Separator for electrochemical device and electrochemical device including the same

Abstract

The present invention relates to a separator for an electrochemical device and an electrochemical device including the same, and more particularly to a separator for an electrochemical device including the same, the separator comprising a resin mixture of an ethylene vinyl acetate copolymer (EVA) and polyethylene (PE), in which the vinyl acetate (VA) content in the ethylene vinyl acetate copolymer is 20 wt % or less, and an electrochemical device including the separator.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0099239, filed with the Korean Intellectual Property Office on August 9, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same, and more particularly to a separator for an electrochemical device having improved electrolyte impregnation and an electrochemical device including the same. [Background technology]

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions, and in recent years, lithium secondary batteries have been widely used because they have high energy density, high voltage, long cycle life, and can be used in a variety of fields.

[0004] Such lithium secondary batteries are composed of a positive electrode, a negative electrode, an electrolyte, and a separator, among which the separator separates the positive and negative electrodes, prevents electrical shorts between the two electrodes, and allows the electrolyte and ions to pass through. Although the separator is not involved in the electrochemical reaction of lithium secondary batteries, its physical properties, such as electrolyte impregnation, porosity, and thermal shrinkage, have a significant impact on the performance and safety of lithium secondary batteries.

[0005] Separation membranes are divided into dry and wet separation membranes depending on the formation method. Dry separation membranes are manufactured by 1) melting a porous substrate component such as polypropylene to form a primary film, 2) slightly stretching and heat-setting the formed primary film to form a lamellar film with a mixed amorphous / crystalline structure, and 3) uniaxially stretching the lamellar film to form pores, forming a porous substrate. Dry separation membranes have regularly formed pores in the vertical direction of the membrane, and the highly linear pores facilitate lithium ion movement, providing excellent electrical properties and higher heat resistance than wet separation membranes. Wet separation membranes are manufactured by 1) mixing a polymer resin and wax, melting it, and extruding it to form a film, 2) stretching the formed film biaxially to form pores, and 3) removing the wax to form a porous substrate. In the case of wet separators, the irregular pores may reduce heat resistance, but they are advantageous in terms of thickness uniformity, ease of thinning, ensuring MD / TD strength, and battery stability.

[0006] In recent years, there has been an increasing demand for lithium secondary batteries with larger capacities and higher energy densities, such as for electric vehicles. These lithium secondary batteries for electric vehicles mainly use wet separators. While these wet separators have excellent insulation properties, chemical resistance, voltage stability, and mechanical strength, they suffer from a problem of somewhat reduced electrolyte impregnation due to their low affinity for electrolytes. Summary of the Invention [Problem to be solved by the invention]

[0007] The technical problem to be solved by the present invention is to provide a separator for an electrochemical device that can improve electrolyte impregnation without reducing mechanical strength.

[0008] Another technical object of the present invention is to provide an electrochemical device including the above-mentioned separator.

[0009] The problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0010] To achieve the above object, according to an embodiment of the present invention, there is provided a separator for an electrochemical device, which comprises a resin mixture of ethylene vinyl acetate copolymer (EVA) and polyethylene (PE), wherein the content of vinyl acetate (VA) in the ethylene vinyl acetate copolymer is 20 wt % or less.

[0011] The content of vinyl acetate (VA) in the ethylene vinyl acetate copolymer may be 1% to 20% by weight.

[0012] The ethylene (C2) content in the ethylene vinyl acetate copolymer may be 80% to 99% by weight.

[0013] In the ethylene vinyl acetate copolymer, the content ratio of ethylene (C2) to vinyl acetate (VA) may be 3.5-20.

[0014] The content of the ethylene vinyl acetate copolymer in the resin mixture may be 1% by weight to 20% by weight.

[0015] In the resin mixture, the content of vinyl acetate may be 0.1% to 3% by weight, and the content of ethylene may be 97% to 99.9% by weight.

[0016] The ethylene vinyl acetate copolymer may have a weight average molecular weight (Mw) of 320,000 g / mol or less, and a melting point (Tm) of 80°C to 130°C.

[0017] The resin mixture may have a crystallinity of 20% to 50%.

[0018] The separator for an electrochemical device may have a thickness of 1 μm to 100 μm, a porosity of 20 vol % to 70 vol %, and an average pore diameter of 0.01 μm to 1 μm.

[0019] The separator for an electrochemical device may have a puncture strength of 160 gf or more, and a standard deviation of the puncture strength of 8.0 or less.

[0020] A 2 μL droplet of propylene carbonate (PC) was dropped onto the separator for electrochemical devices, and after 5 minutes, the area of ​​the droplet was 8 mm 2 It could be more than that.

[0021] The separator for an electrochemical device may have a shutdown temperature of 100°C to 145°C.

[0022] The separator for an electrochemical device may be a wet separator.

[0023] Meanwhile, the separator for an electrochemical device may further include a porous coating layer formed on one or both sides of the separator for an electrochemical device, and the porous coating layer may include inorganic particles and a binder polymer.

[0024] According to another embodiment of the present invention, there is provided an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator for an electrochemical device described above. [Effects of the Invention]

[0025] According to an embodiment of the present invention, a separator for an electrochemical device having improved electrolyte impregnation property without reducing mechanical strength can be realized by including a resin mixture containing an ethylene-vinyl acetate copolymer having a specific content of highly polar vinyl acetate groups.

[0026] Furthermore, since the separator contains ethylene vinyl acetate copolymer, which has a relatively low melting point, the shutdown temperature of the separator is lowered, thereby improving the safety of the electrochemical device. DETAILED DESCRIPTION OF THE INVENTION

[0027] Examples of the present invention will be described in detail below.

[0028] The examples of the present invention described below are provided to more clearly explain the present invention to those skilled in the art, and the scope of the present invention is not limited by the following examples, which may be modified into various different forms.

[0029] The terms used herein are used to describe specific embodiments and are not intended to limit the present invention. As used herein, singular terms may include plural forms unless the context clearly dictates otherwise. Furthermore, the terms "comprise" and / or "comprising" as used herein specify the presence of a referenced shape, step, number, operation, member, element, and / or group thereof, but do not exclude the presence or addition of one or more other shapes, steps, numbers, operations, members, elements, and / or groups thereof. Furthermore, the term "connected" as used herein not only refers to a direct connection between certain members, but also encompasses an indirect connection between members via an intervening member.

[0030] In addition, when a member is said to be "on" another member in this specification, this includes not only when the member is in contact with the other member, but also when another member is present between the two members. The term "and / or" as used in this specification includes any one of the listed items and all combinations of one or more of the listed items. In addition, terms indicating degrees, such as "about" and "substantially," used in this specification, are used to mean a range of values ​​or degrees or their approximations, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting disclosures that refer to exact or absolute values ​​provided to facilitate understanding of this application.

[0031] A separator for an electrochemical device according to one aspect of the present invention includes a resin mixture of ethylene vinyl acetate copolymer (EVA) and polyethylene (PE), in which the content of vinyl acetate (VA) in the ethylene vinyl acetate copolymer is 20 wt % or less.

[0032] While conventional wet separation membranes have been primarily made of polyethylene, which consists solely of carbon (C) and hydrogen (H) atoms, the separation membrane of the present invention contains an ethylene-vinyl acetate copolymer. Vinyl acetate has a higher polarity than polyethylene, and therefore has the advantage of having excellent affinity with polar electrolytes. This allows the separation membrane of the present invention to have further improved electrolyte impregnation.

[0033] However, if the vinyl acetate content in the ethylene-vinyl acetate copolymer exceeds 20 wt%, the crystallinity of the polyethylene may decrease, potentially resulting in a decrease in the mechanical strength of the separator. Therefore, the vinyl acetate content must be 20 wt% or less in the ethylene-vinyl acetate copolymer. Preferably, the vinyl acetate content in the ethylene-vinyl acetate copolymer may be greater than 0 wt% and less than 20 wt%. More preferably, the vinyl acetate content in the ethylene-vinyl acetate copolymer may be 1 wt% to 20 wt% based on the total weight of the ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer may contain 20 wt% or less of vinyl acetate, preferably 1 wt% to 20 wt%, 3 wt% to 18 wt%, 5 wt% to 15 wt%, 7 wt% to 12 wt%, 9 wt% to 11 wt%, 10 wt%, or 10 wt% to 20 wt%.

[0034] As a result, the separator of the present invention containing the ethylene-vinyl acetate copolymer having the above vinyl acetate content can have excellent electrolyte impregnation properties while maintaining high mechanical strength.

[0035] The ethylene (C2) content in the ethylene-vinyl acetate copolymer may be 80 wt% to 99 wt%, preferably 82 wt% to 97 wt%, 85 wt% to 95 wt%, 88 wt% to 93 wt%, 89 wt% to 91 wt%, or 80 wt% to 90 wt%, based on the total weight of the ethylene-vinyl acetate copolymer. A separator of the present invention containing an ethylene-vinyl acetate copolymer having such an ethylene content can improve electrolyte impregnation without reducing mechanical strength.

[0036] The ethylene-vinyl acetate copolymer contains ethylene (C2) and vinyl acetate (VA), and the content ratio of ethylene (C2) to vinyl acetate (VA) may be 3.5 to 20, preferably 3.6 to 18, 3.7 to 15, 3.8 to 12, 5 to 11, or 8 to 10. The separator of the present invention containing the ethylene-vinyl acetate copolymer having the above content ratio of ethylene to vinyl acetate can improve electrolyte impregnation without reducing mechanical strength.

[0037] The vinyl acetate content in the resin mixture may be 0.1 wt % to 3.0 wt %, preferably 0.1 wt % to 2.5 wt %, 0.2 wt % to less than 2.5 wt %, 0.3 wt % to 2.3 wt %, 0.3 wt % to 2.0 wt %, 0.4 wt % to 1.8 wt %, or 1.0 wt % to 1.5 wt %, based on the total weight of the resin mixture. In certain embodiments of the present invention, the resin mixture may be omitted if the vinyl acetate content is less than 2.5 wt %, based on the total weight of the resin mixture. Resin mixtures with such vinyl acetate contents can increase puncture strength and improve electrolyte impregnation. Therefore, separators of the present invention containing the resin mixture may have increased mechanical strength and improved electrolyte impregnation.

[0038] The ethylene content of the resin mixture may be 97.0 wt% to 99.9 wt%, preferably 97.5 wt% to 99.9 wt%, 97.7 wt% to 99.8 wt%, 98 wt% to 99.7 wt%, 98.2 wt% to 99.6 wt%, or 98.5 wt% to 99.0 wt%, based on the total weight of the resin mixture. A separator of the present invention containing a resin mixture having such an ethylene content can improve electrolyte impregnation without reducing mechanical strength.

[0039] As known to those skilled in the art, the content of ethylene, vinyl acetate, ethylene vinyl acetate copolymer in a resin mixture, preferably the content of ethylene vinyl acetate copolymer relative to the total weight of the resin mixture, can be measured by quantitative IR, as described in H. Hagemann, R. G. Snyder, A. J. Peacock, and L. Mandelkern, "Quantitative Infrared Methods for the Measurement of Crystallinity and Its Temperature Dependence: Polyethylene," Macromolecules, 1989, 22(9), pp. 3600-3606 (DOI: 10.1021 / ma00199a017). Alternatively, as known to those skilled in the art, the content of ethylene, vinyl acetate, and ethylene vinyl acetate copolymer in a resin mixture, preferably relative to the total weight of the resin mixture, can be determined by the method described in "Quantitative Determination of Compound Ratios and Polymer End Groups" by Douglas A. L., Dorothee E. Borchmann, Chin Lin, Marcus Weck, and K. A. Woerpel. 13 C NMR spectroscopy ( 13 It can be measured by quantitative C-NMR as described in "C NMR Spectroscopy for the Quantitative Determination of Compound Ratios and Polymer End Groups," Organic Letters, 2014, 16(6), pp. 1566-1569 (DOI: 10.1021 / ol403776k).

[0040] Furthermore, when an ethylene vinyl acetate copolymer having a relatively low melting point is included, the shutdown temperature of the separator can be lowered, thereby providing a further effect of improving the safety of the electrochemical device.

[0041] In this case, the content of the ethylene-vinyl acetate copolymer in the resin mixture may be 30 wt% or less. Preferably, the content of the ethylene-vinyl acetate copolymer may be greater than 0 wt% and less than 30 wt%, 1 wt% to 25 wt%, 5 wt% to 20 wt%, 5 wt% to 15 wt%, 5 wt% to 10 wt%, or 10 wt% to 15 wt%. If the content of the ethylene-vinyl acetate copolymer exceeds the above range, compatibility with polyethylene may decrease, making it difficult to achieve a separator with uniform physical properties. Furthermore, even after the separator is fabricated, the crystallinity of the polyethylene may decrease, reducing the mechanical strength of the separator. If the content of the ethylene-vinyl acetate copolymer is less than the above range, the electrolyte impregnation may not be improved without reducing mechanical strength.

[0042] The weight-average molecular weight (Mw) of the ethylene-vinyl acetate copolymer may be 320,000 g / mol or less, preferably 100,000 g / mol to 320,000 g / mol, 200,000 g / mol to 315,000 g / mol, 250,000 g / mol to 312,000 g / mol, or 280,000 g / mol to 310,000 g / mol. In certain embodiments of the present invention, the weight-average molecular weight of the ethylene-vinyl acetate copolymer may be 307,000 g / mol. If the weight-average molecular weight of the ethylene-vinyl acetate copolymer is outside this range, the separator may not have sufficient mechanical properties, such as puncture strength, or it may be impossible to obtain a mixture in which the ethylene-vinyl acetate and polyethylene are properly mixed. A separator containing an ethylene-vinyl acetate copolymer satisfying the above weight-average molecular weight range may exhibit improved electrolyte impregnation without a decrease in mechanical strength. The weight average molecular weight can be measured by gel permeation chromatography, and an apparatus such as PL GPC220 (Agilent Technologies) can be used.

[0043] The weight-average molecular weight can be measured using an Agilent High Temperature RI detector (detector) under the conditions of a PL Olexis (Polymer Laboratories) column (column temperature 160°C) using TCB (trichlorobenzene) as the solvent, a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μL (corrected by a cubic function, standard: polystyrene).

[0044] Meanwhile, the melting point (Tm) of the ethylene-vinyl acetate copolymer may be 80°C to 130°C, specifically 80°C to 120°C, and more specifically 90°C to 110°C. The melting point may be measured using a differential scanning calorimeter (DSC), such as a TA Instruments DSC 2920. If the melting point (Tm) of the ethylene-vinyl acetate copolymer is below the above range, the heat resistance of the separator may be excessively reduced. If the melting point (Tm) is above the above range, the effect of improving the electrolyte impregnation of the separator may be significantly reduced.

[0045] The crystallinity of the resin mixture may be 20% to 50%, specifically 20% to 45%, and more specifically 30% to 40%. If the crystallinity of the resin mixture is below this range, the content of amorphous regions in the resin mixture may be high, which may result in a decrease in the mechanical properties of the separator. If the crystallinity of the resin mixture is above this range, the effect of improving electrolyte impregnation may be significantly reduced, which is undesirable.

[0046] The crystallinity can be expressed as a percentage by dividing the melting enthalpy (ΔH) value measured by differential scanning calorimetry (DSC) by the melting enthalpy (ΔH) value of a theoretically perfect crystal (100% crystallinity). The theoretical melting enthalpy value of a perfect crystal can be found in a polymer handbook for known polymers, and for unknown or newly synthesized materials, it can be calculated by extrapolation, which involves extending the crystallinity values ​​at two or more points.

[0047] Furthermore, the thickness of the separator for electrochemical devices is not particularly limited, but may be 1 μm to 100 μm, specifically 3 μm to 50 μm, and more specifically 5 μm to 15 μm. If the thickness of the separator is less than the above range, the mechanical properties of the separator may be reduced, and if the thickness exceeds the above range, the resistance of the separator itself may be excessively increased, which is undesirable for achieving the energy density of the electrochemical device.

[0048] Furthermore, the porosity and average pore diameter of the separator for electrochemical devices are not particularly limited, but may be 20 vol% to 70 vol% and 0.01 μm to 1 μm, respectively, specifically 30 vol% to 60 vol% and 0.02 μm to 0.1 μm, respectively, and more specifically 40 vol% to 50 vol% and 0.03 μm to 0.05 μm, respectively.

[0049] In the present invention, the porosity refers to the ratio of the volume occupied by pores to the total volume of a structure, and may be expressed in units of vol%. In the present invention, the porosity may be measured by any method, including, for example, Brunauer-Emmett-Teller (BET) measurement using nitrogen gas, mercury porosimetry (Hg porosimeter), and ASTM D-2873. Alternatively, the true density of the separation membrane may be calculated from the density (apparent density) of the separation membrane, the composition ratio of the materials contained in the separation membrane, and the density of each component, and the porosity of the separation membrane may be calculated from the difference between the apparent density and the true density (net density). Meanwhile, in the present invention, the pore size, pore distribution, and average pore diameter (nm) may be measured using a capillary flow porometer. This method involves wetting the pores of a separation membrane with a liquid of known surface tension, then applying air pressure to measure the pressure at which the first flow occurs (bubble point = max pore).

[0050] An example of such a capillary flow porometer is the CFP-1500-AE manufactured by Porous Materials. The measurement method using the capillary flow porometer involves wetting a porous substrate with a wetting solution with low surface tension, then applying gas pressure to measure the pore size based on the pressure required to expel the wetting solution filling the pores of the porous substrate. For example, after wetting the porous substrate to be measured with a wetting solution such as Galwick solution, air pressure is gradually increased on one side of the porous substrate. When the applied air pressure exceeds the capillary attraction of the wetting solution present in the pores, the wetting solution filling the pores is expelled, and the pore size and distribution can be measured based on the pressure and flow rate at the moment of expulsion. In one embodiment of the present invention, a non-reactive gas can be used instead of air.

[0051] Meanwhile, the separator for electrochemical devices of the present invention may have a puncture strength of 160 gf or more. Preferably, it may be 180 gf or more, 200 gf or more, 210 gf or more, 220 gf to 500 gf, 400 gf or less, 350 gf or less, 300 gf or less, or 160 gf to 500 gf. The standard deviation of the puncture strength of the separator may be 8.0 or less. Preferably, it may be 7.5 or less, 7.0 or less, 6.7 or less, 1 to 6.5, or 1 to 8.0. As described above, a separator with excellent mechanical properties can be provided.

[0052] In the present invention, puncture strength refers to the resistance of a separator to external threats, such as penetration by an external object. It is measured in units of gf or kgf and can be interchangeably referred to as penetration strength or puncture strength. Generally, the higher this value, the lower the separator's internal short-circuit failure rate. In this penetration test, for example, a needle or acupuncture needle with a predetermined diameter is inserted perpendicularly into the separator at a predetermined speed, and the applied force is measured.

[0053] According to the present invention, the ethylene-vinyl acetate copolymer contained in the separator contains 20% by weight or less of vinyl acetate, which has the advantage of improving the impregnation ability with an electrolyte while not reducing the mechanical strength compared to conventional separators.

[0054] Furthermore, the shutdown temperature of the separator for an electrochemical device according to the present invention may be 100° C. to 145° C., specifically 110° C. to 140° C., and more specifically 110° C. to 130° C. When the shutdown temperature is within the above range, the safety of the electrochemical device can be maintained even in a high-temperature environment where thermal runaway due to a short circuit occurs.

[0055] In the present invention, the shutdown temperature refers to the temperature at which the micropores in the separator are closed due to a sudden large current flow caused by an internal or external short circuit. The shutdown temperature of the present invention can be measured by the following method. First, the separator is exposed to a temperature increase condition (starting from 30°C at 5°C / min) while measuring the air permeability of the separator. The shutdown temperature is defined as the temperature at which the air permeability (Gurley value) of the separator first exceeds 100,000 sec / 100 cc. The air permeability of the separator can be measured using an air permeability meter (Asahi Seiko, EGO-IT) in accordance with JIS P8117.

[0056] Meanwhile, the electrolyte impregnation of the separator can be confirmed by measuring the contact area of ​​a propylene carbonate (PC) drop on the separator. More specifically, after cutting the separator to a size of 1 cm horizontally and 4 cm vertically, approximately 2 μL of propylene carbonate solution is dropped onto the surface of the separator. After a certain period of time (approximately 5 minutes), the electrolyte impregnation can be confirmed using a Drop Shape Analysis System (KRUSS, DSA100). When confirmed as above, the separator for electrochemical devices was confirmed to have a contact area of ​​8 mm2 when the area of ​​the PC drop was 8 mm2. 2 It can be more than 8 mm. 2 ~30mm2 , 9mm 2 ~23mm 2 , 10mm 2 ~19mm 2 , 11mm 2 ~18mm 2 , 11.5mm 2 ~16.5mm 2 , 12.0mm 2 ~16.0mm 2 It could be.

[0057] The separator for an electrochemical device according to the present invention is preferably a wet separator prepared by a wet preparation method, which may include (S1) preparing a mixture, (S2) extruding the mixture and forming an extruded sheet, (S3) stretching the extruded sheet, (S4) removing the pore-forming agent, and (S5) heat-setting the extruded sheet.

[0058] In step (S1), a polymer resin is selected according to the final properties of the separator, and the selected polymer resin is mixed with a pore-forming agent. The polymer resin of the present invention includes a resin mixture of ethylene vinyl acetate copolymer (EVA) and polyethylene (PE), and the content of vinyl acetate (VA) in the ethylene vinyl acetate copolymer is 20 wt% or less.

[0059] The pore-forming agent is a substance dispersed in a polymer resin and causes heterogeneity in the separator membrane produced through extrusion, stretching, etc., and is subsequently removed from the separator membrane. Therefore, the portions of the separator membrane where the pore-forming agent was located remain in the form of pores in the separator membrane. The pore-forming agent is preferably a substance that is liquid during the extrusion process, but a substance that maintains a solid state can also be used. The pore-forming agent may be an aliphatic hydrocarbon solvent such as liquid paraffin, paraffin oil, mineral oil, or paraffin wax; a vegetable oil such as soybean oil, sunflower oil, rapeseed oil, palm oil, palm oil, coconut oil, corn oil, grapeseed oil, or cottonseed oil; or a plasticizer such as dialkyl phthalate. In particular, the plasticizer may be di-2-ethylhexyl phthalate (DOP), di-butyl phthalate (DBP), di-isononyl phthalate (DINP), di-isodecyl phthalate (DIDP), butyl benzyl phthalate (BBP), etc. Among these, it is particularly preferable to use liquid paraffin (LP, also called "liquid paraffin").

[0060] Furthermore, the content of the pore-forming agent during the preparation of the separator can be appropriately adjusted to achieve the desired level of porosity. Considering the aspect of improving air permeability, a high content of the pore-forming agent is preferable, but if it is added in an excessive amount, it may have an adverse effect on the strength of the final separator. Therefore, the content of the pore-forming agent may be 1 wt% to 80 wt% based on 100 wt% of the total weight of the polymer resin and pore-forming agent. If necessary, the content may be adjusted within this range to 70 wt% or less, 60 wt% or less, or 50 wt% or less, or 1 wt% or more, 20 wt% or more, or 40 wt% or more.

[0061] The prepared mixture is then extruded using an extruder to form an extruded sheet. The extruder is not particularly limited and may be any extruder commonly used in the art, such as an extruder equipped with a T-die or a tubular die. The extrusion process can be carried out at a standard extrusion temperature, preferably at a temperature 10°C to 100°C higher than the melting point of the polymer resin used. Temperatures above this range are undesirable because they can cause thermal degradation of the polymer resin, making membrane formation difficult and degrading the physical properties of the resulting separator. An extruded sheet can be formed using this extrusion process.

[0062] Next, the extruded sheet is stretched. This stretching process can be carried out using a stretching machine commonly used in the art. The stretching machine can be, but is not limited to, a sequential biaxial stretching machine. Stretching the extruded sheet in this way can increase the mechanical strength of the separator. The stretching process can be carried out in the machine direction (MD) and / or the transverse direction (TD). The stretching causes cleavage between lamellae of the resin mixture, forming numerous fibrils, which are then randomly connected three-dimensionally to form an extremely fine network structure. Furthermore, stretching in all or any one of these directions increases the tensile strength in the corresponding stretching direction. If necessary, the separator of the present invention can be stretched in the machine direction (MD) and / or the transverse direction (TD) independently (e.g., uniaxial stretching), simultaneously, or sequentially (e.g., biaxial stretching) during the stretching process. Meanwhile, according to one embodiment of the present invention, the temperature of the sheet during the stretching can be controlled to 100°C to 130°C, preferably 110°C to 125°C.

[0063] Next, the pore-former is removed from the resulting sheet. The pore-former can be removed by extracting it using a solvent and drying it. Furthermore, this removal can result in the formation of pores in the spaces previously occupied by the pore-former. Any solvent capable of extracting the pore-former can be used to extract the pore-former. However, preferred solvents include methyl ethyl ketone, methylene chloride, and hexane, which have high extraction efficiency and fast drying times. Methylene chloride, e.g., methylene dichloride (MC), is preferred. The extraction method can be any common solvent extraction method, such as immersion, solvent spray, or ultrasonic, either individually or in combination.

[0064] The extruded sheet is then heat-set, ultimately producing a separator membrane with the desired physical properties, porosity, and air permeability. The heat-set step can be performed using a heating device, such as an oven, capable of applying the appropriate temperature required for heat-set. In particular, the previously dried sheet undergoes heat-set to finally remove residual stress and reduce the shrinkage of the final sheet. Heat-set is a process in which the sheet is fixed and heated to forcibly grip the sheet, which tends to shrink, and remove residual stress. While a higher heat-set temperature is advantageous for reducing shrinkage, if the heat-set temperature is too high, the sheet may partially melt, which may block the formed pores and reduce permeability. The preferred heat-set temperature is selected within a temperature range in which approximately 10% to 30% by weight of the crystalline portion of the sheet melts. If the heat setting temperature is selected to be lower than the temperature at which about 10% by weight of the crystalline portion of the sheet melts, the reorientation of the polymer resin molecules in the sheet will be insufficient, and the sheet will not be able to relieve residual stress. If the heat setting temperature is selected to be higher than the temperature at which about 30% by weight of the crystalline portion of the sheet melts, the pores may be blocked due to partial melting, which may reduce the permeability.

[0065] Meanwhile, the separator for an electrochemical device according to the present invention may further include a porous coating layer formed on one or both sides of the separator, and the porous coating layer may include inorganic particles and a binder polymer.

[0066] The porous coating layer may have a porous structure characterized by a large number of micropores therein, which are interconnected, allowing gas or liquid to pass from one side to the other. According to one embodiment of the present invention, the binder polymer and inorganic particles in the porous coating layer may be contained in a weight ratio of 1:99 to 30:70. This ratio may be appropriately adjusted within this range. For example, the binder polymer may be 1 wt % or more, 5 wt % or more, or 10 wt % or more, and the inorganic particles may be 80 wt % or more, 85 wt % or more, 90 wt % or more, or 95 wt % or more, based on a total weight of the binder polymer and inorganic particles (100 wt %). In the present invention, the porous coating layer preferably has a porous structure in terms of ion permeability.

[0067] The porous coating layer may be formed by binding inorganic particles with a binder polymer, and pores may be formed by interstitial volumes between the inorganic particles. The interstitial volumes may be spaces defined by inorganic particles that are in substantial surface contact with each other in a close-packed or densely packed structure.

[0068] In one embodiment of the present invention, the porosity of the porous coating layer may be 30 vol% to 70 vol%, and within this range, the porosity may be 35 vol% or more, or 40 vol% or more, and simultaneously or independently, 65 vol% or less, or 60 vol% or less. For example, the porosity may be 40 vol% to 60 vol%. A porosity of 70 vol% or less ensures mechanical properties that can withstand the pressing process for bonding to the electrode, and is suitable for ensuring adhesive strength because the surface opening ratio is not too high. On the other hand, a porosity of 30 vol% or more is advantageous in terms of ion permeability.

[0069] The thickness of the porous coating layer may be 1 μm to 6 μm on one side of the separator. Within this range, the thickness of the porous coating layer may be 2 μm or more, or 3 μm or more, as needed. Within this range, the adhesion to the electrode may be excellent, and as a result, the cell strength of the electrochemical device may be increased. On the other hand, if the thickness is 6 μm or less, it is advantageous in terms of the cycle characteristics and resistance characteristics of the electrochemical device.

[0070] Non-limiting examples of polymer resins that can be used for the porous coating layer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, and the like. The polymer may be any one selected from the group consisting of polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof.

[0071] In addition, the inorganic particles that can be used for the porous coating layer are not particularly limited as long as they are electrochemically stable, i.e., 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+).

[0072] Non-limiting examples of the inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Tiy 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, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), etc., and one or more of these may be included.

[0073] Independently of or in combination with the components exemplified above, the inorganic particles may include inorganic particles having lithium ion transport capability. Non-limiting examples of inorganic particles having lithium ion transport capability include lithium phosphate (LiPO), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z (PO4)3,0 <x<2、0<y<1、0<z<3)、14Li2O-9Al2O3-38TiO2-39P2O5などといった(LiAlTiP) x O y Glass (0 <x<4、0<y<13)、リチウムランタンチタネート(Li x La y TiO3, 0 <x<2、0<y<3)、Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li S4) x Ge y P z S w , 0 <x<4、0<y<1、0<z<1、0<w<5)、Li3Nなどといったリチウムナイトライド(Li x N y, (0 < x < 4, 0 < y < 2), SiS2-based glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , (0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glasses such as LiI-Li2S-P2S5 (Li x P y S z , (0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc.

[0074] Also, the average diameter (D50) of the inorganic particles is not particularly limited, but for the formation of a porous coating layer with a uniform thickness and an appropriate porosity, it is preferably in the range of 0.3 μm to 1.0 μm. If it is less than 0.3 μm, the dispersibility of the inorganic particles in the slurry prepared for the production of the porous coating layer may decrease, and if it exceeds 1.0 μm, the thickness of the formed porous coating layer may increase.

[0075] In one embodiment of the present invention, the method for forming the porous coating layer is as follows. First, a binder polymer is dissolved in an appropriate organic solvent to produce a polymer solution. As the solvent, it is preferably similar in solubility index to the binder polymer to be used and has a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or mixtures thereof, etc.

[0076] Next, inorganic particles are added and dispersed in the prepared polymer solution. In the present invention, the content ratio of the inorganic particles to the polymer binder is as described above, and can be appropriately adjusted taking into consideration the thickness, pore size, and porosity of the porous coating layer to be finally prepared in the present invention.

[0077] Next, the inorganic particle slurry prepared as above is applied to at least one surface of a separator and dried. The method for coating the slurry onto the separator is not particularly limited, and any conventional coating method known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof can be used.

[0078] The drying process may be performed under appropriate temperature and time conditions to minimize defects on the surface of the porous coating layer, and may be performed using auxiliary drying devices such as a drying oven or hot air.

[0079] Meanwhile, an electrochemical device according to another aspect of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the separator is the separator for an electrochemical device according to the present invention described above.

[0080] In the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer including a positive electrode active material, a conductive material, and a polymer binder. The positive electrode active material may be a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-xO4 (where x is from 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by; chemical formula LiMn 1-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; It can contain one or a mixture of two or more of Fe2(MoO4)3.

[0081] In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a polymer binder on at least one surface of the current collector. As the negative electrode active material, the negative electrode includes carbon such as lithium metal oxide, graphitized carbon, and graphite-based carbon; Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC, Si alloys; Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group III elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; It can contain one or a mixture of two or more selected from titanium oxides.

[0082] In the present invention, the current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the electrochemical element. For example, stainless steel, copper, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can be used.

[0083] In the present invention, the conductive material may be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, carbon nanotube, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. The carbon nanotube is a graphite sheet having a cylindrical shape with a nano-sized diameter, and is sp 2 The graphite sheet has a bonding structure and exhibits conductive or semiconductive properties depending on the angle and structure of the graphite sheet winding. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the wall, and these carbon nanotubes can be appropriately selected depending on the application of the dispersion. More specifically, the conductive material may be one or a mixture of two or more conductive materials selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0084] In the present invention, the polymer binder may be any polymer binder commonly used in electrodes in the art. Non-limiting examples of such polymeric binders include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of suitable polymers include, but are not limited to, cyanoethyl acetatepropionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0085] The electrode assembly according to the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The electrode assembly can be placed in a suitable case and an electrolyte can be injected to manufacture an electrochemical device.

[0086] In the present invention, the electrolyte is A + B - A salt having the structure: + Li + , Na + , K. + or a combination thereof, - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a salt containing an anion such as the above, or an ion consisting of a combination thereof, can be dissolved or dissociated in an organic solvent consisting of, but not limited to, 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 (γ-butyrolactone), or a mixture thereof.

[0087] The present invention also provides a battery module including a battery having the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the devices include, but are not limited to, power tools powered by a battery-powered motor, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters, electric golf carts, and power storage systems.

[0088] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0089] 1. Separation membrane production

[0090] (1) Example 1

[0091] A resin mixture was prepared by mixing 95 wt% polyethylene (MW 374,000 g / mol, PDI 4.25) and 5 wt% ethylene vinyl acetate copolymer (MW 310,000 g / mol, PDI 2.3) containing 10 wt% vinyl acetate, based on 100 wt% resin mixture.

[0092] 30 parts by weight of the resin mixture prepared above and 70 parts by weight of liquid paraffin oil (kinematic viscosity at 40°C: 40 cSt) were fed into a twin-screw extruder, kneaded, and then extruded. After extrusion, the extruded material was formed into a sheet through a T-die and a cooling casting roll, and then biaxially stretched in MD and TD using a tenter-type sequential stretching machine. The liquid paraffin oil diluent was extracted from the stretched sheet with methylene chloride, and the sheet was heat-set at approximately 128°C to produce a separator membrane.

[0093] (2) Example 2

[0094] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 90 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 10 wt% ethylene-vinyl acetate copolymer (Mw 310,000 g / mol, PDI 2.3) containing 10 wt% vinyl acetate.

[0095] (3) Example 3

[0096] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 85 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 15 wt% ethylene-vinyl acetate copolymer (Mw 310,000 g / mol, PDI 2.3) containing 10 wt% vinyl acetate.

[0097] (4) Example 4

[0098] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 80 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 20 wt% ethylene-vinyl acetate copolymer (Mw 310,000 g / mol, PDI 2.3) containing 10 wt% vinyl acetate.

[0099] (5) Example 5

[0100] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 90 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 10 wt% ethylene-vinyl acetate copolymer (Mw 280,000 g / mol, PDI 2.15) containing 20 wt% vinyl acetate.

[0101] (6) Example 6

[0102] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 70 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 30 wt% ethylene-vinyl acetate copolymer (Mw 310,000 g / mol, PDI 2.3) containing 10 wt% vinyl acetate.

[0103] (7) Comparative Example 1

[0104] A separation membrane was prepared in the same manner as in Example 1, except that 100 wt % polyethylene (Mw 374,000 g / mol, PDI 4.25) was used instead of a resin mixture.

[0105] (8) Comparative Example 2

[0106] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 90 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 10 wt% ethylene-vinyl acetate copolymer (Mw 324,000 g / mol, PDI 2.4) containing 25 wt% vinyl acetate.

[0107] (9) Comparative Example 3

[0108] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 90 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 10 wt% ethylene-vinyl acetate copolymer (Mw 307,000 g / mol, PDI 2.2) containing 30 wt% vinyl acetate.

[0109] (10) Comparative Example 4

[0110] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 85 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 15 wt% ethylene-vinyl acetate copolymer (Mw 324,000 g / mol, PDI 2.4) containing 25 wt% vinyl acetate.

[0111] (11) Comparative Example 5

[0112] A separator was prepared in the same manner as in Example 1, except that the resin mixture used was a mixture of 80 wt% polyethylene (Mw 374,000 g / mol, PDI 4.25) and 20 wt% ethylene-vinyl acetate copolymer (Mw 324,000 g / mol, PDI 2.4) containing 25 wt% vinyl acetate.

[0113] 2. Evaluation of separation membrane properties

[0114] (1) Thickness evaluation

[0115] The thickness of the separation membranes prepared according to each of the Examples and Comparative Examples was measured using a thickness measuring device (Mitutoyo Corporation, VL-50S-B) and is shown in Table 1 below.

[0116] (2) Porosity evaluation

[0117] The porosity of the separators prepared according to each of the examples and comparative examples was measured using a CFP-1500-AE device from Porous Materials, and the results are shown in Table 1 below.

[0118] (3) Drilling strength evaluation

[0119] The maximum load value when puncturing the separators prepared according to each Example and Comparative Example with a needle having a diameter of 1 mm (0.5 mmR) at a speed of 120 mm / min was measured and is shown in Table 1. In accordance with ASTM D5748-95 and ASTM D4649, the test was carried out five times for each separator using an Instron testing machine, and the standard deviation and average value were calculated by the testing machine.

[0120] (4) Evaluation of electrolyte impregnation (area of ​​propylene carbonate droplet (PC drop))

[0121] For the separation membranes prepared according to each example and comparative example, 2 μL of propylene carbonate solution was dropped onto the surface of the separation membrane using a Drop Shape Analysis System (KRUSS, DSA100), and the area of ​​the propylene carbonate droplet (PC drop) was measured after 5 minutes. The results are shown in Table 1 below.

[0122] (5) Evaluation of shutdown temperature

[0123] The separators prepared according to each example and comparative example were exposed to a temperature increase condition (starting from 30°C at 5°C / min) while measuring their air permeability. The temperature at which the air permeability (Gurley value) of the separator first exceeded 100,000 sec / 100cc was measured and is shown in Table 1 below. The air permeability of the separators was measured using an air permeability meter (Asahi Seiko, EGO-IT) in accordance with JIS P8117.

[0124] [Table 1]

[0125] Referring to Table 1, no significant differences were observed in the thickness or porosity of the separator between the Examples and Comparative Examples. With regard to puncture strength, the remaining Examples, except for Example 6, measured a low of 208 gf (Example 4) and a high of 251 gf (Example 1). Even Example 6, which showed the lowest puncture strength among the Examples, measured a value of 160 gf or more. Meanwhile, Comparative Examples 2 to 5 measured puncture strength values ​​of less than 160 gf.

[0126] On the other hand, Comparative Example 1 showed a relatively high puncture strength value, but in the area evaluation portion of the propylene carbonate droplet (PC drop) which shows the electrolyte impregnation property, the area was 7.5 mm 2 The very poor measured values ​​show that it is difficult to achieve the object of the present invention.

[0127] Furthermore, the standard deviation of the puncture strength of the Examples was a relatively small value of approximately 7.16 (Example 6) at most, while the standard deviation of the puncture strength of the Comparative Examples was a minimum of 8 or more. This confirms that the separation membranes manufactured according to the Comparative Examples have non-uniform physical properties compared to the separation membranes manufactured according to the Examples.

[0128] As a result of evaluating the physical properties of the separator, Comparative Example 1 had excellent puncture strength but poor electrolyte impregnation, and Comparative Examples 2 to 5 had excellent electrolyte impregnation but poor puncture strength. However, all of the examples according to the present invention showed excellent results in both puncture strength and electrolyte impregnation.

[0129] This specification discloses preferred embodiments of the present invention, and even if specific terms are used, they are used in a general sense merely to facilitate understanding of the technical content of the present invention and are not intended to limit the scope of the present invention. It will be obvious to those skilled in the art to which the present invention pertains that other modifications based on the technical concept of the present invention are possible in addition to the embodiments disclosed herein. For example, those skilled in the art will recognize that the separator for an electrochemical device and an electrochemical device including the same according to the embodiments can be modified in various ways. Therefore, the scope of the invention should be determined not by the described embodiments but by the technical concept set forth in the claims.

Claims

1. A separator for an electrochemical device, comprising a resin mixture of an ethylene-vinyl acetate copolymer and polyethylene, wherein the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 20 wt % or less, The content of the ethylene-vinyl acetate copolymer in the resin mixture is 5% by weight or more and 30% by weight or less, The separator for electrochemical devices has a puncture strength of 160 gf or more, A separator for electrochemical elements, having a standard deviation of puncture strength of 8.0 or less.

2. 2. The separator for an electrochemical device according to claim 1, wherein the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 1% by weight to 20% by weight.

3. 2. The separator for an electrochemical device according to claim 1, wherein the ethylene vinyl acetate copolymer has an ethylene content of 80 to 99 wt %.

4. 2. The separator for electrochemical devices according to claim 1, wherein the ethylene / vinyl acetate copolymer has a content ratio of ethylene to vinyl acetate of 3.5 to 20.

5. 2. The separator for electrochemical devices according to claim 1, wherein the resin mixture has a vinyl acetate content of 0.1 wt % to 3 wt % and an ethylene content of 97 wt % to 99.9 wt %.

6. The weight average molecular weight of the ethylene vinyl acetate copolymer is 320,000 g / mol or less, 2. The separator for an electrochemical device according to claim 1, wherein the melting point of the ethylene-vinyl acetate copolymer is 80°C to 130°C.

7. 2. The separator for an electrochemical device according to claim 1, wherein the resin mixture has a crystallinity of 20% to 50%.

8. The separator for an electrochemical device has a thickness of 1 μm to 100 μm; 2. The separator for an electrochemical device according to claim 1, wherein the porosity is 20 vol % to 70 vol % and the average pore diameter is 0.01 μm to 1 μm.

9. A 2 μL droplet of propylene carbonate was dropped onto the separator for electrochemical devices, and after 5 minutes, the area of ​​the droplet was 8 mm ２ The separator for electrochemical devices according to claim 1 , wherein the separator is a polyimide or a polyisocyanate.

10. 2. The separator for an electrochemical device according to claim 1, wherein the shutdown temperature of the separator for an electrochemical device is 100°C to 145°C.

11. The separator for an electrochemical device according to claim 1 , wherein the separator for an electrochemical device is a wet separator.

12. The separator for an electrochemical device according to any one of claims 1 to 11, further comprising a porous coating layer formed on one or both sides thereof, The separator for an electrochemical device, wherein the porous coating layer comprises inorganic particles and a binder polymer.

13. An electrochemical device comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator for an electrochemical device according to claim 12 .

Images