Separator for lithium secondary battery, method of manufacturing same, and lithium secondary battery including same

Abstract

The present disclosure provides a separator for a lithium secondary battery, including a porous polymer substrate; and an inorganic coating layer present on at least one surface of the porous polymer substrate, the inorganic coating layer including a core-shell composite particle precursor, where the core-shell composite particle precursor includes a core portion and a shell portion covering at least a portion of a surface of the core portion, where the core portion includes inorganic particles, and where the shell portion includes an acrylic monomer or oligomer.

Description

Technical Field

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

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2024-0110042, filed in Korea on August 16, 2024, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Non-aqueous secondary batteries, including lithium-ion batteries, are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras or camcorders, and electric vehicles.

[0004] In lithium-ion battery separators, fundamental requirements include electrical separation and insulation between the positive and negative electrodes, as well as high ionic conductivity attributable to high permeability (air permeability) of ions based on high porosity (e.g., lithium ions). While the separator does not participate in the electrochemical reactions of the secondary battery, it significantly impacts the battery's performance and safety due to physical properties such as electrolyte wettability, porosity, or thermal shrinkage.

[0005] The separators using porous polymer substrates shrink at high temperatures, leading to internal short circuits, and in the event of thermal runaway, the risk of fire increases when the polymer separator substrate melts. Therefore, to address the drawbacks of porous polymer substrates, an inorganic coating can be added to one or both surfaces of the porous polymer substrate. This inorganic coating can include inorganic particles and binder polymers to overcome the disadvantages of porous polymer substrates.

[0006] In inorganic coatings, the binder polymer is located between the inorganic particles, causing pore blockage between the particles. This results in low air permeability and poor wetting of the separator, adversely affecting electrical resistance characteristics. Therefore, it is necessary to develop separators to reduce or prevent these problems. Summary of the Invention

[0007] Technical issues

[0008] This disclosure aims to solve the above-mentioned problems, and therefore relates to providing a separator for lithium secondary batteries and a method for manufacturing the separator, the separator having high adhesion strength (dry adhesion strength) relative to the electrodes and good air permeability, wettability and electrical resistance characteristics.

[0009] The technical problem to be solved by this disclosure is not limited thereto, but includes other problems that will be clearly understood by those skilled in the art based on the detailed description.

[0010] Technical solution

[0011] To achieve the above objectives, according to aspects of this disclosure, a separator for a lithium secondary battery, a method for manufacturing the separator thereof, and a lithium secondary battery including the separator are provided according to the following embodiments.

[0012] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising: a porous polymer substrate; and an inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating comprising a core-shell composite particle precursor, wherein the core-shell composite particle precursor comprises a core and a shell covering at least a portion of the surface of the core, wherein the core comprises inorganic particles, and wherein the shell comprises an acrylic monomer or an oligomer.

[0013] According to the second embodiment, in the first embodiment, the acrylic monomer or oligomer may include a thermally polymerizable acrylic monomer or oligomer.

[0014] According to the third embodiment, in the second embodiment, the thermally polymerizable acrylic monomer or oligomer can be polymerized at a temperature of 45°C to 85°C to form a thermally polymerizable acrylic polymer.

[0015] According to the fourth embodiment, in either the second or third embodiment, the thermally polymerizable acrylic monomer or oligomer may be at least one monomer selected from the following: butylacrylate, β-carboxyethylacrylate, 2-ethylhexylacrylate, 2-methoxyethylacrylate, 4-hydroxybutylacrylate, ethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, pentylmethacrylate, 2-hydroxymethylacrylate, ethylmethacrylate, methylmethacrylate, acrylic acid, and acrylonitrile, or an oligomer containing at least one repeating unit derived therefrom.

[0016] According to the fifth embodiment, in any of the first to fourth embodiments, the thickness of the shell portion can be from 10 nm to 40 nm.

[0017] According to the sixth embodiment, in any of the first to fifth embodiments, the inorganic coating may have a structure in which an interstitial volume is formed between the core-shell composite particle precursors.

[0018] According to the seventh embodiment, in any of the first to sixth embodiments, based on a total of 100% by weight of the core-shell composite particle precursor, the core-shell composite particle precursor may include 10% to 90% by weight of inorganic particles and 10% to 90% by weight of acrylic monomers or oligomers.

[0019] According to the eighth embodiment, in any of the first to seventh embodiments, the inorganic coating contains 95% by weight or more of the core-shell composite particle precursor.

[0020] According to the ninth embodiment, in any one of the first to eighth embodiments, the inorganic coating may include core-shell composite particles formed by polymerization of core-shell composite particle precursors.

[0021] According to a tenth embodiment, a method for manufacturing a separator for a lithium secondary battery is provided, the method comprising: (S10) preparing an inorganic coating slurry composition comprising a core-shell composite particle precursor and a first dispersion medium; (S20) applying the inorganic coating slurry composition to at least one surface of a porous polymer substrate; and (S30) drying the inorganic coating slurry composition.

[0022] According to the eleventh embodiment, in the tenth embodiment, the method for manufacturing a separator for a lithium secondary battery may further include: before (S10), adding acrylic monomers or oligomers and inorganic particles to a second aqueous dispersion medium and mixing them to manufacture a core-shell composite particle precursor.

[0023] According to the tenth embodiment, in the ninth embodiment, the step of manufacturing the core-shell composite particle precursor may include: (S01) adding acrylic monomer and inorganic particles to 2a aqueous dispersion medium; (S02) stirring and mixing acrylic monomer and inorganic particles for 12 hours to 36 hours to coat the acrylic monomer or oligomer onto the surface of the inorganic particles; and (S03) adding the mixture in (S02) to 2b aqueous dispersion medium and separating the inorganic particles coated with acrylic monomer to manufacture the core-shell composite particle precursor.

[0024] According to the twelfth embodiment, in the eleventh embodiment, the precursor for manufacturing core-shell composite particles may include: (S01) adding acrylic monomers or oligomers and inorganic particles to an aqueous dispersion medium 2a; (S02) stirring and mixing the acrylic monomers or oligomers and inorganic particles for 12 to 36 hours to coat the acrylic monomers or oligomers onto the surface of the inorganic particles; and (S03) adding the mixture in (S02) to an aqueous dispersion medium 2b and separating the inorganic particles coated with acrylic monomers or oligomers.

[0025] According to the thirteenth embodiment, in any of the tenth to twelfth embodiments, the method of manufacturing a separator for a lithium secondary battery may further include: after (S20), heating the inorganic coating slurry composition at a temperature of 45°C to 85°C to convert the core-shell composite particle precursor into core-shell composite particles.

[0026] According to the fourteenth embodiment, in any of the tenth to thirteenth embodiments, (S30) drying the inorganic coating slurry composition can be carried out at a temperature of 45°C to 85°C for 1 second to 120 seconds.

[0027] According to the fifteenth embodiment, a lithium secondary battery is provided, comprising a positive electrode; a negative electrode; an electrolyte solution; and a separator located between the positive and negative electrodes, wherein the separator comprises: a porous polymer substrate; and an inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating comprising core-shell composite particles, wherein the core-shell composite particles comprise a core and a shell covering at least a portion of the surface of the core, wherein the core comprises inorganic particles, wherein the shell comprises an acrylic polymer, and wherein the acrylic polymer is formed by polymerization of acrylic monomers or oligomers.

[0028] According to the sixteenth embodiment, in the fifteenth embodiment, the adhesion strength (dry adhesion strength) of the separator relative to the electrode in the dry state can be 45 gf / 15 mm or greater.

[0029] According to the seventeenth embodiment, in either the fifteenth or sixteenth embodiment, the air permeability of the partition may be 67 seconds / 100cc or less.

[0030] According to the eighteenth embodiment, in any of the fifteenth to seventeenth embodiments, the difference between the air permeability of the partition and the air permeability of the porous polymer substrate may be 10 seconds / 100cc or less.

[0031] According to the nineteenth embodiment, in any of the fifteenth to eighteenth embodiments, the resistance characteristic may be 0.5 ohms or less.

[0032] According to the twentieth embodiment, in any of the fifteenth to nineteenth embodiments, the acrylic polymer can be formed by polymerization of acrylic monomers or oligomers during the manufacture of the battery.

[0033] Beneficial effects

[0034] The separator for lithium secondary batteries according to embodiments of this disclosure can have high adhesion strength relative to the electrode (dry adhesion strength) and good air permeability, wettability and electrical resistance characteristics.

[0035] The method for manufacturing a separator for a lithium secondary battery according to embodiments of the present disclosure provides a method for manufacturing a separator having high adhesion strength (dry adhesion strength) relative to the electrode and good air permeability, wettability and resistivity characteristics.

[0036] The effects that can be achieved through this disclosure are not limited thereto, and those skilled in the art will clearly understand these and other technical effects from the following description. Attached Figure Description

[0037] The accompanying drawings illustrate embodiments of the present disclosure and, together with the foregoing description, are intended to provide a better understanding of the technical aspects of the present disclosure; therefore, the present disclosure should not be construed as being limited to any of the drawings.

[0038] Figure 1 The structure of a partition according to an embodiment of the present disclosure is illustrated schematically.

[0039] Figure 2 The diagram schematically illustrates a core-shell composite particle / core-shell composite particle precursor according to an embodiment of the present disclosure. Detailed Implementation

[0040] The terms or words used in the specification and appended claims should not be construed as limited to their general or dictionary meanings, but should be interpreted based on their meanings and concepts corresponding to the technical aspects of this disclosure, based on the principle that the inventors are permitted to appropriately define terms for the best interpretation.

[0041] The terminology used herein is for describing embodiments of this disclosure and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms include the plural forms.

[0042] <Definition>

[0043] The terms “comprising,” “including,” and “having” are used in this specification to specify the presence of the said element, but do not exclude the presence or addition of one or more other elements unless the context clearly indicates otherwise.

[0044] The glass transition temperature (Tg) can be indicated, for example, by a dynamic mechanical analyzer (DMA) or a differential scanning calorimeter (DSC) (TA Instrument). For instance, the glass transition temperature can be indicated by a DMA measurement according to ASTM D4065.

[0045] In this specification, D 50 This refers to the particle size at the 50% point of the cumulative particle size distribution. Furthermore, D... 10 This refers to the particle size at the 10% point of the cumulative particle size distribution, and D 90 It refers to the particle size at the 90% point of the cumulative particle size distribution.

[0046] In this specification, particle size can be measured using the laser diffraction method. Specifically, the particle size distribution is calculated as follows: the powder to be measured is dispersed in a dispersion medium, fed into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in the diffraction pattern as a function of particle size is measured as the particles pass through the laser beam. The particle size distribution (D) can be measured by calculating the particle size at the 10%, 50%, and 90% points of the cumulative particle size distribution in the analyzer. 10 D 50 and D 90 .

[0047] In this specification, "acrylic acid" refers to branched or unbranched acrylic acid or methacrylic acid or derivatives thereof. Furthermore, "(meth)acrylic acid" or "(meth)acrylate" includes all acrylic acids and methacrylic acid, as well as acrylates and methacrylates.

[0048] In this specification, the weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies) under the following conditions.

[0049] - Column: PL Olexis (Polymer Laboratories)

[0050] -Dispersion medium: TCB (trichlorobenzene)

[0051] - Flow rate: 1.0 ml / min

[0052] - Sample concentration: 1.0 mg / ml

[0053] Injection volume: 200 μl

[0054] - Column temperature: 160℃

[0055] - Detector: Agilent High Temperature RI detector

[0056] - Standard: Polystyrene (fitted cubic polynomial)

[0057] <Separator for lithium secondary batteries>

[0058] This disclosure provides a separator for lithium secondary batteries.

[0059] According to aspects of this disclosure, the separator for a lithium secondary battery of this disclosure comprises: a porous polymer substrate; and an inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating comprising a core-shell composite particle precursor, wherein the core-shell composite particle precursor comprises a core and a shell covering at least a portion of the surface of the core, wherein the core comprises inorganic particles, and wherein the shell comprises an acrylic monomer or an oligomer.

[0060] Specifically, such as from Figure 1 As can be seen, the separator 10 for the lithium secondary battery of this disclosure includes: a porous polymer substrate 100; and an inorganic coating 200 present on at least one surface of the porous polymer substrate 100, the inorganic coating 200 including a core-shell composite particle precursor 210, wherein the core-shell composite particle precursor 210 includes a core portion 211 and a shell portion 212 covering at least a portion of the surface of the core portion, wherein the core portion 211 includes inorganic particles, and wherein the shell portion 212 includes acrylic monomers or oligomers.

[0061] Meanwhile, as described below, the core-shell composite particle precursor 210 can undergo polymerization to form the core-shell composite particles 210. Therefore, the inorganic coating 200 may include the core-shell composite particles 210.

[0062] In embodiments of this disclosure, acrylic monomers or oligomers may refer to acrylic monomers or acrylic oligomers.

[0063] In embodiments of this disclosure, the acrylic oligomer is a low molecular weight polymer formed by the polymerization of two or more acrylic monomers, and may be a compound containing reactive functional groups at the ends of the molecule. The acrylic oligomer may be, for example, those in which repeating units are formed by the polymerization of 2 to 10 monomer units.

[0064] Porous polymer substrate

[0065] In embodiments of this disclosure, a porous polymer substrate refers to a substrate having multiple pores internally to act as a porous ion-conducting barrier that allows ions to pass through while preventing electrical contact between the negative and positive electrodes. The pores are interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0066] The material of the porous polymer substrate can include any organic or inorganic material with electrical insulating properties. In particular, from the perspective of imparting a shut-off function to the porous polymer substrate, the material of the porous polymer substrate can preferably include thermoplastic resins. Here, the shut-off function refers to the function of the thermoplastic resin to melt and seal the pores of the porous substrate to prevent ion migration, thereby preventing thermal runaway of the battery when the temperature increases. Thermoplastic resins can include thermoplastic resins with a melting point of less than 200°C, and are preferably, in particular, polyolefins.

[0067] In addition, the porous polymer substrate may also include at least one polymer resin from the following: polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, or polyvinyl naphthalene. The porous polymer substrate may include, but is not particularly limited to, nonwoven fabrics, porous polymer films, or laminates of two or more of these materials.

[0068] In this disclosure, the thickness of the porous polymer substrate is preferably 3 μm to 12 μm, or 5 μm to 12 μm. When the thickness of the porous polymer substrate is less than the above range, its function as a conductive barrier is insufficient. In contrast, when the thickness of the porous polymer substrate is much greater than the above range (or when the porous polymer substrate is too thick), the resistance of the separator may increase too much.

[0069] In embodiments of this disclosure, the weight-average molecular weight of the polyolefin can be from 100,000 to 5,000,000. When the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. Furthermore, when the weight-average molecular weight is greater than 5,000,000, the shut-off properties may not function properly or formation may become difficult. Additionally, the puncture strength of the porous polymer substrate can be 300 gf or greater to improve production yield. The puncture strength of the porous substrate refers to the maximum puncture load (gf) measured by a puncture test using a Kato tech KES-G5 handheld compression tester under conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 4 mm / s.

[0070] In one embodiment of this disclosure, the porous polymer substrate may include any planar porous polymer substrate for use in an electrochemical device, and may include, for example, an insulating film having high ion permeability and mechanical strength, typically a pore size of 10 nm to 200 nm and a thickness typically of 5 μm to 12 μm.

[0071] In embodiments of this disclosure, depending on the type, the air permeability of the porous polymer substrate can be in the range of 40 seconds / 100cc to 70 seconds / 100cc, or 45 seconds / 100cc to 65 seconds / 100cc.

[0072] Inorganic coating

[0073] In embodiments of this disclosure, an inorganic coating is present on at least one surface of a porous polymer substrate and includes a core-shell composite particle precursor, wherein the core-shell composite particle precursor includes a core and a shell covering at least a portion of the surface of the core, wherein the core includes inorganic particles, and wherein the shell includes an acrylic monomer or oligomer.

[0074] In another embodiment of this disclosure, an inorganic coating is present on at least one surface of a porous polymer substrate and includes core-shell composite particles, wherein the core-shell composite particles include a core and a shell covering at least a portion of the surface of the core, wherein the core may include inorganic particles, and wherein the shell may include an acrylic polymer. That is, the shell may include an acrylic polymer formed by polymerization of acrylic monomers or oligomers.

[0075] In embodiments of this disclosure, in an inorganic coating, a core-shell composite particle precursor can be polymerized into a core-shell composite particle. As used herein, "core-shell composite particle / core-shell composite particle precursor" refers to common features shared between the core-shell composite particle and its precursor.

[0076] In embodiments of this disclosure, the inorganic coating may have a structure in which an interstitial volume is formed between the core-shell composite particles / core-shell composite particle precursor. Lithium ions can move through the interstitial volume. That is, the interstitial volume can refer to the pores (voids) formed between the binder polymers, monomers, or oligomers made of binder polymers in the shell when bonded together. Through the interstitial volume, the separator can have high electrode-separator adhesion strength in the dry state (dry adhesion strength) as well as good air permeability and electrical resistance characteristics.

[0077] In embodiments of this disclosure, the core-shell composite particle / core-shell composite particle precursor may have a single-phase particle structure (such as core-shell) or a multi-phase particle structure (such as core-first shell-second shell).

[0078] In embodiments of this disclosure, the core-shell composite particles / core-shell composite particle precursors may have spherical, elliptical, oval, plate-like, or irregular particle shapes. The shape of the core-shell composite particles / core-shell composite particle precursors can be observed, for example, by scanning electron microscopy (SEM).

[0079] In embodiments of this disclosure, based on 100% by weight of the inorganic coating, it may contain 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more of the core-shell composite particles / core-shell composite particle precursor. That is, the inorganic coating may substantially comprise the core-shell composite particles / core-shell composite particle precursor.

[0080] In embodiments of this disclosure, the inorganic coating may substantially exclude other types of adhesive polymers. That is, based on 100% by weight of the inorganic coating, the inorganic coating may contain amounts 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 of other types of adhesive polymers.

[0081] In this context, other types of adhesive polymers may refer to adhesive polymers that are different from those included in the shell of the core-shell composite particle, and are not limited to a specific type. For example, other types of adhesive polymers may include fluorinated adhesive polymers or acrylic adhesive polymers. Fluorinated adhesive polymers and acrylic adhesive polymers may be the same as those described below.

[0082] In embodiments of this disclosure, the inorganic coating can provide good separator heat resistance due to the core of the core-shell composite particles, and ensure the bonding strength of the core-shell composite particles and the electrode-separator adhesion strength due to the shell. Therefore, the inorganic particles can be substantially free of binder polymers. Consequently, the separator can have high electrode-separator adhesion strength as well as good air permeability and electrical resistance characteristics.

[0083] nuclear department

[0084] In embodiments of this disclosure, the core comprises inorganic particles. The inorganic particles are not limited to specific types and may include any electrochemically stable particles. That is, the inorganic particles that can be used in this disclosure are not limited to specific types and may include those within the operating voltage range of the applied electrochemical device (e.g., 0 to 5V for Li / Li). +Inorganic particles of any type that do not drive oxidation and / or reduction reactions. In particular, when inorganic particles with high dielectric constants are used as inorganic particles, they can help increase the degree of dissociation of electrolyte salts (e.g., lithium salts) in liquid electrolytes, thereby improving the ionic conductivity of the electrolyte solution.

[0085] For the reasons stated above, inorganic particles preferably include high dielectric constant inorganic particles with a dielectric constant of 5 or greater, preferably 10 or greater. Non-limiting examples of inorganic particles with a dielectric constant of 5 or greater include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb... 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 Hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, or mixtures thereof.

[0086] Furthermore, inorganic particles may include inorganic particles capable of transporting lithium ions, i.e., inorganic particles containing lithium but not storing lithium and having the function of moving lithium ions. Non-limiting examples of inorganic particles capable of transporting lithium ions include: lithium phosphate (Li3PO4); 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 Base 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 , 0 < x < 4, 0< y < 1, 0 < z < 1, 0 < w <5), such as Li 3.25 Ge0.25 P 0.75 S4; lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as Li3N; SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li3PO4-Li2S-SiS2; P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI-Li2S-P2S5; or a mixture thereof.

[0087] In addition, the average particle size of the inorganic particles is not limited to a specific range, but is preferably 0.1 μm to 2.0 μm, or 0.2 μm to 1.8 μm, to form a coating having a uniform thickness and an optimal porosity. When the average particle size of the inorganic particles is below the lower limit, the heat resistance of the separator can be reduced, and when the average particle size of the inorganic particles is above the upper limit, an inorganic coating having a larger thickness can be formed.

[0088] In an embodiment of the present disclosure, based on 100% by weight of the core-shell composite particles / core-shell composite particle precursors, the inorganic particles can be included in an amount within the range of 10% to 90% by weight. That is, based on 100% by weight of the core-shell composite particles, the core part can be included in an amount within the range of 10% to 90% by weight.

[0089] shell

[0090] In an embodiment of the present disclosure, the core-shell composite particle precursors include a core part and a shell part covering at least a part of the surface of the core part, and the shell part includes an acrylic monomer or oligomer. The acrylic monomer or oligomer can be bonded, attached or applied to at least a part of the surface of the core part.

[0091] In an embodiment of the present disclosure, the thickness of the shell part can be 10 nm to 40 nm, 20 nm to 38 nm, 21 nm to 37 nm, 25 nm to 35 nm, or 28 nm to 33 nm. When the thickness of the shell part falls within the above range, the adhesion strength and air permeability of the core-shell composite particles can be improved. In addition, the inorganic particles are prevented from being exposed, so that the resistance characteristics are improved.

[0092] The shell thickness can be calculated by measuring the size of the inorganic particle, measuring the size of the core-shell composite particle precursor, and subtracting the size of the inorganic particle from the size of the core-shell composite particle precursor. Alternatively, the shell thickness can be determined by scanning electron microscopy (SEM) measurements and image analysis.

[0093] In embodiments of this disclosure, the acrylic monomer or oligomer may include a thermally polymerizable acrylic monomer or oligomer.

[0094] In embodiments of this disclosure, when the acrylic monomer or oligomer includes a thermally polymerizable acrylic monomer or oligomer, the thermally polymerizable acrylic monomer or oligomer can be formed by thermal polymerization of the thermally polymerizable acrylic monomer at a predetermined temperature or above a predetermined temperature. The thermally polymerizable acrylic monomer or oligomer can be a polymer of a thermally polymerizable acrylic monomer polymerized at temperatures of 45°C to 85°C or 50°C to 70°C.

[0095] The temperature at which thermopolymerizable acrylic monomers are thermally polymerized can vary depending on their structure. Therefore, the polymerization initiation temperature of acrylic monomers can be controlled by changing the type of acrylic monomer and the type of initiator. When the polymerization initiation temperature of acrylic monomers falls within the aforementioned temperature range, the acrylic monomers crosslink at temperatures higher than room temperature, and do not polymerize during normal natural drying. Thus, the initiation of polymerization can be controlled. Furthermore, because the polymerization of acrylic monomers does not require high temperatures, the properties of the porous polymer substrate may not deteriorate.

[0096] In embodiments of this disclosure, the thermopolymerizable acrylic monomer can be a branched or linear compound having 2 to 16, 2 to 14, or 2 to 12 carbon atoms. When the number of carbon atoms in the thermopolymerizable acrylic monomer falls within the above range, the adhesive properties of the monomer can be improved.

[0097] In embodiments of this disclosure, the thermally polymerizable acrylic monomer or oligomer may be at least one monomer selected from the following: butylacrylate, β-carboxyethylacrylate, 2-ethylhexylacrylate, 2-methoxyethylacrylate, 4-hydroxybutylacrylate, ethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, pentylmethacrylate, 2-hydroxymethylacrylate, ethylmethacrylate, methylmethacrylate, acrylic acid, and acrylonitrile, or an oligomer comprising at least one repeating unit derived therefrom.

[0098] In embodiments of this disclosure, when the acrylic monomer or oligomer includes a thermally polymerizable acrylic monomer or oligomer, the shell portion may also include a thermal polymerization initiator.

[0099] Thermal polymerization initiators are known in the field of acrylic monomer polymerization technology and can be used in this disclosure. Typical thermal polymerization initiators available in this disclosure include radical-generating organic peroxides, organic hydroperoxides, and azo initiators. Available organic peroxides may include, but are not limited to, compounds such as benzoyl peroxide, di-tert-amyl peroxide, tert-butyl peroxide, and dicumyl peroxide. Available organic hydroperoxides may include, but are not limited to, compounds such as tert-amyl hydroperoxide and tert-butyl hydroperoxide. Available azo initiators may include VAZO compounds from DuPont, such as VAZO TM 52 (2,2′-azobis(2,4-dimethylpentanonitrile)), VAZO TM 64 (2,2′-azobis(2-methylpropionitrile)), VAZO TM 67 (2,2′-azobis(2-methylbutyronitrile)), and VAZO TM 88 (2,2′-azobis(cyclohexanecarboxynitrile)), but not limited to this).

[0100] In embodiments of this disclosure, based on 100 parts by weight of thermally polymerizable acrylic monomer or oligomer, the amount of thermal polymerization initiator contained in the shell portion can be from 0.01 parts by weight to 20 parts by weight, but the amount of thermal polymerization initiator can be varied depending on process efficiency or the properties of the polymer.

[0101] In embodiments of this disclosure, the inorganic coating may substantially exclude particulate binder polymers, or, if present, may include amounts 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 of particulate binder polymers. A small amount of particulate binder may be included for bonding between the core-shell composite particle precursors, or it may be substantially absent. When the above numerical ranges are met, the electrical resistance characteristics and permeability of the separator can be improved.

[0102] Particulate binder polymers can possess the property of retaining their original particle shape without alteration when dispersed in a dispersion medium. Specifically, the particulate binder polymer can exist in a particulate state within an aqueous dispersion medium. Specifically, due to its low solubility in aqueous solvents, the particulate binder polymer can be dispersed in the particulate phase within the aqueous dispersion medium. The aspect ratio of the particulate binder polymer in the aqueous dispersion medium can range from 1.0 to 1.5, 1.0 to 1.3, or 1.0 to 1.2. In this case, the aspect ratio is defined as the ratio of the length of the primary axis to the secondary axis of the particulate binder, and as the aspect ratio approaches 1, the shape can become closer to a sphere. The aspect ratio can be calculated, for example, using a particle shape analyzer (QICPIC-LIXELL, Sympatec GmbH).

[0103] In embodiments of this disclosure, the particulate adhesive polymer may include acrylic particulate adhesive polymers, fluoropolymer particulate adhesive polymers, or combinations thereof.

[0104] In embodiments of this disclosure, the acrylic particulate adhesive polymer may include, for example, an acrylic homopolymer, i.e., a polymer composed of a single type of acrylic monomer, or a copolymer of an acrylic monomer and another monomer. For example, the acrylic particulate adhesive polymer may include poly(methyl methacrylate), poly(ethylhexyl acrylate), poly(butyl acrylate), poly(acrylonitrile), copolymers of ethylhexyl acrylate and methyl methacrylate, copolymers of butyl acrylate and 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.

[0105] In embodiments of this disclosure, the fluorine-based particulate adhesive polymer may include, for example, a polyvinylidene fluoride (PVDF) homopolymer, and a copolymer of repeating units derived from PVDF and another repeating unit. For example, fluoropolymer particulate adhesives may include repeating units derived from vinylidene fluoride and copolymers selected from at least one of the following: repeating units derived from trifluoroethylene (TrFE), repeating units derived from tetrafluoroethylene (TFE), repeating units derived from hexafluoropropylene (HFP), repeating units derived from trichloroethylene (TrCE), repeating units derived from trichlorofluoroethylene (TCFE), repeating units derived from chlorotrifluoroethylene (CTFE), repeating units derived from polymethyl methacrylate (PMMA), and repeating units derived from polyvinylacetate (PVAc), or mixtures of two or more of these.

[0106] In embodiments of this disclosure, the glass transition temperature (Tg) of the particulate adhesive polymer can be from 30°C to 90°C, or from 50°C to 80°C. When the particulate adhesive polymer has the above-mentioned glass transition temperature, the adhesive can lose its particle shape during the manufacture of the separator and form a film under predetermined temperature and pressure conditions.

[0107] In embodiments of this disclosure, the D of the particulate adhesive polymer 50 The size can be from 150 nm to 1 μm, or from 200 nm to 800 nm. When the size of the particulate adhesive polymer falls within the above range, the adhesion strength and porosity of the separator can be improved.

[0108] In embodiments of this disclosure, the inorganic coating may include core-shell composite particles formed by polymerization of core-shell composite particle precursors.

[0109] In embodiments of this disclosure, the core-shell composite particle may include a core and a shell covering at least a portion of the surface of the core, and the shell may include an acrylic polymer. The acrylic polymer may be bonded, attached, or applied to at least a portion of the surface of the core.

[0110] In embodiments of this disclosure, the thickness of the shell containing the acrylic polymer can be substantially the same as the thickness of the shell containing the acrylic monomer or oligomer. The thickness of the shell containing the acrylic polymer can be, for example, 10 nm to 40 nm, 20 nm to 38 nm, 21 nm to 37 nm, 25 nm to 35 nm, or 28 nm to 33 nm. When the shell thickness falls within the above range, the adhesion strength and air permeability of the core-shell composite particles can be improved. Furthermore, the exposure of inorganic particles is avoided, resulting in improved electrical resistance characteristics.

[0111] In embodiments of this disclosure, the acrylic polymer can be formed by the polymerization of the aforementioned acrylic monomers or oligomers.

[0112] <Method for manufacturing separators for lithium secondary batteries>

[0113] This disclosure provides a method for manufacturing a separator for lithium secondary batteries.

[0114] According to aspects of this disclosure, a method for manufacturing a separator for a lithium secondary battery includes: (S10) preparing an inorganic coating slurry composition comprising a core-shell composite particle precursor and a first dispersion medium; (S20) applying the inorganic coating slurry composition to at least one surface of a porous polymer substrate; and (S30) drying the inorganic coating slurry composition.

[0115] The following sections will describe in detail each step of the method for manufacturing separators for lithium secondary batteries.

[0116] First, an inorganic coating slurry composition comprising a core-shell composite particle precursor and a first dispersion medium is prepared (S10).

[0117] Core-shell composite particle precursors refer to particles that can be converted into core-shell composite particles. Core-shell composite particle precursors may include a slurry composition comprising inorganic particles and an acrylic monomer covering at least a portion of the surface of the inorganic particles.

[0118] In embodiments of this disclosure, prior to step (S10), the method may further include the step of adding acrylic monomers and inorganic particles to a second aqueous dispersion medium and mixing them together to prepare a core-shell composite particle precursor.

[0119] In embodiments of this disclosure, the steps for preparing the core-shell composite particle precursor include the following steps: (S01) adding acrylic monomers or oligomers and inorganic particles to an aqueous dispersion medium 2a; (S02) stirring and mixing the acrylic monomers or oligomers and inorganic particles for 12 to 36 hours to coat the acrylic monomers or oligomers onto the surface of the inorganic particles; and (S03) adding the mixture from step (S02) to an aqueous dispersion medium 2b and separating the inorganic particles coated with acrylic monomers or oligomers.

[0120] Specifically, acrylic monomers or oligomers and inorganic particles can be dispersed in an aqueous dispersion medium (2a), and stirred and mixed for a sufficient time of 12 to 36 hours to coat the acrylic monomers onto the surface of the inorganic particles. When the mixing time is below the lower limit, the acrylic monomers or oligomers may not be adequately coated onto the surface of the inorganic particles. When the mixing time is above the upper limit, it may reduce the efficiency of the manufacturing process.

[0121] Subsequently, the solids and particles in the mixture are added to and mixed together in the 2b aqueous dispersion medium, and the inorganic particles coated with acrylic monomers or oligomers are separated from the mixture and dispersed again in the first dispersion medium to produce a core-shell composite particle precursor. When the above steps are further included, the acrylic monomers are not located in the interstitial volume between the core-shell composite particles / core-shell composite particle precursor, thereby improving air permeability and electrical resistance properties.

[0122] In embodiments of this disclosure, the acrylic monomer or oligomer may include thermally polymerizable acrylic monomers or oligomers. Meanwhile, the inorganic particles, acrylic monomers, and thermally polymerizable acrylic monomers or oligomers may be the same as those described above.

[0123] In embodiments of this disclosure, the dispersion medium (i.e., the first dispersion medium) may include an aqueous dispersion medium or an organic dispersion medium.

[0124] In embodiments of this disclosure, the aqueous dispersion medium, 2a, and 2b may include water. Furthermore, when there are limitations on drying rate and temperature, methanol, ethanol, or isopropanol, which have lower boiling points than water, may be used as co-dispersion media.

[0125] In embodiments of this disclosure, the organic dispersion medium may include: for example, cyclic aliphatic hydrocarbons, such as cyclopentane or cyclohexane; aromatic hydrocarbons, such as toluene, xylene, or ethylbenzene; ketones, such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, or ethylcyclohexane; chlorinated aliphatic hydrocarbons, such as dichloromethane, chloroform, or carbon tetrachloride; esters, such as ethyl acetate, butyl acetate, γ-butyrolactone, or ε-caprolactone; nitriles, such as acetonitrile or propionitrile; ethers, such as tetrahydrofuran or ethylene glycol diethyl ether; alcohols, such as methanol, ethanol, isopropanol, ethylene glycol, or ethylene glycol monomethyl ether; or amides, such as N-methylpyrrolidone or N,N-dimethylformamide, and, for its advantages in drying processes, the dispersion medium may include acetone.

[0126] In embodiments of this disclosure, the weight ratio of acrylic monomers or oligomers to inorganic particles can be 1:99 to 99:1, 10:90 to 90:10, or 20:80 to 80:20.

[0127] Subsequently, the inorganic coating slurry composition is applied to at least one surface of the porous polymer substrate (S20).

[0128] Methods of applying an inorganic coating slurry composition to at least one surface of a porous polymer substrate may include, for example, dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roller coating, Mayer bar coating, direct metering coating, or a combination thereof.

[0129] In embodiments of this disclosure, after step (S20), the method may further include the step of heating the inorganic coating slurry composition at a temperature of 45°C to 85°C or 50°C to 70°C to convert the core-shell composite particle precursor into core-shell composite particles. Specifically, when the inorganic coating slurry composition is heated at a temperature within the above range, the thermally polymerizable acrylic monomers of the core-shell composite particle precursor may undergo polymerization to form a thermally polymerized acrylic polymer.

[0130] In embodiments of this disclosure, the step of converting the core-shell composite particle precursor into core-shell composite particles can be performed, for example, simultaneously with the process of placing a separator between the positive and negative electrodes to manufacture an electrode assembly, followed by lamination. In this case, the contact area between the separator and the electrode can be increased, and the electrode-separator bonding strength can be increased.

[0131] The temperature at which thermally polymerized acrylic polymers are polymerized can vary depending on the structure of the thermally polymerizable acrylic monomers or oligomers. Therefore, the starting temperature for the polymerization of acrylic monomers can be controlled by changing the type of acrylic monomer. Because the polymerization of acrylic monomers does not require high temperatures, the properties of the porous polymer substrate may not deteriorate.

[0132] Subsequently, the inorganic coating slurry composition is dried (S30). In embodiments of this disclosure, the drying time can be from 1 minute to 10 hours, and the drying temperature can be in the range of 30°C to 100°C. The drying method is not limited to a particular one and can include any method for removing the dispersion medium from the separator, and, for example, suitable methods can include any one of convection drying and hot air drying, or a combination thereof.

[0133] In embodiments of this disclosure, the step (S30) of drying the inorganic coating slurry composition can be performed at a temperature of 45°C to 85°C for 1 second to 120 seconds. In this case, the conversion of the core-shell composite particle precursor into core-shell composite particles and the drying of the inorganic coating slurry composition can be carried out simultaneously.

[0134] In embodiments of this disclosure, the method for manufacturing a separator for a lithium secondary battery can control the polymerization step to manufacture a separator for a lithium secondary battery comprising an inorganic coating containing a core-shell composite particle precursor, and a separator for a lithium secondary battery comprising an inorganic coating containing a core-shell composite particle.

[0135] <Lithium secondary batteries>

[0136] This disclosure provides a lithium secondary battery.

[0137] According to aspects of this disclosure, the lithium secondary battery of this disclosure includes a positive electrode; a negative electrode; an electrolyte solution; and a separator located between the positive electrode and the negative electrode, wherein the separator includes: a porous polymer substrate; and an inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating including core-shell composite particles, wherein the core-shell composite particles include a core and a shell covering at least a portion of the surface of the core, wherein the core includes inorganic particles, wherein the shell includes an acrylic polymer, and wherein the acrylic polymer is formed by polymerization of acrylic monomers or oligomers.

[0138] In embodiments of this disclosure, the positive electrode can be manufactured by coating a positive electrode composition onto a positive electrode current collector, the positive electrode composition comprising a positive electrode active material, a binder, a conductive material, and a dispersion medium.

[0139] The positive electrode active material may include any positive electrode active material commonly used in the positive electrode of an electrochemical device. For example, positive electrode active materials may include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides thereof.

[0140] In this case, based on the total solid weight of the cathode composition, the content of the cathode active material can be from 80% to 99% by weight, preferably from 85% to 98% by weight. When the amount of cathode active material falls within the above range, improved capacity characteristics can be provided.

[0141] The positive electrode current collector is not limited to a specific type and can include any material that is conductive without causing chemical changes in the corresponding battery. For example, the positive electrode current collector can include: stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver.

[0142] Adhesives are used to help hold the active and conductive materials together and bind them to the current collector, and are typically added in amounts from 1% to 30% by weight based on the total solid weight of the cathode composition. Examples of adhesives may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, or various copolymers.

[0143] Conductive materials can typically be added in amounts ranging from 1% to 30% by weight based on the total solid weight of the positive electrode composition.

[0144] Conductive materials are not limited to a specific type and can include any material that is conductive without causing chemical changes in the corresponding battery. Conductive materials can include, for example, graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or pyrolytic black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black from Chevron Chemical Company or Denka Singapore Private Limited, products from Gulf Oil Company, Ketjenblack, the EC series (from Armak Company), Vulcan XC-72 (from Cabot Company), and Super P (from Timcal).

[0145] In addition, if desired, the positive electrode active material layer may optionally include a dispersant.

[0146] The dispersant is not limited to a specific type and can include any dispersant for the positive electrode, and, for example, aqueous dispersants or organic dispersants can be selectively used as needed. Preferably, the dispersant may include any of the following: cellulose-based compounds, polyepoxides, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosan, starch, amylose, polyacrylamide, poly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly(2-methoxyethoxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile / butadiene / styrene (ABS) polymers, acrylonitrile / styrene / acrylate (ASA) polymers, mixtures of acrylonitrile / styrene / acrylate (ASA) polymers and propylene carbonate, styrene / acrylonitrile (SAN) copolymers, methyl methacrylate / acrylonitrile / butadiene / styrene (MABS) polymers, styrene-butadiene rubber, nitrile rubber, and fluororubber, or mixtures of two or more thereof. Hydrogenated nitrile rubber (H-NBR) may be used. When the positive electrode active material layer further includes a dispersant, the dispersion of the components (especially the conductive material) of the positive electrode active material layer can be improved, but is not limited thereto.

[0147] In addition, the dispersion medium may include any dispersion medium commonly used in the corresponding technical field. For example, the dispersion medium may include any one of the following: dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, or water, or a mixture of two or more of them. The dispersion medium is used in an amount sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder, considering the coating thickness of the slurry or the production yield, and changes the viscosity to achieve high thickness uniformity in the subsequent coating process to manufacture the positive electrode.

[0148] The negative electrode according to the present disclosure can be manufactured by coating a negative electrode composition on a negative electrode current collector, and the negative electrode composition includes a negative electrode active material, a binder, a conductive material, and a dispersion medium. In addition, if necessary, the negative electrode composition may optionally further include a dispersant.

[0149] The negative electrode active material may include a compound capable of reversibly inserting and extracting lithium. Preferably, the negative electrode may also include a negative electrode active material exhibiting high capacity characteristics, such as a silicon-based negative electrode active material; a carbon-based negative electrode active material; a metal composite oxide, such as Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Groups 1, 2, and 3 in the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; tin-based alloy; metal oxides, such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, SbX2O3, SbX2O4, SbX2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers, such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; or lithium titanium oxides. The silicon-based negative electrode active material may include at least one selected from the group consisting of: Si, SiO x (0.1 < x < 5), Si-metal alloy, silicon oxide particles doped or chemically combined with a metal (such as Mg) (SiO x , 0.1 < x < 5), and Si-SiO xAn alloy (0.1 < x < 5). The carbon-based negative electrode active material may include at least one selected from the group consisting of: natural graphite, artificial graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon.

[0150] The negative electrode current collector is not limited to a specific type and may include any material having high electrical conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may include: copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel treated with carbon, nickel, titanium, or silver on the surface, or an aluminum-cadmium alloy. In addition, the thickness of the negative electrode current collector may generally be 3 μm to 500 μm, and in the same manner as the positive electrode current collector, the negative electrode current collector may have a micro-textured surface to increase the bonding strength of the negative electrode active material. The negative electrode current collector may appear in different forms, such as a film, sheet, foil, mesh, porous body, foam, or non-woven fabric.

[0151] The conductive material, binder, dispersion medium, or dispersant contained in the negative electrode composition is not limited to a specific type and may include those commonly used in electrode compositions, and for example, the above-mentioned conductive material, binder, dispersion medium, or dispersant may be used in the positive electrode composition.

[0152] In addition, the lithium secondary battery may further include an electrolyte solution. The electrolyte solution may include, but is not limited to, an organic liquid electrolyte solution, an inorganic liquid electrolyte solution, a solid polymer electrolyte solution, a gel polymer electrolyte solution, a solid inorganic electrolyte solution, or a molten inorganic electrolyte solution that can be used to manufacture a lithium secondary battery.

[0153] Specifically, the electrolyte solution may include an organic dispersion medium and a lithium salt.

[0154] Organic dispersion media are not limited to a specific type and can include any organic dispersion media that acts as a medium for ion movement involved in electrochemical reactions used in batteries. Specifically, organic dispersion media can include: ester-based dispersion media, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether-based dispersion media, such as dibutyl ether or tetrahydrofuran; ketone-based dispersion media, such as cyclohexanone; aromatic hydrocarbon-based dispersion media, such as benzene or fluorobenzene; carbonate-based dispersion media, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate. Carbonate-based dispersion media include: ethanol or isopropanol; nitriles, such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon, and may include exocyclic double bonds or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Carbonate-based dispersion media are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which contribute to improving the charge / discharge performance of the battery, with low-viscosity straight-chain carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, when cyclic carbonates and straight-chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte solution can exhibit improved performance.

[0155] Lithium salts are not limited to a specific type and can include any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, lithium salts may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of lithium salts can range from 0.1 M to 2.0 M. When the concentration of lithium salts falls within the above range, the electrolyte solution can have optimal conductivity and viscosity, thereby improving the performance of the electrolyte solution and the efficient movement of lithium ions.

[0156] In addition to the components described above, the electrolyte solution may also include at least one type of additive, such as alkylene carbonate halogenated compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, prevent battery capacity decay, and increase battery discharge capacity. In this case, the additive content may be from 0.1 parts by weight to 5 parts by weight based on the total weight of 100 parts by weight of the electrolyte solution.

[0157] In embodiments of this disclosure, the adhesion strength of the separator to the electrode in a dry state (dry adhesion strength) can be 45 gf / 15 mm or greater, or 48 gf / 15 mm or greater. Preferably, the dry adhesion strength can be 100 gf / 15 mm or less, or 90 gf / 15 mm or less.

[0158] In embodiments of this disclosure, the air permeability of the partition can be 67 seconds / 100cc or less, or 65 seconds / 100cc or less. Preferably, the air permeability of the partition can be 45 seconds / 100cc or more, or 50 seconds / 100cc or more.

[0159] In embodiments of this disclosure, the difference between the permeability of the separator and the permeability of the porous polymer substrate can be 10 seconds / 100cc or less, 7 seconds / 100cc or less, or 5 seconds / 100cc or less. When the permeability difference falls within the above range, it indicates that the permeability of the separator is substantially not reduced by forming the inorganic coating, which suggests that pore blockage caused by the inorganic coating can be minimized. Furthermore, this structure can help improve electrolyte wettability and prevent a decrease in initial ionic conductivity and charge / discharge characteristics.

[0160] In embodiments of this disclosure, the resistance characteristic may be 0.5 ohms or less, or 0.48 ohms or less. When the resistance characteristic falls within the above range, the initial ionic conductivity can be improved, voltage drop during high-rate charging / discharging can be reduced or prevented, and the battery's output characteristics can be improved. Furthermore, the increase in internal resistance during long-term cycling can be suppressed, thereby preventing a decline in lifespan characteristics.

[0161] In embodiments of this disclosure, the acrylic polymer can be formed by polymerizing acrylic monomers or oligomers during battery manufacturing. After coating formation, the acrylic monomers or oligomers in the inorganic coating can be converted into acrylic polymers through polymerization processes such as lamination, thermal curing, or UV irradiation. Through the above manufacturing method, the acrylic polymer in the coating can be uniformly bonded to the surface of the inorganic particles and the substrate, thereby ensuring good adhesion strength and mechanical stability, and maintaining good permeability and electrolyte wettability without excessively clogging the pore structure.

[0162] The present disclosure will be described in more detail below by way of examples, but the following examples are intended to describe the present disclosure by way of illustration and the scope of the present disclosure is not limited thereto.

[0163] <Example 1>

[0164] At room temperature, aluminum oxide (Al2O3, D 50 Alumina (450 nm, Sumitomo) was added as inorganic particles and butyl acrylate as an acrylic monomer to water (2a, aqueous dispersion medium). The mixture was then stirred at 500 rpm for 24 hours using a homogenizer to coat the alumina surface with butyl acrylate. The stirred mixture was then redispersed in water (2b, aqueous dispersion medium), and the solids (i.e., the core-shell composite particle precursor) were removed from the dispersion and added to water (first dispersion medium) to prepare an inorganic coating slurry composition containing the core-shell composite particle precursor. In this case, the inorganic coating slurry composition had a solids content of 35% by weight and an inorganic particle:acrylic monomer weight ratio of 80:20.

[0165] An inorganic coating slurry composition was applied to both surfaces of a 9 μm thick polypropylene substrate (air permeability: 59 s / 100 cc) using a doctor blade and dried at 60°C for 60 seconds to form an inorganic coating of 1.5 μm thickness on each of the two surfaces, thereby producing a separator of approximately 12 μm thickness.

[0166] In this case, the D of the core-shell composite particle was confirmed.50 The particle size is 510 nm, and the shell thickness is 30 nm. The shell thickness is determined by the D of the inorganic particles. 50 D and core-shell composite particles 50 Calculations were performed. Simultaneously, the weight ratio of the core to the shell was 80:20.

[0167] <Reference Example>

[0168] The reference example was prepared in essentially the same manner as in Example 1, except that the inorganic coating slurry composition was applied to both surfaces of a 9 μm thick polypropylene substrate (air permeability: 59 s / 100 cc) using a doctor blade and dried at 30°C for 60 seconds to form an inorganic coating with a thickness of 1.5 μm on each of the two surfaces, thereby producing a separator with a thickness of approximately 12.2 μm.

[0169] In other words, the difference between the reference example and Example 1 is that the core-shell composite particle precursor was not polymerized.

[0170] In this case, the D of the core-shell composite particle was confirmed. 50 The thickness is 505 nm, and the shell thickness is 27.5 nm.

[0171] <Comparative Example 1>

[0172] At room temperature, aluminum oxide (Al2O3, D 50 (450 nm, Sumitomo) as inorganic particles and methyl (acrylate) monomer as acrylic monomer were added to water. Subsequently, the mixture was mixed for 1 hour using a bead mill disperser to prepare the inorganic coating slurry composition. In this case, the inorganic coating slurry composition had a solids content of 35% by weight and the weight ratio of inorganic particles to acrylic monomer was 80:20.

[0173] An inorganic coating slurry composition was applied to both surfaces of a 9 μm thick polypropylene substrate (air permeability: 59 s / 100 cc) using a doctor blade and dried at 60°C for 60 seconds to form an inorganic coating with a thickness of 1.5 μm on each of the two surfaces, thereby producing a separator with a thickness of approximately 12.1 μm.

[0174] In other words, compared to Example 1, in Comparative Example 1, the alumina and acrylic monomers were not sufficiently mixed, and the acrylic monomers were not coated or not fully coated on the surface of the alumina. Also, unlike Example 1, the step of separating the core-shell composite particle precursor was not performed, so the acrylic monomers existed alone in the inorganic coating slurry composition.

[0175] In this case, the D of the solid in the inorganic coating was confirmed. 50 The particle size is 520 nm.

[0176] <Comparative Example 2>

[0177] At room temperature, aluminum oxide (Al2O3, D 50 (450 nm, Sumitomo) as an inorganic particulate and acrylic particulate binder (polyacrylate, Tg: 40℃, D 50 A particulate binder polymer (400 nm) was added to water and stirred uniformly to prepare a slurry composition. In this case, the solids content of the slurry composition was 35% by weight, and the weight ratio of inorganic particles to particulate binder polymer was 80:20.

[0178] The slurry composition was applied to both surfaces of a 9 μm thick polypropylene substrate (air permeability: 59 s / 100 cc) using a doctor blade and dried at 40°C for 120 seconds to form an inorganic coating of 1.5 μm thickness on each of the two surfaces, thereby producing a separator with a thickness of approximately 12.1 μm.

[0179] <Experimental Example>

[0180] For each of the Examples and Comparative Examples, the air permeability, dry adhesion strength, and electrical properties were evaluated as follows and summarized in Table 1 below.

[0181] [Table 1]

[0182]

[0183] It can be confirmed that, compared to the comparative example, Example 1 exhibits high air permeability and low electrical resistance due to its structure forming interstitial volumes between the core-shell composite particles. Specifically, the separator of Example 1, which has an inorganic coating on a porous polymer substrate (air permeability: 59 sec / 100 cc), shows an increase in air permeability of only 4 sec / 100 cc. Furthermore, it can be confirmed that Example 1, which does not include polymers in its inorganic coating and includes acrylic polymers in its shell, exhibits good dry adhesion strength. On the other hand, it can be confirmed that the reference example has high air permeability because it has a structure forming interstitial volumes between the core-shell composite particle precursors. Specifically, it can be confirmed that the separator of the reference example, which has a porous coating including core-shell composite particle precursors on a porous polymer substrate with an air permeability of 59 sec / 100 cc, shows an increase in air permeability of only 1 sec / 100 cc, indicating substantially the same air permeability. However, because the acrylic monomers are not polymerized, low dry adhesion strength is confirmed.

[0184] Furthermore, as a result of comparing Example 1 with the reference example, it can be confirmed that Example 1 (in which the core-shell composite particle precursor is converted into core-shell composite particles by thermal polymerization) shows an increase in air permeability of 3 seconds / 100cc and an increase in adhesion strength relative to the electrode of at least about 19%.

[0185] In contrast, Comparative Example 1, which includes inorganic particles, incomplete core-shell composite particles, and an acrylic polymer made from acrylic monomers between the particles, has a lower air permeability than Example 1. Furthermore, due to the inclusion of the acrylic polymer, pore blockage occurs, significantly increasing the air permeability compared to Example 1. Additionally, pore blockage was confirmed to lead to high electrical resistance.

[0186] Comparative Example 2 was confirmed to have poor air permeability and increased resistance due to electrolyte absorption by the particulate adhesive.

[0187] <Evaluation Methods>

[0188] Thickness measurement

[0189] The thickness of the partition in each embodiment and comparative example was measured using a thickness gauge (Mitutoyo, VL-50S-B), and the results are summarized in Table 1.

[0190] Breathability evaluation

[0191] The air permeability time of the partitions in each embodiment and comparative example was measured using a measuring instrument (Asahi Seiko Co., Ltd.), and the results are shown in Table 1. As described herein, air permeability time refers to the time (in seconds) required for 100 ml of air to pass through a 1 square inch area under a pressure of 12.2 inches of water column.

[0192] Dry adhesion strength

[0193] The electrode plates manufactured in each of the examples and comparative examples were cut to a width of 15 mm and fixed to a glass slide. The current collector was peeled off at a speed of 300 mm / min to measure the 180-degree peel strength, and the results are shown in Table 1.

[0194] Resistance characteristic evaluation

[0195] LiCoO2 (as the positive electrode active material), carbon black (as the conductive material), and polyvinylidene fluoride (PVdF) (as the binder) were added to N-methylpyrrolidone (NMP) (as the dispersion medium) in a weight ratio of 85:5:15 to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated onto a sheet aluminum current collector and dried to prepare a sample with a capacitance of 3.3 mAh / cm². 2 The final positive electrode load is the positive electrode.

[0196] Artificial graphite as the negative electrode active material, carbon black as the conductive agent, and polyvinylidene fluoride (PVdF) as the binder were mixed in a weight ratio of 75:5:25, and N-methylpyrrolidone (NMP) as the dispersion medium was added to the mixture to prepare a negative electrode slurry. The negative electrode slurry was prepared at a concentration of 3.8 mAh / cm³. 2 The loading amount is coated onto a copper current collector and dried to prepare a negative electrode with a negative electrode active material layer.

[0197] The separators of each of the examples and comparative examples were thoroughly immersed in an electrolyte containing 1 M LiPF6, 2 wt% VC, and ethylene carbonate (EC) / ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and button cells were manufactured using the separators prepared in this way. The button cells were left to stand at room temperature for 1 day, and the separator resistance (ER) and ionic conductivity were measured using a potentiostat by impedance measurement.

Claims

1. A separator for a lithium secondary battery, comprising: Porous polymer substrate; and An inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating comprising a core-shell composite particle precursor. The core-shell composite particle precursor includes a core and a shell covering at least a portion of the surface of the core. The core comprises inorganic particles, and The shell portion comprises acrylic monomers or oligomers.

2. The separator for lithium secondary batteries according to claim 1, The acrylic monomer or oligomer mentioned therein includes thermally polymerizable acrylic monomers or oligomers.

3. The separator for lithium secondary batteries according to claim 2, The thermally polymerizable acrylic monomer or oligomer is polymerized at a temperature of 45°C to 85°C to form a thermally polymerized acrylic polymer.

4. The separator for lithium secondary batteries according to claim 2, The thermally polymerizable acrylic monomer or oligomer mentioned therein is a monomer selected from at least one of the following: butylacrylate, β-carboxyethylacrylate, 2-ethylhexylacrylate, 2-methoxyethylacrylate, 4-hydroxybutylacrylate, ethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, pentylmethacrylate, 2-hydroxymethylacrylate, ethylmethacrylate, methylmethacrylate, acrylic acid, and acrylonitrile, or an oligomer containing at least one repeating unit derived therefrom.

5. The separator for lithium secondary batteries according to claim 1, The thickness of the shell portion is 10 nm to 40 nm.

6. The separator for lithium secondary batteries according to claim 1, The inorganic coating has a structure in which an interstitial volume is formed between the core-shell composite particle precursors.

7. The separator for lithium secondary batteries according to claim 1, wherein Based on a total of 100% by weight of the core-shell composite particle precursor, the core-shell composite particle precursor comprises 10% to 90% by weight of the inorganic particles and 10% to 90% by weight of the acrylic monomer or oligomer.

8. The separator for lithium secondary batteries according to claim 1, The inorganic coating comprises 95% by weight or more of the core-shell composite particle precursor, based on 100% by weight of the inorganic coating.

9. The separator for lithium secondary batteries according to claim 1, The inorganic coating comprises core-shell composite particles formed by polymerization of the core-shell composite particle precursor.

10. A method for manufacturing a separator for a lithium secondary battery, the method comprising: (S10) Prepare an inorganic coating slurry composition comprising a core-shell composite particle precursor and a first dispersion medium; (S20) The inorganic coating slurry composition is applied to at least one surface of a porous polymer substrate; and (S30) Dry the inorganic coating slurry composition.

11. The method for manufacturing a separator for a lithium secondary battery according to claim 10, further comprising: Prior to (S10), acrylic monomers or oligomers and inorganic particles are added to a second aqueous dispersion medium and mixed to produce the core-shell composite particle precursor.

12. The method for manufacturing a separator for a lithium secondary battery according to claim 11, The preparation of the core-shell composite particle precursor includes: (S01) The acrylic monomer or oligomer and the inorganic particles are added to the 2a aqueous dispersion medium; (S02) Stir and mix the acrylic monomer or oligomer and the inorganic particles for 12 to 36 hours to coat the acrylic monomer or oligomer onto the surface of the inorganic particles; and (S03) The mixture in (S02) is added to the aqueous dispersion medium 2b and the inorganic particles coated with the acrylic monomer or oligomer are separated.

13. The method for manufacturing a separator for a lithium secondary battery according to claim 10, further comprising: After (S20), the inorganic coating slurry composition is heated at a temperature of 45°C to 85°C to convert the core-shell composite particle precursor into core-shell composite particles.

14. The method for manufacturing a separator for a lithium secondary battery according to claim 10, (S30) Drying the inorganic coating slurry composition is carried out at a temperature of 45°C to 85°C for 1 to 120 seconds.

15. A lithium secondary battery, comprising: Positive electrode; Negative electrode; An electrolyte solution; and a separator located between the positive electrode and the negative electrode. The partition includes: Porous polymer substrate; and An inorganic coating present on at least one surface of the porous polymer substrate, the inorganic coating comprising core-shell composite particles, The core-shell composite particle comprises a core and a shell covering at least a portion of the surface of the core. The core portion comprises inorganic particles. The shell portion comprises an acrylic polymer, and The acrylic polymer is formed by the polymerization of acrylic monomers or oligomers.

16. The lithium secondary battery according to claim 15, The adhesion strength (dry adhesion strength) of the separator relative to the electrode in the dry state is 45 gf / 15 mm or greater.

17. The lithium secondary battery according to claim 15, The air permeability of the partition is 67 seconds / 100 cc or less.

18. The lithium secondary battery according to claim 15, The difference between the air permeability of the partition and the air permeability of the porous polymer substrate is 10 seconds / 100cc or less.

19. The lithium secondary battery according to claim 15, Its resistance characteristic is 0.5 ohms or less.

20. The lithium secondary battery according to claim 15, The acrylic polymer is formed during the manufacture of the battery by polymerization of the acrylic monomer or oligomer.

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