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

Abstract

Provided is a separator for a lithium secondary battery, the separator including: a porous polymer substrate; and a first binder layer formed on at least one surface of the porous polymer substrate and including a particulate type polyvinylidene fluoride (PVDF)-based binder polymer, wherein the first binder layer i) includes a caprolactone-based dispersant, or ii) has a surface roughness (Sa) of 0.12 µm to 0.22 µm.

Description

Technical Field

[0001] This disclosure relates to a separator for a lithium secondary battery and a lithium secondary battery including the separator.

[0002] By incorporating via reference

[0003] This application is based on and claims priority to Korean Patent Application No. 10-2024-0157405, Korean Patent Application No. 10-2024-0157407, Korean Patent Application No. 10-2024-0157410, and Korean Patent Application No. 10-2024-0157392, filed with the Korean Intellectual Property Office on November 7, 2024, the disclosures of which are incorporated herein by reference in their entirety. Background Technology

[0004] Electrochemical devices (such as lithium-ion batteries) typically have a basic structure of positive electrode / separator / negative electrode / electrolyte. They are energy storage devices capable of being charged / discharged reversibly through the conversion of chemical and electrical energy, and possess high energy density. They are widely used in compact electronic devices such as mobile phones and laptops. Recently, in response to environmental concerns, high oil prices, and the increasing demand for energy efficiency and storage, the application of these electrochemical devices has expanded to hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), e-bikes, and energy storage systems (ESS).

[0005] Ensuring the safety of lithium-ion batteries is a critical concern in their manufacture and use. In particular, separators commonly used in electrochemical devices can experience significant thermal shrinkage under harsh conditions (e.g., high temperatures) due to material properties and manufacturing processes, leading to safety-related issues such as internal short circuits. Therefore, to improve the safety of lithium-ion batteries, composite porous separators formed by coating a mixture of inorganic particles and binder polymers onto a porous polymer substrate have been proposed.

[0006] However, when such composite porous separators are laminated with electrodes to form electrode assemblies, delamination of the laminated structure may occur due to insufficient interlayer adhesion. When the electrodes separate from the separator, the battery may bend or deform due to the volume expansion / contraction of the electrodes during charging / discharging. Furthermore, in the case of composite porous layers comprising inorganic particles and binder polymers in a single layer, adhesion degradation may occur due to the non-uniform dispersion of the components. Therefore, there is a need to develop separators that stably provide high adhesion to the electrodes while ensuring excellent heat resistance.

[0007] Meanwhile, when the adhesive polymer in the composite porous separator is disposed on the surface, it has been observed that during the forming of the electrode assembly, in the pressing step using a rotary pressure roller or the like, the adhesive polymer is transferred to the surface of the rotary pressing member and desorbed from the separator. Therefore, a further step of washing the pressing member is required, leading to increased production time and decreased processability. The inventors of this disclosure have discovered that when the adhesive layer containing the adhesive polymer includes a specific type of dispersant or has a surface roughness (Sa) within a predetermined range, the transfer / desorption phenomenon can be significantly reduced, and the stability of the interfacial adhesion with the electrode can be improved. This disclosure is based on this discovery. Summary of the Invention

[0008] Technical issues

[0009] This disclosure aims to address the problems of the prior art, and therefore relates to providing a separator for lithium secondary batteries that inhibits the transfer of the adhesive polymer to the surface of a pressing member (such as a rotary roller) during the pressing step of forming an electrode assembly by incorporating a caprolactone dispersant into the adhesive layer of the separator for lithium secondary batteries or by controlling the surface roughness (Sa) of the adhesive layer to a predetermined range.

[0010] This disclosure also relates to providing a separator for lithium secondary batteries that can provide improved electrode-separator adhesion (dry adhesion) in a dry state.

[0011] Furthermore, this disclosure relates to providing a separator for lithium secondary batteries with excellent thermal and resistive properties.

[0012] Furthermore, this disclosure relates to providing a separator for a lithium secondary battery, which suppresses or reduces battery bending and shape deformation by controlling the surface roughness of the adhesive layer differently on the two surfaces of the separator to adequately control the electrode-separator adhesion (wet adhesion) in a wetted state.

[0013] Furthermore, this disclosure relates to providing a lithium secondary battery including the aforementioned separator.

[0014] However, the technical problems to be solved by this disclosure are not limited to those described above, and those skilled in the art will clearly understand from the description of this disclosure below that there are other problems not mentioned.

[0015] Technical solution

[0016] To achieve the above objectives, in one aspect of this disclosure, a separator for a lithium secondary battery and a lithium secondary battery including the separator are provided according to the following embodiments.

[0017] According to a first embodiment of the present disclosure, a separator for a lithium secondary battery is provided, comprising: a porous polymer substrate; and a first adhesive layer formed on at least one surface of the porous polymer substrate and comprising a particulate polyvinylidene fluoride (PVDF) adhesive polymer, wherein the first adhesive layer: i) comprises a caprolactone dispersant, or ii) has a surface roughness (Sa) of 0.12 μm to 0.22 μm.

[0018] According to the second embodiment, in the first embodiment, based on 100% by weight of total repeating units, the caprolactone dispersant may include 20% by weight to 40% by weight of caprolactone-derived repeating units.

[0019] According to the third embodiment, in the first or second embodiment, based on 100% by weight of total repeating units, the caprolactone dispersant may include 40% to 60% by weight of ethylene glycol-derived repeating units or 10% to 30% by weight of propylene glycol-derived repeating units.

[0020] According to the fourth embodiment, in any of the first to third embodiments, the surface roughness (Sa) can be determined by using a confocal laser scanning microscope (CLSM) at a magnification of 50X.

[0021] According to the fifth embodiment, in any one of the first to fourth embodiments, the separator for the lithium secondary battery may further include an inorganic heat-resistant layer, which is formed separately on at least one surface of the porous polymer substrate or between the porous polymer substrate and the first adhesive layer, and includes inorganic particles and the first adhesive polymer.

[0022] According to the sixth embodiment, in the fifth embodiment, the first adhesive polymer may include particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

[0023] According to the seventh embodiment, in the fifth or sixth embodiment, the inorganic heat-resistant layer, based on 100% by weight, may include the inorganic particles in an amount of 70% by weight or more and 99% by weight or less.

[0024] According to the eighth embodiment, in any one of the first to seventh embodiments, the particulate PVDF adhesive polymer may have an average particle size (D) of 0.5 μm to 2 μm. 50 ).

[0025] According to the ninth embodiment, in any one of the first to eighth embodiments, the first adhesive layer may further include a second adhesive polymer, and the second adhesive polymer may include a particulate adhesive polymer, a non-particulate adhesive polymer, or a combination thereof.

[0026] According to a tenth embodiment, in a ninth embodiment, the second adhesive polymer may comprise a particulate adhesive polymer, and the particulate adhesive polymer may have an average particle size (D) of 100 nm to 800 nm. 50 ).

[0027] According to the eleventh embodiment, in any one of the first to tenth embodiments, the separator for the lithium secondary battery may further include a second adhesive layer, wherein the first adhesive layer is formed on one surface of the porous polymer substrate, and the second adhesive layer is formed on another surface of the porous polymer substrate, and the second adhesive layer includes a particulate PVDF-type adhesive polymer.

[0028] According to the twelfth embodiment, in the eleventh embodiment, the inorganic heat-resistant layer comprising the inorganic particles and the first adhesive polymer can be formed on each of the first surface and the second surface of the porous polymer substrate, the first adhesive layer can be formed on top of the inorganic heat-resistant layer on the first surface, and the second adhesive layer can be formed on top of the inorganic heat-resistant layer on the second surface.

[0029] According to the thirteenth embodiment, in the twelfth embodiment, the surface roughness (Sa1) of the first adhesive layer may be less than the surface roughness (Sa2) of the second adhesive layer.

[0030] According to the fourteenth embodiment, in the twelfth or thirteenth embodiment, the surface roughness (Sa2) of the second adhesive layer may be 1.1 times or greater than the surface roughness (Sa1) of the first adhesive layer.

[0031] According to the fifteenth embodiment, in any of the twelfth to fourteenth embodiments, the surface roughness (Sa2) of the second adhesive layer may be 1.1 times or greater and 1.4 times or less than the surface roughness (Sa1) of the first adhesive layer.

[0032] According to a sixteenth embodiment, a lithium secondary battery is provided, the lithium secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode and a separator inserted between the positive electrode and the negative electrode; and a battery housing in which the electrode assembly and an electrolyte are received, wherein the separator is the separator according to any one of the first to fifteenth embodiments.

[0033] Beneficial effects

[0034] According to embodiments of this disclosure, the transfer / desorption of particulate PVDF adhesive polymers onto the surface of the pressed component during the rotary pressing step of the electrode assembly can be suppressed by incorporating caprolactone dispersants into the adhesive layer or by controlling the surface roughness (Sa) of the adhesive layer.

[0035] According to embodiments of this disclosure, peeling and wrinkling during lamination, winding, and pressing processes can be reduced by improving electrode-septum adhesion in a dry state (dry adhesion).

[0036] According to embodiments of this disclosure, electrode-separator adhesion (wet adhesion) in the state of being wetted by electrolyte can be controlled by designing different surface roughnesses (controlling the Sa2 / Sa1 ratio) of the adhesive layer on the two surfaces of the separator according to the intended use, thereby suppressing battery bending and shape deformation.

[0037] According to embodiments of the present disclosure, the separator for lithium secondary batteries can separate the inorganic heat-resistant layer and the adhesive layer from each other, so that the adhesive layer can be uniformly distributed on the inorganic heat-resistant layer, thereby achieving excellent electrode-separator dry adhesion.

[0038] The separator for lithium secondary batteries according to embodiments of this disclosure uses a multi-layer coating process and is cost-effective.

[0039] However, the effects obtained through this disclosure are not limited to those described above, and other technical effects not mentioned can be clearly understood by those skilled in the art based on the following description of this disclosure. Attached Figure Description

[0040] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the foregoing disclosure, serve to provide a further understanding of the technical features of the present disclosure; therefore, the present disclosure is not to be construed as limited to the drawings.

[0041] Figure 1 This is a schematic cross-sectional view showing a lithium secondary battery with a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0042] Figure 2 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0043] Figure 3 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0044] Figure 4This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0045] Figure 5 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0046] Figure 6 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0047] Figure 7 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0048] Figure 8 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0049] Figure 9 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0050] Figure 10 This is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure. Detailed Implementation

[0051] It should be understood that the terminology used in the specification and appended claims should not be construed as limited to its general or dictionary meaning, but rather as interpreted based on the meanings and concepts corresponding to the technical aspects of this disclosure, on the basis of the principle that the inventors are permitted to properly define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes only and is not intended to limit the scope of this disclosure; thus, it should be understood that other equivalents and modifications may be made therein without departing from the scope of this disclosure.

[0052] <Definition>

[0053] Throughout the specification, the statement "a component includes elements" does not exclude the presence of any additional elements, but rather means that the component may include other elements.

[0054] Throughout this specification, "glass transition temperature (Tg)" may be expressed as a value determined, for example, by a dynamic mechanical analysis (DMA) or differential scanning calorimetry (DSC, TA Instrument) apparatus. For instance, the glass transition temperature may be expressed as a value determined by the DMA method as defined in ASTM D4065.

[0055] Throughout the instruction manual, D nThis refers to the particle diameter at the n% point of the cumulative distribution of the number of particles based on particle size. In other words, D 50 This refers to the particle diameter at the 50% point of the cumulative distribution of the number of particles based on particle size. Furthermore, D... 10 It refers to the particle diameter at the 10% point of the cumulative distribution of particle number based on particle size, and D 90 It refers to the particle diameter at the 90% point of the cumulative distribution of the number of particles based on particle size.

[0056] Particle size can be determined using the laser diffraction method. Specifically, the powder to be analyzed is dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) to measure the differences in the diffraction pattern depending on the particle size as the particles pass through the laser beam, and then the particle size distribution is calculated. D can then be determined by calculating the particle size at the 10%, 50%, and 90% points of the cumulative distribution of particle size according to particle number in the analyzer system. 10 D 50 and D 90 .

[0057] Throughout the instruction manual, "primary grains" refers to grains that do not have grain boundaries when observed using a scanning electron microscope at a field of view of 5,000 to 20,000x.

[0058] Throughout this specification, "secondary particles" are particles formed by the aggregation of primary particles.

[0059] Figure 1 This is a schematic cross-sectional view showing a lithium secondary battery with a separator for a lithium secondary battery according to an embodiment of the present disclosure, and Figures 2 to 10 Each of these is a schematic cross-sectional view showing a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0060] In one aspect of this disclosure, a separator 10 for a lithium secondary battery is provided.

[0061] According to embodiments of the present disclosure, a separator 10 for a lithium secondary battery includes: a porous polymer substrate 1; and a first adhesive layer 5a formed on at least one surface of the porous polymer substrate 1 and comprising a particulate polyvinylidene fluoride (PVDF) adhesive polymer, wherein the first adhesive layer 5a: i) comprises a caprolactone dispersant, or ii) has a surface roughness (Sa) of 0.12 μm to 0.22 μm.

[0062] <Porous polymer substrate>

[0063] According to this disclosure, the separator 10 for a lithium secondary battery includes a porous polymer substrate 1.

[0064] According to embodiments of this disclosure, a porous polymer substrate refers to a porous ion-conducting barrier that allows ions to pass through while interrupting the electrical contact between the negative and positive electrodes, and has multiple pores formed therein. The pores are interconnected, allowing gas or liquid to pass from one surface of the substrate to the other.

[0065] The material forming the porous polymer substrate can be any organic or inorganic material with electrical insulating properties. In particular, from the perspective of imparting a shut-off function to the substrate, thermoplastic resins are preferred as the material forming the porous polymer substrate. Herein, the term "shut-off function" refers to the function of preventing battery thermal runaway by allowing the thermoplastic resin to melt, such that when the battery temperature rises, the pores of the porous substrate can close and ion conduction can be interrupted. Thermoplastic resins with a melting point less than 200°C are suitable, and polyolefins are particularly preferred.

[0066] In addition to polyolefins, thermoplastic resins may include at least one polymer resin selected from the following: polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyvinyl naphthalene. The porous polymer substrate may include, but is not limited to, a nonwoven mesh, a porous polymer membrane, or a laminate of two or more layers thereof.

[0067] According to this disclosure, the porous polymer substrate preferably has a thickness of 3 μm to 50 μm, or 5 μm to 12 μm. When the thickness is less than the above-defined range, the porous polymer substrate exhibits insufficient function as a conductive barrier and has deteriorated physical properties, and therefore may be easily damaged during battery use. On the other hand, when the thickness is excessively greater than the above-defined range (i.e., the porous substrate is too thick), the separator may exhibit excessively increased resistance.

[0068] According to embodiments of this disclosure, the polyolefin preferably has a weight-average molecular weight of 100,000 to 5,000,000. When the weight-average molecular weight is less than 100,000, it is difficult to ensure sufficient dynamic physical properties. Furthermore, when the weight-average molecular weight is greater than 5,000,000, the shut-off properties may deteriorate, or molding may become difficult. In addition, for improving yield, the porous polymer substrate can have a puncture strength of 300 gf or higher. The puncture strength of the porous substrate refers to the highest puncture load (gf) measured by puncture testing with a Kato tech KES-G5 handheld compression tester under conditions of a needle tip radius of curvature of 0.5 mm and a puncture rate of 4 mm / s.

[0069] According to embodiments of this disclosure, the size and porosity of the pores present in the porous polymer substrate are not particularly limited, but can be from 0.01 μm to 50 μm and from 10 vol% to 95 vol%, respectively.

[0070] <Inorganic heat-resistant layer>

[0071] According to the present disclosure, the separator 10 for a lithium secondary battery may include an inorganic heat-resistant layer 3, which is formed separately on at least one surface of a porous polymer substrate 1, or formed between the porous polymer substrate 1 and the first adhesive layer 5a, and includes inorganic particles and the first adhesive polymer.

[0072] The inorganic heat-resistant layer 3 comprises a plurality of inorganic particles mixed with a first adhesive polymer. By coating the porous polymer substrate 1 with an inorganic heat-resistant layer comprising inorganic particles, the separator 10 can have improved heat resistance and mechanical properties.

[0073] According to embodiments of this disclosure, the inorganic heat-resistant layer 3 can be disposed on only one surface of the porous polymer substrate 1. When the inorganic heat-resistant layer 3 is formed on one surface of the porous polymer substrate 1 as described above, the thickness of the electrode assembly can be controlled and excellent energy density can be achieved.

[0074] According to embodiments of this disclosure, the inorganic heat-resistant layer 3 can be disposed on both surfaces of the porous polymer substrate 1. When the inorganic heat-resistant layer 3 is formed on both surfaces of the porous polymer substrate 1 as described above, the partition 10 can achieve better heat resistance and mechanical properties with improved symmetry, and provide excellent porosity.

[0075] According to embodiments of the present disclosure, a first adhesive polymer can be used to connect inorganic particles to each other and fix them in an inorganic heat-resistant layer.

[0076] According to embodiments of this disclosure, the first adhesive polymer may include particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

[0077] In this specification, the term "particulate" can refer to a particulate adhesive polymer added to a dispersion medium for forming an inorganic heat-resistant layer or adhesive layer, and retaining the added particulate shape in the resulting coating after coating and drying. "Non-particulate" adhesive polymers can refer to adhesive polymers that, when forming an inorganic heat-resistant layer, are applied and dried in particulate form dissolved in a solvent or added to a dispersion medium, but do not retain the particulate shape after coating and drying.

[0078] According to embodiments of this disclosure, the first adhesive polymer may be an acrylic adhesive polymer. The acrylic adhesive polymer may include an acrylic homopolymer prepared by polymerizing acrylic monomers individually, or a copolymer of an acrylic monomer with another monomer. For example, the acrylic adhesive polymer may include poly(methyl methacrylate), poly(ethyl hexyl acrylate), poly(butyl acrylate), poly(acrylonitrile), poly(ethyl hexyl acrylate-co-methyl methacrylate), poly(butyl acrylate-co-methyl methacrylate), ethyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylamide-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, ethyl acrylate-acrylamide-2-(diethylamino)ethyl acrylate copolymer, or a mixture of two or more thereof.

[0079] According to embodiments of this disclosure, the inorganic heat-resistant layer may have a microporous structure derived from the interstitial volume between inorganic particles. The inorganic particles can also serve as spacers capable of maintaining the physical shape of the inorganic heat-resistant layer. The interstitial volume refers to the limited space in which the inorganic particles are substantially in contact with each other. Furthermore, since inorganic particles are typically characterized by not undergoing changes in their physical properties even at temperatures of 200°C or higher, the partition exhibits excellent heat resistance due to the inorganic heat-resistant layer.

[0080] The inorganic particles are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles that can be used in the present disclosure are not particularly limited as long as they do not cause oxidation and / or reduction within the operating voltage range of the applicable electrochemical device (e.g., 0 V to 5 V based on Li / Li⁺). In particular, when inorganic particles with a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by increasing the dissociation degree of the electrolyte salt (e.g., lithium salt) in the liquid electrolyte.

[0081] For these reasons, the inorganic particles may preferably include high dielectric constant inorganic particles having a dielectric constant of 5 or greater, particularly 10 or greater. Non-limiting examples of inorganic particles having a dielectric constant of 5 or greater include BaTiO3, Pb(Zr,Ti)O3 (PZT), 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 )O3 - PbTiO3 (PMN - PT), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, or a mixture thereof, etc.

[0082] In addition, the inorganic particles may include inorganic particles having lithium ion transportability, that is, inorganic particles containing the element lithium and not storing lithium but used for transporting lithium ions. Non-limiting examples of inorganic particles having lithium ion transportability include: lithium phosphate (Li3PO^4), 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), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13) such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w, where 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as Li 3.25 Ge 0.25 P 0.75 S4, lithium nitride (Li x N y , where 0 < x < 4, 0 < y < 2), such as Li3N, SiS2-based glass (Li x Si y S z , where 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li3PO4-Li2S-SiS2, P2S5-based glass (Li x P y S z , where 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI-Li2S-P2S5, or a mixture thereof, and so on.

[0083] According to an embodiment of the present disclosure, the average particle size (D 50 ) of the inorganic particles is not particularly limited. However, for example, the inorganic particles may have an average particle size of 100 nm to 1000 nm, specifically 100 nm to 800 nm.

[0084] According to an embodiment of the present disclosure, based on 100% by weight of the inorganic heat-resistant layer, the content of the inorganic particles may be 70% by weight or more and 99% by weight or less, 80% by weight or more and 97% by weight or less, or 85% by weight or more and 96% by weight or less. When the content of the inorganic particles satisfies the above-defined range, the inorganic heat-resistant layer may have a high density, and the separator may achieve excellent porosity and resistance characteristics.

[0085] According to an embodiment of the present disclosure, based on 100% by weight of the inorganic heat-resistant layer, the content of the first binder polymer may be 1% by weight or more and 30% by weight or less, 3% by weight or more and 20% by weight or less, or 4% by weight or more and 10% by weight or less. When the content of the first binder polymer satisfies the above-defined range, the separator may maintain excellent heat resistance while not causing desorption of the inorganic particles in the inorganic heat-resistant layer.

[0086] According to an embodiment of the present disclosure, based on the inorganic heat-resistant layer formed on any one surface of the porous polymer substrate, the inorganic heat-resistant layer may have a thickness of 0.5 μm or more, 0.6 μm or more, 0.8 μm or more, or 1 μm or more, and 50 μm or less, 30 μm or less, 5 μm or less, 2 μm or less, or 1.8 μm or less.

[0087] Furthermore, according to embodiments of this disclosure, the inorganic heat-resistant layer may further comprise a first dispersant. As described below, the first dispersant allows the hydrophobic porous polymer substrate to be adequately wetted by the aqueous slurry used to form the inorganic heat-resistant layer, thereby improving coatability. Such a first dispersant can be any known wetting agent (surfactant), specific examples of which include fluoropolymer surfactants, siloxane surfactants, hydrocarbon surfactants, and ether surfactants, and ether surfactants may be preferred, but the scope of this disclosure is not limited thereto. For example, the first dispersant may be sodium carboxymethyl cellulose.

[0088] According to embodiments of this disclosure, the first dispersant may be included in an amount of 0.1% to 10% by weight based on 100% by weight of the inorganic heat-resistant layer.

[0089] <First adhesive layer>

[0090] According to embodiments of the present disclosure, a first adhesive layer 5a is formed on at least one surface of a porous polymer substrate 1 and comprises a particulate PVDF-type adhesive polymer, and the first adhesive layer: i) comprises a caprolactone dispersant, or ii) has a surface roughness (Sa) of 0.12 μm to 0.22 μm.

[0091] According to embodiments of this disclosure, the caprolactone-based dispersant may include caprolactone-derived repeating units, and in addition to caprolactone-derived repeating units, it may include ethylene glycol-derived repeating units, propylene glycol-derived repeating units, or two or more of these repeating units. By using the dispersant, particulate PVDF-based adhesive polymers, second adhesive polymers, etc., can be further dispersed in the dispersion medium, thereby controlling the surface roughness of the adhesive layer to prevent the formation of large powders of the PVDF-based adhesive polymer on the first adhesive layer and to prevent the desorption of the PVDF-based adhesive polymer.

[0092] According to embodiments of this disclosure, based on 100% by weight of total repeating units, a caprolactone dispersant may include 20% to 40% by weight, 25% to 35% by weight, or 27% to 33% by weight of caprolactone-derived repeating units. Furthermore, in this specification, "caprolactone dispersant" may refer to a dispersant containing caprolactone-derived repeating units, or a dispersant containing at least 5% by weight, at least 10% by weight, at least 15% by weight, or at least 20% by weight of caprolactone-derived repeating units.

[0093] According to embodiments of this disclosure, based on 100% by weight of total repeating units, a caprolactone dispersant may comprise 40% to 60% by weight, or 45% to 55% by weight, of ethylene glycol-derived repeating units, or may comprise 10% to 30% by weight, or 15% to 25% by weight, of propylene glycol-derived repeating units. In this document, based on 100% by weight of total repeating units, a caprolactone dispersant may comprise 40% to 60% by weight, or 45% to 55% by weight, of ethylene glycol-derived repeating units, and 10% to 30% by weight, or 15% to 25% by weight, of propylene glycol-derived repeating units.

[0094] According to embodiments of this disclosure, the adhesive layer may have a surface roughness (Sa) of 0.12 μm to 0.22 μm, or 0.15 μm to 0.205 μm. When the surface roughness (Sa) of the adhesive layer meets the above-defined range, the adhesive polymer is not transferred to the pressing member during the pressing step performed when manufacturing the electrode assembly by stacking separators. Therefore, excellent electrode-separator adhesion in a dry state (dry adhesion) can be achieved, and the time required to manufacture lithium secondary batteries can be reduced.

[0095] Furthermore, according to embodiments of this disclosure, there are no specific limitations on the methods used to determine surface roughness (Sa). For example, surface roughness can be determined using a roughness measuring instrument (e.g., a surface profiler) or a confocal laser scanning microscope (CLSM). For instance, surface roughness can be determined by magnifying a predetermined scanning area at a magnification of 50X using a confocal laser scanning microscope, measuring each sample 10 times, and using the average value. Specific examples of confocal laser scanning microscopes include, but are not limited to, the OLS 5100, OLS 4100, etc., available from Olympus Corporation. The confocal laser scanning microscope can be controlled at magnifications of 10X, 50X, 100X, 1000X, 2000X, etc.

[0096] According to embodiments of this disclosure, based on an adhesive layer formed on any surface of a porous polymer substrate, the first adhesive layer may have a thickness of 0.3 μm or greater, 0.4 μm or greater, 0.5 μm or greater, or 0.6 μm or greater, and 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. When the thickness of the first adhesive layer meets the above-defined ranges, the separator can exhibit excellent negative electrode-separator adhesion and excellent resistive characteristics.

[0097] According to embodiments of the present disclosure, the particulate PVDF adhesive polymer is an adhesive polymer that is added in particulate form to a dispersion medium for coating and drying and retains the shape of the added particulates.

[0098] According to embodiments of this disclosure, for example, particulate PVDF-based adhesive polymers may include polyvinylidene fluoride (PVDF) homopolymers, or copolymers of PVDF-derived repeating units and repeating units copolymerizable therewith. For example, particulate PVDF-based adhesive polymers may be copolymers of PVDF-derived repeating units and at least one repeating unit selected from: trifluoroethylene (TrFE)-derived repeating units, tetrafluoroethylene (TFE)-derived repeating units, hexafluoropropylene (HFP)-derived repeating units, trichloroethylene (TrCE)-derived repeating units, trichlorofluoroethylene (TCFE)-derived repeating units, chlorotrifluoroethylene (CTFE)-derived repeating units, polymethyl methacrylate (PMMA), and poly(ethylene fluoride)-derived repeating units. Repeating units derived from PMMA, repeating units derived from 1,2-difluoroethylene, repeating units derived from perfluoro(methyl vinyl) ether, repeating units derived from perfluoro(ethyl vinyl) ether, repeating units derived from perfluoro(propyl vinyl) ether, repeating units derived from difluoro(1,3-dioxolane), repeating units derived from perfluoro(2,2-dimethyl-1,3-dioxolane), and repeating units derived from polyvinyl acetate (PVAc).

[0099] According to embodiments of the present disclosure, preferably, the particulate PVDF adhesive polymer can be a copolymer containing repeating units derived from vinylidene fluoride and repeating units derived from hexafluoropropylene (PVDF-HFP).

[0100] According to embodiments of this disclosure, based on 100% by weight of the total copolymer weight, the content of hexafluoropropylene-derived repeating units can be from 1% to 20% by weight, 5% to 15% by weight, or 10% to 13% by weight. When the content of hexafluoropropylene-derived repeating units meets the above-defined ranges, the PVDF-based adhesive polymer exhibits increased polarity and excellent dry adhesion, and shows non-excessive solubility in the electrolyte, allowing the separator to exhibit excellent wet adhesion, and the particulate PVDF-based adhesive polymer can be uniformly distributed in the adhesive layer.

[0101] According to embodiments of this disclosure, the content of comonomers in PVDF polymers, i.e., the content of repeating units derived from hexafluoropropylene, can be determined by using a Varian 500 MHz... 1 The method involves H-NMR determination. For details on this method, refer to the Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. NMR spectroscopy can be performed using suitable equipment, such as a Bruker Avance III HD 700 MHz NMR or a Varian 500 MHz NMR.

[0102] According to embodiments of this disclosure, the particulate PVDF adhesive polymer may be an adhesive polymer having a glass transition temperature (Tg) of -30°C to 40°C or -20°C to 20°C. Furthermore, the particulate PVDF adhesive polymer may have a melting point (Tm) of 100°C to 180°C or 130°C to 150°C.

[0103] According to embodiments of this disclosure, the PVDF-based adhesive polymer may have an average particle size (D) of 0.5 μm to 5 μm or 0.8 μm to 3.5 μm upon introduction. 50 Furthermore, according to embodiments of this disclosure, the PVDF-based adhesive polymer can have an average particle size (D) of 0.5 μm to 1.5 μm or 0.8 μm to 1.2 μm in the adhesive layer. 50 When the particle size of the PVDF-based adhesive polymer meets the above-defined range, the separator exhibits excellent adhesion and porosity. Simultaneously, the average particle size (D) of the PVDF-based adhesive polymer... 50 ")" refers to the average particle size (D) of the primary particles of PVDF adhesive polymers. 50 ).

[0104] According to embodiments of this disclosure, the first adhesive layer 5a may further comprise a second adhesive polymer. The first adhesive layer 5a can be formed by mixing multiple particulate PVDF-type adhesive polymers and a second adhesive polymer.

[0105] According to embodiments of this disclosure, the second adhesive polymer may include particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

[0106] According to embodiments of this disclosure, when the second adhesive polymer is a particulate adhesive polymer, it may include an average particle size (D) having a particle size of 100 nm to 800 nm or 200 nm to 700 nm. 50 ) granular acrylic adhesive polymer.

[0107] According to one embodiment of this disclosure, when the second adhesive polymer is a particulate adhesive polymer, it may mean that the adhesive polymer material has a glass transition temperature (Tg) of -40°C or higher and 40°C or lower, or -30°C or higher and 30°C or lower.

[0108] According to embodiments of this disclosure, the second adhesive polymer may include an acrylic adhesive polymer. The acrylic adhesive polymer may include an acrylic homopolymer prepared by polymerizing an acrylic monomer alone, or a copolymer of an acrylic monomer with another monomer. For example, the acrylic adhesive polymer may include poly(methyl methacrylate), poly(ethylhexyl acrylate), poly(butyl acrylate), poly(acrylonitrile), poly(ethylhexyl acrylate-co-methyl methacrylate), poly(butyl acrylate-co-methyl methacrylate), ethyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, or a mixture of two or more thereof.

[0109] According to embodiments of this disclosure, based on 100% by weight of the adhesive layer, PVDF-based adhesive polymers may be included in an amount of 80% to 90% by weight, or 83% to 87% by weight.

[0110] According to embodiments of this disclosure, based on 100% by weight of the adhesive layer, the second adhesive polymer may be included in an amount of 8% to 15% by weight, or 10% to 12% by weight. When the content of the second adhesive polymer meets the above-defined range, the second adhesive polymer can be uniformly distributed, thereby achieving excellent resistivity and adhesion.

[0111] According to embodiments of this disclosure, a caprolactone dispersant may be included in an amount of 1% to 3% by weight based on 100% by weight of the adhesive layer. When the content of the caprolactone dispersant meets the above-defined range, excellent electrical resistance characteristics can be achieved without electrochemical side reactions.

[0112] According to embodiments of this disclosure, the adhesive layer may further include a wetting agent, which allows the particulate PVDF adhesive polymer to be well dispersed in the dispersion medium.

[0113] Such a wetting agent can be any known wetting agent (surfactant), with specific examples including fluorinated surfactants, siloxane surfactants, hydrocarbon surfactants and ether surfactants, and ether surfactants may be preferred, but the scope of this disclosure is not limited thereto.

[0114] According to embodiments of this disclosure, based on 100% by weight of the adhesive layer, a wetting agent may be included in an amount of 0.1% to 10% by weight, or 0.5% to 2% by weight.

[0115] <Second adhesive layer>

[0116] According to embodiments of this disclosure, the separator for a lithium secondary battery may further include a second adhesive layer 5b. The porous polymer substrate 1 has a first adhesive layer 5a formed on one surface thereon, and the second adhesive layer 5b is formed on the other surface of the porous polymer substrate 1. The second adhesive layer comprises a particulate PVDF-based adhesive polymer. Here, the particulate PVDF-based adhesive polymer may be the same as or different from the PVDF-based adhesive polymer included in the first adhesive layer, and its description is replaced as described above.

[0117] According to embodiments of the present disclosure, a separator 10 for a lithium secondary battery includes a porous polymer substrate 1 and a first adhesive layer 5a formed on at least one surface thereon. Additionally, as described above, an inorganic heat-resistant layer 3 may be formed separately 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. Therefore, the separator for a lithium secondary battery according to embodiments of the present disclosure can have the following characteristics: Figures 2 to 10 Any of the structures shown.

[0118] like Figure 2 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, a first adhesive layer 5a may be formed on one surface of a porous polymer substrate 1.

[0119] like Figure 3 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, a first adhesive layer 5a may be formed on both surfaces of the porous polymer substrate 1.

[0120] like Figure 4 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, a first adhesive layer 5a and a second adhesive layer 5b may be formed on a first surface and a second surface of a porous polymer substrate 1, respectively.

[0121] like Figure 5 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer 3 may be formed on one surface of a porous polymer substrate 1, and a first adhesive layer 5a may be formed on top of it.

[0122] like Figure 6 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer 3 may be formed on one surface of a porous polymer substrate 1, a first adhesive layer 5a may be formed on top of it, and the first adhesive layer 5a may also be formed on another surface (second surface) of the porous polymer substrate.

[0123] like Figure 7 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer 3 may be formed on one surface of a porous polymer substrate 1, a first adhesive layer 5a may be formed thereon, and a second adhesive layer 5b may be formed on another surface (the second surface).

[0124] like Figure 8 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer 3 may be formed on both surfaces of a porous polymer substrate 1, and a first adhesive layer 5a may be formed on top of the inorganic heat-resistant layer on the first surface.

[0125] like Figure 9 As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer 3 may be formed on both surfaces of a porous polymer substrate 1, and a first adhesive layer 5a may be formed on top of the inorganic heat-resistant layer on each of the first and second surfaces.

[0126] like Figure 10As shown, in the separator 10 for a lithium secondary battery according to an embodiment of the present disclosure, an inorganic heat-resistant layer comprising inorganic particles and a first adhesive polymer can be formed on each of the first and second surfaces of a porous polymer substrate, and the first adhesive layer and the second adhesive layer can be formed on top of the inorganic heat-resistant layer on the first and second surfaces, respectively.

[0127] According to embodiments of this disclosure, the second adhesive layer 5b differs from the first adhesive layer 5a in that it does not use caprolactone dispersants.

[0128] According to embodiments of the present disclosure, the second adhesive layer 5b contains a second dispersant, or may have a higher surface roughness compared to the first adhesive layer 5a.

[0129] According to embodiments of this disclosure, each of the first adhesive layer 5a and the second adhesive layer 5b can be formed by mixing multiple particulate PVDF-based adhesive polymers. Here, the first adhesive layer 5a exhibits high dispersibility due to the caprolactone-based dispersant, and the second adhesive layer 5b includes a second dispersant, thus exhibiting slightly lower dispersibility compared to the first adhesive layer 5a. Therefore, the first adhesive layer 5a can have a lower surface roughness after drying compared to the second adhesive layer 5b. Furthermore, since the first adhesive layer 5a includes a caprolactone-based dispersant, it can have the effect of reducing transfer phenomena caused by pressure rollers during separator manufacturing due to the properties of the dispersant.

[0130] According to embodiments of this disclosure, the second dispersant is not limited to any particular type. For example, the second dispersant may be a polyvinylpyrrolidone compound, a cellulose compound, or an organic acid compound.

[0131] According to embodiments of this disclosure, specific examples of cellulose compounds include ethyl hydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose sodium salt (CMC-Na), hydroxyalkyl methyl cellulose, or two or more thereof.

[0132] According to embodiments of this disclosure, specific examples of organic acid compounds include citric acid, stearic acid, oxalic acid, acetic acid, formic acid, or two or more of the above.

[0133] According to embodiments of this disclosure, based on 100% by weight of the second adhesive layer, the second dispersant may be included in an amount of 1% to 5% by weight, or 2% to 4% by weight.

[0134] According to embodiments of this disclosure, the second adhesive layer 5b may further include a third adhesive polymer.

[0135] According to embodiments of this disclosure, the third adhesive polymer may include particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

[0136] According to embodiments of this disclosure, the third adhesive polymer may be an acrylic adhesive polymer.

[0137] According to embodiments of this disclosure, acrylic adhesive polymers may include acrylic homopolymers prepared by polymerizing acrylic monomers alone, or copolymers of acrylic monomers with another monomer. For example, acrylic adhesive polymers may include poly(methyl methacrylate), poly(ethyl hexyl acrylate), poly(butyl acrylate), poly(acrylonitrile), poly(ethyl hexyl acrylate-co-methyl methacrylate), poly(butyl acrylate-co-methyl methacrylate), ethyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, or mixtures of two or more thereof.

[0138] According to embodiments of this disclosure, when the third adhesive polymer is a particulate adhesive polymer, it may mean that the adhesive polymer material has a glass transition temperature (Tg) of -40°C or higher and 40°C or lower, or -35°C or higher and 35°C or lower.

[0139] According to embodiments of this disclosure, when the third adhesive polymer is a particulate adhesive polymer, it may have an average particle size (D) of 100 nm to 800 nm or 200 nm to 700 nm. 50 ).

[0140] According to embodiments of this disclosure, based on 100% by weight of the second adhesive layer, a third adhesive polymer may be included in an amount of 8% to 15% by weight, or 10% to 12% by weight. When the content of the third adhesive polymer meets the above-defined range, the third adhesive polymer can be uniformly distributed, thus achieving excellent resistivity and adhesion.

[0141] According to embodiments of this disclosure, the adhesive layer may further include a wetting agent, which allows the particulate PVDF adhesive polymer to be well dispersed in the dispersion medium.

[0142] Such a wetting agent can be any known wetting agent (surfactant), with specific examples including fluorinated surfactants, siloxane surfactants, hydrocarbon surfactants, and ether surfactants, and ether surfactants may be preferred, but the scope of this disclosure is not limited thereto.

[0143] According to embodiments of this disclosure, based on 100% by weight of the adhesive layer, a wetting agent may be included in an amount of 0.1% to 10% by weight, or 0.5% to 2% by weight.

[0144] Lithium-ion secondary batteries are manufactured through the following assembly steps: introducing electrode components into the battery casing, injecting electrolyte into it, and performing a sealing process; a pre-aging step that allows the electrodes, separators, etc., to be fully wetted with the electrolyte; and an activation step that stabilizes the battery structure and transforms it into a usable state. In this activation step, during the first charge / discharge cycle, the positive electrode active material is activated and a stable solid electrolyte interphase (SEI) is formed on the surface of the negative electrode. However, the positive and negative electrodes undergo volume expansion during such activation steps, and particularly in the case of batteries with laminated and stacked structures in which multiple electrode components are stacked, a bending phenomenon occurs, causing the battery to bend or curl in the longitudinal direction of the battery.

[0145] To address the aforementioned issues, the inventors of this disclosure have conducted intensive research and discovered that this bending phenomenon becomes severe when there is an excessively large difference between the negative electrode-separator adhesion force and the positive electrode-separator adhesion force in an electrolyte-wetted state. This stems from the difference between the positive electrode containing a PVDF-based adhesive polymer and the negative electrode containing a styrene-butadiene rubber (SBR) adhesive. In other words, when a PVDF-based adhesive polymer is used in the adhesive layer of the separator, it has a high affinity for the positive electrode adhesive, and the positive electrode-separator adhesion force becomes relatively large, thus potentially exacerbating the bending phenomenon.

[0146] In this regard, according to embodiments of the present disclosure, the balance between the positive electrode-separator adhesion force and the negative electrode-separator adhesion force 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 1.1 times or more, preferably 1.1 times or more and 1.4 times or less, the surface roughness of the adhesive layer. By controlling the surface roughness of the adhesive layer in the manner described above, the adhesion force between the first adhesive layer and the electrode and the adhesion force between the second adhesive layer and the electrode can be maintained differently in the electrolyte-wetted state, and thus the adhesion force can be uniformly distributed during the lamination of the electrode assembly, thereby effectively suppressing or reducing battery bending that may occur during the activation step.

[0147] <Lithium secondary batteries>

[0148] In another aspect of this disclosure, a lithium secondary battery is provided.

[0149] Figure 1 This is a schematic cross-sectional view showing a lithium secondary battery with a separator for a lithium secondary battery according to an embodiment of the present disclosure.

[0150] According to an embodiment of the present disclosure, a lithium secondary battery includes: an electrode assembly including a positive electrode 30, a negative electrode 20, and a separator 10 inserted between the positive and negative electrodes; and a battery casing receiving the electrode assembly and an electrolyte, wherein the separator 10 is a separator according to an embodiment of the present disclosure.

[0151] According to embodiments of this disclosure, when the separator 10 includes a first adhesive layer 5a and a second adhesive layer 5b, the first adhesive layer 5a can be disposed in a manner that allows it to face the negative electrode 20, such as... Figure 1 As shown. Here, the first adhesive layer 5a can have a smaller surface roughness compared to the second adhesive layer 5b.

[0152] Furthermore, the positive electrode may include a PVDF-based adhesive polymer, and the negative electrode may include a styrene-butadiene rubber (SBR) adhesive. When a PVDF-based adhesive polymer is used in the adhesive layer of the separator, it exhibits a high affinity for the positive electrode adhesive, and therefore the positive electrode-separator adhesion becomes relatively large, and the bending resistance of the battery can be enhanced.

[0153] Therefore, according to embodiments of this disclosure, the balance between the negative electrode-separator adhesion force and the positive electrode-separator adhesion force can be controlled by setting the surface roughness Sa1 of the first adhesive layer to be lower than the surface roughness Sa2 of the second adhesive layer, and by setting the first adhesive layer 5a with the lower surface roughness to face the negative electrode. In this way, the bending phenomenon can be effectively improved.

[0154] According to embodiments of this disclosure, the electrodes are not particularly limited and can be obtained by allowing electrode active materials to adhere to the electrode current collector using methods generally known in the art. Non-limiting examples of positive electrode active materials include conventional positive electrode active materials that can be used as the positive electrode in conventional electrochemical devices. In particular, lithium intercalation materials, such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides formed by combinations thereof, are preferred. Non-limiting examples of negative electrode active materials include conventional negative electrode active materials that can be used as the negative electrode in conventional electrochemical devices. In particular, lithium intercalation materials, such as lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials, are preferred. Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, nickel alloys, or combinations thereof.

[0155] According to embodiments of this disclosure, the binder polymer used for the positive electrode is a component that facilitates the bonding of the positive electrode active material with conductive materials and the like, and with the current collector, and is typically added in an amount from 1% to 30% by weight, based on the total solids content of the composition used to form the positive electrode. Specific examples of binder polymers include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or combinations thereof, with polyvinylidene fluoride being preferred.

[0156] According to embodiments of this disclosure, the adhesive polymer used for the negative electrode may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or combinations thereof, with styrene-butadiene rubber (SBR) being preferred.

[0157] The electrolyte that can be used according to this disclosure is one having A + B - Salts with a structure in which A + Including alkali metal cations such as Li + Na + K + Or a combination of them, and B -Including anions such as PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Or combinations thereof, wherein the salt is dissolved or dissociated in an organic solvent including propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone, or combinations thereof. However, this disclosure is not limited thereto.

[0158] According to embodiments of this disclosure, the battery casing can be a pouch-shaped casing, a cylindrical can, a prismatic can, or a combination thereof. According to embodiments of this disclosure, the pouch-shaped casing can be made of a multilayer laminated film using aluminum foil film or the like.

[0159] <Manufacturing Method of Separator for Lithium-ion Secondary Batteries>

[0160] In another aspect of this disclosure, a method for manufacturing a separator for a lithium secondary battery is provided.

[0161] (First Implementation)

[0162] According to embodiments of the present disclosure, a method for manufacturing a separator for a lithium secondary battery may include the following steps: (S1) preparing an aqueous slurry comprising inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer, and an aqueous slurry comprising a particulate PVDF-type binder polymer and a caprolactone-type dispersant for forming a first binder layer; (S2) applying the aqueous slurry for forming the inorganic heat-resistant layer to at least one surface of a porous polymer substrate, and then drying it to form an inorganic heat-resistant layer; and (S3) applying the slurry for forming the first binder layer to at least one surface of the inorganic heat-resistant layer, and then drying it to form the first binder layer.

[0163] The following sections will explain each step of the method for manufacturing a separator for lithium-ion secondary batteries. Meanwhile, the descriptions of 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 replaced as described above.

[0164] First, in step (S1), an aqueous slurry containing inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer is prepared, as well as an aqueous slurry containing particulate PVDF-type binder polymer and caprolactone-type dispersant for forming a first binder layer.

[0165] According to embodiments of this disclosure, the dispersion medium is an aqueous dispersion medium. The aqueous dispersion medium can be water or an aqueous dispersion medium containing water. Furthermore, when there are limitations on drying rate and temperature, C1 to C5 compounds with lower boiling points than water, such as methanol, ethanol, isopropanol, etc., can be used in combination. In this method, by using an aqueous dispersion medium, the particulate binder polymer does not dissolve in the dispersion medium, but rather maintains its particulate shape while being dispersed.

[0166] Furthermore, according to embodiments of this disclosure, in addition to the dispersion medium being in the range of 20% to 50% by weight, the aqueous slurry used to form the inorganic heat-resistant layer and the aqueous slurry used to form the adhesive layer are preferably controlled in terms of solid concentration (also referred to as solid content).

[0167] According to embodiments of this disclosure, the aqueous slurry used to form the inorganic heat-resistant layer may further include a first dispersant. The first dispersant allows the hydrophobic porous polymer substrate to be well wetted by the slurry used to form the inorganic heat-resistant layer, thereby improving coatability. Meanwhile, any known dispersant can be used as the first dispersant, and its description is replaced as described above.

[0168] According to embodiments of the present disclosure, specifically, the step of preparing an aqueous slurry for forming an inorganic heat-resistant layer may include the following steps: (S1-1) introducing inorganic particles into an aqueous dispersion medium to prepare a first dispersion; and (S1-2) subjecting the first dispersion to bead milling.

[0169] According to embodiments of this disclosure, the first binder polymer can be introduced before or after the bead milling step, but preferably, it can be introduced after the bead milling step. In this case, no bubbles or the like are generated in the first dispersion during the bead milling step, thereby achieving excellent processability.

[0170] According to embodiments of this disclosure, a first dispersant may be introduced before or after the bead milling step.

[0171] Meanwhile, during the bead milling step, depending on the strength, inorganic particles in the state of secondary particles formed by the aggregation of inorganic particles can deagglomerate to transform into primary particles, or inorganic particles in the state of primary particles can become particles with a smaller average particle size (D). 50 Those.

[0172] According to embodiments of this disclosure, the aqueous slurry used to form the first adhesive layer may include a caprolactone dispersant.

[0173] According to embodiments of the present disclosure, the aqueous slurry used to form the first adhesive layer may further include a second adhesive polymer, wherein the second adhesive polymer may be a particulate adhesive polymer, a non-particulate adhesive polymer, or a combination thereof.

[0174] According to embodiments of the present disclosure, specifically, the step of preparing an aqueous slurry for forming a first adhesive layer may include the following steps: (S1a) introducing a particulate PVDF-type adhesive polymer and a caprolactone-type dispersant into an aqueous dispersion medium to prepare a second dispersion; and (S1b) subjecting the second dispersion to bead milling.

[0175] According to embodiments of this disclosure, the second adhesive polymer may be introduced before or after the bead milling step, but preferably, the second adhesive polymer may be introduced after the bead milling step.

[0176] Meanwhile, granular PVDF adhesive polymers can be synthesized in granular form and then introduced into an aqueous dispersion medium as powder after drying. 50 ), and after bead milling, they can have an average particle size (D) of 0.5 μm to 1.5 μm or 0.8 μm to 1.2 μm. 50 Meanwhile, when the average particle size (D) of the granular PVDF adhesive polymer... 50 When the average particle size (D) of the PVDF-type adhesive polymer exceeds the upper limit, the adhesive layer has excessively high surface roughness. Therefore, when manufacturing electrode assemblies, the adhesive polymer can be transferred to a rotary pressing member, such as a pressure roller, during the pressing step. 50 When the value is below the lower limit, the electrode-septum adhesion in the dry state may be low.

[0177] Then, in step (S2), an aqueous slurry for forming an inorganic heat-resistant layer can be applied to at least one surface of a porous polymer substrate and then dried to form an inorganic heat-resistant layer.

[0178] According to embodiments of this disclosure, there are no particular limitations on the method of applying an aqueous slurry for forming an inorganic heat-resistant layer to at least one surface of a porous polymer substrate. For example, the aqueous slurry for forming the inorganic heat-resistant layer can be applied using various methods, such as dip coating, die coating, roll coating, comma coating, microgravure coating, blade coating, reverse roll coating, Mayer bar coating, direct metering coating, or combinations thereof.

[0179] According to embodiments of this disclosure, the method for drying the aqueous slurry used to form the inorganic heat-resistant layer is not limited to any particular method. For example, suitable methods can be used, such as those selected from convection drying, hot air drying, blowing drying, and natural drying, or combinations of two or more of these. Preferably, the drying method can be hot air drying.

[0180] Specifically, according to embodiments of this disclosure, the step of drying the aqueous slurry used to form the inorganic heat-resistant layer can be performed at a temperature of 50°C to 70°C for 10 to 120 seconds.

[0181] Subsequently, in step (S3), a slurry for forming the first adhesive layer may be applied to at least one surface of the inorganic heat-resistant layer and then dried to form the adhesive layer.

[0182] According to embodiments of this disclosure, there are no particular limitations on the method of applying the aqueous slurry for forming the first adhesive layer, and the method of applying the aqueous slurry for forming the inorganic heat-resistant layer described above can be used as is.

[0183] According to embodiments of this disclosure, the method for drying the aqueous slurry used to form the first adhesive layer is not limited to any particular method. For example, suitable methods can be used, such as those selected from convection drying, hot air drying, blowing drying, and natural drying, or combinations of two or more of these. Preferably, the drying method can be hot air drying.

[0184] According to embodiments of this disclosure, the step of drying the aqueous slurry used to form the first adhesive layer can be performed at a temperature of 50°C to 70°C for 10 to 120 seconds.

[0185] (Second Implementation)

[0186] According to another embodiment of this disclosure, a method for manufacturing a separator for a lithium secondary battery may include the following steps: (S1) preparing an aqueous slurry comprising inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer, and an aqueous slurry comprising a particulate PVDF-type binder polymer for forming a first binder layer; (S2) applying the aqueous slurry for forming the inorganic heat-resistant layer to at least one surface of a porous polymer substrate, and then drying to form the inorganic heat-resistant layer; and (S3) applying the aqueous slurry for forming the first binder layer to at least one surface of the inorganic heat-resistant layer, and then drying to form the first binder layer, wherein step (S1) may include bead milling the aqueous slurry for forming the first binder layer at a linear velocity of 10 m / s to 15 m / s. Each step of the method for manufacturing a separator for a lithium secondary battery will be explained below.

[0187] First, in step (S1), an aqueous slurry containing inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer is prepared, as well as an aqueous slurry containing a particulate PVDF-type binder polymer for forming a first binder layer.

[0188] According to an embodiment of the present disclosure, step (S1) may include bead milling the aqueous slurry used to form the first adhesive layer at a linear velocity of 10 m / s to 15 m / s. According to an embodiment of the present disclosure, step (S1) may include bead milling the aqueous slurry used to form the first adhesive layer at a linear velocity of 11 m / s to 14 m / s.

[0189] According to embodiments of this disclosure, bead milling can be performed using a bead milling apparatus comprising a grinding chamber configured to receive slurry and a plurality of beads and stirring blades disposed within the grinding chamber. The stirring blades can be rotated via a rotating shaft within the grinding chamber and a motor configured to operate thereon. Furthermore, the stirring blades extend a predetermined distance from the circumference of the rotating shaft toward the inner wall of the grinding chamber and can be arranged in a manner spaced apart from the inner wall of the grinding chamber. One or more stirring blades can be provided at the same location on the rotating shaft.

[0190] According to embodiments of this disclosure, the rotating device may be a paddle type, a propeller type, a spiral type, a turbine type, or a combination thereof.

[0191] According to embodiments of this disclosure, the term "linear velocity" in the phrase "bead milling the slurry within the above-defined linear velocity range" can refer to the linear velocity at the end of the stirring blade extending from the rotating shaft. The linear velocity can be calculated based on the rotational speed of the rotating device and the length of the stirring blade. When the rotational speed of the rotating device meets the above-defined range, the energy of the impact force of the bead collision and the shear force generated by the rotation of the beads is appropriate, and the particulate PVDF-based adhesive polymer in the adhesive layer depolymerizes, thus controlling the surface roughness of the adhesive layer within a predetermined range. If the linear velocity exceeds the above-defined upper limit, the particulate PVDF-based adhesive polymer is excessively depolymerized and pulverized to form microparticles, which then re-aggregate, resulting in an increase in particle size and surface roughness. If the linear velocity is less than the above-defined lower limit, the adhesive layer exhibits increased surface roughness, leading to deterioration of electrode-separator adhesion.

[0192] According to embodiments of this disclosure, based on 100% by volume of the internal volume of the grinding chamber, it can contain 60% to 80% by volume, or 65% to 75% by volume, beads. When beads are included within the aforementioned range, the probability of slurry colliding with the beads increases, and therefore bead milling can be performed more efficiently, and the flow of the slurry can be smooth. Meanwhile, the degree to which the internal volume of the grinding chamber is filled with beads can be determined by conventional methods, for example, by calculating the volume of water required to completely fill the grinding chamber when the grinding chamber is equipped with and without beads.

[0193] In this specification, the shear force can be calculated using the distance between the rotor and the grinding chamber (in meters, etc.) and the linear velocity of the bead mill (in meters per second, etc.). Specifically, the shear force here can be calculated by dividing the linear velocity by the distance.

[0194] Therefore, according to embodiments of this disclosure, the interval between the grinding chamber and the stirring blade can be 20% to 50% of the diameter of the grinding chamber. Specifically, the interval can be calculated by dividing the difference between the diameter of the stirring blade and the diameter of the grinding chamber by 2.

[0195] According to embodiments of this disclosure, the aqueous slurry used to form the inorganic heat-resistant layer may further include a first dispersant.

[0196] According to embodiments of the present disclosure, specifically, the step of preparing an aqueous slurry for forming an inorganic heat-resistant layer may include the following steps: (S1-1) introducing inorganic particles into an aqueous dispersion medium to prepare a first dispersion; and (S1-2) subjecting the first dispersion to bead milling.

[0197] According to embodiments of this disclosure, the first binder polymer can be introduced before or after the bead milling step, but preferably, it can be introduced after the bead milling step. In this case, no bubbles or the like are generated in the first dispersion during the bead milling step, thereby achieving excellent processability.

[0198] According to embodiments of this disclosure, the first dispersant may be introduced before or after the bead milling step, but preferably, the first dispersant may be introduced after the bead milling step.

[0199] Meanwhile, during the bead milling step, depending on the strength, inorganic particles in the state of secondary particles formed by the aggregation of inorganic particles can deagglomerate to transform into primary particles, or inorganic particles in the state of primary particles can become particles with a smaller average particle size (D). 50 Those.

[0200] According to embodiments of the present disclosure, specifically, the step of preparing an aqueous slurry for forming a first adhesive layer may include the following steps: (S1a) introducing a particulate PVDF-type adhesive polymer into an aqueous dispersion medium to prepare a second dispersion; and (S1b) subjecting the second dispersion to bead milling.

[0201] According to embodiments of the present disclosure, the aqueous slurry used to form the adhesive layer may further include a second adhesive polymer, wherein the second adhesive polymer may be a particulate adhesive polymer, a non-particulate adhesive polymer, or a combination thereof.

[0202] According to embodiments of this disclosure, when the aqueous slurry used to form the adhesive layer further includes a second adhesive polymer, the second adhesive polymer may be introduced before or after the bead milling step.

[0203] According to embodiments of this disclosure, prior to the bead milling step, an additional dispersant for dispersing and wetting the particulate PVDF adhesive polymer may be further introduced.

[0204] Simultaneously, granular PVDF-based adhesive polymers can be synthesized in granular form and then, after drying, introduced into an aqueous dispersion medium as a powder. The description regarding this point is replaced with the one described above.

[0205] Then, in step (S2), an aqueous slurry for forming an inorganic heat-resistant layer can be applied to at least one surface of a porous polymer substrate and then dried to form an inorganic heat-resistant layer.

[0206] Subsequently, in step (S3), an aqueous slurry for forming the first adhesive layer may be applied to at least one surface of the inorganic heat-resistant layer and then dried to form the first adhesive layer.

[0207] (Third Implementation)

[0208] According to another embodiment of the present disclosure, a method for manufacturing a separator for a lithium secondary battery may include the following steps: (S1) preparing an aqueous slurry for forming an inorganic heat-resistant layer comprising inorganic particles and a first binder polymer, an aqueous slurry for forming a first binder layer comprising a particulate PVDF binder polymer and a caprolactone dispersant, and an aqueous slurry for forming a second binder layer comprising a particulate PVDF binder polymer and a second dispersant; (S2) applying the aqueous slurry for forming the inorganic heat-resistant layer to two surfaces of a porous polymer substrate, and then drying it to form the inorganic heat-resistant layer; (S3) applying the aqueous slurry for forming the first binder layer to one surface of the inorganic heat-resistant layer, and then drying it; and (S4) applying the aqueous slurry for forming the second binder layer to the inorganic heat-resistant layer on the other surface not coated with the aqueous slurry for forming the first binder layer, and then drying it.

[0209] First, in step (S1), an aqueous slurry containing inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer, an aqueous slurry containing particulate PVDF binder polymer and caprolactone dispersant for forming a first binder layer, and an aqueous slurry containing particulate PVDF binder polymer and a second dispersant for forming a second binder layer are prepared.

[0210] According to embodiments of the present disclosure, the aqueous slurry used to form the first adhesive layer may further include a second adhesive polymer. According to embodiments of the present disclosure, the aqueous slurry used to form the second adhesive layer may further include a third adhesive polymer.

[0211] Next, in step (S2), an aqueous slurry for forming an inorganic heat-resistant layer can be formed on both surfaces of a porous polymer substrate and then dried to form an inorganic heat-resistant layer.

[0212] Then, in step (S3), the aqueous slurry for forming the first adhesive layer can be applied to one surface of the inorganic heat-resistant layer and then dried, and in step (S4), the aqueous slurry for forming the second adhesive layer can be applied to the inorganic heat-resistant layer on the other surface that is not coated with the aqueous slurry for forming the first adhesive layer and then dried.

[0213] (Fourth Implementation)

[0214] According to another embodiment of this disclosure, a method for manufacturing a separator for a lithium secondary battery may include the following steps: (S1) preparing an aqueous slurry comprising inorganic particles and a first binder polymer for forming an inorganic heat-resistant layer, an aqueous slurry comprising a particulate PVDF-type binder polymer for forming a first binder layer, and an aqueous slurry comprising a particulate PVDF-type binder polymer for forming a second binder layer; (S2) applying the aqueous slurry for forming the inorganic heat-resistant layer to both surfaces of a porous polymer substrate, followed by drying, to form the inorganic heat-resistant layer; (S3) applying the aqueous slurry for forming the first binder layer to one surface of the inorganic heat-resistant layer, followed by drying; and (S4) applying the aqueous slurry for forming the second binder layer to the inorganic heat-resistant layer on the other surface not coated with the aqueous slurry for forming the first binder layer, and then drying. Each step of the method for manufacturing a separator for a lithium secondary battery will be explained below.

[0215] First, in step (S1), an aqueous slurry containing inorganic particles and a first adhesive polymer for forming an inorganic heat-resistant layer, an aqueous slurry containing a particulate PVDF adhesive polymer for forming a first adhesive layer, and an aqueous slurry containing a particulate PVDF adhesive polymer for forming a second adhesive layer are prepared.

[0216] According to embodiments of the present disclosure, the aqueous slurry used to form the first adhesive layer may further include a second adhesive polymer. According to embodiments of the present disclosure, the aqueous slurry used to form the second adhesive layer may further include a third adhesive polymer. According to embodiments of the present disclosure, the dispersion medium is an aqueous dispersion medium. The aqueous dispersion medium may include water or an aqueous dispersion medium containing water.

[0217] Meanwhile, step (S1) may include bead milling of the aqueous slurry used to form the first adhesive layer at a linear velocity of 10 m / s to 15 m / s, and bead milling of the aqueous slurry used to form the second adhesive layer at a linear velocity of 5 m / s to 10 m / s.

[0218] According to embodiments of this disclosure, the aqueous slurry used to form the inorganic heat-resistant layer may further include a first wetting agent. The first wetting agent allows the hydrophobic porous polymer substrate to be adequately wetted by the aqueous slurry used to form the inorganic heat-resistant layer, thereby improving coatability. Furthermore, the first wetting agent can be any known wetting agent (surfactant), and its description is replaced as described above.

[0219] Next, in step (S2), an aqueous slurry for forming the inorganic heat-resistant layer can be applied to both surfaces of the porous polymer substrate and then dried to form the inorganic heat-resistant layer. Specifically, according to embodiments of the present disclosure, the step of drying the aqueous slurry for forming the inorganic heat-resistant layer can be performed at a temperature of 50°C to 70°C, or 55°C to 65°C for 1 second to 200 seconds, or 10 seconds to 120 seconds.

[0220] Then, in step (S3), an aqueous slurry for forming the first adhesive layer can be applied to one surface of the inorganic heat-resistant layer and then dried, and in step (S4), an aqueous slurry for forming the second adhesive layer can be formed on the inorganic heat-resistant layer on the other surface that is not coated with the aqueous slurry for forming the first adhesive layer and then dried.

[0221] According to embodiments of this disclosure, there are no particular limitations on the methods of applying the aqueous slurry for forming the first adhesive layer and the aqueous slurry for forming the second adhesive layer, and the methods of applying the aqueous slurry for forming the inorganic heat-resistant layer can be used as is.

[0222] According to embodiments of this disclosure, the steps of drying the aqueous slurry for forming the first adhesive layer and the aqueous slurry for forming the second adhesive layer can be performed at a temperature of 50°C to 70°C for 10 to 120 seconds.

[0223] In this disclosure, the first to fourth embodiments of manufacturing a separator for a lithium secondary battery can be performed individually or in combination, and there are no particular restrictions on the order in which the embodiments are performed.

[0224] <Methods for Manufacturing Lithium Secondary Batteries>

[0225] In another aspect of this disclosure, a method for manufacturing a lithium secondary battery is provided.

[0226] A method for manufacturing a lithium secondary battery according to embodiments of the present disclosure includes the following steps: stacking a first separator, a negative electrode on the first separator, and a second separator on the negative electrode to form a laminate; pressing the laminate using a rotary pressing member; and stacking a positive electrode on the pressed laminated material on the second separator, wherein each of the first and second separators is the separator described above for a lithium secondary battery, and a particulate PVDF-type adhesive polymer with substantially no adhesive layer is transferred to the surface of the rotary pressing member by a pressing step. Each step of the method for manufacturing a lithium secondary battery will be explained below.

[0227] First, a first separator, a negative electrode on the first separator, and a second separator on the negative electrode can be stacked to form a laminated material. Each of the first separator and the second separator can be the separator described above.

[0228] According to embodiments of this disclosure, the laminated material can be obtained by conventional methods known in the art. According to embodiments of this disclosure, the laminated material can be formed by inserting the aforementioned separator between the positive and negative electrodes.

[0229] Next, the laminate material can be pressed using a rotary pressing component.

[0230] According to embodiments of this disclosure, laminated materials can be compressed by using rotating pressing members (such as two or more rollers that rotate simultaneously facing each other).

[0231] According to embodiments of this disclosure, the pressing step using a rotary pressing member can be performed at a temperature of 5°C to 30°C or 10°C to 25°C. In this case, the adhesive polymer of the partition does not deform and adheres less to the rotary roller.

[0232] According to embodiments of this disclosure, the pressing step can be performed at a pressure of 0.1 MPa to 1 MPa or 0.1 MPa to 0.5 MPa.

[0233] According to embodiments of this disclosure, the pressing step can be performed for 1 to 10 seconds.

[0234] According to embodiments of this disclosure, a particulate PVDF-based adhesive polymer with essentially no adhesive layer is transferred onto the surface of a rotary-pressed member via a pressing step.

[0235] According to embodiments of the present disclosure, based on 100% by weight of the granular PVDF adhesive polymer of the adhesive layer, the granular PVDF adhesive polymer of the adhesive layer can be transferred onto the surface of the rotary pressed member in an amount of less than 5% by weight, less than 4% by weight, less than 3% by weight, less than 2% by weight, or less than 1% by weight through a pressing step.

[0236] The positive electrode can then be stacked on a second separator of pressed laminated material to obtain the electrode assembly of a lithium secondary battery.

[0237] Furthermore, according to embodiments of this disclosure, depending on the manufacturing process of the final product and the desired characteristics of the final product, the electrolyte can be injected at appropriate steps during the battery manufacturing process. In other words, the electrolyte can be injected before battery assembly or in the final step of battery assembly.

[0238] The present disclosure will be described in more detail below by way of examples, but the examples are for illustrative purposes only and the scope of the disclosure is not limited thereto.

[0239] <Example 1: Determining the Improvement of Print Transfer to Contactless Rollers Based on the Use of Caprolactone Dispersants>

[0240] <Example 1-1>

[0241] First, at room temperature, 96 parts by weight of aluminum oxide (Al2O3, D) 50 A first dispersion was prepared by introducing 1 part by weight of sodium carboxymethyl cellulose (450 nm, purchased from Sumitomo) as inorganic particles and 1 part by weight of sodium carboxymethyl cellulose as a first dispersant into water, followed by bead milling of the first dispersion. Next, 3 parts by weight of acrylic polymer (CSB Toyo Ink, Tg: -30°C) was introduced as a first binder polymer to prepare an aqueous slurry for forming an inorganic heat-resistant layer.

[0242] In addition, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight) was introduced. 50 A 3 μm PVDF-based adhesive polymer and a caprolactone dispersant were used to prepare a second dispersion, and the second dispersion was subjected to bead milling. After bead milling, the PVDF-based adhesive polymer had a D0.05 of 1 μm. 50 Then, an acrylic adhesive polymer (Tg: -35°C) emulsion is further introduced as a second adhesive polymer to prepare an aqueous slurry for forming the adhesive layer. Here, based on a total repeating unit quantity of 100%, the caprolactone dispersant comprises 50% ethylene glycol-derived repeating units, 20% propylene glycol-derived repeating units, and 30% caprolactone-derived repeating units.

[0243] An aqueous slurry for forming the inorganic heat-resistant layer was applied to one surface of a porous polymer substrate made of polyethylene (40% porosity, 9 μm thickness) using a doctor blade process, and then dried at 60°C for 30 seconds. Then, an aqueous slurry for forming the adhesive layer was applied to the inorganic heat-resistant layer using a doctor blade process, and then dried at 60°C for 30 seconds. In the same manner, the inorganic heat-resistant layer and the adhesive layer were formed on the other surface of the porous polymer substrate made of polyethylene. Here, the resulting inorganic heat-resistant layer has a thickness of 1.5 μm based on one surface, and the adhesive layer has a thickness of 0.75 μm based on one surface. Furthermore, based on the total weight of 100% of the inorganic heat-resistant layer, the content of inorganic particles in the inorganic heat-resistant layer is 95% by weight.

[0244] <Examples 1-2>

[0245] Repeat Example 1-1, except that the thickness of the adhesive layer is 0.5 μm based on one surface and 1 μm based on both surfaces.

[0246] <Examples 1-3>

[0247] The process of Example 1-1 is repeated, except that: an aqueous slurry for forming the inorganic heat-resistant layer is applied to one surface (first surface) of a porous polymer substrate using a doctor blade process, and then dried at 60°C for 30 seconds. Then, an aqueous slurry for forming the adhesive layer is applied to the inorganic heat-resistant layer using a doctor blade process, and then dried at 60°C for 30 seconds. Subsequently, an aqueous slurry for forming the adhesive layer is applied to the other surface (second surface) of the porous polymer substrate using a doctor blade process, and then dried at 60°C for 30 seconds. In this study, the resulting inorganic heat-resistant layer has a thickness of 2 μm, and the adhesive layer has a thickness of 0.75 μm based on one surface. In other words, a layer with the following characteristics is obtained: Figure 6 The partition shown is a structural feature.

[0248] <Comparative Example 1-1>

[0249] Repeat Example 1-1, except that a copolymer-type dispersant containing repeating units derived from ethylene glycol, propylene glycol, ethylene, and styrene is used instead of a caprolactone-based dispersant.

[0250] <Comparative Examples 1-2>

[0251] Repeat Example 1-1, except as follows: First, 75 parts by weight of alumina (Al2O3, D) were placed at room temperature. 50 A 450 nm (purchased from Sumitomo) inorganic particles and 2 parts by weight of caprolactone dispersant (CYR301 purchased from Miwon Commercial Co., Ltd.) were introduced into acetone to prepare a dispersion, which was then subjected to bead milling. Next, 23% by weight of PVDF-HFP (HFP-derived repeating unit content: 12% by weight) was introduced. 50 The slurry for forming the organic / inorganic composite layer was prepared by a second bead milling process (3 μm). The slurry was then applied to one surface of a porous polymer substrate (40% porosity, 9 μm thickness) made of polyethylene to a thickness of 2.5 μm using a doctor blade process, and then dried at 60°C for 30 seconds. The same application and drying steps were then performed on the other surface.

[0252] <Manufacturing of Lithium Secondary Batteries>

[0253] In each embodiment and comparative example, the lithium secondary battery is manufactured by the following method.

[0254] First, LiNi, used as the positive electrode active material, was mixed in a weight ratio of 97.0:1.5:1.5. 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride (PVDF) as a binder for the positive electrode, and carbon black as a conductive material were used to prepare a positive electrode slurry by dispersing the resulting mixture in N-methyl-2-pyrrolidone. The positive electrode slurry was then coated onto an aluminum current collector, followed by drying and pressing to obtain the positive electrode.

[0255] Next, graphite as the negative electrode material, styrene-butadiene rubber (SBR) as the negative electrode binder, and carboxymethyl cellulose (CMC) as the thickener were mixed in a weight ratio of 89.2:10:0.8, and the mixture was dispersed in distilled water to prepare a negative electrode slurry. Then, the negative electrode slurry was coated onto a copper current collector, and then dried and pressed to obtain the negative electrode.

[0256] The negative electrode is stacked on the separator according to each of the embodiments and comparative examples, and the separator is stacked on the negative electrode to form a laminate, which is then pressed using a rotary pressing member. The positive electrode is then stacked on a second separator of the pressed laminate to obtain a single-cell sample.

[0257] In this study, the laminations were pressed for 5 seconds at 60°C and 1000 kgf. The laminated assembly was secured on both sides with nylon tape to prevent decomposition. The sample dimensions were 37 mm × 59 mm.

[0258] The sample was introduced into a bag-shaped shell, and 0.5 g of electrolyte (ethylene carbonate: methyl ethyl carbonate = 7:3 (volume ratio), 1M LiPF6, ethylene carbonate (VC) 2% by weight) was injected to obtain a secondary cell, which was then allowed to stand at room temperature for 3 hours. The secondary cell was then subjected to a test at 5 kgf / cm². 2 The secondary battery was pressed at 60°C for 5 minutes under pressure. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) 2 When the battery is compressed at 60°C under pressure, it is charged to SOC (State of Charge) 3 at a current of 0.2 C, and then charged to SOC 60 at a current of 1 C. The rechargeable battery is then released from pressure and aged at 60°C for 1 day.

[0259] <Test Example 1: Electrode Adhesion, Thermal Shrinkage, Resistance Characteristics, and Transfer to the Contactless Roller>

[0260] For each of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2, electrode adhesion, surface roughness, thermal shrinkage, resistance characteristics, and transfer to the accessible roller were measured. The results are shown in Table 1 below.

[0261] [Table 1]

[0262]

[0263] Example 1-1 includes a caprolactone dispersant, thus preventing transfer to the contactable roller and exhibiting excellent electrode adhesion, thermal properties, and electrical resistance characteristics. Example 1-2 includes a caprolactone dispersant and therefore prevents transfer to the contactable roller. Example 1-3 includes an inorganic heat-resistant layer on only one surface of a porous polymer substrate and an adhesive layer on both surfaces, but the adhesive layer includes a caprolactone dispersant, thus preventing transfer to the contactable roller. However, because it includes an inorganic heat-resistant layer on only one surface, it causes thermal shrinkage and exhibits slightly poorer thermal properties, but achieves excellent electrical resistance characteristics. Conversely, Comparative Example 1-1 does not include a caprolactone dispersant and has a high surface roughness, thus causing transfer to the contactable roller. When Examples 1-1, 1-2, and 1-3 are compared with Comparative Example 1-1, it is shown that a separator with a separate adhesive layer and a caprolactone dispersant in the adhesive layer does not cause transfer to the contactable roller. Meanwhile, unlike Examples 1-1, Comparative Examples 1-2 comprise an organic / inorganic composite layer formed by dissolving a PVDF-based adhesive polymer in an organic solvent, applying the resulting solution, and then drying it. Therefore, the organic / inorganic composite layer has a shape different from the adhesive layer of Examples 1-1. Furthermore, the organic / inorganic composite layer has a large thickness, leading to thermal shrinkage and exhibiting poor electrical resistance characteristics.

[0264] <Example 2: Determining the Transfer of Printing onto Contactless Rollers Based on Surface Roughness Improvement>

[0265] <Example 2-1>

[0266] First, at room temperature, 96 parts by weight of aluminum oxide (Al2O3, D) 50 A first dispersion was prepared by introducing 1 part by weight of sodium carboxymethyl cellulose (450 nm, purchased from Sumitomo) as inorganic particles and 1 part by weight of sodium carboxymethyl cellulose as a first dispersant into water, and then bead milling the first dispersion at a linear velocity of 13 m / s. Next, 3 parts by weight of acrylic polymer (CSB Toyo Ink, Tg: -30°C) was introduced as a first binder polymer to prepare an aqueous slurry for forming an inorganic heat-resistant layer.

[0267] In addition, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight, D) will be increased. 50A 3 μm PVDF-based adhesive polymer and a copolymer dispersant (including repeating units derived from ethylene glycol, propylene glycol, ethylene, and styrene) were introduced into the grinding chamber and bead-milled at a linear velocity of 13 m / s. Subsequently, an acrylic adhesive polymer emulsion (Tg: -30℃) was further introduced as a second adhesive polymer to prepare an aqueous slurry for forming the adhesive layer.

[0268] An aqueous slurry for forming the inorganic heat-resistant layer was applied to one surface of a porous polymer substrate made of polyethylene (40% porosity, 9 μm thickness) using a doctor blade process, and then dried at 60°C for 30 seconds. Then, a slurry for forming the adhesive layer was applied to the inorganic heat-resistant layer using a doctor blade process, and then dried at 60°C for 30 seconds. In the same manner, the inorganic heat-resistant layer and the adhesive layer were formed on the other surface of the porous polymer substrate made of polyethylene. Here, each resulting inorganic heat-resistant layer has a thickness of 1.5 μm, and each adhesive layer has a thickness of 0.75 μm. Furthermore, based on the total weight of 100% by weight of the inorganic heat-resistant layer, the content of inorganic particles in the inorganic heat-resistant layer is 95% by weight.

[0269] <Example 2-2>

[0270] Repeat Example 2-1, except that the second dispersion is bead-milled at a linear velocity of 20 m / s.

[0271] <Comparative Example 2-1>

[0272] Repeat Example 2-1, except that the second dispersion is bead-milled at a linear velocity of 7 m / s.

[0273] <Comparative Example 2-2>

[0274] Repeat Example 2-1, with the following differences. First, 75 parts by weight of alumina (Al2O3, D) were added at room temperature. 50 A dispersion was prepared by introducing acetone with 450 nm (purchased from Sumitomo) as inorganic particles and 2 parts by weight of caprolactone dispersant (CYR301 purchased from Miwon Commercial) as a dispersant. The dispersion was then bead-milled at a linear velocity of 10 m / s. Next, 12 wt% PVDF-HFP (HFP-derived repeating unit content: 12 wt% D) was introduced. 50The slurry for forming the organic / inorganic composite layer was prepared by a second bead milling process at a linear velocity of 10 m / s (3 μm). The slurry was then applied to a surface of a porous polymer substrate (40% porosity, 9 μm thickness) made of polyethylene to a thickness of 2.5 μm using a doctor blade process, and then dried at 60°C for 30 seconds. The same application and drying steps were then performed on the other surface.

[0275] <Manufacturing of Lithium Secondary Batteries>

[0276] Lithium secondary batteries were obtained in the same manner as described above by using each of the examples and comparative examples.

[0277] <Test Example 2: Dry adhesion between negative electrode and separator, surface roughness, thermal shrinkage rate, resistance characteristics, and transfer to the contactable roller>

[0278] For each of Examples 2-1 and 2-2, and Comparative Examples 2-1 and 2-2, electrode adhesion, surface roughness, thermal shrinkage, resistance characteristics, and transfer to the accessible roller were measured. The results are shown in Table 2 below.

[0279] [Table 2]

[0280]

[0281] Example 2-1 demonstrates a surface roughness within a predetermined range, thus preventing transfer to the contactable roller and achieving excellent electrode adhesion, thermal properties, and resistivity. Furthermore, compared to Example 2-1, Example 2-2 uses a higher bead milling line speed, resulting in a slightly higher surface roughness and lower adhesion to the electrode, but overall, no transfer to the contactable roller is caused. Compared to Example 2-1, Comparative Example 2-1 uses a lower bead milling line speed, resulting in a higher surface roughness and thus causing transfer to the contactable roller. When comparing Examples 2-1 and 2-2 with Comparative Example 2-1, it is shown that a partition with a separate adhesive layer and a surface roughness within a predetermined range does not cause transfer to the contactable roller. Meanwhile, unlike Example 2-1, Comparative Example 2-2 includes an organic / inorganic composite layer formed by dissolving a PVDF-based adhesive polymer in an organic solvent, applying the resulting solution, and then drying. Therefore, the shape of the organic / inorganic composite layer differs from the shape of the adhesive layer in Example 2-1. Furthermore, the organic / inorganic composite layer has a large thickness, which leads to thermal shrinkage and exhibits poor electrical resistance characteristics.

[0282] <Example 3: Improving Battery Bending Based on Differences in Surface Roughness of Adhesive Layers>

[0283] <Example 3-1>

[0284] First, 96 parts by weight of alumina (Al2O3, D) are introduced. 50 The inorganic particles (450 nm, purchased from Sumitomo) and 1 part by weight of sodium carboxymethyl cellulose were used as the first dispersant and bead milled. Next, 3 parts by weight of acrylic polymer (CSB Toyo Ink, Tg: -30°C) were introduced into water at room temperature as the first binder polymer to prepare an aqueous slurry for forming an inorganic heat-resistant layer.

[0285] In addition, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight) was introduced. 50 A 3 μm PVDF-based adhesive polymer and a caprolactone dispersant were used to prepare a second dispersion, and the second dispersion was subjected to bead milling. After bead milling, the PVDF-based adhesive polymer had a D0.05 of 1 μm. 50 Then, an acrylic adhesive polymer (Tg: -35°C) emulsion is further introduced as a second adhesive polymer to prepare an aqueous slurry for forming the first adhesive layer. Here, based on the total number of repeating units of 100%, the caprolactone dispersant comprises 50% ethylene glycol-derived repeating units, 20% propylene glycol-derived repeating units, and 30% caprolactone-derived repeating units.

[0286] In addition, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight) was introduced. 50 A third dispersion was prepared by using a PVDF-based adhesive polymer (3 μm) as particulates and methylcellulose as a second dispersant, and the third dispersion was then bead-milled. After bead milling, the PVDF-based adhesive polymer had a density of 1 μm. 50 Then, an acrylic adhesive polymer (Tg: -35℃) emulsion is further introduced as a third adhesive polymer to prepare an aqueous slurry for forming the second adhesive layer.

[0287] Here, the second and third adhesive polymers are shown to exist in the form of particles on the emulsion when they are introduced, but they cannot maintain the particle shape upon application due to their low Tg.

[0288] An aqueous slurry for forming the inorganic heat-resistant layer was applied to one surface of a porous polymer substrate made of polyethylene (40% porosity, 9 μm thickness) using a doctor blade process, and then dried at 60°C for 30 seconds. Then, the aqueous slurry for forming the inorganic heat-resistant layer was applied to the other surface of the porous polymer substrate using a doctor blade process, and then dried at 60°C for 30 seconds.

[0289] Then, an aqueous slurry for forming the first adhesive layer was applied to the inorganic heat-resistant layer and dried at 60°C for 30 seconds. A second aqueous slurry for forming the second adhesive layer was then applied to the inorganic heat-resistant layer on the other surface uncoated with the first adhesive slurry using a doctor blade process, and dried at 60°C for 30 seconds, thereby forming the first and second adhesive layers. In this study, the resulting inorganic heat-resistant layer has a thickness of 1.5 μm, and the adhesive layer has a thickness of 0.75 μm. Furthermore, based on the total weight of 100% of the inorganic heat-resistant layer, the inorganic particle content in the inorganic heat-resistant layer is 95% by weight.

[0290] <Comparative Example 3-1>

[0291] Repeat Example 3-1, except that the aqueous slurry for forming the first adhesive layer is applied to both surfaces of the inorganic heat-resistant layer.

[0292] <Comparative Example 3-2>

[0293] Repeat Example 3-1, except that an aqueous slurry for forming the second adhesive layer is applied to both surfaces of the inorganic heat-resistant layer.

[0294] <Example 3-2>

[0295] First, at room temperature, 96 parts by weight of aluminum oxide (Al2O3, D) 50 A first dispersion was prepared by introducing water with 1 part by weight of sodium carboxymethyl cellulose (450 nm, purchased from Sumitomo) as inorganic particles, 1 part by weight of sodium carboxymethyl cellulose as the first dispersant, and 3 parts by weight of acrylic polymer (CSB Toyo Ink, Tg: -30℃) as the first binder polymer. The first dispersion was then introduced into a grinding chamber and bead-milled at a linear velocity of 9.5 m / s to prepare an aqueous slurry for forming an inorganic heat-resistant layer.

[0296] Next, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight, D) will be adjusted. 50 A 3 μm PVDF-type adhesive polymer and a copolymer dispersant (the copolymer dispersant includes repeating units derived from ethylene glycol, propylene glycol, ethylene, and styrene) are introduced into a grinding chamber and bead-milled at a linear velocity of 13 m / s. Then, an acrylic adhesive polymer (Tg: -30°C) emulsion is further introduced as a second adhesive polymer to prepare an aqueous slurry for forming a first adhesive layer.

[0297] Then, the content of PVDF-HFP (HFP-derived repeating units: 12% by weight, D) was increased. 50 A 3 μm PVDF-type adhesive polymer and a copolymer dispersant (including repeating units derived from ethylene glycol, propylene glycol, ethylene, and styrene) were introduced into a grinding chamber and bead-milled at a linear velocity of 7 m / s. Then, an acrylic adhesive polymer (Tg: -30°C) emulsion was further introduced as a third adhesive polymer to prepare an aqueous slurry for forming a second adhesive layer.

[0298] An aqueous slurry for forming the inorganic heat-resistant layer was applied to one surface of a porous polymer substrate made of polyethylene (40% porosity, 9 μm thickness) using a doctor blade process, and then dried at 60°C for 30 seconds. Then, the aqueous slurry for forming the inorganic heat-resistant layer was applied to the other surface of the porous polymer substrate using a doctor blade process, and then dried at 60°C for 30 seconds.

[0299] Subsequently, an aqueous slurry for forming the first adhesive layer was applied to the inorganic heat-resistant layer and dried at 60°C for 30 seconds. Then, an aqueous slurry for forming the second adhesive layer was applied to the inorganic heat-resistant layer on the other surface uncoated with the aqueous slurry for forming the first adhesive layer using a doctor blade process, and dried at 60°C for 30 seconds. Each resulting inorganic heat-resistant layer has a thickness of 1.5 μm, and the adhesive layer has a thickness of 0.75 μm. Furthermore, based on the total weight of 100% of the inorganic heat-resistant layer, the content of inorganic particles in the inorganic heat-resistant layer is 95% by weight.

[0300] <Comparative Example 3-3>

[0301] Repeat Examples 3-2, except that the aqueous slurry used to form the first adhesive layer is applied to both surfaces of the inorganic heat-resistant layer.

[0302] <Comparative Examples 3-4>

[0303] Repeat Examples 3-2, except that an aqueous slurry for forming the second adhesive layer is applied to both surfaces of the inorganic heat-resistant layer.

[0304] <Example 3-3>

[0305] Example 3-1 was repeated, with the following differences. An aqueous slurry for forming the first adhesive layer was applied to one surface of a porous polymer substrate and then dried at 60°C for 30 seconds to form the first adhesive layer. A slurry for forming the inorganic heat-resistant layer was then applied to the other surface, which was not coated with the aqueous slurry for forming the first adhesive layer, using a doctor blade process, and dried at 60°C for 30 seconds to form the inorganic heat-resistant layer. Then, an aqueous slurry for forming the second adhesive layer was applied to the inorganic heat-resistant layer using a doctor blade process and dried at 60°C for 30 seconds to form the second adhesive layer on the inorganic heat-resistant layer. Here, the resulting inorganic heat-resistant layer has a thickness of 2 μm, and the adhesive layer has a thickness of 0.75 μm. Furthermore, based on the total weight of 100% by weight of the inorganic heat-resistant layer, the content of inorganic particles in the inorganic heat-resistant layer is 95% by weight.

[0306] <Manufacturing of Lithium Secondary Batteries>

[0307] In each of the embodiments and comparative examples, a lithium secondary battery is manufactured by the following method.

[0308] First, LiNi, used as the positive electrode active material, was mixed in a weight ratio of 97.0:1.5:1.5. 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride (PVDF) as a binder for the positive electrode, and carbon black as a conductive material were mixed and dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was then coated onto an aluminum current collector, dried, and pressed to obtain the positive electrode.

[0309] Next, graphite as the negative electrode material, styrene-butadiene rubber (SBR) as the negative electrode binder, and carboxymethyl cellulose (CMC) as the thickener were mixed in a weight ratio of 89.2:10:0.8, and the mixture was dispersed in distilled water to prepare a negative electrode slurry. Then, the negative electrode slurry was coated onto a copper current collector, and then dried and pressed to obtain the negative electrode.

[0310] A negative electrode is stacked on a first separator according to each of the embodiments and comparative examples, and a second separator is stacked on top of the negative electrode to form a laminate. The laminate is then pressed using a rotary pressing member. A positive electrode is then stacked on the pressed laminated material on a second separator to obtain a single-cell sample.

[0311] Here, in Examples 3-1, 3-2, and 3-3, the laminate is formed such that the adhesive layer of the separator with a low surface roughness faces the negative electrode. In other words, the laminate is formed such that the surface with a high negative electrode-separator dry adhesion force faces the negative electrode.

[0312] In this study, the lamination was pressed for 5 seconds at 60°C and 1000 kgf. The laminated assembly was secured on both sides with nylon tape to prevent decomposition. The sample dimensions were 37 mm × 59 mm.

[0313] The sample was introduced into a bag-shaped shell, and 0.5 g of electrolyte (ethylene carbonate: methyl ethyl carbonate = 7:3 (volume ratio), 1 M LiPF6, 2% wt% vinylene carbonate (VC)) was injected to obtain a secondary battery. The secondary battery was then allowed to stand at room temperature for 3 hours. Then, the secondary battery was subjected to a temperature of 5 kgf / cm². 2 The secondary battery was pressed at 60°C for 5 minutes under pressure. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) 2 When pressed under pressure at 60°C, it is charged to SOC (State of Charge) 3 with a current of 0.2 C, and then charged to SOC 60 with a current of 1 C. The rechargeable battery is then released from pressure and aged at 60°C for 1 day.

[0314] <Test Example 3: Dry adhesion between negative electrode and separator, wet adhesion between electrode and separator, surface roughness (Sa), resistance characteristics (ER), and battery bending>

[0315] For each of Examples 3-1 to 3-3 and Comparative Examples 3-1 to 3-4, electrode adhesion, surface roughness, resistance characteristics, and battery bending were measured. The results are shown in Table 3 below.

[0316] [Table 3]

[0317]

[0318] In Examples 3-1 to 3-3, the first adhesive layer, including the caprolactone dispersant, exhibits a lower surface roughness compared to the second adhesive layer. This lower surface roughness results in higher dry adhesion between the first adhesive layer and the electrode-separator, causing the first adhesive layer to face the negative electrode, while the side with higher surface roughness faces the positive electrode. In this way, the difference between the wet adhesion between the positive and negative electrode and the wet adhesion between the electrode and separator is smaller compared to Comparative Examples 3-1 to 3-4, thus preventing battery bending.

[0319] Meanwhile, unlike Example 3-1, in Example 3-3, the first adhesive layer is formed on a porous polymer substrate, and the second adhesive layer is formed on an inorganic heat-resistant layer (the inorganic heat-resistant layer is formed on a porous polymer substrate). However, in this case, battery bending does not occur, just like in Example 3-1.

[0320] Meanwhile, in Comparative Examples 3-1 and 3-2, the adhesive layers had the same surface roughness and exhibited similar dry adhesion strength between the negative electrode and the separator. However, compared to Example 3-1, the difference between the wet adhesion strength between the positive electrode and the separator and the wet adhesion strength between the negative electrode and the separator was greater. As a result, battery bending occurred.

[0321] In Example 3-2, because the first adhesive layer exhibits a lower surface roughness compared to the second adhesive layer, and the first adhesive layer with a lower surface roughness exhibits higher electrode-separator dry adhesion, it faces the negative electrode, while the second adhesive layer, with a higher surface roughness and exhibiting lower electrode-separator dry adhesion, faces the positive electrode. In this way, compared to Comparative Examples 3-3 and 3-4, the difference between the positive electrode-separator wet adhesion and the negative electrode-separator wet adhesion is smaller, and therefore no battery bending occurs.

[0322] Meanwhile, in Comparative Examples 3-3 and 3-4, the adhesive layers had the same surface roughness and exhibited similar dry adhesion strength between the negative electrode and the separator. However, compared to Example 3-2, the difference between the wet adhesion strength between the positive electrode and the separator and the wet adhesion strength between the negative electrode and the separator was greater. As a result, battery bending occurred.

[0323] Therefore, it can be seen that asymmetric adhesive layers can be achieved by using caprolactone dispersants or by controlling the surface roughness through linear velocity, and this can be used to reduce battery bending in the battery.

[0324] <Measurement Method>

[0325] Measurement of dry adhesion force between negative electrode and separator

[0326] The negative electrode, prepared for manufacturing a lithium secondary battery, was cut to a size of 20 mm × 60 mm. The separators prepared from each of the examples and comparative examples were also cut to a size of 20 mm × 60 mm. The prepared separators were laminated with the negative electrode, and the resulting structure was inserted between 100 μm PET films and adhered using a flatbed press. Here, the flatbed press was used in such a manner that heating and pressing were performed for 1 second at a temperature of 60°C and a pressure of 6.5 MPa. The adhered separators and negative electrodes were attached to a glass slide using double-sided adhesive tape. The dry adhesion force was measured by peeling the separator with the adhered negative electrode at 180° using a UTM.

[0327] Measurement of wet adhesion force between negative electrode and separator

[0328] The negative and positive electrodes prepared for manufacturing lithium-ion secondary batteries, along with the separators prepared for each of the examples and comparative examples, were cut to a size of 20 mm × 60 mm. A battery with a negative electrode-separator-positive electrode-separator-negative electrode structure was then assembled, and an electrolyte prepared for manufacturing lithium-ion secondary batteries was injected into it. The battery was then charged to SOC 60 while being pressed at a temperature of 60°C and a pressure of 6.5 MPa, and then discharged. Afterward, the battery was disassembled to obtain two negative electrode-separator assemblies, and the wet adhesion force was measured by peeling the separator at 90° using a UTM.

[0329] Measurement of wet adhesion force between positive electrode and separator

[0330] A positive electrode and a separator were cut into 20 mm × 60 mm pieces, stacked in an aluminum bag, and then injected with electrolyte before sealing. The bag was then subjected to a temperature of 60°C and a pressure of 5 kgf / cm². 2 The bag was pressed under pressure for 5 minutes. The separator-positive electrode assembly was removed from the bag, and the wet adhesion force was measured by peeling the separator at 90° using a UTM.

[0331] Surface roughness measurement

[0332] The partitions of each of the embodiments and comparative examples were flatly fixed on the silicon wafer, and the surface roughness of each sample was measured 10 times in a dry environment using a confocal laser scanning microscope (CLSM, Olympus OLS5100) (measurement environment: dry chamber, laser source: 405 nm, measurement mode: 3D, lenses used: 20, 50 and 100x (objectives), 1x (zoom)).

[0333] Then, data processing is performed: data analysis applications are used as follows to determine 2D and 3D images and the roughness (Sa) of each surface.

[0334] 1. Noise cancellation: using environmental height compensation

[0335] 2. Gradient Removal: Assign 4 points to each image to correct the gradient.

[0336] 3. Scale Adjustment: Apply the same scale to all images (-2 μm to 2 μm) and extract 2D and 3D results.

[0337] 4. Extract surface roughness using an L filter value of 50.

[0338] Determination of heat shrinkage rate

[0339] The partitions according to each of the examples and comparative examples were cut into 50 mm × 50 mm sizes, placed between A4 sheets of paper, introduced into a convection oven at 120°C and allowed to stand there for 1 hour, and then the heat shrinkage rate was measured in the longitudinal (MD) and transverse (TD) directions.

[0340] In this paper, the thermal shrinkage rate is calculated according to the following formula:

[0341] [(Initial length - Length after heat treatment) / (Initial length) × 100].

[0342] Measurement of resistance characteristics

[0343] The separators in each of the Examples and Comparative Examples were wetted with electrolyte, and then the AC resistance was measured. The results are shown in Tables 1 to 3. In this paper, the AC resistance is the value measured at 1 kHz using a ohmmeter purchased from Hiokki.

[0344] Measurement of transfer to the contactable roller

[0345] The negative electrode was stacked on the separator according to each of the embodiments and comparative examples, and the separator according to each of the embodiments and comparative examples was stacked on the negative electrode. The resulting structure was then pressed using a rotary pressing member. Here, it was determined whether the particulate PVDF-based adhesive polymer in the adhesive layer of the separator was transferred to the surface of the rotary pressing member. The results are shown in Tables 1 and 2.

[0346] Measurement of battery bending

[0347] For each of the lithium secondary batteries (battery cells) according to the embodiments and comparative examples, the height difference between the center and the edge of the battery cell is measured using a ruler.

[0348] The present disclosure has been described above with reference to limited embodiments and accompanying drawings. However, the present disclosure is not limited thereto, and it should be noted that various changes and modifications can be made by those skilled in the art without departing from the technical spirit of the present disclosure and within the scope of the appended claims. Therefore, the embodiments disclosed above should be considered from an interpretative rather than restrictive perspective. In other words, the true scope of the technical spirit of the present disclosure is shown in the claims, and all differences within the scope of their equivalents should be interpreted as including within the present disclosure.

Claims

1. A separator for a lithium secondary battery, comprising: Porous polymer substrate; and A first adhesive layer is formed on at least one surface of the porous polymer substrate and comprises a particulate polyvinylidene fluoride (PVDF)-based adhesive polymer. Wherein the first adhesive layer: i) Including caprolactone dispersants, or ii) It has a surface roughness (Sa) of 0.12 μm to 0.22 μm.

2. The separator for lithium secondary batteries according to claim 1, wherein Based on 100% by weight of total repeating units, the caprolactone dispersant comprises 20% by weight to 40% by weight of caprolactone-derived repeating units.

3. The separator for lithium secondary batteries according to claim 1, in, Based on 100% by weight of total repeating units, the caprolactone dispersant comprises 40% to 60% by weight of ethylene glycol-derived repeating units or 10% to 30% by weight of propylene glycol-derived repeating units.

4. The separator for lithium secondary batteries according to claim 1, in, The surface roughness (Sa) was determined using a confocal laser scanning microscope (CLSM) at a magnification of 50X.

5. The separator for a lithium secondary battery according to claim 1, further comprising: An inorganic heat-resistant layer is formed individually on at least one surface of the porous polymer substrate, or between the porous polymer substrate and the first adhesive layer, and comprises inorganic particles and a first adhesive polymer.

6. The separator for lithium secondary batteries according to claim 5, The first adhesive polymer includes particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

7. The separator for lithium secondary batteries according to claim 5, in, The inorganic heat-resistant layer comprises 100% by weight of the inorganic particles, with an amount of 70% by weight or more and 99% by weight or less.

8. The separator for lithium secondary batteries according to claim 1, in, The particulate PVDF-based binder polymer has an average particle size (D 50 ) of 0.5 to 2 μm.

9. The separator for lithium secondary batteries according to claim 1, in, The first adhesive layer further includes a second adhesive polymer, and The second adhesive polymer includes particulate adhesive polymers, non-particulate adhesive polymers, or combinations thereof.

10. The separator for a lithium secondary battery according to claim 9, The second adhesive polymer includes a particulate adhesive polymer, and The particulate type binder polymer has an average particle diameter (D 50 ) of 100 nm to 800 nm.

11. The separator for a lithium secondary battery according to claim 1, further comprising: A second adhesive layer is formed on one surface of the porous polymer substrate, wherein the first adhesive layer is formed on one surface of the porous polymer substrate, and the second adhesive layer is formed on the other surface of the porous polymer substrate, wherein the second adhesive layer comprises a particulate PVDF-type adhesive polymer.

12. The separator for a lithium secondary battery according to claim 11, in, The inorganic heat-resistant layer, comprising the inorganic particles and the first adhesive polymer, is formed on each of the first and second surfaces of the porous polymer substrate. The first adhesive layer is formed on top of the inorganic heat-resistant layer on the first surface, and The second adhesive layer is formed on top of the inorganic heat-resistant layer on the second surface.

13. The separator for a lithium secondary battery according to claim 12, The surface roughness (Sa1) of the first adhesive layer is less than the surface roughness (Sa2) of the second adhesive layer.

14. The separator for a lithium secondary battery according to claim 12, The surface roughness (Sa2) of the second adhesive layer is 1.1 times or greater than the surface roughness (Sa1) of the first adhesive layer.

15. The separator for a lithium secondary battery according to claim 12, The surface roughness (Sa2) of the second adhesive layer is 1.1 times or greater and 1.4 times or less than the surface roughness (Sa1) of the first adhesive layer.

16. A lithium secondary battery, comprising: An electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a partition inserted between the positive electrode and the negative electrode; as well as The battery housing contains the electrode assembly and the electrolyte. The partition is the partition according to any one of claims 1 to 15.

Images