Separator for electrochemical device and method for manufacturing same

Abstract

A separator according to the present invention not only has excellent adhesion to an electrode, but also can secure sufficient porosity, thereby exhibiting excellent resistance and ion conductivity characteristics. Additionally, the lamination process time can be shortened during the manufacture of an electrode assembly, thereby achieving high process efficiency in the manufacture of batteries. Furthermore, the energy density of lithium secondary batteries can be maximized by minimizing the height of an inorganic particle filling part.

Description

Separator for electrochemical devices and method for manufacturing the same

[0001] This application claims priority to Korean Patent Application No. 10-2023-0194081, 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 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 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,

[0013] 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,

[0014] At least one polymer column is spaced apart from the other polymer columns by a predetermined distance,

[0015] The space between the polymer columns is filled with an inorganic particle filling portion, and the inorganic particle filling portion includes inorganic particles and a binder resin, and the binder resin includes a first binder resin satisfying the following [Formula 1], wherein in the following Formula 1, X represents the surface energy of the polymer column, and Y represents the surface energy of the binder resin.

[0016]

[0017] [Formula 1]

[0018] 0.75X < Y < 1.15X.

[0019]

[0020] In the above-described aspect of the present invention, the thickness of the inorganic particle filling portion may be 5% or more and 40% or less of the diameter D50 of the polymer column.

[0021] The present invention, in any one of the aforementioned aspects, has a height (T) of the inorganic particle filling portion i ) may be less than 5㎛.

[0022] The present invention, in any one of the aforementioned aspects, wherein the separation membrane is formed such that the protrusion height (T) of the polymer column is increased after a pressure of 3.0 MPa to 4.0 MPa is applied for less than 20 seconds under a temperature condition of 55°C to 65°C. p ) is the height of the inorganic particle filling (T i ) or T i It may be less than 1.1 times.

[0023] The present invention, in any one of the aforementioned aspects, wherein the separation membrane is formed such that the protrusion height (T) of the polymer column is increased after a pressure of 3.0 MPa to 4.0 MPa is applied for less than 20 seconds under a temperature condition of 55°C to 65°C. p ) may be less than 1㎛.

[0024] In any one of the aforementioned aspects of the present invention, the separation membrane may have a crater formed by the detachment of the polymer column in an SEM image of the surface of the separation membrane of less than 1% compared to 100% of the polymer column before detachment.

[0025] In any one of the aforementioned aspects of the present invention, the polymer column may have a storage modulus (G') of 1,000 Pa or more and 3,500 Pa or more.

[0026] In any of the aforementioned aspects of the present invention, the polymer column may have an electrolyte uptake of 30% or more. The electrolyte uptake is according to the following [Formula 2].

[0027] [Formula 2]

[0028] Electrolyte uptake = {(Total weight of polymer column after electrolyte impregnation - Weight of polymer column before electrolyte impregnation) / (Weight of polymer column before electrolyte impregnation)} x 100.

[0029]

[0030] The present invention relates to any one of the aforementioned aspects, wherein the D of the polymer column 50 D of silver inorganic particles50 It can be more than twice as large.

[0031] The present invention relates to any one of the aforementioned aspects, wherein the D of the polymer column 10 Silver D 50 More than 30% of D90 is D 50 It may be less than 200% of .

[0032] In any one of the aforementioned aspects of the present invention, the area occupied by the polymer column may be 10% to 50% of the surface area of ​​the inorganic coating layer relative to 100% of the surface area of ​​the separation membrane (top view).

[0033] In any one of the aforementioned aspects of the present invention, at least one polymer column included in the inorganic coating layer may have an area (a) of a cross-section of the polymer column confirmed in the lower 5% from the lowest portion of the inorganic coating layer toward the surface, and an area (b) of a cross-section of the column confirmed in the upper 5% from the top portion toward the bottom, wherein the area (a) is greater than the area (a).

[0034] In any one of the aforementioned aspects of the present invention, 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 the ratio of the diameter (b) to the diameter (a) may be 2 to 20.

[0035] 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.

[0036] The present invention relates to an electrochemical device, wherein the electrochemical device includes a separator according to any one of the aforementioned aspects.

[0037] 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.

[0038]

[0039] The separator according to the present invention not only exhibits excellent adhesion to the electrode 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. Furthermore, by minimizing the height of the inorganic particle filling, the energy density of lithium secondary batteries can be maximized.

[0040]

[0041] 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.

[0042] Figure 1 is a schematic diagram showing one embodiment of the separation membrane of the present invention.

[0043] Figure 2 is an SEM image of a portion near the center of the winding of the surface of the membrane of Comparative 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 own 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] 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.

[0047] 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.

[0048] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0049] 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 10 D 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.

[0050] 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.

[0051] 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).

[0052]

[0053] 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.

[0054]

[0055] membrane

[0056] 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. 1 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. In particular, the diagram illustrates an aspect 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.

[0057] The above-described separation membrane may have a total thickness of 5.0 μm to 30 μm and may be appropriately adjusted within the above range. For example, the thickness 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 separation membrane preferably has a thickness of 15.0 μm or less, 14.0 μm or less, 13.0 μm or less, 12.0 μm or less, or 11.0 μm or less after flattening by pressing as described below. In addition, the separation membrane may have a porosity of about 25 vol% to 80 vol%. The porosity may be appropriately adjusted within the above-described 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 adjusted 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 / 100 cc or less, or 200 sec / 100 cc or less, or 180 sec / 100 cc or less.

[0058] 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.

[0059] 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 3] below.

[0060]

[0061] [Formula 3]

[0062] Porosity (vol%) = {1-(apparent density / true density)} × 100

[0063]

[0064] Meanwhile, the apparent density in the above formula can be calculated from [Formula 3] below.

[0065]

[0066] [Formula 4]

[0067] Apparent density (g / cm) 3 ) = {Weight of the measurement object [g] / (Thickness of the measurement object [cm] × Area of ​​the measurement object [cm 2 ])}

[0068]

[0069] 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.

[0070] 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.

[0071]

[0072] porous substrate

[0073] 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.

[0074] 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.

[0075] 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.

[0076]

[0077] Specifically, the porous polymer substrate is one of the following a) to e).

[0078]

[0079] a) A porous film formed by melting / extruding a polymer resin,

[0080] b) A multilayer film in which two or more layers of the porous film of a) above are laminated,

[0081] c) A nonwoven web manufactured by accumulating filaments obtained by melting / spinning a polymer resin.

[0082] d) A multilayer film in which two or more layers of the nonwoven web of the above b) are laminated,

[0083] e) A porous composite membrane having a multilayer structure comprising two or more of the above a) to d).

[0084]

[0085] 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.

[0086] In one embodiment of the present invention, the weight average molecular weight of the polyolefin may be from 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 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 curvature radius of 0.5 mm and a puncture speed of 2 mm / sec.

[0087] 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 2 μm to 12 μm may be used. Meanwhile, the porous substrate may have a porosity of 20 vol% to 60 vol% or 30 vol% to 60 vol%, and a pore size of 10 nm to 200 nm, but is not particularly limited thereto.

[0088]

[0089] Inorganic coating layer

[0090] In the present invention, the separator comprises an inorganic coating layer formed on one surface of the porous substrate. The inorganic coating layer comprises a plurality of polymer columns, a plurality of inorganic particles, and a binder resin. The binder resin comprises binder resin A having a surface energy similar to that of the polymer columns.

[0091] In a specific embodiment of the present invention, the inorganic particles in the inorganic coating layer may be at least about 65% based on 100 wt% of the inorganic coating layer, and may be included in a range of, for example, about 70 wt% to 90 wt%. In addition, the polymer column may be included in a range of 10 wt% to 40 wt%, and preferably 20 wt% to 35 wt%, based on 100 wt% of the inorganic particles.

[0092] 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.

[0093]

[0094] 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 10% to 80% of the total area of ​​the inorganic coating layer, and preferably 10% to 50%.

[0095]

[0096] In the above-described inorganic coating layer, the polymer columns may be clustered by two or more polymer columns, or the 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 polymer columns forming the clusters be 10 vol% or less based on 100 vol% of the total polymer columns. In one embodiment of the present invention, it is preferable that the polymer columns are distributed in an island-in-the-sea configuration in the inorganic coating layer without directly contacting other polymer columns and spaced apart by a predetermined interval. In the inorganic coating layer, a plurality of polymer columns are embedded so as to be exposed or protruded outside the surface of the inorganic coating layer, and the protruding height of some of the polymer columns may exceed 1 μm. Additionally, some of the above-described exposed or protruding polymer columns may be in contact with the porous substrate. Here, the polymer columns protruding beyond 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.

[0097]

[0098] 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.

[0099]

[0100] In one embodiment of the present invention, the porosity of the inorganic coating layer (porosity in a state where the polymer columns are included) is preferably 30% to 80%. 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.

[0101]

[0102] Meanwhile, in one embodiment of the present invention, it is preferable that the separator has a crater formed by the detachment of the polymer column in an SEM image observation of the surface of the inorganic coating layer of less than 1% of the polymer column before detachment, compared to 100% of the polymer column before detachment. As described / proposed, the separator according to the present invention has a thin inorganic coating layer, but contains a binder resin A having a small surface energy difference with the polymer column, so that the polymer column is well bound to the binder resin A and the inorganic coating layer, and detachment occurs less frequently.

[0103]

[0104] polymer column

[0105] The polymer column may comprise a polymer resin in an amount of 90 wt% or more, 95 wt% or more, or 99 wt% or more, based on 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.

[0106] 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.

[0107] 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.

[0108] 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 D 50may 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.

[0109] In one embodiment of the present invention, D of the polymer column 50 silver It can be about 2.0 to 7.0㎛ and can be appropriately adjusted within the above range. For example, D of the polymer column 50 This can have a range of 4㎛ to 6㎛. D of the polymer column 50 It reflects the state before the membrane is pressurized, preferably before slurry preparation.

[0110]

[0111] 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. 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 It may be less than 85% of the total.

[0112]

[0113] 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.

[0114] 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.

[0115]

[0116] 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.

[0117]

[0118] The separation membrane according to the present invention has a height (T) of the inorganic coating layer when compressed under pressure conditions of 2.0 MPa to 7.0 MPa and 55°C to 65°C. 코팅층 ) is 1.1 x T i is less than . In addition, T, the protrusion height of the polymer column after compression under the above conditions, p The separation membrane is flattened by being 1㎛ or less or less than 1㎛. 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 equal to the height of the tallest protruding member among the polymer columns. In addition, the T p It is based on the highest part of the inorganic coating layer from the inorganic particle filling part.

[0119]

[0120] Meanwhile, in the present invention, the pressurization may be performed for a period of 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.

[0121]

[0122] 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.

[0123] In the present specification, the term "flattening" means that the thickness of the inorganic particle filling portion and the height of the polymer column are the same under the aforementioned pressurization conditions, or that the deviation between the heights of the inorganic particle filling portion and the polymer column is 1 μm or less, preferably less than 0.5 μm, and more preferably less than 0.3 μm. In one embodiment of the present invention, the height of the polymer column may be based on the height of the polymer column having the highest height.

[0124] That is, when the separator according to the present invention is applied to battery manufacturing, the thickness of the inorganic particle filling part after lamination of the electrode and the separator is polymer column D 50 Smaller is preferable.

[0125] 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.

[0126]

[0127] In the present invention, it is preferable that the polymer column has 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. The storage modulus may be more preferably 1,000 Pa to 3,000 Pa. Preferably, the storage modulus may be for the material forming the polymer column. When the storage modulus at room temperature exists in the above range, when pressurizing the electrode / separator laminate, the low elastic modulus facilitates deformation of the polymer column and the anchoring mechanism of the pores on the surface of the electrode, and the bonding force can be maintained due to the high elastic modulus after pressure is removed. In one embodiment of the present invention, the room temperature may have a range of 20°C to 25°C. In addition, in one embodiment, the polymer column may have a storage modulus at a high temperature (50°C to 80°C or 60°C to 80°C, for example, 60°C) in the range of 0.05 Pa to 100 Pa. Meanwhile, considering the temperature application situation in an actual battery assembly process, the polymer column may have a ratio of the storage modulus at 60°C to the storage modulus at room temperature (G'(60°C) / G'(room temperature)) of 0.1 or less.

[0128]

[0129] 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 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 pressurization.

[0130] 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 slope of the storage modulus (G', storage modulus) at 45°C and the storage modulus (G', storage modulus) at 70°C can be measured through the DMA.

[0131]

[0132] In one embodiment of the present invention, there is a concern that the polymer column may dissolve and lose adhesiveness after the liquid electrolyte is injected during battery manufacturing, 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 that the polymer column have appropriate solubility. For example, the solubility in organic solvents or electrolytes can be reduced by cross-linking the surface of the material forming the polymer column.

[0133] In a specific embodiment, the polymer column is dissolved in THF (Tetrahydrofuran) for 1 to 48 hours, and the dissolved amount (weight) is 55% or less, preferably 35% or less, more preferably 25% or less, even more preferably 22% or less, and most preferably 20% or less.

[0134]

[0135] Meanwhile, in another embodiment, it is preferable that the polymer column have an electrolyte uptake of 30% or more. The electrolyte uptake can be calculated by [Formula 2] below.

[0136]

[0137] [Formula 2]

[0138] Electrolyte uptake (%) = {(Total weight of polymer column after electrolyte impregnation - Weight of polymer column before electrolyte impregnation) / (Weight of polymer column before electrolyte impregnation)} x 100.

[0139] In addition, when the above properties are satisfied, it is possible to prevent the polymer column from dissolving and losing adhesiveness after liquid electrolyte injection, or the viscosity of the liquid electrolyte from increasing due to the dissolved component, thereby preventing the resistance of the lithium secondary battery from increasing.

[0140] The above electrolyte uptake is calculated by immersing a polymer column of a predetermined size in the electrolyte for several minutes to an hour, for example, 5 minutes, then removing the column, removing the electrolyte remaining on the surface, and measuring the weight.

[0141] The above electrolyte may be, for example, 1 MLiPF6 in an ethylene carbonate / ethyl methyl carbonate (EC / EMC, volume ratio 30:70) electrolyte, but is not limited thereto, and any electrolyte that can be applied as an electrolyte for a lithium ion secondary battery may be used without limitation.

[0142]

[0143] 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 material 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.

[0144] Meanwhile, in one embodiment of the present invention, the acrylic polymer may have a weight average molecular weight of about 20,000 to 800,000.

[0145] 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.

[0146]

[0147] 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.

[0148]

[0149] In one embodiment of the present invention, the height of the polymer column, the length of the diameter of the polymer column, and / or the size of the cross-section can be calculated from an SEM image of a horizontal or vertical cross-section of the membrane. Fig. 2 shows an SEM image of the surface of the membrane of Comparative Example 1, and the dimensions of each component can be confirmed. 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 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) equipment on a cross-section of an electrode obtained by argon ion milling, and then performing image processing.

[0150] 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.

[0151] Meanwhile, in one embodiment of the present invention, the inorganic coating layer may further include additives such as a dispersant and a thickener. It is appropriate for the additive to be included in an amount of 5 wt% or less relative to 100 wt% of the inorganic coating layer.

[0152]

[0153] Inorganic particle filling section

[0154] The space between the polymer columns in the inorganic coating layer of the above-described separation membrane may be filled with a mixture containing inorganic particles and a binder resin. In the present specification, the portion filled with the mixture containing inorganic particles and a binder resin is referred to as an “inorganic particle filling portion.” 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 bound by the adhesive properties of the polymer columns or may be bound by means of a binder resin.

[0155]

[0156] 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 may be less than 85% of the total. For example, it may range from 5% to 40%. In a specific embodiment, T i The T may be 0.5㎛ to 5㎛ or less and can be appropriately adjusted within the above range. i For example, it can be 4㎛ or less, 3㎛ or less, 2㎛ or less, and preferably 1.5㎛ or less, 1.0㎛ or less. T i go Within the above numerical range, adhesion to the electrode 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 the value measured for the inorganic coating layer disposed on either side.

[0157]

[0158] In one embodiment of the present invention, the height (thickness, T) of the inorganic particle filling portion (one side) i ) is a cross-section of a membrane specimen, observed through SEM, and the thickness of two or more arbitrary points in an area where no polymer column is located is measured, and the average value thereof is taken as the height. If the thickness of four or more points is measured, the lowest and / or highest values ​​are excluded, and the average value of the remaining values ​​is taken. The lowest point of the inorganic particle-filled portion is the surface of the porous substrate.

[0159] 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.

[0160]

[0161] inorganic particles

[0162] 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.

[0163] 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.

[0164] 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.

[0165]

[0166] In addition, the average particle diameter 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. Meanwhile, in one embodiment of the present invention, the inorganic particles may be included in about 50 wt% to 90 wt% of the inorganic coating layer.

[0167] According to a non-limiting embodiment of the present invention, the inorganic particles have a diameter (D 50 ) can be appropriately adjusted in the range of 0.1㎛ to 1.5㎛, and may have a range of, for example, 200nm to 1㎛.

[0168]

[0169] binder resin

[0170] The above-mentioned inorganic coating layer includes a binder resin to secure bonding between the inorganic particles and between the inorganic particles and the porous substrate. In the above-mentioned 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. Together with or independently of this, the binder resin may be included in an amount of 0.1 to 10 parts by weight or 0.1 to 5 parts by weight relative to 100 parts by weight of the inorganic particles.

[0171]

[0172] Meanwhile, in one embodiment of the present invention, it is preferable that the binder resin includes a binder resin having a surface energy similar to that of the polymer column. The binder resin having a surface energy similar to that of the polymer column is referred to as binder resin A for convenience of description below. The surface energy of the binder resin A may have a range as shown in [Formula 1] below. In [Formula 1] below, X represents the surface energy of the polymer column, and Y represents the surface energy of the binder resin A. The surface energy may use a unit of dyne / cm or mN / m.

[0173] The surface energy of binder resin A can be measured by the following method. First, a film composed of binder resin A is prepared, and then the contact angles for each liquid are measured on the surface using water and methylene iodide (Diiodomethane), and the surface energy is calculated by the Owens-Wendt Method. In one embodiment of the present invention, the film can be obtained by preparing a polymer solution by dissolving the binder resin in an appropriate organic solvent, applying the polymer solution onto a glass plate, and then drying at about 80°C.

[0174]

[0175] [Formula 1]

[0176] 0.75X < Y < 1.15X

[0177]

[0178] Among the 100 wt% of the above binder resin, binder resin A may be included in an amount of 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more. In one embodiment, the binder resin may be composed of binder resin A.

[0179] In one embodiment of the present invention, the binder resin A is preferably nonionic. In one embodiment of the present invention, the binder resin A is preferably soluble in a solvent. The binder resin A is preferably not in the form of an emulsion.

[0180] In another embodiment of the present invention, the binder resin A is nonionic. In a specific embodiment of the present invention, the binder resin A is soluble in a solvent. In a specific embodiment of the present invention, the binder resin A does not have an emulsion form.

[0181] Meanwhile, in a specific embodiment of the present invention, non-limiting examples of the binder resin and binder resin A include (meth)acrylic polymers, vinylidene fluoride polymers, polyvinyl alcohol, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose. Examples thereof include cyanoethylsucrose, pullulan, carboxyl methyl cellulose, hydroxyalkylmethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylhydroxyethyl cellulose, and methyl cellulose, and these may be used alone or in combination of two or more thereof. In one embodiment of the present invention, the binder resin A may include polyvinyl alcohol. As a specific example, the binder resin A may be polyvinyl alcohol.

[0182]

[0183] The above (meth)acrylic polymer may include, but is not limited to, one or more of (meth)acrylic acid ester, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, butylacrylate, 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.

[0184] The above vinylidene fluoride polymer may include at least one of a homopolymer of vinylidene fluoride (polyvinylidene fluoride), a copolymer of vinylidene fluoride and a monomer capable of copolymerizing the same, 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. For example, it may be polyvinylidene fluoride-co-hexafluoropropylene or polyvinylidene fluoride-co-trichloroethylene.

[0185]

[0186] In one embodiment of the present invention, one or more materials having a surface energy value according to [Formula 1] among the binder resins exemplified above may be selected and used as binder resin A. Meanwhile, in addition to binder resin A, one or more of the above-mentioned binder resins may be further included to supplement adhesive strength.

[0187]

[0188] Additionally, in one embodiment of the present invention, the inorganic coating layer may further include additives such as a dispersant and / or a thickener in an amount ranging from 0.5 to 3.0 parts by weight relative to 100 parts by weight of the inorganic particles. If there is a material among the examples of the binder resins described above that can improve dispersibility and / or viscosity, it can be used as an additive for such purposes.

[0189]

[0190] Membrane manufacturing method

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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℃ or lower than the glass transition temperature of the polymer column material to prevent deformation of the polymer column. 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.

[0195]

[0196] 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.

[0197]

[0198] The above slurry can be applied using conventional coating methods such as a Meyer bar, die coater, reverse roll coater, or gravure coater.

[0199] 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.

[0200]

[0201] 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.

[0202]

[0203] 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.

[0204]

[0205] 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.

[0206]

[0207] 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.

[0208]

[0209] 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.

[0210]

[0211] 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.

[0212]

[0213] Battery manufacturing

[0214] The battery manufacturing method of the present invention is characterized in that a first compression is performed during the manufacturing of the electrode assembly or before impregnation with an electrolyte (dry compression), and then a second compression is performed after the electrode assembly is impregnated with an electrolyte and the polymer column is softened by the electrolyte.

[0215] First, a laminate including one or more positive electrodes, one or more separators, and one or more negative electrodes is prepared. The laminate is laminated one or more times with a separator interposed between the positive electrode and the negative electrode. The electrodes and separators, etc., constituting the laminate are not in close contact with each other but are simply stacked. Thereafter, the laminate is pressed at a strength of 3.0 MPa to 4.0 MPa under temperature conditions of 55°C to 65°C to manufacture a first electrode assembly. Here, the polymer columns in the separator are not completely flattened. In this way, since the separator and the electrode are not completely flattened before electrolyte impregnation and a certain distance is maintained between them, the electrolyte can easily flow into the first electrode assembly. That is, there is an advantage of securing a movement path of the electrolyte.

[0216] Thereafter, the first electrode assembly is impregnated with an electrolyte, and a second compression is performed thereafter. The second compression includes a step of applying a pressure of 0.5 MPa to 1.5 MPa to the impregnated first electrode assembly. Pressure is applied to the impregnated first electrode assembly so that the separator and the positive electrode and / or the separator and the negative electrode are in close contact with each other, and the pressure application is preferably performed under a temperature condition of 35°C to 45°C. After the electrode assembly is sufficiently impregnated with the electrolyte in this way, the second compression is performed so that the electrode and the separator are in close contact with each other. Therefore, there is an advantage in that the wettability of the electrode assembly is improved. Meanwhile, the step of impregnating the first electrode assembly with the electrolyte includes housing the first electrode assembly in a battery case, and an aging step may be further performed after the impregnation and before the pressure application. The aging may preferably be performed at a temperature of 20°C or higher. An excessively high temperature may deteriorate the materials used in the battery, and is therefore not preferable. The above aging temperature can be performed within a range of, for example, the glass transition temperature (Tg) of the binder resin used + 20°C or less.

[0217]

[0218] In the present invention, the electrolyte is A + B - As a salt with the same structure, 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.

[0219]

[0220] 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.

[0221] In a specific embodiment of the present invention, the ester compound includes 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.

[0222]

[0223] 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.

[0224] 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.

[0225] 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.

[0226]

[0227] Example

[0228] Measurement of surface energy

[0229] An aqueous emulsion of the acrylic polymer A15 shown in Table 1 below was prepared, applied to a glass plate at a predetermined thickness, and dried at 80°C. A thin film having a thickness of approximately 100 μm was thus obtained. Water and methylene iodide (Diiodomethane) were dripped onto the surface of the thin film thus obtained, and the contact angles for each liquid were measured. The surface energy was calculated using the Owens-Wendt method using the measured values. The surface energy of the polyvinyl alcohol used in Example 1 was also calculated using the same method.

[0230]

[0231] Membrane thickness measurement

[0232] In the Examples and Comparative Examples, the thickness of the membrane was determined by cross-sectioning the membrane specimen, observing it through an SEM, and measuring the thickness at the thickest point. This is summarized and shown in [Table 1] below. Meanwhile, the thickness of the inorganic particle-filled portion was determined as the average of the values ​​measured at three random points.

[0233]

[0234] Measurement of storage modulus of polymer columns

[0235] A 40 cm x 60 cm sample was fabricated using the polymer material to be used as the polymer column in the comparative examples and examples. The thickness of the sample was 1 mm. The elastic modulus was measured for the sample. The storage elastic modulus was measured using a rheological property measuring equipment (Dynamic Mechanical Analyzer (DMA), ARES-G2, TA Instrument). The storage elastic modulus was confirmed by conducting a temperature sweep test under temperature conditions of -60°C to 80°C and a frequency of 1.0 rad / s. The results are summarized in Table 1 below.

[0236]

[0237] Solubility measurement of polymer columns

[0238] A 0.3 g sample was prepared at 60°C using the polymer material to be used as the polymer column in the comparative examples and examples. The sample was placed in an 80-mesh mesh bag and dissolved in THF (Tetrahydrofuran) for 24 hours. The residual weight was compared to the initial weight. The solubility was calculated based on the following [Equation 5]. This is summarized and presented in Table 1 below.

[0239]

[0240] [Formula 5]

[0241] Solubility (%) = {(Weight measured before immersion - Weight measured after immersion) / (Weight measured before immersion)} x 100

[0242]

[0243] Measurement of molecular weight

[0244] 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.

[0245] - Column (maker, model no.): 2 x TSKgel SupermultiporeHZ-M + TSKgel SuperHZ-2500

[0246] - Eleunt: THF

[0247] - Temperature: 40℃

[0248] - Flow rate: 1.0 mL / min

[0249] - Injection volume, sample concentration: 30 ㎕, 1~10 mg / mL

[0250] - Standard: Polystyrene

[0251] - Detector: RI

[0252]

[0253] Measurement of glass transition temperature

[0254] 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.

[0255]

[0256] Storage modulus (25℃, Pa) Storage modulus (60℃, Pa) G' (60℃) / G' (room temperature, ℃) tan δ peak (℃, 45℃ to 80℃) Solubility (%) Tg (℃) Surface energy (dyne / cm) Acrylic polymer A151,381.050.10.03669.919%60.040.7

[0257]

[0258] Example 1

[0259] Inorganic particles (Al2O3, D 50 Approximately 0.3㎛), acrylic binder (Toyo, CSB-130), sodium carboxymethyl cellulose (Daicel, Daicel1220, CMC-Na, surface energy 20 dyne / cm or less) 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.

[0260] Acrylic polymer A15 (D) for polymer column in the above mixture 50Polyvinyl alcohol (Apac, SBC-1810, surface energy 37.2 dyne / cm) as binder resin A (3.84㎛) was added and stirred to obtain a dispersion slurry. The concentration of solids in the dispersion slurry was 15 wt%. The content of polymer particles for the polymer column in the mixture was about 30 parts by weight per 100 parts by weight of inorganic particles, and binder resin A was included in an amount of 4 parts by weight per 100 parts by weight of the polymer column. The dispersion slurry was applied to a porous 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. The loading amount of the inorganic coating layer based on one side of the porous substrate in the separator was 2.1 g / m 2 It was. The obtained separation membrane was then pressurized using a hot press at 3.5 MPa and 60°C for 20 seconds.

[0261]

[0262] Comparative Example 1

[0263] Inorganic particles (Al2O3, D 50 Approximately 0.6㎛), acrylic binder (Toyo, CSB-130) and carboxymethyl cellulose (Daicel, Daicel1220) were added to a water:ethanol 95:5 solution at a ratio of 96:2:2 and stirred to obtain a mixture.

[0264] Acrylic polymer A15 (D) for polymer column in the above mixture 50 3.84㎛) was added and stirred to obtain a dispersion slurry. The concentration of solids in the dispersion slurry was 30 wt%.

[0265] The above mixture was applied to a porous substrate (Toray, B09PJ1, thickness 9 ㎛) by a microgravure coating method and dried at a temperature of 80°C. The loading amount of the inorganic coating layer on one side of the porous substrate in the above separator was 2.0 / m 2The manufactured separator was wound 2,000 m long. The manufactured separator was stored in a wound state for 7 days, then unwound and an SEM image near the core was measured, which is shown in Fig. 2. Meanwhile, the obtained separator was compressed with a hot press at 3.5 MPa and 65°C for 20 seconds to flatten the surface.

[0266]

[0267] Comparative Example 2

[0268] Inorganic particles (Al2O3, D50 approximately 0.6㎛), acrylic binder (Toyo, CSB-130) and carboxymethylcellulose (Daicel, Daicel1220) were added to a water:ethanol 95:5 solution at a ratio of 96:2:2 and stirred to obtain a mixture.

[0269] Acrylic polymer A15(D) for polymer column in the above mixture 50 3.84㎛) was added and stirred to obtain a dispersion slurry. The concentration of solids in the dispersion slurry was 15 wt%.

[0270] The above mixture was applied to a porous substrate (Toray, B09PJ1, 9 ㎛ thick) by a microgravure coating method and dried at a temperature of 80°C. The loading amount of the inorganic coating layer on one side of the porous substrate in the above separator was 3.2 g / m 2 Meanwhile, the obtained separation membrane was compressed with a hot press at 3.5 MPa and 65°C for 20 seconds to flatten the surface.

[0271]

[0272]

[0273] Example 1 Comparative Example 1 Comparative Example 2 Total thickness of the membrane (㎛) (before compression) 13.6 13.5 13.8 Thickness of the inorganic particle filling part (㎛, T) i , excluding polymer columns) (before compression)1.41.53.1 Thickness of inorganic particle packing (T i ) / Polymer column D 50(%)36.539.180.1Polymer column coverage (%)15.510.315.3Membrane thickness after pressing (㎛)10.610.712.3Desorption frequency ((crater / total), %)038.20

[0274]

[0275] Referring to Table 2 above, the separator of Comparative Example 1 had a problem of low coverage of the polymer column due to detachment of the polymer column after winding. In addition, although the thickness of the inorganic coating layer of Comparative Example 2 was thick enough to prevent detachment, the thickness of the separator did not decrease to the desired level after pressing, making it difficult to secure the energy density of the lithium secondary battery. Therefore, it was confirmed that the separator according to the present invention has excellent adhesive strength and can secure the energy density of the lithium secondary battery, and is advantageous in terms of processability.

[0276] [Explanation of symbols]

[0277] 10 Porous substrates

[0278] 20 layers of weapon coating

[0279] 100 polymer columns

[0280] 200 inorganic particles

[0281] T s Thickness of the membrane

[0282] T p Protrusion height of polymer column

[0283] T i Height of the inorganic particle filling, 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, At least one polymer column is spaced apart from the other polymer columns by a predetermined distance, A separation membrane in which the space between the polymer columns is filled with an inorganic particle filling portion, the inorganic particle filling portion includes inorganic particles and a binder resin, and the binder resin includes a binder resin A satisfying the following [Formula 1], wherein in the following Formula 1, X represents the surface energy of the polymer column, and Y represents the surface energy of the binder resin A: [Formula 1] 0.75X < Y < 1.15X.

2. In paragraph 1, Inorganic particle filling part (T i ) is a separation membrane having a thickness of 5% to 40% of the diameter D50 of the polymer column.

3. In paragraph 1, The height of the above inorganic particle filling part (T) i ) is a separation membrane having a thickness of 2㎛ or less.

4. In paragraph 1, The above separation membrane is applied with a pressure of 3.0 MPa to 4.0 MPa for less than 20 seconds under temperature conditions of 55°C to 65°C, after which the protrusion height (T) of the polymer column p ) is the height of the inorganic particle filling part (T i ) or equal to T i A membrane having a thickness less than 1.1 times that of the membrane.

5. In paragraph 1, The above separation membrane is applied with a pressure of 3.0 MPa to 4.0 MPa for less than 20 seconds under temperature conditions of 55°C to 65°C, after which the protrusion height (T) of the polymer column p ) is a separation membrane having a thickness of 1㎛ or less.

6. In paragraph 1, The above separation membrane is a separation membrane in which, when observing a SEM image of the surface, the craters generated by the detachment of the polymer column are less than 1% compared to 100% of the polymer column before detachment.

7. In paragraph 1, The above polymer column is a separation membrane having a storage modulus (G') of 1,000 Pa or more and 3,000 Pa or more.

8. The above polymer column has an electrolyte uptake of 30% or more, The above electrolyte uptake is according to the following [Formula 2], a separator for an electrochemical device [Formula 2] Electrolyte uptake = {(total weight of polymer column after electrolyte impregnation - weight of polymer column before electrolyte impregnation) / (weight of polymer column before electrolyte impregnation)} x 100.

9. In paragraph 1, D of the above polymer column 50 D of silver inorganic particles 50 A separator for electrochemical devices that is more than twice as large.

10. In paragraph 1, The thickness of the above inorganic particle filling part (T) i ) is a polymer column D 50 A separator for electrochemical devices having a particulate matter content of 85% or less.

11. In paragraph 1, D of the above polymer column 10 Silver D 50 More than 30% of D90 is D 50 A separator for electrochemical devices having a particulate matter content of 200% or less.

12. In paragraph 1, A separator for an electrochemical device, wherein the area occupied by the polymer column is 10% to 50% of the surface area of ​​the inorganic coating layer based on the surface view of the separator (top view).

13. 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).

14. 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.

15. 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.

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

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