Separation membrane for electrochemical elements and electrochemical elements containing the same

Abstract

The present invention provides a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer including a polymer binder, inorganic particles, and an organic filler, the polymer binder being included in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the inorganic particles having a packing density of 2 g / cm. 3 More than 2.5g / cm 3 The following separator for an electrochemical device is provided.

Description

[Technical Field]

[0001] This application is a priority application claiming based on Korean Patent Application No. 10-2023-0026219, filed with the Korean Intellectual Property Office on February 27, 2023, the contents of which are entirely included in this application by reference.

[0002] The present invention relates to a separation membrane for electrochemical elements and an electrochemical element containing the same. [Background technology]

[0003] Electrochemical devices can convert chemical energy into electrical energy using electrochemical reactions. In recent years, lithium-ion batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, have become widely used.

[0004] A lithium secondary battery may include an electrode assembly made of a positive electrode, a negative electrode, and a separation membrane placed between the positive and negative electrodes, and the electrode assembly may be manufactured by housing the electrode assembly together with an electrolyte in a case. The separation membrane may include a porous coating layer containing a polymer binder and inorganic particles on at least one surface of a porous substrate. The inorganic particles can be linked with other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions can move through the interstitial volume. In addition to fixing the inorganic particles, the polymer binder can provide adhesion to the porous coating layer, and the porous coating layer can be adhered to the porous substrate and the electrodes, respectively.

[0005] A porous coating layer containing a polymer binder and inorganic particles can prevent thermal shrinkage of the porous polymer substrate, and the separation membrane containing the porous coating layer exhibits excellent dimensional stability in a dry state without electrolyte. However, in a wet state where the separation membrane is impregnated with electrolyte, the polymer binder may be swollen by the electrolyte, or the separation membrane may be exposed to temperatures of approximately 130°C or higher due to the operation of the lithium secondary battery containing the separation membrane, potentially reducing the adhesive strength of the polymer binder. In such a high-temperature wet state, the adhesive strength of the porous coating layer decreases, causing the separation membrane to shrink significantly. In particular, cylindrical batteries, in which the electrode assembly is wound up and inserted into a case while tension is applied to the electrode assembly, have a relatively lower adhesive strength between the electrode and the separation membrane compared to pouch-type batteries. Therefore, a reduction in the polymer binder content leads to a further decrease in dimensional stability in the wet state.

[0006] Therefore, research is being conducted on separation membranes that ensure dimensional stability under high temperature and wet conditions while maintaining a relatively low content of polymer binders in the porous coating layer. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a separation membrane for electrochemical elements that exhibits excellent heat resistance and improved shrinkage rate when impregnated in an electrolyte, by adjusting the packing density of inorganic particles contained in a porous coating layer and further configuring it to include organic fillers. [Means for solving the problem]

[0008] One aspect of the present invention includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises a polymer binder, inorganic particles, and an organic filler, the polymer binder is present in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the packing density of the inorganic particles is 2 g / cm³ 3 More than 2.5g / cm 3 The following separation membrane for electrochemical devices is provided.

[0009] The organic filler may be one or more selected from the group consisting of polyethylene, polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate.

[0010] The polymer binder and the organic filler may be present in a weight ratio of 5:1 to 1:5.

[0011] The polymer binder may be one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these.

[0012] The weight-average molecular weight of the polymer binder can range from 100,000 to 500,000.

[0013] The packing density of the inorganic particles is 2.1 g / cm³. 3 More than 2.3g / cm 3 The following are possible:

[0014] Another aspect of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is a separation membrane for another electrochemical element in the aforementioned aspect.

[0015] The electrochemical element may be a lithium secondary battery.

[0016] The electrochemical element may further contain an electrolyte containing EC / EMC in a weight ratio of 3 / 7. [Effects of the Invention]

[0017] The separation membrane for electrochemical elements according to the present invention can provide improved dimensional stability in a wet state impregnated with an electrolyte. Specifically, the separation membrane has a thermal shrinkage rate of 10% or less in the TD direction at high temperatures of 130°C or higher, thereby preventing electrode exposure due to thermal shrinkage of the separation membrane. [Modes for carrying out the invention]

[0018] The following describes in more detail each component of the present invention so that a person with ordinary skill in the art to which the present invention belongs can easily implement it. However, this is merely an example, and the scope of the rights of the present invention is not limited to the following.

[0019] As used herein, the term “including” is used to enumerate materials, compositions, apparatus, and methods useful for the present invention, and is not limited to such enumerated examples.

[0020] As used herein, “about” and “substantially” are used to mean a range or similar of numerical values ​​or degrees, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting disclosures that refer to precise or absolute numerical values ​​provided to aid in understanding the invention.

[0021] As used herein, "electrochemical elements" may refer to primary batteries, secondary batteries, supercapacitors, and the like.

[0022] As used herein, "wet state" may mean a state in which the separation membrane is impregnated with at least a portion of the electrolyte.

[0023] One specific example of the present invention includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises a polymer binder, inorganic particles, and an organic filler, the polymer binder is present in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the packing density of the inorganic particles is 2 g / cm³ 3 More than 2.5g / cm 3 The following separation membrane for electrochemical devices is provided.

[0024] The porous polymer substrate is a porous membrane with multiple pores formed therein, which can electrically insulate the positive and negative electrodes to prevent short circuits. For example, if the electrochemical element is a lithium secondary battery, the porous polymer substrate can be an ion-conducting barrier that blocks electrical contact between the positive and negative electrodes while allowing lithium ions to pass through. At least some of the pores can form a three-dimensional network connecting the surface and interior of the porous polymer substrate, allowing fluids to pass through the porous polymer substrate via the pores.

[0025] The porous polymer substrate can be made of a material that is physically and chemically stable with respect to an electrolyte, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, resins such as polyethylene, polypropylene, polybutylene and other polyolefins, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidoamide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, polyolefin resins can be used. Polyolefin resins can be processed to a relatively thin thickness and are easy to apply coating slurries to, making them suitable for the manufacture of electrochemical elements with higher energy density.

[0026] The porous polymer substrate may have a single-layer or multi-layer structure. The porous polymer substrate can provide a shutdown function in the event of a high-temperature runaway of the battery by including two or more polymer resin layers with different melting points (Tm). For example, the porous polymer substrate may include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. Preferably, the porous polymer substrate may have a three-layer structure in which polypropylene, polyethylene, and polypropylene are laminated in that order. The polyethylene layer melts as the battery temperature rises above a predetermined temperature, thereby shutting down the pores and preventing thermal runaway of the battery.

[0027] The thickness of the porous polymer substrate may be between 1 μm and 100 μm. Specifically, the thickness of the porous polymer substrate may be between 10 μm and 90 μm, between 20 μm and 80 μm, between 30 μm and 70 μm, or between 40 μm and 60 μm. Preferably, the thickness of the polymer substrate may be between 1 μm and 30 μm. More preferably, the thickness of the polymer substrate may be between 5 μm and 15 μm, or between 8 μm and 13 μm. By adjusting the thickness of the porous polymer substrate within the above range, it is possible to minimize the volume of the electrochemical element while electrically insulating the positive and negative electrodes, thereby increasing the amount of active material contained in the electrochemical element.

[0028] The porous polymer substrate may contain pores with an average diameter of 0.01 μm or more and 1 μm or less. Specifically, the size of the pores contained in the porous polymer substrate may be 0.01 μm or more and 0.09 μm or less, 0.02 μm or more and 0.08 μm or less, 0.03 μm or more and 0.07 μm or less, or 0.04 μm or more and 0.06 μm or less. Preferably, the size of the pores may be 0.02 μm or more and 0.06 μm or less. By adjusting the pore size of the porous polymer substrate within the above range, the permeability and ionic conductivity of the entire separation membrane produced can be adjusted.

[0029] The porous polymer substrate can have an air permeability of 10 s / 100 cc or more and 100 s / 100 cc or less. Specifically, the air permeability of the porous polymer substrate may be 10 s / 100 cc or more and 90 s / 100 cc or less, 20 s / 100 cc or more and 80 s / 100 cc or less, 30 s / 100 cc or more and 70 s / 100 cc or less, or 40 s / 100 cc or more and 60 s / 100 cc or less. Preferably, the air permeability of the porous polymer substrate may be 50 s / 100 cc or more and 70 s / 100 cc or less. When the air permeability of the porous polymer substrate is within the above range, the air permeability of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0030] The aforementioned air permeability (s / 100cc) refers to the time (in seconds) it takes for 100cc of air to pass through a predetermined area of ​​a porous polymer substrate or separation membrane under constant pressure. This air permeability can be measured using a Gurley densometer in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, using a Gurley 4110N instrument, with air at a pressure of 0.304 kPa or 1.215 kN / m³ 2 Under water pressure, 100cc of air covers 1 square inch (or 6.54cm). 2The time it takes for a sample to pass through can be measured. For example, using the EG01-55-1MR instrument from Asahi Seiko, the time it takes for 100cc of air to pass through a 1 square inch sample can be measured at room temperature and under constant pressure in 4.8 inches of water.

[0031] The porous polymer substrate may have a porosity of 10 vol% to 60 vol%. Specifically, the porosity of the porous polymer substrate may be 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. Preferably, the porosity of the porous polymer substrate may be 30 vol% to 50 vol%. When the porosity of the porous polymer substrate is within the above range, the ionic conductivity of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0032] The porosity refers to the ratio of the volume of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, it can be measured by the Brunauer-Emmett-Teller (BET) method utilizing nitrogen gas adsorption, the capillary flow porometer, or the water or mercury osmosis method.

[0033] The porous coating layer is formed on at least one surface of the porous polymer substrate and comprises a polymer binder, inorganic particles, and an organic filler. The porous coating layer can be formed by coating at least one surface of the porous polymer substrate with a coating slurry comprising a polymer binder, inorganic particles, an organic filler, and a dispersion medium. The porous coating layer adheres to the porous polymer substrate, allowing lithium ions to pass through, while containing interstitial volumes in which the inorganic particles are linked by the polymer binder, thereby preventing thermal shrinkage of the porous polymer substrate.

[0034] The coating slurry contains a dispersion medium that can dissolve or disperse at least a portion of the polymer binder and organic filler, and disperse inorganic particles. The coating slurry can be used in which the polymer binder, inorganic particles, and organic filler are uniformly dispersed by adjusting the type and content of the dispersion medium. For example, the dispersion medium may be one selected from the group consisting of water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. Preferably, the dispersion medium may be NMP. Using the above-described types of dispersion medium, a porous coating layer in which the polymer binder and inorganic particles are uniformly dispersed can be formed.

[0035] The coating slurry may further contain additives such as dispersants, surfactants, defoamers, and flame retardants to improve dispersibility and flame retardancy, and to improve the uniformity of the porous coating layer formed. For example, the dispersant may contain one or more selected from the group consisting of polyacrylic acid, oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. By using the above-mentioned types of dispersants, the stability of the coating slurry can be improved and the uniformity of the porous coating layer formed from the coating slurry can be ensured.

[0036] The additive may be present in an amount of 0% to 5% by weight relative to the total weight of the coating slurry. Specifically, the content of the additive may be 0.01% to 4% by weight, 0.1% to 3% by weight, or 1% to 2% by weight. Preferably, the content of the additive may be 1% to 5% by weight. By adjusting the content of the additive within the above range, uniform dispersion and stability of the inorganic particles contained in the coating slurry can be achieved.

[0037] The dispersion medium contained in the coating slurry can be removed by drying or heating after the formation of the porous coating layer. For example, the porous coating layer may contain the dispersion medium at a concentration of 5 ppm or less. Preferably, the porous coating layer may consist of a polymer binder and inorganic particles. During the process of removing the dispersion medium, multiple pores may be formed on the surface and inside the porous coating layer. These pores may include interstitial volumes formed between the inorganic particles, forming a three-dimensional network that allows fluid to pass through.

[0038] The thickness of the porous coating layer may be 1 μm or more and 15 μm or less. Specifically, the thickness of the porous coating layer may be 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 4 μm or more and 12 μm or less, 5 μm or more and 11 μm or less, 6 μm or more and 10 μm or less, or 7 μm or more and 9 μm or less. Preferably, the thickness of the porous coating layer may be 1 μm or more and 5 μm or less, more preferably 1 μm or more and 3 μm or less. By adjusting the thickness of the porous coating layer within the above range, shrinkage of the porous polymer substrate can be minimized and stable adhesion to the porous polymer substrate can be achieved.

[0039] The polymer binder can bind inorganic particles contained in the porous coating layer and impart adhesive force to the porous coating layer. The polymer binder may be spherical or elliptical, but may encompass other shapes except amorphous.

[0040] The polymer binder may include an acrylic binder. For example, the acrylic binder may be one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these. The acrylic binder can bind inorganic particles to form a network structure and exhibit adhesive strength to the porous polymer substrate and electrodes. Preferably, the polymer binder may include a copolymer of polyacrylic acid and polyacrylamide. While polymer binders may swell due to electrolytes, potentially reducing their adhesive strength, the copolymer of polyacrylic acid and polyacrylamide swells less with electrolytes and has good heat resistance. Therefore, a separation membrane containing this copolymer may have improved thermal shrinkage in a wet state.

[0041] The weight-average molecular weight of the polymer binder may be between 100,000 and 500,000. Specifically, the weight-average molecular weight of the polymer binder may be between 150,000 and 450,000, between 200,000 and 400,000, or between 250,000 and 350,000. Preferably, the weight-average molecular weight of the polymer binder may be between 100,000 and 300,000. By adjusting the weight-average molecular weight of the polymer binder within the above range, the swelling of the polymer binder by the electrolyte can be reduced, and the thermal shrinkage rate of the separation membrane containing it can be improved.

[0042] The weight-average molecular weight can be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies). For example, the weight-average molecular weight can be measured using a PL Olexis (Polymer Laboratories) column (column temperature 160°C) with TCB (trichlorobenzene) as the solvent, under the conditions of a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μl, using an Agilent High Temperature Differential Refractive Index (RI) detector (reference: polystyrene).

[0043] The porous coating layer may contain 1 to 10 parts by weight of the polymer binder, based on the total weight of the porous coating layer. Specifically, the porous coating layer may contain the polymer binder in amounts of 1 to 9 parts by weight, 2 to 8 parts by weight, 3 to 7 parts by weight, or 4 to 6 parts by weight. Preferably, the porous coating layer may contain 1 to 5 parts by weight of the polymer binder. If the polymer binder content is less than 1 part by weight, interstitial volume will not be formed due to bonding between inorganic particles, making lithium ion transfer difficult and increasing the electrical resistance of the separation membrane. If the polymer binder content exceeds 10 parts by weight, the amount of polymer binder swollen by the electrolyte will increase, potentially causing the porous coating layer to peel off from the porous polymer substrate.

[0044] The organic filler is a polymer resin having a melting point (Tm) or glass transition temperature (Tg) of 100°C or higher, which imparts heat resistance properties to the porous coating layer and prevents the separation membrane from shrinking when it is in a high-temperature wet state. For example, the organic filler may be one or more selected from the group consisting of polyethylene, polyacetal, polysulfone, polyethersulfone, polyetherimide, polyphenylene sulfide, polyetheretherketone, polycarbonate, polyamideimide, polyimide, polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate. Preferably, the organic filler may be one or more selected from the group consisting of polyethylene, polysulfone, polyethersulfone, polyimide, and polyamideimide.

[0045] In the porous coating layer, the polymer binder and the organic filler may be present in a weight ratio of 5:1 to 1:5. Specifically, the weight ratio of the polymer binder to the organic filler may be 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, or 1:1. Preferably, the weight ratio of the polymer binder to the organic filler may be 2:1 to 1:2. By adjusting the content of the polymer binder and organic filler within the above range, it is possible to obtain a separation film with reduced thermal shrinkage even in a high-temperature wet state, while simultaneously ensuring the adhesion and heat resistance of the porous coating layer.

[0046] The porous coating layer may contain the polymer binder and the inorganic particles in a weight ratio of 5:95 to 80:20. Specifically, the weight ratio of the polymer binder to the inorganic particles in the porous coating layer may be 10:90 to 80:20, 20:80 to 80:20, 30:70 to 70:30, 40:60 to 60:40, or 50:50. Preferably, the weight ratio of the polymer binder to the inorganic particles may be 60:40 to 80:20. By adjusting the composition of the porous coating layer within the above range, it is possible to simultaneously ensure the adhesion strength of the separation film and dimensional stability in a high-temperature wet state.

[0047] The inorganic particles can be used as long as they are electrochemically stable. The inorganic particles are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the electrochemical device (e.g., 0 to 5 V based on Li / Li + standard). In particular, when using inorganic particles with a high dielectric constant as the inorganic particles, it can contribute to an increase in the dissociation degree of electrolyte salts in the liquid electrolyte, such as lithium salts, and improve the ionic conductivity of the electrolyte solution. For the reasons described above, it is preferable that the inorganic particles contain high-dielectric-constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), b 1-x La x Zr 1-y Ti y O₃ (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O₃-PbTiO₃ (PMN-PT), hafnia (HfO₂), SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, SiO₂, Y₂O₃, Al₂O₃, Al(OH)₃, SiC, AlOOH, TiO₂, or mixtures thereof, etc.

[0048] Also, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing lithium element but having a function of moving lithium ions without storing lithium can be used. Non-limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li₃PO₄), lithium titanium phosphate (Li x Ti y (PO₄)₃, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO₄)₃, 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li₂O - 9Al₂O₃ - 38TiO₂ - 39P₂O₅, etc., such as (LiAlTiP) x Oy System glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate such as S4 (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI - Li2S - P2S5 (Li x P y S​​​​​​​​​The average particle size (D50) of the inorganic particles may be between 50 nm and 5,000 nm. Specifically, the average particle size (D50) of the inorganic particles may be between 100 nm and 4,500 nm, between 200 nm and 4,000 nm, between 300 nm and 3,000 nm, between 400 nm and 2,000 nm, or between 500 nm and 1,000 nm. If the average particle size of the inorganic particles is less than 50 nm, as the specific surface area increases, more polymer binder is required for bonding between the inorganic particles, which is disadvantageous in terms of electrical resistance. If the average particle size of the inorganic particles exceeds 5,000 nm, the uniformity of the coating layer surface decreases, which may cause damage to the porous polymer substrate or electrode during lamination.

[0051] The aspect ratio of the inorganic particles may be between 1 and 2. Specifically, the aspect ratio of the inorganic particles may be between 1.1 and 1.9, 1.2 and 1.8, 1.3 and 1.7, or 1.4 and 1.6. Preferably, the aspect ratio of the inorganic particles may be between 1.5 and 1.8. By adjusting the aspect ratio of the inorganic particles within the above range, the movement of the polymer binder through the voids between the inorganic particles is facilitated, and the formation of a film-forming region after the movement of the polymer binder allows for the formation of a porous coating layer in which the film-forming region is uniformly distributed.

[0052] The BET specific surface area of ​​the inorganic particles is 5m². 2 / g or more 25m 2 It may be less than / g. Specifically, the BET specific surface area of ​​the inorganic particles is 6m². 2 / g or more 24m 2 / g or less, 7m 2 / g or more 23m 2 / g or less, 8m 2 / g or more 22m 2 / g or less, 9m 2 / g or more 21m 2 / g or less, 10m 2 / g or more 20m 2 / g or less, 11m 2 / g or more 19m 2 / g or less, 12m 2 / g or more 18m 2 / g or less, 13m 2 / g or more 17m 2 / g or less, or 14m 2 / g or more 26m 2 It may be less than / g. By adjusting the BET specific surface area of ​​the inorganic particles within the range described above, the movement of the polymer binder through the voids between the inorganic particles can be controlled.

[0053] The packing density of the inorganic particles is 2 g / cm³. 3 More than 2.5g / cm 3 The following may be true. The packing density is a value based on the porous coating layer formed after coating and drying of the coating slurry. Specifically, the packing density of the inorganic particles is 2.1 g / cm³. 3 More than 2.4g / cm 3 The following, or 2.2 g / cm³ 3 More than 2.3g / cm 3 The following may be the case. Preferably, the packing density of the inorganic particles is 2.1 g / cm³. 3 More than 2.3g / cm 3 The following may be true: The packing density of the inorganic particles is 2 g / cm³. 3 If the packing density of the inorganic particles is less than 2.5 g / cm³, the separation membrane will shrink in the high-temperature wet state, exposing the electrodes. 3 Beyond this point, the permeability and resistance of the separation membrane increase, making it impossible to ensure stable cycle characteristics.

[0054] The separation membrane for the electrochemical element may have an air permeability of 20 s / 100 cc or more and 90 s / 100 cc or less. Specifically, the air permeability of the separation membrane may be 25 s / 100 cc or more and 85 s / 100 cc or less, 30 s / 100 cc or more and 80 s / 100 cc or less, 35 s / 100 cc or more and 75 s / 100 cc or less, 40 s / 100 cc or more and 70 s / 100 cc or less, 45 s / 100 cc or more and 65 s / 100 cc or less, or 50 s / 100 cc or more and 55 s / 100 cc or less. Preferably, the air permeability of the separation membrane may be 80 s / 100 cc or more and 90 s / 100 cc or less. When the air permeability of the separation membrane is within the above range, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0055] When a cell is manufactured using the aforementioned separation membrane for electrochemical elements, the cell may have an electrical resistance of 0.5 Ohm or more and 1.5 Ohm or less. Specifically, the electrical resistance of the cell may be 0.6 Ohm or more and 1.4 Ohm or less, 0.7 Ohm or more and 1.3 Ohm or less, 0.8 Ohm or more and 1.2 Ohm or less, or 0.9 Ohm or more and 1.1 Ohm or less. Preferably, the electrical resistance of the cell may be 0.6 Ohm or more and 0.8 Ohm or less.

[0056] Another specific example of the present invention provides a method for producing a separation membrane for an electrochemical element, comprising the steps of: coating at least one surface of a porous polymer substrate with a coating slurry containing a polymer binder, inorganic particles, an organic filler, and a dispersion medium to form a coating layer; and drying the coating layer to remove the dispersion medium. Any content that overlaps with the description of the separation membrane for the electrochemical element described above will be replaced by the description of the above specific example.

[0057] In the step of forming the coating layer, at least one surface of the porous polymer substrate is coated with a coating slurry containing a polymer binder, inorganic particles, an organic filler, and a dispersion medium. For example, the coating can be formed by methods such as a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, and direct metering coater, but is not limited thereto. Preferably, in the step of forming the coating layer, the coating slurry can be simultaneously coated on both sides of the porous polymer substrate using a bar coater or slot die coater.

[0058] The step of forming the coating layer may further include a step of corona-discharging at least one surface of the porous polymer substrate. After the corona-discharging step, the coating slurry can be coated onto the porous polymer substrate. In the step of corona-discharging at least one surface of the porous polymer substrate, it is possible to prevent a decrease in the bonding strength between the surface of the porous polymer substrate and the surface of the coating layer at high temperatures, and to prevent a decrease in the bonding strength between the surface of the polymer substrate and the surface of the coating layer due to electrolytes.

[0059] The corona discharge treatment may involve treating at least one surface of the porous polymer substrate in air with a voltage of 0.1kV to 10kV. Specifically, the corona discharge treatment may be performed in air with voltages of 0.2kV to 9kV, 0.3kV to 8kV, 0.4kV to 7kV, 0.5kV to 6kV, 0.6kV to 5kV, 0.7kV to 4kV, 0.8kV to 3kV, 0.9kV to 2kV, or 1.0kV to 2kV. Preferably, the corona discharge treatment may be performed in air with a voltage of 1.8kV. By adjusting the applied voltage of the corona discharge treatment within the range described above, an appropriate number of functional groups can be formed on the surface of the polymer substrate, preventing damage to the surface of the polymer substrate.

[0060] The step of removing the dispersion medium may involve drying or heating the coating layer to evaporate the dispersion medium contained in the coating layer. The dispersion medium removal step may be performed at a temperature that allows only the dispersion medium contained in the coating layer to evaporate without deforming the polymer binder contained in the coating layer. For example, the dispersion medium removal step may involve heating the coating layer to a predetermined temperature, provided that the temperature of the coating layer surface does not exceed 60°C. When the coating layer is heated under the above conditions, the thermal energy may be used first to heat the dispersion medium and cause a phase change, and not to deform the polymer binder.

[0061] Another specific example of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is a separation membrane for an electrochemical element having the features described above. The electrochemical element can be manufactured by inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode into a case or pouch and sealing it. Before sealing the case or pouch, an electrolyte can be poured in to impregnate the electrode assembly with the electrolyte. The shape of the case or pouch is not limited. For example, the electrochemical element may be cylindrical, rectangular, coin-type, or pouch-type lithium secondary battery.

[0062] The positive electrode and the negative electrode may be configured by coating at least one surface of each current collector with an electrode active material, which is then dried. The current collector can be made of a material that is conductive without causing a chemical change to the electrochemical element. For example, the positive electrode current collector may be made of aluminum, nickel, titanium, calcined carbon, stainless steel, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the negative electrode current collector may be made of copper, nickel, titanium, calcined carbon, stainless steel, or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. The current collector may be in various forms such as a thin metal sheet, film, foil, net, porous material, or foam.

[0063] 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, comprising a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented as O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 1-x M xLithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compound; It may contain one or a mixture of two or more of Fe2(MoO4)3.

[0064] 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 binder resin 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; LixFe2O3 (0≦x≦1), Li x WO2 (0≦x≦1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC and 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 3 elements of the periodic table, halogen; 0 < x≦1; 1≦y≦3; 1≦z≦8), etc.; 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 may contain one or a mixture of two or more selected from titanium oxides.

[0065] 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 has a cylinder shape with a nanosize diameter of a graphite sheet and sp 2The carbon nanotubes have a bonding structure and exhibit conductive or semiconductor properties depending on the angle and structure in which the graphite surface is wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) 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, they may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials from this group.

[0066] As the binder resin, a binder resin commonly used for electrodes of electrochemical elements can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples include, but are not limited to, acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methylcellulose.

[0067] The aforementioned electrolyte is A + B - A salt with a structure like this, + is Li + kaNa + , K+ contains ions consisting of alkali metal cations such as, or combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - salts containing anions such as, or combinations thereof, can be dissolved or dissociated in an organic solvent consisting 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 mixtures thereof, but are not limited thereto.

[0068] The electrochemical element including the electrode assembly may be a lithium secondary battery. The battery can be used as a unit cell, and can be used as a battery module including the unit cell, a battery pack including the battery module, or a device including the battery pack as a power source. Examples of such devices include, but are not limited to, small devices such as computers, mobile phones, and power tools, and electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are powered by electric motors; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0069] The present invention will be described in more detail below with reference to specific examples and experimental cases. The following examples and experimental cases are for illustrative purposes only and do not limit the present invention to the following examples and experimental cases.

[0070] Example 1 Preparation of coating slurry

[0071] At room temperature (25°C), 100 mL of distilled water was mixed with an acrylic polymer binder (a copolymer of polyacrylic acid and polyacrylamide copolymerized in a 50:50 ratio, Mw: 300,000) and an organic filler (polyethylene particles) in a 2:1 weight ratio. 20 g of inorganic particles (Al2O3, aspect ratio: 1.5:1, particle size: 500 nm) were added, and the mixture was stirred in a shaker for 60 minutes to produce a coating slurry in which the polymer binder, inorganic particles, and organic filler were dispersed.

[0072] Preparation of porous substrate As a porous substrate (MI: 0.2g / 10min, T mA polyethylene film measuring 20cm x 30cm with a thickness of 9μm was used, with a temperature of 135℃, porosity of 45%, and average pore size of 45nm.

[0073] Manufacturing of separation membranes A polyethylene film was coated on both sides with the coating slurry using a bar coater to form a porous coating layer with a thickness of 2 μm for each layer.

[0074] A polyethylene film with a porous coating layer is subjected to a low-temperature airflow, and while adjusting the surface temperature of the porous coating layer so as not to exceed 60°C, the drying process to remove the dispersion medium is repeated five times until the packing density of inorganic particles contained in the porous coating layer is 2.0 g / cm³. 3 A separation membrane with a total thickness of 13 μm was manufactured.

[0075] Example 2 During the manufacturing of the coating slurry, the solid content is adjusted to achieve a packing density of inorganic particles of 2.5 g / cm³. 3 The separation membrane was manufactured using the same method as in Example 1, except that the following was done.

[0076] Example 3 The separation membrane was manufactured in the same manner as in Example 1, except that the polymer binder and organic filler were mixed in a weight ratio of 1:2 during the production of the coating slurry.

[0077] Example 4 The separation membrane was manufactured in the same manner as in Example 1, except that the polymer binder and organic filler were mixed in a weight ratio of 5:1 during the production of the coating slurry.

[0078] Comparative Example 1 The separation membrane was manufactured using the same method as in Example 1, except that an organic filler was not used during the production of the coating slurry.

[0079] Comparative Example 2 The separation membrane was manufactured in the same manner as in Example 1, except that the polymer binder and organic filler were mixed in a weight ratio of 6:1 during the production of the coating slurry.

[0080] Comparative Example 3 The separation membrane was manufactured in the same manner as in Example 1, except that the polymer binder and organic filler were mixed in a weight ratio of 1:6 during the production of the coating slurry.

[0081] Comparative Example 4 During the manufacturing of the coating slurry, the solid content is adjusted to achieve a packing density of inorganic particles of 1.5 g / cm³. 3 The separation membrane was manufactured using the same method as in Example 1, except that the following was done.

[0082] Comparative Example 5 During the manufacturing of the coating slurry, the solid content is adjusted to achieve a packing density of inorganic particles of 3.0 g / cm³. 3 The separation membrane was manufactured using the same method as in Example 1, except that the following was done.

[0083] Experimental example: Confirmation of physical properties of separation membranes Measurement of air permeability Air permeability was measured using an air permeability tester (Gurley densometer) (Gurley, 4110N), with 100cc of air measuring a diameter of 28.6mm and an area of ​​645mm². 2 The time it took for the substance to pass through the separation membrane was measured.

[0084] Confirmation of dimensional stability Separation membranes for the examples and comparative examples were prepared to a size of 5 cm x 5 cm and inserted into 7 cm x 10 cm aluminum pouches. 1 g of electrolyte was injected into each pouch, and the pouches were sealed. The electrolyte used was a solvent mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3 / 7, containing 3 mol of vinylene carbonate (VC), 1.5 mol of propane sultone (PS), 1 mol of ethylene sulfate (ESa), and 6 mol of lithium salt LiPF as additives.

[0085] The sealed pouch was placed in an oven at 135°C for 30 minutes, and then the pouch was disassembled to measure the shrinkage rate in the TD direction. The results are shown in Tables 1 and 2 below.

[0086] [Table 1]

[0087] [Table 2]

Claims

1. The material comprises a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate. The porous coating layer comprises a polymer binder, inorganic particles, and organic fillers. The polymer binder is included in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer. The polymer binder and the organic filler are contained in a weight ratio of 5:1 to 1:

5. The packing density of the inorganic particles is 2 g / cm³. ３ 2.5g / cm or more ３ The following are separation membranes for electrochemical devices.

2. The separation membrane for an electrochemical element according to claim 1, wherein the organic filler is one or more selected from the group consisting of polyethylene, polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate.

3. The separation membrane for an electrochemical element according to claim 1, wherein the polymer binder is one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these.

4. The separation membrane for an electrochemical element according to claim 3, wherein the weight-average molecular weight of the polymer binder is 100,000 to 500,000.

5. The packing density of the inorganic particles is 2.1 g / cm³. ３ 2.3g / cm or more ３ The separation membrane for an electrochemical element according to claim 1 is as follows:

6. An electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, The separation membrane is an electrochemical element according to any one of claims 1 to 5.

7. The electrochemical element according to claim 6, further comprising an electrolyte containing EC / EMC in a weight ratio of 3 / 7.

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