Separation membrane for electrochemical element and electrochemical element including the same

Abstract

The present invention relates to a separator for an electrochemical device and an electrochemical device including the same. The separator according to one embodiment of the present invention is a separator for an electrochemical device, the separator comprising a porous polymer substrate and a porous coating layer formed on at least one surface of the substrate, the porous coating layer comprising inorganic hydroxide particles, cellulose nanofibers, and a water-based binder polymer, and the content of the cellulose nanofibers is 25% by weight to 70% by weight based on the total weight of the porous coating layer.

Description

Technical Field

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2021-0184392, filed with the Korean Intellectual Property Office on December 21, 2021, and all of its contents are incorporated herein by reference. The present invention relates to a separator for an electrochemical device having improved compression resistance and an electrochemical device including the same.

Background Art

[0002] In recent years, interest in energy storage technologies has been increasing. As the application fields expand from mobile phones, camcorders, and notebook computers to the energy of electric vehicles, efforts for research and development of electrochemical devices have gradually materialized. From this perspective, electrochemical devices are the most prominent fields, and among them, the development of secondary batteries capable of charge and discharge and lithium secondary batteries having a high energy density are attracting particular attention. Recently, in developing such secondary batteries, ensuring safety has been attracting great attention.

[0003] In currently produced lithium secondary batteries, a porous substrate using a polyolefin-based polymer resin as a separator substrate is used to prevent short circuits between the positive and negative electrodes. However, the porous substrate has a problem of low heat resistance due to shrinkage or melting at high temperatures. Therefore, when the battery becomes hot due to internal / external stimuli, there is a high possibility that the positive and negative electrodes come into contact with each other and short-circuit due to shrinkage or melting of the separator, resulting in a rapid release of electrical energy and causing battery explosion or ignition.

[0004] Therefore, in order to solve the above problems, a method of forming a porous coating layer in which inorganic particles and a binder polymer are mixed on at least one surface of the porous substrate to improve heat resistance is widely used.

[0005] On one hand, during the battery assembly process, a lamination process is performed to apply heat and pressure to impart adhesion between the electrode and the separator membrane. At this time, due to the pressure applied to the separator membrane, the inorganic particles in the porous coating layer push the porous substrate. In particular, since most of the inorganic particles used in the porous coating layer of the separator membrane are spherical particles, the inorganic particles in the porous coating layer come into contact with the porous substrate at points (dots), thereby causing local pressure to be applied to the porous substrate, and as a result, the pore structure is damaged / deformed. A battery employing such a separator membrane will have an impact on resistance and life characteristics, resulting in a problem of performance degradation.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention was conceived to solve the problems of the prior art as described above, and an object thereof is to provide a separator membrane for an electrochemical element having improved compressibility and an electrochemical element including the same.

[0007] Another object of the present invention is to provide a method for manufacturing a separator membrane for an electrochemical element having improved compressibility.

[0008] It will be easily understood that other objects and advantages of the present invention can be achieved by the means or methods described in the claims and combinations thereof.

Means for Solving the Problems

[0009] The inventors of the present invention have discovered that the above problems can be solved by the following separator membrane for an electrochemical element, an electrochemical element including the same, and a method for manufacturing the same.

[0010] According to one embodiment of the present invention, there is provided a separation membrane for an electrochemical element, wherein the separation membrane includes a porous polymer substrate and one porous coating layer formed on at least one surface of the porous polymer substrate, and the porous coating layer contains inorganic hydroxide particles, cellulose nano fibers, and an aqueous binder polymer, and the content of the cellulose nano fibers is 25% by weight or more and 70% by weight or less based on the total weight of the porous coating layer.

[0011] According to one embodiment of the present invention, the content of the cellulose nano fibers may be 30% by weight or more and 60% by weight or less based on the total weight of the porous coating layer.

[0012] According to one embodiment of the present invention, the inorganic hydroxide particles may be those that form hydrogen bonds with at least one or more of the cellulose nano fibers and the aqueous binder polymer.

[0013] According to one embodiment of the present invention, the content of the inorganic hydroxide particles may be 10% by weight or more and 60% by weight or less based on 100% by weight of the total weight of the porous coating layer.

[0014] According to one embodiment of the present invention, the inorganic hydroxide particles may include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, or a mixture of two or more of these.

[0015] According to one embodiment of the present invention, the aqueous binder polymer may include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacrylamide (PAM), or a mixture of two or more of these.

[0016] According to one embodiment of the present invention, the length of the cellulose nanofiber may be from 1 μm to 100 μm.

[0017] According to one embodiment of the present invention, when a pressure of 1 MPa to 10 MPa is applied to the separation membrane in a temperature range of 60 °C to 70 °C for 1 second to 60 seconds, the thickness change rate of the porous polymer substrate before and after the pressure application may be 5% or less.

[0018] One embodiment of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is the above-described separation membrane.

[0019] According to one embodiment of the present invention, the electrochemical device may be a lithium secondary battery.

[0020] One embodiment of the present invention is a method for manufacturing a separation membrane for an electrochemical device, the method including the steps of preparing a porous polymer substrate, and coating a slurry containing inorganic hydroxide particles, cellulose nanofibers, an aqueous binder polymer, and an aqueous solvent on at least one surface of the porous polymer substrate to form at least one porous coating layer.

Advantages of the Invention

[0021] The separation membrane according to the present invention exhibits improved compression resistance, and thus can show the effect of suppressing the deformation of the separation membrane even when pressure is applied. In particular, in the separation membrane of the present invention, when pressure is applied, at least one porous coating layer formed on at least one surface of the porous substrate serves as a buffer, thereby reducing the pressure on the porous substrate and suppressing the deformation of the separation membrane.

[0022] The drawings attached to this specification illustrate preferred embodiments of the present invention and play a role in better understanding the technical idea of the present invention together with the content of the invention described above. Therefore, the present invention is not construed as being limited only to the matters described in such drawings. On the other hand, the shape, size, scale, or ratio of elements in the drawings described in this specification may be exaggerated for the purpose of emphasizing a clearer explanation.

Brief Description of the Drawings

[0023]

Figure 1

Modes for Carrying Out the Invention

[0024] Hereinafter, the present invention will be described in detail. Terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they must be construed in meanings and concepts consistent with the technical idea of the present invention.

[0025] Throughout the specification of the present application, when a certain part says that a certain component "includes" or "comprises", this means that, unless otherwise stated, it does not exclude other components, but can further include or comprise other components.

[0026] Throughout the specification of the present application, the description "A and / or B" means "A or B, or both".

[0027] The separation membrane for an electrochemical element according to one embodiment of the present invention includes a porous polymer substrate and one porous coating layer formed on at least one surface of the substrate. The porous coating layer contains inorganic hydroxide particles, cellulose nanofibers, and an aqueous binder polymer, and the content of the cellulose nanofibers is 25% by weight or more and 70% by weight or less based on the total weight of the porous coating layer.

[0028] Generally, for improving the heat resistance, the separation membrane contains inorganic particles in the porous coating layer, and spherical particulate inorganic particles are mainly used as the inorganic particles. However, when pressure is applied to the separation membrane, the inorganic particles in the porous coating layer come into dot contact with the porous polymer substrate, and local pressure is applied to the porous polymer substrate, so that the pore structure existing in the porous polymer substrate is damaged and / or deformed. Therefore, a battery employing a separation membrane with a damaged pore structure in the porous polymer substrate will have problems with decreased performance due to the influence on resistance and life characteristics.

[0029] In order to solve such problems, the inventors of the present invention attempt to reduce the influence on the porous substrate by adjusting the composition in the porous coating layer so that the porous coating layer serves as a buffer even when pressure is applied to the separation membrane.

[0030] First, by including a substance that can make line contact in the porous coating layer, an attempt is made to reduce the local pressure in the porous polymer substrate, that is, the local pressure applied by dot contact. Specifically, in the present invention, by including linear cellulose nanofibers in the porous coating layer at a predetermined content, the pressure applied to the porous polymer substrate can be reduced.

[0031] Second, each component contained in the porous coating layer can be combined through interaction, so that the pressure exerted by the inorganic particles on the porous polymer substrate can be dispersed. In the present invention, one porous coating layer contains cellulose nanofibers and an aqueous binder polymer together with inorganic hydroxide particles. The inorganic hydroxide particles, cellulose nanofibers, and aqueous binder polymer may contain functional groups capable of forming hydrogen bonds between the components, so that the components can be organically bonded. For example, since the inorganic hydroxide particles can form hydrogen bonds with cellulose nanofibers and / or an aqueous binder polymer, the pressure exerted by the inorganic hydroxide particles on the porous polymer substrate can be dispersed. Also, for example, cellulose nanofibers can form hydrogen bonds with an aqueous binder polymer. Therefore, since the binding force between the cellulose nanofibers and the aqueous binder polymer is strengthened, the detachment of the porous coating layer itself is prevented, and the peel strength of the porous coating layer to the porous polymer substrate is increased, etc., the physical properties are improved, which may lead to maintaining the form of the porous coating layer. Also, when pressure is applied to the separation membrane, the pressure transmitted to the cellulose nanofibers is also dispersed to the aqueous binder polymer, and the entire porous coating layer can serve as a buffer. In particular, the inorganic hydroxide particles and cellulose nanofibers of the present invention receive pressure over a larger area than spherical inorganic particles, so that damage to the porous polymer substrate can be reduced. Also, since the substances present in the porous coating layer have a large number of functional groups such as OH groups forming hydrogen bonds and have a high tensile modulus, they can serve as a buffer for the porous coating layer against the porous polymer substrate. Therefore, even when pressure is applied to the separation membrane, the deformation of the separation membrane is reduced, so that the problem of deterioration of the battery performance can be suppressed.

[0032] The porous polymer substrate is a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode, and refers to a substrate in which a plurality of pores are formed inside. Since the pores are connected to each other, gas or liquid can pass from one surface of the substrate to the other surface. As such a substrate, from the viewpoint of imparting a shut-down function, a porous polymer film containing a thermoplastic resin can be used. Here, the shut-down function means a function of preventing thermal runaway of the battery by blocking the movement of ions by dissolving the thermoplastic resin and closing the pores of the porous substrate when the battery temperature rises. Those with a melting point of the thermoplastic resin of less than 200 °C, and polyolefin resins such as polyethylene, polypropylene, polybutylene, and polypentene are preferred.

[0033] The thickness of the porous polymer substrate is not particularly limited, but can be 1 μm or more and 100 μm or less, or 5 μm or more and 50 μm or less. The size and porosity of the pores present in the porous polymer substrate are also not particularly limited, but can be 0.01 μm or more and 50 μm or less, and 10% or more and 95% or less, respectively.

[0034] The porous coating layer is formed on at least one surface of the porous polymer substrate. The porous coating layer contains inorganic hydroxide particles, cellulose nanofibers, and an aqueous binder polymer.

[0035] The inorganic hydroxide particles contained in the porous coating layer may be bound by cellulose nanofibers and / or aqueous binder polymers. In the present invention, each of the inorganic hydroxide particles, cellulose nanofibers, and aqueous binder polymers, or between them, can form hydrogen bonds, and an interstitial volume, which is a space limited by a structure linked by hydrogen bonds, is formed, and the interstitial volume can form pores. For example, since the cellulose nanofibers are not perfectly packed together, there may be pores between the fibers.

[0036] According to one embodiment of the present invention, the porous coating layer may be formed by the binding of two or more components among the inorganic hydroxide particles, cellulose nanofibers, and aqueous binder polymers. For example, the binding may be a hydrogen bond. In the present invention, the formation of hydrogen bonds between the components can be confirmed through X-ray diffraction analysis (XRD). Specifically, since the bond length between molecules can be confirmed through X-ray diffraction analysis, the presence or absence of hydrogen bond formation can be analyzed.

[0037] Specifically, since the inorganic hydroxide particles can form hydrogen bonds with cellulose nanofibers and / or aqueous binder polymers, the pressure exerted by the inorganic hydroxide particles on the porous polymer substrate can be dispersed, so that even when pressure is applied to the separation membrane, deformation of the porous polymer substrate can be suppressed.

[0038] In particular, the present invention is characterized in that one porous coating layer simultaneously contains inorganic hydroxide particles, cellulose nanofibers, and an aqueous binder polymer. Since inorganic hydroxide particles are present between the cellulose nanofibers and hydrogen bonds are formed between the components, it can exhibit a more excellent effect in terms of compression resistance. Therefore, when a plurality of porous coating layers each contain inorganic hydroxide particles and cellulose nanofibers, they are excluded from the present invention.

[0039] The specific type of the inorganic hydroxide particles is not limited. For example, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, or a mixture thereof can be used. Preferably, aluminum hydroxide can be used.

[0040] When the content of the inorganic hydroxide particles is based on 100% by weight of the total weight of the porous coating layer, it can be 10% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more, and can be 60% by weight or less, or 50% by weight or less. When the content of the inorganic hydroxide particles with respect to the total weight of the porous coating layer satisfies the above range, there are advantageous effects in terms of heat resistance and dispersion stability. In particular, when the inorganic hydroxide particles are contained in an amount more than the above range, the dispersion stability may decrease, and it may be difficult to control the slurry viscosity for forming the porous coating layer, which may make it difficult to adjust the thickness of the porous coating layer. Also, when pressure is applied to the separation membrane, a high internal pressure acts on the inorganic hydroxide particles, which may be disadvantageous in terms of compression resistance.

[0041] The average particle size of the inorganic hydroxide particles is not particularly limited, but is preferably in the range of 0.001 μm or more and 10 μm or less, more preferably 100 nm or more and 2 μm or less, and even more preferably 150 nm or more and 1 μm or less for forming a porous coating layer with a uniform thickness and an appropriate porosity.

[0042] The cellulose nanofiber is light in weight, but has high strength and does not expand even when heated. Therefore, it can be more advantageously used in the porous coating layer of the separation membrane to improve the strength and heat resistance characteristics.

[0043] In one embodiment of the present invention, the content of the cellulose nanofiber may be 25% by weight or more and 70% by weight or less based on 100% by weight of the total weight of the porous coating layer. According to one embodiment of the present invention, the content of the cellulose nanofiber may be 30% by weight or more and 60% by weight or less based on 100% by weight of the total weight of the porous coating layer. When the cellulose nanofiber is contained in an amount more than the presented content range, it may show a poor effect in terms of heat resistance. When the cellulose nanofiber is contained in an amount less than the presented content range, it may show a poor effect in terms of compression resistance.

[0044] The cellulose nanofiber may contain functional groups capable of forming hydrogen bonds with inorganic hydroxide particles and / or aqueous polymers. For example, the cellulose nanofiber may contain, as functional groups capable of forming hydrogen bonds, -OH, -COO-, -COOH, -NH 2 groups and the like. Therefore, the cellulose nanofiber can form hydrogen bonds with inorganic hydroxide particles and / or aqueous polymers in the porous coating layer to disperse the pressure applied by the inorganic hydroxide particles to the porous polymer substrate. Thus, the porous coating layer can better serve as a buffer, and a separation membrane with further improved compression resistance can be provided.

[0045] Further, the diameter of the cellulose nanofiber can be 1 nm or more and 1 μm or less, preferably 50 nm or more and 500 nm or less, and more preferably 100 nm or more and 200 nm or less. When the diameter of the cellulose nanofiber is within the above range, more pores can be formed in the porous coating layer, and more hydrogen bonds can be formed with the inorganic hydroxide particles and / or the aqueous binder polymer, so that the wetting property after electrolyte injection can be further improved.

[0046] Further, the length of the cellulose nanofiber can be 1 μm or more and 100 μm or less, preferably 30 μm or more and 100 μm or less, and more preferably 50 μm or more and 100 μm or less. When the length of the cellulose nanofiber is within the above range, it is easy to absorb the pressure that the inorganic hydroxide particles will receive when pressure is applied to the separation membrane, and the pressure can be dispersed in the porous coating layer, so it may be more advantageous in terms of compression resistance.

[0047] The aqueous binder polymer is soluble in an aqueous solvent such as water. Further, the aqueous binder polymer may contain a functional group capable of forming a hydrogen bond with the inorganic hydroxide particles and / or the aqueous polymer. The specific type of the aqueous binder polymer is not limited, and for example, it may include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacrylamide (PAM), or a mixture of two or more of these. Preferably, carboxymethyl cellulose may be included as the aqueous binder polymer in terms of ensuring uniform coating properties.

[0048] When the content of the aqueous binder polymer is based on 100% by weight of the total weight of the porous coating layer, it can be 5% by weight or more and 60% by weight or less, 5% by weight or more and 30% by weight or less, or 10% by weight or more and 20% by weight or less. When the content of the aqueous binder polymer with respect to the total weight of the porous coating layer satisfies the above range, the dispersibility of the inorganic hydroxide particles and the cellulose nanofibers can be improved during the formation of the porous coating layer, and sufficient hydrogen bonds can be formed with the inorganic hydroxide particles and / or the cellulose nanofibers, which has an advantageous effect in terms of compression resistance.

[0049] According to one embodiment of the present invention, when a pressure of 1 MPa or more and 10 MPa or less is applied to the separation membrane of the present invention in a temperature range of 60°C or more and 70°C or less for 1 second or more and 60 seconds or less, when comparing the thickness of the porous polymer substrate before and after the pressure is applied, the thickness change rate of the porous polymer substrate can be 5% or less, 4.5% or less, or 3% or more and 4.5% or less. For example, at a temperature of 70°C, a pressure of 5.2 MPa is applied for 10 seconds, and the thickness change rate of the porous polymer substrate before and after the pressure is applied can be measured. At this time, pressure can be applied to the separation membrane using a hot-press device, and the thickness of the porous polymer substrate can be measured using a thickness measuring instrument (Mitutoyo, VL-50S-B).

[0050] According to one embodiment of the present invention, a method for manufacturing a separation membrane for an electrochemical element includes: preparing a porous polymer substrate; and coating at least one surface of the porous polymer substrate with a slurry containing inorganic hydroxide particles, cellulose nanofibers, an aqueous binder polymer, and an aqueous solvent to form at least one porous coating layer.

[0051] In the method for manufacturing a separation membrane according to an embodiment of the present invention, after dispersing inorganic hydroxide particles and cellulose nanofibers in an aqueous solvent as a dispersion medium, an aqueous binder polymer can be added to produce a slurry. The aqueous solvent, which is the dispersion medium used at this time, is a polar solvent and can be water, methanol, ethanol, ethylene glycol, diethylene glycol, glycerol, or a mixture of two or more of these.

[0052] Thereafter, by applying and drying the prepared slurry on at least one surface of a porous polymer substrate to form a coating, at least one porous coating layer can be formed on at least one surface of the porous polymer substrate.

[0053] An electrochemical element according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, and the separation membrane is the separation membrane according to an embodiment of the present invention described above.

[0054] In one embodiment of the present invention, the electrochemical element is a device that converts chemical energy into electrical energy by an electrochemical reaction, and includes all elements that perform an electrochemical reaction. Specific examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In particular, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferred.

[0055] The electrode applied together with the separation membrane of the present invention is not particularly limited, and can be manufactured in a form in which an electrode active material is bound to an electrode current collector according to a conventional method known in the art.

[0056] Among the electrode active materials, as non-limiting examples of the positive electrode active material, ordinary positive electrode active materials that can be used for the positive electrode of a conventional lithium secondary battery can be used. In particular, it is preferable to use lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide obtained by combining these.

[0057] As non-limiting examples of the negative electrode active material, ordinary negative electrode active materials that can be used for the negative electrode of a conventional lithium secondary battery can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials such as lithium adsorbents are preferable.

[0058] Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of the negative electrode current collector include foils made of copper, gold, nickel or copper alloy, or combinations thereof.

[0059] The electrolytic solution that can be used in the electrochemical element of the present invention is a salt having a structure such as A + B - wherein A + is an ion composed of an alkali metal cation such as Li + , Na + , K + or a combination thereof, and B - is PF 6 - , BF 4 - , Cl - , Br - , I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - , CF 3 SO 3 -, N(CF 3 SO 2 ) 2 - , C(CF 2 SO 2 ) 3 - Salts containing anions such as these, or ions composed of a combination of these, are dissolved or dissociated in an organic solvent composed of 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 of these, but are not limited thereto.

[0060] The injection of the electrolyte can be carried out at an appropriate stage during the battery manufacturing process according to the manufacturing process of the final product and the required physical properties. That is, it can be applied before battery assembly or at the final stage of battery assembly.

[0061] The present invention also provides a battery module including a battery including an 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 a power tool powered by a battery 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-wheeler including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; a power storage system, etc., but are not limited thereto.

[0062] Hereinafter, examples will be given to specifically describe the present invention in detail. However, the examples according to the present invention can be deformed into various different forms, and the scope of the present invention should not be construed as being limited to the examples described in detail below. The examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the industry.

[0063] [Examples] Examples 1 to 4 and Comparative Examples 1 to 5 According to the following method, the separation membranes of Examples 1 to 4 and Comparative Examples 1 to 5 were manufactured. The ratios of the components contained in the porous coating layer of the manufactured separation membranes are as described in Table 1.

[0064] [Manufacture of Cellulose Nanofibers] 1. Cellulose powder was put into a 2 wt% NaOH solution and stirred vigorously for 1 hour.

[0065] 2. After washing the treated cellulose powder with distilled water, it was added to a mixed solvent of IPA (isopropyl alcohol)-distilled water, and then stirred for 12 hours using a homogenizer.

[0066] 3. The cellulose nanofibers (CNF) produced in the cellulose solution were filtered.

[0067] 4. After drying at 80°C for 2 days, the cellulose nanofibers were recovered.

[0068] The recovered cellulose nanofibers had a diameter of 50 nm to 500 nm and a length of 30 μm to 100 μm, and cellulose nanofibers were mixed.

[0069] [Manufacture of Separation Membrane] 1. A polyethylene porous film (thickness 9 μm, porosity 45%) was prepared as a porous polymer substrate.

[0070] 2. Prepare distilled water, add the produced cellulose nanofibers (CNF), aluminum hydroxide with an average particle size of 400 nm (inorganic hydroxide particles), and carboxymethyl cellulose (aqueous binder polymer), and then stir to produce a slurry for forming a porous coating layer. The solid content of the produced slurry was 30%.

[0071] 3. After applying the slurry to one side of a polyethylene porous film using a bar coater, dry it to produce a separation membrane including a porous coating layer described in Table 1 below.

[0072] [Comparative Example 6] 1. Prepare a polyethylene porous film (thickness 9 μm, porosity 45%) as a porous polymer substrate.

[0073] 2. Prepare distilled water, add the produced cellulose nanofibers (CNF) and carboxymethyl cellulose (aqueous binder polymer), and then stir to produce a slurry for forming a first porous coating layer. The solid content of the produced slurry was 30%.

[0074] 3. Prepare distilled water, add aluminum hydroxide with an average particle size of 400 nm (inorganic hydroxide particles) and carboxymethyl cellulose (aqueous binder polymer), and then stir to produce a slurry for forming a second porous coating layer. The solid content of the produced slurry was 30%.

[0075] 4. After applying the slurry for forming the first porous coating layer to one side of the polyethylene porous film using a bar coater, dry it to form a first porous coating layer (first layer, thickness 3 μm) described in Table 1 below. Then, apply the slurry for forming the second porous coating layer to one side on the first porous coating layer, and dry it to form a second porous coating layer (second layer, thickness 3 μm) described in Table 1 below, thereby producing a separation membrane.

[0076] Evaluation results For the separation membranes of Example 1 to Example 4 and Comparative Example 1 to Comparative Example 6, each physical property before applying pressure and after applying a pressure of 5.2 MPa for 10 seconds at a temperature of 70 °C was measured, and the change rate was shown in Table 1.

[0077] The specific method for measuring the physical properties for evaluating the compression resistance is as follows.

[0078] (1) Thickness of the porous polymer substrate and change rate of the thickness of the porous polymer substrate The thickness of the porous polymer substrate was measured using a thickness measuring instrument (Mitutoyo, VL-50S-B).

[0079] The change rate of the thickness of the porous polymer substrate was calculated by the following formula 1.

[0080] [Formula 1] Change rate of the thickness of the porous polymer substrate (%) = [(thickness before pressurization - thickness after pressurization) / (thickness before pressurization)] × 100 (2) Air permeability of the separation membrane and change rate of the air permeability of the separation membrane The air permeability of the separation membrane was measured using the Wang research type air permeability measuring device of Asahi Seiko. At this time, the time for 100 cc of air to pass through a diameter of 28.6 mm and an area of 645 mm 2 was measured.

[0081] The change rate of the air permeability of the separation membrane was calculated by the following formula 2.

[0082] [Formula 2] Change rate of the air permeability of the separation membrane (%) = [(air permeability before pressurization - air permeability after pressurization) / (air permeability before pressurization)] × 100 (3) Resistance of the separation membrane and change rate of the resistance of the separation membrane The resistance value when the separation membrane is impregnated with the electrolytic solution, measured at 25°C by the AC method (frequency: 10,000 Hz to 100,000 Hz) using the following electrolytic solution. The electrolytic solution is prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as solvents in a composition ratio of 3:7 (volume ratio), adding vinylene carbonate (VC) at 2% by weight based on the solvent, and adding LiPF 6 to a concentration of 1 M.

[0083] The rate of change in the resistance of the separation membrane was calculated using the following Equation 3.

[0084] [Equation 3] Rate of change in the resistance of the separation membrane (%) = [(Resistance before pressurization - Resistance after pressurization) / (Resistance before pressurization)] × 100

[0085]

Table 1

Claims

1. A separation membrane for an electrochemical device, wherein the separation membrane comprises a porous polymer substrate and one porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer contains inorganic hydroxide particles, cellulose nanofibers, and an aqueous binder polymer, the content of the cellulose nanofibers is 25% by weight or more and 70% by weight or less based on the total weight of the porous coating layer, when a pressure of 1 MPa or more and 10 MPa or less is applied to the separation membrane within a temperature range of 60°C or more and 70°C or less for 10 seconds, the thickness change rate of the porous polymer substrate before and after the pressure application is 5% or less. A separation membrane for an electrochemical device characterized by this.

2. The separation membrane for an electrochemical device according to Claim 1, wherein the content of the cellulose nanofibers is 30% by weight or more and 60% by weight or less based on the total weight of the porous coating layer.

3. The separation membrane for an electrochemical device according to Claim 1, wherein the inorganic hydroxide particles are hydrogen-bonded to at least one or more of the cellulose nanofibers and the aqueous binder polymer.

4. The separation membrane for an electrochemical device according to Claim 1, wherein the content of the inorganic hydroxide particles is 10% by weight or more and 60% by weight or less based on 100% by weight of the total weight of the porous coating layer.

5. The separation membrane for an electrochemical device according to Claim 1, wherein the inorganic hydroxide particles include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, or a mixture of two or more of these.

6. The aqueous binder polymer includes carboxymethyl cellulose (CMC: carboxymethyl - cellulose), styrene butadiene rubber (SBR: styrene butadiene rubber), polyvinyl alcohol (PVA: polyvinyl alcohol), polyacrylic acid (PAA: polyacrylic acid), polyethylene glycol (PEG: polyethylene glycol), polyacrylonitrile (PAN: polyacrylonitrile), polyacrylamide (PAM: polyacrylamide), or a mixture of two or more of these. The separation membrane for an electrochemical device according to claim 1 is characterized by this.

7. The separation membrane for an electrochemical device according to claim 1 is characterized in that the length of the cellulose nanofibers is 1 μm or more and 100 μm or less.

8. An electrochemical device comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, The electrochemical device is characterized in that the separation membrane is the separation membrane according to any one of claims 1 to 7.

9. The electrochemical device according to claim 8 is characterized in that the electrochemical device is a lithium secondary battery.

10. A method for manufacturing a separation membrane for an electrochemical device according to any one of claims 1 to 7, A step of preparing a porous polymer substrate, A step of coating at least one surface of the porous polymer substrate with a slurry containing inorganic hydroxide particles, cellulose nanofibers, an aqueous binder polymer, and an aqueous solvent to form at least one porous coating layer. The method for manufacturing a separation membrane for an electrochemical device is characterized by including this.

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