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

Abstract

The present invention provides a separator for a lithium secondary battery, the separator comprising a porous polymer substrate and an inorganic coating layer which is provided on at least one surface of the porous polymer substrate and contains core-shell composite particle precursors, wherein each core-shell composite particle precursor comprises a core part and a shell part surrounding at least a portion of the surface of the core part, the core part contains inorganic particles, and the shell part contains an acrylic monomer or oligomer.

Description

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

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0110042, filed August 16, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Non-aqueous secondary batteries, such as lithium secondary batteries, are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras, and camcorders, as well as electric vehicles.

[0005] The fundamental requirements for separators in lithium secondary batteries are to electrically isolate the positive and negative electrodes, while simultaneously enhancing ionic conductivity by enhancing the permeability of ions, such as lithium ions, through high porosity. While these separators themselves do not participate in the electrochemical reactions of secondary batteries, their physical properties, such as wettability to electrolytes, porosity, and thermal shrinkage, significantly impact the performance and safety of the battery.

[0006] Membranes using porous polymer substrates can experience shrinkage at high temperatures, causing internal short circuits. Furthermore, the polymer membrane substrate can melt during thermal runaway, increasing the risk of ignition. Therefore, to address these shortcomings, an inorganic coating layer can be added to one or both sides of the porous polymer substrate, and inorganic particles and a binder polymer that can address these shortcomings can be added to the inorganic coating layer.

[0007] Meanwhile, conventional inorganic coating layers contain binder polymers positioned between the inorganic particles, blocking the pores between the particles. This reduces the membrane's air permeability and wetting properties, and degrades its resistance characteristics. Consequently, the development of a membrane capable of minimizing these problems is urgently needed.

[0008]

[0009] The present invention was invented to solve the above-described problems, and specifically, the purpose is to provide a lithium secondary battery separator having excellent electrode adhesion (dry adhesion) as well as excellent breathability, wettability and resistance characteristics, and a method for manufacturing the same.

[0010] Meanwhile, the technical problem to be solved by the present invention is not limited to the above purpose, and also includes other problems that can be clearly understood by those skilled in the art from the detailed description of the specification.

[0011]

[0012] To achieve this purpose, according to one aspect of the present invention, a separator for a lithium secondary battery and a method for manufacturing the same and a lithium secondary battery including the same are provided according to the following embodiments.

[0013] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including a core-shell composite particle precursor; wherein the core-shell composite particle precursor includes a core portion and a shell portion surrounding at least a portion of a surface of the core portion, wherein the core portion includes inorganic particles and the shell portion includes an acrylic monomer or oligomer.

[0014] According to a second embodiment, in the first embodiment, the acrylic monomer or oligomer may include a thermally polymerizable acrylic monomer or oligomer.

[0015] According to a third embodiment, in the second embodiment, the thermally polymerizable acrylic monomer or oligomer may be polymerized under conditions of a temperature of 45°C to 85°C to form a thermally polymerizable acrylic polymer.

[0016] According to a fourth embodiment, in any one of the second to third embodiments, the thermally polymerizable acrylic monomer or oligomer is butyl acrylate, β-carboxyethyl acrylate, 2-ethylhexylacrylate, 2-methoxyethylacrylate, 4-hydroxybutylacrylate, ethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, pentylmethacrylate, 2-hydroxymethyl acrylate, ethylmethacrylate, It may be an oligomer containing one or more monomers selected from methylmethacrylate, acrylic acid, and acrylonitrile, or one or more repeating units derived therefrom.

[0017] According to a fifth embodiment, in any one of the first to fourth embodiments, the thickness of the shell portion may be 10 nm to 40 nm.

[0018] According to a sixth embodiment, in any one of the first to fifth embodiments, the inorganic coating layer may have a structure in which an interstitial volume is formed between core-shell composite particle precursors.

[0019] According to a seventh embodiment, in any one of the first to sixth embodiments, the core-shell composite particle precursor may include 10 to 90 wt% of inorganic particles and 10 to 90 wt% of an acrylic monomer or oligomer, based on 100 wt% of the total.

[0020] According to the eighth embodiment, in any one of the first to seventh embodiments, the core-shell composite particle precursor may be included in an amount of 95 wt% or more based on 100 wt% of the inorganic coating layer.

[0021] According to a ninth embodiment, in any one of the first to eighth embodiments, the inorganic coating layer may include core-shell composite particles formed by polymerizing the core-shell composite particle precursor.

[0022] According to a tenth embodiment, a method for manufacturing a separator for a lithium secondary battery is provided, comprising the steps of: (S10) preparing a slurry composition for forming an inorganic coating layer, which comprises a core-shell composite particle precursor; and a first dispersion medium; (S20) applying the slurry composition for forming an inorganic coating layer onto at least one surface of a porous polymer substrate; and (S30) drying the slurry composition for forming an inorganic coating layer.

[0023] According to the eleventh embodiment, in the tenth embodiment, before the step (S10), a step of introducing and mixing an acrylic monomer or oligomer and inorganic particles into a second aqueous dispersion medium to prepare a core-shell composite particle precursor may be further included.

[0024] According to a tenth embodiment, in the ninth embodiment, the core-shell composite particle precursor precursor may be manufactured by including the steps of (S01) adding an acrylic monomer and inorganic particles to a second aqueous dispersion medium; (S02) mixing the acrylic monomer and inorganic particles for 12 to 36 hours so that the acrylic monomer is coated on the surface of the inorganic particles; and (S03) adding the mixture of step (S02) to a second aqueous dispersion medium and then separating the inorganic particles coated with the acrylic monomer.

[0025] According to a twelfth embodiment, in the eleventh embodiment, the step of manufacturing the core-shell composite particle precursor may include: (S01) a step of introducing an acrylic monomer or oligomer and inorganic particles into a second a aqueous dispersion medium; (S02) a step of mixing the acrylic monomer or oligomer and inorganic particles by stirring for 12 to 36 hours so that the acrylic monomer or oligomer is coated on the surface of the inorganic particles; and (S03) a step of introducing the mixture of step (S02) into a second b aqueous dispersion medium, and then separating the inorganic particles coated with the acrylic monomer or oligomer.

[0026] In the 13th embodiment, in any one of the 10th to 12th embodiments, after the step (S20), a step of heating the slurry composition for forming the inorganic coating layer at a temperature of 45°C to 85°C to convert the core-shell composite particle precursor into core-shell composite particles may be further included.

[0027] According to the 14th embodiment, in any one of the 10th to 13th embodiments, the step of drying the slurry composition for forming the inorganic coating layer (S30) may be performed at a temperature of 45°C to 85°C for 1 to 120 seconds.

[0028] According to a 15th embodiment, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode; an electrolyte; and a separator interposed between the positive electrode and the negative electrode; wherein the separator comprises: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including core-shell composite particles; wherein the core-shell composite particles include a core portion and a shell portion surrounding at least a portion of a surface of the core portion, wherein the core portion includes inorganic particles, and the shell portion includes an acrylic polymer, wherein the acrylic polymer is formed by polymerizing an acrylic monomer or oligomer.

[0029] According to the 16th embodiment, in the 15th embodiment, the separator may have an electrode-separator adhesion strength in a dry state (dry adhesion strength) of 45 gf / 15 mm or more.

[0030] According to the 17th embodiment, in any one of the 15th to 16th embodiments, the air permeability of the separation membrane may be 67 sec / 100cc or less.

[0031] According to the 18th embodiment, in any one of the 15th to 17th embodiments, the difference between the air permeability of the separation membrane and the air permeability of the porous polymer substrate may be 10 sec / 100 cc or less.

[0032] According to the 19th embodiment, in any one of the 15th to 18th embodiments, the resistance characteristic may be 0.5 ohm or less.

[0033] According to the 20th embodiment, in any one of the 15th to 19th embodiments, the acrylic polymer may be formed by polymerizing an acrylic monomer or oligomer during the manufacturing process of the battery.

[0034]

[0035] A separator for a lithium secondary battery according to one embodiment of the present invention may have excellent electrode adhesion (dry adhesion) as well as excellent breathability, wettability, and resistance characteristics.

[0036] A method for manufacturing a separator for a lithium secondary battery according to one embodiment of the present invention can provide a method for manufacturing a separator having excellent electrode adhesion (dry adhesion) as well as excellent breathability and resistance characteristics.

[0037] However, the effects that can be obtained through the present invention are not limited to the effects described above, and other technical effects not mentioned can be clearly understood by those skilled in the art from the description of the invention described below.

[0038]

[0039] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0040] Figure 1 schematically illustrates the structure of a separation membrane according to one embodiment of the present invention.

[0041] FIG. 2 schematically illustrates a core-shell composite particle / core-shell composite particle precursor according to one embodiment of the present invention.

[0042]

[0043] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0044] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0045] Justice

[0046] Throughout this specification, when it is said that a part "includes" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0047] The glass transition temperature (Tg) may be a value measured, for example, by a dynamic mechanical analysis (DMA) or DSC (TA Instrument) device. For example, the glass transition temperature may be a value measured according to the DMA method specified in ASTM D4065.

[0048] D in the original specification 50 refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size. In addition, D 10 D means the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. 90 refers to the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size.

[0049] In the present specification, the particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in diffraction pattern according to particle size is measured when the particles pass through the laser beam, thereby calculating the particle size distribution. By calculating the particle diameters at points where the number of particles is 10%, 50%, and 90% of the cumulative distribution according to particle size in the measuring device, D is calculated, respectively. 10 , D50 and D 90 can be measured.

[0050] In this specification, "acrylic" means branched or unbranched acrylic acid or methacrylic acid, or a derivative thereof. In addition, "(meth)acrylic acid" or "(meth)acrylate" includes both acrylic acid and methacrylic acid, and both acrylate and methacrylate, respectively.

[0051] In the present specification, the weight average molecular weight (Mw) may be measured by gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies) under the following conditions.

[0052] - Column: PL Olexis (Polymer Laboratories)

[0053] - Dispersion medium: TCB (Trichlorobenzene)

[0054] - Flow rate: 1.0 ml / min

[0055] - Sample concentration: 1.0 mg / ml

[0056] - Injection volume: 200 ㎕

[0057] - Column temperature: 160℃

[0058] - Detector: Agilent High Temperature RI detector

[0059] - Standard: Polystyrene (corrected with a cubic function)

[0060]

[0061] Separator for lithium secondary batteries

[0062] The present invention provides a separator for a lithium secondary battery.

[0063] According to one aspect of the present invention, a separator for a lithium secondary battery of the present invention comprises: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including a core-shell composite particle precursor; wherein the core-shell composite particle precursor includes a core portion and a shell portion surrounding at least a portion of a surface of the core portion, wherein the core portion includes inorganic particles and the shell portion includes an acrylic monomer or oligomer.

[0064] Specifically, as can be seen in FIG. 1, the separator (10) for a lithium secondary battery of the present invention comprises: a porous polymer substrate (100); and an inorganic coating layer (200) formed on at least one surface of the porous polymer substrate (100) and 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) surrounding at least a portion of the surface of the core portion, wherein the core portion (211) includes inorganic particles, and the shell portion (212) includes an acrylic monomer or oligomer.

[0065] Meanwhile, as described below, the core-shell composite particle precursor (210) can be polymerized to form core-shell composite particles (210). Accordingly, the inorganic coating layer (200) can include core-shell composite particles (210).

[0066] In one embodiment of the present invention, the acrylic monomer or oligomer may mean the acrylic monomer or the acrylic oligomer.

[0067] In one embodiment of the present invention, the acrylic oligomer may be a low-molecular weight polymer obtained by polymerizing two or more acrylic monomers, and may be a compound containing a reactive functional group at the molecular terminal. The acrylic oligomer may be, for example, a polymerization of monomers having 2 to 10 repeating units.

[0068]

[0069] porous polymer substrate

[0070] In one embodiment of the present invention, the porous polymer substrate refers to a substrate having a plurality of pores formed therein as a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the cathode and the anode. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other.

[0071] The material constituting the porous polymer substrate can be any organic or inorganic material with electrical insulation properties. In particular, from the perspective of imparting a shutdown function to the porous polymer substrate, it is preferable to use a thermoplastic resin as the constituent material of the porous polymer substrate. Here, the shutdown function refers to the function of preventing thermal runaway of the battery by blocking the movement of ions by melting the thermoplastic resin and closing the pores of the porous substrate when the battery temperature rises. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200°C is suitable, and polyolefin is particularly preferred.

[0072] In addition, at least one of polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene may be further included. The porous polymer substrate may be, but is not particularly limited to, a nonwoven fabric, a porous polymer film, or a laminate of two or more thereof.

[0073] In the present invention, the porous polymer substrate preferably has a thickness of 3 μm to 12 μm or 5 μm to 12 μm. If the thickness falls short of the above values, the conductive barrier function is insufficient, whereas if the thickness exceeds the above range (i.e., is too thick), the resistance of the separator may excessively increase.

[0074] In one embodiment of the present invention, the weight average molecular weight of the polyolefin may be 100,000 to 5,000,000. If the weight average molecular weight is less than 100,000, it may be difficult to secure sufficient mechanical properties. In addition, if it exceeds 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult. In addition, the puncture strength of the porous polymer substrate may be 300 gf or more from the viewpoint of improving the manufacturing yield. The puncture strength of the porous substrate refers to the maximum puncture load (gf) measured by performing a puncture test under the conditions of a needle tip radius of 0.5 mm and a puncture speed of 4 mm / sec using a Kato tech KES-G5 handy compression tester.

[0075] In a specific embodiment of the present invention, the porous polymer substrate may be any planar porous polymer substrate used in an electrochemical device, and for example, an insulating thin film having high ion permeability and mechanical strength, a pore diameter of generally 10 nm to 200 nm, and a thickness of generally 5 ㎛ to 12 ㎛ may be used.

[0076] In one embodiment of the present invention, the air permeability of the porous polymer substrate may be within a range of 40 sec / 100cc to 70 sec / 100cc, or 45 sec / 100cc to 65 sec / 100cc, depending on the type.

[0077]

[0078] Inorganic coating layer

[0079] In one embodiment of the present invention, the inorganic coating layer is formed on at least one surface of the porous polymer substrate and includes a core-shell composite particle precursor, the core-shell composite particle precursor includes a core portion and a shell portion surrounding at least a portion of the surface of the core portion, the core portion includes inorganic particles, and the shell portion includes an acrylic monomer or oligomer.

[0080] In another embodiment of the present invention, the inorganic coating layer is formed on at least one surface of the porous polymer substrate and includes core-shell composite particles, the core-shell composite particles include a core portion and a shell portion surrounding at least a portion of the surface of the core portion, the core portion includes inorganic particles, and the shell portion may include an acrylic polymer. That is, the shell portion may include an acrylic polymer polymerized with an acrylic monomer or oligomer.

[0081] In one embodiment of the present invention, the core-shell composite particle precursor in the inorganic coating layer can be polymerized into core-shell composite particles through a polymerization process. When this is described as "core-shell composite particle / core-shell composite particle precursor" in the present specification, this means that the two components (core-shell composite particle and its precursor) have common characteristics.

[0082] In one embodiment of the present invention, the inorganic coating layer may have a structure in which an interstitial volume is formed between core-shell composite particles / core-shell composite particle precursors. Lithium ions can move through the interstitial volume. That is, the interstitial volume may refer to pores (spaces) between binder polymers of the shell portion or monomers or oligomers formed from the binder polymers. Due to the interstitial volume, the separator may have excellent electrode-separator adhesion in a dry state (dry adhesion), excellent air permeability, and excellent resistance characteristics.

[0083] In one embodiment of the present invention, 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.

[0084] In one embodiment of the present invention, the core-shell composite particle / core-shell composite particle precursor may have a spherical, elliptical, plate-shaped, or irregularly shaped particle shape. The shape of the core-shell composite particle / core-shell composite particle precursor can be confirmed, for example, using a scanning electron microscope (SEM).

[0085] In one embodiment of the present invention, the core-shell composite particle / core-shell composite particle precursor may comprise 95 wt% or more, 96 wt% or more, 97 wt% or more, 98 wt% or more, or 99 wt% or more based on 100 wt% of the inorganic coating layer. That is, the inorganic coating layer may be substantially composed of the core-shell composite particle / core-shell composite particle precursor.

[0086] In one embodiment of the present invention, the inorganic coating layer may substantially not contain a heterogeneous binder polymer. That is, the inorganic coating layer may contain a heterogeneous binder polymer in an amount of less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, or less than 1 wt% based on 100 wt% of the inorganic coating layer.

[0087] At this time, the heterogeneous binder polymer may refer to a binder polymer other than the binder polymer included in the shell portion of the core-shell composite particle, and there is no limitation on its type. For example, the heterogeneous binder polymer may include a fluorinated binder polymer, an acrylic binder polymer, etc. The fluorinated binder polymer and the acrylic binder polymer may be the same as those described below.

[0088] In one embodiment of the present invention, the inorganic coating layer may have excellent heat resistance of the separator due to the core portion of the core-shell composite particles, and may achieve cohesion of the core-shell composite particles and adhesion between the electrode and the separator due to the shell portion. Accordingly, the inorganic particles may substantially not include a separate binder polymer. Accordingly, the separator may have excellent electrode-separator adhesion, as well as excellent air permeability and resistance characteristics.

[0089]

[0090] Core

[0091] In one embodiment of the present invention, the core portion includes inorganic particles. The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the applied electrochemical device (e.g., Li / Li). +There are no particular limitations as long as no oxidation and / or reduction reaction occurs at a voltage of 0 to 5 V as a standard. In particular, when using inorganic particles with a high dielectric constant as inorganic particles, it can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0092] For the reasons mentioned above, it is preferable that the inorganic particles include high-k inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), 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), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2 or mixtures thereof.

[0093] In addition, inorganic particles having lithium ion transfer capability, i.e., inorganic particles containing lithium element but having the function of transferring lithium ions without storing lithium, can be used. Non-limiting examples of inorganic particles having lithium ion transfer capability 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), 14Li2O-9Al2O3-38TiO2-39P2O5, etc. (LiAlTiP) x O ySeries Glass (0 <x < 4, 0 < y < 13), 리튬란탄티타네이트(Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li 3 N ), etc. x N y , 0 < x < 4, 0 < y < 2), SiS2 series glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 글래스(Li x P y S z , 0 < x < 3, 0< y < 3, 0 < z < 7) or mixtures thereof.

[0094] In addition, the average particle diameter of the inorganic particles is not particularly limited, but is preferably in the range of 0.1 ㎛ to 2.0 ㎛, or 0.2 to 1.8 ㎛, for the formation of a coating layer of uniform thickness and an appropriate porosity. If the average particle diameter of the inorganic particles is less than the lower limit, the heat resistance of the separator may be reduced, and if it exceeds the upper limit, the thickness of the inorganic coating layer formed may increase.

[0095] In one embodiment of the present invention, the inorganic particles may be included in an amount of 10 wt% to 90 wt% relative to 100 wt% of the core-shell composite particle / core-shell composite particle precursor. That is, the core portion may be included in an amount of 10 wt% to 90 wt% relative to 100 wt% of the core-shell composite particle.

[0096]

[0097] Shell

[0098] In one embodiment of the present invention, the core-shell composite particle precursor comprises a core portion and a shell portion surrounding at least a portion of the surface of the core portion, wherein the shell portion comprises an acrylic monomer or oligomer. The acrylic monomer or oligomer may be bonded to, attached to, or coated on at least a portion of the surface of the core portion.

[0099] In one embodiment of the present invention, the thickness of the shell portion may 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 portion satisfies the above-described range, the core-shell composite particles may have better adhesion and better air permeability. In addition, since there is no part where only the inorganic particles are exposed, the resistance characteristics may be better.

[0100] The thickness of the shell portion can be calculated by measuring the size of the inorganic particles, measuring the size of the core-shell composite particle precursor, and then calculating the difference in the size of the inorganic particles from the size of the core-shell composite particle precursor. Alternatively, the thickness of the shell portion can be determined by measuring a scanning electron microscope (SEM) and analyzing the image.

[0101] In one embodiment of the present invention, the acrylic monomer or oligomer may include a thermally polymerizable acrylic monomer or oligomer.

[0102] In one embodiment of the present invention, when the acrylic monomer or oligomer includes the thermally polymerizable acrylic monomer or oligomer, the thermally polymerizable acrylic monomer or oligomer may be formed by polymerizing the thermally polymerizable acrylic monomer by heat at a predetermined temperature or higher. The thermally polymerizable acrylic monomer or oligomer may be a polymer of a thermally polymerizable acrylic monomer that is polymerized under conditions of a temperature of 45°C to 85°C, or 50°C to 70°C.

[0103] The above-mentioned thermally polymerizable acrylic monomer may have a different polymerization temperature due to heat depending on the structure of the thermally polymerizable acrylic monomer, and thus, the temperature at which polymerization of the acrylic monomer begins can be controlled by changing the type of the acrylic monomer and the type of the initiator. When the temperature at which polymerization of the acrylic monomer begins satisfies the above-mentioned temperature range, the acrylic monomer is crosslinked at a temperature higher than room temperature, so that the acrylic monomer does not polymerize in the general natural drying stage, and thus, the start of polymerization can be controlled. In addition, since the acrylic monomer does not require a high temperature to polymerize, the physical properties of the porous polymer substrate may not be deteriorated.

[0104] In one embodiment of the present invention, the thermopolymerizable acrylic monomer may be a branched or unbranched compound having 2 to 16, 2 to 14, or 2 to 12 carbon atoms. When the carbon number of the thermopolymerizable acrylic monomer satisfies the above-described range, the monomer may have better adhesive properties.

[0105] In one embodiment of the present invention, the thermally polymerizable acrylic monomer or oligomer is butyl acrylate, β-carboxyethyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, pentylmethacrylate, 2-hydroxymethyl acrylate, ethylmethacrylate, methylmethacrylate, acrylic acid, It may be an oligomer comprising one or more monomers selected from acrylonitrile or one or more repeating units derived therefrom.

[0106] In one embodiment of the present invention, when the acrylic monomer or oligomer comprises the thermally polymerizable acrylic monomer or oligomer, the shell portion may further comprise a thermal polymerization initiator.

[0107] Thermal polymerization initiators are well known in the art of acrylic monomer polymerization and can also be used in the present invention. Typical thermal polymerization initiators useful in the present invention include organic peroxides, organic hydroperoxides, and azo initiators that generate free radicals. Useful organic peroxides include, but are not limited to, compounds such as benzoyl peroxide, di-t-amyl peroxide, t-butyl peroxybenzoate, and di-cumyl peroxide. Useful organic hydroperoxides include, but are not limited to, compounds such as t-amyl hydroperoxide and t-butyl hydroperoxide. Useful azo initiators include, but are not limited to, DuPont VAZO compounds, such as VAZO 52 (2,2'-azobis(2,4-dimethylpentanenitrile)), VAZO 64 (2,2'-azobis(2-methylpropanenitrile)), VAZO 67 (2,2'-azobis(2-methylbutanenitrile)), and VAZO 88 (2,2'-azobis(cyclohexanecarbonitrile)).

[0108] In one embodiment of the present invention, the content of the thermal polymerization initiator may be included in the shell portion at 0.01 to 20 parts by weight per 100 parts by weight of the thermal polymerizable acrylic monomer or oligomer, but this may be changed in consideration of process efficiency, physical properties of the polymer, etc.

[0109]

[0110] In one embodiment of the present invention, the inorganic coating layer may contain substantially no, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, or less than 1 wt% of a particulate binder polymer. The particulate binder may be contained in a small amount for bonding between core-shell composite particle precursors, or may be contained substantially free. When the above numerical range is satisfied, the resistance characteristics and air permeability of the separator may be better.

[0111] The above-mentioned particulate binder polymer may have a property of maintaining its original particle shape without being deformed even when dispersed in a dispersion medium. Specifically, the above-mentioned particulate binder polymer may mean that it exists in a particle state in an aqueous dispersion medium. Specifically, the above-mentioned particulate binder polymer may mean that it has low solubility in an aqueous dispersion medium and thus has a form that is dispersed in the form of particles in the aqueous dispersion medium. The above-mentioned particulate binder polymer may have an aspect ratio in the range of 1.0 to 1.5, 1.0 to 1.3, or 1.0 to 1.2 in the aqueous dispersion medium. Here, the aspect ratio is defined as the ratio of the length of the major axis to the minor axis of the first particulate binder, and the closer it is to 1, the closer it is to a sphere. The aspect ratio can be calculated, for example, using a particle shape analyzer (QICPIC-LIXELL, Sympatec GmbH).

[0112] In one embodiment of the present invention, the particulate binder polymer may be an acrylic particulate binder polymer, a fluorine-based particulate binder polymer, or a combination thereof.

[0113] In one embodiment of the present invention, the acrylic particle-type binder polymer may include, for example, an acrylic homopolymer polymerized only with an acrylic monomer, or may include a copolymer of an acrylic monomer and another monomer. For example, the acrylic particle-type binder polymer is poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexylacrylate and methylmethacrylate, a copolymer of butylacrylate and methylmethacrylate, an ethylacrylate-acrylic acid-N,N-dimethylacrylamide copolymer, an ethylacrylate-acrylic acid-2-(dimethylamino)ethylacrylate copolymer, an ethylacrylate-acrylic acid-N,N-diethylacrylamide copolymer, It may include an ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer or a mixture of two or more thereof.

[0114] In one embodiment of the present invention, the fluorine-based particle-type binder polymer may include, for example, a polyvinylidene fluoride (PVDF) homopolymer, and may include a copolymer of repeating units derived from vinylidene fluoride and other repeating units. For example, the fluorine-based particle-type binder polymer may include a copolymer of one or more selected from among repeating units derived from vinylidene fluoride, repeating units derived from trifluoroethylene (TrFE), repeating units derived from tetrafluoroethylene (TFE), repeating units derived from hexafluoropropylene (HFP), repeating units derived from trichloroethylene (TrCE), repeating units derived from trichlorofluoroethylene (TCFE), repeating units derived from chlorotrifluoroethylene (CTFE), repeating units derived from polymethylmethacrylate (PMMA), and repeating units derived from polyvinylacetate (PVAc), or a mixture of two or more thereof.

[0115] In one embodiment of the present invention, the glass transition temperature (Tg) of the particulate binder polymer may be 30°C to 90°C, or 50°C to 80°C. When the particulate binder polymer has the above-described glass transition temperature, the binder in the form of particles may collapse under certain temperature and pressure conditions at the time of manufacturing the separation membrane, thereby forming a film.

[0116] In one embodiment of the present invention, D of the particle-type binder polymer 50The size of the particulate binder polymer may be 150 nm to 1 μm or 200 nm to 800 nm. When the size of the particulate binder polymer satisfies the above-described range, the adhesion and porosity of the membrane may be better.

[0117] In one embodiment of the present invention, the inorganic coating layer may include core-shell composite particles formed by polymerizing the core-shell composite particle precursor.

[0118] In one embodiment of the present invention, the core-shell composite particle comprises a core portion and a shell portion surrounding at least a portion of the surface of the core portion, wherein the shell portion may comprise an acrylic polymer. The acrylic polymer may be bonded to, attached to, or coated on at least a portion of the surface of the core portion.

[0119] In one embodiment of the present invention, the thickness of the shell portion including the acrylic polymer may be substantially the same as the thickness of the shell portion including the acrylic monomer or oligomer. The thickness of the shell portion including the acrylic polymer may 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 thickness of the shell portion satisfies the above-described range, the core-shell composite particles may have better adhesion and better air permeability. In addition, since there is no part where only the inorganic particles are exposed, the resistance characteristics may be better.

[0120] In one embodiment of the present invention, the acrylic polymer may be a polymerization of the above-described acrylic monomer or oligomer.

[0121]

[0122] <Method for manufacturing a separator for lithium secondary batteries>

[0123] The present invention provides a method for manufacturing a separator for a lithium secondary battery.

[0124] According to one aspect of the present invention, a method for manufacturing a separator for a lithium secondary battery of the present invention comprises the steps of (S10) preparing a slurry composition for forming an inorganic coating layer, which comprises a core-shell composite particle precursor; and a first dispersion medium; (S20) applying the slurry composition for forming an inorganic coating layer onto at least one surface of a porous polymer substrate; and (S30) drying the slurry composition for forming an inorganic coating layer.

[0125] Below, we will examine in detail each step the manufacturing method of a separator for lithium secondary batteries.

[0126] First, a slurry composition for forming an inorganic coating layer including (S10) a core-shell composite particle precursor and a first dispersion medium is prepared.

[0127] The above core-shell composite particle precursor refers to a particle that can be converted into a core-shell composite particle. The core-shell composite particle precursor may include a slurry composition comprising an inorganic particle and an acrylic monomer surrounding at least a portion of a surface of the inorganic particle.

[0128] In one embodiment of the present invention, prior to the step (S10), a step of introducing and mixing an acrylic monomer and inorganic particles into a second aqueous dispersion medium to prepare a core-shell composite particle precursor may be further included.

[0129] In one embodiment of the present invention, the step of preparing the core-shell composite particle precursor may include: (S01) a step of introducing an acrylic monomer or oligomer and inorganic particles into a second a aqueous dispersion medium; (S02) a step of mixing the acrylic monomer or oligomer and inorganic particles by stirring for 12 to 36 hours so that the acrylic monomer or oligomer is coated on the surface of the inorganic particles; and (S03) a step of introducing the mixture of step (S02) into a second b aqueous dispersion medium, and then separating the inorganic particles coated with the acrylic monomer or oligomer.

[0130] Specifically, after dispersing the acrylic monomer or oligomer and the inorganic particles in the second a aqueous dispersion medium, the mixture may be stirred for a sufficient time of 12 to 36 hours to coat the surfaces of the inorganic particles with the acrylic monomer. If the mixing time is shorter than the lower limit, the acrylic monomer or oligomer may not be sufficiently coated on the surfaces of the inorganic particles. If the mixing time exceeds the upper limit, the efficiency of the manufacturing process may decrease.

[0131] Thereafter, the solids and particles in the mixed mixture are introduced into the second aqueous dispersion medium, mixed, and then the inorganic particles coated with the acrylic monomer or oligomer are separated therefrom and dispersed again in the first dispersion medium to manufacture a core-shell composite particle precursor. When the above-described step is further included, the acrylic monomer is not located in the interstitial volume between the core-shell composite particles / core-shell composite particle precursor, so that the air permeability and resistance characteristics can be better.

[0132] In one embodiment of the present invention, the acrylic monomer or oligomer may include a thermally polymerizable acrylic monomer or oligomer. Meanwhile, the inorganic particles, acrylic monomer, and thermally polymerizable acrylic monomer or oligomer are replaced with those described above.

[0133] In one embodiment of the present invention, the dispersion medium, i.e., the first dispersion medium, may be an aqueous dispersion medium or an organic dispersion medium.

[0134] In one embodiment of the present invention, the aqueous dispersion medium, the second a aqueous dispersion medium, and the second b aqueous dispersion medium may contain water. In addition, when there are limitations on drying speed and temperature, methanol, ethanol, isopropyl alcohol, or the like, which have a lower boiling point than water, may be used as a co-dispersing medium.

[0135] In one embodiment of the present invention, the organic dispersion medium is, for example, cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and ethylbenzene; ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane and ethylcyclohexane; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitrile such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methylpyrrolidone, N,N-dimethylformamide and the like. Amides may be mentioned, and the dispersion medium may include acetone in consideration of the advantage in the drying process.

[0136] In one embodiment of the present invention, the weight ratio of the acrylic monomer or oligomer and the inorganic particles may be 1:99 to 99:1, 10:90 to 90:10, or 20:80 to 80:20.

[0137]

[0138] Thereafter, (S20) the slurry composition for forming the inorganic coating layer is applied on at least one surface of the porous polymer substrate.

[0139] As a method of applying the slurry composition for forming the above-mentioned inorganic coating layer onto at least one surface of a porous polymer substrate, various methods may be used, for example, dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, Mayer Bar coating, direct metering coating, or a mixture thereof.

[0140]

[0141] In one embodiment of the present invention, after the step (S20), a step of heating the slurry composition for forming the inorganic coating layer 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 may be further included. Specifically, by heating the slurry composition for forming the inorganic coating layer at a temperature in the above-described range, the thermally polymerizable acrylic monomer of the core-shell composite particle precursor may be polymerized to form a thermally polymerizable acrylic polymer.

[0142] In one embodiment of the present invention, the step of converting the core-shell composite particle precursor into core-shell composite particles can be performed simultaneously with, for example, interposing a separator between the positive and negative electrodes to manufacture an electrode assembly and then laminating the same. In this case, the contact area between the separator and the electrode can be increased, thereby improving the bonding strength of the electrode-separator.

[0143] Since the temperature at which the above-mentioned thermally polymerizable acrylic polymer is polymerized by heat may vary depending on the structure of the thermally polymerizable acrylic monomer or oligomer, the temperature at which polymerization of the acrylic monomer begins can be controlled by changing the type of acrylic monomer. Since the acrylic monomer does not require a high temperature to polymerize, the properties of the porous polymer substrate may not deteriorate.

[0144]

[0145] Thereafter, (S30) the slurry composition for forming the inorganic coating layer is dried. In one embodiment of the present invention, the drying time may be performed for 1 minute to 10 hours, and the drying temperature may be performed in the range of 30°C to 100°C. The drying is not limited to a specific method as long as the dispersion medium can be removed from the separation membrane, and for example, an appropriate method such as one or a combination of two or more of convection drying and hot air drying may be applied.

[0146] In one embodiment of the present invention, (S30) the step of drying the slurry composition for forming the inorganic coating layer may be performed at a temperature of 45°C to 85°C for 1 to 120 seconds. In this case, conversion of the core-shell composite particle precursor into core-shell composite particles and drying of the slurry composition for forming the inorganic coating layer may occur simultaneously.

[0147] In one embodiment of the present invention, the method for manufacturing a separator for a lithium secondary battery can manufacture a separator for a lithium secondary battery including an inorganic coating layer including a core-shell composite particle precursor by controlling a polymerization step, etc., and can manufacture a separator for a lithium secondary battery including an inorganic coating layer including core-shell composite particles.

[0148]

[0149] Lithium secondary battery

[0150] The present invention provides a lithium secondary battery.

[0151] According to one aspect of the present invention, a lithium secondary battery of the present invention comprises: a positive electrode; an negative electrode; an electrolyte; and a separator interposed between the positive electrode and the negative electrode; wherein the separator comprises: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including core-shell composite particles; wherein the core-shell composite particles include a core portion and a shell portion surrounding at least a portion of a surface of the core portion, wherein the core portion includes inorganic particles, and the shell portion includes an acrylic polymer, wherein the acrylic polymer is characterized in that it is formed by polymerizing an acrylic monomer or oligomer.

[0152] In one embodiment of the present invention, the positive electrode can be manufactured by coating a composition for forming a positive electrode including a positive electrode active material, a binder, a conductive agent, and a dispersion medium on a positive electrode current collector.

[0153] The above-mentioned cathode active material may be a conventional cathode active material that can be used in the cathode of a conventional electrochemical device. For example, the above-mentioned cathode active material may be lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide comprising these.

[0154] At this time, the positive electrode active material may be included in an amount of 80 to 99 wt%, preferably 85 to 98 wt%, based on the total solid content of the composition for forming the positive electrode. When the content of the positive electrode active material satisfies the above-described range, excellent capacity characteristics can be exhibited.

[0155] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0156] The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and can typically be added in an amount of 1 to 30 wt% based on the total solid weight of the composition for forming the positive electrode. Examples of such binders 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, various copolymers, etc.

[0157] The above-mentioned conductive agent can typically be added in an amount of 1 wt% to 30 wt% based on the total solid weight of the composition for forming the anode.

[0158] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include: graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powders; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive agents include acetylene black series (Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company), Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

[0159] In addition, the positive electrode active material layer may optionally further include a dispersant as needed.

[0160] The above dispersant can be used without any special restrictions as long as it is used as a dispersant of the anode, and for example, an aqueous dispersant or an organic dispersant can be selectively used as needed. Preferably, the dispersant is a cellulose compound, polyalkylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, 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) polymer, acrylonitrile / styrene / acrylate ester (ASA) polymer, a mixture of acrylonitrile / styrene / acrylate ester (ASA) polymer and propylene carbonate, styrene / acrylonitrile (SAN) Examples thereof include copolymers, methyl methacrylate / acrylonitrile / butadiene / styrene (MABS) polymers, styrene butadiene rubber, nitrile butadiene rubber, and fluoroelastomers, and any one or a mixture of two or more thereof may be used. Hydrogenated nitrile butadiene rubber (H-NBR) may be used. When the positive electrode active material layer further includes a dispersant, the dispersibility of the components of the positive electrode active material layer, particularly the conductive material, may be increased, but is not limited thereto.

[0161] In addition, the dispersion medium may be a dispersion medium generally used in the relevant technical field, and may include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the dispersion medium used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0162]

[0163] The negative electrode according to the present invention can be manufactured by coating a negative electrode forming composition including the above-described negative electrode active material, binder, conductive agent, and dispersant, etc., on a negative electrode current collector. In addition, the negative electrode forming composition may optionally further include a dispersant, if necessary.

[0164] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Preferably, the negative electrode is a silicon-based negative electrode active material, a carbon-based negative electrode active material, or Li that exhibits high-capacity characteristics. 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 group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등의 음극 활물질을 더 사용할 수 있다. 상기 규소계 음극 활물질은 음극 활물질은 Si, SiOx(0.1<x<5), Si-금속 합금, Mg와 같은 금속이 도핑 또는 화학 결합된 실리콘 산화물 입자(SiOx, 0.1<x<5) 및 Si와 SiOx(0.1<x<5)의 합금으로 이루어진 군에서 선택된 하나 이상을 포함할 수 있다. 상기 탄소계 음극 활물질은 천연 흑연, 인조 흑연, 비정질 하드카본(hard carbon), 저결정질 소프트카본(soft carbon), 카본 블랙, 아세틸렌 블랙, 케첸 블랙, 수퍼 P, 그래핀 (graphene), 및 섬유상 탄소로 이루어진 군으로부터 선택되는 하나 이상을 포함할 수 있다.

[0165] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0166] The conductive material, binder, dispersion medium or dispersant included in the above-described composition for forming the cathode may be applied without any special limitation as long as it is generally usable in a composition for forming an electrode. For example, the conductive material, binder, dispersion medium or dispersant described in the above-described composition for forming the anode may be applied.

[0167]

[0168] In addition, the lithium secondary battery may further include an electrolyte. The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

[0169] Specifically, the electrolyte may include an organic dispersion medium and a lithium salt.

[0170] As the organic dispersion medium, any medium that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic dispersion medium includes ester dispersion mediums such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether dispersion mediums such as dibutyl ether or tetrahydrofuran; ketone dispersion mediums such as cyclohexanone; aromatic hydrocarbon dispersion mediums such as benzene and fluorobenzene; Carbonate dispersion media such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol dispersion media such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate-based dispersion medium is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0171] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0172] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte.

[0173] In one embodiment of the present invention, the separator may have an electrode-separator adhesion in a dry state (dry adhesion) of 45 gf / 15 mm or more or 48 gf / 15 mm or more. Preferably, the dry adhesion may be 100 gf / 15 mm or less or 90 gf / 15 mm or less.

[0174] In one embodiment of the present invention, the air permeability of the separation membrane may be 67 sec / 100cc or less or 65 sec / 100cc or less. Preferably, the air permeability of the separation membrane may be 45 sec / 100cc or more or 50 sec / 100cc or more.

[0175] In one embodiment of the present invention, the difference between the air permeability of the separator and the air permeability of the porous polymer substrate may be 10 sec / 100cc or less, 7 sec / 100cc or less, or 5 sec / 100cc or less. The difference in air permeability within this range means that the air permeability of the separator is not substantially reduced by the formation of the inorganic coating layer, which indicates that pore closure by the inorganic coating layer can be minimized. Furthermore, this structure can contribute to improving the impregnation property of the electrolyte and preventing the deterioration of the initial ion conductivity characteristics and charge / discharge characteristics.

[0176]

[0177] In one embodiment of the present invention, the resistance characteristic may be 0.5 ohm or less or 0.48 ohm or less. When the resistance characteristic satisfies the above-described range, the initial ionic conductivity is excellent, the voltage drop is small even during high-rate charge / discharge, and the output characteristics of the battery can be improved. In addition, the effect of suppressing the increase in internal resistance during long-term cycling can be exhibited, thereby preventing the deterioration of the life characteristics.

[0178]

[0179] In one embodiment of the present invention, the acrylic polymer may be formed by polymerizing an acrylic monomer or oligomer during the battery manufacturing process. The acrylic monomer or oligomer in the inorganic coating layer may be converted into an acrylic polymer through a polymerization process such as lamination, thermal curing, or UV irradiation after the coating layer is formed. By this manufacturing method, the acrylic polymer in the coating layer can be uniformly bonded to the inorganic particles and the substrate surface, thereby ensuring excellent adhesion and mechanical stability, and the pore structure can be maintained without being excessively closed, thereby maintaining good air permeability and electrolyte impregnation properties.

[0180]

[0181] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0182]

[0183] <Example 1>

[0184] Aluminum oxide (Al2O3, D) as inorganic particles 50 : 450 nm, Sumitomo Corporation), butyl acrylate as an acrylic monomer was added to water (second aqueous dispersion medium) at room temperature. Thereafter, the mixture was stirred at a rotation speed of 500 rpm for 24 hours using a homogenizer so that the butyl acrylate was coated on the surface of aluminum oxide. Thereafter, the stirred mixture was dispersed again in water (second bqueous dispersion medium), and only the solid content in the dispersion, i.e., the core-shell composite particle precursor, was separated, and this was added to water (first dispersion medium) to prepare a slurry composition for forming an inorganic coating layer including the core-shell composite particle precursor. At this time, the solid content of the slurry composition for forming an inorganic coating layer was 35 wt%, and the weight ratio of the inorganic particles: acrylic monomer was 80:20.

[0185] The slurry composition for forming the above inorganic coating layer was applied to both sides of a polypropylene substrate (ventilation: 59 sec / 100cc) with a thickness of 9 ㎛ using a doctor blade, and then dried at a temperature of 60°C for 60 seconds to form an inorganic coating layer with a thickness of 1.5 ㎛ on each side, thereby manufacturing a separator with a thickness of approximately 12 ㎛.

[0186] At this time, D of the core-shell composite particle 50 was 510 nm, and the thickness of the shell was confirmed to be 30 nm. At this time, the thickness of the shell was D of the inorganic particle 50 and D of core-shell composite particles 50 It was calculated from . Meanwhile, the weight ratio of the core and shell was 80:20.

[0187]

[0188] <Reference Example>

[0189] In Example 1, the slurry composition for forming the inorganic coating layer was applied to both sides of a polypropylene substrate (ventilation: 59 sec / 100cc) having a thickness of 9 μm using a doctor blade, and then dried at a temperature of 30°C for 60 seconds to form an inorganic coating layer having a thickness of 1.5 μm on each side, thereby manufacturing a separator having a thickness of approximately 12.2 μm.

[0190] That is, the reference example has a difference compared to Example 1 in that the core-shell composite particle precursor is not polymerized.

[0191] At this time, D of the core-shell composite particle 50 The thickness of the shell was confirmed to be 27.5 nm, and the thickness of the silver was 505 nm.

[0192]

[0193] <Comparative Example 1>

[0194] Aluminum oxide (Al2O3, D) as inorganic particles 50: 450 nm, Sumitomo Corporation), (meth)acrylate monomer as an acrylic monomer was added to water at room temperature. Afterwards, mixing was performed using a bead mill disperser for 1 hour, and a slurry composition for forming an inorganic coating layer was prepared. At this time, the solid content of the slurry composition for forming an inorganic coating layer was 35 wt%, and the weight ratio of the inorganic particles: acrylic monomer was 80:20.

[0195] The slurry composition for forming the above inorganic coating layer was applied to both sides of a polypropylene substrate (ventilation: 59 sec / 100cc) with a thickness of 9 ㎛ using a doctor blade, and then dried at a temperature of 60°C for 60 seconds to form an inorganic coating layer with a thickness of 1.5 ㎛ on each side, thereby manufacturing a separator with a thickness of approximately 12.1 ㎛.

[0196] That is, in Comparative Example 1, compared to Example 1, aluminum oxide and an acrylic monomer were not sufficiently mixed, so that the acrylic monomer was not coated on the surface of the aluminum oxide or was coated incompletely, and unlike Example 1, there was no step of separating only the core-shell composite particle precursor, so the acrylic monomer existed solely in the slurry composition for forming an inorganic coating layer.

[0197] At this time, D of the solid particles of the inorganic coating layer 50 It was confirmed that silver is 520 nm.

[0198]

[0199] <Comparative Example 2>

[0200] Aluminum oxide (Al2O3, D) as inorganic particles 50 : 450 nm, Sumitomo Corporation), acrylic particle-type binder (polyacrylate, Tg: 40℃, D) as a particle-type binder polymer 50: 400 nm) was added to water at room temperature and stirred uniformly to prepare a slurry composition. At this time, the solid content of the slurry composition was 35 wt%, and the weight ratio of the inorganic particles: the first particle-type binder polymer was 80:20.

[0201] The first slurry composition was applied to both sides of a polypropylene substrate (ventilation: 59 sec / 100cc) having a thickness of 9 ㎛ using a doctor blade, and then dried at a temperature of 40°C for 120 seconds to form an inorganic coating layer having a thickness of 1.5 ㎛ on each side, thereby manufacturing a separation membrane having a thickness of approximately 12.1 ㎛.

[0202]

[0203] <Experimental Example>

[0204] For the above examples and comparative examples, the air permeability, dry adhesion, and resistance performance were evaluated as follows, and are shown in Table 1 below.

[0205] Air permeability (sec / 100cc) Air permeability of membrane - Air permeability of fabric (sec / 100cc) Dry adhesion (gf / 15mm) Resistance (ohm) Example 1634500.46 Reference Example 601420.44 Comparative Example 19637640.81 Comparative Example 27011550.52

[0206] Example 1, compared to the comparative example, had a structure in which an interstitial volume was formed between core-shell composite particles, and it was confirmed that it had excellent air permeability and low resistance. Specifically, the separator of Example 1 showed an increase in air permeability of only 4 sec / 100cc even when an inorganic coating layer was formed on a porous polymer substrate (air permeability: 59 sec / 100cc). In addition, it was confirmed that Example 1 had excellent dry adhesion even when an acrylic polymer was included in the shell portion without including a separate polymer in the inorganic coating layer. On the other hand, the reference example had a structure in which an interstitial volume was formed between core-shell composite particle precursors, and it was confirmed that it had excellent air permeability. Specifically, it was confirmed that even when a porous coating layer including a core-shell composite particle precursor was formed on a porous polymer substrate with an air permeability of 59 sec / 100cc, the increase in air permeability was only 1 sec / 100cc, which was substantially the same. However, it was confirmed that the dry adhesive strength was inferior because the acrylic monomer was not polymerized.

[0207] In addition, as a result of comparing Example 1 with the reference example, it was confirmed that in Example 1, the core-shell composite particle precursor was polymerized into the core-shell composite particle by thermal polymerization, and accordingly, the increase in air permeability was only 3 sec / 100 cc, while the electrode adhesion was improved by about 19% points or more.

[0208]

[0209] On the other hand, Comparative Example 1, compared to Example 1, contained an acrylic polymer polymerized from inorganic particles, imperfect core-shell composite particles, and an acrylic monomer contained therein, resulting in low air permeability. In addition, since it contained a separate acrylic polymer, the pores were closed, resulting in a significant increase in air permeability compared to Example 1. In addition, it was confirmed that the resistance was high due to such pore closure, etc.

[0210] Comparative Example 2 confirmed that the particle-type binder absorbed the electrolyte, resulting in somewhat poor air permeability and increased resistance.

[0211]

[0212] <Evaluation Method>

[0213] Thickness measurement

[0214] The thickness of the membranes manufactured in each example and comparative example was measured using a thickness measuring device (Mitutoyo, VL-50S-B) and is shown in Table 1.

[0215]

[0216] Air permeability evaluation

[0217] The ventilation time of the membranes of the examples and each comparative example was measured using a measuring device (Asahi Seiko), and the results are shown in Table 1. The ventilation time described here is the time when 100 cc of air is injected into 1 in at a pressure of 12.2 in H2O. 2 The time (in seconds) it takes to pass through the cross section is expressed as the ventilation time.

[0218]

[0219] Dry adhesion

[0220] The electrode plates manufactured in the above examples and each comparative example were cut to a width of 15 mm and fixed to a slide glass, and then the current collector was peeled off at a speed of 300 mm / min to measure the 180-degree peeling strength, and the results are shown in Table 1.

[0221]

[0222] Resistance Characteristics Evaluation

[0223] LiCoO as a cathode active material 　2 , carbon black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a dispersion medium at a weight ratio of 85:5:15 to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on a sheet-shaped aluminum current collector and dried to obtain a final positive electrode loading of 3.3 mAh / cm2 The polarity was prepared to make this happen.

[0224] A negative electrode slurry was prepared by mixing artificial graphite as a negative active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 75:5:25, and adding N-methylpyrrolidone (NMP) as a dispersion medium. The negative electrode slurry was prepared at a capacity of 3.8 mAh / cm 2 A negative electrode having a negative active material layer formed by coating and drying a copper current collector with a loading amount of was prepared.

[0225] The separators of the examples and comparative examples were sufficiently soaked in an electrolyte containing ethylene carbonate (EC) / ethyl methyl carbonate (EMC) in a volume ratio of 3:7, 1 M LiPF6, and 2 wt% VC, and coin cells were manufactured using only these separators. The manufactured coin cells were left at room temperature for 1 day, and the membrane resistance (ER) and ionic conductivity were measured by impedance measurement using a potentiostat.

Claims

1. Porous polymer substrate; and An inorganic coating layer formed on at least one surface of the porous polymer substrate and including a core-shell composite particle precursor; The core-shell composite particle precursor comprises a core portion and a shell portion surrounding at least a portion of the surface of the core portion, The above core portion includes inorganic particles, A separator for a lithium secondary battery, characterized in that the shell portion comprises an acrylic monomer or oligomer.

2. In claim 1, A separator for a lithium secondary battery, characterized in that the acrylic monomer or oligomer comprises a thermally polymerizable acrylic monomer or oligomer.

3. In claim 2, A separator for a lithium secondary battery, characterized in that the above thermally polymerizable acrylic monomer or oligomer is polymerized under conditions of a temperature of 45°C to 85°C to form a thermally polymerizable acrylic polymer.

4. In claim 2, The above thermally polymerizable acrylic monomer or oligomer is butyl acrylate, β-carboxyethyl acrylate, 2-ethylhexylacrylate, 2-methoxyethylacrylate, 4-hydroxybutylacrylate, ethylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, pentylmethacrylate, 2-hydroxymethyl acrylate, ethylmethacrylate, methylmethacrylate, acrylic acid, acrylonitrile. A separator for a lithium secondary battery, characterized in that it is an oligomer comprising at least one monomer selected from the group consisting of a monomer and a repeating unit derived therefrom.

5. In claim 1, A separator for a lithium secondary battery, characterized in that the thickness of the shell portion is 10 nm to 40 nm.

6. In claim 1, A separator for a lithium secondary battery, characterized in that the inorganic coating layer has a structure in which an interstitial volume is formed between core-shell composite particle precursors.

7. In claim 1, A separator for a lithium secondary battery, characterized in that the core-shell composite particle precursor comprises 10 to 90 wt% of inorganic particles and 10 to 90 wt% of acrylic monomer or oligomer based on 100 wt% of the total.

8. In claim 1, A separator for a lithium secondary battery, characterized in that the core-shell composite particle precursor comprises 95 wt% or more based on 100 wt% of the inorganic coating layer.

9. In claim 1, A separator for a lithium secondary battery, characterized in that the inorganic coating layer comprises core-shell composite particles formed by polymerization of the core-shell composite particle precursor.

10. (S10) A step of preparing a slurry composition for forming an inorganic coating layer including a core-shell composite particle precursor and a first dispersion medium; (S20) a step of applying the slurry composition for forming the inorganic coating layer on at least one surface of a porous polymer substrate; and (S30) A method for manufacturing a separator for a lithium secondary battery, comprising a step of drying a slurry composition for forming the above inorganic coating layer.

11. In claim 10, A method for manufacturing a separator for a lithium secondary battery, characterized in that, prior to the above step (S10), it further comprises a step of manufacturing a core-shell composite particle precursor by introducing and mixing an acrylic monomer or oligomer and inorganic particles into a second aqueous dispersion medium.

12. In claim 11, The step of manufacturing the core-shell composite particle precursor comprises: (S01) A step of introducing an acrylic monomer or oligomer and inorganic particles into a second aqueous dispersion medium; (S02) A step of mixing the acrylic monomer or oligomer and the inorganic particles by stirring for 12 to 36 hours so that the acrylic monomer or oligomer is coated on the surface of the inorganic particles; and (S03) A method for manufacturing a separator for a lithium secondary battery, characterized in that it comprises a step of introducing a mixture of step (S02) into a second-b aqueous dispersion medium and then separating inorganic particles coated with an acrylic monomer or oligomer.

13. In claim 10, A method for manufacturing a separator for a lithium secondary battery, characterized in that, after the above step (S20), the method further comprises a step of heating the slurry composition for forming the inorganic coating layer at a temperature of 45°C to 85°C to convert the core-shell composite particle precursor into core-shell composite particles.

14. In claim 10, (S30) A method for manufacturing a separator for a lithium secondary battery, characterized in that the step of drying the slurry composition for forming the inorganic coating layer is performed at a temperature of 45°C to 85°C for 1 to 120 seconds.

15. Including a positive electrode; a negative electrode; an electrolyte; and a separator interposed between the positive electrode and the negative electrode; The above separator porous polymer substrate; and An inorganic coating layer formed on at least one surface of the porous polymer substrate and including core-shell composite particles; The core-shell composite particle comprises a core portion and a shell portion surrounding at least a portion of the surface of the core portion, The above core portion includes inorganic particles, The above shell portion comprises an acrylic polymer, A lithium secondary battery characterized in that the above acrylic polymer is formed by polymerization of an acrylic monomer or oligomer.

16. In claim 15, A lithium secondary battery, characterized in that the above separator has an electrode-separator adhesion strength (dry adhesion) of 45 gf / 15 mm or more in a dry state.

17. In claim 15, A lithium secondary battery, characterized in that the air permeability of the above separator is 67 sec / 100cc or less.

18. In claim 15, A lithium secondary battery characterized in that the difference between the air permeability of the separator and the air permeability of the porous polymer substrate is 10 sec / 100cc or less.

19. In claim 15, A lithium secondary battery characterized by a resistance characteristic of 0.5 ohm or less.

20. In claim 15, A lithium secondary battery characterized in that the acrylic polymer is formed by polymerizing an acrylic monomer or oligomer during the manufacturing process of the battery.

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