Composite separator for lithium secondary battery containing organic polymer adhesive layer, manufacturing method thereof, and lithium secondary battery having same

Abstract

A composite separator for a lithium secondary battery, according to one aspect of the present invention, comprises: a porous organic polymer substrate; a porous inorganic heat-resistant layer coated on at least one surface of the organic polymer substrate and including inorganic particles and an organic binder polymer for binding the inorganic particles to each other; and an organic polymer adhesive layer coated on the outer surface of the porous inorganic heat-resistant layer and including an organic binder polymer, wherein: the inorganic particles are a mixture of irregularly shaped particles having mixed therein i) plate-shaped particles, which are aluminum oxide particles, aluminum hydroxide particles, or mixtures thereof and ii) needle-shaped particles, which are aluminum oxide particles, aluminum hydroxide particles, or mixtures thereof; and the organic binder polymer included in the organic polymer adhesive layer includes a gelatin resin.

Description

A composite separator for a lithium secondary battery comprising an organic polymer adhesive layer, a method for manufacturing the same, and a lithium secondary battery having the same

[0001] The present invention relates to a lithium secondary battery having a composite separator having an inorganic heat-resistant layer and an organic polymer adhesive layer sequentially provided on the surface of a porous organic polymer substrate.

[0002] This application is a priority claim application for Korean Patent Application No. 10-2024-0143089 filed on October 18, 2024, and all contents disclosed in the specification of said application are incorporated into this application by reference.

[0003] Lithium-ion batteries are energy storage devices with high energy density that can be charged and discharged by reversibly converting chemical and electrical energy, typically composed of a cathode, separator, anode, and electrolyte. They are widely used in small electronic devices such as mobile phones and laptops. Recently, in response to environmental issues, high oil prices, and the need for energy efficiency and storage, their applications are rapidly expanding into hybrid electric vehicles (HEVs), plug-in electric vehicles (Plug-in EVs), e-bikes, and energy storage systems (ESS).

[0004] Ensuring safety in the manufacturing and use of such lithium secondary batteries is a critical challenge. In particular, separators made of commonly used porous organic polymer substrates exhibit extreme thermal shrinkage behavior under conditions such as high temperatures due to their material and manufacturing process characteristics, leading to safety issues such as internal short circuits. Accordingly, to ensure the safety of lithium secondary batteries, a separator has been developed that forms an inorganic heat-resistant layer by coating a mixture of inorganic particles and an organic binder polymer that binds them together onto an organic porous polymer substrate. Specifically, for purposes such as resistance reduction, the organic binder polymer in the inorganic heat-resistant layer is formed by dispersing the inorganic particles and the organic binder polymer particles in water (a non-solvent) to maintain their particle shape, and then coating and drying this mixture onto the porous organic polymer substrate.

[0005] When a composite separator equipped with such an inorganic heat-resistant layer is laminated with the anode and cathode to form an electrode assembly, the interlayer adhesion may be insufficient, leading to separation. If the electrode and separator separate, problems arise where the cell bends or becomes distorted due to the volume expansion or contraction of the electrode during the charging and discharging process. This problem is exacerbated in pouch-type batteries and becomes more severe when increasing the number of stacks or manufacturing them in a long cell shape.

[0006] Accordingly, to improve the adhesion between the electrode and the composite separator, a composite separator coated with a vinylidene fluoride-based polymer binder or an acrylic-based polymer binder on the surface of an inorganic heat-resistant layer has been proposed. However, there is a need to develop an environmentally friendly organic polymer adhesive layer that is good at adhesion to the electrode while also improving environmental conditions.

[0007] Meanwhile, thinning of the inorganic heat-resistant layer is required to increase the energy density of lithium secondary batteries.

[0008] The first objective of the present invention is to provide a composite separator for a lithium secondary battery having a composite separator having an inorganic heat-resistant layer and an organic polymer adhesive layer sequentially provided on the surface of a porous organic polymer substrate, wherein the inorganic heat-resistant layer can be made into a thin film and the organic polymer adhesive layer is environmentally friendly while having good adhesion to the electrode.

[0009] In addition, the second objective of the present invention is to provide a lithium secondary battery equipped with a composite separator having the aforementioned characteristics.

[0010] Other objects and advantages of the present invention will be understood from the following description. Meanwhile, it will be readily apparent that the objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof.

[0011] A composite separator for a lithium secondary battery according to the first aspect of the present invention is,

[0012] porous organic polymer substrate,

[0013] A porous inorganic heat-resistant layer comprising an organic binder polymer that binds inorganic particles to each other and is coated on at least one surface of the above-mentioned organic polymer substrate.

[0014] The above-mentioned porous inorganic heat-resistant layer is coated on the outer surface and comprises an organic polymer adhesive layer containing an organic binder polymer, and

[0015] The above inorganic particles are a mixture of heterogeneous particles comprising i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof.

[0016] The organic binder polymer included in the above organic polymer adhesive layer includes gelatin resin.

[0017] The second aspect of the present invention is, in the first aspect,

[0018] The above-mentioned mixing weight ratio of i) plate-shaped particles and ii) needle-shaped particles is 20 to 80 : 80 to 20.

[0019] A third aspect of the present invention is, in the first or second aspect,

[0020] The above i) average particle size (D50) of the plate-shaped particles is 80 to 300 nm, and the above ii) average length of the needle-shaped particles is 80 to 600 nm.

[0021] The fourth aspect of the present invention is, in any one of the first to third aspects,

[0022] The above organic polymer adhesive layer consists of a plurality of dispersed organic polymer adhesive layers arranged on the outer surface of the porous inorganic heat-resistant layer in a state where they are separated or connected to each other, covering only a portion of the surface of the porous inorganic heat-resistant layer.

[0023] The fifth aspect of the present invention is, in the fourth aspect,

[0024] The above organic polymer adhesive layer covers a dispersed portion of 10 to 60% of the total surface area of ​​the porous inorganic heat-resistant layer.

[0025] The sixth aspect of the present invention is, in any one of the first to fifth aspects,

[0026] The loading amount of the organic polymer adhesive layer is 0.5 to 3.0 g / m² based on the organic polymer adhesive layer coated on one surface of the porous inorganic heat-resistant layer. 2 am.

[0027] The seventh aspect of the present invention is, in any one of the first to sixth aspects,

[0028] The thickness of the porous inorganic heat-resistant layer is 1 to 5 μm based on the porous inorganic heat-resistant layer coated on one side of the porous organic polymer substrate.

[0029] The eighth aspect of the present invention is, in any one of the first to seventh aspects,

[0030] The organic binder polymer included in the above porous inorganic heat-resistant layer includes an acrylic polymer.

[0031] The ninth aspect of the present invention is, in the eighth aspect,

[0032] The above acrylic polymer is of a non-particulate form.

[0033] The tenth aspect of the present invention is, in the eighth or ninth aspect,

[0034] The above acrylic polymer is (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate n-propyl, (meth)acrylate i-propyl, (meth)acrylate n-butyl, (meth)acrylate i-butyl, (meth)acrylate n-amyl, (meth)acrylate i-amyl, (meth)acrylate hexyl, (meth)acrylate cyclohexyl, (meth)acrylate 2-ethylhexyl, (meth)acrylate n-octyl, (meth)acrylate nonyl, (meth)acrylate decyl, (meth)acrylate hydroxymethyl, (meth)acrylate hydroxyethyl, (meth)acrylate ethylene glycol, di(meth)acrylate ethylene glycol, di(meth)acrylate propylene glycol, tri(meth)acrylate trimethylolpropane, It is one or more selected from the group consisting of tetra(meth)acrylate pentaerythritol, hexa(meth)acrylate dipentaerythritol, allyl (meth)acrylate, and ethylene di(meth)acrylate.

[0035] The eleventh aspect of the present invention relates to a method for manufacturing a composite separator for a lithium secondary battery, wherein

[0036] (S1) forming a porous inorganic heat-resistant layer by coating and drying an aqueous slurry comprising i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and iii) an organic binder polymer on at least one surface of a porous organic polymer substrate; and;

[0037] (S2) Includes the step of spraying a solution of gelatin resin dissolved in an aqueous solvent onto the outer surface of the porous inorganic heat-resistant layer and drying it.

[0038] The 12th aspect of the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein

[0039] The above-mentioned separator is a composite separator according to any one of the first to ten sides.

[0040] The composite separation membrane according to the present invention utilizes a mixture of heterogeneous particles as inorganic particles of the porous inorganic heat-resistant layer, comprising i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof. Accordingly, the inorganic heat-resistant layer can be made thin, and the porosity of the inorganic heat-resistant layer can be maintained well.

[0041] In addition, the composite separator according to the present invention maintains good adhesion to the electrode and improves eco-friendliness by utilizing gelatin resin, a natural material, as an organic polymer adhesive layer. This organic polymer adhesive layer can be disposed on the outer surface of the porous inorganic heat-resistant layer in a state where a plurality of dispersed organic polymer adhesive layers are separated or connected to each other. Accordingly, by covering only a part rather than the entire surface of the porous inorganic heat-resistant layer, the phenomenon of increased resistance due to the formation of the adhesive layer can be improved.

[0042] The attached drawings illustrate preferred embodiments of the invention and explain the principles of the invention together with the detailed description, but the scope of the invention is not limited thereto. Meanwhile, the shapes, sizes, scales, or proportions of elements in the drawings included in this specification may be exaggerated to emphasize clearer explanations.

[0043] FIG. 1 is a cross-sectional view schematically illustrating a cross-section of a lithium secondary battery having a composite separator according to one embodiment of the present invention.

[0044] Figure 2 is a schematic plan view illustrating the surface of the first organic polymer adhesive layer of Figure 1.

[0045] Terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely one preferred embodiment of the invention and do not represent all of the technical spirit of the invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0046] <Definition>

[0047] In the present specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0048] D in the present specification 50represents the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. The above particle size is measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to calculate the particle size distribution by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam. By calculating the particle diameter at the point where the cumulative distribution of particle numbers according to particle size in the measuring device reaches 50%, D 50 Measures.

[0049] In the present specification, the average length of the needle-shaped particles is determined by collecting 100 of the needle-shaped particles used and measuring their average length.

[0050] In the present specification, plate-shaped particles refer to plate-shaped particles commercially available as plate alumina, etc., which have a shape having a long length and width relative to their thickness.

[0051] In the present specification, needle-shaped particles refer to needle-shaped particles commercially available as needle-shaped alumina, etc., which have a shape having a long length relative to their diameter.

[0052] In this specification, the aspect ratio of needle-shaped particles refers to the length / diameter of the needle-shaped particles.

[0053] In the present specification, the term "particle form" for an organic binder polymer, such as an acrylic polymer or a vinylidene fluoride polymer, means that the organic binder polymer in the form of particles is added to a dispersion medium to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer, and that the organic binder polymer within the coating layer formed by coating and drying maintains the added particle form. Additionally, the term "non-particle form" in the present specification means that the organic binder polymer in the form of particles is added to a solvent to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer, and then dissolves in the solvent and loses its particle form, or is added to a dispersion medium and, even if it does not dissolve, loses its particle form and deforms into a film-like form during the drying process when forming the coating layer.

[0054]

[0055] FIG. 1 schematically illustrates a cross-section of a composite separator and a lithium secondary battery equipped with the same according to a specific embodiment of the present invention. For convenience of explanation, the negative electrode (20) and the positive electrode (30) in FIG. 1 are shown as being spaced apart from the composite separator (10), but in an actual lithium secondary battery, the negative electrode (20), the composite separator (10), and the positive electrode (30) are in close contact with each other. Additionally, the composite separator (10) of FIG. 1 is illustrated in an embodiment in which the first inorganic heat-resistant layer (3a) and the second inorganic heat-resistant layer (3b) and the first organic polymer adhesive layer (5a) and the second organic polymer adhesive layer (5b) are formed on both sides of the porous organic polymer substrate (1), respectively. However, it is also possible to form only the first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) facing the cathode (20) without forming the second inorganic heat-resistant layer (3b) and the second organic polymer adhesive layer (5b) facing the anode (30).

[0056] Referring to FIG. 1, a composite separator (10) according to one aspect of the present invention is coated on both sides of an organic polymer substrate (1) and comprises a first porous inorganic heat-resistant layer (3a) and a first porous inorganic heat-resistant layer (3a), which is a porous inorganic heat-resistant layer (3) comprising inorganic particles and an organic binder polymer that binds the inorganic particles together. Additionally, it comprises a first organic polymer adhesive layer (5a) and a second organic polymer adhesive layer (5b) which are coated on the outer surfaces of the first porous inorganic heat-resistant layer (3a) and the first porous inorganic heat-resistant layer (3a), respectively, and which comprise a gelatin resin.

[0057] When an inorganic heat-resistant layer (3) and an organic polymer adhesive layer (5) are formed on only one side of a porous organic polymer substrate (1), the second inorganic heat-resistant layer (3b) and the second organic polymer adhesive layer (5b) facing the anode (30) may not be formed, and only the first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) facing the cathode (20) may be formed, or the first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) facing the cathode (20) may not be formed, and only the second inorganic heat-resistant layer (3b) and the second organic polymer adhesive layer (5b) facing the anode (30) may be formed.

[0058] The inorganic particles of the porous inorganic heat-resistant layer (3) are a mixture of i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof. Accordingly, the inorganic heat-resistant layer can be made thinner compared to a porous inorganic heat-resistant layer using, for example, spherical alumina particles, and the porosity of the inorganic heat-resistant layer can be maintained better than when only plate-shaped particles are used due to the mixing of needle-shaped particles.

[0059] In addition, the first organic polymer adhesive layer (5a) and the second organic polymer adhesive layer (5b), which are respectively coated on the outer surface of the first porous inorganic heat-resistant layer (3a) and the first porous inorganic heat-resistant layer (3a), contain gelatin resin, which is a natural material, thereby maintaining good adhesion to the electrode and improving eco-friendliness.

[0060] Hereinafter, each component constituting the composite separator of the present invention and the lithium secondary battery equipped with the same will be described in more detail.

[0061]

[0062] porous organic polymer substrate

[0063] According to a specific embodiment of the present invention, the porous organic polymer substrate (1) can provide a path for the movement of lithium ions while electrically insulating the negative electrode and the positive electrode to prevent short circuits, and can be used without special limitations as long as it is capable of being used as an organic polymer separator substrate for a lithium secondary battery. As such a separator substrate, for example, a porous organic polymer film or an organic polymer nonwoven fabric comprising one or more of the following polymer resins may be used: polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

[0064] In the present invention, the thickness of the organic polymer substrate may be 3 μm to 50 μm. Although the range of the organic polymer substrate is not specifically limited to the aforementioned range, if the thickness is excessively thin compared to the aforementioned lower limit, the mechanical properties may deteriorate, and the separator may be easily damaged during battery use. Meanwhile, the pore size and porosity present in the organic polymer substrate are also not specifically limited, but may be 0.01 μm to 50 μm and 10 vol% to 95 vol%, respectively.

[0065]

[0066] porous inorganic heat-resistant layer

[0067] Referring to FIG. 1, the first porous inorganic heat-resistant layer (3a) comprises a plurality of inorganic particles and an organic binder polymer that binds the inorganic particles together, as is well known. By coating the organic polymer substrate (1) with the porous inorganic heat-resistant layer (3a) containing the inorganic particles in this way, the heat resistance and mechanical properties of the composite separation membrane (10) are improved.

[0068] The inorganic particles constituting the porous inorganic heat-resistant layer (3a) exist in a state where they are substantially packed together, thereby acting as a kind of spacer that maintains its physical shape even when the battery overheats, and thus the thermal shrinkage phenomenon of the separator is improved. An organic binder polymer is interposed between the inorganic particles to bind the inorganic particles together.

[0069] The inorganic particles included in the inorganic heat-resistant layer (3a) are a mixture of i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof.

[0070] Accordingly, for example, compared to a porous inorganic heat-resistant layer using spherical alumina particles, it is possible to thin the inorganic heat-resistant layer; and since needle-shaped particles are interposed between plate-shaped particles due to the mixing of needle-shaped particles, the porosity of the inorganic heat-resistant layer can be maintained well compared to using only plate-shaped particles. In this regard, the mixing weight ratio of i) plate-shaped particles and ii) needle-shaped particles may be 20 to 80:80 to 20, and more specifically, 40 to 60:60 to 40. Preferably, it is more desirable for the amount of needle-shaped particles added to be greater than the amount of plate-shaped particles added in terms of securing porosity.

[0071] The plate-shaped particles and needle-shaped particles added as inorganic particles constituting the porous inorganic heat-resistant layer (3a) are each independently aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof. Examples of such particles include Al2O3, AlO(OH), Al(OH)3, etc.

[0072] Since these aluminum oxide particles or aluminum hydroxide particles generally do not change their physical properties even when heated to a high temperature of 200°C or higher, the composite separator (10) has excellent heat resistance due to the porous inorganic heat-resistant layers (3a, 3b). In the present invention, the first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b) may each have a thickness of 1 to 5 μm based on the porous inorganic heat-resistant layer coated on one side of the porous organic polymer substrate, and more preferably 2 to 4 μm.

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

[0074] Both non-particle and particle organic binder polymers can be used as the organic binder polymer included in the porous inorganic heat-resistant layer (3) and binding the inorganic particles together.

[0075] Examples of non-particle organic binder polymers include acrylic polymers with a Tg of room temperature or lower. Acrylic polymers with a Tg of room temperature (25°C) or lower are introduced into a dispersion medium along with inorganic particles to form a slurry, and then, during a coating process at room temperature or higher, they lose their shape at the time of introduction and change into a film shape.

[0076] As for the acrylic polymer, more specifically, it may be a polymer containing a carboxylic acid ester as a repeating unit, preferably a (meth)acrylic acid ester. Specific examples of such (meth)acrylic acid esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, di(meth)acrylate ethylene glycol, di(meth)acrylate propylene glycol. Examples include tri(meth)acrylate trimethylolpropane, tetra(meth)acrylate pentaerythritol, hexa(meth)acrylate dipentaerythritol, allyl (meth)acrylate, ethylene di(meth)acrylate, etc., and one or more selected from these may be used. Among these, in particular, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate may be used. The acrylic polymer may have a glass transition temperature (Tg) of 40°C or lower, but is not limited thereto.

[0077] Additionally, as a non-particle organic binder polymer, vinylidene fluoride-based polymers, such as polyvinylidene fluoride-co-hexafluoropropylene and polyvinylidene fluoride-co-trichloroethylene, may be used individually or in a mixture of two or more of these, but are not limited thereto. The first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b) using a non-particle organic binder polymer can be prepared by dispersing inorganic particles in a solvent such as acetone and then adding and dissolving a non-particle organic binder in the solvent to prepare a slurry, or by adding a particle organic binder with a Tg of room temperature (25°C) or lower to a dispersion medium together with inorganic particles to prepare a slurry, and then coating the mixture onto a porous organic polymer substrate (1) by a method such as dip coating.

[0078] In the porous inorganic heat-resistant layer (3), as the organic binder polymer that binds the inorganic particles together, it may be preferred to use an organic binder polymer in the form of a slurry in which the organic binder polymer is dispersed in a dispersion medium in terms of reducing the resistance of the inorganic heat-resistant layer.

[0079] As the particulate organic binder polymer, known particulate organic binder polymers used in organic polymer adhesive layers may be used, for example, particles of vinylidene fluoride-based polymers may be used. The vinylidene fluoride-based polymer may be an electrolyte-insoluble homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride with other polymerizable monomers, or a mixture of two or more of these. Examples of vinylidene fluoride and other polymerizable monomers may include, but are not limited to, one or more selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methylvinyl)ether, perfluoro(ethylvinyl)ether, perfluoro(propylvinyl)ether, perfluoro(1,3-dioxol), perfluoro(2,2-dimethyl-1,3-dioxol), and trichloroethylene. In particular, the vinylidene fluoride-based polymer may be a copolymer of vinylidene fluoride and hexafluoropropylene. The content of vinylidene fluoride and other polymerizable monomers may be 1 to 20 weight percent of the copolymer, but is not limited thereto.

[0080] Average particle size (D of particulate organic binder polymer) 50 ) is not particularly limited, but may be, for example, 100 to 1000 nm, more specifically 200 to 600 nm. When an acrylic polymer is used as the particulate organic binder polymer, the average particle size (D 50 ) is not particularly limited, but can be, for example, 100 to 500 nm, more specifically 100 to 300 nm.

[0081] In the porous inorganic heat-resistant layer (3), the content ratio of inorganic particles and organic binder polymer is determined by considering the thickness, pore size, and porosity of the inorganic heat-resistant layer to be finally manufactured, and the inorganic particles may be included in a range of 70% to 99% by weight relative to 100% by weight of the inorganic heat-resistant layer based on weight ratio.

[0082] A porous inorganic heat-resistant layer (3) using a particulate organic binder polymer can be manufactured by dispersing inorganic particles in an aqueous dispersion medium, then introducing and dispersing a particulate organic binder polymer into the aqueous dispersion medium to prepare a slurry, and then coating and drying the slurry on a porous organic polymer substrate (1) by a method such as dip coating. The aqueous dispersion medium may include one or more of water and alcohols having 1 to 5 carbon atoms. By using an aqueous dispersion medium, the particles of the organic binder polymer are not dissolved in the dispersion medium but are dispersed within the aqueous dispersion medium while maintaining their particle shape, and the particle shape is maintained even after coating and drying the slurry on a porous organic polymer substrate (1).

[0083]

[0084] Organic polymer adhesive layer

[0085] 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) include gelatin resin.

[0086] As described above, the organic polymer adhesive layer (5) coated on the outer surface of the porous inorganic heat-resistant layer (3) contains gelatin resin, which is a natural material, thereby maintaining good adhesion to the electrode and improving eco-friendliness. When considering both adhesion to the electrode and air permeability, the loading amount of the organic polymer adhesive layer (5) is 0.5 to 3.0 g / m² based on the organic polymer adhesive layers (5a, 5b) coated on one side of the porous inorganic heat-resistant layer (3). 2It may be, more specifically, 0.7 to 2.0 g / m 2 It can be, most specifically 0.8 to 1.3 g / m² 2 It could be.

[0087] If necessary, the organic binder polymer included in the organic polymer adhesive layer (5) may further include one or more types such as carboxymethylcellulose (CMC), polyarylamine hydrochloride, etc., but is not limited thereto.

[0088] FIG. 2 is a schematic plan view illustrating the surface of the first organic polymer adhesive layer (5a) of FIG. 1.

[0089] Referring to FIG. 2, when a slurry for forming the first organic polymer adhesive layer (5a) is coated onto the porous inorganic heat-resistant layer (3a) and then dried, a plurality of dispersed first organic polymer adhesive layers (5a-1) may be disposed on the outer surface of the first porous inorganic heat-resistant layer (3a) in a state where they are separated or connected to each other due to aggregation. At this time, for example, the first organic polymer adhesive layer (5a) may cover 10 to 60%, more specifically 20 to 40%, of the total surface area of ​​the first porous inorganic heat-resistant layer (3a). By covering only a part, rather than the entire surface of the first porous inorganic heat-resistant layer (3a), the phenomenon of increased resistance due to the formation of the adhesive layer can be improved.

[0090]

[0091] Method for manufacturing a composite separation membrane

[0092] The aforementioned composite separation membrane can be manufactured by a manufacturing method according to one embodiment of the present invention below, but is not limited thereto.

[0093] First, a porous inorganic heat-resistant layer is formed by coating and drying an aqueous slurry comprising i) plate-shaped particles, which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, ii) needle-shaped particles, which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and iii) an organic binder polymer on at least one surface of a porous organic polymer substrate (Step S1).

[0094] One or more of water and alcohols having 1 to 5 carbon atoms may be included as dispersion media for preparing an aqueous slurry. By using an aqueous dispersion media, the organic binder polymer is not dissolved in the dispersion media. In the aqueous dispersion media, depending on the type and Tg of the organic binder polymer, the organic binder polymer is dispersed while maintaining the shape of the particles initially added in the aqueous dispersion media, or loses the shape of the particles initially added and becomes non-particle in the form of a film.

[0095] Next, a solution in which gelatin resin is dissolved in an aqueous solvent is sprayed onto the outer surface of the porous inorganic heat-resistant layer and dried (Step S2).

[0096] The gelatin resin completely dissolves when, for example, it is added to water and heated to a predetermined temperature, for example, 60°C or higher. The aforementioned composite separation membrane can be manufactured by spraying this aqueous solution onto the outer surface of a porous inorganic heat-resistant layer and drying it.

[0097]

[0098] cathode and anode

[0099] In a specific embodiment according to the present invention, the lithium secondary battery may be manufactured according to conventional methods known in the art. According to an embodiment according to the present invention, the battery may be configured by interposing the aforementioned composite separator (10) between the negative electrode (20) and the positive electrode (30).

[0100] That is, the composite separator (10) manufactured by the above-described method is interposed between the cathode (20) and the anode (30) and is manufactured into an electrode assembly by a lamination process in which heat and / or pressure is applied to bond them. In one embodiment of the present invention, the lamination process may be performed by a roll press device comprising a pair of pressure rollers. That is, the cathode, the separator, and the anode may be sequentially stacked and placed between the pressure rollers to achieve interlayer bonding. At this time, the lamination process may be performed by a hot pressing method.

[0101] In one embodiment of the present invention, the electrode is not particularly limited and can be manufactured in a form in which the electrode active material is adhered to the electrode current collector according to conventional methods known in the art. Among the electrode active materials, non-limiting examples of the positive electrode active material include conventional positive electrode active materials that can be used in the positive electrode of a conventional lithium secondary battery, and in particular, lithium intercalation materials such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or composite oxides formed by a combination thereof are preferred. Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used in the negative electrode of a conventional lithium secondary battery, and in particular, lithium intercalation materials such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons are preferred. Non-limiting examples of positive current collectors include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative current collectors include foils made of copper, gold, nickel, or copper alloys or combinations thereof.

[0102]

[0103] electrolytes

[0104] A lithium secondary battery is manufactured by loading an electrode assembly, in which a negative electrode, a separator, and a positive electrode are stacked and assembled, into a battery case, injecting an electrolyte, and undergoing an activation process. The electrolyte that can be used in the present invention is A + B - As a salt with a structure like that, A + is Li + , Na + , K + It includes alkali metal cations such as or ions composed of combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , NCF3SO2)2 - , CCF2SO2)3 - Salts comprising anions such as or combinations thereof are dissolved or dissociated in organic solvents composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or mixtures thereof, but are not limited thereto.

[0105] The injection of the electrolyte can be performed at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly. In addition to the general winding process, the electrode assembly of the present invention can also be applied as a battery through lamination (stacking) and folding processes of the bonded separator and electrode.

[0106] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0107]

[0108] Example 1

[0109] [Manufacturing of Composite Membranes]

[0110] A composite separation membrane (10) of Fig. 1 was manufactured.

[0111] Plate-shaped inorganic particles (Al2O3, D50: 120 nm) 40 parts by weight, needle-shaped inorganic particles (Al2O3, An emulsion containing 60 parts by weight of an 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 to achieve a solid content of 35% by weight. Then, zirconia beads with a particle size of 0.7 mm, equal to the amount of inorganic particles, were added and milled with a bead mill for 2 hours to prepare a slurry. This slurry was dip-coated onto both sides of a porous organic polymer separation membrane substrate made of polyethylene (porosity 45%, thickness 9 μm) and dried to form a first inorganic heat-resistant layer and a second inorganic heat-resistant layer with a thickness of 3 μm on each side.

[0112] Next, gelatin resin was added to water to achieve a solid content of 25 wt%, heated to 80°C, and stirred at 1000 rpm for 10 minutes to prepare a gelatin resin solution. Then, this solution was sprayed onto the surfaces of the first inorganic heat-resistant layer and the second inorganic heat-resistant layer, respectively, and dried to form an organic polymer adhesive layer. The loading amount of the organic polymer adhesive layer was 1.0 g / m² based on the adhesive layer formed on the first inorganic heat-resistant layer. 2 It was.

[0113] [Manufacturing of Lithium Secondary Batteries]

[0114] LiNi 0.8 Co 0.1 Mn 0.1 O2, PVdF, and carbon black were mixed in a weight ratio of 97.0:1.5:1.5 and dispersed in 2-methyl-2-pyrrolidone to prepare an anode slurry, which was then coated onto an aluminum current collector and dried and rolled to produce an anode.

[0115] A cathode slurry was prepared by mixing graphite, SBR, and CMC in a weight ratio of 89.2:10:0.8 and dispersing it in distilled water, and the slurry was coated onto a copper current collector, followed by drying and rolling to produce a cathode.

[0116] A monocell specimen was fabricated by interposing the above-mentioned composite separator between the anode and the cathode, laminating them using a hot press, and then laminating. At this time, the pressure was applied at 70°C and 5 kgf for 5 minutes. The size of the specimen was 2 cm x 6 cm.

[0117] After loading the above specimen into a pouch-type case, 1.0 g of electrolyte (ethylene carbonate:ethyl methyl carbonate = 7:3, content ratio, LiPF6 1M) was injected to manufacture a secondary battery, which was then left at room temperature for 3 hours. Subsequently, the secondary battery was heated at 55°C for 5 minutes at 6 kgf / cm² 2 Pressurized to a pressure of 6 kgf / cm² at 55℃. 2The battery was charged to SOC3 with a current of 0.2C under pressurized conditions, and then charged to SOC60 with a current of 1C. Once charging was complete, the pressure was released, and the battery was aged for one day at 55℃.

[0118] Examples 2~4

[0119] The loading amounts of the organic polymer adhesive layer of Example 1 were 1.2, 1.13, and 1.1 g / m², respectively, based on the adhesive layer formed on the first inorganic heat-resistant layer. 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that it was changed to [the desired form].

[0120] Comparative Example 1

[0121] A lithium secondary battery was manufactured in the same manner as in Example 1, except that all plate-shaped inorganic particles were used instead of using plate-shaped inorganic particles and needle-shaped inorganic particles in combination.

[0122] Comparative Example 2

[0123] A lithium secondary battery was manufactured in the same manner as in Example 1, except that chitosan was used instead of gelatin resin.

[0124]

[0125] Measurement of the air permeability of composite membranes

[0126] For the membranes obtained in each example and comparative example, the air permeability was measured using an Asahi Seico EG01-55-1MR air permeability tester.

[0127] Measurement of adhesion to electrodes

[0128] Dry adhesion and wet adhesion were evaluated using each specimen prepared above, and the results are summarized in Table 1 below. Specimens prior to electrolyte injection were used for dry adhesion measurement.

[0129] After preparing each specimen, the adhesion strength was measured after leaving it at room temperature for 1 hour. Adhesion strength was measured using a tensile testing machine (UTM equipment) by peeling at an angle of 180° for dry adhesion and 90° for wet adhesion.

[0130] Measurement of coverage

[0131] For the separation membranes obtained in each example and comparative example, the area covered by the organic polymer adhesive layer on the surface of the inorganic heat-resistant layer was measured using SEM images.

[0132] Coverage (%) Air Permeability (sec / 100 sec) Dry Adhesion / Wet Adhesion (gf / 20mm) Example 1 30 170 30 / 20 Example 2 35 180 35 / 25 Example 3 33 177 33 / 24 Example 4 32 175 31 / 22 Comparative Example 1 32 22 30 / 21 Comparative Example 2 33 178 25 / 10

[0133] As can be seen in Table 1 above, the composite separator membranes of Examples 1-4 according to the present invention have good air permeability and adhesion, but the composite separator membrane of Comparative Example 1, which has a porous inorganic heat-resistant layer using only plate-shaped inorganic particles, had relatively low air permeability, and the composite separator membrane of Comparative Example 2, which has an organic polymer adhesive layer formed using chitosan, had relatively low adhesion.

[0134]

[0135] <Explanation of Symbols>

[0136] 1: Porous organic polymer substrate

[0137] 3a: First porous inorganic heat-resistant layer, 3b: Second porous inorganic heat-resistant layer

[0138] 3: Porous inorganic heat-resistant layer

[0139] 5a: First organic polymer adhesive layer, 5b: Second organic polymer adhesive layer

[0140] 5a-1: Multiple first organic polymer adhesive layers, 5: Organic polymer adhesive layer

[0141] 10: Composite membrane

[0142] 20: Cathode

[0143] 30: Anode

Claims

1. Porous organic polymer substrate, A porous inorganic heat-resistant layer comprising an organic binder polymer that binds inorganic particles to each other and is coated on at least one surface of the above-mentioned organic polymer substrate. The above-mentioned porous inorganic heat-resistant layer is coated on the outer surface and comprises an organic polymer adhesive layer containing an organic binder polymer, and The above inorganic particles are a mixture of heterogeneous particles comprising i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof. The organic binder polymer included in the above organic polymer adhesive layer comprises a gelatin resin. Composite separator for lithium secondary batteries.

2. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the mixing weight ratio of i) plate-shaped particles and ii) needle-shaped particles is 20 to 80 : 80 to 20.

3. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that i) the average particle size (D50) of the plate-shaped particles is 80 to 300 nm, and ii) the average length of the needle-shaped particles is 80 to 600 nm.

4. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the above organic polymer adhesive layer comprises a plurality of dispersed organic polymer adhesive layers arranged on the outer surface of the porous inorganic heat-resistant layer in a state separated or connected to each other, thereby covering only a portion of the surface of the porous inorganic heat-resistant layer.

5. In Paragraph 4, A composite separator for a lithium secondary battery, characterized in that the organic polymer adhesive layer covers a plurality of dispersed portions of 10 to 60% of the total surface area of ​​the porous inorganic heat-resistant layer.

6. In Paragraph 1, The loading amount of the organic polymer adhesive layer is 0.5 to 3.0 g / m² based on the organic polymer adhesive layer coated on one surface of the porous inorganic heat-resistant layer. 2 A composite separator for a lithium secondary battery characterized by being.

7. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the thickness of the porous inorganic heat-resistant layer is 1 to 5 μm based on the porous inorganic heat-resistant layer coated on one surface of the porous organic polymer substrate.

8. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the organic binder polymer included in the porous inorganic heat-resistant layer includes an acrylic polymer.

9. In Paragraph 8, A composite separator for a lithium secondary battery characterized by the above acrylic polymer being of a non-particulate type.

10. In Paragraph 8, The above acrylic polymer is (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate n-propyl, (meth)acrylate i-propyl, (meth)acrylate n-butyl, (meth)acrylate i-butyl, (meth)acrylate n-amyl, (meth)acrylate i-amyl, (meth)acrylate hexyl, (meth)acrylate cyclohexyl, (meth)acrylate 2-ethylhexyl, (meth)acrylate n-octyl, (meth)acrylate nonyl, (meth)acrylate decyl, (meth)acrylate hydroxymethyl, (meth)acrylate hydroxyethyl, (meth)acrylate ethylene glycol, di(meth)acrylate ethylene glycol, di(meth)acrylate propylene glycol, tri(meth)acrylate trimethylolpropane, A composite separator for a lithium secondary battery characterized by being one or more selected from the group consisting of tetra(meth)acrylate pentaerythritol, hexa(meth)acrylate dipentaerythritol, allyl (meth)acrylate, and ethylene di(meth)acrylate.

11. (S1) A step of forming a porous inorganic heat-resistant layer by coating and drying an aqueous slurry comprising i) plate-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, ii) needle-shaped particles which are aluminum oxide particles, aluminum hydroxide particles, or a mixture thereof, and iii) an organic binder polymer on at least one surface of a porous organic polymer substrate; and; (S2) A method for manufacturing a composite separator for a lithium secondary battery according to claim 1, comprising the step of spraying a solution in which gelatin resin is dissolved in an aqueous solvent onto the outer surface of the porous inorganic heat-resistant layer and drying it.

12. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, A lithium secondary battery characterized in that the above-mentioned separator is a composite separator according to any one of claims 1 to 10.

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