Separation membrane containing inorganic material with core-shell structure and method for manufacturing the same

Abstract

The present invention relates to a separation membrane comprising a separation membrane substrate having a porous structure and a coating layer formed on at least one surface of the separation membrane substrate, wherein the coating layer comprises a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2021-0124468 dated September 17, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a separator including an inorganic material with a core-shell structure, specifically to a separator including an inorganic material with a core-shell structure in which a polymer is bound to the surface of inorganic particles contained in a separator coating layer, and a method for manufacturing the same. [Background technology]

[0003] Lithium secondary batteries prevent short circuits caused by contact between the positive and negative electrodes by interposing a separator between the positive and negative electrodes. Lithium secondary batteries not only generate heat during normal charging and discharging, but also may short circuits between the positive and negative electrodes due to external impacts. Therefore, to improve the heat resistance of the separator, a porous separator substrate may be used with a coating layer containing an inorganic material added to its outer surface.

[0004] The coating layer may be made of inorganic materials, polymeric materials, etc., depending on the function to be imparted to the separator.

[0005] Generally, when moisture is present inside a lithium secondary battery cell, gas may be generated due to a decomposition reaction of the electrolyte, which may shorten the lifespan and reduce the performance of the battery cell.

[0006] Therefore, when a hygroscopic material is used as an inorganic material constituting the separator coating layer, the moisture content in the separator increases, which can cause the above-mentioned problems.

[0007] In this regard, Patent Document 1 discloses a separation membrane containing particles with a core-shell structure, which are composed of an inorganic particle core and a degradable polymer shell coated on the surface of the core, in an active layer coated on one or both sides of a porous substrate.

[0008] The separation membrane of Patent Document 1 includes particles with a structure in which the surface of inorganic particles is coated with a degradable polymer, and the thickness of the separation membrane decreases by the amount of the polymer decomposition, thereby solving the problem of thickness increase due to swelling.

[0009] Patent Document 2 discloses microcapsules for electrochemical devices that include a capsule coating surrounding the surface of metal hydroxide particles, the capsule coating containing a flame-retardant resin.

[0010] Patent Document 2 discloses a separation membrane with improved flame retardancy by using metal hydroxide particles on which an encapsulation film containing a flame-retardant resin is formed.

[0011] However, no technology has been presented that can suppress gas generation due to moisture present in a battery cell in a separator for a secondary battery and prevent deterioration of battery performance by using an inorganic material with low hygroscopicity. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Korean Patent Publication No. 2017-0071204 [Patent Document 2] Korean Patent Publication No. 2019-0130977 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above problems, and aims to provide a separator including an inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles having hygroscopic properties so as to suppress moisture generation by modifying the surface of the inorganic particles. [Means for solving the problem]

[0014] To achieve this object, the separation membrane according to the present invention includes a separation membrane substrate having a porous structure and a coating layer formed on at least one surface of the separation membrane substrate, and the coating layer may include a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles.

[0015] The core-shell structure is formed by bonding functional groups on the surface of a central inorganic particle with a polymer.

[0016] The core-shell structure may be configured to have a shape in which an inorganic particle at the center and a polymer on the surface are bonded via a coupling agent.

[0017] The inorganic substances include Al(OH)3, AlOOH, Mg(OH)2, Al2O3, SiO2, TiO2, ZrO2, BaTiO3, BaSO4, 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, and SiC.

[0018] The coupling agent may be a silane-based coupling agent, including amino silane, epoxy silane, methacryloxy silane, vinyl silane, chlorine silane, and mercapto silane.

[0019] The coupling agent substitutes the surface of the inorganic particles, and the coupling agent reacts with the functional group of the polymer to form a bond.

[0020] The polymer may contain a hydroxyl group (-OH), an amino group (-NH2), a carboxyl group (-COOH), or a thiol group (-SH).

[0021] The surface-modified inorganic material may have a moisture content of 1,500 ppm or less.

[0022] The method for manufacturing the separation membrane may include the steps of: (a) preparing a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles; (b) preparing a separation membrane coating slurry by mixing the surface-modified inorganic material with a binder; and (c) coating both sides of a separation membrane substrate with the separation membrane coating slurry.

[0023] The step (a) may include a process of reacting inorganic particles with a coupling agent, and then adding and reacting a polymer thereto.

[0024] The present invention provides a lithium secondary battery in which an electrode assembly including the separator is housed in a battery case.

[0025] Furthermore, the present invention can also be provided in the form of a combination of various means for solving the above problems. [Effects of the Invention]

[0026] As described above, the separator according to the present invention forms an inorganic material having a core-shell structure in which the surface of the inorganic particle is modified by bonding a polymer to the surface of the inorganic particle or by bonding a coupling agent bonded to the inorganic particle to the polymer.

[0027] Therefore, even if inorganic particles having high moisture absorption properties are used, it is possible to prevent the inorganic particles from decomposing to form moisture or from absorbing moisture.

[0028] Furthermore, it is possible to prevent the performance of the battery cell from being reduced due to moisture generated within the battery cell. [Brief explanation of the drawings]

[0029] [Figure 1] 1A to 1C are diagrams illustrating a manufacturing process of an inorganic material according to an embodiment. [Figure 2] 10A to 10C are diagrams illustrating a process for manufacturing an inorganic material according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of an embodiment of the present invention that will enable a person skilled in the art to easily carry out the present invention. However, in describing the operation principle of the preferred embodiment of the present invention in detail, detailed description of related well-known functions or configurations will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0031] Furthermore, the same reference numerals are used throughout the drawings for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element therebetween. Furthermore, unless otherwise specified, "including a certain element" does not mean that other elements are excluded, but that other elements may also be included.

[0032] Furthermore, descriptions that limit or add specific elements are applicable to all inventions and are not limited to a particular invention unless otherwise specified.

[0033] Furthermore, throughout the description of the present invention and the claims, the singular includes the plural unless otherwise stated.

[0034] Furthermore, throughout the description of the present invention and the claims, unless otherwise specified, "or" includes "and." Therefore, "including A or B" means the three cases of including A, including B, or including both A and B.

[0035] The separation membrane according to the present invention includes a separation membrane substrate having a porous structure and a coating layer formed on at least one surface of the separation membrane substrate, and the coating layer includes a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles.

[0036] If the inorganic particles have properties that allow them to easily adsorb moisture from the atmosphere, such as by containing hydroxyl groups on their surfaces, moisture may form inside the battery cell. The moisture present inside the battery cell reacts with the electrolyte salt, decomposing the electrolyte and generating gas. The electrode coating formed as a by-product of this reaction increases resistance.

[0037] In addition, gas not only increases the contact resistance between the positive electrode / separator / negative electrode, but also forms gas traps on the surfaces of the negative and positive electrodes. Resistance increases in areas where gas traps occur on the surface of the negative electrode, which can lead to lithium deposition during charging and result in capacity loss. Capacity cannot be expressed in areas where gas traps occur on the surface of the negative electrode.

[0038] Furthermore, as the charge-discharge cycle progresses, side reactions such as decomposition of the electrolyte and deposition of lithium continue to occur, gradually increasing the resistance and gradually decreasing the capacity retention rate.

[0039] However, when using an inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles as in the present invention, the above-mentioned problems can be avoided because the inorganic particles can be prevented from adsorbing moisture by surface modification of the inorganic particles.

[0040] The separator substrate is an insulating thin film having high ion permeability and mechanical strength, and may be a polyolefin-based separator commonly used in the art, such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylenenaphthalene, and mixtures thereof.

[0041] The coating layer includes a surface-modified inorganic material and a binder for maintaining the bond between the surface-modified inorganic material and improving the adhesive strength between the electrode and the separator.

[0042] The surface-modified inorganic material may have a core-shell structure in which a polymer is bound to the surface of an inorganic particle, and the inorganic particle is the core and the polymer is the shell.

[0043] In the inorganic material according to the first embodiment, functional groups on the surface of inorganic particles react with and bond to a polymer, thereby forming an inorganic material with a core-shell structure in which the surface of the inorganic particles is modified. For example, when metal hydroxides containing hydroxyl groups on their surfaces are used as inorganic particles, the hydroxyl groups can react with and bond to a polymer containing a hydroxyl group (-OH), an amino group (-NH2), a carboxyl group (-COOH), or a thiol group (-SH), thereby forming a core-shell structure.

[0044] In the inorganic material according to the second embodiment, a coupling agent is bonded to functional groups on the surface of inorganic particles, and the coupling agent bonded to the inorganic particles is then bonded to a polymer, thereby forming an inorganic material with a core-shell structure in which the surface of the inorganic particles is modified. For example, when an epoxy silane coupling agent is used, the silane end of the coupling agent is bonded to the inorganic particles, and the epoxy end is bonded to the polymer, thereby forming a core-shell structure.

[0045] In such cases, the inorganic particles form the core, the polymer forms the shell, and the coupling agent serves as a means for connecting the inorganic particles and the polymer.

[0046] On the other hand, when functional groups on the surface of inorganic particles react with a polymer or a coupling agent to form an inorganic material with a core-shell structure, as in the case of the inorganic material of the present invention, the bonding reaction occurs on the surface of the inorganic particles, so the core-shell structure can be stably formed.

[0047] However, when the surface of inorganic particles is simply coated with a polymer resin to form a core-shell structure, no bond is formed between the polymer resin and the inorganic particles on the surface of the inorganic particles. Therefore, if the coating is not successful, the polymer resin may not be present on the surface of the inorganic particles, and the two may exist separately. In such cases, the surface modification conversion rate of the inorganic particles is low, and the moisture formation suppression effect of the inorganic particles is reduced.

[0048] The inorganic particles are not particularly limited as long as they are generally used in the manufacture of separator coating layers for secondary batteries and are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0V to 5V based on Li / Li+). In particular, when inorganic particles with a high dielectric constant are used as the inorganic particles, they 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 solution.

[0049] The inorganic particles preferably contain inorganic particles with a high dielectric constant of 5 or more, preferably 10 or more. Examples of inorganic particles with a dielectric constant of 5 or more include Al(OH)3, AlOOH, Mg(OH)2, Al2O3, SiO2, TiO2, ZrO2, BaTiO3, BaSO4, 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 )O 3- It may be one or more selected from the group consisting of PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0050] In addition, inorganic particles having lithium ion transfer ability, i.e., inorganic particles containing lithium element but having the function of transferring lithium ions without storing lithium, may be used. Non-limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (LiPO), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, (LiAlTiP) x O y series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4, such as 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 lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as SiS2 series glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as P2S5 series glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or one or more selected from the group consisting of these mixtures, but not limited thereto.

[0051] Meanwhile, in one embodiment of the present invention, the inorganic coating layer may include a heat-absorbing material as inorganic particles. Such a heat-absorbing material can improve safety by absorbing heat when heat is generated due to abnormal battery operation. Examples of such a heat-absorbing material include, but are not limited to, oxides or hydroxides containing one or more elements selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc, and rare earth elements. More specifically, metal oxides include alumina, aluminum peroxide, tin-zinc oxide (ZnSnO, ZnSnO), antimony trioxide (SbO), antimony tetroxide (SbO), and antimony pentoxide (SbO). Metal hydroxides include aluminum hydroxide (Al(OH)), magnesium hydroxide (Mg(OH)), and zinc-tin hydroxide (ZnSn(OH)).

[0052] When inorganic particles having the above characteristics are used as a coating layer component, if an internal short circuit occurs between the positive and negative electrodes due to an external impact such as a needle-shaped conductor, the coating layer coated on the separator not only prevents direct contact between the positive and negative electrodes, but also prevents shrinkage of the separator substrate when exposed to high temperatures due to the inorganic particles packed in the coating layer.

[0053] The type of binder is not particularly limited as long as it does not cause a chemical change in the separation membrane coating layer. Examples of the binder include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymers and hydrogenated products thereof; (meth)acrylic acid ester copolymers such as methacrylic acid ester copolymers, acrylonitrile acrylic acid ester copolymers, and styrene acrylic acid ester copolymers; rubbers such as ethylene propylene rubber; polyvinyl acetate; polyphenylene ether, polysulfone, polyethersulfone, poly The resin may be a resin having a melting point or glass transition temperature of 180°C or higher, such as polyphenylene sulfide, polyetherimide, polyamide, polyimide, polyamideimide, polyetheramide, polyester, aromatic polyester, or polyetheretherketone; polycarbonate; polyacetal; or a water-soluble resin, such as carboxyalkyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinyl alcohol, sodium alginate, polyethylene glycol, cellulose ester, polyacrylic acid, polyacrylate, polyacrylamide, or polymethacrylic acid, or may be a polymer containing two or more of these.

[0054] The coupling agent may be a silane-based coupling agent, such as amino silane, epoxy silane, methacryloxy silane, vinyl silane, chlorine silane, or mercapto silane. Specifically, the epoxy silane may be, for example, diethoxy(3-glycidyloxypropyl)methylsilane.

[0055] The polymer may contain a hydroxyl group (-OH), an amino group (-NH2), a carboxyl group (-COOH), or a thiol group (-SH). The type of polymer is not particularly limited as long as it does not cause a chemical change in the separation membrane coating layer. Examples of the polymer include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydrogenated derivatives; (meth)acrylic acid ester copolymers such as methacrylic acid ester copolymer, acrylonitrile acrylic acid ester copolymer, and styrene acrylic acid ester copolymer; rubbers such as ethylene propylene rubber; polyvinyl acetate; polyphenylene ether, polysulfone, and polyether sulfonate. The polymer may be a resin having a melting point or glass transition temperature of 180°C or higher, such as propylene, polyphenylene sulfide, polyetherimide, polyamide, polyimide, polyamideimide, polyetheramide, polyester, aromatic polyester, or polyetheretherketone; polycarbonate; polyacetal; or a water-soluble resin, such as carboxyalkyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinyl alcohol, sodium alginate, polyethylene glycol, cellulose ester, polyacrylic acid, polyacrylate, polyacrylamide, or polymethacrylic acid, or a polymer containing two or more of these. At least a portion of the polymer may be substituted with a hydroxyl group (-OH), an amino group (-NH), a carboxyl group (-COOH), or a thiol group (-SH).

[0056] The weight average molecular weight of the polymer may be 1,000 g / mol to 5,000,000 g / mol.

[0057] In one specific example, when inorganic particles of metal hydroxide, a silane coupling agent having an epoxy group, and the polymer are stirred together at high temperature, the hydroxyl groups on the surface of the inorganic particles react with the silane coupling agent to epoxidize the surface of the inorganic material, and the epoxy groups of the silane coupling agent bonded to the surface of the inorganic material react with the hydroxyl groups, amino groups, carboxyl groups, or thiol groups at the end of the polymer, thereby bonding the silane coupling agent to the polymer.

[0058] As a result of such a reaction, FIG. 1 shows the process for producing an inorganic substance according to the first embodiment.

[0059] Referring to FIG. 1, the inorganic material is shown to have a core-shell structure formed by bonding a polymer to the surface of an inorganic particle.

[0060] That is, when a metal hydroxide is used as the inorganic material according to the first embodiment, a reaction occurs in which the hydroxyl groups on the surface bond with the polymer, so that even without a coupling agent, a core-shell structured inorganic material can be formed in which the polymer is bonded to the periphery of the inorganic particles, thereby modifying the surface of the inorganic particles.

[0061] FIG. 2 shows the process for producing an inorganic material according to the second embodiment.

[0062] 2, the inorganic material is shown as a core-shell structure in which a coupling agent is bonded to the surface of an inorganic particle, and the coupling agent bonded to the inorganic particle is bonded to a polymer, i.e., the inorganic material according to the second embodiment is a structure in which the inorganic particle constituting the core is bonded to the polymer constituting the shell via the coupling agent.

[0063] To manufacture a separation membrane according to the present invention, the steps of (a) preparing a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles, (b) preparing a separation membrane coating slurry by mixing the surface-modified inorganic material with a binder, and (c) coating both sides of a separation membrane substrate with the separation membrane coating slurry may be carried out.

[0064] The step (a) may include a process of reacting inorganic particles with a coupling agent, and then adding and reacting a polymer thereto.

[0065] In this way, when the inorganic particles and the coupling agent are reacted first in step (a), the surface modification conversion rate of the inorganic particles can be increased due to the reaction of the inorganic particles and the coupling agent bonding together, and therefore, even when hygroscopic inorganic particles are used, moisture formation can be prevented and the gas generation reduction effect can be improved.

[0066] The reaction temperature in step (a) may be 25°C to 200°C.

[0067] When the reaction temperature in step (a) is high, the reaction between the inorganic particles, the coupling agent, and the polymer becomes active, and the surface modification ratio of the core-shell structured inorganic material can be increased. The reaction temperature range may vary depending on the type of solvent used, but may be, for example, 25°C to 200°C, and more specifically, 60°C to 80°C.

[0068] The method may further include filtering and drying the surface-modified inorganic material prepared in step (a).

[0069] The surface-modified inorganic material prepared in step (a) may have a moisture content of 1,500 ppm or less.

[0070] Therefore, when a separator is manufactured using this method, a separator with a significantly reduced water content can be manufactured, thereby suppressing gas generation due to a reaction between water and the electrolyte.

[0071] A lithium secondary battery can be manufactured by incorporating the electrode assembly including the separator into a battery case. The electrode assembly may be a stack-type electrode assembly in which one or more positive electrodes and one or more negative electrodes are stacked with a separator interposed therebetween, a stack-folding type electrode assembly in which stacked unit cells including a positive electrode and a negative electrode are wound around a separator sheet, a lamination-stack type electrode assembly in which stacked unit cells including a positive electrode and a negative electrode are stacked with a separator interposed therebetween, or a winding type electrode assembly in which one positive electrode and one negative electrode are wound with a separator interposed therebetween.

[0072] The positive electrode is manufactured by, for example, applying a positive electrode mixture containing a positive electrode active material onto a positive electrode current collector and then drying the applied mixture. The positive electrode mixture may further selectively include a binder, a conductive material, a filler, etc., as needed.

[0073] The positive electrode current collector generally has a thickness of 3 μm to 500 μm. There are no particular limitations on the positive electrode current collector, as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. Furthermore, the positive electrode current collector can have micro-irregularities on its surface to enhance the adhesive strength of the positive electrode active material, and can be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0074] The positive electrode active material is a material capable of inducing an electrochemical reaction, and is a lithium transition metal oxide containing two or more transition metals. For example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; and lithium manganese oxides with the chemical formula LiNi 1-y M y Lithium nickel-based oxides represented by the formula: LiO2 (wherein M=Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, or Ga, and containing one or more elements among the above elements, and 0.01≦y≦0.8); 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li 1+z Ni 0.4 Mn 0.4 Co 0.2 Li, such as O2 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (wherein -0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1, M=Al, Mg, Cr, Ti, Si or Y, A=F, P or Cl) Lithium nickel cobalt manganese composite oxide; chemical formula Li 1+x M 1-y M' y PO 4-z X z (wherein M=transition metal, preferably Fe, Mn, Co, or Ni; M′=Al, Mg, or Ti; X=F, S, or N; and −0.5≦x≦0.5, 0≦y≦0.5, and 0≦z≦0.1).

[0075] The conductive material is usually added in an amount of 1 wt % to 30 wt % based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0076] The binder is a component that helps bind the active material and conductive material together and to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the mixture including the positive electrode active material. 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, styrene-butylene, fluororubber, and various copolymers.

[0077] The filler is a component that suppresses electrode expansion and is used selectively. It is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, and other fibrous materials.

[0078] The negative electrode is manufactured, for example, by applying a negative electrode mixture containing a negative electrode active material onto a negative electrode current collector and then drying the mixture. The negative electrode mixture may contain components such as the conductive material, binder, and filler as described above, as necessary.

[0079] The negative electrode current collector is generally made to have a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. can be used. Also, similar to the positive electrode current collector, minute irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc. can be used.

[0080] The negative electrode active material is, for example, silicon; carbon-based materials such as artificial graphite, natural graphite, amorphous hard carbon, soft carbon; 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, Group 1, Group 2, and Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), metal composite oxides such as lithium titanate; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as Sn, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used.

[0081] Hereinafter, the embodiments of the present invention will be described with reference to examples, which are for easier understanding of the present invention and do not limit the scope of the present invention thereby.

[0082] <Example 1> Al(OH)3 as inorganic particles, diethoxy(3-glycidyloxypropyl)methylsilane as a coupling agent, and carboxy-substituted polyvinylidene fluoride (PVDF) as a polymer were charged into a mixer in a weight ratio of 9:1:2 and stirred at 1,000 rpm at 60°C for 24 hours.

[0083] The stirred solution was separated using filter paper and then dried to produce Al(OH)3 with a core-shell structure, in which the core was Al(OH)3 and the shell was polyvinylidene fluoride substituted with carboxyl groups, connected by a coupling agent.

[0084] <Example 2> A surface-modified inorganic material was prepared in the same manner as in Example 1, except that Al(OH)3 as inorganic particles and diethoxy(3-glycidyloxypropyl)methylsilane as a coupling agent were added to a mixer and stirred at 60°C at 1,000 rpm for 24 hours, and then carboxy-substituted polyvinylidene fluoride (PVDF) as a polymer was added to the mixer and stirred at 60°C at 1,000 rpm for 24 hours.

[0085] Example 3 In Example 1, the coupling agent was omitted and Al(OH)3 and carboxy-substituted polyvinylidene fluoride (PVDF) were used as the polymer to prepare a core-shell Al(OH)3 with Al(OH)3 in the core and carboxy-substituted polyvinylidene fluoride in the shell.

[0086] <Comparative Example 1> Al(OH)3 was prepared without any treatment.

[0087] <Moisture measurement> A 0.2 g sample of each of the inorganic materials prepared in Examples 1 to 3 and Comparative Example 1 was taken and the moisture content was measured using a moisture measuring device (831 Coulometer, Metrohm) at 120°C for 300 seconds at a N2 flow rate of 60 ml / min. The moisture contents thus measured are shown in the table below.

[0088] <Gas generation rate measurement> 16 g of each of the inorganic materials prepared in Examples 1 to 3 and Comparative Example 1 and 15.4 ml of an electrolyte containing LiPF61M and a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 were placed in each aluminum pouch. The aluminum pouches were vacuum sealed and then stored in a convection oven at 60°C for 7 days.

[0089] Thereafter, the amount of gas generated in the aluminum pouch was measured using a volume measuring device (TWD-150DM, Matsuhaku), and the results are shown in Table 1 below.

[0090] [Table 1]

[0091] Referring to Table 1, it can be seen that the moisture contents of the inorganic substances of Examples 1 and 2 are only about 42% and about 33% of the moisture content of the inorganic substance of Comparative Example 1, which was not subjected to any treatment, and are reduced by about 58% and 67%, respectively. In addition, it can be seen that the gas generation amounts of the inorganic substances of Examples 1 and 2 are about 14% and about 11% of the gas generation amount of the inorganic substance of Comparative Example 1, respectively.

[0092] Furthermore, Example 3, which forms a core-shell structure without including a coupling agent, shows a result in which the moisture content is reduced by approximately 46% and the amount of gas generated is reduced by approximately 31% based on the moisture content of Comparative Example 1.

[0093] In Examples 1 to 3, the inorganic particles react with the coupling agent on the surface of the inorganic particles in Examples 1 and 2, resulting in a high surface modification conversion rate of the inorganic particles, which reduces moisture generation by the inorganic particles and significantly reduces the amount of gas generated.

[0094] In addition, since the coupling agent bonded to the surface of the inorganic particles binds with the polymer added later to form an inorganic material with a core-shell structure, the type of polymer bonded to the surface can be selectively applied to set or control the desired physical properties of the inorganic material.

[0095] Thus, when a separation membrane is manufactured using the inorganic material according to the present invention, the moisture adsorption is reduced, so that a separation membrane with a low moisture content can be manufactured.

[0096] Furthermore, since the amount of gas generated is significantly reduced, the capacity retention rate of the battery can be increased and the rate of increase in resistance can be suppressed.

[0097] Those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content.

Claims

1. The method includes the steps of: forming a porous membrane substrate; and forming a coating layer on at least one surface of the porous membrane substrate; The coating layer includes a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of an inorganic particle, The inorganic substance is Al(OH)3, The core-shell structure is configured to have a form in which an inorganic particle at the center and a polymer at the surface are bonded via a coupling agent, the coupling agent is diethoxy(3-glycidyloxypropyl)methylsilane; The polymer is polyvinylidene fluoride (PVDF) substituted with a carboxy group, and the separator for a lithium secondary battery is

2. 2. The separator for a lithium secondary battery according to claim 1, wherein the surface-modified inorganic material has a moisture content of 1,500 ppm or less.

3. A method for producing a separator for a lithium secondary battery according to claim 1 or 2, (a) preparing a surface-modified inorganic material having a core-shell structure in which a polymer is bound to the surface of inorganic particles; (b) mixing the surface-modified inorganic material with a binder to prepare a separator coating slurry; (c) coating both sides of a separation membrane substrate with the separation membrane coating slurry; A method for producing a separator for a lithium secondary battery, comprising:

4. 4. The method of claim 3, wherein step (a) comprises reacting inorganic particles with a coupling agent, and then adding a polymer thereto and reacting the resulting mixture.

5. A lithium secondary battery comprising an electrode assembly including the separator for lithium secondary batteries according to claim 1 or 2 housed in a battery case.

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