of 4.0 mAh / cm 2A negative electrode having a negative active material layer formed by coating and drying a copper current collector with a loading amount of was prepared.

[0288] The above-mentioned manufactured cathode was laminated between separators, a separator was laminated on the cathode, and an anode was further laminated on the separator.

[0289]

[0290] Evaluation method and results

[0291] The membrane samples obtained in Examples 1 to 3 and Comparative Examples 2 to 3 were cut into a size of 100 mm (length) x 25 mm (width) to prepare each test piece. After each test piece was laminated with the negative electrode, a laminate was obtained by heating and pressing at 70°C for 20 seconds. The laminate was fixed to an adhesive strength measuring device (LLOYD Instrument, LF plus), and the membrane portion was peeled at an angle of 180° at a speed of 25 mm / min at 25°C, and the strength at this time was measured, which is shown in Table 2.

[0292]

[0293] <Experimental Example 5: Measurement of the average sphericity of polymer columns, average diameter of polymer columns, ratio of dumbbell-shaped polymer columns, and average overlap length (o)>

[0294] The surfaces of the pressurized membranes of Examples 1 to 3 and Comparative Examples 2 to 3 were obtained by taking SEM images from the top view, and the gray levels of the polymer columns and the gray levels of the inorganic particles were distinguished in the obtained images. The sphericity of the polymer columns exposed to the surface of the inorganic coating layer and the average diameter of the polymer columns were measured relative to 100% of the surface area of ​​the inorganic coating layer, and the results are shown in Table 2.

[0295] In addition, the two homopolymer columns in contact in the obtained image were viewed as dumbbell-shaped polymer columns, and the ratio thereof was measured and shown in Table 2. In addition, the dumbbell-shaped polymer columns were distinguished into two homopolymer columns, the radius at the center of gravity of each homopolymer column was obtained, and the difference in the sum of the radii at the distance between each center of gravity was obtained to calculate the average overlap length, which was shown in Table 2.

[0296]

[0297] <Experimental Example 6: Resistance Measurement>

[0298] The resistance of the separators of Examples 1 to 3 and Comparative Examples 1 to 3 was measured by an impedance measurement method. Specifically, each separator was sandwiched between stainless steel to fabricate coin cells, and an ethylene carbonate / ethyl methyl carbonate (EC / EMC, volume ratio 30:70) electrolyte containing 1 M LiPF6 was injected. The resistance was measured through electrochemical impedance spectroscopy analysis using Solaton's 1470E cell test system and Frequency response analyzer 1255B at 25°C with a scan range of 100,000 Hz to 10,000 Hz, and the results are shown in Table 2.

[0299]

[0300] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness of membrane (um) 13.6 13.3 13.9 11.8 13.1 14.0 Coverage of polymer column (%) 11.8 15.1 19.9-22.2 45.4 Cathode-membrane dry adhesion (gf / 25mm) 24.6 35.1 33.3-30.1 39.1 Average sphericity of polymer column (short axis / long axis) 0.8 3 0.8 10.85-0.9 2 0.89 Average diameter of polymer column (㎛) 5.1 6.1 6.3-1.9 9.7 Ratio of dumbbell-shaped polymer column (%) 1.8 9.1 9.8-30.2 2 3.5 Average overlap length (um) 0.6 1.3 1.4-n / a 4.3 Resistance (ohm)0.720.740.760.710.890.80

[0301] According to Table 2, it was confirmed that the separators of Examples 1 to 3 had excellent adhesion between the cathode and the separator while also having a resistance value at an appropriate level for battery operation. Meanwhile, Comparative Example 2, which used polymer particles for a polymer column having a higher zeta potential than the polymer particles of Example 1, had a higher proportion of dumbbell-shaped polymer columns compared to Comparative Example 3, and through this, it was confirmed that the resistance characteristics were inferior because they were not evenly distributed on the inorganic coating layer.

[0302] In addition, Comparative Example 3, which has a higher zeta potential than the polymer particles of Example 1 and contains an excessive amount of polymer particles for polymer columns, has a higher ratio of dumbbell-shaped polymer columns compared to Examples 1 to 3, and through this, it was confirmed that the resistance characteristics are inferior because they are not evenly distributed on the inorganic coating layer.

[0303]

[0304] <Experimental Example 7: Comparison of the Shapes of Polymer Columns Before and After Pressurization>

[0305] The SEM images of the membrane of Example 1 before and after pressurization were measured, and the SEM images are shown in Figures 6a and 6b. Using the SEM images, the ratio of the length of the lower diameter (a) and the upper diameter (b) of the polymer column was confirmed, and is shown in Table 3 below. Specifically, the upper and lower surfaces of the membrane were measured, and these are separately described. Referring to Table 3, it was confirmed that the ratio of b / a before and after pressurization exceeded 2.

[0306] a(㎛)b(㎛)b / aPressurized upper surface0.834.415.31Lower surface2.114.572.17Pressurized upper surface2.426.192.56Lower surface1.072.372.21

Claims

1. Includes a porous polymer substrate and an inorganic coating layer covering one surface or both surfaces of the porous polymer substrate. The above-mentioned inorganic coating layer comprises a plurality of adhesive polymer columns of a predetermined volume, wherein the polymer columns are made of a polymer material and do not have pores, At least a portion of the polymer column is exposed to the surface of the inorganic coating layer and another portion is in contact with the surface of the porous polymer substrate, At least one polymer column is spaced apart from the other polymer columns by a predetermined distance, The space between the above polymer columns is filled with inorganic particles, Based on the planar image (top view) of the membrane, the surface area of ​​the polymer column exposed to the surface of the inorganic coating layer is 10% to 80% of the surface area of ​​the inorganic coating layer compared to 100% of the surface area of ​​the inorganic coating layer. The above polymer column is a separation membrane for an electrochemical device, characterized in that the zeta potential is -20 mV or less at room temperature.

2. In claim 1, The above separation membrane is characterized in that when pressurized under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C for 1 to 60 seconds, the average sphericity of the polymer column according to the following formula 1 is 0.5 or more and 1.0 or less: [Formula 1] Sphericity of polymer column = (short axis / long axis) At this time, the sphericity of the polymer column is a value calculated by obtaining a planar image (top view) by photographing the surface of the inorganic coating layer obtained when the separation membrane is pressurized under the pressure and temperature conditions using a scanning electron microscope (SEM), obtaining the average length of the major axis of the polymer column particles from the planar image, and obtaining the average length of the minor axis of the polymer column particles.

3. In claim 1, The above separation membrane has a ratio of a homopolymer column of the following formula 2 of 80% or more when pressurized for 1 to 60 seconds under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C, The above homopolymer column is a separator for an electrochemical device, characterized in that the sphericity of the polymer column of the following formula 1 is 0.9 or more: [Formula 1] Sphericity of polymer column = (short axis / long axis) [Formula 2] Proportion of homopolymer columns (%) = Number of homopolymer columns / Number of total polymer columns x 100 At this time, the number of the polymer columns is determined by photographing the surface of the inorganic surface layer obtained when the membrane is pressurized under the pressure and temperature conditions using a scanning electron microscope (SEM) to obtain a planar image (top view) of the membrane, and a polymer column distinguished by inorganic particles regardless of shape in the planar image is defined as one polymer column.

4. In claim 3, When the above membrane is pressurized under conditions of a pressure of 0.5 MPa to 20 MPa and a temperature of 20°C to 85°C for 1 to 60 seconds, the ratio of dumbbell-shaped polymer columns is 20% or less. The above dumbbell-shaped polymer column is a separator for an electrochemical device, characterized in that two or more homopolymer columns are overlapped.

5. In claim 1, The average diameter (D) of the polymer column based on the planar image (top view) of the above separation membrane 50 ) is a separator for an electrochemical device, characterized in that it has a thickness of 2 ㎛ or more and 20 ㎛ or less.

6. In claim 1, A separator for an electrochemical device, characterized in that the content of the polymer column in the above separator is 5 to 40 parts by weight based on 100 parts by weight of inorganic particles.

7. In claim 1, D of the above polymer column 10 D of the above polymer column 50 30% or more of the D of the polymer column 90 D of the above polymer column 50 A separator for an electrochemical device, characterized in that its p-value is 200% or less.

8. In claim 1, The thickness of the inorganic particle filling portion consisting of inorganic particles filled between the above polymer columns is D of the polymer columns. 50 A separator for an electrochemical device, characterized in that the particulate matter content is 85% or less.

9. In claim 1, A separator for an electrochemical device, characterized in that the surface area of ​​the polymer column exposed to the surface of the inorganic coating layer is 10% to 45% of the surface area of ​​the inorganic coating layer relative to 100% of the surface area of ​​the inorganic coating layer based on a planar image (top view) of the separator.

10. In claim 1, A separator for an electrochemical device, wherein the above-mentioned inorganic coating layer has a pore structure due to the interstitial volume between inorganic particles.

11. An electrochemical device comprising a separator for an electrochemical device according to claim 1.

Images