Separator for electrochemical device and electrochemical device comprising same

Abstract

The present invention provides a separator for an electrochemical device and an electrochemical device comprising same, the separator being capable of, by securing adhesion between the separator and an electrode, implementing an electrode adhesive layer having low resistance while improving lifespan characteristics, and being capable of improving electrolyte impregnation. The separator for an electrochemical device according to an embodiment of the present invention comprises: a porous layer; and an electrode adhesive layer formed on at least one surface of the porous layer, wherein the electrode adhesive layer includes a particle-type binder in the form of a disk having a convex central portion, and the short axis of the particle-type binder is 50 nm to 500 nm.

Description

Separator for electrochemical devices and electrochemical devices containing the same

[0001] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same.

[0002] This application claims priority to Korean Application No. 10-2023-0082152, filed June 26, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] Interest in energy storage technology has been growing steadily. As its applications expand to include energy storage for mobile phones, camcorders, laptops, and even electric vehicles, research and development efforts on electrochemical devices are becoming increasingly concrete. Among these, the development of secondary batteries, energy storage devices that can be recharged and discharged based on electrochemical principles, is a focus of attention. Recent research and development efforts are focused on novel electrode and battery designs to improve capacity density and specific energy.

[0004] Among them, lithium secondary batteries are rapidly increasing in demand as an energy source due to technological development and increasing demand for mobile devices, and their use as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has recently become a reality, becoming a major growth driver for the secondary battery market.

[0005] These secondary batteries are structured to have a rechargeable electrode assembly of a positive electrode / separator / negative electrode structure mounted on a battery case, and the positive and negative electrodes are manufactured by applying an electrode active material, etc. to one or both sides of a metal current collector and drying and rolling them.

[0006] Among these, the separator is one of the important elements that determines the lifespan of a secondary battery, and plays a role in electrically insulating the positive and negative electrodes. In order to be used as a separator, it is desirable to have high ion permeability, excellent mechanical strength, and stability against the electrolyte, such as allowing the electrolyte to pass smoothly.

[0007] However, the conventionally used separator has insufficient adhesive strength with the electrode due to its material properties, and thus has problems such as partial lifting or wrinkles occurring at the interface depending on the manufacturing process. To solve this problem, a mixture of binder polymers was coated on a porous substrate to form an adhesive layer. However, in this case, there was a problem that the formation of an additional adhesive layer made it difficult for the electrolyte to pass through, and the adhesive layer itself acted as a resistor, which deteriorated the output and cycle characteristics of the battery.

[0008]

[0009] Accordingly, the problem to be solved by the present invention is to solve the above-mentioned problem, and to provide a separator for an electrochemical device and an electrochemical device including the same, which can improve the lifespan characteristics by securing the adhesive strength between the separator and the electrode, while implementing an electrode adhesive layer with low resistance and improving the electrolyte impregnation property.

[0010]

[0011] The present inventors have discovered that the above problem can be solved through the following electrochemical device separator and electrochemical device including the same.

[0012] According to the first implementation example,

[0013] As a separator for electrochemical devices,

[0014] The above separator comprises a porous layer; and an electrode adhesive layer formed on at least one surface of the porous layer;

[0015] The porous layer includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate,

[0016] The above porous coating layer comprises a binder polymer and an inorganic filler,

[0017] The above electrode adhesive layer includes a particle-shaped binder having a convex central disk shape,

[0018] The present invention relates to a separator for an electrochemical device, wherein the shortening of the above particle-type binder is 50 nm to 500 nm.

[0019] According to the second embodiment, in the first embodiment,

[0020] The present invention relates to a separator for an electrochemical device, characterized in that the electrode adhesive layer additionally includes a swelling agent capable of swelling the particle-type binder.

[0021] According to the third embodiment, in the second embodiment,

[0022] The present invention relates to a separator for an electrochemical device, characterized in that the swelling ratio of the particle-type binder calculated by the following equation 1 is in the range of 120 to 500%.

[0023] [Formula 1]

[0024] Swelling ratio (%) = [Weight after swelling] / [Initial weight] x 100

[0025] According to the fourth embodiment, in the second embodiment or the third embodiment,

[0026] The above swelling agent relates to a separator for an electrochemical device, characterized in that it comprises a linear carbonate compound, a cyclic carbonate compound, an ester compound, or two or more thereof.

[0027] According to the fifth embodiment, in any one of the second to fourth embodiments,

[0028] The above swelling agent relates to a separator for an electrochemical device, characterized in that it is a solid or liquid at room temperature.

[0029] According to the sixth embodiment, in any one of the second to fifth embodiments,

[0030] The above swelling agent relates to a separator for an electrochemical device, characterized in that the solubility in water is 10 g / 100 mL or more.

[0031] According to the seventh embodiment, in any one of the second to sixth embodiments,

[0032] The present invention relates to a separator for an electrochemical device, characterized in that the swelling agent is ethylene carbonate (EC), dimethyl carbonate (DMC) or a mixture thereof.

[0033] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0034] The present invention relates to a separator for an electrochemical device, characterized in that the above particle-type binder polymer comprises a polyvinylidene fluoride (PVdF)-based polymer, a styrene-butadiene-based polymer, an acrylic-based polymer, or two or more thereof.

[0035] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0036] The present invention relates to a separator for an electrochemical device, characterized in that the surface contact angle of the porous layer with respect to water is 30 degrees or less.

[0037] According to the tenth embodiment, in any one of the first to ninth embodiments,

[0038] The present invention relates to a separator for an electrochemical device, characterized in that the particle-type binder is substantially absent on the surface of the porous polymer substrate.

[0039] According to the eleventh embodiment, in any one of the first to tenth embodiments,

[0040] The present invention relates to a separator for an electrochemical device, characterized in that the surface of the porous polymer substrate has a peak area ratio of 0.1 or less, and the peak area ratio is calculated according to the following equation 2.

[0041] [Formula 2]

[0042] Peak area ratio = Ifunctional group / Iporous polymer substrate

[0043] In the above formula 2, I porous polymer substrate is the area of ​​the peak for SP3 CH bond in the IR spectrum for the surface of the porous polymer substrate, for example, the peak existing between 2850 cm-1 and 2950 cm-1,

[0044] The functional group is the area of ​​a peak for a region representing a specific bond present in the particulate binder polymer in the IR spectrum for the surface of the porous polymer substrate, and the peak corresponds to a peak of the IR spectrum for the electrode adhesive layer component present on the surface of the porous polymer substrate.

[0045] According to the 12th implementation example,

[0046] In an electrochemical device comprising an anode, a cathode, and a separator interposed between the anode and the cathode,

[0047] The present invention relates to an electrochemical device in which the above separator is a separator according to any one of the first to eleventh embodiments.

[0048] According to the 13th embodiment, in the 12th embodiment,

[0049] The present invention relates to an electrochemical device characterized in that the electrochemical device is a lithium secondary battery.

[0050]

[0051] The separator according to the present invention exhibits excellent adhesion to the electrode. These characteristics prevent partial lifting or wrinkling at the separator-electrode interface, thereby enhancing safety even under high-temperature conditions.

[0052] In addition, the electrode adhesive layer formed on one surface of the separator does not interfere with ion conduction between the electrode and the porous layer, so the resistance increase rate is low and the life characteristics are excellent.

[0053] In addition, the electrode adhesive layer includes a particle-shaped binder of a predetermined shape, thereby enabling control of the formation of pores between the binder particles and the application area, thereby improving the electrolyte impregnation property.

[0054]

[0055] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0056] Figure 1 is a cross-sectional SEM image of a separation membrane according to Example 2.

[0057] Figure 2 is a surface SEM image of a separation membrane according to Example 4.

[0058] Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her invention. Accordingly, the configurations described in the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the entire technical spirit of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0059]

[0060] Throughout this specification, when it is said that a part “includes” or “contains” a component, this does not mean that other components are excluded, but rather that other components may be included or provided.

[0061] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0062]

[0063] The inventors of the present invention have developed a separator that secures adhesive strength between a separator and an electrode by providing an electrode adhesive layer including a predetermined particle-type binder on the outermost layer of the separator, and at the same time, has low resistance and improved electrolyte impregnation properties within a secondary battery.

[0064]

[0065] A separator for an electrochemical device according to one embodiment of the present invention,

[0066] A porous layer; and an electrode adhesive layer formed on at least one surface of the porous layer; wherein the electrode adhesive layer includes a particle-shaped binder having a convex central portion and a disk-shaped particle-shaped binder, and the short axis of the particle-shaped binder is 50 nm to 500 nm.

[0067]

[0068] electrode adhesive layer

[0069] The above electrode adhesive layer is formed on at least one surface of the porous layer and can serve to adhere the separator and the electrode.

[0070] The electrode adhesive layer includes a particle-shaped binder having a convex center and a disc shape, and the short axis of the particle-shaped binder is 50 nm to 500 nm. Specifically, the short axis of the particle-shaped binder may be 100 nm to 500 nm, or 120 nm to 480 nm, or 140 nm to 480 nm, or 160 nm to 480 nm, or 180 nm to 480 nm, or 220 nm to 480 nm, or 140 nm to 250 nm. The short axis of the particle-shaped binder can be obtained by cutting a cross-section of a separator, observing it with a scanning electron microscope (SEM) or an optical microscope to obtain an image, and then averaging the measured lengths.

[0071] By including a particle-type binder having the above shape, pores and / or passages can be formed within the electrode adhesive layer. Accordingly, the movement of Li ions is easy, so that the resistance increase rate is low and the life characteristics are excellent. In addition, since the particle-type binder does not penetrate into the pores of the porous layer, the porosity of the porous layer is not affected, and the content of the adhesive layer binder within the composite separator can be minimized. Specifically, since the particle-type binder does not penetrate into the pores within the porous coating layer, the particle-type binder is substantially absent from the surface of the porous polymer substrate, so that even though an adhesive layer is formed, the resistance increase rate is low and the electrolyte impregnation property is excellent.

[0072] The long axis of the above particle-shaped binder may be in the range of 100 nm to 1000 nm.

[0073] In the present invention, ‘short axis’ means the shortest diameter passing through the center of the particle, and ‘major axis’ means the longest diameter passing through the center of the particle.

[0074] The above particulate binder may have an aspect ratio in the range of 0.7 to 1.0, or 0.7 to 0.99, or 0.7 to 0.98, or 0.7 to 0.96, or 0.7 to 0.88, or 0.7 to 0.84, or 0.84 to 0.99. The aspect ratio refers to the ratio of the shortest diameter of the particle to the longest diameter of the particle, and may be calculated as 'length of the short axis / length of the long axis'.

[0075] The above particle-shaped binders can be bonded to each other, and specifically, the short and / or long axes of the particles can be connected to adjacent particles.

[0076]

[0077] The above particle-type binder may include a polyvinylidene fluoride (PVdF) polymer, a styrene-butadiene polymer, an acrylic polymer, or two or more thereof.

[0078] For example, the polyvinylidene fluoride (PVdF) polymer may include polyvinylidene fluoride homopolymer, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, and polyvinylidene fluoride-co-chlorotrifluoroethylene, and may include at least one selected from these. In addition, a PVdF polymer including a vinylidene fluoride repeating unit (A) and another repeating unit (B) copolymerizable with the repeating unit may be used.

[0079] The above styrene-butadiene polymer may mean one containing a styrene monomer-derived repeating unit and a butadiene monomer repeating unit.

[0080] The above acrylic polymer may refer to a polymer compound including a polymerization unit derived from a (meth)acrylate monomer, or a polymer compound including a repeating unit of a monomer in which some of the substituents include a (meth)acryloyl group. For example, the acrylic binder resin may include, as a monomer, an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester having an alkyl group of 1 to 8 carbon atoms. The acrylic acid alkyl ester may include, for example, at least one selected from methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butylacrylate, isobutylacrylate, cyclohexylacrylate, and 2-ethylhexylacrylate. In addition, as the methacrylic acid alkyl ester, at least one selected from, for example, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, and 2-ethylhexyl methacrylate may be included. However, it is not particularly limited thereto.

[0081]

[0082] The above electrode adhesive layer may additionally include a swelling agent capable of swelling the particulate binder.

[0083] The swelling agent can melt the surface of the particle-shaped binder within the electrode adhesive layer, thereby allowing the particle-shaped binder to have a disc-shaped shape with a convex center. Specifically, in the case of a particle-shaped binder having an initial spherical shape, the introduction of the swelling agent causes the particle surface to melt from side to side, while a spherical shape remains in the center, thereby allowing the particle-shaped binder to have a disc-shaped shape with a convex center within the electrode adhesive layer.

[0084] The above swelling agent may include a linear carbonate compound, a cyclic carbonate compound, an ester compound, or two or more thereof.

[0085] Specific examples of the linear carbonate compounds may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, and the like.

[0086] Specific examples of the above cyclic carbonate compounds may include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, or halides thereof.

[0087] Specific examples of the above ester compounds may include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, and the like.

[0088] Specifically, the swelling agent may be dimethyl carbonate (DMC), ethylene carbonate (EC), or a mixture thereof.

[0089] Furthermore, according to one embodiment of the present invention, the swelling agent may have a solubility in water of 10 g / 100 mL or more. Preferably, the swelling agent is soluble in water as a solvent at room temperature. Since the swelling agent can perform a swelling function by dissolving it in a water-dispersible binder during the manufacture of a coating separator, the manufacturing process is advantageously simplified.

[0090] Additionally, the swelling agent may be solid or liquid at room temperature. In the present specification, room temperature means a range of about 18°C ​​to 30°C.

[0091]

[0092] Meanwhile, the particulate binder may be swollen by the swelling agent, and at this time, the swelling ratio of the particulate binder may be in the range of 120 to 500%, or 150 to 350%. At this time, the swelling ratio may be calculated by the following Equation 1. This means that after the particulate binder comes into contact with the swelling agent, the surface of the particulate binder may melt, but the entire particle except the surface may be swollen by the swelling agent and / or the electrolyte present in the battery.

[0093] [Formula 1]

[0094] Swelling ratio (%) = [Weight after swelling] / [Initial weight] x 100

[0095] The above swelling weight can be measured by dissolving LiPF6 to 1.0 M in a mixed solvent containing ethylene carbonate and ethylene methylene carbonate in a volume ratio of 7:3 at room temperature (25°C), then adding the particle-type binder and allowing sufficient swelling.

[0096]

[0097] According to a specific embodiment of the present invention, if the porous layer includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, the particulate binder may be substantially absent from the surface of the porous polymer substrate. As described above, the particulate binders in the electrode adhesive layer are bonded to each other, so that the particulate binder cannot penetrate into the interior of the porous layer. That is, the particulate binder cannot pass through the interior of the porous coating layer, and thus the particulate binder does not exist on the surface of the porous polymer substrate.

[0098] This can be confirmed by analyzing the surface of the porous polymer substrate through an IR spectrum to confirm the absence of the particulate binder. Specifically, the surface of the porous polymer substrate has a peak area ratio of 0.1 or less, and the peak area ratio can be calculated according to the following Equation 2.

[0099] [Formula 2]

[0100] Peak area ratio = I functional group / I 다공성 고분자 기재

[0101] In the above equation 2, I 다공성 고분자 기재 is a peak for SP3 CH bonds in the IR spectrum of the surface of the porous polymer substrate, for example, 2850 cm -1 2950 cm inland -1 The area of ​​the peak that exists between the regions,

[0102] I functional group is the area of ​​a peak for a region representing a specific bond present in a particulate binder polymer in the IR spectrum for the surface of the porous polymer substrate, and the peak corresponds to a peak of the IR spectrum for the electrode adhesive layer component present on the surface of the porous polymer substrate.

[0103] For example, when a PVDF-based binder is used as a particle-type binder polymer included in the electrode adhesive layer, a peak for CF bonding, for example, 1000 cm -1 1400cm inland -1 The area of ​​the peak existing between the regions of I functional group It can be a value. Also, as a particle-type binder polymer included in the electrode adhesive layer, when an acrylic binder is used, the peak for the C=O bond is, for example, 1500 cm -1 1800cm in height -1 The area of ​​the peak existing between the regions of I functional groupIt can be of value.

[0104]

[0105] porous layer

[0106] The above porous layer is not limited to a structure having pores, and includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate.

[0107] In one embodiment of the present invention, the surface contact angle of the porous layer with respect to water may be 30 degrees or less.

[0108] By having a contact angle within the above range, the coating processability of the electrode adhesive layer formed on the porous layer can be improved. The surface contact angle for water is a value obtained by measuring the angle between the surface of the porous layer and water at 25°C using a contact angle meter. Specifically, the surface contact angle for water may be a value obtained by measuring the angle between the surface of the porous coating layer and water.

[0109] The above porous polymer substrate can be any planar porous polymer substrate commonly used in secondary batteries, such as a porous polymer film substrate formed of various polymers or a porous non-woven fabric substrate.

[0110] The porous polymer film substrate may be a porous polymer film made of an olefin polymer such as polyethylene or polypropylene, and such an olefin polymer porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80 to 130°C.

[0111] At this time, the porous polymer film may be formed of an olefin polymer such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, or a polymer or a derivative thereof, either alone or in combination of two or more thereof.

[0112] Representative examples of olefin polymer porous polymer films that can be applied as such porous polymer films include, but are not limited to, wet polyethylene series (Asahi-Kasei E-Materials, Toray, SK IE Technology, Shanghai Energy, Sinoma, Entek), dry polypropylene series (Shenzhen Senior, Cangzhou Mingzhu), and dry polypropylene / polyethylene multilayer structure series (Polypore, Ube).

[0113] In addition, the porous polymer film substrate may be manufactured by forming a film shape using various polymers such as polyester in addition to olefin polymers. In addition, the porous polymer film substrate may be formed in a structure in which two or more film layers are laminated, and each film layer may be formed of a polymer such as the above-mentioned olefin polymer, polyester, etc. alone, or a polymer obtained by mixing two or more types thereof.

[0114] In addition, the porous polymer film substrate and the porous nonwoven fabric substrate may be formed of polymers such as polyester (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalene, etc.), polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, etc., either singly or as a mixture thereof, in addition to the above olefin polymers.

[0115] The thickness of this porous polymer substrate is not particularly limited, but may be 1 ㎛ or more, 3 ㎛ or more, 15 ㎛ or less, or 10 ㎛ or less. When the thickness satisfies this range, the problem of acting as a resistance layer can be improved while maintaining mechanical properties.

[0116] There are no particular limitations on the pore size and porosity of the above porous polymer substrate, but the porosity may be in the range of 10 to 95%, and the pore size (diameter) may be in the range of 0.1 to 50 ㎛. When the pore size and porosity satisfy these ranges, the problem of acting as a resistance layer is prevented, and mechanical properties can be maintained.

[0117]

[0118] The porous coating layer may be formed on at least one surface of a porous polymer substrate and includes a binder polymer and an inorganic filler. The porous coating layer, as a component layer of a separator, functions as an insulating layer that prevents short circuiting between the positive and negative electrodes, while simultaneously preventing the porous polymer substrate from directly contacting lithium metal.

[0119] The porosity of the porous coating layer may be in the range of 5 to 95%, but is not limited thereto. The thickness of the porous coating layer may be 1 ㎛ or more, 3 ㎛ or more, 15 ㎛ or less, or 10 ㎛ or less. When the thickness satisfies this range, heat resistance can be improved, the occurrence of short circuits can be suppressed, a thin film of the separator can be achieved, and excellent insulating properties can be achieved.

[0120] In the porous coating layer, the inorganic fillers are filled and in contact with each other and are bound to each other by the binder polymer, thereby forming an interstitial volume between the inorganic fillers, and the interstitial volume between the inorganic fillers can become an empty space and form pores. That is, the binder polymer can attach the inorganic fillers to each other so that they can maintain a state in which they are bound to each other, for example, the binder polymer can connect and fix the inorganic fillers. In addition, the pores of the porous coating layer are pores formed by the interstitial volume between the inorganic fillers becoming an empty space, and this can be a space defined by the inorganic fillers that are substantially in contact in a filled structure (closed packed or densely packed) by the inorganic fillers.

[0121]

[0122] The above inorganic filler has the function of forming micropores by enabling the formation of empty spaces between inorganic fillers and also acts as a kind of spacer that can maintain a physical shape, and generally has the property of not changing physical properties even at high temperatures of 200°C or higher, so the formed organic / inorganic composite porous film can have excellent heat resistance.

[0123] Accordingly, in a lithium secondary battery including the separator, even if the porous polymer substrate inside the battery is ruptured due to excessive conditions caused by internal or external factors such as high temperature, overcharge, or external impact, it is difficult for the two electrodes to be completely short-circuited due to the porous coating layer, and even if a short-circuit occurs, the short-circuited area is prevented from expanding significantly, thereby improving the safety of the battery.

[0124] The above inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler that can be used in the present invention is not particularly limited as long as it does not undergo oxidation and / or reduction reactions within the operating voltage range of the applied battery (e.g., 0 to 5 V based on Li / Li+). Examples of such inorganic fillers include alumina (Al2O3), fumed alumina, aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), boehmite (AlOOH), barium titanate (BaTiO3), or a mixture of two or more thereof.

[0125] The average particle diameter (D50) of the above-mentioned inorganic filler is preferably in the range of 20 nm to 700 nm for the formation of a porous coating layer of uniform thickness and its appropriate porosity. Specifically, it may be in the range of 100 nm to 500 nm. When the average particle diameter (D50) of the above-mentioned inorganic filler satisfies this range, the dispersibility of the slurry for the porous coating layer is maintained, making it easy to control the properties of the separator, and problems such as excessive increase in the thickness of the separator, resulting in a decrease in the mechanical properties, or excessively large pore sizes causing internal short circuits during battery charging and discharging can be prevented. In addition, the packing density increases, which can contribute to the thermal shrinkage rate, and excellent high heat resistance can be exhibited at the particle size in the above range.

[0126] In the present invention, the average particle diameter (D50) of the inorganic filler can be defined as the particle diameter at 50% of the particle diameter distribution. The average particle diameter (D50) of the inorganic filler in the present invention can be measured by, for example, electron microscopy using a scanning electron microscopy (SEM) or a field emission scanning electron microscopy (FE-SEM), or by using a laser diffraction method. When measuring by the laser diffraction method, more specifically, after the inorganic filler is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and then the average particle diameter (D50) at 50% of the particle diameter distribution in the measuring device can be calculated.

[0127] Additionally, the inorganic filler may be a primary particle, which is a single particle, or a secondary particle formed as an aggregate of primary particles.

[0128]

[0129] The above binder polymer is not particularly limited as long as it can provide bonding force between inorganic fillers, bonding force between the porous coating layer and the porous polymer substrate, and bonding force between the porous coating layer and the electrode. For example, binder resins include polyvinylidene fluoride-co-hexafluoropropylene (PVdF), polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethylflurane. Any one binder polymer selected from the group consisting of (cyanoethylpullulan), cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof, may be used, but is not limited thereto.In addition, heat-resistant polymers having a high Tm (150°C or higher or 180°C or higher) such as polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyacrylamide (PAAm), polyarylate (PA), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, wholly aromatic polyamide (aramid), polyphenylene oxide, polybutylene terephthalate, polyethylene terephthalate, polyether ketone, or a mixture of two or more thereof may be used, but are not limited thereto.

[0130] The content of the above binder polymer may be 0.1 to 10% relative to the total weight of the porous coating layer. Specifically, the content of the binder polymer may be 0.1% or more, 1% or more, 3% or more, 10% or less, or 8% or less relative to the total weight of the porous coating layer. When the binder polymer is included in the above content range, not only can the heat resistance characteristics be improved, but the resistance of the separator can be reduced, and there is an advantage in that the energy density of the battery can be increased.

[0131]

[0132] A secondary battery according to the present invention comprises a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The electrode applicable to the present invention is not particularly limited, and an electrode active material can be manufactured in a form in which it is bound to an electrode current collector using a conventional method known in the art.

[0133] Non-limiting examples of the positive electrode active material among the above electrode active materials include conventional positive electrode active materials that can be used in the positive electrode of a conventional lithium secondary battery, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these is preferably used.

[0134] Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used in the negative electrode of a conventional lithium secondary battery, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons, and lithium adsorbents are preferable.

[0135] Non-limiting examples of positive current collectors include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

[0136]

[0137] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more fully explain the present invention to those of average skill in the art.

[0138]

[0139] Example

[0140] [Manufacturing of membranes]

[0141] Example 1

[0142] 1) A polyethylene substrate film (Toray B09PJ1, thickness: 9 um) was prepared as a porous polymer substrate.

[0143] 2) A slurry of alumina Al2O3 (Daehan Ceramics Co., Ltd., ALK-S1): acrylic binder polymer (Toyo Co., Ltd., CSB-400): dispersant CMC (GL Chem, SG-L02) = 96:2:2) mixed with water as a solvent was applied to both sides to a thickness of 2 μm to prepare a ceramic coating (porous coating layer) separator on the polyethylene substrate.

[0144] 3) An aqueous emulsion containing 97 wt% of water as a solvent and 3 wt% of acrylic polymer particles (ZEON, trademark name AFL, BM2570, D50=500 nm, aspect ratio=0.96) was applied and dried on one side of the ceramic coating separator to form an electrode adhesive layer. After the adhesive layer was formed, the short axis length of the AFL particles was 480 nm.

[0145]

[0146] Example 2

[0147] An aqueous emulsion containing 97 wt% of water as a solvent and 3 wt% of PVDF-HFP particles (Arkema, LBG4330LX, D50:200 nm, aspect ratio=0.98) was applied and dried to one surface of the ceramic coating separator prepared in 2) of the above Example 1 to form an electrode adhesive layer. After the adhesive layer was formed, the short axis length of the PVDF-HFP particles was 180 nm. The surface SEM image of the manufactured separator is shown in Fig. 1.

[0148]

[0149] Example 3

[0150] An aqueous emulsion containing 97 wt% of water as a solvent and 3 wt% of binder particles was applied and dried on one side of the ceramic coating separator prepared in 2) of the above Example 1 to form an electrode adhesive layer. At this time, the binder particles were used by mixing PVDF-HFP particles (Arkema, LBG4330LX, D50:200 nm, aspect ratio: 0.98) and acrylic particles (Hansol Chemical, HES202, D50:250 nm, aspect ratio: 0.99). After the formation of the adhesive layer, the short axis lengths of the PVDF-HFP particles and acrylic particles were 180 nm and 220 nm, respectively.

[0151]

[0152] Example 4

[0153] A mixture of 97 wt% of water as a solvent, 2.7 wt% of PVDF-HFP particles (Arkema, LBG4330LX, D50:200 nm, aspect ratio: 0.98), and 0.3 wt% of ethylene carbonate was applied and dried to form an electrode adhesive layer. The aspect ratio of the PVDF-HFP particles decreased to 0.88 after coating due to the introduction of a swelling agent. After the formation of the adhesive layer, the length of the short axis of the PVDF-HFP particles was 160 nm. The surface SEM image of the manufactured separator is shown in Fig. 2.

[0154]

[0155] Example 5

[0156] A mixture of 95 wt% of water as a solvent, 2.5 wt% of PVDF-HFP particles (Arkema, LBG4330LX, D50:200 nm, aspect ratio: 0.98), and 2.5 wt% of dimethyl carbonate was applied and dried to form an electrode adhesive layer. The aspect ratio of the PVDF-HFP particles decreased to 0.84 after coating due to the introduction of a swelling agent. The length of the short axis of the PVDF-HFP particles after the formation of the adhesive layer was 140 nm.

[0157]

[0158] Comparative Example 1

[0159] An electrode adhesive layer identical to that of Example 2 was formed on one side of the polyethylene separator of 1) of Example 1.

[0160]

[0161] Comparative Example 2

[0162] On one side of the ceramic coating separator prepared in 2) of the above Example 1, 2 wt% of PVDF-HFP powder (Arkema, LBG) was dissolved in 98 wt% of acetone, and then applied and dried to form an electrode adhesive layer.

[0163]

[0164] [Manufacturing of positive and negative electrodes]

[0165] LiCoO2 97 wt%, carbon black powder 1.5 wt% as a conductive material, and polyvinylidene fluoride (PVdF, Kureha) 1.5 wt% were mixed and added to N-methyl-2-pyrrolidone solvent, and stirred for 30 minutes using a mechanical stirrer to prepare a slurry of positive electrode active material.

[0166] The slurry was applied to a thickness of about 60 μm on a 20 μm thick aluminum current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hour, dried again for 4 hours under vacuum at 120°C, and rolled to manufacture a positive electrode.

[0167] A slurry of a negative electrode active material was prepared by mixing 96.5 wt% of artificial graphite particles (LC1, Shanshan) with an average particle size of 16 μm, 2.3 wt% of styrene-butadiene rubber (SBR) binder (ZEON), and 1.2 wt% of carboxymethyl cellulose (CMC, Daicel) in distilled water and stirring for 60 minutes using a mechanical stirrer. The slurry was applied to a thickness of about 60 μm on an 8 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hour, and then dried again for 4 hours under vacuum at 120°C, and then roll pressing to prepare a negative electrode.

[0168]

[0169] Manufacturing of secondary batteries

[0170] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured above, and then embedded in an electrode case, and an organic electrolyte solution in which 1M LiPF6 was dissolved in a 3 / 7 (volume ratio) mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) was injected to manufacture a secondary battery.

[0171]

[0172] Evaluation Results

[0173] The physical properties of the above examples and comparative examples were evaluated, and the results are shown in Table 1 below.

[0174] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Separator thickness (㎛) 14.5 14.8 14.6 14.7 14.7 14.9 15.0 Cathode / separator adhesion (gf / 25mm) 15.9 18.2 21.3 20.9 21.2 20.3 25.8 Electrolyte impregnation length after adhesion (mm) 14.2 11.8 13.2 13.8 14.14.9 6.3 Resistance (ohm) 0.83 0.82 0.84 0.79 0.77 1.04 0.89 Aspect ratio 0.96 0.98 0.99 0.88 0.84 0.98 Not specified I functional group / I2920n.dn.dn.dn.dn.dn.d0.3

[0175]

[0176] [Shortening of particle-type binder] The shortening of the particle-type binder used in Examples 1 to 5 was obtained by cutting a cross-section of the membrane, observing it with a scanning electron microscope (SEM), obtaining an image, and then averaging the measured lengths.

[0177]

[0178] [Membrane thickness]

[0179] The coated membrane was cut to a 50x50mm size using a die-cutting machine, and its thickness was measured using a MITUTOYO VL-50S-B. Five measurements were taken per sample, and the average value was reported.

[0180]

[0181] [Adhesion]

[0182] The coated separator (25 mm wide x 13 cm long) and electrode were placed between A4 papers and pressed for 10 seconds at a temperature of 60°C and a pressure of 1000 kg using a heat press device to bond them together. Then, the bonded electrode and separator were peeled off by applying force in a 180° direction using a UTM device to measure the electrode adhesion of the separator.

[0183]

[0184] [Length of electrolyte impregnation after bonding]

[0185] The coated separator (25 mm wide x 13 cm long) and electrode were placed between A4 papers and pressed for 10 seconds at a temperature of 60°C and a pressure of 1000 kg using a heat press device to adhere them to each other. The short end of the laminated separator / electrode sample was impregnated with an electrolyte prepared by adding 1 M lithium salt LiPF6 and 2 wt% VC to a solvent mixed in a volume ratio of EC:EMC = 30:70, and the distance penetrated by the electrolyte was measured after 10 minutes.

[0186]

[0187] [resistance]

[0188] The coated separator was cut using a puncher to fit the coin cell structure below and then assembled according to the structure below. The electrolyte was prepared by adding 1M lithium salt LiPF6 and 2 wt% VC to a solvent mixed in a volume ratio of EC:EMC = 30:70. After dropping 4-5 drops, it was placed in a coin cell compressor and the cap was completely sealed. After aging at room temperature for 3 hours, the resistance was measured.

Claims

1. As a separator for electrochemical devices, The above separator comprises a porous layer; and an electrode adhesive layer formed on at least one surface of the porous layer; The porous layer includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, The above porous coating layer comprises a binder polymer and an inorganic filler, The above electrode adhesive layer includes a particle-shaped binder having a convex central disk shape, A separator for an electrochemical device, wherein the short axis of the particle-shaped binder is 50 nm to 500 nm.

2. In paragraph 1, A separator for an electrochemical device, characterized in that the electrode adhesive layer additionally includes a swelling agent capable of swelling the particle-type binder.

3. In paragraph 2, A separator for an electrochemical device, characterized in that the swelling ratio of the particle-type binder calculated by the following equation 1 is in the range of 120 to 500%. [Formula 1] Swelling ratio (%) = [Weight after swelling] / [Initial weight] x 100 4. In paragraph 2, A separator for an electrochemical device, characterized in that the swelling agent comprises a linear carbonate compound, a cyclic carbonate compound, an ester compound, or two or more thereof.

5. In paragraph 2, A separator for an electrochemical device, characterized in that the swelling agent is solid or liquid at room temperature.

6. In paragraph 2, A separator for an electrochemical device, characterized in that the swelling agent has a solubility in water of 10 g / 100 mL or more.

7. In paragraph 2, A separator for an electrochemical device, characterized in that the swelling agent is ethylene carbonate (EC), dimethyl carbonate (DMC) or a mixture thereof.

8. In paragraph 1, A separator for an electrochemical device, characterized in that the particle-type binder polymer comprises a polyvinylidene fluoride (PVdF)-based polymer, a styrene-butadiene-based polymer, an acrylic polymer, or two or more thereof.

9. In paragraph 1, A separator for an electrochemical device, characterized in that the surface contact angle of the porous layer with respect to water is 30 degrees or less.

10. In paragraph 1, A separator for an electrochemical device, characterized in that the particle-type binder is substantially absent on the surface of the porous polymer substrate.

11. In paragraph 1, A separator for an electrochemical device, characterized in that the surface of the porous polymer substrate has a peak area ratio of 0.1 or less, and the peak area ratio is calculated according to the following equation 2: [Formula 2] Peak area ratio = I functional group / I 다공성 고분자 기재 In the above equation 2, I 다공성 고분자 기재 is the area of ​​the peak for SP3 CH bond in the IR spectrum for the surface of the above porous polymer substrate, I functional group is the area of ​​a peak for a region representing a specific bond present in a particulate binder polymer in the IR spectrum for the surface of the porous polymer substrate, and the peak corresponds to a peak of the IR spectrum for the electrode adhesive layer component present on the surface of the porous polymer substrate.

12. In an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrochemical device wherein the separator is a separator according to any one of claims 1 to 11.

13. In paragraph 12, An electrochemical device characterized in that the electrochemical device is a lithium secondary battery.

Images