Separator for electrochemical device and method for manufacturing same

Abstract

A separator according to the present invention not only demonstrates excellent adhesion to electrodes but also ensures sufficient porosity, thereby exhibiting outstanding resistance and ion conductivity characteristics. In addition, the present invention enables a reduction in lamination process time during the manufacture of electrode assemblies, thereby achieving high process efficiency in battery production.

Description

Separator for electrochemical devices and method for manufacturing the same

[0001] This application claims priority to Korean Patent Application No. 10-2023-0194078, filed December 28, 2023. The present invention relates to a separator for electrochemical devices such as lithium-ion secondary batteries.

[0002]

[0003] 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.

[0004] 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 fire.

[0005] Accordingly, in order to solve the above problems, a method of improving heat resistance by forming a porous filler layer in which inorganic particles and binder resin are mixed on at least one side of a polymer substrate 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, and thus the electrode and the separator may become separated during the battery manufacturing process or battery operation.

[0006] Meanwhile, electrode assemblies are typically manufactured using a roll-to-roll continuous process, followed by a lamination process that pressurizes (and, if necessary, applies hot presses) the laminated 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, including reduced production speeds.

[0007] Accordingly, continuous research and development is required to secure sufficient porosity and adhesive strength (between electrodes and separators) and process efficiency in separators for electrochemical devices.

[0008]

[0009] 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.

[0010]

[0011] The first 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.

[0012] The above-mentioned inorganic coating layer includes a plurality of adhesive polymer columns of a predetermined volume, the polymer columns being made of a polymer material and having no pores, at least a portion of the polymer columns being exposed to the surface of the inorganic coating layer and another portion being in contact with the surface of the porous substrate, each polymer column being spaced apart from each other by a predetermined distance, the space between the polymer columns being filled with inorganic particles, and the polymer columns having a storage elastic modulus at room temperature of 1,000 Pa to 3,500 Pa.

[0013] In the aforementioned aspect of the present invention, the polymer column may have a ratio of the storage elastic modulus at 60°C to the storage elastic modulus at room temperature (G'(60°C) / G'(room temperature)) of 0.1 or less.

[0014] In at least one of the aforementioned aspects, the present invention provides that in the first or second aspect, the polymer column may have at least one tan δ peak in the range of 45°C to 80°C when measured by a Dynamic Mechanical Analyzer (DMA; Rheovibron).

[0015] In at least one of the aforementioned aspects, the present invention may be such that the area (a) of the polymer column cross-section confirmed in the lower 5% from the lowest portion of the inorganic coating layer toward the surface and the area (b) of the column cross-section confirmed in the upper 5% from the top portion toward the bottom may be greater than the area (a).

[0016] In at least one of the aforementioned aspects, the present invention provides that at least one polymer column included in the inorganic coating layer may have a diameter (a) at the bottom of the polymer column that is shorter than a diameter (b) at the top of the column in a cross-section of the polymer column confirmed in a vertical cross-section of the inorganic coating layer, and the ratio of the diameter (b) to the diameter (a) may be 2 to 20.

[0017] In at least one of the aforementioned aspects of the present invention, the polymer column can protrude a predetermined height outside the surface of the inorganic coating layer, and when pressurized with a pressure of 0.5 MPa or more and 20.0 MPa or less, the protruding portion can be flattened so that the thickness of the inorganic coating layer can be uniform.

[0018] In at least one of the aforementioned aspects, the inorganic coating layer may have a pore structure due to interstitial volume between inorganic particles.

[0019] Meanwhile, the present invention relates to an electrochemical device, and includes a separator for an electrochemical device according to any one of the aforementioned aspects.

[0020] 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.

[0021]

[0022] The separator according to the present invention not only exhibits excellent adhesion to electrodes but also secures sufficient porosity, resulting in superior resistance and ionic conductivity characteristics. Furthermore, it can shorten the lamination process time during electrode assembly manufacturing, thereby achieving high process efficiency in battery manufacturing.

[0023]

[0024] 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.

[0025] Figures 1a to 1c show SEM images of the surface of the inorganic coating layer of the separator manufactured in Example 1.

[0026] Figures 1d and 1e show SEM images of the surface of the inorganic coating layer after flattening of the separator manufactured in Example 1.

[0027] Figures 2a to 2c are SEM images of the surface of the inorganic coating layer of the separator manufactured in Example 2.

[0028] Figures 3a to 3c are SEM images of the surface of the inorganic coating layer of the separator manufactured in Example 3.

[0029] Figures 4a to 4c are SEM images of the surface of the inorganic coating layer of the separator manufactured in Example 4.

[0030] Figures 5a to 5c are SEM images of the surface of the inorganic coating layer of the separator manufactured in Comparative Example 1.

[0031] Figures 6a to 6c are SEM images of the surface of the inorganic coating layer of the separator manufactured in Comparative Example 2.

[0032] Figures 7a and 7b are SEM images of the inorganic coating layer of the separator manufactured in Comparative Example 3 after flattening.

[0033] Figure 8 is a schematic diagram showing a cross-section of the separation membrane of the present invention.

[0034] Figure 9 shows the change in storage elastic modulus according to temperature of the polymer column used in the example and the polymer column used in the comparative example.

[0035]

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0040] Entry D in the original specification 50 D means the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. That is, D 50 refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. In addition, D 10D means the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. 90 It means the particle size at the 90% point of the cumulative distribution of the number of particles according to the particle size. The particle size 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 size when the particles pass through the laser beam. By calculating the particle diameters at the points where the particle number is 10%, 50% and 90% of the cumulative distribution of the number of particles according to the particle size in the measuring device, respectively, D 10, D 50 and D 90 can be measured.

[0041]

[0042] 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.

[0043] 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).

[0044]

[0045] The present invention relates to a separator for an electrochemical device and an electrochemical device including 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.

[0046]

[0047] A separation membrane according to the present invention comprises a porous substrate including a plurality of pores and an inorganic coating layer formed on at least one surface of the porous substrate.

[0048]

[0049] membrane

[0050] In one embodiment of the present invention, the separator includes a porous substrate (10) and an inorganic coating layer (20) formed on at least one side or both sides of the porous substrate. Fig. 8 is a schematic diagram illustrating a cross-section of the separator of the present invention, in which inorganic particles (200) and polymer columns (100) are arranged. Fig. 8 particularly illustrates an embodiment of the separator before compression (pressurization) during the manufacturing process of the separator, in which the polymer columns protrude beyond the inorganic particle filling portion. The compression may mean that an external force is artificially applied during the battery assembly process.

[0051] The separator may have a total thickness of 5.0 μm to 30.0 μm and may be appropriately adjusted within the above range. For example, the range may be 25.0 μm or less, 20.0 μm or less, 15.0 μm or less, 12.0 μm or less, or 10.0 μm or less. In one embodiment of the present invention, the separator may be introduced during the manufacture of an electrode assembly and, after being flattened by performing a pressurizing process such as lamination, may have a thickness of 15.0 μm or less, 14.0 μm or less, 13.0 μm or less, 12.0 μm or less, 11.0 μm or less, or 10.0 μm or less. In addition, the separator may have a porosity of about 25 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 / 100 cc or more and about 250 sec / 100 cc or less. The permeability may be appropriately controlled within the above-mentioned range. For example, the permeability may be 60 sec / 100 cc or more, or 70 sec / 100 cc or more, or 100 sec / 100 cc or more, or 120 sec / 100 cc or more, or 150 sec / 100 cc or more. Alternatively, the porosity may be 220 sec / 100cc or less, or 200 sec / 100cc or less, or 180 sec / 100cc or less.

[0052] In one embodiment of the present invention, the thickness of the separator can be determined by cutting a cross-section of a separator sample, observing it through an SEM, and then taking the thickness of the thickest point as the thickness of the separator. Alternatively, the thicknesses of two or more arbitrary points can be measured and the average value thereof can be taken as the thickness of the separator. If the thicknesses of four or more points are measured, the lowest and / or highest values ​​can be excluded and the average value of the remaining values ​​can be taken.

[0053] 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 (net density). For example, the porosity can be calculated by [Formula 1] below.

[0054]

[0055] [Formula 1]

[0056] Porosity (vol%) = {1-(apparent density / true density)} × 100

[0057]

[0058] Meanwhile, the apparent density in the above formula can be calculated from [Formula 2] below.

[0059]

[0060] [Formula 2]

[0061] Apparent density (g / cm) 3 ) = {Weight of the measurement object [g] / (Thickness of the measurement object [cm] × Area of ​​the measurement object [cm 2 ])}

[0062]

[0063] 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.

[0064] 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 porous 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 µm by the formula: P2 = (P1 × 20) / T1.

[0065]

[0066] porous substrate

[0067] The above porous substrate refers to a substrate having multiple pores formed therein as an ion-conducting barrier that allows ions to pass through while blocking electrical contact between the cathode and anode. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0068] The material constituting the porous 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 constituent material of the substrate. Here, the shutdown function refers to a function in which, when the battery temperature rises, the thermoplastic resin melts and closes the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. Suitable thermoplastic resins include those with a melting point below 200°C, and polyolefin is particularly preferred.

[0069] 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 substrate may be, but is not particularly limited to, a non-woven fabric, a porous polymer film, or a laminate of two or more thereof.

[0070]

[0071] Specifically, the porous polymer substrate is one of the following a) to e).

[0072]

[0073] a) A porous film formed by melting / extruding a polymer resin,

[0074] b) A multilayer film in which two or more layers of the porous film of a) above are laminated,

[0075] c) A nonwoven web manufactured by accumulating filaments obtained by melting / spinning a polymer resin.

[0076] d) A multilayer film in which two or more layers of the nonwoven web of the above b) are laminated,

[0077] e) A porous composite membrane having a multilayer structure comprising two or more of the above a) to d).

[0078]

[0079] In the present invention, the porous 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.

[0080] In one embodiment of the present invention, the weight average molecular weight (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 substrate may have a value of 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 curvature radius of 0.5 mm and a puncture speed of 2 mm / sec.

[0081] 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 μm to 12 μm may be used. Meanwhile, for example, the porous substrate may have a porosity of 20 vol% to 80 vol% or 30 vol% to 60 vol%, and a pore size of 10 nm to 200 nm, but is not particularly limited thereto.

[0082]

[0083] Inorganic coating layer

[0084] In the present invention, the separation membrane includes an inorganic coating layer formed on one surface of the porous substrate. The inorganic coating layer includes a plurality of polymer columns and a plurality of inorganic particles.

[0085] In a specific embodiment of the present invention, the inorganic particles in the inorganic coating layer may be included in a range of about 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%, based on 100 wt% of the inorganic coating layer. In addition, the polymer column may be included in a range of 5 wt% to 30 wt%, preferably 10 wt% to 25 wt%, based on 100 wt% of the inorganic particles.

[0086] If the content of the polymer column in the inorganic coating layer is low, it is difficult to secure the desired level of adhesive strength. However, if the content exceeds the above range and is too large, the Gurley value and / or porosity of the separation membrane may decrease, which is not desirable.

[0087] Meanwhile, in the planar image of the inorganic coating layer, the total area of ​​the polymer columns before or after compression or both may be 5% to 80%, 5% to 60%, or 5% to 40% of the total area of ​​the inorganic coating layer. In one embodiment of the present invention, preferably, the total area of ​​the polymer columns may be 10% to 35% of the total area of ​​the inorganic coating layer.

[0088] In the above-described inorganic coating layer, the polymer columns may be clustered in groups of two or more polymer columns, or the individual polymer columns may be spaced apart from each other by a predetermined interval. In one embodiment of the present invention, the amount of the two or more polymer columns clustered is 30 vol% or less, preferably 20 vol% or less, and more preferably 10 vol% or less, based on 100 vol% of the total polymer columns. If the polymer columns are excessively clustered, it may cause non-uniformity of resistance in the separation membrane. Therefore, in terms of increasing the uniformity of resistance, it is preferable that the amount of the polymer columns forming the cluster is 10 vol% or less based on 100 vol% of the total polymer columns.

[0089] 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 direct contact with other polymer columns. In the 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 among these, the protrusion height (T) of some of the polymer columns p ) can exceed 1㎛. For example, T pmay be greater than 1㎛ and less than or equal to 10㎛, for example, less than or equal to 7㎛, 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 fact that the polymer columns protrude outside the surface of the inorganic coating layer means that the height of the polymer columns is higher than the height of the inorganic particle filling portion in the inorganic coating layer, and thus has a higher height than the inorganic particle filling portion.

[0090]

[0091] 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 in combination 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.

[0092]

[0093] In one embodiment of the present invention, the porosity of the inorganic coating layer (porosity in a state where the polymer column is included) is preferably 30 vol% to 80 vol%. The porosity can 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% or more, it is advantageous in terms of lithium ion permeability, and if the porosity is 80% or less, the surface opening ratio is not too high, which is suitable for securing adhesion between the separator and the electrode.

[0094]

[0095] polymer column

[0096] The polymer column may comprise at least 90 wt% of a polymer resin relative to 100 wt% of the polymer column. Preferably, the polymer column may be formed of a 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 substrate.

[0097] 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.

[0098] 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.

[0099] In one embodiment of the present invention, D of the polymer column 10 Silver D 50 It can be more than 30% of D 90 Silver D50 may be less than 200% of the D of the polymer column, together with or independently of this. 50 Silver mineral particles D 50 The contrast can be twice or more.

[0100] In one embodiment of the present invention, D of the polymer column 50 can be about 2.0 to 7.0㎛ and can be appropriately controlled within the above range. For example, the above D 50 This can have a range of 3㎛ to 6㎛. D of the polymer column 50 It reflects the state before the membrane is pressurized, preferably before slurry preparation.

[0101]

[0102] In one embodiment of the present invention, the separation membrane may have one or more polymer columns higher than the height of the inorganic particle filling portion when not artificially pressurized after manufacture. That is, they may protrude from the surface of the inorganic particle filling portion. In one embodiment of the present invention, when the polymer columns protrude outside the inorganic coating layer, the thickness of the inorganic particle filling portion is D of the polymer columns. 50 may be 85% or less of the D of the polymer column. Meanwhile, in one embodiment of the present invention, the thickness of the inorganic filling portion is 50 may be 20% or more. Meanwhile, 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.

[0103] Meanwhile, 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.

[0104]

[0105] Meanwhile, in one embodiment of the present invention, when the one or more polymer columns are pressed at a pressure of 0.5 MPa or more and 20.0 MPa or less, for example, when pressed at a pressure of 2.0 MPa to 8.0 MPa, the protruding portions are pressed and flattened, so that the thickness of the inorganic coating layer becomes uniform. Meanwhile, the pressing may be hot pressing. This property is advantageous in strengthening the adhesion between the electrode and the separator during the manufacture of the electrode assembly and in preventing the occurrence of 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.

[0106]

[0107] In one embodiment of the present invention, the separation membrane has a height (T) of the inorganic coating layer when compressed under pressure conditions of 2.0 MPa to 8.0 MPa and 55°C to 65°C. c ) is the height of the inorganic particle filling part (T i ) is 1.1 times the height of the inorganic particle filling part (T i )× 1.1) can be less than that. In addition, T, which is the protrusion height of the polymer column 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 part and the polymer column is reduced, so that the separation membrane is flattened. Referring to FIG. 8, 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 equal to the height of the tallest protruding member of the polymer column.

[0108] Meanwhile, in the present invention, the T pIt is based on the highest part of the inorganic coating layer from the inorganic particle filling part.

[0109]

[0110] 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.

[0111]

[0112] The above compression conditions typically assume the lamination process conditions for electrodes and separators used in electrode assembly manufacturing. These properties are advantageous in strengthening the adhesion between the electrodes and separators during battery manufacturing and ensuring close contact between the electrodes and separators, preventing gaps.

[0113] Meanwhile, in the present specification, the flattening means that the thickness of the inorganic particle filling portion and the height of the polymer column are the same or the difference between the heights of the inorganic particle filling portion and the polymer column is 1 ㎛ or less or less than 1 ㎛, preferably 0.5 ㎛ or less than 0.5 ㎛, more preferably 0.3 ㎛ or less than 0.3 ㎛. In one embodiment of the present invention, the height of the polymer column is the highest height (T) among the polymer columns. c ) can be used as a standard.

[0114] That is, when the separator according to the present invention is applied to battery manufacturing, an inorganic coating layer (T) is formed after laminating the electrode and the separator. c ) thickness of polymer column D 50 Smaller is preferable.

[0115]

[0116] 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.

[0117] In the present invention, the polymer column preferably has a storage modulus (G') of 1,000 to 3,500 Pa at room temperature in terms of flattening by pressurization. The storage modulus may be more preferably 1,000 to 3,000 Pa. The storage modulus may be controlled to 2,000 Pa or less, or 1,500 Pa within the above range. Preferably, the storage modulus may be for a material forming the polymer column. In addition, the polymer column has a ratio of the storage modulus at 60°C to the storage modulus at room temperature (G'(60°C) / G'(room temperature)) of 0.05 or less, taking into account the temperature application situation in an actual battery assembly process. More preferably, it is 0.01 or more and 0.05 or less. In one embodiment of the present invention, the room temperature may have a range of 20°C to 25°C. In one embodiment of the present invention, the polymer column may have a storage modulus at a high temperature, for example, from 55°C to 65°C, in a range of from 0.05 Pa to 100 Pa. In a more specific embodiment, the storage modulus may be a storage modulus at 60°C.

[0118] In addition, more preferably, the polymer column may have at least one tan δ peak in the range of 45°C to 80°C when measured by a Dynamic Mechanical Analyzer (ARES-G2, TA Instrument). If the tan δ peak appears at a temperature lower than 45°C, the adhesive properties between the wound membranes are expressed, which is not preferable, and if the temperature exceeds 80°C, the storage elastic modulus does not drop sharply even when the temperature is applied, making it difficult to flatten the polymer column in high-temperature pressurized fixation.

[0119]

[0120] 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', storage modulus) at 45°C and the slope of the storage modulus (G', storage modulus) at 60°C to 70°C can be measured through the DMA.

[0121]

[0122] In a specific embodiment of the present invention, the polymer column may have a dissolved amount (weight) of 55% or less after being dissolved in THF (Tetrahydrofuran) for 1 to 48 hours. The amount (weight) may be preferably 35% or less, more preferably 25% or less, even more preferably 22% or less, and most preferably 20% or less.

[0123] During battery manufacturing, there is a risk that the polymer column may dissolve and lose adhesive strength after liquid electrolyte injection, or that the dissolved components may increase the viscosity of the liquid electrolyte, thereby increasing the resistance of the lithium secondary battery. Therefore, it is desirable to have appropriate solubility as described above. For example, the surface of the material forming the polymer column can be cross-linked to reduce its solubility in organic solvents or electrolytes.

[0124]

[0125] 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 acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexylacrylate, heptyl acrylate, 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, octyl methacrylate, It may include one or more repeating units of 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 unit 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.

[0126] Meanwhile, in a specific 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.

[0127]

[0128] 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.

[0129]

[0130] 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 when it is flattened by pressing. 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.

[0131]

[0132] In one embodiment of the present invention, the length of the diameter and / or the size of the cross-section of the polymer column can be measured for an area corresponding to a specific gray level corresponding to the polymer column by dividing the SEM image for the horizontal or vertical cross-section of the separation membrane into gray levels. 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 may be a value of 0 to 255. In a specific embodiment of the present invention, the polymer column may have a gray level of 10 to 50, and the inorganic particle may have a gray level of 160 to 220. Accordingly, the area of ​​the polymer column can be set and defined from pixels having gray levels of 10 to 50 in the SEM image of any cross-section of the separation membrane, and its length and area can be calculated. In the present invention, the electrode cross-section SEM image 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) on a cross-section of an electrode obtained by argon ion milling, and then performing image processing.

[0133] In another specific embodiment of the present invention, the diameter or area of ​​the polymer column can be calculated by three-dimensionally modeling the separation membrane and / or the inorganic coating layer and then obtaining an arbitrary cross-section therefrom.

[0134]

[0135] Inorganic particle filling section

[0136] In the inorganic coating layer of the above-described separation membrane, the space between the polymer columns may be filled with inorganic particles or a mixture including inorganic particles and a binder resin. In the present specification, the portion filled with inorganic particles, etc., is referred to as an “inorganic particle filling portion.” The inorganic filling portion may further include a binder resin to secure adhesion between the inorganic particles and between the inorganic particles and the porous 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.

[0137]

[0138] 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 5% to 40% of T. In a specific embodiment, T i The T may be 1.0㎛ to 5㎛ and can be appropriately adjusted within the above range. i For example, it can be 4㎛ or less, 3㎛ or less, or 2㎛ or less. Within the above numerical range, the adhesion to the electrode is excellent, and as a result, the cell strength of the battery can be increased. Meanwhile, if the thickness is 5.0㎛ or less, it is advantageous in terms of the cycle characteristics and resistance characteristics of the battery. In addition, since the thickness of the separator is reduced, the energy density of the battery can be improved when applied to 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.

[0139]

[0140] In one embodiment of the present invention, the height (thickness, T) of the inorganic particle filling portion (one side) 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 measuring the thickness of four or more points, the lowest and / or highest values ​​can be excluded, and the average value of the remaining values ​​can be taken. In the present invention, the lowest point of the inorganic particle filling portion is the surface of the porous substrate.

[0141] 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.

[0142]

[0143] inorganic particles

[0144] In a specific embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, they can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0145] 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), b 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC and TiO2 or mixtures thereof.

[0146] 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 Al y 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 glass (Li) such as Li3PO4-Li2S-SiS2 x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass(Li x P y S z , 0 < x < 3, 0< y < 3, 0 < z < 7) or mixtures thereof.

[0147]

[0148] In addition, the average particle size of the inorganic particles is not particularly limited, but is preferably in the range of 0.1 µm to 1.5 µm for the formation of a coating layer of uniform thickness and an appropriate porosity. If it is less than 0.1 µm, dispersibility may be reduced, and if it exceeds 1.5 µm, the thickness of the formed coating layer may increase.

[0149] According to a non-limiting embodiment of the present invention, the diameter (D50) of the inorganic particles can be appropriately adjusted in the range of 0.1 μm to 1.5 μm, and for example, can have a range of 200 nm to 1 μm.

[0150]

[0151] binder resin

[0152] 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.

[0153]

[0154] 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.

[0155] 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 (meth)acrylic acid ester as a monomer, and non-limiting examples thereof include a (meth)acrylic polymer containing butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as monomers.

[0156]

[0157] In addition, 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 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), hydroxy alkyl methyl cellulose, and cyanoethylene polyvinyl alcohol.

[0158]

[0159] Membrane manufacturing method

[0160] 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.

[0161] Specifically, a mixture is first prepared by adding inorganic particles to an appropriate solvent. Next, polymer particles for polymer columns are added to the mixture to prepare a slurry for an inorganic coating layer. Next, the slurry is applied to a porous substrate and dried.

[0162] In one embodiment of the present invention, when the inorganic coating layer further comprises a binder resin, the binder resin may be dissolved in a solvent to prepare a polymer solution, and then inorganic particles and polymer particles for polymer columns may be sequentially or simultaneously added to the polymer solution to prepare a slurry for the inorganic coating layer. The binder resin is preferably a water-soluble binder resin or a material having high affinity with the polymer particles for polymer columns.

[0163] Thereafter, the obtained separator can be dried to form an inorganic coating layer integrally on the porous substrate. At this time, the drying temperature of the separator is preferably set to a temperature of +20°C or lower than the temperature at which the tan δ peak of the polymer column material is observed, in order to prevent deformation of the polymer column.

[0164]

[0165] In the production 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.

[0166]

[0167] The above slurry can be applied using conventional coating methods such as a Meyer bar, die coater, reverse roll coater, or gravure coater. Meanwhile, the drying can be performed using a conventional method for removing the solvent. Examples of the drying method include, but are not limited to, natural drying, air drying, warm air or hot air drying, high-temperature drying, and convection drying.

[0168]

[0169] 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.

[0170]

[0171] Meanwhile, the present invention provides a secondary battery including the separator. The battery includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is a separator having the characteristics described above.

[0172]

[0173] 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 xNi-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); 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.

[0174]

[0175] 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 Me 1-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.

[0176]

[0177] 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.

[0178]

[0179] 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.

[0180]

[0181] 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.

[0182]

[0183] The electrode assembly prepared as above can be placed in an appropriate case and an electrolyte can be injected to manufacture a battery.

[0184]

[0185] 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, such as - 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.

[0186]

[0187] 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.

[0188] 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.

[0189]

[0190] 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.

[0191] Hereinafter, the present invention will be described in detail with examples to specifically illustrate it. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. These examples are provided to more fully explain the present invention to those of average skill in the art.

[0192]

[0193] Example

[0194] Membrane thickness measurement

[0195] In the examples and comparative examples, the thickness of the membrane was measured by cutting a cross-section of the membrane specimen and observing it through SEM, and then measuring the thickness of the thickest point as the thickness of the membrane (T s ) was used. Meanwhile, the thickness of the inorganic particle filling part (T i ) was the average of the values ​​measured at three random points. This was summarized and recorded in [Table 1] below.

[0196]

[0197] Measurement of storage modulus of polymer columns

[0198] A 40 x 6 mm sample was fabricated using polymer materials A15 and A25 to be used as polymer columns. The thickness of the sample was 1 mm. The storage 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 temperature conditions of -60℃ to 80℃ and a frequency of 1.0 rad / s. The results are summarized in Table 1 below. Meanwhile, Fig. 9 shows the storage modulus for each of A15 and A25 at different temperatures. Referring to this, it was confirmed that A15 has a higher storage modulus at room temperature than A25, and that the slope of the tangent to the inflection point of A15 is steeper than that of A25 at high temperatures.

[0199]

[0200] Solubility measurement of polymer columns

[0201] In the comparative examples and examples, polymer materials used as polymer columns were dried at 60°C to produce 0.3 g samples. The samples were placed in an 80-mesh mesh bag and dissolved in THF (Tetrahydrofuran, 25°C) for 24 hours. The residual weight was compared to the initial weight. The solubility was calculated based on [Formula 3] below. This is summarized and presented in [Table 1] below.

[0202]

[0203] [Formula 3]

[0204] Solubility (%) = {(Weight measured before immersion - Weight measured after immersion) / Weight measured before immersion)} x 100

[0205]

[0206] Storage modulus (25℃, Pa) Storage modulus (60℃, Pa) G' (60℃) / G' (room temperature, ℃) tan δ peak (℃, 40℃ to 80℃) Solubility (%) Tg (℃) Acrylic polymer A1 5 1,381.0 5 0.10.0 3 6 6 9.9 1 9 % 59.3 Acrylic polymer A2 5 25.11.8 0.07 2 6 2.8 8 2 % 41.1

[0207]

[0208] Example 1

[0209] Inorganic particles (Al2O3, D50 approximately 0.6 ㎛), acrylic emulsion (Toyo, CSB-130) as binder resin, and carboxyl methyl cellulose (Daicel, Daicel1220) were added in a 96:2:2 ratio to a 95:5 water:ethanol solution and a dispersion process using a bead mill was performed to obtain a mixture. Polymer particles for a polymer column (acrylic polymer A15, D) were added to the mixture. 503.84㎛) was added and stirred to obtain a dispersion slurry. The concentration of solids in the dispersion slurry was 30 wt%. The content of polymer particles for polymer columns in the mixture was about 11 parts by weight per 100 parts by weight of inorganic particles. The dispersion slurry was applied to a porous substrate (Asahi, ND506, thickness 6㎛) 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. The loading amount (one side) of the inorganic coating layer in the separator was 5.3 g / m 2 It was.

[0210] Figures 1a and 1b illustrate SEM images of the surface of the obtained membrane. Additionally, Figure 1c illustrates an SEM image of a cross-section of the membrane. Referring to these, it can be seen that the polymer columns are exposed on the surface of the inorganic coating layer, and their lower ends are in contact with the porous substrate. Furthermore, it was confirmed that each polymer column is spaced apart at a predetermined interval and distributed in a sea-island pattern.

[0211] Meanwhile, the obtained membrane was hot pressed at 2.5 MPa and 65°C for 20 seconds to flatten its surface. Figures 1d and 1e show SEM images of the membrane surface after flattening. Referring to these images, it was confirmed that the protruding portion of the polymer column was pressed and flattened.

[0212]

[0213] Meanwhile, the ratio of the length of the lower diameter (a) and the upper diameter (b) of the polymer column before and after pressurization was confirmed using the SEM image of the separation membrane of Example 1, and the values ​​are summarized and shown in Table 2 below. Measurements were made on both sides of the separation membrane below, and are listed separately as the upper surface and the lower surface in Table 2. Referring to this, it was confirmed that the ratio of b / a before and after pressurization both exceeded 2.

[0214]

[0215] a(㎛)b(㎛)b / aPressurized upper surface0.834.415.31Lower surface2.114.572.17Pressurized upper surface2.426.192.56Lower surface1.072.372.21

[0216]

[0217] Example 2

[0218] 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 set to about 16 parts by weight per 100 parts by weight of inorganic particles, and the separation membrane substrate (Toray, B09PJ1, thickness 9 ㎛) was changed and coated only on the cross-section.

[0219] Figures 2a and 2b illustrate SEM images of the surface of the obtained membrane. Additionally, Figure 2c illustrates an SEM image of a cross-section of the membrane. Referring to these images, it can be seen that the polymer columns are exposed on the surface of the inorganic coating layer, and their lower ends are in contact with the porous substrate. Furthermore, it was confirmed that each polymer column is spaced apart at a predetermined interval and distributed in a sea-island pattern.

[0220] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 65°C for 20 seconds to flatten the surface.

[0221]

[0222] Example 3

[0223] A separation membrane was manufactured in the same manner as in Example 2, except that the content of polymer particles for the polymer column was set to about 21 parts by weight per 100 parts by weight of inorganic particles.

[0224] Figures 3a and 3b illustrate SEM images of the surface of the obtained membrane. Additionally, Figure 3c illustrates an SEM image of a cross-section of the membrane. Referring to these images, it can be seen that the polymer columns are exposed on the surface of the inorganic coating layer, and their lower ends are in contact with the porous substrate. Furthermore, it was confirmed that each polymer column is spaced apart at a predetermined interval and distributed in a sea-island pattern.

[0225] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 65°C for 20 seconds to flatten the surface.

[0226]

[0227] Example 4

[0228] A separation membrane was manufactured in the same manner as in Example 2, except that the content of polymer particles for the polymer column was set to about 26 parts by weight per 100 parts by weight of inorganic particles.

[0229] Figures 4a and 4b illustrate SEM images of the surface of the obtained membrane. Additionally, Figure 4c illustrates an SEM image of a cross-section of the membrane. Referring to these images, it can be seen that the polymer columns are exposed on the surface of the inorganic coating layer, and their lower ends are in contact with the porous substrate. Furthermore, it was confirmed that each polymer column is spaced apart at a predetermined interval and distributed in a sea-island pattern.

[0230] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 65°C for 20 seconds to flatten the surface.

[0231]

[0232] Comparative Example 1

[0233] Inorganic particles (Al2O3, D50 approximately 0.6㎛), acrylic emulsion as binder resin (Toyo, CSB-130), and carboxyl methyl cellulose (Daicel, Daicel1220) were added at a ratio of 96:2:2 to a water:ethanol 95:5 solution and stirred to obtain a mixture. The mixture was applied to a porous substrate (Toray, B09PJ1) by microgravure coating and dried at a temperature of 80°C.

[0234] Figures 5a and 5b show SEM images of the surface of the obtained separator. In addition, Figure 5c shows an SEM image of a cross-section of the separator.

[0235] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 65°C for 20 seconds to flatten the surface.

[0236]

[0237] Comparative Example 2

[0238] A separation membrane was manufactured in the same manner as in Example 2, except that the content of polymer particles for the polymer column was set to about 6 parts by weight per 100 parts by weight of inorganic particles.

[0239] Figures 6a and 6b show SEM images of the surface of the obtained membrane. Additionally, Figure 6c shows an SEM image of a cross-section of the membrane. Referring to the SEM images, Comparative Example 2 had a smaller proportion of polymer columns per unit area compared to the Examples.

[0240]

[0241] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 65°C for 20 seconds to flatten the surface.

[0242]

[0243] Comparative Example 3

[0244] Change the polymer particles for the polymer column (acrylic polymer A25, D 50A membrane was manufactured in the same manner as in Example 4, except that the thickness was 3.92 μm.

[0245] Meanwhile, the obtained separation membrane was pressed with a hot press at 2.5 MPa and 45°C for 20 seconds to flatten the surface. Referring to Figures 7a and 7b, which show SEM images after flattening, the polymer column of Comparative Example 3 was not sufficiently flattened compared to the example.

[0246]

[0247] Manufacturing of anodes

[0248] LiCoO as a cathode active material 　2 , carbon black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent at a weight ratio of 96:2:2 to prepare a cathode active material slurry. The cathode active material slurry was coated on a sheet-shaped aluminum current collector and dried to obtain a final cathode loading of 3.8 mAh / cm. 2 To achieve this, a positive electrode active material layer was formed.

[0249]

[0250] Manufacturing of cathode

[0251] 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 2 A negative electrode having a negative active material layer formed by coating and drying a copper current collector with a loading amount of was prepared.

[0252]

[0253] Evaluation of dry adhesion between cathode and separator

[0254] The membrane samples obtained in each example or comparative example 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.

[0255] Referring to Tables 3 and 4 below, it was confirmed that Comparative Example 1 had lower adhesive strength than Examples 1 to 4. Examples 1 to 4 secured higher adhesive strength than Comparative Example 2 for the same pressurization time. Accordingly, it was confirmed that the separator according to the present invention has excellent adhesive strength and can shorten the time required for lamination, which is also advantageous in terms of processability.

[0256]

[0257] Method for evaluating wet adhesion between anode and separator

[0258] The membrane samples obtained in each example or comparative example 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 anode, a laminate was obtained by heating and pressing at 50°C for 20 seconds. This was immersed in an electrolyte and maintained for 24 hours. Afterwards, each laminate was taken out of the electrolyte and 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. The electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 7:3 and contained LiPF6 in a concentration of 1 M.

[0259] Referring to Tables 3 and 4 below, it was confirmed that Examples 1 to 4 had higher adhesive strength than Comparative Examples 1 and 2.

[0260]

[0261] Resistance measurement method

[0262] The resistance of the separators of each example and comparative example was measured by impedance measurement. Coin cells were fabricated by sandwiching each separator between stainless steel plates, and 1 MLiPF6 was injected into an ethylene carbonate / ethyl methyl carbonate (EC / EMC, volume ratio 30:70) electrolyte. 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.

[0263] Referring to Tables 3 and 4 below, it was confirmed that Examples 1 to 4 had resistance values ​​at levels appropriate for battery operation.

[0264]

[0265] Thickness measurement

[0266] For the membranes manufactured in each example and comparative example, the thickness was measured by image analysis of the obtained SEM images. The thickness of the membrane was measured based on the thickest point among the measured points. Meanwhile, the thickness of the inorganic particle-filled portion was determined as the average of the values ​​measured at three random points.

[0267]

[0268] In Examples 1 to 4, it was confirmed that the polymer column was flattened after pressing, and that the thickness of the polymer column and the thickness of the inorganic particle filling were almost the same. However, in the case of Comparative Example 3, it was confirmed that the polymer column was not pressed well, and that it protruded beyond the surface of the inorganic particle filling by more than 1 μm even after pressing.

[0269]

[0270] Example 1 Example 2 Example 3 Example 4 Thickness of the separation membrane (T s ) (㎛)10.613.713.513.3 Thickness of inorganic particle filling (CCS) (T i )(㎛) : SEM (㎛)3.23.23.13.1 Application amount of inorganic coating layer (g / m 2 )5.35.44.64.7 Coverage of polymer column (%)16.221.627.433.8 Cathode / Separator Dry Adhesion (gf / 25mm)1 sec press6.68.215.722.810 sec press24.629.233.335.1 Membrane thickness after press (T s )(㎛)9.412.512.412.3 Thickness of polymer column protrusion after pressing (T p )(㎛)0.20.10.20.1 Wet adhesion of positive electrode / separator (g / m) 2 )18.624.526.036.2Resistance (ohm)0.8420.8590.8630.877

[0271]

[0272] Comparative Example 1 Comparative Example 2 Comparative Example 3 Membrane thickness (T s ) (㎛)11.813.813.6 Thickness of inorganic particle filling (CCS) (T i )(㎛) : SEM2.84.13.9 Application amount of inorganic coating layer (g / m) 2 )4.55.04.9 Coverage of polymer column (%)n / a8.432.9 Cathode / membrane Dry adhesion (gf / 25mm)1 sec pressn / an / a19.610 sec pressn / a11.132.2 Membrane thickness after press (T s)(㎛)11.013.314.2 Thickness of polymer column protrusion after pressing (T p )(㎛)n / a0.21.3Anode / Separator Wet Adhesion (g / m) 2 )n / a9.633.1Resistance (ohm)0.8020.8140.833

[0273]

[0274] Measurement of molecular weight

[0275] Molecular weight (weight-average molecular weight / number-average molecular weight) was measured using gel permeation chromatography (GPC). Agilent Technologies PL GPC220 was used, and the measurement conditions were as follows.

[0276] - Column (maker, model no.): 2 x TSKgel SupermultiporeHZ-M + TSKgel SuperHZ-2500

[0277] - Eleunt: THF

[0278] - Temperature: 40℃

[0279] - Flow rate: 1.0 mL / min

[0280] - Injection volume, sample concentration: 30 ㎕, 1~10 mg / mL

[0281] - Standard: Polystyrene

[0282] - Detector: RI

[0283]

[0284] Measurement of glass transition temperature

[0285] The glass transition temperature (Tg) was measured using a DSC (Differential Scanning Calorimetry, TA Instrument). Samples weighing 10 to 15 mg each were obtained, cooled from ambient temperature to -30°C, and then heated to 200°C at 10°C / min. Measurements were then taken after cooling to -30°C and reheating at 10°C / min.

[0286]

[0287] [Explanation of symbols]

[0288] 10 Porous substrates

[0289] 20 layers of weapon coating

[0290] 100 polymer columns

[0291] 200 inorganic particles

[0292] T s Thickness of the membrane

[0293] T p Protrusion height of polymer column

[0294] T i Height of the inorganic particle filling part

[0295] T c Height of the inorganic coating layer

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 substrate, Each polymer column is spaced apart from each other by a predetermined distance, The space between the above polymer columns is filled with inorganic particles, The above polymer column is a separator for an electrochemical device having a storage elastic modulus at room temperature of 1,000 Pa to 3,500 Pa.

2. In paragraph 1, The above polymer column is a separator for an electrochemical device, wherein the ratio of the storage elastic modulus at 60°C to the storage elastic modulus at room temperature (G'(60°C) / G'(room temperature)) is 0.1 or less.

3. In paragraph 1, A separator for an electrochemical device, wherein the polymer column has at least one tan δ peak in a range of 45°C to 80°C as measured by a Dynamic Mechanical Analyzer (DMA; Rheovibron).

4. In paragraph 1, An electrochemical device separator, wherein at least one polymer column included in the inorganic coating layer has a cross-sectional area (a) of the polymer column confirmed in a cross-section at the lower 5% from the lowest portion of the inorganic coating layer toward the surface, and a cross-sectional area of ​​the column confirmed in a cross-section at the upper 5% from the highest portion toward the bottom, wherein the area (b) is larger than the area (a).

5. In paragraph 1, A separator for an electrochemical device, wherein at least one polymer column included in the inorganic coating layer has a diameter (a) of a lower portion of the polymer column that is shorter than a diameter (b) of an upper portion of the column in a cross-section of the polymer column confirmed in a vertical cross-section of the inorganic coating layer, and a ratio of the diameter (b) to the diameter (a) is 2 to 20.

6. In paragraph 1, A separator for an electrochemical device, wherein the polymer column can protrude to a predetermined height outside the surface of the inorganic coating layer, and when pressurized with a pressure of 0.5 MPa to 20.0 MPa, the protruding portion becomes flat, thereby making the thickness of the inorganic coating layer uniform.

7. In paragraph 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.

8. An electrochemical device comprising a separator for an electrochemical device according to paragraph 1.

Images