Composite separator for lithium secondary battery comprising an organic polymer binder layer, method of manufacturing the same, and lithium secondary battery having the same

Abstract

A composite separator for a lithium secondary battery according to aspects of this disclosure comprises: a porous organic polymer substrate; a porous inorganic heat-resistant layer coated on at least one surface of the organic polymer substrate, the porous inorganic heat-resistant layer comprising inorganic particles and an organic binder polymer holding the inorganic particles together; and an organic polymer adhesive layer coated on the outer surface of the porous inorganic heat-resistant layer, the organic polymer adhesive layer comprising an organic binder polymer, wherein the inorganic particles comprise a mixture of particles with different shapes, the particles comprising i) plate-shaped particles and ii) needle-shaped particles, the plate-shaped particles comprising alumina particles, aluminum hydroxide particles, or mixtures thereof, the needle-shaped particles comprising alumina particles, aluminum hydroxide particles, or mixtures thereof, wherein the organic binder polymer included in the organic polymer adhesive layer comprises gelatin resin.

Description

Technical Field

[0001] This disclosure relates to a lithium secondary battery including a composite separator having a porous inorganic heat-resistant layer and an organic polymer adhesive layer sequentially arranged on the surface of a porous organic polymer substrate.

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2024-0143089, filed with the Korean Intellectual Property Office on October 18, 2024, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Lithium-ion batteries are typically designed to store energy with high energy density, and they essentially consist of a positive electrode / separator / negative electrode / electrolyte, and can be charged and discharged through the reversible conversion of chemical and electrical energy. They are used in a wide range of applications, including small electronic devices such as mobile phones or laptops. Recently, in response to environmental concerns, high oil prices, energy efficiency, and storage needs, their applications have rapidly expanded to hybrid electric vehicles (HEVs), plug-in electric vehicles (EVs), e-bikes, and energy storage systems (ESS).

[0004] Ensuring safety is a major challenge in the manufacture and use of lithium-ion batteries. In particular, due to the characteristics of material properties and manufacturing processes, separators, including those on commonly used porous organic polymer substrates, exhibit extreme thermal shrinkage behavior at high temperatures, leading to stability issues such as internal short circuits. Therefore, to ensure the safety of lithium-ion batteries, separators with an inorganic heat-resistant layer formed by coating a mixture of inorganic particles and an organic binder polymer that holds the inorganic particles together onto a porous organic polymer substrate have been developed. Specifically, to reduce resistance, the inorganic heat-resistant layer is formed by dispersing the inorganic particles and organic binder polymer particles in a non-solvent (e.g., water) to maintain particle shape and then coating / drying it onto a porous organic polymer substrate.

[0005] When composite separators with inorganic heat-resistant layers are stacked with positive and negative electrodes to manufacture electrode assemblies, they may separate from each other due to insufficient interlayer adhesion strength. With the electrodes and separators separated, the volumetric expansion / contraction of the electrodes during charging / discharging can cause the battery to bend or twist. This problem is particularly severe in pouch cells, and its severity increases with the number of stacked components and the length of the battery.

[0006] To increase the adhesion strength between the electrode and the composite separator, composite separators with coatings of vinylidene fluoride-based polymer adhesives or acrylic polymer adhesives on the surface of the inorganic heat-resistant layer have been proposed. However, there is a need to develop environmentally friendly organic polymer adhesive layers to increase the adhesion strength relative to the electrode and minimize environmental damage.

[0007] To increase the energy density of lithium secondary batteries, it is necessary to reduce the thickness of the inorganic heat-resistant layer. Summary of the Invention

[0008] Technical issues

[0009] This disclosure relates to a composite separator for lithium secondary batteries, the composite separator having, sequentially, a porous inorganic heat-resistant layer and an organic polymer adhesive layer on the surface of a porous organic polymer substrate, wherein the porous inorganic heat-resistant layer has a small thickness and the organic polymer adhesive layer has good adhesion strength relative to the electrode and is eco-friendly.

[0010] This disclosure also relates to providing a lithium secondary battery including a composite separator having the above-described features.

[0011] These and other objects and advantages of this disclosure will be understood from the following description. It will also be apparent that the objects and advantages of this disclosure can be achieved by the means or methods set forth in the appended claims and combinations thereof.

[0012] Technical solution

[0013] The composite separator for lithium secondary batteries according to the first aspect of this disclosure includes:

[0014] Porous organic polymer substrate,

[0015] A porous inorganic heat-resistant layer coated on at least one surface of the porous organic polymer substrate, the porous inorganic heat-resistant layer comprising inorganic particles and an organic binder polymer holding the inorganic particles together, and

[0016] An organic polymer adhesive layer is coated on the outer surface of the porous inorganic heat-resistant layer, the organic polymer adhesive layer comprising an organic binder polymer.

[0017] The inorganic particles comprise a mixture of particles with different shapes, including i) plate-shaped particles and ii) needle-shaped particles. The plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof.

[0018] The organic adhesive polymer included in the organic polymer adhesive layer includes gelatin resin.

[0019] According to the second aspect of this disclosure, in the first aspect...

[0020] i) The weight mixing ratio of the plate-shaped particles to ii) the needle-shaped particles is (20 to 80):(80 to 20).

[0021] According to the third aspect of this disclosure, in the first or second aspect,

[0022] i) The average particle size (D) of the plate-shaped particles 50 (i) the length of the needle-shaped particles is 80 nm to 300 nm, and (ii) the average length of the needle-shaped particles is 80 nm to 600 nm.

[0023] According to the fourth aspect of this disclosure, in any one of the first to third aspects,

[0024] The organic polymer adhesive layer is positioned on the outer surface of the porous inorganic heat-resistant layer in a dispersed state where multiple organic polymer adhesive layers are separated or connected, and covers a portion of the surface of the porous inorganic heat-resistant layer.

[0025] According to the fifth aspect of this disclosure, in the fourth aspect,

[0026] The organic polymer adhesive layer comprises a plurality of dispersed organic polymer adhesive layers, covering 10% to 60% of the total surface area of ​​the porous inorganic heat-resistant layer.

[0027] According to the sixth aspect of this disclosure, in any of the first to fifth aspects,

[0028] Based on the organic polymer adhesive layer coated on one surface of the porous inorganic heat-resistant layer, the organic polymer adhesive layer has a loading of 0.5 g / m³. 2 Up to 3.0 g / m 2 .

[0029] According to the seventh aspect of this disclosure, in any of the first to sixth aspects,

[0030] The porous inorganic heat-resistant layer is coated on one surface of the porous organic polymer substrate, and the thickness of the porous inorganic heat-resistant layer is from 1 μm to 5 μm.

[0031] According to the eighth aspect of this disclosure, in any of the first to seventh aspects,

[0032] The organic binder polymer included in the porous inorganic heat-resistant layer includes an acrylic polymer.

[0033] According to the ninth aspect of this disclosure, in the eighth aspect,

[0034] The acrylic polymer is non-particulate.

[0035] According to the tenth aspect of this disclosure, in the eighth or ninth aspect,

[0036] The acrylic polymer comprises at least one selected from the group consisting of: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, ethylene glycol methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, and allyl methacrylate.

[0037] The eleventh aspect of this disclosure relates to a method for manufacturing a composite separator for lithium secondary batteries, and the method includes the following steps:

[0038] (S1) An aqueous slurry is coated onto at least one surface of a porous organic polymer substrate and dried to form a porous inorganic heat-resistant layer, the aqueous slurry containing i) plate-shaped particles, ii) needle-shaped particles, and iii) an organic binder polymer, wherein the plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof; and

[0039] (S2) Spray a solution of gelatin resin dissolved in an aqueous solvent onto the outer surface of the porous inorganic heat-resistant layer and dry the solution.

[0040] The twelfth aspect of this disclosure relates to a lithium secondary battery, comprising a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode.

[0041] The partition is a composite partition according to any one of the first to tenth aspects.

[0042] Beneficial effects

[0043] The composite separator according to this disclosure comprises a mixture of particles with different shapes, namely i) plate-shaped particles and ii) needle-shaped particles, serving as inorganic particles in a porous inorganic heat-resistant layer. The plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof. Therefore, the thickness of the porous inorganic heat-resistant layer can be reduced, and the porosity of the porous inorganic heat-resistant layer can be maintained at a high level.

[0044] Furthermore, the composite separator according to this disclosure comprises gelatin resin, a natural material in the organic polymer binder layer, thereby achieving good adhesion strength relative to the electrode and improving eco-friendliness. The organic polymer binder layer can be disposed on the outer surface of the porous inorganic heat-resistant layer in a state of separating or connecting multiple dispersed organic polymer binder layers, and thus can cover only a portion of the surface of the porous inorganic heat-resistant layer, thereby preventing or reducing the resistance rise driven by the formation of the organic polymer binder layer. Attached Figure Description

[0045] The accompanying drawings illustrate embodiments of the present disclosure and, together with the detailed description, serve to describe the principles of the disclosure; therefore, the scope of the disclosure is not limited thereto. Here, for clarity, the shape, size, scale, or ratio of the elements in the drawings may be exaggerated.

[0046] Figure 1 This is a schematic cross-sectional view of a lithium secondary battery including a composite separator according to an embodiment of the present disclosure.

[0047] Figure 2 It is shown schematically. Figure 1 A plan view of the surface of the first organic polymer adhesive layer. Detailed Implementation

[0048] The terms or words used in the specification and appended claims should not be construed as limited to their general or dictionary meanings, but should be interpreted based on their meanings and concepts corresponding to the technical aspects of this disclosure, based on the principle that the inventors are permitted to appropriately define terms for best interpretation. Therefore, the embodiments described herein and the illustrations shown in the accompanying drawings are embodiments of this disclosure to describe its technical aspects, but are not intended to be restrictive, and it should be understood that various other equivalents and modifications can be made thereto at the time of filing.

[0049] <Definition>

[0050] Unless the context clearly indicates otherwise, the terms “comprising” or “including” are used in this specification to specify the presence of the stated element, but do not exclude the presence or addition of one or more other elements.

[0051] In this specification, D 50 This refers to the particle size at the 50% point of the cumulative particle size distribution. Particle size is measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and fed into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500). As the particles pass through the laser beam, the particle size distribution is calculated by measuring the difference in the diffraction pattern as a function of particle size. D is measured by calculating the particle size at the 50% point of the cumulative particle size distribution in the measuring device. 50 .

[0052] In this specification, the average length of the needle-shaped particles is determined by collecting 100 needle-shaped particles used and measuring their average length.

[0053] In this specification, plate-shaped particles are commercially available plate-shaped particles, such as plate-shaped alumina, and refer to particles having a length and width greater than their thickness.

[0054] In this specification, needle-shaped particles are commercially available needle-shaped particles, such as needle-shaped alumina, and refer to particles having a shape with a length greater than their diameter.

[0055] In this specification, the aspect ratio of needle-shaped particles is the ratio of the length of the needle-shaped particle to its diameter.

[0056] In this specification, the term "particulate" in organic binder polymers such as acrylic polymers or vinylidene fluoride polymers means that the organic binder polymer retains its particulate shape within a coating formed by adding the particulate organic binder polymer to a dispersion medium, coating it, and drying it to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer. Furthermore, the term "non-particulate" means that the particulate organic binder polymer dissolves and loses its particulate shape when added to a solvent to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer, or that the organic binder polymer does not dissolve when added to a dispersion medium but loses its particulate shape during drying and transforms into a film to form a coating.

[0057] Figure 1 This is a schematic diagram illustrating a composite separator and a cross-section of a lithium secondary battery including the same according to a specific embodiment of the present disclosure. For ease of description, although... Figure 1 The negative electrode 20 and positive electrode 30 are depicted as being spaced apart from the composite separator 10, but in reality, the negative electrode 20 / composite separator 10 / positive electrode 30 in the lithium secondary battery are in close contact with each other. Furthermore, although... Figure 1An embodiment in which the composite separator 10 has a porous inorganic heat-resistant layer 3 and an organic polymer adhesive layer 5 is shown. It includes a first porous inorganic heat-resistant layer 3a and a second porous inorganic heat-resistant layer 3b, as well as a first organic polymer adhesive layer 5a and a second organic polymer adhesive layer 5b, respectively on two surfaces of the porous organic polymer substrate 1. However, the composite separator 10 may not have the second porous inorganic heat-resistant layer 3b and the second organic polymer adhesive layer 5b facing the positive electrode 30, but may have the first porous inorganic heat-resistant layer 3a and the first organic polymer adhesive layer 5a facing the negative electrode 20.

[0058] Reference Figure 1 According to an embodiment of the present disclosure, the composite separator 10 has a porous inorganic heat-resistant layer 3, which includes a first porous inorganic heat-resistant layer 3a and a second porous inorganic heat-resistant layer 3b coated on two surfaces of a porous organic polymer substrate 1. The porous inorganic heat-resistant layer 3 contains inorganic particles and an organic binder polymer that holds the inorganic particles together. Additionally, the composite separator 10 has a first organic polymer adhesive layer 5a and a second organic polymer adhesive layer 5b coated on the outer surfaces of the first porous inorganic heat-resistant layer 3a and the second porous inorganic heat-resistant layer 3b, respectively. The first organic polymer adhesive layer 5a and the second organic polymer adhesive layer 5b contain gelatin resin.

[0059] When the porous inorganic heat-resistant layer 3 and the organic polymer adhesive layer 5 are formed only on one surface of the porous organic polymer substrate 1, the second porous inorganic heat-resistant layer 3b and the second organic polymer adhesive layer 5b facing the positive electrode 30 are not formed, but the first porous inorganic heat-resistant layer 3a and the first organic polymer adhesive layer 5a facing the negative electrode 20 can be formed. Optionally, the first porous inorganic heat-resistant layer 3a and the first organic polymer adhesive layer 5a facing the negative electrode 20 are not formed, but the second porous inorganic heat-resistant layer 3b and the second organic polymer adhesive layer 5b facing the positive electrode 30 can be formed.

[0060] The inorganic particles of the porous inorganic heat-resistant layer (3) comprise a mixture of particles with different shapes, namely i) plate-shaped particles and ii) needle-shaped particles, wherein the plate-shaped particles comprise alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles comprise alumina particles, aluminum hydroxide particles, or mixtures thereof. Therefore, for example, the porous inorganic heat-resistant layer can have a smaller thickness than a porous inorganic heat-resistant layer using spherical alumina particles, and the porosity of the porous inorganic heat-resistant layer comprising the combination of plate-shaped and needle-shaped particles can be maintained at a higher level than when using plate-shaped particles alone.

[0061] Furthermore, the organic polymer adhesive layer 5, which includes the first organic polymer adhesive layer 5a and the second organic polymer adhesive layer 5b respectively coated on the outer surfaces of the first porous inorganic heat-resistant layer 3a and the second porous inorganic heat-resistant layer 3b, contains gelatin resin, which is a natural material, thereby maintaining good adhesion strength relative to the electrode and improving eco-friendliness.

[0062] The composite separator of this disclosure and each component of the lithium secondary battery including the separator will be described in more detail below.

[0063] Porous organic polymer substrate

[0064] According to specific embodiments of this disclosure, the porous organic polymer substrate 1 can electrically insulate the negative electrode from the positive electrode to prevent short circuits and provide a path for the movement of lithium ions. It can include, but is not limited to, any commonly used porous organic polymer substrate for lithium secondary batteries. The porous organic polymer substrate 1 can include, for example, a porous organic polymer membrane or an organic polymer nonwoven fabric, comprising at least one of a polymer resin (such as polyolefins (e.g., polyethylene or polypropylene), polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, or polyvinylnaphthalene).

[0065] In this disclosure, the thickness of the porous organic polymer substrate can be from 3 μm to 50 μm. The range of the porous organic polymer substrate is not limited to the above range; however, when the thickness is much smaller than the lower limit, the mechanical properties may decrease, potentially damaging the separator during battery use. Simultaneously, the pore size and porosity of the porous organic polymer substrate are not limited to specific ranges, but the pore size can be from 0.01 μm to 50 μm, and the porosity can be from 10% to 95% by volume.

[0066] Porous inorganic heat-resistant layer

[0067] refer to Figure 1 As is well known, the first porous inorganic heat-resistant layer 3a contains multiple inorganic particles and an organic binder polymer that holds the inorganic particles together. When the porous organic polymer substrate 1 is coated with the porous inorganic heat-resistant layer 3a containing inorganic particles, the heat resistance and mechanical properties of the composite separator 10 are improved.

[0068] The inorganic particles forming the porous inorganic heat-resistant layer 3a are substantially tightly assembled together and act as spacers to maintain their physical shape in the event of battery overheating, thereby preventing or reducing thermal shrinkage of the separator. An organic binder polymer is located between the inorganic particles to hold them together.

[0069] The inorganic particles included in the porous inorganic heat-resistant layer 3a are a mixture of particles with different shapes, namely i) plate-shaped particles and ii) needle-shaped particles, wherein the plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof.

[0070] Therefore, for example, porous inorganic heat-resistant layers can have a smaller thickness than porous inorganic heat-resistant layers using spherical alumina particles, and the porosity of porous inorganic heat-resistant layers comprising a combination of plate-shaped and needle-shaped particles can be maintained at a higher level than when using plate-shaped particles alone, due to the presence of needle-shaped particles between the plate-shaped particles. From this perspective, the weight mixing ratio of i) plate-shaped particles to ii) needle-shaped particles can be (20 to 80):(80 to 20), more specifically, (40 to 60):(60 to 40). Preferably, it may be advantageous in terms of porosity when the amount of needle-shaped particles is greater than the amount of plate-shaped particles.

[0071] The plate-shaped and needle-shaped particles added as inorganic particles to form the porous inorganic heat-resistant layer 3a each independently include alumina particles, aluminum hydroxide particles, or mixtures thereof. These particles may include, for example, Al2O3, AlO(OH), or Al(OH)3.

[0072] Because alumina or aluminum hydroxide particles typically do not change their physical properties when exposed to temperatures of 200°C or higher, the composite separator 10 exhibits high heat resistance due to the porous inorganic heat-resistant layers 3a and 3b. In this disclosure, each of the first porous inorganic heat-resistant layer 3a and the second porous inorganic heat-resistant layer 3b, based on a porous inorganic heat-resistant layer coated on one surface of a porous organic polymer substrate, can have a thickness of 1 μm to 5 μm, more preferably 2 μm to 4 μm.

[0073] The average particle size (D) of plate-shaped inorganic particles 50 The average length of the needle-shaped particles is not limited to a specific range, but can be, for example, 80 nm to 300 nm, and the average length of the needle-shaped particles is not limited to a specific range, but can be, for example, 80 nm to 600 nm. More specifically, the average particle size (D) of the plate-shaped inorganic particles... 50 The length of the needle-shaped particles can be from 100 nm to 200 nm, and the average length of the needle-shaped particles is not limited to a specific range, but can be, for example, from 200 nm to 400 nm. The aspect ratio of the needle-shaped particles can be, for example, from 10 to 60, and more specifically, from 30 to 50.

[0074] The organic binder polymer contained in the porous inorganic heat-resistant layer 3 to hold the inorganic particles together may include non-particulate organic binder polymers and particulate organic binder polymers.

[0075] Non-particulate organic binder polymers may include, for example, acrylic polymers with a Tg equal to or below room temperature. Acrylic polymers with a Tg equal to or below room temperature (25°C) lose their original shape and become film-shaped during coating processes at room temperature or above room temperature after being added to a dispersion medium along with inorganic particles to prepare a slurry.

[0076] More specifically, the acrylic polymer is a polymer containing a carboxylic acid ester as a repeating unit, and preferably may include (meth)acrylates. Specific examples of (meth)acrylates may include, for example, at least one selected from methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, ethylene glycol methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, and allyl methacrylate. In particular, (meth)acrylates may include at least one selected from methyl methacrylate, ethyl methacrylate, and 2-ethylhexyl methacrylate. The glass transition temperature (Tg) of the acrylic polymer may be equal to or lower than 40°C, but is not limited thereto.

[0077] Furthermore, the non-particulate organic binder polymer may include, but is not limited to, vinylidene fluoride-based polymers used alone or in combination, such as polyvinylidene fluoride-co-hexafluoropropylene or polyvinylidene fluoride-co-trichloroethylene. The first porous inorganic heat-resistant layer 3a and the second porous inorganic heat-resistant layer 3b using the non-particulate organic binder polymer can be manufactured by: dispersing inorganic particles in a solvent (e.g., acetone), then adding the non-particulate organic binder to the solvent and dissolving it to prepare a slurry; or adding a particulate organic binder with a Tg equal to or below room temperature (25°C) together with the inorganic particles to a dispersion medium to prepare a slurry; and coating the slurry onto the porous organic polymer substrate 1 by dip coating.

[0078] In the porous inorganic heat-resistant layer 3, in order to reduce the resistance of the porous inorganic heat-resistant layer, the organic binder polymer that holds the inorganic particles together may preferably include an organic binder polymer using a slurry, wherein the organic binder polymer is dispersed in a dispersion medium.

[0079] The particulate organic binder polymer can include any known particulate organic binder polymer used in organic polymer adhesive layers, and can include particles of polymers such as vinylidene fluoride (PVDF). PVDF polymers are insoluble in electrolyte solutions and can include homopolymers of PVDF, copolymers of PVDF with another polymerizable monomer, or mixtures thereof. Monomers copolymerized with PVDF can include, but are not limited to, at least one selected from the group consisting of: tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxacyclopentene), perfluoro(2,2-dimethyl-1,3-dioxacyclopentene), and trichloroethylene. In particular, PVDF polymers can include copolymers of PVDF and hexafluoropropylene. The amount of monomers copolymerized with PVDF can be from 1% to 20% by weight of the copolymer, but is not limited thereto.

[0080] The average particle size (D) of the particulate organic binder polymer 50 The average particle size (D) is not limited to a specific range, but can be, for example, 100 nm to 1000 nm, and more specifically 200 nm to 600 nm. When the particulate organic binder polymer includes an acrylic polymer, the average particle size (D) is... 50 It is not limited to a specific range, but can be, for example, 100 nm to 500 nm, and more specifically 100 nm to 300 nm.

[0081] In the porous inorganic heat-resistant layer 3, taking into account the thickness, pore size and porosity of the finally formed porous inorganic heat-resistant layer, the ratio of the amount of inorganic particles to the amount of organic binder polymer can be determined, and based on weight percentage, based on 100% by weight of porous inorganic heat-resistant layer, inorganic particles can be included in an amount of 70% to 99% by weight.

[0082] The porous inorganic heat-resistant layer 3 using a particulate organic binder polymer can be manufactured by: dispersing inorganic particles in an aqueous dispersion medium; adding the particulate organic binder polymer to the aqueous dispersion medium; dispersing it to prepare a slurry; coating the slurry onto a porous organic polymer substrate 1 by dip coating; and drying the slurry. The aqueous dispersion medium may include water or at least one of an alcohol having 1 to 5 carbon atoms. Using an aqueous dispersion medium, the organic binder polymer particles do not dissolve in the dispersion medium and remain dispersed in the aqueous dispersion medium, maintaining their particle shape, and retaining their particle shape after coating and drying on the porous organic polymer substrate 1.

[0083] Organic polymer adhesive layer

[0084] The first organic polymer adhesive layer 5a coated on the outer surface of the first porous inorganic heat-resistant layer 3a and the second organic polymer adhesive layer 5b coated on the outer surface of the second porous inorganic heat-resistant layer 3b contain gelatin resin.

[0085] As described above, the organic polymer adhesive layer 5 coated on the outer surface of the porous inorganic heat-resistant layer 3 comprises gelatin resin, a natural material, thereby maintaining good adhesion strength relative to the electrode and improving eco-friendliness. When considering adhesion strength and air permeability relative to the electrode, the loading of the organic polymer adhesive layer 5 based on the organic polymer adhesive layers 5a and 5b coated on one surface of the porous inorganic heat-resistant layer 3 can be 0.5 g / m³. 2 Up to 3.0 g / m 2 More specifically 0.7 g / m 2 Up to 2.0 g / m 2 And most specifically 0.8 g / m 2 Up to 1.3 g / m 2 .

[0086] If desired, the organic binder polymer included in the organic polymer binder layer 5 may further include at least one of carboxymethyl cellulose (CMC) or polyallylamine hydrochloride, but is not limited thereto.

[0087] Figure 2 It is shown schematically. Figure 1 A plan view of the surface of the first organic polymer adhesive layer.

[0088] Reference Figure 2 The first organic polymer adhesive layer 5a can be disposed on the porous inorganic heat-resistant layer 3a in such a state that, after the slurry is coated onto the porous inorganic heat-resistant layer 3a, the dispersed plurality of first organic polymer adhesive layers 5a-1 can be separated or joined by agglomeration during the drying of the slurry used to form the first organic polymer adhesive layer 5a. In this case, for example, the first organic polymer adhesive layer 5a can cover 10% to 60% of the total surface area of ​​the first porous inorganic heat-resistant layer 3a, and more specifically 20% to 40%. The first organic polymer adhesive layer 5a can cover a portion of the first porous inorganic heat-resistant layer 3a, thereby preventing or reducing the increase in resistance driven by the formation of the organic polymer adhesive layer.

[0089] Methods for manufacturing composite partitions

[0090] The aforementioned composite partition can be manufactured using the manufacturing method according to the embodiments of this disclosure as described below, but is not limited thereto.

[0091] First, an aqueous slurry is coated on at least one surface of a porous organic polymer substrate and dried to form a porous inorganic heat-resistant layer. The aqueous slurry contains i) plate-shaped particles, ii) needle-shaped particles, and iii) an organic binder polymer, wherein the plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof (step S1).

[0092] The dispersion medium used to prepare the aqueous slurry may include water or at least one of an alcohol having 1 to 5 carbon atoms. Because an aqueous dispersion medium is used, the organic binder polymer does not dissolve in the dispersion medium. Depending on the type of organic binder polymer and its temperature gradient (Tg), the organic binder polymer dispersed in the aqueous dispersion medium may retain its particle shape or lose its particle shape and transform into a film (becoming non-particulate).

[0093] Subsequently, a solution of gelatin resin dissolved in an aqueous solvent is sprayed onto the outer surface of the porous inorganic heat-resistant layer and dried (step S2).

[0094] For example, after adding gelatin resin to water, the gelatin resin completely dissolves when heated to a predetermined temperature, such as 60°C or higher. The aqueous solution is then sprayed onto the outer surface of a porous inorganic heat-resistant layer and dried to manufacture a composite separator.

[0095] Negative and positive electrodes

[0096] In specific embodiments of this disclosure, lithium secondary batteries can be manufactured using common methods well-known in the art. According to embodiments of this disclosure, a lithium secondary battery can be manufactured by placing a composite separator 10 between the negative electrode 20 and the positive electrode 30.

[0097] In other words, the composite separator 10 manufactured by the above method is placed between the negative electrode 20 and the positive electrode 30, followed by a lamination process involving the application of heat and / or pressure to hold them together in order to manufacture the electrode assembly. In embodiments of this disclosure, the lamination process can be performed by a roller press comprising a pair of pressure rollers. That is, the negative electrode, separator, and positive electrode can be stacked sequentially and fed between the pressure rollers to form an interlayer bond. In this case, the lamination process can be performed by a hot pressing method.

[0098] In embodiments of this disclosure, electrodes can be manufactured by attaching electrode active materials to electrode current collectors using methods well-known in the art, but the method is not limited to any particular method. Non-limiting examples of positive electrode active materials may include any positive electrode active material commonly used in the positive electrodes of lithium secondary batteries, and particularly preferably may include lithium intercalation materials, such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or composite oxides thereof. Non-limiting examples of negative electrode active materials may include any negative electrode active material commonly used in the negative electrodes of lithium secondary batteries, and particularly preferably may include lithium intercalation materials, such as lithium metal, lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbon materials. Non-limiting examples of positive electrode current collectors may include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative electrode current collectors may include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

[0099] electrolytes

[0100] An electrode assembly, including stacked negative electrode, separator, and positive electrode components, is placed in a battery casing, followed by electrolyte injection and activation to manufacture a lithium secondary battery. Electrolytes that can be used in this disclosure may include a salt and an organic solvent in which the salt is dissolved or dissociated, wherein the salt has A + B - The structure, where A + Including alkali metal cations such as Li + Na + K + Or a combination of them, and B - Including anions such as PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 -Or combinations thereof, wherein the organic solvent includes, but is not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or mixtures thereof.

[0101] Electrolyte injection can be performed at appropriate steps in the battery manufacturing process, depending on the desired characteristics of the manufacturing process and the final product. That is, electrolyte injection can be completed before battery pack assembly or in the final stage of battery pack assembly. The process of applying the electrode assemblies of this disclosure to the battery can include the winding process commonly used in the art, as well as the lamination, stacking, and folding processes of composite separators and electrodes.

[0102] The present disclosure will be described in detail below using embodiments. However, many different variations can be made to the embodiments according to the present disclosure, and the scope of the present disclosure should not be construed as limited to the following embodiments. Embodiments of the present disclosure are provided to explain the present disclosure more fully and thoroughly to those skilled in the art.

[0103] Example 1

[0104] [Preparation of Composite Partitions]

[0105] manufacture Figure 1 Composite partition 10.

[0106] The mixture contained 40 parts by weight of plate-shaped inorganic particles (Al2O3, D) 50 An emulsion of 60 parts by weight of needle-shaped inorganic particles (Al₂O₃, average length: 300 nm, aspect ratio: 40) and 5 parts by weight of acrylic polymer particles (CSB-130, Toyo Ink, Tg: -30℃) was added to water at a solids concentration of 35% by weight. The mixture was then bead-milled for 2 hours using zirconia beads with a particle size of 0.7 mm in the same amount as the inorganic particles to prepare a slurry. The slurry was dip-coated onto both surfaces of a porous organic polymer separator substrate made of polyethylene (porosity 45%, thickness 9 μm) and dried to form a first porous inorganic heat-resistant layer and a second porous inorganic heat-resistant layer, each with a thickness of 3 μm, on both surfaces.

[0107] Subsequently, gelatin resin was added to water at a solid content of 25% by weight, and the temperature was raised to 80°C. oFollowing step C, the mixture was stirred at 1000 rpm for 10 minutes to prepare a gelatin resin solution. Subsequently, the solution was sprayed onto the surface of each of the first and second porous inorganic heat-resistant layers and dried to form an organic polymer adhesive layer. Based on the organic polymer adhesive layer formed on the first porous inorganic heat-resistant layer, the loading of the organic polymer adhesive layer was 1.0 g / m³. 2 .

[0108] [Preparation of Lithium-ion Secondary Batteries]

[0109] LiNi 0.8 Co 0.1 Mn 0.1 O2, PVdF and carbon black were mixed and dispersed in 2-methyl-2-pyrrolidone at a weight ratio of 97.0:1.5:1.5 to prepare a positive electrode slurry. The positive electrode slurry was then coated on an aluminum current collector, dried and rolled to manufacture the positive electrode.

[0110] Graphite, SBR and CMC were mixed and dispersed in distilled water at a weight ratio of 89.2:10:0.8 to prepare a negative electrode slurry. The negative electrode slurry was then coated onto a copper current collector, dried and rolled to prepare the negative electrode.

[0111] The prepared separators were sandwiched and stacked between the positive and negative electrodes, and then laminated using a hot press to fabricate a single-cell sample. In this case, a pressure of 70°C and 5 kgf was applied for 5 minutes. The sample dimensions were 2 cm × 6 cm.

[0112] The sample was placed in a pouch-shaped casing and 1.0 g of electrolyte (ethylene carbonate: methyl ethyl carbonate ratio of 7:3, 1 M LiPF6) was injected to construct a secondary battery. The secondary battery was then kept uncontacted at room temperature for 3 hours. Subsequently, it was subjected to a 6 kgf / cm³ load at 55 °C. 2 Pressure was applied to the secondary battery for 5 minutes. At 55°C, 6 kgf / cm² was applied. 2 Under pressure, the secondary battery was charged to SOC 3 at 0.2C and then to SOC 60 at 1C. The pressure was then removed from the rechargeable battery, and it was aged at 55°C for 1 day.

[0113] Examples 2-4

[0114] The lithium secondary battery was manufactured using the same method as in Example 1, except that the loading of the organic polymer binder layer from Example 1 was changed to 1.2 g / m³ based on the organic polymer binder layer formed on the first porous inorganic heat-resistant layer. 2 1.13 g / m 2 and 1.1 g / m 2 .

[0115] Comparative Example 1

[0116] The lithium secondary battery was manufactured using the same method as in Example 1, except that only plate-shaped inorganic particles were used instead of both plate-shaped and needle-shaped inorganic particles.

[0117] Comparative Example 2

[0118] The lithium secondary battery was manufactured using the same method as in Example 1, except that chitosan was used instead of gelatin resin.

[0119] Measurement of air permeability of composite partition

[0120] The air permeability of the partitions obtained in each embodiment and each comparative embodiment was measured using an Asahi-seco EG01-55-1MR air permeability tester.

[0121] Measurement of adhesion strength relative to the electrode

[0122] Dry adhesion strength and wet adhesion strength were evaluated using each prepared sample, and the results are summarized in Table 1 below. Samples used for measuring dry adhesion strength were those before electrolyte injection.

[0123] After preparation, each sample was left uncontacted at room temperature for 1 hour, and the adhesion strength was measured. The adhesion strength was measured using a tensile testing machine (UTM) by peeling at a 180° angle for dry adhesion strength and peeling at a 90° angle for wet adhesion strength.

[0124] Coverage measurement

[0125] For each partition obtained in the examples and comparative examples, the coverage area of ​​the organic polymer adhesive layer on the surface of the porous inorganic heat-resistant layer was measured by SEM images.

[0126] Table 1

[0127]

[0128] As can be seen from Table 1 above, the composite partitions of Examples 1-4 of this disclosure have good air permeability and adhesion strength. However, the composite partition of Comparative Example 1, which has a porous inorganic heat-resistant layer using individual plate-shaped inorganic particles, has low air permeability, and the composite partition of Comparative Example 2, which has an organic polymer adhesive layer using chitosan, has low adhesion strength.

[0129] <List of reference numerals>

[0130] 1: Porous organic polymer substrate

[0131] 3a: First porous inorganic heat-resistant layer; 3b: Second porous inorganic heat-resistant layer

[0132] 3: Porous inorganic heat-resistant layer

[0133] 5a: First organic polymer adhesive layer; 5b: Second organic polymer adhesive layer

[0134] 5a-1: Multiple first organic polymer adhesive layers, 5: Organic polymer adhesive layer

[0135] 10: Composite partition

[0136] 20: Negative electrode

[0137] 30: Positive electrode

Claims

1. A composite separator for lithium secondary batteries, the composite separator comprising: Porous organic polymer substrate; A porous inorganic heat-resistant layer coated on at least one surface of the organic polymer substrate, the porous inorganic heat-resistant layer comprising inorganic particles and an organic binder polymer holding the inorganic particles together; and An organic polymer adhesive layer is coated on the outer surface of the porous inorganic heat-resistant layer, the organic polymer adhesive layer comprising an organic binder polymer. The inorganic particles comprise a mixture of particles with different shapes, including i) plate-shaped particles and ii) needle-shaped particles. The plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof. The organic adhesive polymer included in the organic polymer adhesive layer includes gelatin resin.

2. The composite separator for lithium secondary batteries according to claim 1, Wherein the weight mixing ratio of the plate-shaped particles (i) to the needle-shaped particles (ii) is 20 to 80: 80 to 20.

3. The composite separator for lithium secondary batteries according to claim 1, Wherein i) the average particle size (D50) of the plate-shaped particles is 80 nm to 300 nm, and ii) the average length of the needle-shaped particles is 80 nm to 600 nm.

4. The composite separator for lithium secondary batteries according to claim 1, The organic polymer adhesive layer is positioned on the outer surface of the porous inorganic heat-resistant layer in a dispersed state where multiple organic polymer adhesive layers are separated or connected, and covers a portion of the surface of the porous inorganic heat-resistant layer.

5. The composite separator for lithium secondary batteries according to claim 4, The organic polymer adhesive layer comprises a plurality of dispersed organic polymer adhesive layers and covers 10% to 60% of the total surface area of ​​the porous inorganic heat-resistant layer.

6. The composite separator for lithium secondary batteries according to claim 1, The organic polymer adhesive layer is coated on one surface of the porous inorganic heat-resistant layer, and the organic polymer adhesive layer has a loading of 0.5 g / m³. 2 Up to 3.0 g / m 2 .

7. The composite separator for lithium secondary batteries according to claim 1, The porous inorganic heat-resistant layer is coated on one surface of the porous organic polymer substrate, and the thickness of the porous inorganic heat-resistant layer is from 1 μm to 5 μm.

8. The composite separator for lithium secondary batteries according to claim 1, The organic binder polymer included in the porous inorganic heat-resistant layer includes an acrylic polymer.

9. The composite separator for lithium secondary batteries according to claim 8, The acrylic polymer thereon is non-particulate.

10. The composite separator for lithium secondary batteries according to claim 8, The acrylic polymer thereon comprises at least one selected from the group consisting of: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, ethylene glycol methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, allyl methacrylate, and diethylene glycol dimethacrylate.

11. A method for manufacturing a composite separator for a lithium secondary battery according to claim 1, the method comprising the following steps: (S1) An aqueous slurry is coated onto at least one surface of a porous organic polymer substrate and dried to form a porous inorganic heat-resistant layer, the aqueous slurry containing i) plate-shaped particles, ii) needle-shaped particles, and iii) an organic binder polymer, wherein the plate-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof, and the needle-shaped particles include alumina particles, aluminum hydroxide particles, or mixtures thereof; and (S2) Spray a solution of gelatin resin dissolved in an aqueous solvent onto the outer surface of the porous inorganic heat-resistant layer and dry the solution.

12. A lithium secondary battery, comprising a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. The partition is a composite partition as defined in any one of claims 1 to 10.

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