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 a first adhesive layer formed on at least one surface of the porous polymer substrate and including a particulate PVDF-based binder polymer, wherein the first adhesive layer: i) includes a caprolactone-based dispersant; or ii) has a surface roughness (Sa) within a range of 0.12-0.22 µm.

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] The present application claims the benefit of priority based on Korean patent applications No. 10-2024-0157405, No. 10-2024-0157407, No. 10-2024-0157410 and No. 10-2024-0157392 filed on November 7, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.

[0004]

[0005] Electrochemical devices, such as lithium-ion batteries, typically consist of a cathode, separator, anode, and electrolyte as their basic components. As high-energy-density energy storage devices capable of reversibly converting chemical and electrical energy for charging and discharging, they are widely used in small electronic devices such as mobile phones and laptops. Recently, in response to environmental concerns, high oil prices, and increasing demand for energy efficiency and storage, their applications are rapidly expanding into hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), e-bikes, and energy storage systems (ESS).

[0006] Ensuring safety in the manufacturing and use of such lithium secondary batteries is a critical challenge. In particular, separators commonly used in electrochemical devices undergo significant thermal shrinkage under harsh conditions, such as high temperatures, due to their material and manufacturing process characteristics, which can lead to stability issues like internal short circuits. Accordingly, to improve the safety of lithium secondary batteries, composite porous separators formed by coating a mixture of inorganic particles and binder polymers onto a porous polymer substrate have been proposed.

[0007] However, when such a composite porous separator is laminated with an electrode to form an electrode assembly, the interlayer adhesion may be insufficient, leading to delamination of the laminate. If the electrode and the separator separate, there is a risk that bending or shape distortion of the cell may occur due to the volume expansion / contraction of the electrode during the charging and discharging process. Furthermore, in the case of a composite porous layer containing inorganic particles and a binder polymer as a single layer, a problem of reduced adhesion may occur due to the non-uniform dispersion of the components. Therefore, there is a need to develop a separator that ensures excellent heat resistance while stably providing high adhesion to the electrode.

[0008] Meanwhile, when a binder polymer is located on the surface of a composite porous separator, a phenomenon was observed in which the binder polymer is transferred to the surface of a rotary pressurizing member and detached from the separator during a pressurizing process using a rotary pressurizing roll or the like when manufacturing an electrode assembly. This necessitates an additional cleaning process for the pressurizing member, leading to increased manufacturing time and reduced processability. The inventors of the present invention arrived at the present invention by confirming that if the adhesive layer containing the binder polymer includes a specific type of dispersant or the surface roughness (Sa) of the adhesive layer satisfies a predetermined range, the aforementioned transfer and detachment phenomenon can be significantly reduced, and at the same time, the interfacial adhesion stability with the electrode can be improved.

[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 that suppresses the phenomenon of a binder polymer being transferred to the surface of a pressurizing member, such as a rotary pressurizing roll, during the pressurizing process when manufacturing an electrode assembly by including a caprolactone-based dispersant in the adhesive layer of the separator for a lithium secondary battery or by controlling the surface roughness (Sa) of the adhesive layer to a predetermined range.

[0011] Another objective of the present invention is to provide a separator for a lithium secondary battery that can improve the adhesion between the electrode and the separator (dry adhesion) in a dry state.

[0012] In addition, another objective of the present invention is to provide a separator for a lithium secondary battery having excellent thermal and resistance characteristics.

[0013] In addition, another objective of the present invention is to provide a separator for a lithium secondary battery that suppresses or reduces bending and shape distortion of the cell by appropriately controlling the electrode-separator adhesion force (wet adhesion force) in the electrolyte-impregnated state by differently adjusting the surface roughness of the adhesive layer on both sides of the separator.

[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; a first adhesive layer formed on at least one surface of the porous polymer substrate and comprising a particulate PVDF-based binder polymer; wherein the first adhesive layer comprises i) a caprolactone-based dispersant or ii) a surface roughness (Sa) within the range of 0.12 μm to 0.22 μm.

[0019] According to the second embodiment, in the first embodiment, the caprolactone-based dispersant may contain 20% to 40% by weight of caprolactone-derived repeating units based on 100% by weight of the total repeating units.

[0020] According to the third embodiment, in any one of the first and second embodiments, the caprolactone-based dispersant may comprise 40% to 60% by weight of repeating units derived from ethylene glycol or 10% to 30% by weight of repeating units derived from propylene glycol, based on 100% by weight of the total repeating units.

[0021] According to the fourth embodiment, in any one of the first to third embodiments, the surface roughness (Sa) may be measured by magnifying it 50 times with a confocal laser scanning microscope (CLSM).

[0022] According to the fifth embodiment, in any one of the first to fourth embodiments, an inorganic heat-resistant layer comprising inorganic particles and a first binder polymer may be further included, which is formed alone on at least one surface of the porous polymer substrate or formed between the porous polymer substrate and the first adhesive layer.

[0023] According to the sixth embodiment, in the fifth embodiment, the first binder polymer may include a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0024] According to the seventh embodiment, in any one of the fifth to sixth embodiments, the inorganic particles may be 70% by weight or more and 99% by weight or less based on 100% by weight of the inorganic heat-resistant layer.

[0025] According to the eighth embodiment, in any one of the first to seventh embodiments, the average particle size (D) of the particulate PVDF-based binder polymer 50 ) may be 0.5 μm to 2 μm.

[0026] According to the ninth embodiment, in any one of the first to eighth embodiments, the first 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.

[0027] According to the 10th embodiment, in the 9th embodiment, the second binder polymer comprises a particulate binder polymer, and the average particle size (D) of the particulate binder polymer 50 ) may be 100 nm to 800 nm.

[0028] According to the 11th embodiment, in any one of the 1st to 10th embodiments, a second adhesive layer comprising a particulate PVDF-based binder polymer is formed on the other side of the porous polymer substrate on which the first adhesive layer is formed.

[0029] According to the 12th embodiment, in the 11th embodiment, an inorganic heat-resistant layer comprising inorganic particles and a first binder polymer is formed on each of the first surface and the second surface of the porous polymer substrate, and a first adhesive layer is formed on the upper surface of the inorganic heat-resistant layer on the first surface, and a second adhesive layer is formed on the upper surface of the inorganic heat-resistant layer on the second surface.

[0030] According to the 13th embodiment, in the 12th embodiment, the surface roughness (Sa1) of the first adhesive layer may be smaller than the surface roughness (Sa2) of the second adhesive layer.

[0031] According to the 14th embodiment, in any one of the 12th to 13th embodiments, the surface roughness (Sa2) of the second adhesive layer may be 1.1 times or more of the surface roughness (Sa1) of the first adhesive layer.

[0032] According to the 15th embodiment, in any one of the 12th to 14th embodiments, the surface roughness (Sa2) of the second adhesive layer may be 1.1 times or more and 1.4 times or less of the surface roughness (Sa1) of the first adhesive layer.

[0033] According to the 16th embodiment, a lithium secondary battery is provided comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and a battery housing accommodating the electrode assembly and an electrolyte, wherein the separator is according to any one of the 1st to 15th embodiments.

[0034]

[0035] According to one embodiment of the present invention, by including a caprolactone-based dispersant in the adhesive layer or by controlling the surface roughness (Sa) of the adhesive layer, the phenomenon of particulate PVDF-based binder polymer being transferred to and detached from the surface of the pressurizing member during the rotary pressurizing process of the electrode assembly can be suppressed.

[0036] According to one embodiment of the present invention, the adhesion between the electrode and the separator (dry adhesion) in a dry state is improved, so that delamination and wrinkling can be reduced during the lamination, winding, and pressurization processes.

[0037] According to one embodiment of the present invention, by designing the surface roughness of the adhesive layer on both sides of the separator differently (Sa2 / Sa1 ratio control), the electrode-separator adhesion force (wet adhesion force) in the electrolyte-impregnated state can be controlled to suit the purpose, and as a result, bending and shape distortion of the cell can be suppressed or reduced.

[0038] A separator for a lithium secondary battery according to one embodiment of the present invention separates an inorganic heat-resistant layer and an adhesive layer, so that the adhesive layer can be uniformly distributed on the inorganic heat-resistant layer, thereby enabling excellent dry adhesion between the electrode and the separator.

[0039] A separator for a lithium secondary battery according to one embodiment of the present invention may be economically manufactured by applying a multilayer coating method.

[0040] However, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by those skilled in the art from the description of the invention below.

[0041]

[0042] 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.

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

[0044] FIG. 2 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0045] FIG. 3 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0046] FIG. 4 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0047] FIG. 5 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0048] FIG. 6 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0049] FIG. 7 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0050] FIG. 8 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0051] FIG. 9 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0052] FIG. 10 schematically shows a cross-section of a separator for a lithium secondary battery according to one embodiment of the present invention.

[0053]

[0054] 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 that can replace them may exist at the time of filing this application.

[0055]

[0056] <Definition>

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Throughout the entire specification, 'secondary particle' refers to a particle formed by the aggregation of the primary particle.

[0063]

[0064] FIG. 1 is a cross-sectional view schematically illustrating a cross-section of a lithium secondary battery according to one embodiment of the present invention, and FIG. 2 to 10 are schematically illustrating a cross-sectional view of a separator (10) for a lithium secondary battery according to one embodiment of the present invention.

[0065]

[0066] The present invention provides a separator (10) for a lithium secondary battery.

[0067] According to one aspect of the present invention, a separator (10) for a lithium secondary battery of the present invention comprises a porous polymer substrate (1); a first adhesive layer (5a) formed on at least one surface of the porous polymer substrate (1) and comprising a particulate PVDF-based binder polymer, wherein the first adhesive layer (5a) comprises i) a caprolactone-based dispersant or ii) a surface roughness (Sa) within the range of 0.12 μm to 0.22 μm.

[0068]

[0069] <Porous polymer substrate>

[0070] The separator (10) for a lithium secondary battery of the present invention comprises a porous polymer substrate (1).

[0071] 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.

[0072] 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 the movement of ions 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.

[0073] 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.

[0074] 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 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.

[0075] 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.

[0076] 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.

[0077]

[0078] Inorganic heat-resistant layer

[0079] In one embodiment of the present invention, the separator (10) for a lithium secondary battery may be formed alone on at least one surface of the porous polymer substrate (1) or formed between the porous polymer substrate (1) and the first adhesive layer (5a), and may include an inorganic heat-resistant layer (3) comprising inorganic particles and a first binder polymer.

[0080] The above inorganic heat-resistant layer (3) may be formed by mixing a plurality of inorganic particles and a first binder polymer. By covering the porous polymer substrate (1) with the inorganic heat-resistant layer (3) containing such inorganic particles, the heat resistance and mechanical properties of the separation membrane (10) can be further improved.

[0081] In one embodiment of the present invention, the inorganic heat-resistant layer (3) may be disposed on only one side of the porous polymer substrate (1). By forming the inorganic heat-resistant layer (3) on one side of the porous polymer substrate (1) in this manner, the thickness of the electrode assembly can be controlled to achieve excellent energy density.

[0082] In one embodiment of the present invention, the inorganic heat-resistant layer (3) may be disposed on both sides of the porous polymer substrate (1). By forming the inorganic heat-resistant layer (3) on both sides of the porous polymer substrate (1) in this manner, the heat resistance and mechanical properties of the separator (10) may be symmetrically superior, and the porosity may be superior.

[0083]

[0084] 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.

[0085] In one embodiment of the present invention, the first binder polymer may comprise a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0086] In the present specification, the term "particle form" may mean that the binder polymer within the coating layer formed by adding the binder polymer in a particle form to a dispersion medium for the formation of an inorganic heat-resistant layer or an adhesive layer, and then coating and drying the mixture, retains the added particle form. The "non-particle form" binder polymer may mean that when forming the inorganic heat-resistant layer, it is coated and dried in a form dissolved in a solvent, or that it is added to the dispersion medium in a particle form but fails to retain the particle form upon coating and drying.

[0087] In one embodiment of the present invention, the first binder polymer may include an acrylic binder polymer, and the acrylic binder polymer may include an acrylic homopolymer formed by polymerizing only acrylic monomers, or may include a copolymer of an acrylic monomer and another monomer. For example, the above acrylic binder polymer is poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexylacrylate and methylmethacrylate, a copolymer of butylacrylate and methylmethacrylate, an ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, an ethyl acrylate-acrylic acid-2-(dimethylamino)ethylacrylate copolymer, an ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, or an ethyl acrylate-acrylic acid-2-(diethylamino)ethylacrylate copolymer. It may include a copolymer or a mixture of two or more of these.

[0088] 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 in which the inorganic particles substantially come into contact. 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 has excellent heat resistance due to the inorganic heat-resistant layer.

[0089] 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.

[0090] For the reasons stated above, it is preferable that the inorganic particles comprise high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 There are O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, or mixtures thereof.

[0091] In addition, as inorganic particles, inorganic particles having lithium ion transport capability may be used, that is, inorganic particles containing lithium elements but having the function of transporting lithium ions without storing lithium. Non-limiting examples of inorganic particles having lithium ion transport capability include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as (LiAlTiP) 14Li2O-9Al2O3-38TiO2-39P2O5 x O y Series glass (0 <x < 4, 0 < y < 13), 리튬란탄티타네이트(Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4, etc. x Ge y P z S w Lithium nitrides such as , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), Li3N, etc. (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 series glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 글래스(Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc.

[0092] In one embodiment of the present invention, the average particle size (D) of the inorganic particles 50 ) is not particularly limited, but can be, for example, 100 to 1,000 nm, more specifically 100 to 800 nm.

[0093] In one embodiment of the present invention, the inorganic particles may be 70% or more, 99% or less, 80% or more, or 97% or less, or 85% or more, or 96% or less, based on 100% by weight of the inorganic heat-resistant layer. When the content of the inorganic particles satisfies a predetermined range, the inorganic coating layer may have a high density, and the porosity and resistance characteristics of the separator may be excellent.

[0094] In one embodiment of the present invention, the first binder polymer may be in an amount of 1% or more and 30% or less, 3% or more and 20% or less, and 4% or more and 10% or less, based on 100% by weight of the inorganic heat-resistant layer. When the content of the first binder polymer satisfies a predetermined range, the heat resistance of the separator can be maintained even more excellently without causing detachment of inorganic particles within the adhesive layer.

[0095] In one embodiment of the present invention, the thickness of the inorganic heat-resistant layer may be 0.5 μm or more, 0.6 μm or more, 0.8 μm or more, or 1 μm or more based on being formed on one side of a porous polymer substrate, and may be 50 μm or less, 30 μm or less, 5 μm or less, 2 μm or less, or 1.8 μm or less.

[0096] Meanwhile, in one embodiment of the present invention, the inorganic heat-resistant layer may further include a first dispersant. As described below, the first dispersant 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 dispersant (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. For example, the first dispersant may be sodium carboxymethylcellulose.

[0097] 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.

[0098]

[0099] <1st Adhesive Layer>

[0100] According to one aspect of the present invention, a first adhesive layer (5a) is formed on at least one surface of the porous polymer substrate (1) and comprises a particulate PVDF-based binder polymer, wherein the first adhesive layer comprises i) a caprolactone-based dispersant or ii) a surface roughness (Sa) within the range of 0.12 μm to 0.22 μm.

[0101] In one embodiment of the present invention, the caprolactone-based dispersant comprises a caprolactone-derived repeating unit, and may further comprise an ethylene glycol-derived repeating unit, a propylene glycol-derived repeating unit, or two or more of these repeating units in addition to the caprolactone-based repeating unit. By using the dispersant, the particulate PVDF-based binder polymer, the second binder polymer, etc., can be further dispersed in the dispersion medium, thereby controlling the surface roughness of the adhesive layer, preventing the formation of a large amount of the PVDF-based binder polymer on the first adhesive layer, and preventing the detachment of the PVDF-based binder polymer.

[0102] 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.

[0103] 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.

[0104] In one embodiment of the present invention, the surface roughness (Sa) of the adhesive layer may be within the range of 0.12 μm to 0.22 μm, or 0.15 μm to 0.205 μm. Since the surface roughness (Sa) of the adhesive layer satisfies the above-described range, the binder polymer is not transferred to the pressurizing member during the pressurizing process performed when manufacturing an electrode assembly by laminating the separator, so the adhesion strength between the electrode and the separator in a dry state (dry adhesion strength) may be excellent, and the manufacturing process time of the lithium secondary battery may be shortened.

[0105] 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 instrument (e.g., a surface profiler) or a confocal laser scanning microscope (CLSM). For example, the surface roughness can be measured 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, etc.

[0106] In one embodiment of the present invention, the thickness of the first adhesive layer may be 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, or 0.6 μm or more based on being formed on one side of a porous polymer substrate, and may be 1.3 μm or less, 1.25 μm or less, 1.2 μm or less, 1.1 μm or less, or 1.0 μm or less. Since the thickness of the first 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.

[0107]

[0108] 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.

[0109] 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).

[0110] 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).

[0111] In one embodiment of the present invention, the content of the hexapropylene-derived repeating unit may be 1% to 20% by weight, 5% to 15% by weight, or 10% 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.

[0112] 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.

[0113] In one embodiment of the present invention, the glass transition temperature (Tg) of the particulate PVDF-based binder polymer may be -30°C to 40°C or -20°C to 20°C. Additionally, the melting point (Tm) of the particulate PVDF-based binder polymer may be 100°C to 180°C or 130°C to 150°C.

[0114] In one embodiment of the present invention, the average particle size (D at the time of introduction of the PVDF-based binder polymer) 50 ) may be 0.5 μm to 5 μm, or 0.8 μm to 3.5 μm. Meanwhile, in one embodiment of the present invention, the average particle size (D) within the adhesive layer of the PVDF-based binder polymer is 50) may be 0.5 μm to 1.5 μm, or 0.8 μm to 1.2 μm. When the size of the PVDF-based binder polymer satisfies the above-described range, the adhesion and porosity of the separation membrane may be superior. Meanwhile, at this time, the average particle size (D) of the PVDF-based binder polymer 50 ) is the average particle size (D) of the primary particles of the PVDF-based binder polymer. 50 It means ).

[0115]

[0116] In one embodiment of the present invention, the first adhesive layer (5a) may further include a second binder polymer. The first adhesive layer (5a) may be formed by mixing a plurality of particulate PVDF-based binder polymers and a second binder polymer.

[0117] 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.

[0118] In one embodiment of the present invention, when the second binder polymer is a particulate binder polymer, the average particle size (D) of the particulate binder polymer 50 ) 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 ).

[0119] 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 -30°C or higher and 30°C or lower.

[0120] In one embodiment of the present invention, the second binder polymer may include an acrylic binder polymer. The acrylic binder polymer may include an acrylic homopolymer formed by polymerizing only acrylic monomers, or it 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.

[0121] 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.

[0122] 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. The second binder polymer satisfies the above-described range so that the second binder polymer is evenly distributed, resulting in excellent resistance characteristics and excellent adhesion.

[0123] In one embodiment of the present invention, the caprolactone-based dispersant may be included in an amount of 1% to 3% by weight based on 100% by weight of the adhesive layer. The caprolactone-based dispersant satisfies the above-described range, so that excellent resistance characteristics may be achieved and no electrochemical side reactions may occur.

[0124] In one embodiment of the present invention, the adhesive layer may further include a wetting agent to better disperse the particulate PVDF-based binder polymer in the dispersion medium.

[0125] These wetting agents 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.

[0126] In one embodiment of the present invention, the 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.

[0127]

[0128] <Second Adhesive Layer>

[0129] In one embodiment of the present invention, a second adhesive layer (5b) comprising a particulate PVDF-based binder polymer may be further included, which is formed on the other side of the porous polymer substrate (1) on which the first adhesive layer (5a) is formed. In this case, the particulate PVDF-based binder polymer may be the same as or different from the PVDF-based binder polymer included in the first adhesive layer, and the description thereof is substituted with the foregoing description.

[0130]

[0131] A separator (10) for a lithium secondary battery according to one aspect of the present invention comprises a porous polymer substrate (1) and a first adhesive layer (5a) formed on at least one surface thereof. Additionally, as described above, an inorganic heat-resistant layer (3) may be formed alone on at least one surface of the porous polymer substrate (1) or formed between the porous polymer substrate (1) and the first adhesive layer (5a). Accordingly, a separator for a lithium secondary battery according to an embodiment of the present invention may have a structure as illustrated in FIGS. 2 to FIGS. 10.

[0132] A separator (10) for a lithium secondary battery according to one embodiment of the present invention may have a first adhesive layer (5a) formed on one surface of a porous polymer substrate (1), as shown in FIG. 2.

[0133] A separator (10) for a lithium secondary battery according to one embodiment of the present invention may have a first adhesive layer (5a) formed on both sides of a porous polymer substrate (1), as shown in FIG. 3.

[0134] As shown in FIG. 4, a separator (10) for a lithium secondary battery according to one embodiment of the present invention may have a first adhesive layer (5a) formed on a first surface of a porous polymer substrate (1) and a second adhesive layer (5b) formed on a second surface.

[0135] As shown in FIG. 5, a separator (10) for a lithium secondary battery according to one embodiment of the present invention may have an inorganic heat-resistant layer (3) formed on one surface of a porous polymer substrate (1) and a first adhesive layer (5a) formed on the upper surface thereof.

[0136] As shown in FIG. 6, a separator (10) for a lithium secondary battery according to one embodiment of the present invention may have an inorganic heat-resistant layer (3) and a first adhesive layer (5a) formed on one side of a porous polymer substrate (1), and a first adhesive layer (5a) formed on the other side (second side).

[0137] As shown in FIG. 7, a separator (10) for a lithium secondary battery according to one embodiment of the present invention may have an inorganic heat-resistant layer (3) and a first adhesive layer (5a) formed on one side of a porous polymer substrate (1), and a second adhesive layer (5b) formed on the other side (second side).

[0138] As shown in FIG. 8, a separator (10) for a lithium secondary battery according to one embodiment of the present invention may have an inorganic heat-resistant layer (3) formed on both sides of a porous polymer substrate (1), and a first adhesive layer (5a) formed on the upper part of the inorganic heat-resistant layer on the first side.

[0139] As shown in FIG. 9, a separator (10) for a lithium secondary battery according to one embodiment of the present invention has an inorganic heat-resistant layer (3) formed on both sides of a porous polymer substrate (1), and a first adhesive layer (5a) may be formed on the upper surface of the inorganic heat-resistant layer on the first surface and the second surface, respectively.

[0140] In one embodiment of the present invention, as shown in FIG. 10, an inorganic heat-resistant layer (3) comprising inorganic particles and a first binder polymer is formed on each of the first surface and the second surface of the porous polymer substrate (1), and a first adhesive layer is formed on the upper surface of the inorganic heat-resistant layer on the first surface, and a second adhesive layer is formed on the upper surface of the inorganic heat-resistant layer on the second surface.

[0141] In one embodiment of the present invention, the second adhesive layer (5b) can be distinguished from the first adhesive layer (5a) by not using a caprolactone-based dispersant.

[0142] In one embodiment of the present invention, the second adhesive layer (5b) may include a second dispersant or have a higher surface roughness compared to the first adhesive layer (5a).

[0143] In one embodiment of the present invention, the first adhesive layer (5a) and the second adhesive layer (5b) may be formed by mixing a plurality of particulate PVDF-based binder polymers. In this case, the first adhesive layer (5a) has excellent dispersion due to a caprolactone-based dispersant, and the second adhesive layer (5b) may have slightly lower dispersion compared to the first adhesive layer (5a) as it contains the second dispersant. Therefore, the surface roughness of the first adhesive layer (5a) after drying may be lower than that of the second adhesive layer (5b). Additionally, by including a caprolactone-based dispersant in the first adhesive layer (5a), the transfer phenomenon caused by the pressure roll during the separation membrane manufacturing process may be reduced depending on the characteristics of the dispersant.

[0144] In one embodiment of the present invention, the second dispersant is not limited in type, but may be, for example, a polyvinylpyrrolidone-based compound, a cellulose-based compound, or an organic acid-based compound.

[0145] 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.

[0146] 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.

[0147] In one embodiment of the present invention, the second dispersant may be included in an amount of 1% to 5% by weight, or 2% to 4% by weight, based on 100% by weight of the second adhesive layer.

[0148]

[0149] In one embodiment of the present invention, the second adhesive layer (5b) may further include a third binder polymer.

[0150] In one embodiment of the present invention, the third binder polymer may be a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

[0151] In one embodiment of the present invention, the third binder polymer may be an acrylic binder polymer.

[0152] 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.

[0153] In one embodiment of the present invention, when the third 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.

[0154] In one embodiment of the present invention, when the third binder polymer is in the form of particles, the average particle size (D) of the third binder polymer is 100 nm to 800 nm, or 200 nm to 700 nm. 50 It may be having ).

[0155] In one embodiment of the present invention, the third 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 second adhesive layer. The third binder polymer satisfies the above-described range so that the third binder polymer is evenly distributed, resulting in excellent resistance characteristics and excellent adhesion.

[0156]

[0157] In one embodiment of the present invention, the adhesive layer may further include a wetting agent to better disperse the particulate PVDF-based binder polymer in the dispersion medium.

[0158] These wetting agents 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.

[0159] In one embodiment of the present invention, the 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.

[0160]

[0161] Lithium-ion batteries are manufactured through an assembly process in which electrode assemblies are housed in a battery case, electrolyte is injected, and the case is sealed; a pre-aging process to ensure sufficient impregnation of the electrolyte into the electrodes and separator; and an activation process to stabilize the battery structure and make it ready for use. During the activation process, the positive electrode active material is activated and a stable solid electrolyte interface (SEI) is formed on the surface of the negative electrode during the first charge-discharge cycle. However, during this activation process, the positive and negative electrodes undergo volume expansion; in particular, in batteries with a lamination-and-stack structure where multiple electrode assemblies are stacked, there has been a problem of bending, where the electrodes flex or warp along the battery's electric field.

[0162] As a result of conducting in-depth research to solve the above problem, the inventors of the present invention discovered that when the difference between the adhesion force between the cathode and the separator and the adhesion force between the anode and the separator is excessive while the electrolyte is impregnated, the bending phenomenon is exacerbated. This is due to the difference in that the anode mainly contains a PVDF-based binder polymer, while the cathode contains an SBR (styrene-butadiene rubber) binder. That is, when a PVDF-based binder polymer is used in the separator adhesive layer, it has a higher affinity with the anode binder, and as the adhesion force between the anode and the separator becomes relatively larger, the bending phenomenon may be exacerbated.

[0163] In this regard, in one embodiment of the present invention, the balance of adhesion force between the anode, cathode, and separator can be controlled by setting the surface roughness (Sa1) of the first adhesive layer to be smaller than the surface roughness (Sa2) of the second adhesive layer. Specifically, the surface roughness (Sa2) of the second adhesive layer can be formed to be at least 1.1 times the surface roughness (Sa1) of the first adhesive layer, and more preferably at least 1.1 times and no more than 1.4 times. By controlling the surface roughness of the adhesive layer in this way, the adhesion force between the electrodes of the first adhesive layer and the second adhesive layer is maintained differently in the electrolyte impregnation state, so that the adhesion force is distributed evenly when the electrode assembly is laminated, and as a result, the bending phenomenon of the battery that may occur during the activation process can be effectively suppressed or reduced.

[0164]

[0165] Lithium secondary battery

[0166] The present invention provides a lithium secondary battery.

[0167] FIG. 1 is a cross-sectional view schematically illustrating a cross-section of a lithium secondary battery having a separator for a lithium secondary battery according to one embodiment of the present invention.

[0168] According to one aspect of the present invention, the lithium secondary battery of the present invention comprises an electrode assembly including a positive electrode (30), a negative electrode (20), and a separator (10) interposed between them, and a battery housing that accommodates the electrode assembly and an electrolyte, wherein the separator (10) is characterized according to one embodiment of the present invention.

[0169] In one embodiment of the present invention, when the separator (10) comprises a first adhesive layer (5a) and a second adhesive layer (5b), the first adhesive layer (5a) may be positioned to face the cathode (20) as shown in FIG. 1. In this case, the first adhesive layer (5a) may have a smaller surface roughness than the second adhesive layer (5b).

[0170] In addition, the anode may include a PVDF-based binder polymer, and the cathode may include an SBR (styrene-butadiene rubber) binder. However, when a PVDF-based binder polymer is used in the separator adhesive layer, the affinity with the anode binder increases, resulting in a relatively larger adhesion between the anode and the separator, which may exacerbate the bending phenomenon of the battery.

[0171] Accordingly, in one embodiment of the present invention, the surface roughness (Sa1) of the first adhesive layer is set lower than the surface roughness (Sa2) of the second adhesive layer, and by arranging the first adhesive layer (5a) with low roughness to face the negative electrode, the adhesion force between the negative electrode-separator and the positive electrode-separator is balanced, thereby effectively improving the bending phenomenon of the battery.

[0172] 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.

[0173] 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.

[0174] 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).

[0175] 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.

[0176] 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. 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.

[0177]

[0178] Method for manufacturing a separator for a lithium secondary battery

[0179] The present invention provides a method for manufacturing a separator for a lithium secondary battery.

[0180] (First embodiment)

[0181] A method for manufacturing a separator for a lithium secondary battery according to one embodiment of the present invention 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 a water-based first adhesive layer forming slurry comprising a particulate PVDF-based binder polymer and a caprolactone-based dispersant; (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; and (S3) a step of forming a first adhesive layer by applying and drying the first adhesive layer forming slurry on at least one surface of the inorganic heat-resistant layer.

[0182] Hereinafter, the method for manufacturing a separator for a lithium secondary battery will be examined step by step. Meanwhile, the inorganic particles, the first binder polymer, the PVDF-based binder polymer, the second binder polymer, the caprolactone-based dispersant, the first dispersant, and the second dispersant are substituted for those described above.

[0183] First, (S1) a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer, and a water-based first adhesive layer forming slurry comprising a particulate PVDF-based binder polymer and a caprolactone-based dispersant are prepared.

[0184] 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.

[0185] Meanwhile, in one embodiment of the present invention, the aqueous inorganic heat-resistant layer forming slurry and the aqueous first adhesive layer forming slurry may be controlled so that the concentration of solids (or content of solids), excluding the dispersion medium, is in the range of 20 wt% to 50 wt%.

[0186] In one embodiment of the present invention, the aqueous inorganic heat-resistant layer forming slurry may further comprise a first dispersant. The first dispersant can improve coating properties by allowing the inorganic heat-resistant layer forming slurry to wet well onto a hydrophobic porous polymer substrate. Meanwhile, the first dispersant may be a known dispersant and may substitute for the one described above.

[0187] In one embodiment of the present invention, specifically, the step of preparing the water-based inorganic heat-resistant layer forming slurry may include (S1-1) a step of preparing a first dispersion by introducing inorganic particles into a water-based dispersion medium; and (S1-2) a step of bead milling the first dispersion.

[0188] In one embodiment of the present invention, the first binder polymer may be introduced before or after the bead milling step, but preferably, the first binder polymer may be introduced after the bead milling step. In this case, the processability may be excellent as no bubbles or the like appear in the first dispersion during the bead milling step.

[0189] In one embodiment of the present invention, the first dispersant may be added before or after the bead milling step.

[0190] Meanwhile, the bead milling step above separates inorganic particles in a secondary particle state, where the inorganic particles are clustered according to intensity, into the form of primary particles, or the average particle size (D) of the inorganic particles of the primary particles 50 ) can be made smaller.

[0191] In one embodiment of the present invention, the aqueous first adhesive layer forming slurry may include a caprolactone-based dispersant.

[0192] In one embodiment of the present invention, the aqueous first adhesive layer forming slurry 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.

[0193]

[0194] In one embodiment of the present invention, the step of preparing the water-based first adhesive layer forming slurry may specifically include: (S1a) a step of preparing a second dispersion by adding the particulate PVDF-based binder polymer and the caprolactone-based dispersant to a water-based dispersion medium; and (S1b) a step of bead milling the second dispersion.

[0195] In one embodiment of the present invention, the second binder polymer may be introduced before or after the bead milling step, and preferably, the second binder polymer may be introduced after the bead milling step.

[0196] Meanwhile, the above-mentioned particulate PVDF-based binder polymer may be synthesized in the form of particles, dried, and then introduced into an aqueous dispersion medium in powder form. The above-mentioned powder-form particulate PVDF-based binder polymer has an average particle size (D 50 ) may be 2 μm to 6 μm, and the average particle size (D) after bead milling 50) may have a particle size of 0.5 μm to 1.5 μm, or 0.8 μm to 1.2 μm. Meanwhile, the average particle size (D) of the particulate PVDF-based binder polymer is 50 If the above upper limit is exceeded, the surface roughness of the adhesive layer is high, and the binder polymer may be transferred to a rotating pressurizing member, such as a pressurizing roller, during the pressurizing process when manufacturing the electrode assembly, and if it is below the above lower limit, the adhesion strength between the electrode and the separator in a dry state may be inferior.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] Specifically, in one embodiment of the present invention, the step of drying the water-based inorganic heat-resistant layer forming slurry may be performed at a temperature of 50°C to 70°C for 10 seconds to 120 seconds.

[0201] Afterwards, (S3) an adhesive layer can be formed by applying and drying the slurry for forming the first adhesive layer on at least one surface of the inorganic heat-resistant layer.

[0202] In one embodiment of the present invention, the method of applying the water-based first 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.

[0203] In one embodiment of the present invention, the method of drying the water-based first adhesive layer forming slurry is not limited, and an appropriate method such as convection drying, hot air drying, blowing air drying, or a combination of two or more of natural drying methods may be applied. Preferably, the drying method may be hot air drying.

[0204] In one embodiment of the present invention, the step of drying the water-based first adhesive layer forming slurry may be performed at a temperature of 50°C to 70°C for 10 seconds to 120 seconds.

[0205]

[0206] (Second embodiment)

[0207] A method for manufacturing a separator for a lithium secondary battery according to another embodiment of the present invention comprises: (S1) a step of preparing a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer and a water-based first adhesive layer forming slurry comprising a particulate PVDF-based binder polymer; (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; and (S3) a step of forming an adhesive layer by applying and drying the water-based first adhesive layer forming slurry on at least one surface of the inorganic heat-resistant layer, wherein step (S1) may include a step of bead milling the water-based first adhesive layer forming slurry at a linear speed of 10 m / s to 15 m / s. Hereinafter, the method for manufacturing a separator for a lithium secondary battery will be examined step by step.

[0208] First, (S1) a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer and a water-based first adhesive layer forming slurry comprising a particulate PVDF-based binder polymer can be prepared.

[0209] In one embodiment of the present invention, step (S1) may include a step of bead milling the water-based adhesive layer forming slurry at a linear speed of 10 m / s to 15 m / s. In one embodiment of the present invention, step (S1) may include a step of bead milling the water-based adhesive layer forming slurry at a linear speed of 11 m / s to 14 m / s.

[0210] In one embodiment of the present invention, the bead milling may be performed by a bead milling device comprising a milling chamber for receiving a slurry and a plurality of beads and stirring blades within the milling chamber. The stirring blades may rotate by a rotating shaft within the milling chamber and a motor for driving the same. Additionally, the stirring blades may extend a certain distance from the circumference of the rotating shaft toward the inner wall of the milling chamber and may be positioned spaced apart from the inner wall of the milling chamber. One or multiple stirring blades may be provided at the same position on the rotating shaft.

[0211] In one embodiment of the present invention, depending on the shape of the stirring blade, the rotating device may be of the furnace type, propeller type, screw type, turbine type, or a combination thereof.

[0212] In one embodiment of the present invention, the meaning of "linear velocity" in "the slurry is bead milled at a linear velocity within the above range" may refer to the linear velocity at one end of the stirring blade that rotates the bead, which is extended from the axis of rotation. The linear velocity can be calculated from the rotational speed of the rotating device and the length of the stirring blade. When the rotational speed of the rotating device satisfies the above-described range, the energy of the impact force of the bead colliding and the shear force generated by the rotation of the bead is appropriate, so that the particulate PVDF-based binder polymer within the adhesive layer is deagglomerated, and the surface roughness of the adhesive layer can be controlled to a predetermined range. If the linear velocity exceeds the above-described upper limit, the particulate PVDF-based binder polymer is excessively deagglomerated and pulverized to form fine particles, and the fine particles may re-agglomerate, increasing the particle size and surface roughness. If the linear velocity is below the above-described lower limit, the surface roughness of the adhesive layer is high, and the adhesion strength of the electrode-separator may be reduced.

[0213] In one embodiment of the present invention, the plurality of beads may be included in an amount of 60% to 80% or 65% to 75% based on 100% of the interior volume of the milling chamber. When the beads are included within the above-described range, the probability of collision between the slurry and the beads increases, so that bead milling can be performed more efficiently and the flow of the slurry can be smooth. Meanwhile, how much the interior of the milling chamber is filled by beads can be measured by conventional methods, for example, by calculating the volume of water required to fill the milling chamber when beads are provided in the milling chamber and when they are not provided.

[0214] In this specification, the shear force can be calculated based on the gap (unit: m, etc.) between the rotor and the milling chamber and the linear velocity of the bead milling (unit: m / s, etc.). Specifically, in this specification, the shear force can be calculated by dividing the linear velocity by the gap.

[0215] Accordingly, in one embodiment of the present invention, the gap between the milling chamber and the stirring blade may be 20% to 50% of the diameter of the milling chamber. Specifically, the gap can be calculated by dividing the difference between the diameter of the milling chamber and the diameter of the stirring blade by 2.

[0216] In one embodiment of the present invention, the water-based inorganic heat-resistant layer forming slurry may further include a first dispersant.

[0217] In one embodiment of the present invention, specifically, the step of preparing the water-based inorganic heat-resistant layer forming slurry may include (S1-1) a step of preparing a first dispersion by introducing inorganic particles into a water-based dispersion medium; and (S1-2) a step of bead milling the first dispersion.

[0218] In one embodiment of the present invention, the first binder polymer may be introduced before or after the bead milling step, but preferably, the first binder polymer may be introduced after the bead milling step. In this case, the processability may be excellent as no bubbles or the like appear in the first dispersion during the bead milling step.

[0219] In one embodiment of the present invention, the first dispersant may be added before or after the bead milling step, but preferably, the first dispersant may be added after the bead milling step.

[0220] Meanwhile, the bead milling step above separates inorganic particles in a secondary particle state, where the inorganic particles are clustered according to intensity, into the form of primary particles, or the average particle size (D) of the inorganic particles of the primary particles 50 ) can be made smaller. At this time, bead milling can be performed in the bead milling device described above.

[0221] In one embodiment of the present invention, the step of preparing the water-based first adhesive layer forming slurry may specifically include: (S1a) a step of preparing a second dispersion by introducing the particulate PVDF-based binder polymer into a water-based dispersion medium; and (S1b) a step of bead milling the second dispersion.

[0222] 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.

[0223] In one embodiment of the present invention, when the water-based adhesive layer forming slurry further comprises a second binder polymer, the second binder polymer may be introduced before or after the bead milling step.

[0224] In one embodiment of the present invention, an additional dispersant for dispersing and wetting the particulate PVDF-based binder polymer may be added prior to the bead milling step.

[0225] Meanwhile, the above-mentioned particulate PVDF-based binder polymer may be synthesized in the form of particles, and then, after drying, introduced into an aqueous dispersion medium in powder form. This is stipulated as described above in the first embodiment.

[0226] 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.

[0227] Afterwards, (S3) a slurry for forming the first adhesive layer can be applied and dried on at least one surface of the inorganic heat-resistant layer to form the first adhesive layer.

[0228]

[0229] (Third embodiment)

[0230] A method for manufacturing a separator for a lithium secondary battery according to another embodiment of the present invention may include: (S1) preparing a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer, a first water-based adhesive layer forming slurry comprising a particulate PVDF-based binder polymer and a caprolactone-based dispersant, and a second water-based adhesive layer forming slurry comprising a particulate PVDF-based binder polymer and a second dispersant; (S2) forming an inorganic heat-resistant layer by applying and drying the water-based inorganic heat-resistant layer forming slurry on both sides of a porous polymer substrate; (S3) applying and drying the first water-based adhesive layer forming slurry on one side of the inorganic heat-resistant layer; and (S4) applying and drying the second water-based adhesive layer forming slurry on the other side of the inorganic heat-resistant layer on which the first water-based adhesive layer forming slurry is not applied.

[0231] First, (S1) a slurry for forming an inorganic heat-resistant layer in a water-based form including inorganic particles and a first binder polymer, a slurry for forming a first water-based adhesive layer in a particulate PVDF-based binder polymer and a first dispersant, and a slurry for forming a second water-based adhesive layer in a particulate PVDF-based binder polymer and a second dispersant are prepared.

[0232] In one embodiment of the present invention, the slurry for forming the first water-based adhesive layer may further include a second binder polymer. In one embodiment of the present invention, the slurry for forming the second water-based adhesive layer may further include a third binder polymer.

[0233] 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 both sides of a porous polymer substrate.

[0234] Afterwards, (S3) the slurry for forming the first water-based adhesive layer can be applied and dried on one side of the inorganic heat-resistant layer, and (S4) the slurry for forming the second water-based adhesive layer can be applied and dried on the other side of the inorganic heat-resistant layer where the slurry for forming the first water-based adhesive layer is not applied.

[0235]

[0236] (Fourth embodiment)

[0237] A method for manufacturing a separator for a lithium secondary battery according to another embodiment of the present invention may include: (S1) a step of preparing a water-based inorganic heat-resistant layer forming slurry comprising inorganic particles and a first binder polymer, a first water-based adhesive layer forming slurry comprising a particulate PVDF-based binder polymer, and a second water-based adhesive layer forming slurry comprising a particulate PVDF-based binder polymer; (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 two sides of a porous polymer substrate; (S3) a step of applying and drying the first water-based adhesive layer forming slurry on one side of the inorganic heat-resistant layer; and (S4) a step of applying and drying the second water-based adhesive layer forming slurry on the other side of the inorganic heat-resistant layer on which the first water-based adhesive layer forming slurry is not applied. Hereinafter, the method for manufacturing a separator for a lithium secondary battery will be examined step by step.

[0238] First, (S1) a slurry for forming an inorganic heat-resistant layer in a water-based manner comprising inorganic particles and a first binder polymer, a slurry for forming a first water-based adhesive layer comprising a particulate PVDF-based binder polymer, and a slurry for forming a second water-based adhesive layer comprising a particulate PVDF-based binder polymer can be prepared.

[0239] In one embodiment of the present invention, the slurry for forming the first water-based adhesive layer may further include a second binder polymer. In one embodiment of the present invention, the slurry for forming the second water-based adhesive layer may further include a third binder polymer. In one embodiment of the present invention, the dispersion medium is a water-based dispersion medium. The water-based dispersion medium may use water or a water-based dispersion medium containing water.

[0240] Meanwhile, the above step (S1) may include the step of bead milling the first water-based adhesive layer forming slurry at a linear speed of 10 m / s to 15 m / s and bead milling the second water-based adhesive layer forming slurry at a linear speed of 5 m / s to 10 m / s.

[0241] In one embodiment of the present invention, the aqueous inorganic heat-resistant layer forming slurry may further comprise a first wetting agent. The first wetting agent can improve coating properties by allowing the inorganic heat-resistant layer forming slurry to wet a hydrophobic porous polymer substrate well. Meanwhile, the first wetting agent may be a known wetting agent and may substitute for the one described above.

[0242] Subsequently, (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 both sides of a porous polymer substrate. Specifically, in one embodiment of the present invention, the step of drying the above-mentioned water-based inorganic heat-resistant layer forming slurry may be performed at a temperature of 50°C to 70°C or a temperature of 55°C to 65°C for 1 second to 200 seconds or 10 seconds to 120 seconds.

[0243] Afterwards, (S3) the slurry for forming the first water-based adhesive layer is applied and dried on one side of the inorganic heat-resistant layer, and (S4) the slurry for forming the second water-based adhesive layer is applied and dried on the other side of the inorganic heat-resistant layer where the slurry for forming the first water-based adhesive layer is not applied.

[0244] In one embodiment of the present invention, the method of applying the first water-based adhesive layer forming slurry and the second 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.

[0245] In one embodiment of the present invention, the step of drying the first water-based adhesive layer forming slurry and the second water-based adhesive layer forming slurry may be performed at a temperature of 50°C to 70°C for 10 seconds to 120 seconds.

[0246]

[0247] In this specification, the first to fourth 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.

[0248]

[0249] Method for manufacturing a lithium secondary battery

[0250] The present invention provides a method for manufacturing a lithium secondary battery.

[0251] A method for manufacturing a lithium secondary battery according to one aspect of the present invention comprises the steps of: forming a laminate by laminating a first separator, a negative electrode on the first separator, and a second separator on the negative electrode; pressing the laminate with a rotary pressing member; and laminating a positive electrode on the second separator of the pressed laminate, wherein the first separator and the second separator are each the aforementioned separators for a lithium secondary battery, and the particulate PVDF-based binder polymer of the adhesive layer is not substantially transferred onto the surface of the rotary pressing member by the pressing step. Below, the method for manufacturing a lithium secondary battery will be examined step by step.

[0252] First, a laminate can be formed by laminating a first separator, a cathode on the first separator, and a second separator on the cathode. The first separator and the second separator may refer to the separator described above.

[0253] In one embodiment of the present invention, the laminate may be manufactured according to conventional methods known in the art. According to one embodiment of the present invention, it may be configured by interposing the aforementioned separator between the anode and the cathode.

[0254] Next, the above laminate can be pressed with a rotary pressing member.

[0255] In one embodiment of the present invention, the laminate can be compressed using a rotary pressing member, such as two or more facing and rotating rolls.

[0256] In one embodiment of the present invention, the step of applying pressure with the rotary pressurizing member may be performed in a temperature range of 5°C to 30°C or 10°C to 25°C. In this case, the binder polymer of the separator is not deformed, and adhesion to the rotary roll may be minimal.

[0257] In one embodiment of the present invention, the pressurizing step may be performed in a pressure range of 0.1 MPa to 1 MPa, or 0.1 MPa to 0.5 MPa.

[0258] In one embodiment of the present invention, the pressurizing step may be performed for 1 second to 10 seconds.

[0259] In one embodiment of the present invention, the particulate PVDF-based binder polymer of the adhesive layer on the surface of the rotary pressurizing member may not be substantially transferred by the pressurizing step.

[0260] In one embodiment of the present invention, the particulate PVDF-based binder polymer of the adhesive layer may be transferred onto the surface of the rotary pressurizing member by the pressurizing step in an amount of less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, or less than 1 wt% based on 100 wt% of the particulate PVDF-based binder polymer of the adhesive layer.

[0261] Next, an electrode assembly of a lithium secondary battery can be manufactured by laminating an anode on the second separator of the pressurized laminate.

[0262] Meanwhile, in one embodiment of the present invention, the method for manufacturing the lithium secondary battery may inject the electrolyte at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it may be applied before battery assembly or at the final stage of battery assembly.

[0263]

[0264] 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.

[0265] <Example 1: Verification of Improvement in Tack Roll Transfer Phenomenon by Using Caprolactone-Based Dispersant>

[0266] <Example 1-1>

[0267] Aluminum oxide (Al2O3, D) as an inorganic particle 50 96 parts by weight of : 450 nm, Sumitomo Co., Ltd. and 1 part by weight of sodium carboxymethylcellulose as a first dispersant were added to water at room temperature to prepare a first dispersion, and the mixture was bead milled. Subsequently, 3 parts by weight of an acrylic polymer (CSB Toyo Ink Co., Ltd., Tg: -30℃) as a first binder polymer were added to prepare a water-based inorganic heat-resistant layer forming slurry.

[0268] In addition, as a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A second dispersion was prepared by adding : 3 μm) and a caprolactone-based dispersant, and this was bead milled. After bead milling, D of the PVDF-based binder polymer 50The thickness was 1 μm. Subsequently, an acrylic binder polymer (Tg: -35°C) emulsion was added as a second binder polymer to prepare a slurry for forming a water-based adhesive layer. 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.

[0269] A water-based inorganic heat-resistant layer forming slurry was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method and dried at a temperature of 60°C for 30 seconds. Subsequently, an adhesive layer forming slurry was applied to the inorganic heat-resistant layer using the doctor blade method and dried at a temperature of 60°C for 30 seconds. In the same way, an inorganic heat-resistant layer and an adhesive layer were formed on the other side of the porous polymer substrate made of polyethylene. At this time, the formed inorganic heat-resistant layer was 1.5 μm on one side, and the adhesive layer was 0.75 μm on one side. In addition, the content of inorganic particles in the inorganic heat-resistant layer satisfied 95 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0270]

[0271] <Example 1-2>

[0272] In the above Example 1-1, the procedure was carried out in the same manner as Example 1-1, except that the thickness of the adhesive layer was 0.5 μm on one side and 1 μm on both sides.

[0273]

[0274] <Examples 1-3>

[0275] In Example 1-1 above, a slurry for forming an aqueous inorganic heat-resistant layer was applied to one side (first side) of a porous polymer substrate using the doctor blade method and dried at a temperature of 60°C for 30 seconds. Subsequently, a slurry for forming an adhesive layer was applied to the inorganic heat-resistant layer using the doctor blade method and dried at a temperature of 60°C for 30 seconds. Subsequently, a slurry for forming an adhesive layer was applied to the other side (second side) of the porous polymer substrate using the doctor blade method and dried at a temperature of 60°C for 30 seconds. At this time, the formed inorganic heat-resistant layer was 2 μm thick, and the adhesive layer was 0.75 μm thick on one side. That is, a separator membrane of the form shown in Fig. 6 was manufactured.

[0276]

[0277] <Comparative Example 1-1>

[0278] The above Example 1-1 was carried out in the same manner as Example 1-1, except that a copolymer-type dispersant comprising repeating units derived from ethyleneglycol, repeating units derived from propyleneglycol, repeating units derived from ethylene, and repeating units derived from styrene was used instead of a caprolactone-based dispersant.

[0279]

[0280] <Comparative Example 1-2>

[0281] In Example 1-1, aluminum oxide (Al2O3, D) is used as an inorganic particle. 50 : 450 nm, Sumitomo Co.) 75 parts by weight and 2 parts by weight of a caprolactone-based dispersant (Miwon Commercial CYR301) as a dispersant were added to acetone at room temperature to prepare a dispersion, which was then bead-milled. Subsequently, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50A slurry for forming an organic-inorganic composite layer was prepared by adding 23 parts by weight (3 μm) and performing secondary bead milling. The slurry for forming the organic-inorganic composite layer was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method to a thickness of 2.5 μm, and then dried at a temperature of 60°C for 30 seconds. In addition, the same application and drying steps were performed on the other side.

[0282]

[0283] Manufacture of Lithium Secondary Batteries

[0284] In each example and comparative example, a lithium secondary battery was manufactured in the following manner.

[0285] LiNi as a 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 in a weight ratio of 97.0:1.5:1.5 and dispersing them in 2-methyl-2-pyrrolidone, and then coating the slurry onto an aluminum current collector and drying and rolling it to produce an anode.

[0286] A cathode slurry was prepared by mixing graphite as a cathode active material, styrene-butadiene rubber (SBR) as a cathode binder, and carboxymethylcellulose (CMC) as a thickener in a weight ratio of 89.2:10:0.8 and dispersing it in distilled water, and then coating the slurry onto a copper current collector and drying and rolling it to produce a cathode.

[0287] A cathode was laminated onto the separator of each example and comparative example, and the 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.

[0288] At this time, pressure was applied at 60°C and 1,000 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.

[0289] 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℃ 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℃.

[0290]

[0291] <Experimental Example 1: Electrode adhesion, thermal shrinkage, resistance characteristics, and tack roll transfer status>

[0292] For the above Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-2, electrode adhesion strength, surface roughness, thermal shrinkage, resistance characteristics, and tack roll transfer status were measured and are shown in Table 1 below.

[0293] Unit Example 1-1 Example 1-2 Example 1-3 Comparative Example 1-1 Comparative Example 1-2 Thickness of adhesive layer or organic-inorganic composite layer (single side) um 0.75 0.5 0.75 0.75 2.5 Cathode-separator dry adhesion gf / 20mm 218 21 / 2118 40 Surface roughness um 0.20 10.11 Adhesive layer on first surface: 0.195 / Adhesive layer on second surface: 0.20 80.23 60.24 Thermal shrinkage (130℃, 30min) % (MD) 00 50 3% (TD) 00 50 Resistance characteristics EROhm 0.72 0.68 0.61 0.71 0.89 Tack roll transfer XXXOX

[0294] Example 1-1 contained a caprolactone-based dispersant, and thus did not undergo tack roll transfer, while exhibiting excellent electrode adhesion, thermal properties, and resistance properties. Example 1-2 contained a caprolactone-based dispersant, and thus did not undergo tack roll transfer. Example 1-3 included an inorganic heat-resistant layer on only one side of a porous polymer substrate and adhesive layers on both sides; however, even in this case, a caprolactone-based dispersant was included in the adhesive layer, resulting in no tack roll transfer. Meanwhile, it was confirmed that although the thermal properties were somewhat inferior due to thermal shrinkage caused by including the inorganic heat-resistant layer on only one side, the resistance properties became excellent. On the other hand, Comparative Example 1-1 did not contain a caprolactone-based dispersant, and due to high surface roughness, the tack roll transfer phenomenon occurred. Examples 1-1, 1-2, and 1-3 confirmed that when compared to Comparative Example 1-1, a separate adhesive layer is provided and a caprolactone-based dispersant is included in the adhesive layer, thereby preventing the tack roll phenomenon. Meanwhile, unlike Example 1-1, Comparative Example 1-2 formed an organic-inorganic composite layer by dissolving a PVDF-based binder polymer in an organic solvent, applying it, and drying it. As a result, the shape of the organic-inorganic composite layer differed from the shape of the adhesive layer in Example 1-1. Furthermore, the thickness of the organic-inorganic composite layer was thick, thermal shrinkage occurred, and the resistance characteristics were inferior.

[0295]

[0296] <Example 2: Confirmation of Improvement in Tack Roll Phenomenon According to Surface Roughness>

[0297] <Example 2-1>

[0298] Aluminum oxide (Al2O3, D) as an inorganic particle 5096 parts by weight of : 450 nm, Sumitomo Co.) and 1 part by weight of sodium carboxymethylcellulose as a first dispersant were added to water at room temperature to prepare a first dispersion, and this was bead milled at a linear speed of 13 m / s. Subsequently, 3 parts by weight of an acrylic polymer (CSB Toyo Ink Co., Tg: -30℃) as a first binder polymer were added to prepare a water-based inorganic heat-resistant layer forming slurry.

[0299] In addition, as a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A dispersant in the form of a copolymer containing repeating units derived from ethylene glycol, repeating units derived from propylene glycol, repeating units derived from ethylene, and repeating units derived from styrene was introduced into a milling chamber and bead milled at a linear speed of 13 m / s. Subsequently, an acrylic binder polymer (Tg: -30℃) emulsion was further introduced as a second binder polymer to prepare a slurry for forming a water-based adhesive layer.

[0300] A water-based inorganic heat-resistant layer forming slurry was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method and dried at a temperature of 60°C for 30 seconds. Subsequently, an adhesive layer forming slurry was applied to the inorganic heat-resistant layer using the doctor blade method and dried at a temperature of 60°C for 30 seconds. In the same way, an inorganic heat-resistant layer and an adhesive layer were formed on the other side of the porous polymer substrate made of polyethylene. At this time, the formed inorganic heat-resistant layer was 1.5 μm thick, and the adhesive layer was 0.75 μm thick. In addition, the content of inorganic particles in the inorganic heat-resistant layer satisfied 95 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0301]

[0302] <Example 2-2>

[0303] In the above Example 2-1, the procedure was carried out in the same manner as Example 2-1, except that the linear speed of bead milling the second dispersion was set to 20 m / s.

[0304]

[0305] <Comparative Example 2-1>

[0306] In the above Example 2-1, the procedure was carried out in the same manner as Example 2-1, except that the linear speed of bead milling the second dispersion was set to 7 m / s.

[0307]

[0308] <Comparative Example 2-2>

[0309] In Example 2-1, aluminum oxide (Al2O3, D) is used as an inorganic particle. 50 : 450 nm, Sumitomo Co.) 75 parts by weight and 2 parts by weight of a dispersant (Miwon Co., CYR301) were added to acetone at room temperature to prepare a dispersion, which was then bead-milled at a linear speed of 10 m / s. Subsequently, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A slurry for forming an organic-inorganic composite layer was prepared by adding 12 parts by weight (3 μm) and performing secondary bead milling at a linear speed of 10 m / s. Subsequently, the slurry for forming the organic-inorganic composite layer was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method to a thickness of 2.5 μm, and then dried at a temperature of 60°C for 30 seconds. In addition, the same application and drying steps were performed on the other side.

[0310]

[0311] Manufacture of Lithium Secondary Batteries

[0312] In each example and comparative example, a lithium secondary battery was manufactured in the same manner as described above.

[0313]

[0314] <Experimental Example 2: Cathode-separator dry adhesion, surface roughness, thermal shrinkage, resistance characteristics, and tack roll transfer status>

[0315] For the above Examples 2-1 to 2-2 and Comparative Examples 2-1 to 2-2, electrode adhesion strength, surface roughness, thermal shrinkage, resistance characteristics, and tack roll transfer were measured and are shown in Table 2 below.

[0316] Unit Example 2-1 Example 2-2 Comparative Example 2-1 Comparative Example 2-2 Adhesive layer thickness or organic-inorganic composite layer thickness (single side) ㎛ 0.75 0.75 0.75 2.5 Cathode-separator dry adhesion gf / 20mm 25 18 17 40 Surface roughness ㎛ 0.20 10.21 80.23 60.24 Thermal shrinkage (130℃, 30min) % (MD) 000 3% (TD) 000 1 Resistance characteristic ohm 0.72 0.71 0.71 0.89 Tack roll transfer XX OX

[0317] Example 2-1 satisfied a predetermined range of surface roughness, so no tack roll transfer occurred, and the electrode adhesion, thermal properties, and resistance properties were excellent. In addition, Example 2-2 had a faster bead milling linear speed compared to Example 2-1; consequently, the surface roughness was somewhat higher, resulting in lower adhesion to the electrode, but the tack roll transfer phenomenon did not occur across the board. Comparative Example 2-1 had a slower bead milling linear speed and higher surface roughness compared to Example 2-1, causing the tack roll transfer phenomenon to appear. When comparing Examples 2-1 and 2-2 with Comparative Example 2-1, it was confirmed that the tack roll phenomenon does not occur when an adhesive layer is provided separately and the surface roughness of the adhesive layer satisfies a predetermined range. Meanwhile, unlike Example 2-1, Comparative Example 2-2 was prepared by dissolving a PVDF-based binder polymer in an organic solvent, and then applying and drying it to form an organic-inorganic composite layer. As a result, the shape of the organic-inorganic composite layer differed from the shape of the adhesive layer in Example 2-1. In addition, the organic-inorganic composite layer was thick, thermal shrinkage occurred, and resistance characteristics were inferior.

[0318]

[0319] <Example 3: Improvement of Cell Bending Phenomenon Due to Difference in Surface Roughness of Adhesive Layer>

[0320] <Example 3-1>

[0321] Aluminum oxide (Al2O3, D) as an inorganic particle 50 96 parts by weight of : 450 nm, Sumitomo Co.) and 1 part by weight of sodium carboxymethylcellulose as a first dispersant were added, and then bead milled. Subsequently, 3 parts by weight of an acrylic polymer (CSB Toyo Ink Co., Tg: -30℃) as a first binder polymer were added to water at room temperature to prepare a water-based inorganic heat-resistant layer forming slurry.

[0322] As a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A second dispersion was prepared by adding : 3 μm) and a caprolactone-based dispersant, and this was bead-milled. After bead-milling, D of the PVDF-based binder polymer 50 The thickness was 1 μm. Subsequently, an acrylic binder polymer (Tg: -35°C) emulsion was added as a second binder polymer to prepare a first aqueous adhesive layer forming slurry. At this time, the caprolactone-based dispersant contained 50% ethylene glycol-derived repeating units, 20% propylene glycol-derived repeating units, and 30% caprolactone-derived repeating units relative to 100% of the total repeating units.

[0323] And, as a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 : 3 μm) and methyl cellulose was added as a second dispersant to prepare a third dispersion, which was then bead-milled. After bead-milling, the D of the PVDF-based binder polymer 50 The thickness was 1 μm. Subsequently, an acrylic binder polymer (Tg: -35°C) emulsion was added as a third binder polymer to prepare a slurry for forming a second water-based adhesive layer.

[0324] At this time, it was confirmed that the second binder polymer and the third binder polymer existed in the form of particles on the emulsion at the time of addition, but when applied, the particle form could not be maintained due to the low Tg.

[0325] A water-based inorganic heat-resistant layer forming slurry was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method and dried at a temperature of 60°C for 30 seconds, and the water-based inorganic heat-resistant layer forming slurry was applied to the other side of the porous polymer substrate using the doctor blade method and dried at a temperature of 60°C for 30 seconds.

[0326] Subsequently, a slurry for forming a first water-based adhesive layer was applied to the inorganic heat-resistant layer and dried at a temperature of 60°C for 30 seconds. Then, a slurry for forming a second water-based adhesive layer was applied to the other side of the inorganic heat-resistant layer, which was not coated with the slurry for forming the first water-based adhesive layer, using the doctor blade method, and dried at a temperature of 60°C for 30 seconds to form the first adhesive layer and the second adhesive layer. At this time, the formed inorganic heat-resistant layer was 1.5 μm each, and the adhesive layer was 0.75 μm. In addition, the content of inorganic particles in the inorganic heat-resistant layer satisfied 95 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0327]

[0328] <Comparative Example 3-1>

[0329] In the above Example 3-1, the preparation was made in the same manner as Example 3-1, except that a slurry for forming a first water-based adhesive layer was applied to both sides of the inorganic heat-resistant layer.

[0330]

[0331] <Comparative Example 3-2>

[0332] In the above Example 1, the preparation was made in the same manner as Example 3-1, except that a slurry for forming a second water-based adhesive layer was applied to both sides of the inorganic heat-resistant layer.

[0333]

[0334] <Example 3-2>

[0335] Aluminum oxide (Al2O3, D) as an inorganic particle 50 96 parts by weight of : 450 nm, Sumitomo Co., Ltd., 1 part by weight of sodium carboxymethylcellulose as a first dispersant, and 3 parts by weight of an acrylic polymer (CSB Toyo Ink Co., Ltd., Tg: -30℃) as a first binder polymer were added to water at room temperature to prepare a first dispersion, which was then introduced into a milling chamber and bead milled at a linear speed of 9.5 m / s to prepare a water-based inorganic heat-resistant layer forming slurry.

[0336] As a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A dispersant in the form of a copolymer containing repeating units derived from ethylene glycol, repeating units derived from propylene glycol, repeating units derived from ethylene, and repeating units derived from styrene was introduced into a milling chamber and bead milled at a linear speed of 13 m / s, after which an acrylic binder polymer (Tg: -30℃) was introduced as a second binder polymer to prepare a slurry for forming a first water-based adhesive layer.

[0337] And, as a particulate PVDF-based binder polymer, PVDF-HFP (HFP-derived repeating unit content 12 wt%, D 50 A dispersant in the form of a copolymer containing repeating units derived from ethylene glycol, repeating units derived from propylene glycol, repeating units derived from ethylene, and repeating units derived from styrene was introduced into a milling chamber and bead milled at a linear speed of 7 m / s, after which an acrylic binder polymer (Tg: -30℃) was introduced as a third binder polymer to prepare a slurry for forming a second adhesive layer.

[0338] A water-based inorganic heat-resistant layer forming slurry was applied to one side of a porous polymer substrate made of polyethylene (porosity 40%, thickness 9 μm) using the doctor blade method and dried at a temperature of 60°C for 30 seconds, and the water-based inorganic heat-resistant layer forming slurry was applied to the other side of the porous polymer substrate using the doctor blade method and dried at a temperature of 60°C for 30 seconds.

[0339] Subsequently, a slurry for forming a first water-based adhesive layer was applied onto the inorganic heat-resistant layer and dried at a temperature of 60°C for 30 seconds. Then, a slurry for forming a second water-based adhesive layer was applied using the doctor blade method onto the other side of the inorganic heat-resistant layer that was not coated with the first water-based adhesive layer slurry, and dried at a temperature of 60°C for 30 seconds. 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 satisfied 95 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0340]

[0341] <Comparative Example 3-3>

[0342] In the above Example 3-2, the preparation was carried out in the same manner as Example 3-2, except that a slurry for forming a first water-based adhesive layer was applied to both sides of the inorganic heat-resistant layer.

[0343]

[0344] <Comparative Example 3-4>

[0345] In the above Example 3-2, the preparation was carried out in the same manner as Example 3-2, except that a slurry for forming a second water-based adhesive layer was applied to both sides of the inorganic heat-resistant layer.

[0346]

[0347] <Example 3-3>

[0348] In the above Example 3-1, the above was manufactured in the same manner as Example 3-1, except that a slurry for forming a first water-based adhesive layer was applied to one side of the porous polymer substrate and dried at a temperature of 60°C for 30 seconds to form a first adhesive layer, and an inorganic heat-resistant layer-forming slurry was applied to the other side, which was not coated with the slurry for forming the first water-based adhesive layer, using the doctor blade method and dried at a temperature of 60°C for 30 seconds to form an inorganic heat-resistant layer, and then a slurry for forming a second water-based adhesive layer was applied to the inorganic heat-resistant layer using the doctor blade method and dried at a temperature of 60°C for 30 seconds to form a second adhesive layer formed on the inorganic heat-resistant layer. At this time, the thickness of the formed inorganic heat-resistant layer was 2 μm, the thickness of the adhesive layer was 0.75 μm, and the content of inorganic particles in the inorganic heat-resistant layer satisfied 95 wt% based on 100 wt% of the total inorganic heat-resistant layer.

[0349]

[0350] Manufacture of Lithium Secondary Batteries

[0351] In each example and comparative example, a lithium secondary battery was manufactured in the following manner.

[0352] 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 an anode conductive material in a weight ratio of 97.0:1.5:1.5, then dispersing the mixture in 2-methyl-2-pyrrolidone to prepare an anode slurry, coating the mixture onto an aluminum current collector, and then drying and rolling it to produce an anode.

[0353] A cathode slurry was prepared by mixing graphite as a cathode active material, styrene-butadiene rubber (SBR) as a cathode binder, and CMC as a cathode dispersant in a weight ratio of 89.2:10:0.8 and dispersing it in distilled water, and then coating the slurry onto a copper current collector and drying and rolling it to produce a cathode.

[0354] 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.

[0355] In this case, for Examples 3-1, 3-2, and 3-3, a laminate was formed such that the side with lower surface roughness of the separator faces the adhesive layer to the cathode. That is, a laminate was formed such that the side with higher cathode-separator dry adhesion faces the cathode.

[0356] 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.

[0357] 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℃ 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℃.

[0358]

[0359] <Experimental Example 3: Cathode-Separator Dry Adhesion, Electrode-Separator Wet Adhesion, Surface Roughness (Sa), Resistance Characteristics (ER), Cell Bending>

[0360] For the above Examples 3-1 to 3-3 and Comparative Examples 3-1 to 3-4, electrode adhesion strength, surface roughness, thermal shrinkage, resistance characteristics, and tack roll transfer were measured and are shown in Table 3 below.

[0361]

[0362] In Examples 3-1 and 3-3, the surface roughness of the first adhesive layer containing a caprolactone-based dispersant was lower compared to the surface roughness of the second adhesive layer, and the first adhesive layer with low surface roughness faced the cathode because it had high electrode-separator dry adhesion, while the side with high surface roughness faced the anode. As a result, the difference between the anode-separator wet adhesion and the cathode-separator wet adhesion became smaller compared to Comparative Examples 1 and 2, and consequently, no cell bending phenomenon occurred.

[0363] Meanwhile, in Example 3-3, unlike in Example 3-1, the first adhesive layer is formed on a porous polymer substrate and the second adhesive layer is formed on an inorganic heat-resistant layer formed on the porous polymer substrate, but in this case, cell bending did not occur in the same way as in Example 3-1.

[0364] Meanwhile, Comparative Examples 3-1 and 3-2 had the same surface roughness of the adhesive layer, so the dry adhesion strength of the cathode-separator was similar, but the difference between the wet adhesion strength of the anode-separator and the cathode-separator was greater than in Example 3-1, and as a result, cell bending occurred.

[0365] In Example 3-2, the surface roughness of the first adhesive layer was lower compared to the surface roughness of the second adhesive layer. Since the first adhesive layer with low surface roughness had high electrode-separator dry adhesion, it faced the cathode, and since the second adhesive layer with high surface roughness had low electrode-separator dry adhesion, it faced the anode. As a result, the difference between the anode-separator wet adhesion and the cathode-separator wet adhesion was smaller compared to Comparative Examples 3-3 and 3-4, and consequently, no cell bending phenomenon occurred.

[0366] Meanwhile, Comparative Examples 3-3 and 3-4 had the same surface roughness of the adhesive layer, so the dry adhesion strength of the cathode-separator was similar, but the difference between the wet adhesion strength of the anode-separator and the wet adhesion strength of the cathode-separator was greater than that of Example 3-2, and as a result, cell bending occurred.

[0367] Therefore, it was possible to implement an asymmetric adhesive layer by controlling the surface roughness of the adhesive layer through the application of a caprolactone-based dispersant or the control of the slurry linear velocity, and it was confirmed that cell bending was reduced in the battery to which this was applied.

[0368] <Measurement Method>

[0369] Cathode-Separator Dry Adhesion Measurement Method

[0370] The negative electrode prepared for manufacturing a lithium secondary battery was cut to a size of 20 mm x 60 mm. The separator prepared in the examples and comparative examples was cut to a size of 20 mm x 60 mm. The prepared separator and negative electrode were overlapped, placed between 100 μm PET films, and bonded using a flatbed press. At this time, the conditions of the flatbed press were a temperature of 60°C and a pressure of 6.5 MPa, heated and pressed for 1 second. The bonded separator and negative electrode were attached to a slide glass using double-sided tape. The separator bonded to the negative electrode was peeled off at a 180° angle using a UTM and measured.

[0371]

[0372] Cathode-Separator Wet Adhesion Measurement Method

[0373] The negative electrode, positive electrode, and separator prepared in the examples and comparative examples for manufacturing a lithium secondary battery were prepared by cutting the negative electrode to a size of 20 mm X 60 mm. A cell with a negative electrode-separator-positive electrode-separator-negative electrode structure was assembled, and the electrolyte prepared for manufacturing the lithium secondary battery was injected. Subsequently, the cell was charged to SOC 60 under a pressure of 6.5 MPa at 60°C and then discharged. Afterward, the cell was disassembled to obtain two negative electrode-separator assemblies, and the separator was peeled off at 90° using a UTM for measurement.

[0374]

[0375] Method for measuring wet adhesion between anode and separator

[0376] A separator and an anode, cut to 20mm x 60mm, were stacked one on top of the other inside an aluminum pouch, electrolyte was injected, and the pouch was sealed. Subsequently, the pouch was subjected to 5kgf / cm² at a temperature of 60℃. 2 Pressurized for 5 minutes at a pressure. The separator-anode assembly inside the pouch was removed, and the separator was peeled off at 90° in the UTM for measurement.

[0377]

[0378] Surface roughness measurement method

[0379] Surface roughness was measured by using a confocal laser scanning microscope (CLSM (confocal laser scanning microscope), OLS5100, Olympus) in a dry environment, by fixing the separators of the examples and comparative examples flatly on a silicon wafer and measuring 10 times per sample (measurement environment: dry room, laser light source: 405 nm, measurement mode: 3D, lenses used: 20, 50, and 100x (objective lens), 1x (zoom)).

[0380] Subsequently, Data processing: After applying the data analysis application as shown below, 2D and 3D images and each surface roughness (Sa) were measured.

[0381] 1. Noise removal: Interpolate to surrounding heights.

[0382] 2. Tilt Removal: Correct tilt by specifying 4 points per image.

[0383] 3. Scale bar adjustment: Apply the same scale bar (-2 to 2 μm) to all images and extract 2D & 3D results.

[0384] 4. Surface roughness extracted with an L-filter value of 50

[0385]

[0386] Thermal shrinkage measurement method

[0387] The separators prepared in each example and comparative example were cut to a size of 50 mm * 50 mm, placed between A4 papers, and placed in a convection oven at 120°C for 1 hour, after which the thermal shrinkage rates in the machine direction (MD) and transverse direction (TD) were measured.

[0388] At this time, the thermal shrinkage rate was calculated as [(Initial length - Length after heat treatment) / (Initial length)Y100].

[0389]

[0390] Resistance characteristic measurement method

[0391] 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 the table. At this time, the AC resistance is the value of the resistance at 1KHz measured with a Hioki.

[0392]

[0393] Method to measure whether tack roll transfer is possible

[0394] After laminating the separator of each example and comparative example, the cathode on the separator, and the separator of each example and comparative example on the cathode, the mixture was pressed with a rotary pressurizing member. At this time, it was checked whether the particulate PVDF-based binder polymer of the adhesive layer of the separator was transferred onto the surface of the rotary pressurizing member, and the presence or absence was indicated in a table.

[0395]

[0396] Cell bending measurement

[0397] For the lithium secondary batteries (cells) manufactured in each example and comparative example, the difference in height between the cell edge and the cell center was measured using a ruler.

[0398]

[0399] Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims set forth below by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed above should be considered in an illustrative rather than a restrictive sense. That is, the scope of the true technical spirit of the present invention is indicated in the claims, and all variations within the equivalent scope thereof should be interpreted as being included in the present invention.

Claims

1. Porous polymer substrate; A first adhesive layer formed on at least one surface of the above-mentioned porous polymer substrate and comprising a particulate PVDF-based binder polymer; The first adhesive layer above i) containing a caprolactone-based dispersant, or ii) A separator for a lithium secondary battery characterized by a surface roughness (Sa) within the range of 0.12 μm to 0.22 μm.

2. In Claim 1, A separator for a lithium secondary battery, characterized in that the above-mentioned caprolactone-based dispersant contains 20% to 40% by weight of caprolactone-derived repeating units based on 100% by weight of the total repeating units.

3. In Claim 1, The above-mentioned caprolactone-based dispersant comprises 40% to 60% by weight of ethylene glycol-derived repeating units based on 100% by weight of the total repeating units, or A separator for a lithium secondary battery characterized by containing 10% to 30% by weight of repeating units derived from propylene glycol.

4. In Claim 1, A separator for a lithium secondary battery characterized by the above surface roughness (Sa) being measured by magnifying it 50 times with a confocal laser scanning microscope (CLSM).

5. In Claim 1, It is formed alone on at least one surface of the porous polymer substrate, or formed between the porous polymer substrate and the first adhesive layer, A separator for a lithium secondary battery, characterized by further comprising an inorganic heat-resistant layer comprising inorganic particles and a first binder polymer.

6. In Claim 5, A separator for a lithium secondary battery, characterized in that the first binder polymer comprises a particulate binder polymer, a non-particulate binder polymer, or a combination thereof.

7. In Claim 5, A separator for a lithium secondary battery characterized in that the above-mentioned inorganic particles are 70% by weight or more and 99% by weight or less based on 100% by weight of the inorganic heat-resistant layer.

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

9. In Claim 1, The first 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.

10. In Claim 9, The above second binder polymer includes a particulate binder polymer, and 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.

11. In Claim 1, A separator for a lithium secondary battery, characterized by further comprising: a second adhesive layer formed on the other side of a porous polymer substrate on which the first adhesive layer is formed, and comprising a particulate PVDF-based binder polymer.

12. In Claim 11, An inorganic heat-resistant layer comprising inorganic particles and a first binder polymer is formed on each of the first and second surfaces of the above-mentioned porous polymer substrate, and A first adhesive layer is formed on the upper part of the inorganic heat-resistant layer of the first surface, A separator for a lithium secondary battery, characterized in that a second adhesive layer is formed on the upper portion of the inorganic heat-resistant layer of the second surface.

13. In Claim 12, A separator for a lithium secondary battery, characterized in that the surface roughness (Sa1) of the first adhesive layer is smaller than the surface roughness (Sa2) of the second adhesive layer.

14. In Claim 12, A separator for a lithium secondary battery, characterized in that the surface roughness (Sa2) of the second adhesive layer is at least 1.1 times the surface roughness (Sa1) of the first adhesive layer.

15. In Claim 12, A separator for a lithium secondary battery, characterized in that the surface roughness (Sa2) of the second adhesive layer is 1.1 times or more and 1.4 times or less of the surface roughness (Sa1) of the first adhesive layer.

16. An electrode assembly comprising an anode, a cathode, and a separator interposed between the anode and the cathode; and A battery housing accommodating the electrode assembly and electrolyte; comprising A lithium secondary battery characterized in that the separator above is in accordance with any one of claims 1 to 15.

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