Lithium secondary battery

Abstract

A lithium secondary battery according to one aspect of the present invention comprises: a composite separator including a porous organic polymer substrate, a first porous inorganic heat-resistant layer coated on one surface of the organic polymer substrate and including inorganic particles and an organic binder polymer binding the inorganic particles to each other, a first organic polymer adhesive layer coated on the outer surface of the first porous inorganic heat-resistant layer and including an organic binder polymer and a compound having a reduction reaction site, a second porous inorganic heat-resistant layer coated on the other surface of the organic polymer substrate and including inorganic particles and an organic binder polymer binding the inorganic particles to each other, and a second organic polymer adhesive layer coated on the outer surface of the second porous inorganic heat-resistant layer, including an organic binder polymer, but not including a compound having a reduction reaction site; a negative electrode provided to face the first organic polymer adhesive layer; a positive electrode provided to face the second organic polymer adhesive layer; and an electrolyte.

Description

lithium secondary battery

[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. 10-2024-0128876 filed on September 24, 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 organic binder polymer particles 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 an organic binder polymer on an inorganic heat-resistant layer to improve wet adhesion between the aforementioned composite separator and the electrode. There is a demand for the development of a lithium secondary battery equipped with a composite separator that can improve the lifespan of the secondary battery, such as cycle characteristics, along with improved wet adhesion.

[0008] The first objective of the present invention is to provide 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 lithium secondary battery with good cycle characteristics in addition to the first objective described above.

[0010] In addition to the aforementioned second objective, the third objective of the present invention is to provide a lithium secondary battery equipped with a composite separator having good adhesion to the negative electrode in a dry state before the injection of the electrolyte and suppressed side reactions with the positive electrode.

[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 lithium secondary battery according to the first aspect of the present invention is,

[0013] porous organic polymer substrate,

[0014] A first porous inorganic heat-resistant layer coated on one surface of the above organic polymer substrate and comprising inorganic particles and an organic binder polymer that binds the inorganic particles together,

[0015] A first organic polymer adhesive layer coated on the outer surface of the first porous inorganic heat-resistant layer and comprising an organic binder polymer and a compound having reduction reaction sites,

[0016] A second porous inorganic heat-resistant layer coated on the other side of the above organic polymer substrate and comprising inorganic particles and an organic binder polymer that binds the inorganic particles together, and

[0017] A composite separation membrane having a second organic polymer adhesive layer coated on the outer surface of the second porous inorganic heat-resistant layer, the second organic polymer adhesive layer comprising an organic binder polymer but not comprising a compound having a reduction reaction site;

[0018] A cathode arranged to face the first organic polymer adhesive layer;

[0019] An anode arranged to face the second organic polymer adhesive layer; and

[0020] It contains electrolytes.

[0021] The second aspect of the present invention is, in the first aspect,

[0022] The above reduction reaction sites are one or more selected from the group consisting of double bond groups, triple bond groups, carbonyl groups, nitrile groups, quinone groups, and epoxy groups.

[0023] A third aspect of the present invention is, in the first or second aspect,

[0024] The above reduction reaction site is a vinyl terminal group.

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

[0026] The compound having the above reduction reaction site is one or more of vinyl-terminated polydimethylsiloxane or compounds having a double bond at the end while having an ethylene oxide repeating unit.

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

[0028] The weight ratio of the organic binder polymer and the compound having reduction reaction sites included in the first organic polymer adhesive layer is 99:1 to 80:20.

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

[0030] The basis weight of the compound having reduction reaction sites included in the first organic polymer adhesive layer is 0.001 to 1.0 g / m² 2 am.

[0031] The seventh aspect of the present invention is, in any one of the first to sixth aspects,

[0032] The organic binder polymers included in the first organic polymer adhesive layer and the second organic polymer adhesive layer are each of the non-particulate type.

[0033] The eighth aspect of the present invention is, in any one of the first to seventh aspects,

[0034] The organic binder polymer included in the first organic polymer adhesive layer and the second organic polymer adhesive layer each includes a vinylidene fluoride-based polymer.

[0035] The ninth aspect of the present invention is, in the eighth aspect,

[0036] The above vinylidene fluoride-based polymer is a vinylidene fluoride-hexafluoropropylene copolymer.

[0037] The tenth aspect of the present invention is, in the eighth aspect,

[0038] The organic binder polymer included in the first organic polymer adhesive layer and the second organic polymer adhesive layer each further includes a polymer having a cyano group.

[0039] The 11th aspect of the present invention is, in the 10th aspect,

[0040] The polymer having the cyano group is one or more selected from the group consisting of cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, and cyanoethyl pullane.

[0041] The 12th aspect of the present invention is, in any one of the 1st to 11th aspects,

[0042] The organic binder polymers included in the first porous inorganic heat-resistant layer and the second porous inorganic heat-resistant layer are each of the non-particulate type.

[0043] A composite separator provided in a secondary battery according to the present invention sequentially comprises an inorganic heat-resistant layer and an organic polymer adhesive layer on each side of a porous organic polymer substrate, wherein the first organic polymer adhesive layer facing the negative electrode comprises an organic binder polymer and a compound having a reduction reaction site, and the second organic polymer adhesive layer facing the positive electrode comprises an organic binder polymer but does not comprise a compound having a reduction reaction site.

[0044] The organic binder polymers included in the first and second organic polymer adhesive layers, respectively, maintain 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 shape stability of the composite separator.

[0045] Compounds having reduction sites included in the first organic binder polymer adhesive layer facing the cathode are presumed to be reduced during the battery activation process after electrolyte injection to participate in the reaction forming the cathode film (SEI), thereby improving wet adhesion. Meanwhile, the second organic binder polymer adhesive layer facing the anode does not contain compounds having reduction sites, which are substances capable of reacting with the anode to cause side reactions such as gas generation. Accordingly, the cycle characteristics of the lithium secondary battery are well maintained or improved.

[0046] 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.

[0047] FIG. 1 is a cross-sectional view schematically illustrating a cross-section of a lithium secondary battery according to one embodiment of the present invention.

[0048] 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.

[0049] <Definition>

[0050] 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.

[0051] In the present specification, D50 refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. The 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. D50 is measured by calculating the particle diameter at the point that is 50% of the cumulative distribution of particle numbers according to particle size in the measuring device.

[0052] In the present specification, the term “particle-type” organic binder polymer refers to an organic binder polymer that retains its added particle shape within a coating layer formed by adding the organic binder polymer in a particle shape to a dispersion medium to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer, and then coating and drying the mixture. Additionally, in the present specification, the term “non-particle-type” organic binder polymer refers to an organic binder polymer that loses its added particle shape when dissolved in a solvent to form a porous inorganic heat-resistant layer or an organic polymer adhesive layer, or an organic binder polymer that loses its added particle shape during the drying process when forming a coating layer, even if it is not dissolved when added to a dispersion medium, and is deformed into a film-like form.

[0053]

[0054] FIG. 1 schematically illustrates a cross-section of a lithium secondary battery 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 reality, the negative electrode (20), the composite separator (10), and the positive electrode (30) are in close contact with each other.

[0055] In the present invention, the composite separator (10) is coated on one side of an organic polymer substrate (1) and comprises a first porous inorganic heat-resistant layer (3a) comprising inorganic particles and an organic binder polymer that binds the inorganic particles together, and a first organic polymer adhesive layer (5) coated on the outer surface of the first porous inorganic heat-resistant layer (3a) and comprising an organic binder polymer and a compound having a reduction reaction site. In addition, in the present invention, the composite separator (10) is coated on the other side of the organic polymer substrate (1) and comprises a second porous inorganic heat-resistant layer (3b) comprising inorganic particles and an organic binder polymer that binds the inorganic particles together, and a second organic polymer adhesive layer (7) coated on the outer surface of the second porous inorganic heat-resistant layer (3b) and comprising an organic binder polymer but not a compound having a reduction reaction site.

[0056] In the lithium secondary battery of the present invention, the first organic polymer adhesive layer (5) faces the negative electrode (20) and the second organic polymer adhesive layer (7) faces the positive electrode (30), and an electrolyte is injected.

[0057] The organic binder polymer included in the first organic polymer adhesive layer (5) and the second organic polymer adhesive layer (7), respectively, forms an organic polymer adhesive layer and adheres to the cathode and anode, respectively, thereby maintaining 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 first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b) are well fixed without detaching.

[0058] A compound having a reduction reaction site included in the first organic binder polymer adhesive layer (5) facing the negative electrode (20) is presumed to be reduced during the activation process of the battery after electrolyte injection and participate in the reaction to form a negative electrode film (SEI), and accordingly, wet adhesion is improved. Meanwhile, the second organic binder polymer adhesive layer (7) facing the positive electrode (30) does not contain a compound having a reduction reaction site, which is a substance that can react with the positive electrode (30) and cause side reactions such as gas generation. Accordingly, the cycle characteristics of the lithium secondary battery are maintained or improved.

[0059] Hereinafter, each component constituting the lithium secondary battery of the present invention will be described in more detail.

[0060]

[0061] porous organic polymer substrate

[0062] 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.

[0063] 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.

[0064] First porous inorganic heat-resistant layer and second porous inorganic heat-resistant layer

[0065] As is well known, the first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b) include 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 layers (3a, 3b) containing inorganic particles in this way, the heat resistance and mechanical properties of the composite separation membrane (10) are improved.

[0066] The inorganic particles constituting the porous inorganic heat-resistant layers (3a, 3b) exist in a state of substantially adhering to each other, forming an interstitial volume 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 them together, and the inorganic particles also serve as a kind of spacer that can maintain the physical shape of the porous inorganic heat-resistant layers (3a, 3b). 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 layers (3a, 3b) 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.

[0067] The inorganic particles included in the porous inorganic heat-resistant layers (3a, 3b) 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, using inorganic particles capable of transporting lithium ions can improve performance by increasing the ion conductivity within the electrochemical device. Additionally, using inorganic particles with a high dielectric constant can improve the ion conductivity of the electrolyte by contributing to an increase in the dissociation degree 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 transporting 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.

[0068] The average particle size (D50) of the inorganic particles is not particularly limited, but may be, for example, 100 to 1000 nm, more specifically 100 to 800 nm.

[0069] 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) and the second porous inorganic heat-resistant layer (3b) that binds the inorganic particles together.

[0070] 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 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.

[0071] In the first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b), 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.

[0072] 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.

[0073] 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.

[0074] As a particulate organic binder polymer, a vinylidene fluoride-based polymer may be included independently or together with the aforementioned particulate or non-particulate acrylic polymer. The vinylidene fluoride-based polymer may be insoluble in electrolytes and 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 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.

[0075] The average particle size (D50) of the particulate organic binder polymer is not particularly limited, but may be, for example, 50 to 1000 nm, more specifically 100 to 500 nm.

[0076] In the first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b), 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.

[0077] The first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b) 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 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).

[0078] First organic polymer adhesive layer and second organic polymer adhesive layer

[0079] The first organic polymer adhesive layer (5) coated on the outer surface of the first porous inorganic heat-resistant layer (3a) faces the cathode (20) and comprises an organic binder polymer and a compound having a reduction reaction site.

[0080] As described above, the compound having a reduction reaction site included in the first organic binder polymer adhesive layer (5) is presumed to be reduced during the activation process of the battery after electrolyte injection and participate in the reaction to form a negative electrode film (SEI), and accordingly, wet adhesion is improved. Furthermore, by including the compound having a reduction reaction site in the first organic polymer adhesive layer (5), 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.

[0081] These reduction sites may be one or more selected from the group consisting of double bond groups, triple bond groups, carbonyl groups, nitrile groups, quinone groups, and epoxy groups, and in particular may be vinyl terminal groups. Examples of compounds having reduction sites include vinyl-terminated polydimethylsiloxane represented by the following chemical formula 1, or compounds having ethylene oxide repeating units and double bonds at the ends.

[0082] [Chemical Formula 1]

[0083]

[0084] As for compounds having reduction reaction sites, one type may be used alone or two or more types may be used in combination.

[0085] The weight ratio of the organic binder polymer and the compound having reduction reaction sites included in the first organic polymer adhesive layer may be 99:1 to 80:20 when considering the aforementioned effects, more specifically 98:2 to 85:15, and most specifically 95:5 to 90:10.

[0086] The basis weight of the compound having reduction reaction sites included in the first organic polymer adhesive layer is 0.001 to 1.0 g / m² 2 It may be 0.01 to 0.2 g / m 2 It may be 0.025 to 0.05 g / m 2 It could be.

[0087] On the other hand, the second organic polymer adhesive layer (7) coated on the outer surface of the second porous inorganic heat-resistant layer (3b) faces the anode (30) and includes an organic binder polymer but does not include a compound having a reduction reaction site. This is because if the second organic polymer adhesive layer (7) facing the anode (30) includes a compound having a reduction reaction site, it reacts with the anode (30) to cause side reactions such as gas generation, and the cycle characteristics of the lithium secondary battery are also degraded.

[0088] Both particulate and non-particulate organic binder polymers can be used as the organic binder polymers included in the first organic polymer adhesive layer (5) and the second organic polymer adhesive layer (7). Among these, non-particulate organic binder polymers are more preferred so that the reduction of the compound having the aforementioned reduction reaction site and the reaction forming the cathode film (SEI) are sufficiently utilized.

[0089] Vinylidene fluoride-based polymers can be cited as non-particulate organic binder polymers.

[0090] 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.

[0091] In addition, acrylic polymers can be used as non-particulate organic binder polymers, and in particular, they can be used in combination with the aforementioned vinylidene fluoride-based polymer.

[0092] As an acrylic polymer, it may be a polymer containing carboxylic acid esters as repeating units, 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.

[0093] Examples of non-particulate organic binder polymers include, in addition to the aforementioned vinylidene fluoride-based and acrylic-based polymers, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, etc., and the aforementioned non-particulate organic binder polymers may be used individually or among them Two or more types may be mixed and used, but are not limited thereto. In particular, as non-particulate organic binder polymers, vinylidene fluoride-based polymers and cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, and polymers having cyanoethyl pullane groups may be mixed and used. Of course, acrylic-based polymers may also be mixed.

[0094] The first organic polymer adhesive layer (5) and the second organic polymer adhesive layer (7) using a non-particulate organic binder polymer can be manufactured by introducing and dissolving the organic binder polymer in a solvent such as acetone to prepare a slurry, and then coating the slurry onto the first porous inorganic heat-resistant layer (3a) and the second porous inorganic heat-resistant layer (3b), respectively, by a method such as die coating. At this time, a compound having a reduction reaction site is further added to the slurry for forming the first organic polymer adhesive layer (5), while a compound having a reduction reaction site is not added to the slurry for forming the second organic polymer adhesive layer (7).

[0095] Meanwhile, when using a particulate organic binder polymer, the particulate organic binder polymer included in the aforementioned first porous inorganic heat-resistant layer (3a) and second porous inorganic heat-resistant layer (3b) can be exemplified.

[0096] The coating amount of the first organic polymer adhesive layer (5) and the second organic polymer adhesive layer (7) 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.

[0097] cathode and anode

[0098] 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).

[0099] That is, the composite separator manufactured by the aforementioned method is interposed between the cathode and the anode and is manufactured into an electrode assembly by a lamination process in which heat and / or pressure are 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. In this case, the lamination process may be performed by a hot pressing method.

[0100] 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.

[0101] electrolytes

[0102] 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.

[0103] 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.

[0104] 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.

[0105] .

[0106] Example 1

[0107] [Manufacturing of Composite Membranes]

[0108] A composite separation membrane (10) of Fig. 1 was manufactured.

[0109] An emulsion containing 96 parts by weight of inorganic particles (Al2O3, D50: 500 nm) and 3 parts by weight of acrylic polymer particles (CSB-130, Toyo Ink, Tg: -30 ℃) and 1 part by weight of sodium carboxymethyl cellulose were 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 in a bead mill for 1 hour to prepare a slurry. This slurry was gravure-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.

[0110] Next, an organic binder solution for forming a first organic polymer adhesive layer was prepared by adding a PVdF-HFP copolymer (Solef 20808, Solvay), a cyano-group polymer (SYR301, Miwon), and vinyl-terminated polydimethylsiloxane in a weight ratio of 92:5:3 to acetone such that the total solid content concentration was 5 wt%. This organic binder solution was coated onto the outer surface of the first inorganic heat-resistant layer and dried to form the first organic polymer adhesive layer. The temperature and humidity of drying zone 1 of the coater were controlled to 40 ℃ and RH 55%, respectively, and the coating amount of the first organic polymer adhesive layer after drying was 0.5 g / m² 2 It was.

[0111] Then, an organic binder solution for forming a second organic polymer adhesive layer was prepared by excluding vinyl-terminated polydimethylsiloxane from the organic binder solution for forming the first organic polymer adhesive layer described above, and adjusting the weight ratio of the PVdF-HFP copolymer to a polymer having cyano groups to 97:3, and the second organic polymer adhesive layer was formed on the outer surface of the second inorganic heat-resistant layer in the same manner as the method for forming the first organic polymer adhesive layer.

[0112] [Manufacturing of Lithium Secondary Batteries]

[0113] 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.

[0114] 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.

[0115] A monocell specimen was fabricated by interposing the above-manufactured composite separator between the anode and the cathode and facing the outermost cathode, such that the first organic polymer adhesive layer faced the cathode, and then laminating the assembly using a hot press. At this time, the pressure was applied at 60°C and 1000 kgf for 5 seconds. The size of the specimen was 37 mm x 59 mm. Seven of these fabricated assemblies were stacked, and a half-cell with a separator-cathode-separator bonded was stacked on top of the outermost anode. Both sides of the stacked assemblies were secured with nylon tape to prevent separation. After loading the specimen into a pouch-type case, 3.0 g of electrolyte (ethylene carbonate:ethyl methyl carbonate = 3:7 weight ratio, LiPF6 1M, VC (vinylene carbonate) 2 wt%) was injected to manufacture a secondary battery, which was then left at room temperature for 3 hours. Next, the secondary battery is heated at 60 ℃ for 5 minutes at 5 kgf / cm² 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. After charging was complete, the pressure was released, and the battery was degassed after aging for 1 day at 60°C. Subsequently, the capacity was checked by performing 3 charge-discharge cycles from SOC0 to SOC100 with a current of 0.33C.

[0116] Example 2

[0117] The procedure was carried out in the same manner as Example 1, except that the content of vinyl-terminated polydimethylsiloxane was changed as described in Table 1 below.

[0118] Comparative Example 1

[0119] A secondary battery was manufactured in the same manner as in Example 1, except that a second organic polymer adhesive layer without vinyl-terminated polydimethylsiloxane was formed on the outer surfaces of the first inorganic heat-resistant layer and the second inorganic heat-resistant layer, respectively.

[0120] Comparative Example 2

[0121] A secondary battery was manufactured in the same manner as in Example 1, except that a first organic polymer adhesive layer with added vinyl-terminated polydimethylsiloxane was formed on the outer surfaces of the first inorganic heat-resistant layer and the second inorganic heat-resistant layer, respectively.

[0122]

[0123] [Measurement of adhesion to electrode]

[0124] Dry adhesion measurement

[0125] 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 ℃ 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.

[0126] Wet adhesion measurement

[0127] 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.

[0128] After loading the above specimen into a pouch-type case, 0.5g of electrolyte (ethylene carbonate:ethyl methyl carbonate = 3:7 (volume ratio), LiPF6 1M, VC (vinylene carbonate) 2w%) 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 under a pressurized state, and then charged to SOC60 with a current of 1C. After charging was complete, the pressure was released, and aging was performed at 60°C for 1 day. The monocell, having completed the aging process, was discharged to SOC0. The discharged monocell was disassembled in a dry room. The disassembled assembly was cut to a width of 2 mm, 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 to measure the wet adhesion strength.

[0129] [Measurement of Capacity Retention Rate]

[0130] Charge and discharge were repeated at a rate of 1 C at 45 ℃ in the range of approximately 2.5 V to 4.25 V, and the cycle performance (capacity retention rate) was measured by calculating the ratio of the discharge capacity after 400 cycles to the initial discharge capacity.

[0131] [Measurement of Gas Generation]

[0132] After the cell that has undergone the above 400 cycle repetitions was discharged with SCO0 and pierced to collect the gas inside the cell, the amount of gas contained in the gas was quantified using a flame ionization detector (FID) and a thermal conductivity detector (TCD).

[0133]

[0134] [Explanation of the symbol]

[0135] 1: Porous organic polymer substrate

[0136] 3a: First porous inorganic heat-resistant layer, 3b: Second porous inorganic heat-resistant layer

[0137] 5: First organic polymer adhesive layer, 7: Second organic polymer adhesive layer

[0138] 10: Composite membrane

[0139] 20: Cathode

[0140] 30: Anode

Claims

1. Porous organic polymer substrate, A first porous inorganic heat-resistant layer coated on one surface of the above organic polymer substrate and comprising inorganic particles and an organic binder polymer that binds the inorganic particles together, A first organic polymer adhesive layer coated on the outer surface of the first porous inorganic heat-resistant layer and comprising an organic binder polymer and a compound having reduction reaction sites, A second porous inorganic heat-resistant layer coated on the other side of the above organic polymer substrate and comprising inorganic particles and an organic binder polymer that binds the inorganic particles together, and A composite separation membrane having a second organic polymer adhesive layer coated on the outer surface of the second porous inorganic heat-resistant layer, the second organic polymer adhesive layer comprising an organic binder polymer but not comprising a compound having a reduction reaction site; A cathode arranged to face the first organic polymer adhesive layer; An anode arranged to face the second organic polymer adhesive layer; and A lithium secondary battery containing an electrolyte.

2. In Paragraph 1, A lithium secondary battery characterized in that the above reduction reaction site is one or more selected from the group consisting of a double bond group, a triple bond group, a carbonyl group, a nitrile group, a quinone group, and an epoxy group.

3. In Paragraph 1, A lithium secondary battery characterized in that the above reduction reaction site is a vinyl terminal group.

4. In Paragraph 1, A lithium secondary battery characterized in that the compound having the above-mentioned reduction reaction site is one or more of vinyl-terminated polydimethylsiloxane or a compound having a double bond at the end while having an ethylene oxide repeating unit.

5. In Paragraph 1, A lithium secondary battery characterized in that the weight ratio of an organic binder polymer and a compound having reduction reaction sites included in the first organic polymer adhesive layer is 99:1 to 80:

20.

6. In Paragraph 1, The basis weight of the compound having reduction reaction sites included in the first organic polymer adhesive layer is 0.001 to 1.0 g / m² 2 A lithium secondary battery characterized by being.

7. In Paragraph 1, A lithium secondary battery characterized in that the organic binder polymer included in the first organic polymer adhesive layer and the second organic polymer adhesive layer is each of a non-particle type.

8. In Paragraph 1, A lithium secondary battery characterized in that the organic binder polymer included in the first organic polymer adhesive layer and the second organic polymer adhesive layer each includes a vinylidene fluoride-based polymer.

9. In Paragraph 8, A lithium secondary battery characterized in that the above vinylidene fluoride-based polymer is a vinylidene fluoride-hexafluoropropylene copolymer.

10. In Paragraph 8, A lithium secondary battery characterized in that the organic binder polymer included in the first organic polymer adhesive layer and the second organic polymer adhesive layer further includes a polymer having a cyano group.

11. In Paragraph 10, A lithium secondary battery characterized in that the polymer having the cyano group is one or more selected from the group consisting of cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, and cyanoethyl pullane.

12. In Paragraph 1, A lithium secondary battery characterized in that the organic binder polymer included in the first porous inorganic heat-resistant layer and the second porous inorganic heat-resistant layer is each of a non-particle type.

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