Composite separator for lithium secondary battery, comprising organic polymer adhesive layer, and lithium secondary battery including 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 that binds the inorganic particles to each other; and an organic polymer adhesive layer coated on an outer surface of the porous inorganic heat-resistant layer and including a vinylidene fluoride–based polymer, wherein the organic polymer adhesive layer further includes a compound having an ethylene oxide repeating unit and a double bond at the terminal end thereof.

Description

Composite separator for a lithium secondary battery comprising an organic polymer adhesive layer 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. 10-2024-0129852 filed on September 25, 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, conventional separators made of porous organic polymer substrates exhibit extreme thermal shrinkage behavior under conditions such as high temperatures due to their material properties 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 in which an inorganic heat-resistant layer is formed by coating a mixture of inorganic particles and an organic binder polymer that binds the inorganic particles together onto an organic porous polymer substrate.

[0005] In particular, for purposes such as reducing resistance, an inorganic heat-resistant layer is formed by dispersing inorganic particles and particulate organic binder polymers in water, a non-solvent, so that the particle shape is maintained, and then coating / drying this onto a porous organic polymer substrate.

[0006] However, after manufacturing an electrode assembly by laminating this type of composite separator with an electrode and injecting and activating the electrolyte, the interlayer adhesion (i.e., wet adhesion) between the electrode and the composite separator may be insufficient, leading to separation. If the electrode and separator separate, problems arise where the cell bends or becomes distorted due to the expansion and contraction of the electrode during the charge-discharge 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.

[0007] A method has been proposed to further form an organic polymer adhesive layer using a vinylidene fluoride-based polymer on an inorganic heat-resistant layer to improve the wet adhesion between the aforementioned composite separator and the electrode, and there is a need to develop a composite separator equipped with an organic polymer adhesive layer that can more effectively improve wet adhesion.

[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 adhesion to the negative electrode is improved in a wet state after the injection of an electrolyte and activation process.

[0009] In addition, the second objective of the present invention is to provide a composite separator for a lithium secondary battery that has good adhesion to the negative electrode in a dry state before the injection of the electrolyte, in addition to the first objective described above.

[0010] In addition, the third objective of the present invention is to provide a lithium secondary battery equipped with a composite separator having the aforementioned characteristics.

[0011] 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.

[0012] A composite separator for a lithium secondary battery according to the first aspect of the present invention is,

[0013] porous organic polymer substrate,

[0014] 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.

[0015] The above-mentioned porous inorganic heat-resistant layer is coated on the outer surface and comprises an organic polymer adhesive layer containing a vinylidene fluoride-based polymer, and

[0016] The above organic polymer adhesive layer further comprises a compound having ethylene oxide repeating units and double bonds at the ends.

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

[0018] The compound having the above-mentioned ethylene oxide repeating unit and a double bond at the end is an acrylic polymer.

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

[0020] The compound having the above-mentioned ethylene oxide repeating unit and having a double bond at the end is one or more selected from the group consisting of poly(ethylene glycol) methyl ether methacrylate, poly(propylene glycol) dimethacrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) diacrylate, and poly(ethylene glycol) dimethacrylate.

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

[0022] The weight ratio of the vinylidene fluoride-based polymer included in the above organic polymer adhesive layer to the compound having ethylene oxide repeating units and double bonds at the ends is 99:1 to 90:10.

[0023] A fifth aspect of the present invention is that, in any one of the first to fourth aspects, the vinylidene fluoride-based polymer included in the organic polymer adhesive layer is in the form of particles.

[0024] The sixth aspect of the present invention is, in any one of the first to fifth aspects,

[0025] The above vinylidene fluoride-based polymer is a vinylidene fluoride-hexafluoropropylene copolymer.

[0026] The seventh aspect of the present invention is, in any one of the first to sixth aspects,

[0027] The organic binder polymer included in the above organic polymer adhesive layer further includes an acrylic polymer.

[0028] The eighth aspect of the present invention is, in the seventh aspect,

[0029] The acrylic polymer included in the above organic polymer adhesive layer is of a non-particulate type.

[0030] The ninth aspect of the present invention is, in the seventh aspect,

[0031] 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.

[0032] The tenth aspect of the present invention is, in any one of the first to ninth aspects,

[0033] The organic binder polymer included in the above porous inorganic heat-resistant layer is of a non-particulate type.

[0034] The eleventh aspect of the present invention is, in any one of the first to ten aspects,

[0035] The organic binder polymer included in the above porous inorganic heat-resistant layer includes an acrylic polymer.

[0036] The 12th aspect of the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein

[0037] The above-mentioned separator is a composite separator according to any one of the first to eleven sides.

[0038] The composite separation membrane according to the present invention sequentially comprises an inorganic heat-resistant layer and an organic polymer adhesive layer on at least one surface of a porous organic polymer substrate, wherein the organic polymer adhesive layer comprises a vinylidene fluoride-based polymer as an organic binder polymer and further comprises a compound having ethylene oxide repeating units and double bonds at the ends.

[0039] The vinylidene fluoride-based polymer included in the organic polymer adhesive layer maintains good dry and wet adhesion of the composite separator to the anode and cathode. In addition, the inorganic particles included in the inorganic heat-resistant layer remain well fixed without detaching, thereby maintaining the structural stability of the composite separator. Furthermore, the compound having ethylene oxide repeating units and double bonds at the ends, included in the organic polymer adhesive layer along with the vinylidene fluoride-based polymer, is presumed to participate in the reaction that forms a negative electrode film (SEI) by being reduced during the battery activation process after electrolyte injection, and consequently, wet adhesion is effectively improved. Moreover, the compound having ethylene oxide repeating units and double bonds at the ends also functions as a dispersant to ensure that the vinylidene fluoride-based polymer is well dispersed when the hydrophobic vinylidene fluoride-based polymer is dispersed in an aqueous dispersion medium such as water to form the organic polymer adhesive layer, thereby further effectively improving wet adhesion.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] <Definition>

[0044] Throughout this 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.

[0045] D in the present specification 50 represents 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 or SEM.

[0046] In the present specification, the term "particle type" for an organic binder polymer, such as a vinylidene fluoride-based polymer or an acrylic-based 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 the organic binder polymer within the coating layer formed by coating and drying maintains the added particle shape. Additionally, the term "non-particle type" in the present specification means that an 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 the added particle shape is lost by dissolving in the solvent, or even if it is not dissolved by adding to a dispersion medium, the added particle shape is lost during the drying process when forming the coating layer and is deformed into a film-like form.

[0047]

[0048] 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 an inorganic heat-resistant layer (3) and an organic polymer adhesive layer (5) are formed on both sides of a porous organic polymer substrate (1), respectively, with a first inorganic heat-resistant layer (3a) and a second inorganic heat-resistant layer (3b) and a first organic polymer adhesive layer (5a) and a second organic polymer adhesive layer (5b). 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 (3).

[0049] Referring to FIG. 1, a composite separator (10) according to one embodiment 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 respectively coated on the outer surfaces of the first porous inorganic heat-resistant layer (3a) and the first porous inorganic heat-resistant layer (3a), and which comprise an organic binder polymer and a compound having a double bond at the end having an ethylene oxide repeating unit.

[0050] In the lithium secondary battery of the present invention, the first organic polymer adhesive layer (5a) faces the negative electrode (20) and the second organic polymer adhesive layer (5b) faces the positive electrode (30), and an electrolyte is injected.

[0051] The organic polymer adhesive layer (5) includes a vinylidene fluoride-based polymer as an organic binder polymer and further includes a compound having a double bond at the end while having an ethylene oxide repeating unit.

[0052] The vinylidene fluoride-based polymer included in the organic polymer adhesive layer (5) maintains good dry and wet adhesion of the composite separator to the anode and cathode. In addition, it also performs the function of ensuring that the inorganic particles included in the porous inorganic heat-resistant layer (3) are well fixed to each other without detaching.

[0053] A compound having ethylene oxide repeating units and double bonds at the ends, included in the organic polymer adhesive layer along with vinylidene fluoride-based polymers, is presumed to participate in a reaction that forms a negative electrode film (SEI) by being reduced during the battery activation process after electrolyte injection, thereby effectively improving wet adhesion. Furthermore, the compound having ethylene oxide repeating units and double bonds at the ends facilitates the good dispersion of the vinylidene fluoride-based polymer when the hydrophobic vinylidene fluoride-based polymer is dispersed in an aqueous dispersion medium such as water to form the organic polymer adhesive layer, thereby further effectively improving wet adhesion. Thus, the organic polymer adhesive layer effectively improves the wet adhesion of the composite separator by simultaneously including a compound having ethylene oxide repeating units and double bonds at the ends along with vinylidene fluoride-based polymers.

[0054] In the case where an inorganic heat-resistant layer (3) and an organic polymer adhesive layer (5) are formed only on 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 (3) are not formed, and only the first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) facing the cathode (20) are formed. Additionally, it is possible to form an inorganic heat-resistant layer (3) and an organic polymer adhesive layer (5) on each side of a porous organic polymer substrate (1), wherein the first organic polymer adhesive layer (5a) facing the cathode (20) includes a vinylidene fluoride-based polymer and a compound having ethylene oxide repeating units and double bonds at the ends, and the second organic polymer adhesive layer (5b) facing the anode (3) includes a vinylidene fluoride-based polymer but does not include a compound having ethylene oxide repeating units and double bonds at the ends.

[0055] 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.

[0056]

[0057] porous organic polymer substrate

[0058] 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.

[0059] 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.

[0060] porous inorganic heat-resistant layer

[0061] As is well known, 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. By coating the organic polymer substrate (1) with the porous inorganic heat-resistant layer (3a) containing the inorganic particles in this manner, the heat resistance and mechanical properties of the composite separation membrane (10) are improved.

[0062] The inorganic particles constituting the porous inorganic heat-resistant layer (3a) exist in a state of substantially adhering to each other, so that an interstitial volume is formed between the inorganic particles, and this interstitial volume forms an empty space, thereby having a microporous structure. At this time, an organic binder polymer is interposed between the inorganic particles to bind the inorganic particles together, and the inorganic particles also serve as a kind of spacer that can maintain the physical shape of the porous inorganic heat-resistant layer (3a). Since the inorganic particles generally have the characteristic that their physical properties do not change even at high temperatures 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 porous inorganic heat-resistant layer (3a) may each have a thickness ranging from 1 μm to 50 μm, or from 1 μm to 30 μm, or from 1 μm to 5 μm.

[0063] The inorganic particles included in the porous inorganic heat-resistant layer (3a) are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). In particular, if inorganic particles capable of carrying lithium ions are used, performance can be improved by increasing the ion conductivity within the electrochemical device. Additionally, if inorganic particles with a high dielectric constant are used, the ion conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of electrolyte salts, such as lithium salts, within the liquid electrolyte. For the reasons mentioned above, the inorganic particles may include high dielectric constant inorganic particles with a dielectric constant of 5 or more, or 10 or more, inorganic particles capable of carrying lithium ions, or mixtures thereof. Non-limiting examples of inorganic particles with a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, where, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, alumina (Al2O3), boehmite, SiC, TiO2, etc., can be used individually or in a mixture of two or more types. Furthermore, when the aforementioned high-dielectric constant inorganic particles are mixed with inorganic particles having lithium ion transport capabilities, their synergistic effects can be doubled. Non-limiting examples of inorganic particles having lithium ion transport capabilities include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Lix Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as (LiAlTiP) 14Li2O-9Al2O3-38TiO2-39P2O5 x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4, etc. x Ge y P z S w Lithium nitrides such as , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), Li3N, etc. (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 series glass such as LiI-Li2S-P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc.

[0064] Average particle size of inorganic particles (D 50 ) is not particularly limited, but can be, for example, 100 to 1000 nm, more specifically 100 to 800 nm.

[0065] Both particulate and non-particulate organic binder polymers can be used as the organic binder polymer included in the first porous inorganic heat-resistant layer (3a) that binds the inorganic particles together.

[0066] Non-particulate organic binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethylpullulan, Examples include cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. These may be used individually or in combination of two or more of them, 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 manufactured by dispersing inorganic particles in a solvent such as acetone, then adding and dissolving a non-particle organic binder in the solvent to prepare a slurry, and then coating the slurry onto a porous organic polymer substrate (1) by methods such as gravure coating or bar coating.

[0067] In the first porous inorganic heat-resistant layer (3a), using a particulate organic binder polymer as the organic binder polymer that binds the inorganic particles together is preferred in terms of reducing the resistance of the inorganic heat-resistant layer. That is, since the particulate organic binder polymer particles maintain a particulate form within the coating layer, they hardly penetrate into the pores of the porous organic polymer substrate, thereby contributing to improving the phenomenon of pore clogging in the organic polymer substrate.

[0068] As for the particulate organic binder polymer, known particulate organic binder polymers used in organic polymer adhesive layers can be used, such as acrylic polymers.

[0069] The acrylic polymer is, more specifically, a polymer containing carboxylic acid esters as repeating units, and preferably may be 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. When the Tg of the aforementioned acrylic polymer is lower than room temperature, it may be used as a non-particulate organic binder polymer.

[0070] As a particulate organic binder polymer, a vinylidene fluoride-based polymer may be included independently or together with the aforementioned acrylic polymer. The vinylidene fluoride-based polymer may be a 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 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.

[0071] Average particle size (D of particulate organic binder polymer) 50 ) is not particularly limited, but can be, for example, 50 to 1000 nm, more specifically 100 to 500 nm.

[0072] In the first porous inorganic heat-resistant layer (3a), 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.

[0073] A first porous inorganic heat-resistant layer (3a) 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 methods such as bar coating or gravure 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).

[0074] Organic polymer adhesive layer

[0075] The first organic polymer adhesive layer (5a) coated on the outer surface of the first porous inorganic heat-resistant layer (3a) faces the cathode (20) and includes a vinylidene fluoride-based polymer as an organic binder polymer, and at the same time includes a compound having ethylene oxide repeating units and double bonds at the ends.

[0076] As described above, the compound having ethylene oxide repeating units and double bonds at the ends included in the first organic polymer adhesive layer (5a) is presumed to participate in the reaction of being reduced during the activation process of the battery after electrolyte injection to form a negative electrode film (SEI), and accordingly, the wet adhesive strength is improved more effectively. In addition, by including the compound having ethylene oxide repeating units and double bonds at the ends in the first organic polymer adhesive layer (5a), the content of the electrolyte additive for forming the negative electrode film (SEI) can be relatively reduced, thereby lowering the viscosity of the electrolyte and improving the ionic conductivity of the electrolyte. Furthermore, the compound having ethylene oxide repeating units and double bonds at the ends allows the vinylidene fluoride-based polymer to be well dispersed when the hydrophobic vinylidene fluoride-based polymer is dispersed in an aqueous dispersion medium such as water to form the first organic polymer adhesive layer (5a), thereby further improving the wet adhesive strength.

[0077] Compounds having ethylene oxide repeating units and double bonds at the ends may be acrylic polymers. Specifically, they may be one or more selected from the group consisting of poly(ethylene glycol) methyl ether methacrylate, poly(propylene glycol) dimethacrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) diacrylate, and poly(ethylene glycol) dimethacrylate, but are not limited thereto.

[0078] The weight ratio of the vinylidene fluoride-based polymer and the compound having double bonds at the ends and ethylene oxide repeating units included in the first organic polymer adhesive layer (5a) may be 99:1 to 90:10 when considering the aforementioned effects.

[0079] The vinylidene fluoride-based polymer included in the first organic polymer adhesive layer (5a) can be in either a particulate or non-particulate form, but it is preferable to use a particulate form in terms of reducing interfacial resistance.

[0080] Examples of vinylidene fluoride-based polymers include homopolymers of vinylidene fluoride, copolymers of vinylidene fluoride with other polymerizable monomers, or mixtures of two or more of these. Examples of vinylidene fluoride and other polymerizable monomers include 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, but are not limited thereto. In particular, vinylidene fluoride-based polymers may be copolymers 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.

[0081] The organic binder polymer included in the first organic polymer adhesive layer (5a) may further include an acrylic polymer, and the acrylic polymer may also be non-particulate or particulate.

[0082] The acrylic polymer is, more specifically, a polymer containing carboxylic acid esters as repeating units, and preferably may be 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.

[0083] The formation of the first organic polymer adhesive layer (5a) using a particulate vinylidene fluoride-based polymer can be achieved by dispersing organic polymer particles, such as particulate vinylidene fluoride-based polymers, in an aqueous dispersion medium together with a compound having ethylene oxide repeating units and double bonds at the ends, preparing a slurry, and then coating and drying it on the first porous inorganic heat-resistant layer (3a) by a method such as bar 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 dispersed within the aqueous dispersion medium without dissolving in the dispersion medium, while maintaining their particle shape, and the particle shape is maintained even after coating and drying it on the first porous inorganic heat-resistant layer (3a).

[0084] 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 100 to 800 nm. Average particle size (D) of particulate vinylidene fluoride-based polymer 50 ) is not particularly limited, but can be, for example, 100 to 1,000 nm, more specifically 100 to 500 nm.

[0085] When an acrylic polymer is further included as a particulate organic binder polymer, the average particle size (D 50 ) is not particularly limited, but can be, for example, 100 to 1000 nm, more specifically 100 to 700 nm.

[0086] Meanwhile, when vinylidene fluoride-based polymers such as polyvinylidene fluoride-co-hexafluoropropylene and polyvinylidene fluoride-co-trichloroethylene are used in a non-particulate form, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate, Cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, etc. may be used in combination, but are not limited thereto.

[0087] When the first inorganic heat-resistant layer (3) and the first organic polymer adhesive layer (5a) are formed only on one side of the porous organic polymer substrate (1), the second inorganic heat-resistant layer (3b) and the second organic polymer adhesive layer (5b) facing the anode (3) are not formed, and only the first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) facing the cathode (20) are formed. Additionally, the aforementioned first inorganic heat-resistant layer (3a) and the first organic polymer adhesive layer (5a) may be formed into the same second inorganic heat-resistant layer (3b) and the second organic polymer adhesive layer (5b).

[0088] In addition, an inorganic heat-resistant layer (3) and an organic polymer adhesive layer (5) are formed on each side of a porous organic polymer substrate (1), respectively. The first organic polymer adhesive layer (5a) facing the cathode (20) may be formed to include a vinylidene fluoride-based polymer and a compound having ethylene oxide repeating units and double bonds at the ends, as described above, and the second organic polymer adhesive layer (5b) facing the anode (3) may be formed to include a vinylidene fluoride-based polymer but not include a compound having ethylene oxide repeating units and double bonds at the ends.

[0089] The coating amount of the first organic polymer adhesive layer (5a) and the second organic polymer adhesive layer (5b) is 0.1 to 30 g / m² each. 2 It may be, specifically 0.2 to 10 g / m² 2 It may be, and more specifically, 0.5 to 5 g / m 2 It could be.

[0090] cathode and anode

[0091] 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).

[0092] 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.

[0093] 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.

[0094] electrolytes

[0095] 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 those 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. In addition, if VC (vinylene carbonate), which is involved in the cathode film formation reaction, is included as an additive, it may be more advantageous for improving wet adhesion to the cathode together with the compound having the reduction reaction site of the present invention.

[0096] 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.

[0097] 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.

[0098]

[0099] Example 1

[0100] [Manufacturing of Composite Membranes]

[0101] A composite separation membrane (10) of Fig. 1 was manufactured.

[0102] Inorganic particles (Al2O3, An emulsion containing 96 parts by weight of D50 (500 nm), 3 parts by weight of acrylic polymer particles (CSB-130, Toyo Ink, Tg: -30 °C), and 1 part by weight of sodium carboxymethyl cellulose were added to water to achieve a solid content of 35 wt%, and then zirconia beads with a particle size of 0.7 mm, equal to the amount of inorganic particles, were added and milled in a bead mill for 2 hours to prepare a slurry. This slurry was bar-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 1.5 μm on both sides.

[0103] Next, PVdF-HFP copolymer particles (KYNAR 2821, Arkema) with a D50 of 200 nm (uniform particle size confirmed by SEM) and poly(ethylene glycol)methyl ether acrylate (#730270, Sigma-Aldrich) were added to water to achieve a total solid content of 10 wt%, and the mixture was stirred at 1000 rpm for 10 minutes. An equal amount of zirconia beads with a particle size of 0.7 mm was added to the mixture, and a slurry was prepared by milling with a paint shaker for 2 hours. Then, an emulsion of acrylic polymer particles (CSB-130, Toyo Ink, Tg: -30 °C) was further added, and the mixture was stirred at 500 rpm for 10 minutes to prepare an organic binder dispersion for forming an organic polymer adhesive layer. The weight ratio of PVdF-HFP copolymer particles:poly(ethylene glycol)methyl ether acrylate:acrylic polymer particles in the binder dispersion was 86:4:10. This organic binder dispersion was bar-coated onto a separator formed with the first inorganic heat-resistant layer and the second inorganic heat-resistant layer, and dried to form an organic polymer adhesive layer on each side. The coating weight of the organic polymer adhesive layer was 0.7 g / m² based on the weight of the coating layer formed on the first inorganic heat-resistant layer. 2 It was, and the coating amount of the coating layer formed on the second inorganic heat-resistant layer was also the same.

[0104] [Manufacturing of Lithium Secondary Batteries]

[0105] 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.

[0106] 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.

[0107] A monocell specimen was fabricated by overlapping the above-manufactured composite separator and porous separator fabric, interposing them between the anode and cathode, laminating them using a hot press, and then laminating them. At this time, the porous separator fabric was positioned to face the anode. Since the composite separator has high adhesion to the anode, measuring the cathode adhesion while both the anode and cathode are adhered would result in the adhesion at the cathode-separator interface not being measured; therefore, to prevent the anode and the composite separator from coming into direct contact, a porous separator fabric that has no adhesion and allows for the movement of Li ions was inserted between the composite separator and the anode. During this process, pressure was applied at 60°C and 1000 kgf for 5 seconds. Both ends of the laminated assembly were secured with nylon tape to prevent separation. The dimensions of the specimen were 37 mm x 59 mm.

[0108] After loading the above specimen into a pouch-type case, 0.5g of electrolyte (ethylene carbonate:ethyl methyl carbonate = 7:3 (volume ratio), LiPF6 1M, VC (vinylene carbonate) 2wt%) was injected to manufacture a secondary battery, which was then left at room temperature for 3 hours. Subsequently, the secondary battery was subjected to 5 kgf / cm² at 60°C for 5 minutes. 2 Pressurized to a pressure of 5 kgf / cm² at 60℃. 2 The battery was charged to SOC3 with a current of 0.2C while under pressure, and then charged to SOC60 with a current of 1C. Once charging was complete, the pressure was released, and aging was performed for 1 day at 60 degrees.

[0109] Examples 2~4

[0110] The procedure was carried out in the same manner as Example 1, except that the type of compound having a double bond at the end and having an ethylene oxide repeating unit was changed as shown in Table 1 instead of poly(ethylene glycol)methyl ether acrylate.

[0111] Comparative Examples 1~2

[0112] The procedure was carried out in the same manner as Example 1, except that poly(ethylene glycol) of Table 1 was used instead of a compound having ethylene oxide repeating units and double bonds at the ends.

[0113]

[0114] [Measurement of adhesion to electrode]

[0115] Wet adhesion and dry adhesion of the cathode and separator were evaluated using each specimen prepared above, and the results are summarized in Table 1 below.

[0116] Dry adhesion measurement

[0117] The negative electrode prepared for manufacturing a lithium secondary battery was cut to a size of 20 mm x 100 mm. The separator prepared in the examples and comparative examples was cut to a size of 20 mm x 100 mm. The prepared separator and negative electrode were overlapped, placed between 100 μm PET films, and bonded using a flatbed press. At this time, the conditions of the flatbed press were heated and pressurized at 60°C and a pressure of 1000 kgf for 5 seconds. The bonded separator and negative electrode were attached to a slide glass using double-sided tape. The separator bonded to the negative electrode was peeled off at a 180° angle using a UTM and measured.

[0118] Wet adhesion measurement

[0119] A lithium secondary battery made by layering the above-manufactured composite separator and porous separator fabric was disassembled, and the wet adhesion strength between the negative electrode and the separator was measured. First, a monocell that had completed aging was discharged to SOC0. The discharged monocell was disassembled in a dry room. The disassembled assembly was cut into 2 mm wide pieces, and after separating the positive electrode and the porous separator, the separator adhered to the negative electrode in a wet state was peeled off at a 90° angle using a UTM and measured.

[0120] Type of compound having ethylene oxide repeating units and double bonds at the ends Product Name / Molecular Weight Dry Adhesion (gf / 20mm) Wet Adhesion (gf / 20mm) Example 1 Poly(ethylene glycol) Methyl Ether Acrylate Aldrich 730270 / Mn: 20002517 Example 2 Poly(ethylene glycol) Diacrylate Aldrich 729086 / Mn: 10002323 Example 3 Poly(ethylene glycol) Methyl Ether Methacrylate Aldrich 906859 / Mn: 10002619 Example 4 Poly(ethylene glycol) Dimethacrylate Aldrich 447951 / Mn: 9502124 Comparative Example 1 Poly(ethylene glycol) Mn: 2000258 Comparative Example 2 Poly(ethylene glycol) Mn: 1000267

[0121] As can be seen in Table 1 above, according to the present invention, Examples 1-3, in which the organic polymer adhesive layer comprises a compound having double bonds at the ends and ethylene oxide repeating units together with a vinylidene fluoride-based polymer, have good dry adhesion and excellent wet adhesion, whereas Comparative Example 1-2 has insufficient wet adhesion.

[0122]

[0123] [Explanation of the symbol]

[0124] 1: Porous organic polymer substrate

[0125] 3a: First porous inorganic heat-resistant layer, 3b: Second porous inorganic heat-resistant layer

[0126] 5a: First organic polymer adhesive layer, 5b: Second organic polymer adhesive layer

[0127] 10: Composite membrane

[0128] 20: Cathode

[0129] 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 a vinylidene fluoride-based polymer, and The above organic polymer adhesive layer is a composite separator for a lithium secondary battery that further comprises a compound having ethylene oxide repeating units and double bonds at the ends.

2. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the compound having the above-mentioned ethylene oxide repeating unit and having a double bond at the end is an acrylic polymer.

3. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the compound having the above-mentioned ethylene oxide repeating unit and having a double bond at the terminal is one or more selected from the group consisting of poly(ethylene glycol) methyl ether methacrylate, poly(propylene glycol) dimethacrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) diacrylate, and poly(ethylene glycol) dimethacrylate.

4. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the weight ratio of a vinylidene fluoride-based polymer included in the organic polymer adhesive layer and a compound having ethylene oxide repeating units and double bonds at the ends is 99:1 to 90:

10.

5. In Paragraph 1, A composite separator for a lithium secondary battery characterized in that the vinylidene fluoride-based polymer included in the above organic polymer adhesive layer is in the form of particles.

6. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the above vinylidene fluoride-based polymer is a vinylidene fluoride-hexafluoropropylene copolymer.

7. In Paragraph 1, A composite separator for a lithium secondary battery, characterized in that the organic binder polymer included in the above organic polymer adhesive layer further includes an acrylic polymer.

8. In Paragraph 7, A composite separator for a lithium secondary battery characterized in that the acrylic polymer included in the above organic polymer adhesive layer is of a non-particulate type.

9. In Paragraph 7, 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.

10. In Paragraph 1, A composite separator for a lithium secondary battery characterized in that the organic binder polymer included in the above porous inorganic heat-resistant layer is of a non-particle type.

11. 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.

12. A composite separator according to any one of paragraphs 1 to 11; A cathode arranged to face the above organic polymer adhesive layer; Anode; and A lithium secondary battery containing an electrolyte.

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