Separator and electrochemical device including the same

Abstract

The present invention relates to a separator comprising: a substrate; an inorganic particle layer formed on at least one surface of the substrate; and an adhesive layer formed on at least one of the inorganic particle layers, in which F40 is 1 nN to 30 nN when an adhesive force between a probe of an atomic force microscope having a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz, measured at a temperature x DEG C of a sample stage, is set as Fx, and the separator satisfies formula 1 below. [Formula 1] F75 / F40 > = 5.

Description

Technical Field

[0001] The present invention relates to a diaphragm and an electrochemical device including the diaphragm. Background Technology

[0002] In recent years, there has been a surge in interest in electrochemical devices and their energy storage technologies used in mobile phones, laptops, electric vehicles, and other applications. In particular, there has been active research into the separator, one of the key components determining the characteristics of secondary batteries as electrochemical devices. The separator is immersed in the electrolyte and functions as an ion channel, thus significantly influencing the physical properties of secondary batteries.

[0003] In this regard, a method is known to improve the thermal resistance performance of a diaphragm by mixing high thermal resistance inorganic particles with a binder and coating them onto a porous substrate, and techniques are being developed and researched to ensure adhesion between the diaphragm and the electrode while fully improving the internal resistance performance. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] One specific embodiment aims to provide a diaphragm in which the surface adhesive force of the diaphragm, measured using a probe of a temperature-adjustable atomic force microscope (AFM), is achieved within a specified range.

[0006] Another specific embodiment aims to provide an electrochemical device including the diaphragm.

[0007] (II) Technical Solution

[0008] One embodiment provides a diaphragm comprising: a substrate; an inorganic particle layer formed on at least one side of the substrate; and an adhesive layer formed on at least one of the inorganic particle layers, wherein, when the adhesive force between the probe and the surface of the diaphragm, measured using an atomic force microscope with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz at a stage temperature of x °C, is set as Fx, F40 is from 1 nN to 30 nN, and the diaphragm satisfies the following formula 1.

[0009] [Formula 1]

[0010] F75 / F40≥5

[0011] In one embodiment, the adhesive layer may comprise a particulate polymer adhesive.

[0012] In one embodiment, the adhesive layer may comprise an acrylic polymer adhesive.

[0013] In one embodiment, the particulate polymer adhesive may be a core-shell structure.

[0014] In one embodiment, the glass transition temperature of the polymer contained in the core of the particulate polymer adhesive may be from 30°C to 70°C, and / or the glass transition temperature of the polymer contained in the shell of the particulate polymer adhesive may be from 70°C to 110°C.

[0015] In one embodiment, the glass transition temperature (Tg,c) of the polymer contained in the core and the glass transition temperature (Tg,s) of the polymer contained in the shell of the particulate polymer adhesive can satisfy the following equation 2.

[0016] [Equation 2]

[0017] 50℃≤(Tg,c+Tg,s) / 2≤90℃

[0018] In one embodiment, the adhesive layer may comprise: a copolymer composed of repeating units derived from acrylic monomers; and a copolymer composed of repeating units derived from acrylic monomers and styrene.

[0019] In one embodiment, the adhesive layer may comprise a particulate polymer adhesive or a particulate acrylic polymer adhesive with an average particle size (D50) of 400 nm to 800 nm.

[0020] In one implementation, the F75 can be from 40nN to 300nN.

[0021] In one implementation, Equation 1 can satisfy F75 / F40≥10.

[0022] In one embodiment, the adhesive layer may comprise a particulate polymeric adhesive or a particulate acrylic polymeric adhesive, the particulate polymeric adhesive or the particulate acrylic polymeric adhesive comprising repeating units derived from compounds represented by the following chemical formula 1.

[0023] [Chemical Formula 1]

[0024]

[0025] In the chemical formula 1, R 1 It is hydrogen or C 1-10 Alkyl; R 2 It is hydrogen or C 1-20 Hydrocarbon group.

[0026] In one embodiment, the inorganic particle layer may comprise inorganic particles and a polymer binder.

[0027] In one embodiment, the inorganic particle layer may comprise inorganic particles with an average particle size (D50) of 100 nm to 1500 nm.

[0028] In one embodiment, the inorganic particle layer may comprise a first inorganic particle with an average particle size (D50) of 100 nm to 500 nm and a second inorganic particle with an average particle size (D50) of 500 nm to 1500 nm.

[0029] In one embodiment, the inorganic particle layer may comprise inorganic particles and a polymer binder, wherein the weight ratio of the inorganic particles to the polymer binder may be from 90:10 to 99:1.

[0030] In one embodiment, the thickness of the inorganic particle layer can be from 0.5 μm to 3.0 μm.

[0031] In one embodiment, the thickness of the adhesive layer can be from 0.05 μm to 2.0 μm.

[0032] Another specific embodiment provides an electrochemical device comprising a diaphragm, the diaphragm comprising: a substrate; an inorganic particulate layer formed on at least one side of the substrate; and an adhesive layer formed on at least one of the inorganic particulate layers, wherein, when the adhesive force between the probe and the surface of the diaphragm, measured using an atomic force microscope (AFM) with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz, is set as Fx, F40 is 1 nN to 30 nN, and the diaphragm satisfies the following formula 1.

[0033] [Formula 1]

[0034] F75 / F40≥5

[0035] Another specific embodiment provides an electrochemical device comprising a diaphragm, the diaphragm comprising: a substrate; an inorganic particulate layer formed on at least one side of the substrate; and an adhesive layer formed on at least one of the inorganic particulate layers, wherein when the number of cycles in which the internal resistance of the electrochemical device increases by 30% compared to the initial resistance before the start of a charge-discharge cycle is defined as C, C is 300 or more, wherein the charge-discharge cycle is performed by discharging the electrochemical device to 2.5V, then charging it from 2.5V to 4.2V at 0.5C and discharging it from 4.2V to 2.5V at 0.5C, which constitutes one cycle.

[0036] (III) Beneficial Effects

[0037] According to one embodiment, the separator includes an adhesive layer located on an inorganic particle layer, and the adhesive force on the separator surface, measured using a probe of an atomic force microscope, is achieved within a specific range, thereby effectively improving the internal resistance of the battery while ensuring the adhesion between the separator and the electrode. Attached Figure Description

[0038] Figure 1 It is a schematic plan view of a secondary battery according to one implementation scheme.

[0039] Figure 2 This is a schematic cross-sectional view of a secondary battery according to one implementation scheme.

[0040] Figure 3 This is a simplified schematic diagram of the cross-section of core-shell polymer particles included in the adhesive layer of a diaphragm according to one embodiment. In this specification, the particle size of core 200 refers to... Figure 3 The length of the part represented by D in the middle, and the thickness of the shell 300 refers to... Figure 3 The length of the portion denoted by T in the text.

[0041] Figure 4 This is a schematic structure of a diaphragm 1 according to one embodiment, the structure including a substrate 10, an inorganic particulate layer 20 and an adhesive layer 30.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1: Diaphragm; 10: Substrate

[0044] 20: Inorganic particle layer; 30: Adhesive layer

[0045] 100: Positive electrode; 105: Positive electrode current collector

[0046] 107: Positive electrode lead; 110: Positive electrode active material layer

[0047] 120: Negative electrode active material layer; 125: Negative electrode current collector

[0048] 127: Negative lead; 130: Negative electrode

[0049] 140: Diaphragm; 150: Electrode assembly

[0050] 160: Shell; 200: Core

[0051] 300: Shell Detailed Implementation

[0052] The embodiments described in this specification can be varied into various other embodiments, and therefore the technology according to a particular embodiment is not limited to the embodiments described below. Furthermore, throughout the specification, unless otherwise specifically stated to the contrary, when a constituent element is described as “comprising,” “including,” “containing,” “having,” or “comprising,” it means that other constituent elements may be further included, rather than excluded, and does not exclude elements, materials, or processes not further listed.

[0053] The numerical ranges used in this specification include lower and upper limits, all values ​​within that range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. As an example, when the content of a component is defined as 10% to 80% or 20% to 50%, it should be interpreted that numerical ranges of 10% to 50% or 50% to 80% are also described in this specification. In this specification, unless otherwise specifically defined, values ​​outside the defined numerical range that may occur due to experimental error or rounding are also included within the defined numerical range.

[0054] Hereinafter, unless otherwise specifically defined, “about” may be considered as a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1%, or 0.5% of the specified value.

[0055] In this specification, unless otherwise defined, "polymer" refers to a molecule with a relatively high molecular weight whose structure may include multiple repetitions of units derived from low molecular weight molecules. In one embodiment, the polymer may be an alternating copolymer, block copolymer, random copolymer, graft copolymer, gradient copolymer, branched copolymer, crosslinked copolymer, or a copolymer comprising all of these copolymers (e.g., a polymer comprising more than one monomer). In another embodiment, the polymer may be a homopolymer (e.g., a polymer comprising one monomer).

[0056] As used in this specification, the term "alkyl" refers to a straight-chain or branched group with a carbon saturated bond, and may be substituted by any substituents.

[0057] The present invention will now be described in detail (with reference to the accompanying drawings). However, this is merely an exemplary embodiment, and the present invention is not limited to the specific embodiments described herein.

[0058] One specific embodiment aims to provide a diaphragm in which the adhesive force between the diaphragm surface and the probe, measured using a probe of an atomic force microscope (AFM) with an adjustable sample stage temperature, is achieved within a specific range at a specific temperature. Specifically, the diaphragm 1 according to one embodiment includes: a substrate 10; an inorganic particulate layer 20 formed on at least one side of the substrate; and an adhesive layer 30 formed on at least one of the inorganic particulate layers, wherein, when the adhesive force between the probe and the surface of the diaphragm, measured using an AFM probe with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz at a sample stage temperature x °C, is set as Fx, F40 is from 1 nN to 30 nN, and the diaphragm satisfies the following formula 1.

[0059] [Formula 1]

[0060] F75 / F40≥5

[0061] When measuring adhesive force using existing large-area probes, the measured adhesive force value may vary depending on the adhesive concentration. However, a method for measuring the adhesive force on a diaphragm surface using an AFM probe, according to a specific embodiment, can measure the inherent adhesive force of the adhesive contained in the adhesive layer using a small-area probe (with a radius of approximately 8 nm). Furthermore, since the temperature of the sample stage can be adjusted, changes in adhesive force based on temperature can be analyzed.

[0062] In one embodiment, the adhesive force is the adhesive force between the surface of the adhesive contained in the adhesive layer, i.e., the outermost layer, and the probe. Specifically, the adhesive force generated when the probe leaves the surface of the diaphragm can be calculated from the Y-axis of the F / D plot based on the F / D (load (Y-axis) / distance (X-axis)) plot that appears when the probe taps the surface of the adhesive contained in the adhesive layer.

[0063] According to one embodiment, the separator including the adhesive layer utilizes the adhesive force of AFM to achieve the adhesive force described above, thereby not only having adhesive force with the electrodes but also effectively suppressing the increase of battery internal resistance, thus effectively improving battery performance. Specifically, in a battery including the separator according to one embodiment, by suppressing the increase of internal resistance, the voltage drop of the battery can be effectively suppressed, thereby extending the battery life. Furthermore, energy loss of the battery can be reduced, thereby improving battery efficiency, and heat generation caused by increased internal resistance can be prevented, thereby preventing problems such as thermal runaway, electrolyte decomposition, fire, or explosion.

[0064] In one embodiment, the adhesive layer may be the surface of the diaphragm, i.e., the outermost layer, but is not necessarily limited to this.

[0065] In one embodiment, the adhesive layer may comprise a particulate polymer adhesive or an acrylic polymer adhesive or a particulate acrylic polymer adhesive. Specifically, the particulate polymer adhesive or the particulate acrylic polymer adhesive may be a core-shell structure, which may be present on at least a portion of the surface of the adhesive layer.

[0066] The core-shell structured polymer adhesive can be prepared by at least one method selected from stepwise emulsion polymerization, seed polymerization, suspension polymerization, precipitation polymerization, interfacial polymerization, graft polymerization and microemulsion polymerization.

[0067] In one embodiment, the glass transition temperature (Tg) of the polymer contained in the core of the granular polymeric adhesive or granular acrylic polymeric adhesive can be 30°C to 70°C, 35°C to 70°C, 30°C to 65°C, 40°C to 70°C, or 40°C to 65°C. In one embodiment, the glass transition temperature of the polymer contained in the shell of the granular polymeric adhesive or granular acrylic polymeric adhesive can be 70°C to 110°C, 70°C to 100°C, 75°C to 100°C, 75°C to 95°C, 80°C to 95°C, or 80°C to 90°C. Although not bound by any particular theory, by giving the polymer contained in the core and / or shell the aforementioned glass transition temperatures, the adhesion between the diaphragm and the electrode in the electrode fusion process can be effectively improved and / or enhanced.

[0068] In one embodiment, the glass transition temperature (Tg,c) of the polymer contained in the core and the glass transition temperature (Tg,s) of the polymer contained in the shell can satisfy the following equation 2.

[0069] [Equation 2]

[0070] 50℃≤(Tg,c+Tg,s) / 2≤90℃

[0071] Although not bound by a specific theory, the value of (Tg,c+Tg,s) / 2 in Equation 2 can exhibit a trend similar to the electrode fusion temperature of the separator according to one embodiment. The value of (Tg,c+Tg,s) / 2 in Equation 2 and the electrode fusion temperature can satisfy 50°C to 90°C, 55°C to 85°C, 50°C to 80°C, 60°C to 90°C, or 60°C to 80°C. When the above temperature ranges are met, the adhesion between the separator and the electrode during the electrode fusion process can be effectively improved and / or enhanced, and the phenomenon of separator blockage during winding and during storage or transportation before the fusion process can be effectively prevented, and / or long-term storage is possible. Furthermore, in the separator according to one embodiment, by preventing the above-mentioned blockage phenomenon, the shedding of inorganic particles caused by blockage is effectively prevented, which can effectively prevent the reduction in battery performance due to increased internal resistance. Therefore, the battery life characteristics are effectively improved and energy efficiency is effectively increased.

[0072] In one embodiment, the adhesive layer may comprise an acrylic polymer adhesive. Specifically, the acrylic polymer adhesive may comprise repeating units derived from (meth)acrylic acid and / or (meth)acrylates, and more specifically, may comprise repeating units derived from compounds represented by the following chemical formula 1.

[0073] In one embodiment, the adhesive layer may simultaneously comprise: a copolymer comprising repeating units derived from acrylic monomers; and a copolymer comprising repeating units derived from acrylic monomers and styrene. Specifically, the adhesive layer may simultaneously comprise: a copolymer composed of repeating units derived from acrylic monomers; and a copolymer composed of repeating units derived from acrylic monomers and styrene. In one embodiment, the acrylic monomers may each be independently (meth)acrylic acid and / or (meth)acrylate, specifically, compounds represented by the following chemical formula 1.

[0074] In one embodiment, the average particle size (D50) of the particulate polymer adhesive or particulate acrylic polymer adhesive may be 400 nm to 800 nm, 400 nm to 700 nm, 400 nm to 600 nm, 450 nm to 550 nm, or about 500 nm.

[0075] In one embodiment, when the particulate polymer adhesive or particulate acrylic polymer adhesive has a core-shell structure, the average particle size of the core (D50, ...) is... Figure 3 The D) can be 320nm to 780nm, 320nm to 680nm, 320nm to 530nm, 350nm to 500nm, 400nm to 500nm, or approximately 450nm, and the average thickness of the shell ( Figure 3 The T) can be 20 nm to 80 nm, 30 nm to 60 nm, 40 nm to 60 nm, or about 50 nm. Although not bound by a specific theory, by giving the core and shell an average particle size or thickness within the above range, an adhesive layer can be uniformly formed on the inorganic particle layer, and the adhesion between the adhesive layer and the electrode can be improved.

[0076] In one embodiment, the mass ratio of the core to the shell can be 5:5 to 9:1, 6:4 to 8:2, or about 7:3. Although not bound by any particular theory, by making the core and shell meet the above ranges, particles with uniform average particle size and / or average thickness can be formed, or the diaphragm can be effectively bonded to the electrode at the electrode fusion temperature.

[0077] In one embodiment, F40 can be 1nN to 25nN, 1nN to 20nN, 2nN to 18nN, 1nN to 18nN, or 3nN to 15nN. And / or, in one embodiment, F75 can be 40nN to 300nN, 40nN to 250nN, 40nN to 230nN, 50nN to 250nN, 50nN to 230nN, 50nN to 200nN, or 60nN to 200nN. However, F40 and F75 are not necessarily limited to the above ranges; F40 and F75 are not particularly limited as long as their ratio F75 / F40 is 5 or greater.

[0078] In one implementation, Equation 1 can satisfy F75 / F40≥10, F75 / F40≥11, F75 / F40≥12, or F75 / F40≥13. In this case, there is no particular restriction on the upper limit of F75 / F40, but it can be, for example, below 50, below 40, below 30, below 25, or below 20.

[0079] In one embodiment, the particulate polymeric adhesive or particulate acrylic polymeric adhesive may comprise repeating units derived from (meth)acrylic acid and / or (meth)acrylates or copolymers thereof. Alternatively, the particulate polymeric adhesive or particulate acrylic polymeric adhesive may comprise repeating units derived from the following chemical formula 1.

[0080] [Chemical Formula 1]

[0081]

[0082] In the chemical formula 1, R 1 It can be hydrogen or C 1-10 Alkyl, C 1-8 Alkyl, C 1-6 Alkyl, C 1-5 Alkyl, C1-3 Alkyl, ethyl, or methyl; and / or R 2 It can be hydrogen, C 1-20 hydrocarbon group, C 1-15 hydrocarbon group, C 1-13 hydrocarbon group or C 1-10 Hydrocarbon group.

[0083] The hydrocarbon group includes, for example, straight-chain alkyl or branched alkyl, alkyl-substituted or unsubstituted cycloalkyl, wherein the cycloalkyl is not limited to bridged rings, spiro rings or fused rings. Therefore, the R 2 It can be hydrogen, C 1-20 Alkyl, C 1-15 Alkyl, C 1-12 Alkyl, C 1-10 Alkyl, C 1-8 Alkyl, C 1-6 Alkyl, C 1-5 Alkyl, C 1-3 Alkyl, ethyl, or methyl, or may be composed of more than one C 1-5 Alkyl, C 1-3 Alkyl, ethyl or methyl substituted or unsubstituted C 5-20 cycloalkyl, C 5-15 cycloalkyl, C 6-20 cycloalkyl, C 6-15 cycloalkyl, C 5-12 cycloalkyl, C 5-10 cycloalkyl or C 6-10 Cycloalkyl.

[0084] Specifically, the granular polymer adhesive or granular acrylic polymer adhesive may contain one or more repeating units derived from methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, 1-ethylhexyl acrylate, 2-ethylhexyl acrylate, 3-ethylhexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, 1-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, and 3-ethylhexyl methacrylate, or may contain copolymers of one or more compounds selected from the above compounds. Although not bound by a specific theory, by using an acrylic polymer adhesive for core-shell particles that meet the above average particle size, thickness, and / or mass ratio, not only can electrode adhesion be effectively achieved, but also an increase in battery internal resistance can be effectively prevented.

[0085] In one embodiment, the inorganic particle layer may comprise inorganic particles and a polymer binder.

[0086] In one embodiment, the inorganic particle layer may comprise inorganic particles with an average particle size (D50) of 100 nm to 1500 nm, 100 nm to 1200 nm, 200 nm to 1000 nm, 200 nm to 800 nm, 200 nm to 600 nm, 300 nm to 500 nm, or 200 nm to 400 nm.

[0087] In one embodiment, the inorganic particle layer may comprise first inorganic particles with an average particle size (D50) of 100 nm to 500 nm and second inorganic particles with an average particle size (D50) of 500 nm to 1500 nm. The average particle size (D50) of the first inorganic particles may be 200 nm to 400 nm, 250 nm to 350 nm, or about 300 nm. The average particle size (D50) of the second inorganic particles may be 500 nm to 1200 nm, 500 nm to 1000 nm, 600 nm to 1000 nm, 600 nm to 800 nm, or about 700 nm.

[0088] In one embodiment, when using inorganic particles with two different average particle sizes, the weight ratio is not particularly limited, but for example, the weight ratio of the first inorganic particle to the second inorganic particle can be mixed at a weight ratio of 10:90 to 50:50, 20:80 to 50:50, 20:80 to 40:60, or about 30:70. However, this is merely an example, and the inorganic particles do not necessarily have to be mixed in the above weight ratios. In this case, the first and second inorganic particles can be inorganic particles of the same kind or inorganic particles of different kinds.

[0089] In one embodiment, the type of inorganic particles included in the inorganic particle layer is not particularly limited, as long as they are known inorganic particles with electrochemical stability. For example, it may include any one or more of boehmite, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and / or SiC.

[0090] In one embodiment, for the polymer adhesive, those skilled in the art disclosed herein may appropriately select a known adhesive depending on the purpose and circumstances. In one embodiment, the polymer adhesive may be a solution-phase water-based adhesive, for example, comprising one or more selected from ester-based polymers, amide-based polymers, imide-based polymers, acrylic-based polymers, acrylamide-based polymers, vinyl alcohol-based polymers, acrylonitrile-based polymers, polyvinyl alcohol-based polymers, fluoropolymers, and / or vinylpyrrolidone-based polymers. In one embodiment, the adhesive may comprise an acrylic polymer. Alternatively, for example, the adhesive may comprise a polymer prepared from one or more monomers selected from (meth)acrylamide-based monomers, hydroxyl-containing (meth)acrylic acid-based monomers, and / or polyfunctional (meth)acrylamide-based monomers, as long as it is used as an adhesive to form a porous inorganic particle layer on the surface of a porous substrate layer of a diaphragm by interlinking inorganic particles with the adhesive.

[0091] In one embodiment, the acrylamide-based polymer may contain repeating units represented by the following chemical formula 2.

[0092] [Chemical Formula 2]

[0093]

[0094] In the chemical formula 2, R 3 For hydrogen, C 1-10 Alkyl, C 1-8 Alkyl, C 1-5 Alkyl or C 1-3 alkyl.

[0095] In one embodiment, the polymer adhesive may further comprise, for example, any one or more water-based polymers selected from polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), and copolymers thereof.

[0096] In one embodiment, the weight-average molecular weight (Mw) of the adhesive (or the polymer contained in the adhesive) may be from 10,000 g / mol to 2,000,000 g / mol, 50,000 g / mol to 2,000,000 g / mol, 50,000 g / mol to 1,000,000 g / mol, 50,000 g / mol to 500,000 g / mol, 50,000 g / mol to 300,000 g / mol, 100,000 g / mol to 300,000 g / mol, or about 120,000 g / mol, but this is merely an example, and any suitable selection can be made according to experimental conditions, provided that the surface roughness range of the diaphragm according to the invention is met. The weight-average molecular weight can be measured by gel permeation chromatography (GPC).

[0097] In one embodiment, the glass transition temperature of the polymer adhesive may be, for example, 100°C to 180°C, 110°C to 160°C, 120°C to 150°C, or 130°C to 140°C, but is not necessarily limited to these.

[0098] In one embodiment, the inorganic particle layer may contain inorganic particles in a weight ratio of 90:10 to 99:1, 92:8 to 99:1, 95:5 to 99:1, 96:4 to 98:2, or about 97:3.

[0099] In one embodiment, the thickness of the inorganic particle layer can be 0.5 μm to 3.0 μm, 0.5 μm to 2.5 μm, 1.0 μm to 3.0 μm, 1.0 μm to 2.5 μm, 1.0 μm to 2.0 μm, or about 1.5 μm. In one embodiment, the inorganic particle layer can be formed on one or both sides of a porous substrate.

[0100] In one embodiment, the thickness of the adhesive layer can be from 0.05 μm to 2.0 μm, 0.1 μm to 2.0 μm, 0.1 μm to 1.5 μm, 0.1 μm to 1.0 μm, 0.2 μm to 0.8 μm, or about 0.5 μm. In one embodiment, the adhesive layer can be formed on any one of the inorganic particle layers, or it can be formed on two inorganic particle layers formed on both sides of the porous substrate.

[0101] In one embodiment, the substrate may be a porous substrate, and is not limited to any substrate commonly used in the art. For example, the substrate may be a woven fabric, a nonwoven fabric, or a porous membrane. Specifically, the porous substrate may be a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate or polybutylene terephthalate, a polyacetal, a polyamide, a polyimide, a polycarbonate, a polyetheretherketone, a polyaryletherketone, a polyetherimide, a polyamideimide, a polybenzimidazole, a polyethersulfone, a polyphenylene ether, a cyclic olefin copolymer, a polyphenylene sulfide, a polyethylene naphthalate, a glass fiber, Teflon, and / or polytetrafluoroethylene, and may also use any two or more of these substances.

[0102] In one embodiment, the thickness of the porous substrate is not particularly limited. For example, the thickness of the porous substrate can be 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, 5 μm to 10 μm, or about 9 μm.

[0103] Another specific embodiment provides a method for manufacturing the diaphragm.

[0104] A method for manufacturing a diaphragm according to one embodiment includes the following steps: preparing a substrate; forming an inorganic particle layer on at least one side of the substrate using an inorganic particle layer forming composition; and forming an adhesive layer on at least one of the inorganic particle layers using an adhesive layer forming composition.

[0105] In one embodiment, the inorganic particle layer forming composition may be a slurry, the solids content of which may be, for example, 15% to 40% by weight, 20% to 40% by weight, 20% to 35% by weight, or 20% to 30% by weight.

[0106] In one embodiment, the formation step of the inorganic particle layer and / or adhesive layer may include a coating composition and drying step. The coating is not particularly limited, but can be performed using methods such as roll coating, spin coating, dip coating, bar coating, die coating, slit coating, or inkjet printing. The drying can be performed using methods such as warm air, hot air, low-humidity air drying, vacuum drying, irradiation with far-infrared light, or electron beams. The drying temperature is not particularly limited and can therefore be appropriately adjusted according to the experimental environment or purpose.

[0107] Another specific embodiment provides an electrochemical device comprising a diaphragm, the diaphragm comprising: a substrate; an inorganic particulate layer formed on at least one side of the substrate; and an adhesive layer formed on at least one of the inorganic particulate layers, wherein, when the adhesive force between the probe and the surface of the diaphragm, measured using an atomic force microscope (AFM) with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz, is set as Fx, F40 is 1 nN to 30 nN, and the diaphragm satisfies the following formula 1.

[0108] [Formula 1]

[0109] F75 / F40≥5

[0110] The above descriptions related to the diaphragm can also be applied to the electrochemical device, therefore, repeated descriptions are omitted below.

[0111] Another specific embodiment provides an electrochemical device that effectively suppresses the increase in internal resistance of an electrochemical device. Specifically, one embodiment provides an electrochemical device comprising a separator, the separator comprising: a substrate; an inorganic particulate layer formed on at least one side of the substrate; and an adhesive layer formed on at least one of the inorganic particulate layers, wherein C is greater than or equal to 300 when the number of cycles in which the internal resistance of the electrochemical device increases by 30% compared to the initial resistance before the start of a charge-discharge cycle is defined as C, wherein the charge-discharge process is performed by discharging the electrochemical device to 2.5V, charging it from 2.5V to 4.2V at 0.5C, and discharging it from 4.2V to 2.5V at 0.5C as one cycle.

[0112] In one implementation, C can be 400 or higher, 450 or higher, 500 or higher, 550 or higher, or 580 or higher, and can be 800 or lower, 700 or lower, 650 or lower, or 600 or lower.

[0113] Similarly, the above descriptions related to the diaphragm can also be applied to the electrochemical device, so repeated descriptions are omitted below.

[0114] The electrochemical device can be any known energy storage device without particular limitation, but as a non-limiting example, a secondary battery can be cited, or specifically, a lithium secondary battery. According to one embodiment, the lithium secondary battery may include the aforementioned separator between the positive and negative electrodes. In this case, the positive and negative electrodes can be used without restriction, as long as they are commonly used in lithium secondary batteries.

[0115] Typically, when the separator according to a specific embodiment is used in a battery, it is assembled by providing a negative electrode, a separator, and a positive electrode. The constituent elements of the secondary battery according to the present invention will be further described below.

[0116] [positive electrode]

[0117] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one side of the positive electrode current collector.

[0118] (Positive current collector)

[0119] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof. It may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is not limited thereto, but for example, it may be from 10 μm to 50 μm.

[0120] (Cathode material)

[0121] The positive electrode mixture layer may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0122] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0123] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystal structure represented by the following chemical formula 3.

[0124] [Chemical Formula 3]

[0125] Li x Ni a M b O 2+z

[0126] In chemical formula 3, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0127] The chemical structure represented by Formula 3 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 3 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 3 includes the introduction and substitution of additional elements.

[0128] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 3.

[0129] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0130] For example, the positive electrode active material or the lithium-nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 3-1.

[0131] [Chemical Formula 3-1]

[0132] Li x Ni a M1 b1 M2 b2 O 2+z

[0133] In chemical formula 3-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 3-1, the elements may be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0134] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0135] The coating element or dopant element may exist on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be contained in the bonding structure represented by chemical formula 3 or chemical formula 3-1.

[0136] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0137] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (High-Ni) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0138] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.

[0139] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0140] In some embodiments, the positive electrode active material may further comprise lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0141] In some embodiments, the positive electrode active material may include, for example, a manganese-rich (Mn-rich) active material having a chemical structure or crystal structure represented by Formula 4, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO) active material, or a cobalt-less active material.

[0142] [Chemical Formula 4]

[0143] p[Li₂MnO₃]·(1-p)[Li q JO2]

[0144] In Chemical Formula 4, 0 < p < 1 and 0.9 ≤ q ≤ 1.2, and J may contain at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0145] (Method for manufacturing the positive electrode)

[0146] For example, the positive electrode active material can be mixed in a solvent to prepare a positive electrode paste. The positive electrode paste can be coated on a positive electrode current collector and then dried and calendered to prepare a positive electrode mixture layer. The coating process can be carried out by methods such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The positive electrode mixture layer may further contain a binder, and may optionally further contain a conductive material, a thickening agent, etc. At this time, the binder and the conductive material can be as described above.

[0147] (Positive electrode solvent)

[0148] Non-limiting examples of the solvent for preparing the positive electrode mixture include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, isobutyl isobutyrate, butyl butyrate, xylene, anisole, etc.

[0149] (Positive electrode binder)

[0150] The binder may include a non-aqueous binder and / or an aqueous binder, or may include a rubber-based binder and / or a fluorine-based binder. The binder may include, for example, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer (PVDF-HFP), polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder can be used as the positive electrode binder.

[0151] (Positive electrode conductive material)

[0152] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode mixture layer. For example, the conductive material can be a linear conductive material and / or a point conductive material. The conductive material can include, for example, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, carbon nanofibers, etc., and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc., but is not limited to these.

[0153] (Positive electrode thickener / dispersant)

[0154] As needed, the positive electrode mixture may further contain thickeners and / or dispersants, etc. As one embodiment, the positive electrode mixture may contain thickeners such as carboxymethyl cellulose (CMC).

[0155] [negative electrode]

[0156] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on at least one side of the negative electrode current collector.

[0157] (Negative electrode current collector)

[0158] Non-limiting examples of negative electrode current collectors include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and polymer substrates coated with conductive metals. The thickness of the negative electrode current collector is not limited thereto, but for example, it can be 10-50 μm thick.

[0159] (Anode material)

[0160] The negative electrode mixture layer may contain a negative electrode active material. The negative electrode active material may be a substance capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials; or tin (Sn)-containing materials.

[0161] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0162] Examples of crystalline carbon include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and other graphite-based carbons.

[0163] As the lithium metal, pure lithium metal or lithium metal formed with a protective layer for suppressing dendrite growth or the like can be cited. In one embodiment, the lithium metal-containing layer deposited or coated on the negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, the lithium thin film layer can also be used as the negative electrode active material layer.

[0164] As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, or the like can be cited.

[0165] The silicon-containing material can provide further increased capacity characteristics. The silicon-containing material can include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composite, or the like. The metal can include lithium and / or magnesium, and the metal-doped SiO x (0 < x < 2) can include metal silicate.

[0166] (Method for manufacturing negative electrode)

[0167] For example, the negative electrode active material can be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry can be coated / deposited on the negative electrode current collector and then dried and calendered to prepare a negative electrode mixture layer. The coating process can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, blade coating, dip coating, rod coating, casting, etc., and is not limited thereto. The negative electrode mixture layer can further contain an adhesive, and can optionally further contain a conductive material, a thickener, or the like.

[0168] In some embodiments, the negative electrode can also include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0169] (Negative electrode solvent)

[0170] As non-limiting examples of the solvent for the negative electrode mixture, water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, isobutyl isobutyrate, butyl butyrate, xylene, anisole, or the like can be cited.

[0171] (Negative electrode adhesive / conductive material / thickener)

[0172] As the above-mentioned adhesive, conductive material, and thickener, the above-mentioned substances that can be used in manufacturing the positive electrode can be used.

[0173] In some implementations, the negative electrode adhesive can be a rubber-based adhesive such as styrene-butadiene rubber (SBR) based adhesive, a carboxymethyl cellulose (CMC) based adhesive, a polyacrylic acid based adhesive, or a poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesive.

[0174] [Septum]

[0175] A membrane can be disposed between the positive and negative electrodes. The membrane can be configured to prevent short circuits between the positive and negative electrodes and to allow ion flow. According to an embodiment, the thickness of the membrane can be from 10 μm to 20 μm, but the invention is not limited thereto.

[0176] For example, the diaphragm may comprise a porous polymer membrane or a porous nonwoven fabric. The porous polymer membrane may comprise polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous nonwoven fabric may comprise high-melting-point glass fibers, polyethylene terephthalate fibers, etc. The diaphragm may also comprise ceramic-based materials. For example, inorganic particles may be coated on or dispersed within the polymer membrane to improve heat resistance.

[0177] The diaphragm may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric.

[0178] [Electrode Assembly]

[0179] According to exemplary embodiments, an electrode assembly can be formed by repeatedly setting up a positive electrode, a negative electrode, and a separator. In some embodiments, the electrode assembly can be of the winding type, stacking type, z-folding type, or stack-folding type.

[0180] Electrolyte

[0181] The electrode assembly can be housed together with the electrolyte in a casing, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0182] (Lithium salt / organic solvent)

[0183] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that, and as the anion (X) of the lithium salt - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0184] The organic solvent may comprise an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. The organic solvent may include at least one of, for example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents. The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), butene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), and diethylene glycol dimethyl ether. These include ether (DEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0185] (additive)

[0186] The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulcolone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.

[0187] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0188] The fluorinated carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0189] The sulfonyl compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0190] The cyclic sulfate-based compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0191] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, etc.

[0192] The phosphate-based compounds may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.

[0193] The borate-based compounds may include lithium bis(oxalate) borate, etc.

[0194] [Solid electrolyte]

[0195] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery can be manufactured as an all-solid-state battery. Furthermore, a solid electrolyte layer can be disposed between the positive and negative electrodes instead of the aforementioned separator.

[0196] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-LiBr, Li₂S-P₂S₅-LiCl-LiBr, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2), etc. These can be used individually or in combination of two or more.

[0197] In one embodiment, the solid electrolyte may further include oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li2O-B2O3-ZnO.

[0198] [Cell Structure]

[0199] For example, the tabs (positive and negative tabs) can protrude from the positive and negative current collectors and extend to one side of the housing, respectively. The tabs can be fused to said side of the housing and connected to electrode leads (positive and negative leads) extending to or exposed outside the housing. For example, pouch-type housings, prismatic housings, cylindrical housings, coin-type housings, etc., can be used.

[0200] The embodiments are further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only used to illustrate a specific implementation and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0201] <Experimental Methods>

[0202] 1. Glass transition temperature (Tg, unit: °C)

[0203] The heat capacity of a sample was measured using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min within the range of -100 °C to 250 °C. The temperature at the midpoint of the range in which the heat capacity of the sample changed rapidly was determined as the glass transition temperature.

[0204] 2. Electrode fusion temperature (unit: °C)

[0205] In the embodiments and comparative examples, two negative electrodes and two positive electrodes were alternately disposed on each of the two sides of the diaphragm. Then, the diaphragm was folded in a zigzag stacking manner to align the negative and positive electrodes. After setting the temperature of the stamping press, it was calendered at a pressure of 1 MPa for 30 seconds. Upon unfolding after calendering, if both the negative and positive electrodes adhered to the diaphragm, this temperature was defined as the electrode fusion temperature.

[0206] 3. Analysis of adhesive force (Fx) (peak force, quantitative nanomechanical (QNM), unit: nN)

[0207] The adhesive force between the probe and the diaphragm surface was measured using an atomic force microscope (AFM, Bruker) equipped with a temperature-adjustable sample stage. The adhesive force at temperature x °C was denoted as Fx. Specifically, the diaphragm was placed on a sample stage at x °C, and the diaphragm was tapped with a probe (RTESPA-300) with a spring constant of 40 N / m, an average radius of 8 nm, and a scan speed of 0.5 Hz. An F / D (load (Y-axis) / distance (X-axis)) plot was obtained. Based on the F / D plot, the adhesive force generated when the probe left the diaphragm surface was calculated from the Y-axis. Specifically, in the following embodiments, the adhesive force at locations where adhesive particles were present on the adhesive layer surface of the diaphragm was measured, a total of 10 measurements were taken, and the average value of the measured values ​​was calculated. The adhesive forces F40 and F75 were calculated at sample stage temperatures of 40 °C and 75 °C, respectively, and F75 / F40 was rounded to two decimal places and shown.

[0208] 4. Measurement of the number of cycles required to increase internal resistance

[0209] The number of cycles in which the internal resistance increases by 30% compared to the initial resistance before the start of the charge-discharge cycle is defined as the number of cycles in which the internal resistance increases. This was measured using a battery assembled as follows.

[0210] Positive electrode fabrication: 92 wt% of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 4 wt% of carbon black as the conductive material, and 4 wt% of polyvinylidene fluoride (PVDF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry. The prepared slurry was coated onto a 30 μm thick aluminum (Al) film and dried at 120 °C, followed by roll-pressing to produce a 140 μm thick positive electrode.

[0211] Anode fabrication: A negative electrode slurry was prepared by adding 96 wt% graphite carbon, 3 wt% PVDF as a binder, and 1 wt% carbon black as a conductive material to NMP as a solvent. The prepared slurry was coated onto a 20 μm thick copper (Cu) film, dried at 120 °C, and rolled to produce a 150 μm thick negative electrode.

[0212] The prepared separators are stacked between 11 positive electrodes and 12 negative electrodes to assemble a pouch cell. An electrolyte solution containing 1M lithium hexafluorophosphate (LiPF6) in a ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) of 3:5:2 (volume ratio) is injected into each assembled cell to produce a lithium secondary battery with a capacity of 2Ah.

[0213] Using a charge-discharge cycling device, the assembled battery was charged at 4.2V with a constant current-constant voltage (CC-CV) charge and then discharged to 2.5V. The charge-discharge cycle consisted of 600 cycles of 0.5C charging from 2.5V to 4.2V and 0.5C discharging from 4.2V to 2.5V. Before each cycle, the initial internal resistance was measured, and the internal resistance was measured during each charge-discharge cycle. The number of cycles in which the internal resistance increased by 30% compared to the initial resistance was counted as the number of cycles in which the internal resistance increased.

[0214] 5. Thickness measurement (unit: μm)

[0215] The thickness of 10 layers of porous substrate was measured using a Mitutoyo (ID-C112X) microscope, and then divided by 10 to obtain the thickness of the porous substrate. An inorganic particle layer was coated onto the porous substrate, and its thickness was measured using the same method. The thickness of the inorganic particle layer was then subtracted from this thickness. An adhesive layer was coated onto the inorganic particle layer, and its thickness was measured using the same method. The thickness of the adhesive layer was then subtracted from both the thickness of the porous substrate and the thickness of the inorganic particle layer.

[0216] <Example 1>

[0217] A coating slurry with a solids concentration of 25% by weight was prepared. The slurry contained 29% by weight boehmite particles with an average particle size (D50) of 300 nm, 68% by weight boehmite particles with an average particle size (D50) of 700 nm, and 3% by weight polyacrylamide. The coating slurry was coated onto both sides of a porous polyethylene substrate with a thickness of 9 μm and then evaporated to form inorganic particulate layers with a thickness of 1.5 μm.

[0218] An acrylic-based particle dispersion (at a concentration of 3% by weight) with an average particle size (D50) of 500 nm was coated onto the inorganic particle layers formed on the two surfaces mentioned above, and then evaporated to form an adhesive layer with a thickness of 0.5 μm, thereby manufacturing a diaphragm. In this case, the core (average particle size: 450 nm) of the acrylic-based particles with a core structure contains a copolymer formed by mixing methyl methacrylate and n-butyl acrylate in a weight ratio of 70:30, and the shell contains a copolymer formed by mixing ethyl acrylate, methyl methacrylate, and styrene in a weight ratio of 12:30:58, with a core-to-shell weight ratio of 7:3.

[0219] <Example 2>

[0220] The diaphragm is manufactured using the same method as in Example 1, except that the core-shell structured acrylic particles (average particle size: 500 nm) contained in the adhesive layer use particles in which the core (average particle size: 450 nm) contains a copolymer formed by mixing methyl methacrylate, n-butyl acrylate, and ethyl acrylate in a weight ratio of 75:10:15, and the shell contains a copolymer formed by mixing ethyl acrylate, methyl methacrylate, and styrene in a weight ratio of 10:50:40.

[0221] <Example 3>

[0222] The membrane was manufactured using the same method as in Example 1, except that 97% by weight of boehmite particles with an average particle size (D50) of 300 nm were used as inorganic particles when forming the inorganic particle layer.

[0223] <Comparative Example 1>

[0224] The diaphragm is manufactured using the same method as in Example 1, except that the core-shell structured acrylic particles (average particle size: 500 nm) contained in the adhesive layer use particles in which the core (average particle size: 450 nm) contains a copolymer formed by mixing methyl methacrylate, n-butyl acrylate, and ethyl acrylate in a weight ratio of 75:10:15, and the shell contains a copolymer formed by mixing methyl methacrylate and styrene in a weight ratio of 50:50.

[0225] <Comparative Example 2>

[0226] The diaphragm is manufactured using the same method as in Example 1, except that the core-shell structured acrylic particles (average particle size: 500 nm) contained in the adhesive layer use particles in which the core (average particle size: 450 nm) contains a copolymer formed by mixing methyl methacrylate, n-butyl acrylate, and ethyl acrylate in a weight ratio of 40:20:40, and the shell contains a copolymer formed by mixing ethyl acrylate and styrene in a weight ratio of 30:70.

[0227] <Comparative Example 3>

[0228] The diaphragm is manufactured using the same method as in Example 1, except that the core-shell structured acrylic particles (average particle size: 500 nm) contained in the adhesive layer use particles in which the core (average particle size: 450 nm) contains a copolymer formed by mixing methyl methacrylate and n-butyl acrylate in a weight ratio of 75:25, and the shell contains a copolymer formed by mixing benzyl acrylate and styrene in a weight ratio of 10:90.

[0229] <Comparative Example 4>

[0230] The diaphragm is manufactured using the same method as in Example 1, except that the core-shell structured acrylic particles (average particle size: 500 nm) contained in the adhesive layer use particles in which the core (average particle size: 450 nm) contains a copolymer formed by mixing methyl methacrylate and n-butyl acrylate in a weight ratio of 60:40, and the shell contains a copolymer formed by mixing methyl methacrylate and styrene in a weight ratio of 30:70.

[0231] <Comparative Example 5>

[0232] A coating slurry with a solids concentration of 25% by weight is prepared. The coating slurry comprises 29% by weight boehmite particles with an average particle size (D50) of 300 nm, 68% by weight boehmite particles with an average particle size (D50) of 700 nm, and 3% by weight polyacrylamide. The coating slurry is coated onto a porous polyethylene substrate with a thickness of 9 μm and then evaporated to form an inorganic particulate layer, thereby manufacturing a diaphragm.

[0233] The glass transition temperature (Tg), fusion temperature with the electrode, adhesive strength (F40, F75) at 40°C and 75°C, ratio of F75 to F40, and number of cycles with increased internal resistance of the core and shell of the acrylic-based particles in the adhesive layer of the diaphragms manufactured in the above embodiments and comparative examples were analyzed according to the above test methods and are shown in Table 1 below.

[0234] [Table 1]

[0235]

[0236] As can be confirmed from Table 1, in the case of the embodiment where the adhesive force F40 measured by the AFM probe is less than 30 nN and the F75 / F40 is more than 5, the phenomenon of increased internal resistance is significantly improved compared with the comparative example.

[0237] The above description is merely an example of applying the principles of the present invention, and other configurations may be further included without departing from the scope of the invention. The above description, through embodiments and experimental examples, details a specific implementation, but the scope of a specific implementation is not limited to the particular embodiment and should be interpreted according to the scope of the claims.

Claims

1. A diaphragm comprising: Substrate; An inorganic particle layer formed on at least one side of the substrate; And an adhesive layer formed on at least one of the inorganic particle layers, Wherein, when the adhesion force between the probe and the surface of the diaphragm, measured at a stage temperature of x °C using an atomic force microscope (AFM) with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz, is defined as Fx, F40 ranges from 1nN to 30nN. The diaphragm satisfies the following formula 1. [Formula 1] F75 / F40≥5.

2. The diaphragm according to claim 1, wherein, The adhesive layer comprises a particulate polymer adhesive.

3. The diaphragm according to claim 1, wherein, The adhesive layer comprises an acrylic polymer adhesive.

4. The diaphragm according to claim 2, wherein, The particulate polymer adhesive has a core-shell structure.

5. The diaphragm according to claim 4, wherein, The polymer contained in the core of the particulate polymer adhesive has a glass transition temperature of 30°C to 70°C.

6. The diaphragm according to claim 4, wherein, The glass transition temperature of the polymer contained in the shell of the granular polymer adhesive is 70°C to 110°C.

7. The diaphragm according to claim 4, wherein, The glass transition temperature Tg,c of the polymer contained in the core and the glass transition temperature Tg,s of the polymer contained in the shell of the particulate polymer adhesive satisfy the following equation 2. [Equation 2] 50℃≤(Tg,c+Tg,s) / 2≤90℃.

8. The diaphragm according to claim 1, wherein, The adhesive layer comprises: Copolymers composed of repeating units derived from acrylic monomers; and A copolymer composed of repeating units derived from acrylic monomers and styrene.

9. The diaphragm according to claim 1, wherein, The adhesive layer comprises a particulate acrylic polymer adhesive with an average particle size D50 of 400 nm to 800 nm.

10. The diaphragm according to claim 1, wherein, The F75 ranges from 40nN to 300nN.

11. The diaphragm according to claim 1, wherein, Equation 1 satisfies F75 / F40≥10.

12. The diaphragm according to claim 1, wherein, The adhesive layer comprises a particulate acrylic polymer adhesive, the particulate acrylic polymer adhesive comprising repeating units derived from compounds represented by the following chemical formula 1. [Chemical Formula 1] In the chemical formula 1, R 1 It is hydrogen or C 1-10 alkyl; R 2 It is hydrogen or C 1-20 Hydrocarbon group.

13. The diaphragm according to claim 1, wherein, The inorganic particle layer comprises inorganic particles and a polymer binder.

14. The diaphragm according to claim 1, wherein, The inorganic particle layer comprises inorganic particles with an average particle size D50 of 100 nm to 1500 nm.

15. The diaphragm according to claim 1, wherein, The inorganic particle layer comprises first inorganic particles with an average particle size D50 of 100 nm to 500 nm and second inorganic particles with an average particle size D50 of 500 nm to 1500 nm.

16. The diaphragm according to claim 1, wherein, The inorganic particle layer comprises inorganic particles and a polymer binder, wherein the weight ratio of the inorganic particles to the polymer binder is 90:10 to 99:

1.

17. The diaphragm according to claim 1, wherein, The thickness of the inorganic particle layer is from 0.5 μm to 3.0 μm.

18. The diaphragm according to claim 1, wherein, The thickness of the adhesive layer is from 0.05 μm to 2.0 μm.

19. An electrochemical device, the electrochemical device comprising a membrane, the membrane comprising: Substrate; An inorganic particle layer formed on at least one side of the substrate; And an adhesive layer formed on at least one of the inorganic particle layers, Wherein, when the adhesion force between the probe and the surface of the diaphragm, measured at a stage temperature of x °C using an atomic force microscope (AFM) with a spring constant of 40 N / m, an average radius of 8 nm, and a scanning speed of 0.5 Hz, is defined as Fx, F40 ranges from 1nN to 30nN. The diaphragm satisfies the following formula 1. [Formula 1] F75 / F40≥5.

20. An electrochemical device, the electrochemical device comprising a membrane, the membrane comprising: Substrate; An inorganic particle layer formed on at least one side of the substrate; And an adhesive layer formed on at least one of the inorganic particle layers, Wherein, when the number of cycles at which the internal resistance of the electrochemical device increases by 30% compared to the initial resistance before the start of the charge-discharge cycle is set as C, C is 300 or more. The charging and discharging process involves discharging the electrochemical device to 2.5V, then charging it at 0.5C from 2.5V to 4.2V and discharging it at 0.5C from 4.2V to 2.5V, which is considered as one cycle.

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