Method for manufacturing a separator for a lithium secondary battery, separator for a lithium secondary battery manufactured therefrom, and lithium secondary battery including the same

Abstract

The present invention provides a method for producing a separator for a lithium secondary battery, comprising the steps of: (S1) adding a binder polymer and inorganic particles to a solvent and mixing them to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed; and (S2) coating the slurry on at least one surface of a porous polyolefin polymer substrate having a plurality of pores, and drying the coating to form a porous coating layer, wherein the porous polyolefin polymer substrate has a thickness of 9 μm or less, the inorganic particles dispersed in the slurry have a D90 of 3 μm or less, and the porous coating layer has a surface roughness Ra of 50 to 500 nm.

Description

Technical Field

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0060057, filed with the Korean Intellectual Property Office on May 17, 2022, and the entire content thereof is incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a separator for a lithium secondary battery, in which a porous coating layer containing a binder polymer and inorganic particles is formed on the surface of a porous polyolefin polymer substrate, a separator for a lithium secondary battery manufactured therefrom, and a lithium secondary battery including the same.

Background Art

[0003] A separator for a lithium secondary battery has a plurality of pores and uses a porous substrate based on a polymer such as polyolefin.

[0004] In order to reinforce the heat resistance characteristics of such a porous polymer substrate, a separator in which a porous coating layer containing a binder polymer and inorganic particles is formed on the surface of the polymer substrate has been developed.

[0005] For the aforementioned separator for a lithium secondary battery, the average pore diameter of the porous polymer substrate can be adjusted according to its use. For example, a separator used in a lithium secondary battery for an electric vehicle has an average pore diameter of about 40 to 80 nm in a porous polyolefin polymer substrate. After manufacturing a slurry by dispersing inorganic particles in a polymer solution in which a binder polymer is dissolved in a solvent, this is coated and dried on the surface of the porous polymer substrate.

[0006] Generally, an electrode assembly is manufactured by a lamination process of joining a separator and an electrode by heat and pressure. The higher the heat and pressure applied in this process, the higher the bonding strength between the electrode and the separator. In recent years, for the purpose of improving productivity, while the process speed has increased, the time for applying heat during lamination has become shorter, and the bonding strength is ensured by increasing the pressure to ensure the adhesive strength.

[0007] However, in order to achieve a high energy density, thinning of the separation membrane is required. In the case of a porous polymer substrate with a normal thickness, even if the local pressure increases due to the inorganic particles of the porous coating layer, the sufficient thickness makes it less likely that insulation becomes a problem. However, when the thickness of the porous polymer substrate is thinned to 9 μm or less, protrusions formed by local aggregation of the inorganic particles of the porous coating layer apply pressure to the porous polymer substrate of the separation membrane and cause damage, and thus the insulation may deteriorate.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention provides a method for manufacturing a separator for a lithium secondary battery, which includes a porous coating layer containing a binder polymer and inorganic particles and a thin porous polyolefin polymer substrate, has improved compressibility, has a high breakdown voltage during a lamination process for manufacturing an electrode assembly, and has good life characteristics.

[0009] Another object of the present invention is to provide a separator for a lithium secondary battery manufactured by the manufacturing method having the above-described characteristics, and a lithium secondary battery including the same.

[0010] It will be easily understood that the objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof.

Means for Solving the Problems

[0011] The first aspect of the present invention is (S1) adding a binder polymer and inorganic particles to a solvent respectively and mixing them to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed; (S2) Coating and drying the slurry on at least one surface of a porous polyolefin polymer substrate having a plurality of pores to form a porous coating layer, a method for manufacturing a separator for a lithium secondary battery, The thickness of the porous polyolefin polymer substrate is 9 μm or less, The D90 of the inorganic particles dispersed in the slurry is 3 μm or less, The surface roughness Ra of the porous coating layer is 50 to 500 nm, Provided is a method for manufacturing a separator for a lithium secondary battery.

[0012] The second aspect of the present invention is as follows in the first aspect, The D90 of the inorganic particles dispersed in the slurry is 2 μm or less. Specifically, the D90 of the inorganic particles dispersed in the slurry is 0.5 to 1.4 μm. More specifically, the D90 of the inorganic particles dispersed in the slurry is 0.9 to 1.3 μm. Provided is a method for manufacturing a separator for a lithium secondary battery.

[0013] The third aspect of the present invention is as follows in the first aspect or the second aspect, The D50 of the inorganic particles added to the slurry is 100 to 700 nm, and the D90 is 2000 nm or less. More specifically, the D50 of the inorganic particles added to the slurry is 100 to 500 nm, and the D90 is 1500 nm or less. Even more specifically, the D50 of the inorganic particles added to the slurry is 200 to 400 nm, and the D90 is 800 nm or less. Provided is a method for manufacturing a separator for a lithium secondary battery.

[0014] The fourth aspect of the present invention is as follows in any one of the first aspect to the third aspect, The surface roughness Ra of the porous coating layer is 200 to 450 nm. More specifically, the surface roughness Ra of the porous coating layer is 250 to 420 nm. Provided is a method for manufacturing a separator for a lithium secondary battery.

[0015] A fifth aspect of the present invention is that, among the first to fourth aspects, in any one of them, a method for manufacturing a separator for a secondary battery is provided, wherein the thickness of the porous coating layer is 3 μm or less based on the thickness of the porous coating layer formed on one surface.

[0016] A sixth aspect of the present invention provides a separator for a lithium secondary battery manufactured by any one of the manufacturing methods of the first to fifth aspects.

[0017] A seventh aspect of the present invention provides a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator according to the sixth aspect.

Advantages of the Invention

[0018] The present invention is a method for manufacturing a separator in which a porous coating layer containing a binder polymer and inorganic particles is provided on the surface of a thin-film porous polymer substrate, and by adjusting the D90 of the inorganic particles dispersed in the slurry for forming the porous coating layer and adjusting the surface roughness of the formed porous coating layer within a predetermined range, the compression resistance of the separator is improved.

[0019] Thereby, even when a high pressure is applied during the lamination process for manufacturing the electrode assembly, the reduction rate of the thickness of the porous polyolefin polymer substrate due to the applied high pressure is small, the possibility of damage is improved, the breakdown voltage of the separator does not decrease, and the insulation characteristics are high.

Embodiments for Carrying Out the Invention

[0020] The present invention will be described in detail below. Prior to this, terms or words used in this specification and the claims should not be construed as ordinary or limited to their dictionary meanings. Based on the principle that the inventor can appropriately define the concept of terms in order to explain his own invention in the best way, they should be construed as meanings and concepts that conform to the technical idea of the present invention. Therefore, the configurations described in the embodiments described in this specification are merely the most desirable embodiments of the present invention and do not represent all of the technical ideas of the present invention. It should be understood that there may be various equivalents and modifications that can replace them at the time of this application.

[0021] Throughout this specification, when a part states that a certain component "includes", unless otherwise stated to the contrary, it means that it can further include other components rather than excluding other components.

[0022] In this specification, the characteristic of having pores means that a fluid in a gas phase and / or a liquid phase can pass from one side surface to the other side surface of the object through a structure in which the object includes a plurality of pores and the pores are interconnected with each other.

[0023] In this specification, the separator has a porous property including a plurality of pores and serves as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode in an electrochemical element.

[0024] The manufacturing method of the separator for a lithium secondary battery according to the present invention will be described in detail below.

[0025] The manufacturing method of the separator for a lithium secondary battery of the present invention includes: (S1) adding a binder polymer and inorganic particles to a solvent respectively, mixing them to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed; (S2) coating and drying the slurry on at least one surface of a porous polyolefin polymer substrate having a plurality of pores to form a porous coating layer. The method for manufacturing a separator for a lithium secondary battery is as follows: The thickness of the porous polyolefin polymer substrate is 9 μm or less. The D90 of the inorganic particles dispersed in the slurry is 3 μm or less. The surface roughness Ra of the porous coating layer is 50 - 500 nm.

[0026] First, a binder polymer and inorganic particles are added to a solvent respectively, mixed to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed (step S1).

[0027] The inorganic particles constituting the skeleton of the porous coating layer are not particularly limited as long as they are electrochemically stable. For example, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the applied battery (for example, 0 - 5V based on Li / Li + standard).

[0028] Examples of the above-mentioned inorganic particles include high dielectric constant inorganic particles having a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectricity, and inorganic particles having lithium ion transfer ability.

[0029] That is, examples of the inorganic particles include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, AlOOH, Al(OH)3, TiO2, and SiC, etc. These can be used alone or in combination of two or more, and are not limited thereto.

[0030] In addition, piezoelectric inorganic particles refer to substances that are insulators under normal pressure but have the property of conducting electricity due to internal structural changes when a certain pressure is applied. Such piezoelectric inorganic particles have a high dielectric constant value with a dielectric constant of 100 or more. Also, when a certain pressure is applied and they are stretched or compressed, charges are generated. One side becomes positively charged and the opposite side becomes negatively charged, resulting in a potential difference between the two sides. When using such piezoelectric inorganic particles, when an internal short circuit occurs between the two electrodes due to an external impact such as Local crush or Nail, a potential difference is generated within the particles due to the piezoelectricity of the inorganic particles. As a result, electron transfer between the two electrodes, that is, a flow of minute current occurs, thereby achieving a gentle reduction in the battery voltage and an improvement in safety. Examples of inorganic particles having piezoelectricity include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), or a mixture thereof, etc., but is not limited thereto.

[0031] Inorganic particles having lithium ion transfer ability refer to inorganic particles that contain lithium elements but have the function of moving lithium ions without storing lithium. Inorganic particles having lithium ion transfer ability can transfer and move lithium ions due to a kind of defect existing inside the particle structure, so the lithium ion conductivity in the battery is improved, and thereby the battery performance can be improved. Examples of inorganic particles having lithium ion transfer ability 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), such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, (LiAlTiP) x O y system 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), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 - based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 - based glass such as LiI - Li2S - P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc., but not limited thereto.

[0032] The D50 of the inorganic particles added to the slurry can be 100 to 700 nm, and the D90 can be 2,000 nm or less. Specifically, the D50 of the inorganic particles can be 150 to 650 nm, 200 to 600 nm, 250 to 550 nm, 300 to 500 nm, or 350 to 450 nm, and the D90 of the inorganic particles can be 1,900 nm or less, 1,800 nm or less, 1,700 nm or less, 1,600 nm or less, 1,500 nm or less, 1,400 nm or less, 1,300 nm or less, 1,200 nm or less, 1,100 nm or less, 1,000 nm or less, 900 nm or less, or 800 nm or less. Preferably, the D50 of the inorganic particles can be 100 to 500 nm, and the D90 can be 1,500 nm or less. More preferably, the D50 of the inorganic particles is 200 to 400 nm, and the D90 can be 800 nm or less. When adding the inorganic particles within the above-mentioned particle size range to the slurry, the D90 of the inorganic particles dispersed in the slurry can be adjusted to the target range, for example, D90 is adjusted to 3 μm. If the D50 of the inorganic particles exceeds 700 nm or the D90 exceeds 2,000 nm, there is a high probability that the inorganic particles will form protrusions on the formed porous coating layer, thereby increasing the possibility of damaging the porous polymer substrate during the lamination process.

[0033] The binder polymer dissolved in the slurry imparts adhesiveness to the polyolefin polymer base material of the porous coating layer and the electrode while connecting and fixing the inorganic particles. The binder polymers that can be used are polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, any one polymer selected from the group consisting of, or a mixture of two or more thereof. However, it is not particularly limited thereto.

[0034] The binder polymer and the inorganic particles can be included in a weight ratio of 1:99 to 50:50. The ratio can be appropriately adjusted within the above range. For example, based on a total of 100 wt% of the binder resin and the inorganic particles, the binder polymer can be 1 wt% or more, 5 wt% or more, or 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, 30 wt% or more, and the inorganic particles can be 70 wt% or more, 75 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, 95 wt% or more, or 99 wt% or more.

[0035] The above-mentioned binder polymer and inorganic particles are each added to a solvent and mixed to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed. After first adding the binder polymer to the solvent to produce a polymer solution, the inorganic particles can be added and mixed here, or after adding the inorganic particles to the solvent, the binder polymer can be added and mixed.

[0036] In the present invention, the D90 of the inorganic particles dispersed in the prepared slurry is adjusted to 3 μm or less. Specifically, the D90 of the inorganic particles dispersed in the slurry can be 2.9 μm or less, 2.8 μm or less, 2.7 μm or less, 2.6 μm or less, 2.5 μm or less, 2.4 μm or less, 2.3 μm or less, 2.2 μm or less, 2.1 μm or less, 2.0 μm or less, 1.9 μm or less, 1.8 μm or less, 1.7 μm or less, 1.6 μm or less, 1.5 μm or less, 1.4 μm or less, or 1.3 μm or less. In the slurry, the added inorganic particles aggregate with each other and the D90 becomes larger. If the D90 of the inorganic particles in the slurry exceeds 3 μm, there is a high possibility that the inorganic particles will form protrusions in the formed porous coating layer, and thereby, there is a high possibility of damaging the porous polymer substrate in the lamination process. Preferably, the D90 of the inorganic particles dispersed in the slurry can be 2 μm or less, more preferably, the D90 of the inorganic particles dispersed in the slurry can be 0.5 to 1.4 μm, and most preferably, the D90 of the inorganic particles dispersed in the slurry can be 0.9 to 1.3 μm.

[0037] Therefore, by adjusting the addition of the dispersant, premixing, and milling processes, etc., the D90 of the inorganic particles dispersed in the slurry is adjusted to 3 μm or less. For example, after further adding a dispersant to the slurry, a slurry obtained by adding inorganic particles and a partial amount of binder polymer is first produced, mixed and milled, and then a polymer solution obtained by adding the remaining amount of polymer to this slurry is added, and the D90 of the inorganic particles dispersed in the slurry can be adjusted by a method of performing mixing and milling, but it is not limited thereto.

[0038] The slurry prepared to have the above-described characteristics is coated and dried on at least one surface of a porous polyolefin polymer substrate having a plurality of pores to form a porous coating layer (S2 step).

[0039] In the present invention, as is well known, the porous polyolefin polymer substrate is produced using a polyolefin as a base polymer. Examples of the polyolefin include polyethylene, polypropylene, polypentene, etc., and one or more of these can be included. A porous polymer substrate produced based on such a polyolefin, that is, having a plurality of pores, is advantageous from the viewpoint of imparting a shutdown function at an appropriate temperature. In particular, when polyethylene and polypropylene are simultaneously included as the polyolefin, physical properties such as shutdown characteristics and mechanical strength can be improved simultaneously.

[0040] When manufacturing the polymer substrate, in addition to the polyolefin-based polymer described above, other polymer components can be further mixed as needed, and filler particles can be further included. The filler particles can be introduced for the purpose of a pressure barrier so that the thickness, pore size, and porosity of the separation membrane substrate do not decrease excessively with respect to the high pressure applied in the lamination process. The filler particles can include organic fillers or inorganic fillers having a predetermined particle size, and are not limited to specific components as long as they have a strength greater than that of the polyolefin resin.

[0041] In the present invention, the thickness of the porous polyolefin polymer substrate is 9 μm or less. Since such a porous polyolefin polymer substrate with a thickness of 9 μm or less is a thin film, it becomes possible to realize a lithium secondary battery having a high energy density. More specifically, the thickness of the porous polyolefin polymer substrate can be 7 to 9 μm, and more specifically, it can be 8 to 9 μm, but is not limited thereto.

[0042] The porous polyolefin polymer substrate described above can be manufactured as follows, but is not limited thereto.

[0043] In one embodiment of the present invention, the porous polyolefin polymer substrate can be manufactured by a method (dry method) in which a polyolefin polymer is melt-extruded and formed into a sheet shape, and then stretched to induce micro cracks between lamellae, which are crystalline portions of the polymer, to form fine voids. In addition to this, the separation membrane can be manufactured by a method (wet method) in which a polyolefin polymer is kneaded with diluents at a high temperature to form a single phase, the polymer material and the diluent are phase-separated during the cooling process, and then the diluent is extracted to form pores.

[0044] When adding a filler, the size of the filler particles can be such that the particle size is from 0.001 μm to less than 100 μm. Preferably, the filler particles can have a particle size of 0.01 μm to 0.1 μm, and after the lamination process of the separation membrane substrate, it can be appropriately adjusted within the above range considering the target thickness.

[0045] The thickness of the formed porous coating layer can be 3 μm or less based on the thickness of the porous coating layer formed on one side, but is not limited thereto.

[0046] On the other hand, the surface roughness Ra of the formed porous coating layer is 50 to 500 nm. If the surface roughness Ra is less than 50 nm, the electrode adhesion may decrease, and if it exceeds 500 nm, there may be protrusions that locally induce deformation of the polymer substrate during lamination. In this regard, the surface roughness Ra of the porous coating layer can be 200 to 450 nm, and more specifically, the surface roughness Ra of the porous coating layer can be 250 to 420 nm.

[0047] The surface roughness Ra of the porous coating layer depends on the D90 of the inorganic particles dispersed in the above-mentioned slurry and the coating method of the slurry. In this regard, it is preferable that the coating method proceeds by a microgravure coating method or a direct metering coating method, but is not limited thereto. Also, for the drying method, the temperature and time conditions are appropriately set so as to minimize the generation of surface defects of the porous coating layer. For the drying, a drying auxiliary device such as a drying oven or hot air can be used within an appropriate range.

[0048] The separator for a lithium secondary battery manufactured by the method described above is interposed between the positive electrode, the negative electrode, and between the positive electrode and the negative electrode to form an electrode assembly and is manufactured as a lithium secondary battery. That is, the separator for a lithium secondary battery manufactured by the method described above is interposed between the negative electrode and the positive electrode and is manufactured as an electrode assembly by a lamination process in which heat and / or pressure is applied to bond them. In one embodiment of the present invention, the lamination process can be performed by a roll press device including a pair of pressure rollers. That is, the negative electrode, the separator, and the positive electrode are sequentially laminated, and this can be introduced between the pressure rollers to achieve interlayer bonding. At this time, the lamination process can be performed by a hot pressing method.

[0049] The positive electrode includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material is a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga and x = 0.01 to 0.3), Ni-site type lithium nickel oxide represented by the formula; chemical formula LiMn 1-x M xA lithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta and x = 0.01 to 0.1), or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; It can contain one or a mixture of two or more of Fe2(MoO4)3.

[0050] The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. As the negative electrode active material, the negative electrode uses carbon such as lithium metal oxide, graphitized carbon, and graphite-based carbon; LixFe2O3 (0 ≦ x ≦ 1), LixWO2 (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, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; It can contain one or a mixture of two or more selected from titanium oxides.

[0051] The conductive material can be any one selected from the group consisting of, for example, graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it can be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0052] The current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, stainless steel, copper, aluminum, nickel, titanium, fired carbon, or those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used.

[0053] For the binder resin, polymers commonly used in electrodes in the art can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyetylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, etc., and are not limited thereto.

[0054] The electrode assembly prepared as described above can be placed in a suitable case and an electrolytic solution can be injected to manufacture a battery.

[0055] The electrolytic solution is A + B- A salt having a structure such as + wherein A + is an alkali metal cation such as Li + Na + K - or an ion composed of a combination thereof, and B - is PF6 - BF4 - Cl - Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - or an ion composed of a combination thereof, and there is a salt dissolved or dissociated in an organic solvent composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), or a mixture thereof, but is not limited thereto.

[0056] A battery module including the battery including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source can be provided. Specific examples of the device include a power tool powered by a battery motor; electric vehicles including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; electric two-wheel vehicles including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; a power storage system, etc., but are not limited thereto.

[0057] Hereinafter, in order to specifically describe the present invention, examples will be given and described in detail. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0058] [Example 1] As the porous polyolefin polymer substrate, a wet polyethylene separator (thickness: 8 μm) with a porosity of 45% from Toray was used.

[0059] On the other hand, a binder polymer and inorganic particles were each added to a solvent and mixed to prepare a slurry in which the binder polymer was dissolved and the inorganic particles were dispersed as follows.

[0060] At room temperature, Al2O3 inorganic particles (D50: 0.29 μm, D90: 0.69 μm) and a dispersant (BYK Disperbyk-111) diluted with acetone to a concentration of 25% were added to acetone and stirred for 1 hour to prepare a pre-dispersion liquid. Among the pre-dispersion liquid, the content of the dispersant was 1.25% based on the content of the inorganic particles, and the solid content of the pre-dispersion liquid was manufactured to be 30%. The pre-dispersion liquid was put into a bead mill disperser (Nano Intec, NITUBM-3) and milled a total of 2 times with 0.7 mm beads and a rotor rotation speed of 1500 rpm. After adding a mixed solution of cyanoethyl PVA (molecular weight 4 million), PVDF-HFP (molecular weight 4 million, HFP 8w%), and PVDF-HFP (molecular weight 5 million, HFP 15w%) dissolved in acetone and manufactured at a concentration of 8% to the milled pre-dispersion liquid, it was milled 2 more times to manufacture a slurry for forming a porous coating layer. At this time, the contents of cyanoethyl PVA (molecular weight 4 million), PVDF-HFP (molecular weight 4 million, HFP 8w%), and PVDF-HFP (molecular weight 5 million, HFP 15w%) were 1.25%, 13.8%, and 8.7% respectively based on the inorganic content, and the solid content of the slurry was prepared to be 18%. The results of measuring the D90 of the slurry manufactured as described above are shown in Table 1.

[0061] After filtering the prepared slurry through a 200-mesh filter, it was coated on the aforementioned polymer base fabric using a direct metering coater and dried under conditions of a relative humidity of 40% and a temperature of 50 °C to form a porous coating layer coated on both sides. The thickness of the polymer base fabric, the particle size of the inorganic particles introduced, the particle size of the inorganic particles in the slurry, the total thickness of the porous coating layer formed on both sides, and the surface roughness Ra of the porous coating layer were measured and shown in Table 1.

[0062] [Example 2] It was manufactured in the same manner as in Example 1, except that the coating thickness was controlled to 3 / 3 μm on both sides.

[0063] [Example 3] It was produced in the same manner as in Example 2, except that the dispersant Disperbyk 111 and cyanoethyl PVA were added without dissolving them in acetone.

[0064] [Example 4] It was produced in the same manner as in Example 3, except that a fabric with the thickness of the PE separation membrane substrate changed to 9 μm was used.

[0065] [Comparative Example 1] It was produced in the same manner as in Example 2, except that the dispersant and the inorganic substance were not pre-dispersed, and were added simultaneously when adding the binder, and then milled a total of 4 times.

[0066] [Comparative Example 2] It was produced in the same manner as in Example 2, except that the content of Cyanoethyl PVA was increased to 2.5% and added to the pre-dispersion liquid, excluding the Disperbyk 111 dispersant.

[0067] [Comparative Example 3] It was produced in the same manner as in Comparative Example 2, except that a fabric with the thickness of the PE separation membrane substrate changed to 10 μm was used.

[0068] [Measurement of D50 and D90 of Inorganic Particles] D50 is defined as the particle size at the 50% standard of the particle size distribution, and D90 is defined as the particle size at the 90% standard of the particle size distribution. It was measured using the laser diffraction method by putting it into wet particle size analysis equipment (Mastersizer 3000, manufactured by Malvern).

[0069] [Measurement of Surface Roughness Ra of Porous Coating Layer] Ten arbitrary points were selected from the entire area of the surface of the porous coating layer, and the surface roughness (Ra) was measured using an Optical profiler (NV-2700), and the average value was obtained.

[0070] [Measurement of Dielectric Breakdown Voltage after Compression] The release PET cut into 10×10 cm was laminated on the upper and lower parts of the separation membrane cut into 5×5 cm. At this time, the release surface of the release PET was made to touch the separation membrane. The separation membrane laminated with PET was hot-pressed for 10 seconds under the conditions of a temperature of 70 °C and a pressure of 5.2 MPa to produce a compressed separation membrane sample.

[0071] The coated separation membrane sample prepared between aluminum jigs (upper jig diameter 30 mm, lower jig 50×100 mm) was placed, and the voltage at which the fail condition (>0.5 mA, 3 sec) occurred was measured with a hi-pot tester. At this time, the measurement conditions were set to DC, a current of 0.5 mA, and a pressure increase of 100 V / s (up to 3 kV).

[0072] [Measurement of capacity retention rate] 1) Manufacture of positive electrode Positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), conductive material (carbon black), dispersant, and binder resin (mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66, and a slurry for the positive electrode active material layer with a concentration of 50 wt% of the remaining components after removing water was prepared. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to manufacture a positive electrode having a positive electrode active material layer (thickness 120 μm).

[0073] 2) Manufacture of negative electrode Graphite (mixture of natural graphite and artificial graphite), conductive material (carbon black), dispersant, and binder resin (mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66, and a slurry for the negative electrode active material layer with a concentration of 50 wt% of the remaining components after removing water was prepared. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to manufacture a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0074] 3) Lamination process The manufactured negative electrode and positive electrode were laminated with the separator of the examples and comparative examples interposed therebetween, and a lamination process was performed to obtain an electrode assembly. The lamination process was carried out for 10 seconds under the conditions of 70 °C and 5.2 MPa using hot pressing.

[0075] 4) Electrolyte injection The electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (the mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0076] The batteries manufactured by the method described above were repeatedly charged and discharged in the range of 2.5 V to 4.25 V at a rate of 2C each at 25 °C, and the ratio of the discharge capacity after 50 cycles was derived by calculation.

[0077]

Table 1

Claims

1. (S1) Adding a binder polymer and inorganic particles to a solvent respectively, and mixing them to prepare a slurry in which the binder polymer is dissolved and the inorganic particles are dispersed; (S2) Coating and drying the slurry on at least one surface of a porous polyolefin polymer substrate having a plurality of pores to form a porous coating layer; A method for manufacturing a separator for a lithium secondary battery, comprising: The thickness of the porous polyolefin polymer substrate is 9 μm or less; D90 of the inorganic particles dispersed in the slurry is 3 μm or less; The surface roughness Ra of the porous coating layer is 50 to 500 nm; D50 of the inorganic particles added to the slurry is 400 nm or less. A method for manufacturing a separator for a lithium secondary battery.

2. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D90 of the inorganic particles dispersed in the slurry is 2 μm or less.

3. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D90 of the inorganic particles dispersed in the slurry is 0.5 to 1.4 μm.

4. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D90 of the inorganic particles dispersed in the slurry is 0.9 to 1.3 μm.

5. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D50 of the inorganic particles added to the slurry is 100 to 400 nm, and D90 is 2,000 nm or less.

6. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D50 of the inorganic particles added to the slurry is 100 to 400 nm, and D90 is 1,500 nm or less.

7. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein D50 of the inorganic particles added to the slurry is 200 to 400 nm, and D90 is 800 nm or less.

8. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein the surface roughness Ra of the porous coating layer is 200 to 450 nm.

9. The method for manufacturing a separator for a lithium secondary battery according to Claim 1, wherein the surface roughness Ra of the porous coating layer is 250 to 420 nm.

10. The manufacturing method of the separator for a lithium secondary battery according to claim 1, wherein the thickness of the porous coating layer is 3 μm or less based on the thickness of the porous coating layer formed on one surface.

11. In a method for manufacturing a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the separator is a separator manufactured by any one of claims 1 to 10, and the method for manufacturing a lithium secondary battery is characterized by this.

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