Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; an electrolyte; and a separator between the positive electrode and the negative electrode, wherein the separator comprises: a porous polymer substrate; an inorganic heat-resistant layer formed on at least one surface of the porous polymer substrate, and including inorganic particles and a first binder polymer; and an adhesive layer formed on at least one surface of the inorganic heat-resistant layer, and including a particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer, wherein the cyano group-containing acrylic binder polymer is a copolymer comprising a repeating unit derived from a monomer having a cyano group and a repeating unit derived from a monomer having a carboxyl group or a monomer having an alkyl group having 1 to 14 carbon atoms, the proportion of the repeating unit derived from the monomer having a cyano group is 4% to 9% of 100% of the total repeating units in the cyano group-containing acrylic binder polymer, and the electrolyte contains 0.4% to 0.75% by weight of a cyclic carbonate compound containing a vinyl group, on the basis of 100% by weight of the total electrolyte.

Description

lithium secondary battery

[0001] The present invention relates to a lithium secondary battery.

[0002] Join by reference

[0003] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0157204 filed November 7, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0004]

[0005] Electrochemical devices such as lithium-ion batteries are typically composed of a cathode, separator, anode, and electrolyte, and are energy storage devices with high energy density capable of reversibly converting chemical and electrical energy for charging and discharging; 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 (HEV), plug-in electric vehicles (Plug-in EV), electric bicycles (e-bike), and energy storage systems (ESS).

[0006] Meanwhile, lithium secondary batteries are manufactured through an assembly process in which an electrode assembly is housed in a battery case, an electrolyte is injected, and the battery is sealed; a pre-aging process to ensure the electrolyte is well impregnated into the electrodes and separator; and an activation process to stabilize the battery structure and make it usable. For lithium secondary batteries, these activation processes must be performed beforehand to activate the positive electrode active material and to create a stable surface film (SEI, Solid Electrolyte Interface) on the negative electrode during the first cycle. Meanwhile, during the activation process described above, the volume of the positive and negative electrodes expands as the lithium secondary battery is charged and discharged. In the activation process of a secondary battery to which a lamination-and-stack type electrode assembly is applied, in which several electrode assemblies are stacked, there was a problem of bending, in which the battery bends or warps in the direction of the electric field.

[0007] The inventors of the present invention have discovered that one of the causes of the bending phenomenon is an imbalance between the adhesion force between the cathode and the separator and the adhesion force between the anode and the separator when the electrolyte is impregnated. Accordingly, there is a need for a method to improve the adhesion force between the cathode and the separator when the electrolyte is impregnated.

[0008] The present invention aims to provide a lithium secondary battery that suppresses or reduces the bending phenomenon of the lithium secondary battery by having excellent adhesion after electrolyte impregnation between the negative electrode and the separator.

[0009] In addition, the present invention aims to provide a lithium secondary battery with excellent adhesion after electrolyte impregnation between the negative electrode and the separator, and excellent initial resistance characteristics.

[0010]

[0011] To achieve this purpose, according to one aspect of the present invention, a lithium secondary battery of the following embodiment is provided.

[0012] According to a first embodiment, the apparatus comprises an anode, a cathode, an electrolyte, and a separator between the anode and the cathode, wherein the separator comprises a porous polymer substrate; and an inorganic heat-resistant layer formed on at least one surface of the porous polymer substrate and comprising inorganic particles and a first binder polymer. A lithium secondary battery is provided, comprising: an adhesive layer formed on at least one surface of the inorganic heat-resistant layer and comprising a particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer; wherein the cyano group-containing acrylic binder polymer is a copolymer comprising repeating units derived from a monomer having a cyano group and repeating units derived from a monomer having a carboxyl group or a monomer having an alkyl group having 1 to 14 carbon atoms, wherein the ratio of repeating units derived from the monomer having a cyano group is 4% to 9% of 100% of the total repeating units of the cyano group-containing acrylic binder polymer, and wherein the electrolyte contains a cyclic carbonate compound containing 0.4% to 0.75% by weight of vinyl groups based on 100% by weight of the total electrolyte.

[0013] According to the second embodiment, in the first embodiment, the monomer having a cyano group may include (meth)acrylonitrile, 2-(vinyloxy)ethanenitrile, 2-(vinyloxy)propanenitrile, or two or more of these.

[0014] According to the third embodiment, in any one of the first and second embodiments, the monomer having a carboxyl group may be (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, acrylic acid dihydrate, itaconic acid, maleic acid, maleic anhydride, or two or more of these.

[0015] According to the fourth embodiment, in any one of the first to third embodiments, the monomer having an alkyl group having 1 to 14 carbon atoms may be methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, or may include two or more of these.

[0016] According to the fifth embodiment, in any one of the first to fourth embodiments, the cyclic carbonate compound containing a vinyl group may include vinylethylene carbonate (VEC), vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 1,2-diethylvinylene carbonate, or two or more of these.

[0017] According to the 6th embodiment, in any one of the 1st to 5th embodiments, the average particle size (D) of the particulate PVDF-based binder polymer 50 ) may be 0.5 μm to 2 μm.

[0018] According to the seventh embodiment, in any one of the first to sixth embodiments, the adhesive layer may further comprise a second binder polymer.

[0019] According to the eighth embodiment, in any one of the first to seventh embodiments, the content of the particulate PVDF-based binder polymer may be 80% to 90% by weight relative to 100% by weight of the adhesive layer.

[0020] According to the ninth embodiment, in any one of the first to eighth embodiments, the content of the cyano group-containing acrylic binder polymer may be 8% to 15% by weight relative to 100% by weight of the adhesive layer.

[0021]

[0022] A lithium secondary battery according to one embodiment of the present invention may have excellent adhesion after electrolyte impregnation between the negative electrode and the separator. Accordingly, the bending phenomenon of the lithium secondary battery may be suppressed or reduced.

[0023] A lithium secondary battery according to one embodiment of the present invention may have excellent adhesion after electrolyte impregnation between the negative electrode and the separator, and excellent initial resistance characteristics of the battery.

[0024]

[0025] 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.

[0026]

[0027] <Definition>

[0028] 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.

[0029] The glass transition temperature (Tg) may represent a value measured, for example, by Dynamic Mechanical Analysis (DMA) or DSC (TA Instrument) equipment. For example, the glass transition temperature may represent a value measured according to the DMA method specified in ASTM D4065.

[0030] D in the present specification m represents the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D 50 represents the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. Also, D 10 represents the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size, and D 90 It refers to the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size.

[0031] The above particle size can be 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 measure the difference in diffraction patterns according to particle size as the particles pass through a laser beam, thereby calculating the particle size distribution. By calculating the particle diameters at the points where the cumulative distribution of the number of particles according to particle size in the measuring device reaches 10%, 50%, and 90%, respectively, D 10 , D 50 and D 90 It can measure.

[0032] Alternatively, the above particle diameter is determined by observing the particles with a scanning electron microscope (SEM), measuring the particle size through image analysis, calculating the particle size distribution, and then calculating the particle diameters at the points corresponding to 10%, 50%, and 90% of the cumulative particle number distribution, respectively, D 10 , D 50and D 90 It can measure.

[0033] Throughout the entire specification, the term "primary particle" refers to a particle that does not appear to have grain boundaries when observed using a scanning electron microscope at a field of view of 5,000 to 20,000 times.

[0034] Throughout the entire specification, 'secondary particle' refers to a particle formed by the aggregation of the primary particle.

[0035] Throughout the entire specification, 'single particle' refers to a particle that exists independently of the secondary particle and has no grain boundaries on the surface.

[0036] Throughout the entire specification, when the term 'particle' is used, it may mean that any one or all of a single particle, a secondary particle, or a primary particle are included.

[0037]

[0038] The present invention provides a lithium secondary battery.

[0039] A lithium secondary battery according to one embodiment of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, wherein the separator comprises a porous polymer substrate; and an inorganic heat-resistant layer formed on at least one surface of the porous polymer substrate and comprising inorganic particles and a first binder polymer. The invention comprises an adhesive layer formed on at least one surface of the inorganic heat-resistant layer and comprising a particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer; wherein the cyano group-containing acrylic binder polymer is a copolymer comprising repeating units derived from a monomer having a cyano group and repeating units derived from a monomer having a carboxyl group or a monomer having an alkyl group having 1 to 14 carbon atoms, wherein the ratio of repeating units derived from the monomer having a cyano group is 4% to 9% of the total repeating units of the cyano group-containing acrylic binder polymer, and the electrolyte contains a cyclic carbonate compound containing 0.4% to 0.75% by weight of vinyl groups based on 100% by weight of the total electrolyte.

[0040]

[0041] Separator

[0042] porous polymer substrate

[0043] The separator included in the lithium secondary battery of the present invention comprises a porous polymer substrate.

[0044] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein, which acts as a porous ion-conducting barrier that blocks electrical contact between a cathode and an anode while allowing ions to pass through. The pores are structured to be interconnected, so that gas or liquid can pass from one side of the substrate to the other.

[0045] The material constituting this porous polymer substrate may be either an organic material or an inorganic material having electrical insulating properties. In particular, from the perspective of imparting a shutdown function to the porous polymer substrate, it is preferable to use a thermoplastic resin as the constituent material of the porous polymer substrate. Here, the shutdown function refers to a function that prevents thermal runaway of the battery by blocking ion movement through the melting of the thermoplastic resin and closing the pores of the porous substrate when the battery temperature rises. As for the thermoplastic resin, a thermoplastic resin with a melting point of less than 200°C is suitable, and polyolefin is particularly preferred.

[0046] In addition, at least one of the following may be further included: polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous polymer substrate may be a nonwoven fabric, a porous polymer film, or a laminate of two or more of these, but is not specifically limited thereto.

[0047] In the present invention, the porous polymer substrate preferably has a thickness of 3 μm to 50 μm or 5 μm to 12 μm. If the thickness falls short of the above values, the function of the conductive barrier is insufficient, and the mechanical properties are degraded, so the separator may be easily damaged during battery use. On the other hand, if the thickness exceeds the above range excessively (i.e., if it is too thick), the resistance of the separator may increase excessively.

[0048] In one embodiment of the present invention, the weight-average molecular weight of the polyolefin may be 100,000 to 5 million. If the weight-average molecular weight is less than 100,000, it may be difficult to secure sufficient mechanical properties. Also, if it is greater than 5 million, shutdown characteristics may deteriorate or molding may become difficult. In addition, the thrust strength of the porous polymer substrate may be 300 gf or more from the perspective of improving manufacturing yield. The thrust strength of the porous substrate refers to the maximum thrust load (gf) measured by performing a thrust test using a Kato tech KES-G5 handheld compression tester under conditions of a needle tip radius of 0.5 mm and a thrust velocity of 4 mm / sec.

[0049] In a specific embodiment of the present invention, the pore size and porosity present in the porous polymer substrate are not particularly limited, but may be 0.01 μm to 50 μm and 10 vol% to 95 vol%, respectively.

[0050]

[0051] Inorganic heat-resistant layer

[0052] The separator of the present invention comprises an inorganic heat-resistant layer formed on at least one surface of the porous polymer substrate and comprising inorganic particles and a first binder polymer.

[0053] The above-described inorganic heat-resistant layer is formed by mixing a plurality of inorganic particles with a first binder polymer. By coating the porous polymer substrate with the inorganic heat-resistant layer containing such inorganic particles, the heat resistance and mechanical properties of the separator membrane can be further improved. According to a preferred embodiment of the present invention, the inorganic heat-resistant layer may be disposed on both sides of the porous polymer substrate. By forming the inorganic heat-resistant layer on both sides of the porous polymer substrate in this manner, the heat resistance and mechanical properties of the separator membrane may be symmetrically superior, and the porosity may be superior.

[0054] In one embodiment of the present invention, the thickness of the inorganic heat-resistant layer may be in the range of 0.5 μm to 5 μm, 0.6 μm to 2 μm, or 0.8 μm to 1.8 μm based on being formed on one side of the porous polymer substrate.

[0055] In one embodiment of the present invention, the first binder polymer can perform the role of connecting and fixing inorganic particles within the inorganic heat-resistant layer.

[0056] In one embodiment of the present invention, the first binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof. The "particulate" binder polymer may refer to a binder polymer that maintains the added particle shape by being added to a dispersion medium in a particle shape and then coated and dried. The "non-particulate" binder polymer may refer to a binder polymer that is coated and dried in a form dissolved in a solvent when forming an inorganic heat-resistant layer, or one that is added to a dispersion medium in a particle shape but fails to maintain the particle shape upon coating and drying.

[0057] In one embodiment of the present invention, the first binder polymer may include, for example, an acrylic binder polymer, and the acrylic binder polymer may include an acrylic homopolymer formed by polymerizing only acrylic monomers, or may include a copolymer of an acrylic monomer and another monomer. For example, the above acrylic binder polymer is poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexylacrylate and methylmethacrylate, a copolymer of butylacrylate and methylmethacrylate, an ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, an ethyl acrylate-acrylic acid-2-(dimethylamino)ethylacrylate copolymer, an ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, or an ethyl acrylate-acrylic acid-2-(diethylamino)ethylacrylate copolymer. It may include a copolymer or a mixture of two or more of these.

[0058] In one embodiment of the present invention, the first binder polymer is not limited to the acrylic binder polymers listed above. The first binder polymer is, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, It may include pullulan, carboxyl methyl cellulose, or a mixture of two or more of these.

[0059] In one embodiment of the present invention, the first binder polymer may comprise a particulate acrylic binder polymer, a non-particulate acrylic binder polymer, or a combination thereof.

[0060] In one embodiment of the present invention, when the first binder polymer is a non-particulate binder polymer, the inorganic heat-resistant layer can be manufactured by dispersing inorganic particles in a solvent such as acetone, then introducing and dissolving the non-particulate binder polymer in the solvent to prepare a slurry, and then coating the slurry onto a porous polymer substrate by methods such as gravure coating or bar coating.

[0061]

[0062] Meanwhile, in one embodiment of the present invention, the first binder polymer may be a particulate binder polymer in terms of reducing the resistance of the inorganic heat-resistant layer. Since the particulate binder polymer maintains its particulate form in the inorganic heat-resistant layer, it does not penetrate into the pores of the porous polymer substrate, thereby contributing to improving the phenomenon of pore clogging in the porous polymer substrate.

[0063]

[0064] In one embodiment of the present invention, when the first binder polymer is in the form of particles, it may mean that the glass transition temperature (Tg) of the material of the aforementioned binder polymer is 15°C or higher and 40°C or lower, or 20°C or higher and 35°C or lower.

[0065] In one embodiment of the present invention, when the first binder polymer is in the form of particles, the average particle size (D 50 ) is not particularly limited, but can be, for example, 50 nm to 1000 nm, more specifically 100 nm to 500 nm.

[0066]

[0067] In one embodiment of the present invention, the inorganic heat-resistant layer may have a microporous structure formed by interstitial volume between inorganic particles. The inorganic particles may also serve as a type of spacer capable of maintaining the physical shape of the inorganic heat-resistant layer. The interstitial volume refers to a limited space formed by the substantial contact of the inorganic particles. Furthermore, since the inorganic particles generally possess the characteristic that their physical properties do not change even at high temperatures of 200°C or higher, the separator membrane possesses excellent heat resistance due to the inorganic heat-resistant layer.

[0068] The above-mentioned inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are within the operating voltage range of the applied electrochemical element (e.g., Li / Li). + There are no particular limitations as long as oxidation and / or reduction reactions do not occur at a standard voltage of 0 to 5V. In particular, when using inorganic particles with a high dielectric constant, it can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0069] For the reasons stated above, it is preferable that the inorganic particles comprise high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having 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, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 There are O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, or mixtures thereof.

[0070] In addition, as inorganic particles, inorganic particles having lithium ion transport capability may be used, that is, inorganic particles containing lithium elements but having the function of transporting lithium ions without storing lithium. Non-limiting examples of inorganic particles having lithium ion transport capability include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x 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), 리튬란탄티타네이트(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 series glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 글래스(Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc.

[0071]

[0072] In one embodiment of the present invention, the average particle size (D) of the inorganic particles 50 ) is not particularly limited, but can be, for example, 100 to 1000 nm, more specifically 100 to 800 nm.

[0073]

[0074] In one embodiment of the present invention, the inorganic particles may be 70% or more, 99% or less, 80% or more and 97% or less, or 90% or more and 96% or less, based on 100% by weight of the inorganic heat-resistant layer. When the content of the inorganic particles satisfies the above-described range, the inorganic heat-resistant layer may have a high density, and the porosity and resistance characteristics of the separator may be excellent.

[0075] In one embodiment of the present invention, the content of the first binder polymer may be 1 wt% or more and 30 wt% or less, 3 wt% or more and 20 wt% or less, and 4 wt% or more and 10 wt% or less, based on 100 wt% of the inorganic heat-resistant layer. When the content of the binder polymer satisfies the above-described range, the heat resistance of the separation membrane may be excellent without causing detachment of inorganic particles within the inorganic heat-resistant layer.

[0076] In one embodiment of the present invention, the thickness of the inorganic heat-resistant layer may be 0.5 μm or more, 0.6 μm or more, 0.8 μm or more, or 1 μm or more based on being formed on one side of a porous polymer substrate, and may be 50 μm or less, 30 μm or less, 5 μm or less, 2 μm or less, or 1.8 μm or less.

[0077] In one embodiment of the present invention, the inorganic heat-resistant layer may further include a first dispersant. When the first dispersant is included, the aggregation of inorganic particles is deaggregated, thereby further increasing the dispersion of inorganic particles in the inorganic heat-resistant layer. The first dispersant may be, for example, a polyvinylpyrrolidone-based compound, a cellulose-based compound, or an organic acid-based compound.

[0078] In one embodiment of the present invention, the cellulose-based compound may be, for example, ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose sodium salt (CMC-Na'), hydroxyalkyl methyl cellulose, or two or more of these.

[0079] In one embodiment of the present invention, the organic acid compound may be, for example, citric acid, stearic acid, oxalic acid, acetic acid, formic acid, or two or more of these.

[0080] In one embodiment of the present invention, the first dispersant may be included in an amount of less than 5 weight%, less than 4 weight%, less than 3 weight%, less than 2 weight%, and less than 1 weight% based on 100 weight% of the inorganic heat-resistant layer.

[0081]

[0082] Meanwhile, in one embodiment of the present invention, the inorganic heat-resistant layer may further include a first wetting agent. As described below, the first wetting agent can improve coating properties by allowing the water-based slurry for forming the inorganic heat-resistant layer to wet the hydrophobic porous polymer substrate well. This first wetting agent may be a known wetting agent (surfactant), for example, a fluorine-based surfactant, a siloxane-based surfactant, a hydrocarbon-based surfactant, or an ether-based surfactant, and while it may be preferable to use an ether-based surfactant, it is not limited thereto.

[0083] In one embodiment of the present invention, the first wetting agent may be included in an amount of 0.1% to 10% by weight based on 100% by weight of the inorganic heat-resistant layer.

[0084]

[0085] adhesive layer

[0086] The adhesive layer of the present invention is formed on at least one surface of the inorganic heat-resistant layer and comprises a particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer. The adhesive layer is formed by mixing a plurality of particulate PVDF-based binder polymers and cyano group-containing acrylic binder polymers.

[0087] In one embodiment of the present invention, the particulate PVDF-based binder polymer is a binder polymer that maintains the added particle shape by being added to a dispersion medium in a particle shape, coated, and dried.

[0088] In one embodiment of the present invention, the particulate PVDF-based binder polymer may comprise, for example, a polyvinylidenefluoride (PVDF) homopolymer, and may be a copolymer comprising repeating units derived from vinylidenefluoride and repeating units capable of copolymerizing with it. For example, the above-mentioned particulate PVDF-based binder polymer comprises repeating units derived from vinylidene fluoride, repeating units derived from trifluoroethylene (TrFE), repeating units derived from tetrafluoroethylene (TFE), repeating units derived from hexafluoropropylene (HFP), repeating units derived from trichloroethylene (TrCE), repeating units derived from trichlorofluoroethylene (TCFE), repeating units derived from chlorotrifluoroethylene (CTFE), repeating units derived from polymethylmethacrylate (PMMA), repeating units derived from 1,2-difluoroethylene, repeating units derived from perfluoro(methylvinyl)ether, repeating units derived from perfluoro(ethylvinyl)ether, repeating units derived from perfluoro(propylvinyl)ether, repeating units derived from perfluoro(1,3-dioxol), and repeating units derived from perfluoro(2,2-dimethyl-1,3-dioxol). It may be one or more copolymers selected from repeating units derived from polyvinyl acetate (PVAc).

[0089] In one embodiment of the present invention, the particulate PVDF-based binder polymer may preferably be a copolymer comprising repeating units derived from vinylidene fluoride and repeating units derived from hexafluoropropylene (PVDF-HFP).

[0090] In one embodiment of the present invention, the content of the hexapropylene-derived repeating unit may be 1% to 20% by weight, 10% to 15% by weight, or 12% to 13% by weight relative to 100% by weight of the total copolymer. When the content of the hexapropylene-derived repeating unit satisfies the above-described range, the polarity of the PVDF-based binder polymer increases, resulting in excellent dry adhesion, and the solubility in the electrolyte is not excessive, so the wet adhesion of the separator may be excellent, and the particulate PVDF-based binder polymer may be uniformly distributed in the adhesive layer.

[0091] In one embodiment of the present invention, the content of the comonomer in the PVDF-based polymer, that is, the content of repeating units derived from hexapropylene, can be measured by the 1H-NMR method using Varian 500 MHz. For detailed measurement methods, refer to Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. Suitable equipment, such as Bruker Avance III HD 700 MHz NMR or Varian 500 MHz NMR, may be used to verify the NMR spectrum.

[0092] In one embodiment of the present invention, the glass transition temperature (Tg) of the particulate PVDF-based binder polymer may be -30°C to 40°C or -20°C to 20°C. Additionally, the melting point (Tm) of the particulate PVDF-based binder polymer may be 100°C to 180°C or 130°C to 150°C.

[0093] In one embodiment of the present invention, the average particle size (D) of the PVDF-based binder polymer 50) may be 0.5 μm to 2 μm, or 0.8 μm to 1.8 μm. When the size of the PVDF-based binder polymer satisfies the above-described range, the adhesion and porosity of the separation membrane may be superior. Meanwhile, at this time, the average particle size (D) of the PVDF-based binder polymer 50 ) is the average particle size (D) of the primary particles of the PVDF-based binder polymer. 50 It means ).

[0094]

[0095] In one embodiment of the present invention, the cyano group-containing acrylic binder polymer is a copolymer comprising a repeating unit derived from a monomer having a cyano group and a repeating unit derived from a monomer having a carboxyl group or a monomer having an alkyl group having 1 to 14 carbon atoms.

[0096] In one embodiment of the present invention, the glass transition temperature (Tg) of the cyano group-containing acrylic binder polymer may be -40 to 0°C. The cyano group-containing acrylic binder polymer may be in a non-particulate state. Specifically, the cyano group-containing acrylic binder polymer may be water-dispersed in a particulate form through emulsion polymerization, but due to the low glass transition temperature, it may not maintain a particulate form when coated at room temperature.

[0097] In one embodiment of the present invention, the monomer having a cyano group is not limited to having a cyano group (-CN) within a repeating unit, and may include, for example, (meth)acrylonitrile, 2-(vinyloxy)ethanenitrile, 2-(vinyloxy)propanenitrile, or two or more of these. The monomer having a cyano group can improve the affinity with the cyclic carbonate group compound containing a vinyl group of the present invention, thereby providing excellent adhesion between the cathode and the separator under the electrolyte (wet adhesion of the cathode and the separator). Specifically, a reduction film can be formed between the cathode and the separator from the cyclic carbonate group compound containing a vinyl group, and since the cyano group may have excellent affinity with the reduction film, the wet adhesion of the cathode and the separator can be excellent.

[0098] In one embodiment of the present invention, the monomer having a carboxyl group may be (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, acrylic acid dihydrate, itaconic acid, maleic acid, maleic anhydride, or two or more of these.

[0099] In one embodiment of the present invention, the monomer having an alkyl group having 1 to 14 carbon atoms may be methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, or may comprise two or more of these.

[0100] Meanwhile, in the present specification, terms written in parentheses such as (meth)acrylonitrile mean that they include both methacrylonitrile and acrylonitrile.

[0101] In one embodiment of the present invention, the proportion of repeating units derived from the monomer having a cyano group is 4% to 9% of the total repeating units of the cyano group-containing acrylic binder polymer. In one embodiment of the present invention, the proportion of repeating units derived from the monomer having a cyano group may be 5% to 8.5%, or 6% to 8%, of the total repeating units of the cyano group-containing acrylic binder polymer. Known methods capable of determining the number of repeating units of a copolymer may be used for the repeating units derived from the monomer having a cyano group. For example, since the repeating units derived from the monomer having a cyano group contain -CN groups, the proportion of repeating units derived from the monomer having a cyano group can be determined through nuclear magnetic resonance spectroscopy (NMR) analysis. Meanwhile, the proportion of repeating units may mean the 'ratio of the number of moles of repeating units'.

[0102]

[0103] In one embodiment of the present invention, the adhesive layer may further comprise a second binder polymer. In one embodiment of the present invention, the second binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0104] In one embodiment of the present invention, the acrylic binder polymer may comprise an acrylic binder polymer. The acrylic binder polymer may comprise an acrylic homopolymer formed by polymerizing only acrylic monomers, and may also comprise a copolymer of an acrylic monomer and another monomer. For example, the above acrylic binder polymer is poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexylacrylate and methylmethacrylate, a copolymer of butylacrylate and methylmethacrylate, an ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, an ethyl acrylate-acrylic acid-2-(dimethylamino)ethylacrylate copolymer, an ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, or an ethyl acrylate-acrylic acid-2-(diethylamino)ethylacrylate copolymer. It may include a copolymer or a mixture of two or more of these.

[0105] In one embodiment of the present invention, when the second binder polymer is in the form of particles, it may mean that the glass transition temperature (Tg) of the material of the aforementioned binder polymer is 15°C or higher and 40°C or lower, or 20°C or higher and 35°C or lower.

[0106] In one embodiment of the present invention, when the second binder polymer is in the form of particles, the second binder polymer has an average particle size (D) of 100 nm to 800 nm or 200 nm to 700 nm. 50 It may be having ).

[0107]

[0108] In one embodiment of the present invention, the adhesive layer may include a second dispersant, and the second dispersant may include a caprolactone-based dispersant.

[0109] In one embodiment of the present invention, the second dispersant may be included in an amount of 1% to 3% by weight based on 100% by weight of the adhesive layer.

[0110] In one embodiment of the present invention, the caprolactone-based dispersant comprises a caprolactone-derived repeating unit, and may comprise an ethylene glycol-derived repeating unit, a propylene glycol-derived repeating unit, or two or more of these repeating units. By using the second dispersant, the particulate PVDF-based binder polymer can be further dispersed in the dispersion medium, thereby controlling the surface roughness of the adhesive layer and making the electrode-separator adhesion even better.

[0111] In one embodiment of the present invention, the second dispersant may comprise 40% to 60% or 45% to 55% of repeating units derived from ethylene glycol relative to 100% of the total number of repeating units, may comprise 20% to 30% or 23% to 27% of repeating units derived from propylene glycol, and may comprise 23% to 27% of repeating units derived from caprolactone.

[0112]

[0113] In one embodiment of the present invention, the second dispersant may be included in an amount of 1% to 3% by weight based on 100% by weight of the adhesive layer. By satisfying the content of the second dispersant, the clumping of the binder polymer within the adhesive layer is prevented, thereby allowing the thickness of the adhesive layer to be uniform and the adhesive strength to be excellent.

[0114]

[0115] In one embodiment of the present invention, the PVDF-based binder polymer may be included in an amount of 80% to 90% by weight or 83% to 87% by weight based on 100% by weight of the adhesive layer. Since the content of the PVDF-based binder polymer satisfies the above-described range, the adhesion between the electrode and the separator may be excellent, and the resistance characteristics of the separator may be excellent, and the difference between the adhesion between the anode and the separator and the adhesion between the cathode and the separator may not be large, so that the banding phenomenon of the battery may not occur.

[0116]

[0117] In one embodiment of the present invention, the cyano group-containing acrylic binder polymer may be included in an amount of 8% to 15% by weight or 10% to 12% by weight based on 100% by weight of the adhesive layer. Since the content of the second binder polymer satisfies the above-described range, the adhesion between the electrode and the separator may be excellent, and the resistance characteristics of the separator may be excellent, and the difference between the adhesion between the anode and the separator and the adhesion between the cathode and the separator may not be large, so that the banding phenomenon of the battery may not occur.

[0118]

[0119] In one embodiment of the present invention, the adhesive layer may further include a second wetting agent to better disperse the particulate PVDF-based binder polymer in the dispersion medium.

[0120] This second wetting agent may use known wetting agents (surfactants), for example, fluorine-based surfactants, siloxane-based surfactants, hydrocarbon-based surfactants, and ether-based surfactants, and it may be preferable to use ether-based surfactants, but is not limited thereto.

[0121] In one embodiment of the present invention, the second wetting agent may be included in an amount of 0.1% to 10% by weight, or 0.5% to 2% by weight, based on 100% by weight of the adhesive layer.

[0122]

[0123] Method for manufacturing a separation membrane

[0124] In one embodiment of the present invention, the method of manufacturing the separation membrane is not limited as long as it can be performed by a person skilled in the art. For example, the separation membrane may be manufactured by the steps of: (S1) preparing a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer and a water-based adhesive layer forming slurry comprising particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer; (S2) applying and drying the water-based inorganic heat-resistant layer forming slurry on at least one surface of a porous polymer substrate to form an inorganic heat-resistant layer; and (S3) applying and drying the adhesive layer forming slurry on at least one surface of the water-based inorganic heat-resistant layer to form an adhesive layer.

[0125]

[0126] In one embodiment of the present invention, the dispersion medium is an aqueous dispersion medium. The aqueous dispersion medium may be water or an aqueous dispersion medium containing water. In addition, if there are limitations on the drying speed and temperature, methanol, ethanol, isopropyl alcohol, etc., having 1 to 5 carbon atoms and having a boiling point lower than water may be used together. In the above manufacturing method, by using an aqueous dispersion medium, the particulate binder polymer is dispersed while maintaining its particle shape without dissolving in the dispersion medium.

[0127] Meanwhile, in one embodiment of the present invention, it is preferable that the water-based inorganic heat-resistant layer forming slurry and the water-based adhesive layer forming slurry have a concentration of solids (or is also referred to as the content of solids) excluding the dispersion medium in the range of 20 wt% to 50 wt%.

[0128] In one embodiment of the present invention, the aqueous inorganic heat-resistant layer forming slurry may further comprise a first wetting agent. The first wetting agent can improve coating properties by allowing the inorganic heat-resistant layer forming slurry to wet a hydrophobic porous polymer substrate well. Meanwhile, the first wetting agent may be a known wetting agent and may substitute for the one described above.

[0129] In one embodiment of the present invention, the slurry for forming a water-based inorganic heat-resistant layer may further include a first dispersant. Meanwhile, the description of the first dispersant is substituted with the foregoing description.

[0130] In one embodiment of the present invention, the first dispersant may be included in an amount of less than 5 weight%, less than 4 weight%, less than 3 weight%, less than 2 weight%, or less than 1 weight% based on a solid content of 100 weight% of the slurry for forming an inorganic heat-resistant layer.

[0131]

[0132] In one embodiment of the present invention, the slurry for forming a water-based adhesive layer further comprises a second dispersant, and the second dispersant may comprise a caprolactone-based dispersant. In any case, the description of the second dispersant is substituted with the foregoing description.

[0133] In one embodiment of the present invention, the second dispersant may be included in an amount of 1% to 3% by weight based on a solid content of 100% by weight of the slurry for forming an adhesive layer.

[0134] Afterwards, (S2) the water-based inorganic heat-resistant layer forming slurry is applied and dried on at least one surface of the porous polymer substrate to form an inorganic heat-resistant layer.

[0135] In one embodiment of the present invention, there are no limitations on the method of applying the aqueous inorganic heat-resistant layer forming slurry onto at least one surface of a porous polymer substrate. For example, the application method may utilize various methods such as dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, Mayer bar coating, direct metering coating, or a combination thereof.

[0136] In one embodiment of the present invention, the drying method of the water-based inorganic heat-resistant layer forming slurry is not limited to a specific method, and, for example, one or more combinations of convection drying, hot air drying, forced air drying, and natural drying methods may be applied. Preferably, the drying method may be hot air drying.

[0137] In one embodiment of the present invention, the drying step may be performed at a temperature of 55°C to 68°C. When the temperature of the drying step satisfies the above-described range, limited inorganic particles may be placed within an inorganic heat-resistant layer to have better durability and mechanical strength.

[0138] In one embodiment of the present invention, the drying step may be performed for 10 to 120 seconds within the temperature range described above.

[0139] Afterwards, (S3) a slurry for forming the adhesive layer is applied and dried on at least one surface of the above-mentioned inorganic heat-resistant layer to form an adhesive layer.

[0140] In one embodiment of the present invention, the method of applying the water-based adhesive layer forming slurry is not limited, and the method of applying the water-based inorganic heat-resistant layer forming slurry described above may be adopted as is.

[0141] In one embodiment of the present invention, the method of drying the water-based adhesive layer forming slurry is not limited, and an appropriate method such as convection drying, hot air drying, blowing air drying, or a combination of two or more of natural drying methods may be applied. Preferably, the drying method may be hot air drying.

[0142] In one embodiment of the present invention, the step of drying the water-based adhesive layer forming slurry may be performed at a temperature of 50°C to 70°C for 10 seconds to 120 seconds.

[0143]

[0144] <Anode and Cathode>

[0145] In the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer comprising a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material is a layered compound such as a lithium manganese complex oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M xIt may include a lithium manganese complex oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions; a disulfide compound; and one or more of Fe2(MoO4)3.

[0146]

[0147] In the present invention, the cathode comprises a cathode current collector and a cathode active material layer comprising a cathode active material, a conductive material, and a binder resin on at least one surface of the current collector. The cathode comprises, as the cathode active material, carbon such as lithium metal oxide, non-graphitizable carbon, and graphite-based carbon; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물 중 선택된 1종 또는 2종 이상의 혼합물을 포함할 수 있다.

[0148] In one embodiment of the present invention, the negative electrode may include a silicon-based material as a negative electrode active material. When the negative electrode includes a silicon-based material, the degree of volume expansion is large, increasing the contact area with the separator in the battery, thereby allowing high adhesion to be maintained.

[0149]

[0150] In a specific embodiment of the present invention, the conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0151]

[0152] The above current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used.

[0153]

[0154] As the above binder resin, polymers commonly used in the industry for electrodes may be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples include acetatepropionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0155]

[0156] <Electrolyte and Electrolyte Additives>

[0157] In the present invention, the electrolyte 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 - , N(CF3SO2)2 - , C(CF2SO2)3 - Salts comprising anions such as or combinations thereof are dissolved or dissociated in organic solvents including 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), ester compounds, and mixtures of one or more selected from these, but are not limited thereto.

[0158]

[0159] Meanwhile, in a specific embodiment of the present invention, the organic solvent comprises an ester-based compound, and preferably, the ester-based compound is 30% by weight or more, 50% by weight or more, 60% by weight or more, or 65% by weight or more relative to 100% by weight of the organic solvent.

[0160] In a specific embodiment of the present invention, the ester compound comprises one or more selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0161]

[0162] In one embodiment of the present invention, the electrolyte contains a cyclic carbonate compound containing vinyl groups in an amount of 0.4% to 0.75% by weight based on 100% by weight of the total electrolyte. The cyclic carbonate containing vinyl groups can form an organic film on the surface of the negative electrode, and the organic film may have excellent affinity with the cyano groups included in the adhesive layer. Meanwhile, if the content of the cyclic carbonate compound exceeds the upper limit described above, the initial resistance of the battery may be unfavorable, and if the content is below the lower limit described above, an organic film is not sufficiently formed on the surface of the negative electrode, and the wet adhesion strength of the negative electrode-separator may be inferior.

[0163]

[0164] In one embodiment of the present invention, the cyclic carbonate compound containing vinyl groups may include vinylethylene carbonate (VEC), vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 1,2-diethylvinylene carbonate, or two or more of these, and preferably, the cyclic carbonate compound may include vinylethylene carbonate (VEC) compound.

[0165]

[0166] Meanwhile, the electrolyte may contain electrolyte additives excluding the cyclic carbonate compound in an amount of 0.1% to 4% by weight, 1% to 3.5% by weight, 2% to 3.5% by weight, or 3% to 3.5% by weight relative to 100% by weight of the electrolyte. The electrolyte additives excluding the cyclic carbonate compound may be, for example, fluoroethylene carbonate (FEC), LiTFSi (Lithium (bis)trifluoromethanesulfonyl imide, LiN(SO2CF3)2), propane sulfone (PS), succinate nitrile (SN), cyclohexylbenzene (CHB), biphenyl (BP), propane sulfone (PRS), etc.

[0167]

[0168] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0169] <Example 1>

[0170] Manufacturing of separation membranes

[0171] Aluminum oxide (Al2O3, D) as an inorganic particle 50 : 450 nm, Sumitomo Co.) and an acrylic polymer as the first binder polymer were added to water at room temperature to prepare a first dispersion, and this was bead-milled to prepare a slurry for forming an aqueous inorganic heat-resistant layer. In addition, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D) was used as a particulate PVDF-based binder polymer. 50A second dispersion was prepared by adding a caprolactone-based dispersant containing a cyano group-containing acrylic binder polymer (: 3 μm) and a caprolactone-derived repeating unit, and the mixture was bead-milled to prepare a water-based adhesive layer forming slurry. At this time, the cyano group-containing acrylic binder was a copolymer containing acrylonitrile-derived repeating units and methyl acrylate-derived repeating units, and the proportion of the acrylonitrile-derived repeating units was 7% of the total repeating units (100%).

[0172] A water-based inorganic heat-resistant layer forming slurry was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method and dried at a temperature of 65°C for 30 seconds. Subsequently, an adhesive layer forming slurry was applied to the inorganic heat-resistant layer using the doctor blade method and dried at a temperature of 60°C for 30 seconds. In the same way, an inorganic heat-resistant layer and an adhesive layer were formed on the other side of the porous polymer substrate made of polyethylene. At this time, the formed inorganic heat-resistant layer was 1.5 μm thick, and the adhesive layer was 0.75 μm thick. In addition, the content of inorganic particles in the inorganic heat-resistant layer satisfied 5 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0173] Manufacturing of lithium secondary batteries

[0174] Li(Ni as a positive electrode active material 1 / 3 Mn 1 / 3 Co 1 / 3 A slurry is prepared by mixing 95 wt% O2, 3 wt% carbon black, and 2 wt% polyvinylidene fluoride (PVdF) as an anode binder, and then this anode composite slurry is used for 4.5 mAh / cm² 2 After applying the amount to aluminum foil, it was dried in a vacuum oven at 100°C for more than 10 hours, and an anode with a thickness of 100 μm was manufactured using a roll-type press.

[0175] In addition, a slurry was prepared by mixing 96 wt% natural graphite and 1 wt% carbon black as a negative electrode active material, and 2 wt% styrene-butadiene rubber (SBR) and 1 wt% CMC as negative electrode binders, and then this negative electrode composite slurry had 5.4 mAh / cm² 2 After applying the amount to the copper foil, it was dried in a vacuum oven at 100°C for more than 10 hours, and a 120㎛ thick cathode was manufactured using a roll-type press.

[0176] A lithium secondary battery was manufactured by using the cathode and anode prepared above, interposing the separator prepared above between the cathode and anode, and then injecting an electrolyte solution in which 1M LiPF6 is dissolved and the electrolyte solution is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, and 0.5 wt% of a vinyl group-containing cyclic carbonate mixed with propane sultone (PRS), vinylene carbonate (VC), and vinylethylene carbonate (VEC) as an electrolyte additive.

[0177]

[0178] <Example 2>

[0179] In the above Example 1, the above was prepared in the same manner as Example 1, except that a vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was included at 0.7 wt% as an electrolyte additive, and a cyano group-containing acrylic binder polymer having a ratio of acrylonitrile-derived repeating units of 6% of the total repeating units was used.

[0180]

[0181] <Comparative Example 1>

[0182] In the above Example 1, the product was prepared in the same manner as Example 1, except that an acrylic binder polymer not containing acrylonitrile-derived repeating units was used instead of a cyano group-containing acrylic binder polymer.

[0183]

[0184] <Comparative Example 2>

[0185] In the above Comparative Example 1, the above was prepared in the same manner as Comparative Example 1, except that vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was not included as an electrolyte additive.

[0186]

[0187] <Comparative Example 3>

[0188] In the above Example 1, the above was prepared in the same manner as Example 1, except that a vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was included at 0.2 wt% as an electrolyte additive, and a cyano group-containing acrylic binder polymer having a ratio of acrylonitrile-derived repeating units of 5% of the total repeating units was used.

[0189]

[0190] <Comparative Example 4>

[0191] In the above Example 1, the above was prepared in the same manner as Example 1, except that a vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was included at 0.8 wt% as an electrolyte additive, and a cyano group-containing acrylic binder polymer having a ratio of acrylonitrile-derived repeating units of 7% of the total repeating units was used.

[0192]

[0193] <Comparative Example 5>

[0194] In the above Example 1, the above was prepared in the same manner as Example 1, except that a vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was included at 0.6 wt% as an electrolyte additive, and a cyano group-containing acrylic binder polymer having a ratio of acrylonitrile-derived repeating units of 3% of the total repeating units was used.

[0195]

[0196] <Comparative Example 6>

[0197] In the above Example 1, the above was prepared in the same manner as Example 1, except that a vinyl group-containing cyclic carbonate mixed with vinylene carbonate (VC) and vinylethylene carbonate (VEC) was included at 0.6 wt% as an electrolyte additive, and a cyano group-containing acrylic binder polymer having a ratio of acrylonitrile-derived repeating units of 10% of the total repeating units was used.

[0198]

[0199] <Experimental Example>

[0200] The negative electrode-separator wet adhesion and cell initial resistance were measured for the separators and lithium secondary batteries of each example and comparative example and are shown in Table 1.

[0201] Comparative Example / Example Inclusion of monomers having cyano groups Ratio of repeating units derived from monomers having cyano groups (%) Vinyl group-containing cyclic carbonate content (wt%) Cathode-separator wet adhesion (gf / 20mm) Cell initial resistance (SOC 50, 2.5C 10s) (Ohm) Example 1: 70.59.50.621 Example 2: 60.710.20.633 Comparative Example 1: XX0.52.30.624 Comparative Example 2: XX02.10.586 Comparative Example 3: 50.24.40.610 Comparative Example 4: 70.812.70.652 Comparative Example 5: 30.61.50.647 Comparative Example 6: 100.612.80.698

[0202] Examples 1 and 2 exhibited excellent wet adhesion and cell initial resistance characteristics of the cathode-separator. In contrast, Comparative Examples 1 and 2 did not contain a cyano group-containing acrylic binder polymer, resulting in inferior wet adhesion of the cathode-separator. Comparative Example 3 contained a small amount of vinyl group-containing cyclic carbonate, resulting in inferior wet adhesion of the cathode-separator. Comparative Example 4 contained an excessive amount of vinyl group-containing cyclic carbonate, causing a slight increase in cell initial resistance. Comparative Example 5 had a low proportion of repeating units derived from monomers containing cyano groups in the cyano group-containing acrylic binder polymer, resulting in inferior wet adhesion of the cathode-separator. Comparative Example 6 had a high proportion of repeating units derived from monomers containing cyano groups in the cyano group-containing acrylic binder polymer, leading to excessive affinity with the electrolyte and causing swelling at the cathode-separator interface, which in turn caused an excessive increase in cell initial resistance characteristics.

[0203]

[0204] Experimental Example 1: Cathode-Separator Wet Adhesion

[0205] The separator obtained through each example and comparative example was cut to a size of 70 mm (length) x 25 mm (width), and the prepared cathode, separator, and anode were laminated into a C-type bicell structure of cathode / separator / anode / separator / anode. Then, a specimen was fabricated by laminating using a press at 60°C and 5 kgf for 5 minutes. The prepared specimen was placed in a battery case along with an electrolyte and maintained for 4 hours to impregnate the specimen with the electrolyte. The electrolyte used was prepared by mixing ethylene carbonate and propionate in a volume ratio of 7:3 and having a concentration of LiPF6 1M. Afterward, the specimen was removed from the case and fixed by attaching it to a glass plate using double-sided tape, positioning the cathode so that it faced the glass plate. The separator portion of the specimen was peeled at a 90° angle at a speed of 15 mm / min at 25°C, and the strength at that time was measured.

[0206]

[0207] Experimental Example 2: Measurement of Resistance Characteristics of the Separator

[0208] The separator prepared in each example and comparative example was cut into 19 phi and then fabricated into a CR2016 coin cell, and then measured by the alternating current method at 25 ℃ using an EIS (Electrochemical Impedance Spectroscopy, Ametek) electrolyte of 1M LiPF6-ethylene carbonate / ethylmethyl carbonate (weight ratio 3:7).

Claims

1. The apparatus comprises an anode, a cathode, an electrolyte, and a separator between the anode and the cathode, and The above separator is a porous polymer substrate; An inorganic heat-resistant layer formed on at least one surface of the above-mentioned porous polymer substrate and comprising inorganic particles and a first binder polymer; and An adhesive layer formed on at least one surface of the above-mentioned inorganic heat-resistant layer and comprising a particulate PVDF-based binder polymer and a cyano group-containing acrylic binder polymer; comprising The above cyano group-containing acrylic binder polymer is a copolymer comprising repeating units derived from a monomer having a cyano group and repeating units derived from a monomer having a carboxyl group or a monomer having an alkyl group having 1 to 14 carbon atoms. The proportion of repeating units derived from the monomer having the above cyano group is 4% to 9% of the total repeating units of the cyano group-containing acrylic binder polymer, and A lithium secondary battery characterized in that the above electrolyte contains a cyclic carbonate compound containing 0.4% to 0.75% by weight of vinyl groups based on 100% by weight of the total electrolyte.

2. In Claim 1, A lithium secondary battery characterized in that the monomer having the above-mentioned cyano group comprises (meth)acrylonitrile, 2-(vinyloxy)ethanenitrile, 2-(vinyloxy)propanenitrile, or two or more of these.

3. In Claim 1, A lithium secondary battery characterized in that the monomer having the carboxyl group comprises (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, acrylic acid dihydrate, itaconic acid, maleic acid, maleic anhydride, or two or more of these.

4. In Claim 1, A lithium secondary battery characterized in that the monomer having an alkyl group having 1 to 14 carbon atoms is methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, or comprises two or more of these.

5. In Claim 1, A lithium secondary battery characterized in that the cyclic carbonate compound containing the vinyl group comprises vinylethylene carbonate (VEC), vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 1,2-diethylvinylene carbonate, or two or more of these.

6. In Claim 1, Average particle size (D) of the above particulate PVDF-based binder polymer 50 A lithium secondary battery characterized by having a thickness of 0.5 μm to 2 μm.

7. In Claim 1, A lithium secondary battery characterized in that the adhesive layer further comprises a second binder polymer.

8. In Claim 1, A lithium secondary battery characterized in that the content of the above-mentioned particulate PVDF-based binder polymer is 80% to 90% by weight relative to 100% by weight of the adhesive layer.

9. In Claim 1, A lithium secondary battery characterized in that the content of the above-mentioned cyano group-containing acrylic binder polymer is 8% to 15% by weight relative to 100% by weight of the adhesive layer.