Separator for lithium secondary battery, and lithium secondary battery comprising same

Abstract

The present invention provides a separator for a lithium secondary battery, comprising: a porous polymer substrate; and 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, wherein, on the basis of 100% of a total surface area of the inorganic heat-resistant layer, a surface area occupied by the inorganic particles is 73% to 88%, and a SPAN value of the inorganic particles is 1.3 or less, the SPAN value being calculated according to equation 1 below. [Equation 1] SPAN value = (particle diameter of inorganic particles (D90) − particle diameter of inorganic particles (D10)) / particle diameter of inorganic particles (D50)

Description

Separator for lithium secondary battery and lithium secondary battery including the same

[0001] The present invention relates to a separator for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Join by reference

[0003] This application claims the benefit of priority based on Korean Patent Applications No. 10-2024-0157408 and No. 10-2024-0157409 filed November 7, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0004]

[0005] Electrochemical devices such as lithium-ion batteries generally consist of a positive electrode, a negative electrode, an electrolyte, and a separator, and are widely used in portable electronic devices, electric vehicles, and energy storage systems (ESS) based on their high energy density and excellent charge / discharge characteristics.

[0006] However, ensuring the safety of lithium-ion batteries remains a critical challenge. In particular, due to the polymeric material properties of the separator, it can undergo thermal shrinkage at high temperatures, potentially causing internal short circuits. Furthermore, if the adhesion to the electrode is insufficient, problems such as the battery bending or the separator being damaged may occur due to the expansion and contraction of the electrode during the charging and discharging process.

[0007] To improve this, a composite separator with an inorganic heat-resistant layer containing inorganic particles and a binder polymer has been proposed, but there is a limitation in that the adhesion strength decreases when the dispersion of inorganic particles and the binder is non-uniform. In addition, in jelly-roll type electrode assemblies applied to cylindrical batteries, damage (impingement) is likely to occur as the separator is locally pressed due to the repeated expansion and contraction of the electrode during charge-discharge cycles, which reduces the reliability of the battery.

[0008] Therefore, there is a need to develop technology that can effectively control the adhesion between the electrode and the separator while simultaneously ensuring heat resistance, durability, and mechanical strength to suppress separator damage occurring during charge-discharge cycles.

[0009]

[0010] The present invention has been devised to solve the aforementioned problems, and one objective is to provide a separator for a lithium secondary battery having excellent heat resistance, durability, mechanical strength, and resistance characteristics.

[0011] Another objective of the present invention is to provide a separator for a lithium secondary battery that can prevent impingement occurring as the charge-discharge cycle of the battery progresses when used in a cylindrical battery.

[0012] Another objective of the present invention is to provide a separator for a lithium secondary battery with excellent electrode-separator adhesion by controlling the surface area (coverage) and distribution of inorganic particles in the inorganic heat-resistant layer so that the surface roughness satisfies a predetermined range.

[0013] Another objective of the present invention is to provide a separator for a lithium secondary battery having excellent resistance characteristics and dielectric breakdown voltage characteristics.

[0014] In addition, another objective of the present invention is to provide a lithium secondary battery comprising the separator.

[0015] However, the technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems will be clearly understood by those skilled in the art from the description of the invention below.

[0016]

[0017] To achieve these objectives, according to one aspect of the present invention, a separator for a lithium secondary battery and a lithium secondary battery including the same are provided according to the following embodiments.

[0018] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising: 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, wherein the surface area of ​​the inorganic heat-resistant layer occupied by inorganic particles is 73% to 88% based on 100% of the total surface area, and the span value of the inorganic particles is 1.3 or less, and the span value is calculated by the following formula 1.

[0019] SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D 50 ) … Equation (1)

[0020] According to the second embodiment, in the first embodiment, the content of the inorganic particles may be 70% to 95% by weight based on 100% by weight of the inorganic heat-resistant layer.

[0021] According to the third embodiment, in any one of the first and second embodiments, the first binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0022] According to the fourth embodiment, in any one of the first to third embodiments, the content of the first binder polymer may be 5% to 30% by weight based on 100% by weight of the inorganic heat-resistant layer.

[0023] According to the fifth embodiment, in any one of the first to fourth embodiments, the surface of the inorganic heat-resistant layer may have a surface area occupied by pores of 12% to 27% based on 100% of the total surface area.

[0024] According to the 6th embodiment, in any one of the 1st to 5th embodiments, the surface of the inorganic heat-resistant layer may have a surface area occupied by the first binder polymer of less than 10% based on 100% of the total surface area.

[0025] According to the seventh embodiment, in any one of the first to sixth embodiments, the inorganic heat-resistant layer may be formed only on one side of the porous polymer substrate.

[0026] According to the eighth embodiment, in any one of the first to seventh embodiments, the thickness of the inorganic heat-resistant layer may be 1.0 μm to 2.0 μm or less.

[0027] According to the ninth embodiment, in any one of the first to eighth embodiments, the loading amount of the inorganic heat-resistant layer is 2.0 g / m² 2 Up to 3.0 g / m² 2 It may be within the range of.

[0028] According to the 10th embodiment, in any one of the 1st to 9th embodiments, the surface roughness (Sa) of the inorganic heat-resistant layer may be 0.07 μm to 0.12 μm.

[0029] According to the 11th embodiment, in any one of the 1st to 10th embodiments, an adhesive layer comprising a particulate PVDF-based binder polymer may be further included, which is formed alone on at least one surface of the porous polymer substrate or formed on the inorganic heat-resistant layer.

[0030] According to the 12th embodiment, in the 11th embodiment, the adhesive layer may further comprise a second dispersant.

[0031] According to the 13th embodiment, in any one of the 11th to 12th embodiments, the adhesive layer further comprises a second binder polymer, and the second binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0032] According to the 14th embodiment, in the 13th embodiment, the average particle size (D) of the particulate binder polymer 50 ) may be 100 nm to 800 nm.

[0033] According to the 15th embodiment, in any one of the 13th to 14th embodiments, the surface area occupied by the particulate PVDF-based binder polymer and the second binder polymer may be 85% or more based on 100% of the total surface area of ​​the adhesive layer.

[0034] According to the 16th embodiment, a lithium secondary battery is provided, comprising: an electrode assembly including a positive electrode, a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a battery housing in which the electrode assembly and an electrolyte are housed, wherein the separator is a separator according to any one of the 1st to 15th embodiments.

[0035] According to the 17th embodiment, in the 16th embodiment, the battery housing is characterized as being a cylindrical can, a rectangular can, a pouch-type case, or a combination thereof.

[0036]

[0037] A separator for a lithium secondary battery according to one embodiment of the present invention may have excellent heat resistance, durability, mechanical strength, and resistance characteristics.

[0038] A separator for a lithium secondary battery according to one embodiment of the present invention can prevent or reduce impingement that occurs as the charge-discharge cycle of the battery progresses when used in a cylindrical battery.

[0039] In the case where a separator for a lithium secondary battery according to one embodiment of the present invention includes an adhesive layer, the electrode-separator adhesion strength, particularly the adhesion strength in a dry state (dry adhesion strength), may be excellent.

[0040] A separator for a lithium secondary battery according to one embodiment of the present invention may have excellent resistance characteristics and dielectric breakdown voltage characteristics.

[0041] Meanwhile, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be obvious to those skilled in the art from the following description of the invention.

[0042]

[0043] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0044] Figure 1a is a photograph of the surface of the inorganic heat-resistant layer of Example 1-1 taken with an SEM.

[0045] Figure 1b shows the inorganic particles of the inorganic heat-resistant layer of Example 1-1 classified by particle size using an image program.

[0046] Figure 1c shows the particle size distribution of the inorganic particles of Example 1-1.

[0047] Figure 2a is a photograph of the surface of the inorganic heat-resistant layer of Comparative Example 1-1 measured by SEM.

[0048] Figure 2b shows the inorganic particles of the inorganic heat-resistant layer of Comparative Example 1-1 classified by their size using an image program.

[0049] Figure 2c shows the particle size distribution of the inorganic particles of Comparative Example 1-1.

[0050]

[0051] 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.

[0052]

[0053] <Definition>

[0054] 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.

[0055] Throughout this specification, 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.

[0056] Throughout this specification, Dn refers to 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.

[0057] 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.

[0058] 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.

[0059] Throughout the entire specification, 'secondary particle' refers to a particle formed by the aggregation of the primary particle.

[0060]

[0061] The present invention provides a separator for a lithium secondary battery.

[0062] A separator for a lithium secondary battery according to one embodiment of the present invention 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; wherein the surface of the inorganic heat-resistant layer has a surface area occupied by inorganic particles of 73% to 88% based on 100% of the total surface area, and the span value of the inorganic particles is 1.3 or less, and the span value is calculated by the following formula 1.

[0063] SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D50 ) … Equation (1)

[0064]

[0065] <Porous polymer substrate>

[0066] The separator for a lithium secondary battery according to the present invention comprises a porous polymer substrate.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073]

[0074] Inorganic heat-resistant layer

[0075] The separator for a lithium secondary battery according to the present invention is formed on at least one surface of the porous polymer substrate and comprises an inorganic heat-resistant layer comprising inorganic particles and a first binder polymer.

[0076] The above-mentioned inorganic heat-resistant layer is formed by mixing a plurality of inorganic particles and a first binder polymer. By coating the porous polymer substrate with an inorganic heat-resistant layer containing such inorganic particles, the heat resistance and mechanical properties of the separation membrane can be improved.

[0077]

[0078] 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.

[0079] 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.

[0080] 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 yO3(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.

[0081] 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 Siy 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.

[0082] 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 nm to 1000 nm, more specifically 100 nm to 800 nm.

[0083] In one embodiment of the present invention, the content of the inorganic particles may be 70% to 95% by weight, 80% to 93% by weight, or 85% to 92% by weight 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.

[0084]

[0085] 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.

[0086] In one embodiment of the present invention, the first binder polymer may include a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0087] The above "particle-type" 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 subsequently coated and dried. The above "non-particle-type" 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.

[0088]

[0089] In one embodiment of the present invention, the first binder polymer may be an acrylic polymer. The acrylic polymer may include an acrylic homopolymer formed by polymerizing only acrylic monomers, and may also 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.

[0090] In one embodiment of the present invention, the first binder polymer is not limited to the acrylic binder polymers listed above. The above 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 -40°C or higher and 40°C or lower, or -35°C or higher and 35°C or lower.

[0095] 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 800 nm.

[0096]

[0097] In one embodiment of the present invention, the content of the first binder polymer may be 5% to 30% by weight, 10% to 25% by weight, or 15% to 20% by weight based on 100% by weight of the inorganic heat-resistant layer. When the content of the first binder polymer satisfies the above-described range, the heat resistance of the separator may be excellent without causing detachment of inorganic particles within the inorganic heat-resistant layer.

[0098]

[0099] In one embodiment of the present invention, the inorganic heat-resistant layer may further include a first dispersant. When the 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 dispersant may be, for example, a polyvinylpyrrolidone-based compound, a cellulose-based compound, or an organic acid-based compound.

[0100] 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.

[0101] 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.

[0102] In one embodiment of the present invention, the inorganic heat-resistant layer may further include a caprolactone-based dispersant.

[0103] Specifically, in one embodiment of the present invention, the caprolactone-based dispersant comprises a caprolactone-based repeating unit and may comprise a polymer compound comprising an ethylene glycol-based repeating unit, a propylene glycol-based repeating unit, or two or more of these repeating units.

[0104] In one embodiment of the present invention, the caprolactone-based dispersant may comprise 20% to 40% by weight, 25% to 35% by weight, or 27% to 33% by weight of caprolactone-derived repeating units based on 100% by weight of the total repeating units. Meanwhile, in this specification, "caprolactone-based dispersant" may refer to a dispersant that comprises caprolactone-derived repeating units, or comprises 5% or more by weight, 10% or more by weight, 15% or more by weight, or 20% or more by weight.

[0105] In one embodiment of the present invention, the caprolactone-based dispersant may comprise 40% to 60% by weight or 45% to 55% by weight of repeating units derived from ethylene glycol, based on 100% by weight of the total repeating units, or may comprise 10% to 30% by weight or 15% to 25% by weight of repeating units derived from propylene glycol. In this case, the caprolactone-based dispersant may comprise 40% to 60% by weight or 45% to 55% by weight of repeating units derived from ethylene glycol, based on 100% by weight of the total repeating units, and may comprise 10% to 30% by weight or 15% to 25% by weight of repeating units derived from propylene glycol.

[0106] 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.

[0107]

[0108] In the present invention, the surface area occupied by inorganic particles on the surface of the inorganic heat-resistant layer is 73% to 88% based on 100% of the total surface area. In one embodiment of the present invention, the surface area occupied by inorganic particles on the surface of the inorganic heat-resistant layer may be 75% to 85% based on 100% of the total surface area. Since the surface area of ​​the inorganic heat-resistant layer satisfies the above-described range, the surface roughness of the inorganic heat-resistant layer may satisfy a predetermined range. Meanwhile, when an adhesive layer is formed on the inorganic heat-resistant layer, the adhesive layer may be formed uniformly.

[0109] In one embodiment of the present invention, the surface area occupied by the inorganic particles can be obtained through scanning electron microscope (SEM) images observed and image analysis thereof.

[0110] For example, an arbitrary area of ​​the surface of the inorganic heat-resistant layer, for example, an area of ​​25 μm x 25 μm, can be observed using a scanning electron microscope (SEM) to obtain an SEM image, and then the SEM image can be divided into gray levels to distinguish the area corresponding to a specific gray level corresponding to the inorganic particles. The gray level refers to the brightness value of a plurality of pixels included in the SEM image. For example, in a 256-gray-level SEM image having steps from 0 to 255, the range of brightness values ​​may be 0 to 255, and the inorganic particles may have, for example, 120 to 220 gray levels. Accordingly, the boundaries of the inorganic particles can be set and defined from pixels having 120 to 220 gray levels in the SEM image of an arbitrary surface of the separator (for example, a surface of 25 μm x 25 μm size), and the size of the inorganic particles and the surface area occupied by the inorganic particles can be calculated. In the present invention, the surface SEM image of the separation membrane can be obtained by mapping the constituent components using an Energy Dispersive X-ray Spectroscopy (EDS) detector of a Scanning Electron Microscope (SEM) equipment on the surface of the separation membrane and then processing the image.

[0111]

[0112] Meanwhile, in the present invention, the span value of the inorganic particle is 1.3 or less. At this time, the span value can be calculated by the following Equation 1:

[0113] SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D 50 ) … Equation (1)

[0114]

[0115] Specifically, after measuring the size of the inorganic particles through the above SEM image analysis, the particle size distribution is calculated, and by calculating the particle diameters at the points corresponding to 10%, 50%, and 90% of the cumulative particle number distribution, respectively D 10 , D 50 and D 90 It is possible to measure and calculate the span value. In this case, if the particle size distribution is widely distributed, the span value is calculated to be large, and if the particle size distribution is narrow, the span value is calculated to be small, so the particle size distribution state can be determined through the span value.

[0116] In one embodiment of the present invention, the span value may be 1.3 or less, 1.28 or less, or 1.25 or less. When the span value is less than the upper limit, the distribution of inorganic particles is narrow, so the mechanical strength and durability of the separation membrane may be excellent.

[0117]

[0118] In one embodiment of the present invention, the surface of the inorganic heat-resistant layer may have a surface area occupied by pores of 12% to 27% or 15% to 25% based on 100% of the total surface area. The surface area occupied by pores can be obtained through scanning electron microscope (SEM) images observed and image analysis. For example, the surface area occupied by pores can be calculated by subtracting the surface area occupied by inorganic particles and / or binder polymers from the observed SEM images. Meanwhile, if the surface area occupied by pores satisfies the above-described range, the porosity and resistance characteristics of the separator may be excellent.

[0119]

[0120] In one embodiment of the present invention, the surface of the inorganic heat-resistant layer may have a surface area occupied by a binder polymer of less than 10%, less than 7%, less than 5%, or less than 3% based on 100% of the total surface area. When the surface area occupied by the binder polymer is less than the upper limit, it may be easier to wind up and store the separator without causing detachment of inorganic particles within the inorganic heat-resistant layer.

[0121] In one embodiment of the present invention, the surface roughness (Sa) of the inorganic heat-resistant layer may be 0.07 μm to 0.12 μm, 0.075 μm to 0.1 μm, or 0.08 μm to 0.09 μm. Since the surface roughness of the inorganic heat-resistant layer satisfies the above-described range, an adhesive layer is uniformly formed on the inorganic heat-resistant layer, so that the adhesion strength between the electrode and the separator in a dry state may be even better.

[0122] Meanwhile, in one embodiment of the present invention, there are no limitations on the method of measuring surface roughness (Sa). For example, the surface roughness can be measured using a roughness measuring device (e.g., a surface profiler) or a confocal laser scanning microscope (CLSM). For example, the measurement can be performed by enlarging a predetermined scanning area at a magnification of 50x using a confocal laser scanning microscope, and the average value can be used after 10 measurements per sample. Examples of confocal laser scanning microscopes, such as the OLS 5100 or OLS 4100 of Olympus, may be used, but are not limited thereto. The magnification of the confocal laser microscope can be adjusted to 10x, 50x, 100x, 1000x, 2000x, 5000x, etc.

[0123]

[0124] Meanwhile, in one embodiment of the present invention, the inorganic heat-resistant layer may further include a wetting agent. As described below, the 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 wetting agent may be a known wetting agent (surfactant), and for example, a fluorine-based surfactant, a siloxane-based surfactant, a hydrocarbon-based surfactant, or an ether-based surfactant may be used, and while it may be preferable to use an ether-based surfactant, it is not limited thereto.

[0125] In one embodiment of the present invention, the 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.

[0126]

[0127] In one embodiment of the present invention, the inorganic heat-resistant layer may be formed on only one side of a porous polymer substrate. Such a separator may be included in a cylindrical battery, and in this case, since the electrode assembly structure of the positive electrode / separator / negative electrode has a jelly-roll type electrode assembly structure wound in one direction, the inorganic heat-resistant layer may be formed on only one side of the porous polymer substrate. By forming the inorganic heat-resistant layer on one side of the porous polymer substrate in this manner, the heat resistance and mechanical properties of the separator are excellent, and the energy density of the lithium secondary battery may be superior.

[0128] In one embodiment of the present invention, the thickness of the inorganic heat-resistant layer may be 0.5 μm to 5 μm, 0.8 μm to 3 μm, or 1.0 μm to 2.0 μm or less. If the thickness of the inorganic heat-resistant layer is less than the lower limit of the above-described range, the durability and heat resistance may be poor, and if it exceeds the upper limit of the above-described range, the energy density may be low and the resistance characteristics of the battery may be unfavorable.

[0129] In one embodiment of the present invention, the loading amount of the inorganic heat-resistant layer is 2.0 g / m² 2 Up to 3.0 g / m² 2 , 2.2 g / m 2 Up to 2.9 g / m² 2 , 2.4 g / m 2 Up to 2.8 g / m² 2 It may be within the range. The loading amount of the inorganic heat-resistant layer satisfies the above-described range, so that the mechanical properties such as resistance characteristics, puncture strength, and dielectric breakdown characteristics of the separator may be excellent.

[0130]

[0131] Meanwhile, the inorganic heat-resistant layer may be formed on both sides of a porous polymer substrate. Such a separator may be included in a pouch-type battery, in which case an electrode assembly of a positive electrode, a separator, and a negative electrode may be formed and then placed into a pouch-type case. 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 the 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.

[0132]

[0133] <Adhesive layer>

[0134] In one embodiment of the present invention, the adhesive layer comprising a particulate PVDF-based binder polymer may be further included, which is formed alone on at least one surface of the porous polymer substrate or formed on the inorganic heat-resistant layer.

[0135] 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.

[0136] In one embodiment of the present invention, the particulate PVDF-based binder polymer may include, 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 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).

[0137] 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).

[0138] 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.

[0139] 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.

[0140] In one embodiment of the present invention, the glass transition temperature (Tg) of the particulate PVDF-based binder polymer may be -40°C to 40°C or -35°C to 35°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.

[0141] 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 5 μm, or 1 μm to 4 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 polymer50 ) is the average particle size (D) of the primary particles of the PVDF-based binder polymer. 50 It means ).

[0142]

[0143] In one embodiment of the present invention, the adhesive layer may further comprise a second binder polymer. In this case, the adhesive layer is formed by mixing a plurality of particulate PVDF-based binder polymers and a second binder polymer.

[0144] 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.

[0145] In one embodiment of the present invention, the second binder polymer may be an acrylic binder polymer. The acrylic binder polymer may be in a particulate or non-particulate form.

[0146] In one embodiment of the present invention, 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.

[0147] 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 -40°C or higher and 40°C or lower, or -35°C or higher and 35°C or lower.

[0148] In one embodiment of the present invention, the particulate acrylic binder polymer has an average particle size (D) of 100 nm to 800 nm, or 200 nm to 700 nm. 50 It may include a particulate acrylic binder polymer having ).

[0149]

[0150] 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.

[0151] 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 and / or the second binder polymer can be further dispersed in the dispersion medium, thereby controlling the surface roughness of the adhesive layer and thus improving the electrode-separator adhesion strength.

[0152] In one embodiment of the present invention, the caprolactone-based dispersant may comprise 40% to 60% by weight or 45% to 55% by weight of repeating units derived from ethylene glycol, based on 100% by weight of the total repeating units, or may comprise 10% to 30% by weight or 15% to 25% by weight of repeating units derived from propylene glycol. In this case, the caprolactone-based dispersant may comprise 40% to 60% by weight or 45% to 55% by weight of repeating units derived from ethylene glycol, based on 100% by weight of the total repeating units, and may comprise 10% to 30% by weight or 15% to 25% by weight of repeating units derived from propylene glycol.

[0153] 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.

[0154] 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.

[0155] In one embodiment of the present invention, the second 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. By satisfying the above-described range of the content of the second binder polymer, 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.

[0156] In one embodiment of the present invention, the surface area occupied by the particulate PVDF-based binder polymer and the second binder polymer may be 85% or more based on 100% of the total surface area of ​​the adhesive layer.

[0157] The surface area occupied by the above-mentioned particulate PVDF-based binder polymer and the second acrylic-based binder polymer can be obtained through scanning electron microscope (SEM) images observed and image analysis thereof.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] In one embodiment of the present invention, the thickness of the adhesive layer may be 0.55 μm or more, 0.6 μm or more, 0.65 μm or more, or 0.7 μm or more based on being formed on one side of a porous polymer substrate, and may be 1.3 μm or less, 1.2 μm or less, 1.1 μm or less, 1.0 μm or less, or 0.9 μm or less. Since the thickness of the adhesive layer satisfies the above-described range, the adhesion strength of the cathode-separator may be excellent, and the resistance characteristics of the separator may also be excellent.

[0162]

[0163] Lithium secondary battery

[0164] The present invention provides a lithium secondary battery.

[0165] According to one aspect of the present invention, the lithium secondary battery of the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between them, and a battery housing accommodating the electrode assembly and an electrolyte, wherein the separator is characterized according to one embodiment of the present invention.

[0166] 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 as the positive electrode of a conventional electrochemical device, 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 as the negative electrode of a conventional electrochemical device, 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.

[0167] In one embodiment of the present invention, the anode binder polymer is a component that assists in the bonding of the anode active material and the conductive material, and the bonding to the current collector, and can typically be added in an amount of 1% to 30% by weight based on the total solid weight of the anode forming composition. Examples of such binders may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or a combination thereof, and preferably may be polyvinylidene fluoride.

[0168] In one embodiment of the present invention, the binder polymer for the cathode may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or a combination thereof, and preferably may be styrene-butadiene rubber (SBR).

[0169] 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 containing anions such as or combinations thereof are dissolved or dissociated in organic solvents composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or mixtures thereof, but are not limited thereto.

[0170] In one embodiment of the present invention, the battery housing may be a pouch-type case, a cylindrical can, a rectangular can, or a combination thereof.

[0171] In one embodiment of the present invention, the pouch-type case may be manufactured as a multilayer laminate film using an aluminum foil film or the like.

[0172] In one embodiment of the present invention, the cylindrical can may have a cylindrical side wall portion, a bottom portion connected to one end of the side wall portion, and an open end provided at the other axial end of the side wall portion, and may be manufactured by forming a conductive metal sheet through a deep drawing process and trimming the front end of the side wall portion with a punch while holding it with a blank holder.

[0173]

[0174] Method for manufacturing a separator for a lithium secondary battery

[0175] The present invention provides a method for manufacturing a separator for a lithium secondary battery.

[0176] (First embodiment)

[0177] In one embodiment of the present invention, a method for manufacturing a separator for a lithium secondary battery may include: (S1) a step of preparing a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer; and (S2) a step of forming an inorganic heat-resistant layer by applying and drying the water-based inorganic heat-resistant layer forming slurry on at least one surface of a porous polymer substrate.

[0178] Below, we will examine the method for manufacturing a separator for a lithium secondary battery step by step. Meanwhile, the inorganic particles and the first binder polymer are replaced by the aforementioned details.

[0179] First, (S1) the step of preparing a slurry for forming a water-based inorganic heat-resistant layer comprising inorganic particles and a first binder polymer may be included.

[0180] 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.

[0181] 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 content of solids) excluding the dispersion medium in the range of 20 wt% to 50 wt%.

[0182] In one embodiment of the present invention, the aqueous inorganic heat-resistant layer forming slurry may further include a wetting agent. The wetting agent can improve coating properties by allowing the inorganic heat-resistant layer forming slurry to wet a hydrophobic porous polymer substrate well. Meanwhile, a known wetting agent may be used as the wetting agent, and the above-mentioned one is substituted.

[0183] In one embodiment of the present invention, the water-based inorganic heat-resistant layer forming slurry may further include a dispersant. The dispersant may be, for example, a polyvinylpyrrolidone-based compound, a cellulose-based compound, or an organic acid-based compound.

[0184] 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.

[0185] 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.

[0186] In one embodiment of the present invention, the 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.

[0187]

[0188] Afterwards, (S2) the above-mentioned water-based inorganic heat-resistant layer forming slurry can be applied and dried on at least one surface of a porous polymer substrate to form an inorganic heat-resistant layer.

[0189] In one embodiment of the present invention, the water-based inorganic heat-resistant layer forming slurry may be applied and dried only on one side of a porous polymer substrate. A separator for a lithium secondary battery according to one embodiment of the present invention may be used in a cylindrical battery, and when an electrode assembly is manufactured using the separator and then wound in one direction, the slurry may be applied and dried only on one side of the porous polymer substrate, rather than on both sides.

[0190] 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, various methods may be used as the application method, 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.

[0191] 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.

[0192] 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.

[0193] In one embodiment of the present invention, the drying step may be performed for 10 to 120 seconds within the temperature range described above.

[0194]

[0195] (Second embodiment)

[0196] In one embodiment of the present invention, a method for manufacturing a separator for a lithium secondary battery comprises: (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 a particulate PVDF-based 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; wherein the surface area occupied by the inorganic particles is 73% to 88% based on 100% of the total surface area of ​​the inorganic heat-resistant layer formed by step (S2), and the span value of the inorganic particles is 1.3 or less, and the span value may be calculated by the following formula 1.

[0197] SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D 50 ) … Equation (1)

[0198] Below, we will examine the method for manufacturing a separator for a lithium secondary battery step by step. Meanwhile, the inorganic particles, the first binder polymer, the particulate PVDF-based binder polymer, and the second binder polymer are substituted for those described above.

[0199] First, (S1) a slurry for forming a water-based inorganic heat-resistant layer comprising inorganic particles and a first binder polymer and a slurry for forming a water-based adhesive layer comprising particulate PVDF-based binder polymer and a second binder polymer can be prepared.

[0200] 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.

[0201] In one embodiment of the present invention, the water-based inorganic heat-resistant layer forming slurry may further include a wetting agent.

[0202] In one embodiment of the present invention, the water-based inorganic heat-resistant layer forming slurry may further comprise a first dispersant. The first dispersant may be, for example, a polyvinylpyrrolidone-based compound, a cellulose-based compound, or an organic acid-based compound.

[0203] 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.

[0204] In one embodiment of the present invention, the slurry for forming the water-based adhesive layer further comprises a second binder polymer, and the second binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0205] In one embodiment of the present invention, the slurry for forming the water-based adhesive layer further comprises a second dispersant, and the second dispersant may comprise a caprolactone-based dispersant. By using the second dispersant, the particulate PVDF-based binder polymer and the particulate acrylic-based binder polymer can be further dispersed in the dispersion medium, thereby controlling the surface roughness of the adhesive layer and thus improving the electrode-separator adhesion strength.

[0206] 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.

[0207] Afterwards, (S2) an inorganic heat-resistant layer can be formed by applying and drying the above-mentioned water-based inorganic heat-resistant layer forming slurry on at least one surface of a porous polymer substrate.

[0208] In one embodiment of the present invention, the method of applying the aqueous inorganic heat-resistant layer forming slurry onto at least one surface of a porous polymer substrate is not limited.

[0209] In one embodiment of the present invention, the drying step may be performed for 10 to 120 seconds within the temperature range described above.

[0210] Meanwhile, based on 100% of the total surface area of ​​the inorganic heat-resistant layer formed by the above step (S2), the surface area occupied by the inorganic particles is 73% to 88%, and the span value of the inorganic particles is 1.3 or less, and the span value may be calculated by the above Equation 1, and the explanation thereof is substituted with the foregoing.

[0211] Afterwards, (S3) an adhesive layer can be formed by applying and drying the adhesive layer forming slurry on at least one surface of the inorganic heat-resistant layer.

[0212] 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.

[0213] 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 one or more of natural drying methods may be applied. Preferably, the drying method may be hot air drying.

[0214] 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.

[0215] In this specification, the first and second embodiments for manufacturing a separator for a lithium secondary battery may be performed alone or in combination with one another, and the order of execution is not particularly limited.

[0216]

[0217] 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.

[0218] <Example 1>

[0219] <Example 1-1>

[0220] Aluminum oxide (Al2O3, D) as an inorganic particle 50 : 450 nm, Sumitomo Co.) and as the first binder polymer, an acrylic polymer (ZEON Co., D 50 A dispersion was prepared by adding a particle (600 nm) to water at room temperature, and a slurry for forming an aqueous inorganic heat-resistant layer was prepared by bead milling. The slurry for forming the aqueous inorganic heat-resistant layer was applied to one surface of a porous polyethylene polymer substrate (porosity 40%, thickness 9 μm) using the doctor blade method and dried at 65°C for 30 seconds. At this time, the formed inorganic heat-resistant layer was 1.5 μm thick. Furthermore, the content of inorganic particles in the inorganic heat-resistant layer was 87 wt% based on 100 wt% of the total inorganic heat-resistant layer, and the first binder polymer satisfied 13 wt%. In addition, the loading amount of the inorganic heat-resistant layer was 2.5 g / m² 2 It was.

[0221] <Example 1-2>

[0222] In Example 1-1, drying was performed at a temperature of 60°C, and the loading amount of the inorganic heat-resistant layer was 2.7 g / m² 2 Except for that, it was performed in the same manner as Example 1-1.

[0223]

[0224] <Comparative Example 1-1>

[0225] In Example 1-1, drying was performed at a temperature of 70°C, and the loading amount of the inorganic heat-resistant layer was 1.8 g / m² 2 Except for that, it was performed in the same manner as Example 1-1.

[0226]

[0227] <Comparative Example 1-2>

[0228] In Example 1-1, drying was performed at a temperature of 55°C, and the loading amount of the inorganic heat-resistant layer was 3.5 g / m² 2 Except for that, it was performed in the same manner as Example 1-1.

[0229]

[0230] <Comparative Example 1-3>

[0231] In Example 1-1, drying was performed at a temperature of 57°C, and the loading amount of the inorganic heat-resistant layer was 3.7 g / m² 2 Except for that, it was performed in the same manner as Example 1-1.

[0232]

[0233] <Comparative Example 1-4>

[0234] In Example 1-1, drying was performed at a temperature of 75°C, and the loading amount of the inorganic heat-resistant layer was 2.6 g / m² 2 Except for that, it was performed in the same manner as Example 1-1.

[0235]

[0236] Manufacture of cylindrical batteries

[0237] In each example and comparative example, 17 positive electrodes and 16 negative electrodes were arranged intersectingly on the upper and lower surfaces of the separator and the separator. At this time, the points where the positive electrode ends are located on one side and the points where the negative electrode ends are located on the other side were spaced apart so that the horizontal spacing on the plane is 3 mm, and the electrodes were wound to manufacture a jelly-roll type electrode assembly.

[0238] Lithium cobalt oxide (LCO) was used as the positive electrode active material, and graphite was used as the negative electrode active material (N / P ratio > 100). Specifically, LiNi was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 An anode slurry was prepared by mixing O2, polyvinylidene fluoride (PVdF) as an anode binder, and carbon black as a conductive material in a weight ratio of 97.0:1.5:1.5 and dispersing it in 2-methyl-2-pyrrolidone, and then coating the mixture onto an aluminum current collector and drying and rolling it to produce an anode. An anode slurry was prepared by mixing graphite as a cathode active material, SBR as a cathode binder, and CMC as a thickener in a weight ratio of 89.2:10:0.8 and dispersing it in distilled water, and then coating the mixture onto a copper current collector and drying and rolling it to produce an anode.

[0239] A positive electrode current collector plate and a negative electrode current collector plate were welded to the upper and lower parts, respectively, of the jelly-roll type electrode assembly manufactured above. Then, the electrode assembly with the welded positive and negative electrode current collector plates was inserted into a cylindrical battery housing with external terminals pre-installed, the positive electrode current collector plate and the external terminals were welded, and the edges of the negative electrode current collector plate were welded to the beading portion. Then, the battery housing was introduced into the chamber of the electrolyte injection device, and the battery housing was erected so that the opening of the battery housing faced in the opposite direction to gravity. Subsequently, a non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a composition of 1:2:1 (volume ratio). Then, the electrolyte was injected through the opening of the battery housing, the pressure in the chamber was increased to 800 kPa over 20 seconds and maintained for 150 seconds, then the pressure in the chamber was lowered to -90 kPa over 20 seconds and a substantial vacuum was maintained for 20 seconds. After the electrolyte impregnation process was completed, the opening of the battery housing was sealed with a gasket to complete the fabrication of the cylindrical cell.

[0240] <Experimental Example 1>

[0241] The ratio of inorganic material area on the surface of each example and comparative example, the span value, the thickness of the inorganic heat-resistant layer, the separator resistance characteristics, the puncture strength, and the dielectric breakdown voltage were measured and are shown in Table 1 below.

[0242] Area (%) of inorganic particles in surface SEM image (5k magnification) Span value of inorganic particles Loading amount of inorganic heat refractory layer (g / m²) 2Thickness of inorganic heat-resistant layer (㎛) Resistance characteristics of separator (Ohm) Perforation strength (gf) Dielectric breakdown voltage (V) Example 1-17 6 1.19 2.5 1.50.725 67 1517 Example 1-28 1 1.21 2.7 1.60.675 89 1620 Comparative Example 1-17 1.85 1.80.80.4365 1365 Comparative Example 1-28 9 1.28 3.52 71.10378 1200 Comparative Example 1-39 1.52 3.73.2 1.12712413 Comparative Example 1-47 8 1.64 2.62 00.828 30382

[0243] Examples 1-1 and 1-2 above had appropriate inorganic area, span value of inorganic particles, and loading amount of the inorganic heat-resistant layer, resulting in excellent mechanical properties such as resistance characteristics and puncture strength, as well as dielectric breakdown voltage characteristics of the separator. On the other hand, Comparative Example 1-1 had a low loading amount of the inorganic heat-resistant layer, so the area occupied by the inorganic material was small and the thickness of the inorganic heat-resistant layer was thin. Accordingly, the separator of Comparative Example 1 had a high span value, and inorganic particles with large particle sizes were locally present, resulting in inferior dielectric breakdown voltage characteristics.

[0244] Comparative Example 1-2 had a high loading amount of the inorganic heat-resistant layer and a high area occupied by inorganic particles, resulting in a thick inorganic heat-resistant layer and consequently inferior resistance characteristics. In addition, it was confirmed that the insulation breakdown voltage characteristics were somewhat degraded during the inorganic packing process because the loading amount of the inorganic heat-resistant layer was excessive and the span value was low.

[0245] Comparative Examples 1-3 had a high loading amount of the inorganic heat-resistant layer, a large area occupied by inorganic particles, and a large span value. That is, there were many inorganic particles with large particle sizes, so the thickness of the inorganic heat-resistant layer was thick, and as a result, the dielectric breakdown voltage characteristics were degraded.

[0246] Comparative Examples 1-4 had a high loading amount of the inorganic heat-resistant layer, a high span value, and a thick inorganic heat-resistant layer. As a result, the dielectric breakdown voltage characteristics were degraded.

[0247]

[0248] <Example 2>

[0249] <Example 2-1>

[0250] 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. 50 : 2 μm), a particulate acrylic binder polymer as a second binder polymer and a polycaprolactic dispersant as a second dispersant were added to prepare a second dispersion, and a slurry for forming a water-based adhesive layer was prepared by bead milling. At this time, the caprolactone-based dispersant contained 50% repeating units derived from ethylene glycol, 20% repeating units derived from propylene glycol, and 30% repeating units derived from caprolactone, relative to 100% of the total number of repeating units.

[0251] A water-based inorganic heat-resistant layer forming slurry was applied to one surface of a porous polyethylene polymer substrate (porosity 40%, thickness 9 μm) using the doctor blade method, and then dried at 65°C for 30 seconds. At this time, the loading amount of the inorganic heat-resistant layer was 5.4 g / cm³. 2 Subsequently, a slurry for forming an adhesive layer was applied onto 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 thickness of the formed inorganic heat-resistant layer was 1.5 μm, and the thickness of the adhesive layer was 0.75 μm. In addition, the content of inorganic particles in the inorganic heat-resistant layer was 87 wt% based on 100 wt% of the total inorganic heat-resistant layer, and the first binder polymer satisfied 13 wt%.

[0252]

[0253] <Example 2-2>

[0254] In Example 2-1, drying was performed at a temperature of 60°C, and the loading amount of the inorganic heat-resistant layer was 5.2 g / m² 2 Except for that, it was performed in the same manner as Example 2-1.

[0255]

[0256] <Comparative Example 2-1>

[0257] In Example 2-1, drying was performed at a temperature of 50°C, and the loading amount of the inorganic heat-resistant layer was 5.6 g / m² 2 Except for that, it was performed in the same manner as Example 2-1.

[0258]

[0259] <Comparative Example 2-2>

[0260] In Example 2-1, drying was performed at a temperature of 70°C, and the loading amount of the inorganic heat-resistant layer was 4.8 g / m² 2 Except for that, it was performed in the same manner as Example 2-1.

[0261]

[0262] <Comparative Example 2-3>

[0263] In Example 2-1, drying was performed at a temperature of 62°C, and the loading amount of the inorganic heat-resistant layer was 5.3 g / m² 2 Except for that, it was performed in the same manner as Example 2-1.

[0264]

[0265] <Comparative Example 2-4>

[0266] In Example 2-1, drying was performed at a temperature of 62°C, and the loading amount of the inorganic heat-resistant layer was 5.8 g / m² 2 Except for that, it was performed in the same manner as Example 2-1.

[0267]

[0268] <Comparative Example 2-5>

[0269] In Example 2-1, drying was performed at a temperature of 68°C, and the loading amount of the inorganic heat-resistant layer was 4.2 g / m²2 Except for that, it was performed in the same manner as Example 2-1.

[0270]

[0271] Battery Manufacturing

[0272] In each example and comparative example, a lithium secondary battery was manufactured in the following manner.

[0273] LiNi as a positive electrode active material 0.8 Co 0.1 Mn 0.1 An anode was prepared by mixing O2, polyvinylidene fluoride (PVdF) as an anode binder, and carbon black as a conductive material in a weight ratio of 97.0:1.5:1.5 and dispersing them in 2-methyl-2-pyrrolidone to prepare an anode slurry, coating the slurry onto an aluminum current collector, and then drying and rolling it to produce an anode.

[0274] Graphite as a cathode active material, SBR as a cathode binder, and CMC as a thickener were mixed in a weight ratio of 89.2:10:0.8 and dispersed in distilled water to prepare a cathode slurry, which was then coated onto a copper current collector and dried and rolled to produce a cathode.

[0275] A cathode was laminated onto the first separator of each example and comparative example, and the second separator was laminated onto the cathode to form a laminate, after which the laminate was pressed with a rotary pressurizing member. Subsequently, an anode was laminated onto the second separator of the pressed laminate to manufacture a monocell specimen.

[0276] At this time, pressure was applied at 60°C and 1000 kgf for 5 seconds. Both sides of the laminated assembly were secured with nylon tape to prevent separation. The size of the specimen was 37 mm x 59 mm.

[0277] After loading the above specimen into a pouch-type case, 0.5g of electrolyte (ethylene carbonate:ethyl methyl carbonate = 7:3 (volume ratio), LiPF6 1M, VC (vinylene carbonate) 2wt%) was injected to manufacture a secondary battery, which was then left at room temperature for 3 hours. Subsequently, the secondary battery was subjected to 5 kgf / cm² at 60°C for 5 minutes. 2 Pressurized to a pressure of 5 kgf / cm² at 60℃. 2 The battery was charged to SOC 3 with a current of 0.2C while under pressure, and then charged to SOC 60 with a current of 1C. Once charging was complete, the pressure was released, and aging was performed for 1 day at 60℃.

[0278]

[0279] <Experimental Example 2>

[0280] For each example and comparative example, the inorganic material area ratio on the surface of the inorganic heat-resistant layer, the span value, the surface roughness of the inorganic heat-resistant layer, the binder polymer area ratio (coverage) on the surface of the adhesive layer, the electrode-separator dry adhesion strength, the resistance characteristics of the separator, and the dielectric breakdown voltage were measured and are shown in Table 2 below.

[0281] Properties of the inorganic heat-resistant layer, properties of the separator after adhesive layer coating, area (%) of inorganic particles in the surface SEM image (5k magnification), span value of inorganic particles, loading amount of the inorganic heat-resistant layer (g / m²) 2Surface roughness (Sa) (㎛) Binder coverage (%) in surface SEM image (5K magnification) Electrode-separator dry adhesion (gf / 20m) Separator resistance (ER) (Ohm) Dielectric breakdown Voltage (kV) Example 2-1771.245.40.08190280.852.21 Example 2-2801.185.20.08387250.832.72 Comparative Example 2-1941.795.60.1027370.920.92 Comparative Example 2-2711.854.80.09895501.210.88 Comparative Example 2-3781.545.30.10385260.840.97 Comparative Example 2-4901.265.80.08471130.982.14 Comparative Example 2-5721.244.20.08088240.710.80

[0282] Examples 2-1 and 2-2 had appropriate surface roughness of the inorganic heat-resistant layer and a suitable ratio of the binder surface area on the adhesive layer, resulting in excellent dry adhesion of the electrode-separator, resistance characteristics of the separator, and dielectric breakdown voltage characteristics. On the other hand, Comparative Example 2-1 had an excessive surface roughness due to the large amount of inorganic particles, and consequently, the binder polymer within the adhesive layer was impregnated into the inorganic heat-resistant layer, resulting in a low content (coverage) of the binder polymer on the surface of the adhesive layer, which in turn resulted in inferior dry adhesion of the electrode-separator. Furthermore, the resistance was inferior due to the excessive loading amount of the inorganic heat-resistant layer, and the dielectric breakdown voltage characteristics were inferior due to the large amount of inorganic particles.

[0283] Comparative Example 2-2 had a small surface area of ​​inorganic particles and an excessive span value, so the dielectric breakdown voltage characteristics of the separator were inferior due to the large amount of inorganic particles. In addition, the resistance characteristics of the separator were very inferior.

[0284] Comparative Examples 2-3 had an excessive span value of inorganic particles, and the dielectric breakdown voltage characteristics of the separator were inferior due to the large amount of inorganic particles.

[0285] Comparative Examples 2-4 had an excessive proportion of inorganic particles on the surface of the inorganic heat-resistant layer, resulting in a low content of binder polymer per surface and consequently inferior dry adhesion between the electrode and the separator. Additionally, the resistance characteristics were inferior due to the excessive content of inorganic particles.

[0286] Comparative Examples 2-5 had a low proportion of inorganic particles on the surface of the inorganic heat-resistant layer. That is, the inorganic heat-resistant layer was not evenly coated on the porous polymer substrate, so there were uncoated portions of the inorganic heat-resistant layer, and the adhesive layer was coated on the uncoated portions, resulting in inferior dielectric breakdown voltage characteristics.

[0287]

[0288] <Measurement Method>

[0289] SEM images, measurement of inorganic particle area and span value

[0290] The surface of the membranes of Example 1-1 and Comparative Example 1-1 was measured using SEM at a magnification of 5K, and the inorganic particles and pores of the examples and comparative examples were separated using an image program, and the particle size distribution of the inorganic particles was measured and shown in Figures 1 and 2 and Table 1.

[0291] Using the difference in shading in the above SEM images, the ratio of the surface area occupied by inorganic particles and the ratio of the surface area occupied by pores were calculated and shown in a table, and this process is shown in Figures 1a and 1b.

[0292] In addition, D of the inorganic particles 10 , D 50 , D 90 The span value of the inorganic particle defined according to Equation 1 of the specification below was measured and is shown in Table 1.

[0293] Equation 1: SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D 50 )

[0294]

[0295] Measurement of the thickness of the inorganic heat-resistant layer

[0296] The thickness of each example and comparative example was measured 10 times at random points using a thickness gauge (Mitutoyo, VL-50S-B), and the average value is shown in Table 2.

[0297]

[0298] Resistance characteristic measurement

[0299] After impregnating the separator prepared in each example and comparative example with an electrolyte, the AC resistance was measured, and the results are shown in Tables 1 and 2. At this time, the AC resistance is the value measured at 1KHz using a Hioki.

[0300]

[0301] Measurement of puncture strength

[0302] Samples were prepared by cutting the membranes of each example and comparative example to 50 mm Y 50 mm. After setting a universal testing machine (Universal Testing Machine, Instron) to operate with a 1 mm round tip at a speed of 120 mm / min, the puncture strength was measured using the prepared samples in accordance with ASTM D2582 and is shown in the table.

[0303]

[0304] Insulation breakdown voltage

[0305] The dielectric breakdown voltage was measured for cylindrical batteries containing separators of each example and comparative example and is shown in Tables 1 and 2. Specifically, for cylindrical batteries containing separators of each example and comparative example, the voltage was increased from 0V to 100V / s, and when the current flowed at 0.5mA or more for 3 seconds or longer, it was determined that the insulation had been broken, and the voltage value at that time was recorded.

[0306]

[0307] Surface roughness (Sa) measurement

[0308] The surface roughness of the inorganic heat-resistant layer of each example and comparative example was measured 10 times using an Olympus OLS 5100 at 50x magnification to determine the average roughness, which is shown in the table below.

[0309]

[0310] Measurement of the surface area (coverage) of the binder polymer (particulate PVDF-based binder polymer and second binder polymer) of the adhesive layer

[0311] The surface of the adhesive layer of each of the above examples and comparative examples was measured using SEM, and the binder polymers (PVDF-based binder polymer and second binder polymer) of each of the above examples and comparative examples were separated using an image processing program, and the surface area they occupied was measured and shown in the table.

[0312]

[0313] Measurement of electrode-separator dry adhesion

[0314] After preparing an electrode adhesion sample by placing a 20 mm x 20 mm die-cut electrode on the cathode and applying pressure under conditions of 60°C, 6.0 MPa, and 0.1 s, the peeling force from the slide glass was measured by pulling at 300 mm / min using a UTM (Instron) instrument. At this time, the measurement angle between the slide glass and the electrode was 180°.

[0315] At this time, the cathode was prepared by applying the cathode-forming composition prepared in the examples and comparative examples to a copper current collector (thickness: 12 μm), drying, and rolling.

Claims

1. Porous polymer substrate; and 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; comprising The surface of the above-mentioned inorganic heat-resistant layer has a surface area occupied by inorganic particles ranging from 73% to 88% based on 100% of the total surface area, and The span value of the above inorganic particles is 1.3 or less, and A separator for a lithium secondary battery characterized in that the above-mentioned span value is calculated by the following Equation 1: SPAN value = (particle diameter of inorganic particles (D 90 ) - Particle size of inorganic particles (D 10 )) / Particle size of inorganic particles (D 50 ) … Equation (1) 2. In Claim 1, A separator for a lithium secondary battery characterized in that the content of the above-mentioned inorganic particles is 70% to 95% by weight based on 100% by weight of the inorganic heat-resistant layer.

3. In Claim 1, A separator for a lithium secondary battery, characterized in that the first binder polymer is a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

4. In Claim 1, A separator for a lithium secondary battery, characterized in that the content of the first binder polymer is 5% to 30% by weight based on 100% by weight of the inorganic heat-resistant layer.

5. In Claim 1, A separator for a lithium secondary battery, characterized in that the surface of the above-mentioned inorganic heat-resistant layer has a surface area occupied by pores ranging from 12% to 27% based on 100% of the total surface area.

6. In Claim 1, A separator for a lithium secondary battery, characterized in that the surface of the above-mentioned inorganic heat-resistant layer has a surface area occupied by the first binder polymer of less than 10% based on 100% of the total surface area.

7. In Claim 1, A separator for a lithium secondary battery characterized in that the above-mentioned inorganic heat-resistant layer is formed only on one side of a porous polymer substrate.

8. In Claim 1, A separator for a lithium secondary battery, characterized in that the thickness of the inorganic heat-resistant layer is 1.0 μm to 2.0 μm or less.

9. In Claim 1, The loading amount of the above-mentioned inorganic heat-resistant layer is 2.0 g / m² 2 Up to 3.0 g / m² 2 A separator for a lithium secondary battery characterized by being within the range of 10. In Claim 1, A separator for a lithium secondary battery characterized in that the surface roughness (Sa) of the above-mentioned inorganic heat-resistant layer is 0.07 μm to 0.12 μm.

11. In Claim 1, A separator for a lithium secondary battery, characterized by further comprising an adhesive layer formed alone on at least one surface of the porous polymer substrate or formed on the inorganic heat-resistant layer, and comprising a particulate PVDF-based binder polymer.

12. In Claim 11, A separator for a lithium secondary battery, characterized in that the adhesive layer further comprises a second dispersant.

13. In Claim 11, The above adhesive layer further comprises a second binder polymer, and A separator for a lithium secondary battery, characterized in that the second binder polymer is a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

14. In Claim 13, Average particle size (D) of the above particulate binder polymer 50 A separator for a lithium secondary battery characterized by having a thickness of 100 nm to 800 nm.

15. In Claim 13, A separator for a lithium secondary battery characterized in that the surface area occupied by the particulate PVDF-based binder polymer and the second binder polymer is 85% or more based on 100% of the total surface area of ​​the adhesive layer.

16. An electrode assembly comprising an anode, a cathode; and a separator interposed between the anode and the cathode; and The above electrode assembly and the battery housing in which the electrolyte is housed; are included, A lithium secondary battery characterized in that the separator is a separator according to any one of claims 1 to 15.

17. In Claim 16, A lithium secondary battery characterized in that the battery housing is a cylindrical can, a rectangular can, a pouch-type case, or a combination thereof.

Images