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

Abstract

According to one aspect of the present invention, there is provided a method for manufacturing a separator for a lithium secondary battery having improved compression resistance, comprising the steps of (S11) coating at least one surface of a porous polymer substrate having a plurality of pores with a polymer solution in which a first polymer having electrolyte solubility is dissolved in a solvent, thereby impregnating the pores of the porous polymer substrate with the polymer solution, and (S12) coating a slurry containing a second polymer having electrolyte insolubility on the coated polymer solution, and drying the slurry.

Description

Technical Field

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0068744, filed with the Korean Intellectual Property Office on June 7, 2022, and all of its contents are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a separator for a lithium secondary battery with improved compression resistance, a separator for a lithium secondary battery manufactured therefrom, and a method for manufacturing a lithium secondary battery using the same.

Background Art

[0003] A separator for a lithium secondary battery having a plurality of pores and using a porous substrate based on a polymer such as polyolefin has been used. In order to improve the adhesion between the porous polymer substrate and the electrode, or to reinforce the heat resistance and the like of the porous polymer substrate, a separator having a polymer layer or a polymer-containing coating layer formed by mixing a polymer and inorganic particles on at least one surface of the porous polymer substrate has been developed.

[0004] Generally, an electrode assembly is manufactured by a lamination process of joining a separator and an electrode with heat and pressure. The higher the heat and pressure applied in this process, the higher the adhesion between the electrode and the separator.

[0005] In recent years, for the purpose of improving productivity, the process speed has increased, the time for applying heat to the separator has decreased, and the adhesion is ensured by increasing the pressure to ensure adhesion. However, there is a risk that the pores of the separator may become smaller or blocked due to high pressure.

Summary of the Invention

Problems to be Solved by the Invention

[0006] When laminating a separation membrane provided with a coating layer containing a polymer on at least one surface of a porous polymer substrate and an electrode, due to the high pressure applied, the present invention aims to provide a method for manufacturing a separation membrane for a lithium secondary battery that can improve the deformation phenomenon in which the pores of the porous polymer substrate become smaller or are blocked, and a lithium secondary battery using the same.

[0007] Another object of the present invention is to provide a separation membrane for a lithium secondary battery having the above-described characteristics.

[0008] 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

[0009] The first aspect of the present invention is

[0010] (S11) Coating at least one surface of a porous polymer substrate having a plurality of pores with a polymer solution in which a first polymer having electrolyte solubility is dissolved in a solvent to impregnate the pores of the porous polymer substrate with the polymer solution;

[0011] (S12) Coating a slurry containing a second polymer insoluble in an electrolyte on the coated polymer solution and drying it, and providing a method for manufacturing a separation membrane for a lithium secondary battery.

[0012] The second aspect of the present invention is, in the first aspect,

[0013] Before coating the slurry according to the step of S12, it is possible to further provide a method for manufacturing a separation membrane for a lithium secondary battery including a step of drying the polymer solution coated according to the step of S11.

[0014] The third aspect of the present invention is, in the first aspect or the second aspect,

[0015] The first polymer can provide a method for manufacturing a separator membrane for a lithium secondary battery, including one or more selected from the group consisting of polyacrylonitrile (PAN), polylactic acid (PLA), and polyacrylic acid (PAA).

[0016] The fourth aspect of the present invention is in any one of the first to third aspects,

[0017] A method for manufacturing a separator membrane for a lithium secondary battery can be provided, wherein the first polymer concentration of the polymer solution is 5% to 70% by weight.

[0018] The fifth aspect of the present invention is in any one of the first to fourth aspects,

[0019] The second polymer can provide a method for manufacturing a separator membrane for a lithium secondary battery, including one or more selected from the group consisting of PVDF-HFP copolymer, PVDF-CTFE copolymer, PVDF-HFP-CTFE terpolymer, and cyanoethyl polyvinyl alcohol.

[0020] The sixth aspect of the present invention is in any one of the first to fifth aspects,

[0021] A method for manufacturing a separator membrane for a lithium secondary battery can be provided, wherein the slurry further contains inorganic particles.

[0022] The seventh aspect of the present invention is

[0023] A porous polymer substrate having a plurality of closed pores and containing a first polymer having electrolyte solubility inside the plurality of closed pores,

[0024] And an outer coating layer disposed on at least one surface of the porous polymer substrate and containing a second polymer having non-solubility in an electrolyte, to provide a separator membrane for a lithium secondary battery.

[0025] The eighth aspect of the present invention is in the seventh aspect,

[0026] Further comprising a coating layer disposed between the porous polymer substrate and the outer coating layer, the coating layer can provide a separator for a lithium secondary battery containing the first polymer.

[0027] A ninth aspect of the present invention is

[0028] A porous polymer substrate having a plurality of pores,

[0029] A coating layer of a first polymer having electrolyte solubility, located inside the pores so that the pores of the porous polymer substrate are closed,

[0030] And an outer coating layer containing a second polymer having non-electrolyte solubility, located on the upper surface of the coating layer of the first polymer, can provide a separator for a lithium secondary battery.

[0031] A tenth aspect of the present invention is, among the seventh to ninth aspects, in any one of them,

[0032] The first polymer can provide a separator for a lithium secondary battery containing one or more selected from the group consisting of polyacrylonitrile (PAN), polylactic acid (PLA), and polyacrylic acid (PAA).

[0033] An eleventh aspect of the present invention is, among the seventh to tenth aspects, in any one of them,

[0034] The second polymer can provide a separator for a lithium secondary battery containing one or more selected from the group consisting of a PVDF-HFP copolymer, a PVDF-CTFE copolymer, a PVDF-HFP-CTFE terpolymer, and cyanoethyl polyvinyl alcohol.

[0035] A twelfth aspect of the present invention is, among the seventh to eleventh aspects, in any one of them,

[0036] The outer coating layer can provide a separator for a lithium secondary battery that further contains inorganic particles.

[0037] According to a 13th aspect of the present invention, in any one of the 7th to 12th aspects,

[0038] it is possible to provide a separator for a lithium secondary battery in which the content ratio of the inorganic particles and the second polymer in the outer coating layer is 50:50 to 99:1.

[0039] A 14th aspect of the present invention is

[0040] (S21) preparing an electrode assembly by laminating a separator for a lithium secondary battery of any one of the 7th to 13th aspects with a positive electrode and a negative electrode;

[0041] (S22) including a step of injecting an electrolytic solution into the laminated electrode assembly and dissolving the first polymer to open the closed pores of the porous polymer base material. A method for manufacturing a lithium secondary battery is provided.

Advantages of the Invention

[0042] In the method for manufacturing a separator provided with a coating layer containing a polymer on at least one surface of a porous polymer base material, a solution of a first polymer soluble in an electrolytic solution is coated on at least one surface of the porous polymer base material to impregnate the pores of the porous polymer base material, and then a slurry containing a second polymer insoluble in the electrolytic solution is coated and dried.

[0043] According to such a manufacturing process, in the pores of the porous polymer base material, the first polymer is located inside the pores due to the coating layer of the first polymer, and the pores are closed. Thus, even when a high pressure is applied during the lamination process with the electrode, the deformation phenomenon in which the pores become smaller or are blocked due to the first polymer located inside the pores is improved.

[0044] After the manufactured electrode assembly is loaded into a battery case, an electrolyte is injected to manufacture a secondary battery. The first polymer located inside the pores of the porous polymer substrate and closing the pores is eluted by the electrolyte, and the passage function of lithium ions is restored when the closed pores are opened.

[0045] The accompanying drawings illustrate preferred embodiments of the invention and, together with the detailed description, explain the principles of the invention, but the scope of the invention is not limited thereto. On the other hand, the shape, size, scale, or ratio of elements in the drawings included in this specification can be exaggerated for the purpose of emphasizing a clearer explanation.

Brief Description of the Drawings

[0046]

Figure 1

[0047]

Figure 2

Modes for Carrying Out the Invention

[0048] Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in this specification and the claims should not be construed as being ordinary or limited to their dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they must be construed in a meaning and concept consistent with the technical idea of the present invention. Therefore, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, so there may be various equivalents and modifications that can replace them at the time of this application.

[0049] Throughout this specification, when a part states that a certain component "includes" something, this means that, unless otherwise stated to the contrary, it does not exclude other components but can further include other components.

[0050] In this specification, the characteristic of having pores means that the object includes a plurality of pores, and a fluid in the gas phase and / or liquid phase can pass through one side surface of the object due to a structure in which the pores are interconnected with each other to the other side surface.

[0051] In this specification, the separator is a porous one having 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 a lithium secondary battery.

[0052] Hereinafter, the manufacturing method of the separator for a lithium secondary battery according to the present invention will be described in detail.

[0053] The manufacturing method of the separator for a lithium secondary battery of the present invention is

[0054] (S11) Coating at least one surface of a porous polymer substrate having a plurality of pores with a polymer solution in which a first polymer having electrolyte solubility is dissolved in a solvent, and impregnating the polymer solution into the pores of the porous polymer substrate;

[0055] (S12) Coating a slurry containing a second polymer insoluble in an electrolyte on the coated polymer solution and drying it.

[0056] First, the step (S11) of coating at least one surface of a porous polymer substrate having a plurality of pores with a polymer solution in which a first polymer having electrolyte solubility is dissolved in a solvent, and impregnating the polymer solution into the pores of the porous polymer substrate will be described.

[0057] In the present invention, the porous polymer substrate can be made of a known polymer known to be usable as a porous polymer substrate for a lithium secondary battery, such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, etc. In particular, it can be made with polyolefin as the base polymer. For example, in the case of polyolefin, polyethylene, polypropylene, polypentene, etc. can be cited, and one or more of these can be included. Such a porous polymer substrate based on polyolefin, that is, a polymer substrate 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.

[0058] When manufacturing the polyolefin polymer substrate, in addition to the aforementioned polyolefin-based polymer, other polymer components or filler particles can be further mixed as necessary. 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 are not reduced too much against the high pressure applied in the lamination process. The filler particles can include organic fillers and inorganic fillers having a predetermined particle size, and are not limited to specific components as long as they have a strength higher than that of the polyolefin resin.

[0059] The thickness of the porous polymer substrate can be 5 μm to 30 μm, but is not limited thereto. Also, the average pore diameter of the porous polymer substrate, particularly the polyolefin porous polymer substrate, can be 20 nm to 80 nm, more specifically 40 nm to 80 nm, but is not limited thereto.

[0060] The average pore diameter of the porous polymer substrate can be calculated from the pore size distribution measured using the Capillary flow Porometer method. For example, first, the separation membrane to be measured is wetted with a wetting agent such as galwick solution, and then the air pressure on one side of the substrate is gradually increased. At this time, when the applied air pressure becomes greater than the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is pushed out, and the pore size and distribution are measured based on the pressure and flow rate at the moment of extrusion, from which the average pore diameter (size) can be confirmed.

[0061] The porous polyolefin polymer substrate most commonly used as the porous polymer substrate can be manufactured as follows, but is not limited thereto.

[0062] In one embodiment of the present invention, the porous polyolefin polymer substrate is produced 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 the crystalline parts of the polymer, to form fine voids. In addition to this, the separation membrane can be produced 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.

[0063] 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. Desirably, the filler particles can have a particle size of 0.01 μm to 0.1 μm, and can be appropriately adjusted within the above range in consideration of the target thickness after the lamination process of the separation membrane substrate.

[0064] The polymer solution coated on the porous polymer substrate is produced by dissolving a first polymer having electrolyte solubility in a solvent.

[0065] The first polymer having electrolyte solubility is a polymer that is injected into the battery case equipped with the electrode assembly and dissolved by the electrolyte that impregnates the electrode assembly, and means the polymer that is finally eluted by the electrolyte in the lithium secondary battery product.

[0066] As the solvent, any liquid that can dissolve the first polymer can be used, but when a solvent having an affinity with the polymer component of the porous polymer substrate is used, it is easy to penetrate into the pores of the porous polymer substrate.

[0067] In this regard, examples of the first polymer include polyacrylonitrile (PAN), polylactic acid (PLA), polyacrylic acid (PAA), etc., and these can be used alone or in a mixture of two or more, but are not limited thereto. As the solvent, one or more of carbonate solvents such as dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, and ethylene carbonate, which are the main components of non-aqueous electrolytes, can be used, but are not limited thereto.

[0068] The concentration of the first polymer in the polymer solution is preferably sufficient to be located inside the pores of the surface layer of the porous polymer substrate after drying and to close the pores and impart pressure resistance. In this regard, the concentration of the first polymer in the polymer solution can be 5 wt% to 70 wt%, but is not limited thereto.

[0069] The step of coating a polymer solution on a porous polymer substrate and impregnating the pores of the porous polymer substrate can use ordinary coating methods. In particular, it is preferably applied by dip coating, die coating, roll coating, comma coating, or a mixed method thereof. The polymer solution can be coated only on one side of the porous polymer substrate or on both sides.

[0070] By such coating of the polymer solution, the polymer solution can penetrate and be located on the surface of the porous polymer substrate or at least the surface layer part of the pores of the porous polymer substrate.

[0071] Next, the step (S12) of coating and drying a slurry containing a second polymer insoluble in the electrolyte on the coated polymer solution will be described.

[0072] The second polymer having electrolyte insolubility means a polymer that is injected into the battery case equipped with the electrode assembly and is not dissolved by the electrolyte that impregnates the electrode assembly, and means a polymer that is not finally eluted by the electrolyte in the lithium secondary battery product. That is, the second polymer having electrolyte insolubility must be interpreted to mean a polymer that does not need to be eluted in the electrolyte, so it includes a polymer that swells but is not dissolved by the electrolyte.

[0073] In such aspects, examples of the second polymer include PVDF-HFP copolymer (vinylidene fluoride-hexafluoropropylene copolymer), PVDF-CTFE copolymer (vinylidene fluoride-chlorotrifluoroethylene copolymer), PVDF-HFP-CTFE terpolymer (vinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene terpolymer), cyanoethyl polyvinyl alcohol, etc. These can be used individually or as a mixture of two or more, but are not limited thereto. Such second polymers and the like are not dissolved even when swollen by a carbonate-based solvent used as a main component of the non-aqueous electrolyte.

[0074] The slurry containing the second polymer can be produced in any one of a form (first form) consisting of a polymer solution obtained by dissolving the second polymer in an organic solvent, a slurry in a form in which the second polymer is dispersed in an aqueous dispersion medium (second form), a slurry in which inorganic particles and the like are further added to and dispersed in the slurry of the first form (third form), and a slurry in which inorganic particles and the like are further added to and dispersed in the slurry of the second form (fourth form).

[0075] Examples of the production methods of the slurry of the third form and the slurry of the fourth form will be described below, but are not limited thereto.

[0076] The slurry of the third form is produced as a polymer solution by dissolving the second polymer in a suitable organic solvent. As the solvent, it is preferable that the solubility index is similar to that of the second polymer to be used and the boiling point is low. This is for uniform mixing and subsequent easy removal of the solvent. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof. Next, inorganic particles are added and dispersed in the produced polymer solution. The content ratio of the inorganic particles to the second polymer can be 50:50 to 99:1, and is appropriately adjusted in consideration of the thickness, pore size, and porosity of the finally produced coating layer.

[0077] The slurry of the fourth form is produced as a slurry by dispersing particles composed of the second polymer and inorganic particles in an aqueous dispersion medium. The aqueous dispersion medium is a hydrophilic liquid such as water or alcohol, and is a dispersion medium that does not dissolve the above-mentioned inorganic particles and binder polymer particles. Since the polymer particles are not dissolved in the aqueous dispersion medium, they maintain their particulate state when added to the slurry, and their shape is usually circular particles, but is not limited thereto. Thus, since the polymer particles maintain their particulate state, they hardly penetrate into the pores of the porous polymer substrate, contributing to improving the pore plugging phenomenon of the polymer substrate.

[0078] The second polymer added during the production of the slurries of the third and fourth forms imparts adhesiveness to the polymer substrate and the electrode to the coating layer while connecting and fixing between the inorganic particles during the formation of the coating layer.

[0079] In the case of the inorganic particles added during the production of the slurry in the third and fourth embodiments, there is no particular limitation 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 they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied battery (e.g., 0 to 5 V based on Li / Li + reference).

[0080] 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, inorganic particles having lithium ion transfer ability, and the like.

[0081] 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.

[0082] In addition, piezoelectric inorganic particles mean a substance that is an insulator at normal pressure but conducts electricity due to internal structure 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 it is stretched or compressed, charges are generated. One side is positive and the opposite side is negative, and each is charged, so a potential difference is generated between the two sides. When such piezoelectric inorganic particles are used, 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 inside the particles due to the piezoelectricity of the inorganic particles. As a result, electron movement between the two electrodes, that is, a fine current flows, so that a gentle decrease in the battery voltage and an improvement in safety can be achieved. 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(Mg1 / 3 Nb 2 / 3 ) O3-PbTiO3 (PMN-PT), hafnium oxide (HfO2), or a mixture thereof, etc., but not limited thereto.

[0083] Inorganic particles having lithium ion transport 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 transport ability can transmit 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 transport 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), (LiAlTiP) x O y -based glass (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, etc., 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 (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (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.

[0084] The particle size of the inorganic particles is not limited, but is preferably in the range of 0.001 μm to 10 μm for forming a porous coating layer with a uniform thickness and an appropriate porosity.

[0085] Of course, a dispersant or the like can be further added to the slurries of the first to fourth forms as necessary.

[0086] The method of coating a slurry containing a second polymer insoluble in the electrolyte on the coated polymer solution is not particularly limited to any one method, and ordinary methods known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination of these can be utilized.

[0087] Also, for the step of drying the coated slurry, the temperature and time conditions are appropriately set so as to minimize the generation of surface defects in the coating layer. For the drying, a drying aid such as a drying oven or hot air can be used within an appropriate range.

[0088] In the present invention, before coating the slurry according to the step S12, the coated polymer solution according to the step S11 can also be dried first. For the drying, a drying aid such as a drying oven or hot air can also be used within an appropriate range.

[0089] According to one aspect of the present invention, there is provided a separator for a lithium secondary battery, comprising a porous polymer substrate having a plurality of closed pores and containing a first polymer having electrolyte solubility inside the plurality of closed pores, and an outer coating layer disposed on at least one surface of the porous polymer substrate and containing a second polymer having non-electrolyte solubility. For example, the impregnation rate of the first polymer having electrolyte solubility into the pores of the porous polymer substrate can be appropriately adjusted according to the coating method and coating conditions.

[0090] The separator for a lithium secondary battery according to still another aspect of the present invention is

[0091] a porous polymer substrate having a plurality of pores,

[0092] a coating layer of a first polymer having electrolyte solubility, which is located inside the pores so that the pores of the porous polymer substrate are closed,

[0093] and an outer coating layer containing a second polymer having non-electrolyte solubility, which is located on the upper surface of the coating layer of the first polymer.

[0094] The configurations of the first polymer, the second polymer, and the outer coating layer have been described in detail above.

[0095] The separator for a lithium secondary battery having the above-described configuration is manufactured as a lithium secondary battery by the following method.

[0096] First, the above-described separator is laminated with a positive electrode and a negative electrode to prepare an electrode assembly (S21).

[0097] 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 manufactured as an electrode assembly by a lamination process in which heat and / or pressure is applied for binding. 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 binding. At this time, the lamination process can be performed by a hot pressing method.

[0098] 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 includes layered compounds such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and compounds 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 oxides represented by; chemical formula LiMn 1-x M x O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which a part of the chemical formula of Li is substituted with alkaline earth metal ions; disulfide compounds; one or a mixture of two or more of Fe2(MoO4)3 can be included.

[0099] 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. The negative electrode can contain, as the negative electrode active material, carbon such as lithium metal oxide, graphitizable carbon, graphite-based 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, 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; one or more mixtures selected from titanium oxides.

[0100] The conductive material can be, for example, any one selected from the group consisting of 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 or a mixture of two or more conductive materials selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0101] 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 obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0102] As the binder resin, polymers that are commonly used for electrodes in the art can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxylmethyl cellulose, etc., and are not limited thereto.

[0103] Next, after loading the laminated electrode assembly into the battery case, an electrolytic solution is injected to dissolve the first polymer, thereby opening the closed pores of the porous polymer substrate (S22).

[0104] The electrolyte contains A + B - As a salt having a structure such as A + is Li + , Na + , K + ions composed of alkali metal cations such as these or combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - anions such as these, or salts containing ions composed of combinations thereof are 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 mixtures thereof, but are not limited thereto. In the electrolyte, a non-aqueous electrolyte in which a lithium salt is dissolved in a carbonate-based organic solvent can be particularly used.

[0105] If the electrode assembly is impregnated with the injected electrolyte, the first polymer located on the surface and pore portion of the separation membrane is dissolved. As a result, the closed pores of the porous polymer base material are opened. In order for the first polymer to be easily dissolved by the electrolyte, the electrolyte can be prepared in a state where the temperature is appropriately raised, or the battery case into which the electrolyte has been injected can be left in a high temperature environment as appropriate.

[0106] A battery module including a 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 may be provided. Specific examples of the device include a power tool powered by a battery-powered motor; an electric vehicle including an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV), etc.; an electric two-wheeler 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.

[0107] 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 deformed into various other forms, and the scope of the present invention should not be construed as being limited to the examples described in detail below. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0108] [Example 1]

[0109] As the porous polymer substrate, a separator fabric of Toray's B09PJ1 (thickness 9 μm, porosity 44%, basis weight 5.0 g / m 2 , Gurley value 70 seconds / 100 cc) was used.

[0110] On the other hand, PAN (Mw = 150,000 g / mol) was used as the first polymer having electrolyte solubility, and the first polymer was completely dissolved in the solvent dimethyl carbonate (DMC) at a concentration of 40% by weight to prepare a polymer solution.

[0111] The prepared polymer solution was dip-coated on a porous polyethylene polymer substrate fabric for 10 seconds and dried at 65 °C to form a polymer coating layer (thickness: 0.2 μm).

[0112] Next, PVDF-HFP copolymer (substitution rate of HFP-derived repeating units: 8 wt%; Mw = 500,000 g / mol) was used as the second polymer insoluble in the electrolyte solution and dissolved in the solvent acetone. Then, Al2O3 powder with an average particle size of about 400 nm was further added so that the weight ratio of the content of the second polymer insoluble in the electrolyte solution to the inorganic particles was 20:80 (total solid content 15 wt%). These components were uniformly mixed to produce a slurry.

[0113] The prepared slurry was coated on the aforementioned polymer coating layer by a roll coating method and dried at 45 °C to form an outer coating layer (thickness: 6.5 μm).

[0114] [Comparative Example 1]

[0115] It was manufactured in the same manner as in Example 1, except that the solution of the first polymer was not coated on the separation membrane fabric.

[0116] [Thickness reduction ratio after hot pressing]

[0117] The separation membranes of Example 1 and Comparative Example 1 manufactured above were pressurized using hot pressing to deform the thickness, and then the thickness was measured. The thickness reduction rate was calculated using the following formula. The pressurization was performed under the conditions of 70 °C, 5.2 MPa, and 10 seconds. The thickness was measured using a thickness gauge (Mitutoyo, VL-50S).

[0118] Thickness reduction ratio of the separation membrane (%) = {(Separation membrane thickness before hot pressing - Separation membrane thickness after hot pressing) / Separation membrane thickness before hot pressing} × 100

[0119] [Weight after coating layer peeling]

[0120] The separation membrane coating layers of the examples and comparative examples were removed using 3M Scotch Magic Tape 810. After attaching and then removing adhesive tape twice on each side of the separation membrane, the outer coating layer composed of a second polymer insoluble in the electrolytic solution was removed, and then the weight of the separation membrane was measured.

[0121] [Weight ratio of the impregnated polymer to the weight of the separation membrane fabric]

[0122] The ratio of the weight of the impregnated first polymer to the weight of the separation membrane fabric was calculated by the following formula. Weight ratio of the impregnated polymer to the weight of the fabric (%) = { (weight after peeling of the coating layer - weight of the separation membrane fabric) / weight of the separation membrane fabric} × 100

[0123] [Measurement of capacity retention rate after 500 cycles at 25°C, 1C / 1C]

[0124] 1) Fabrication of the positive electrode

[0125] Positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), conductive material (carbon black), dispersant, and binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the positive electrode active material layer with a concentration of 50 wt% of the remaining components after removing water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to fabricate a positive electrode having a positive electrode active material layer (thickness 120 μm).

[0126] 2) Fabrication of the negative electrode

[0127] Graphite (a blend of natural graphite and artificial graphite), conductive material (carbon black), dispersant, and binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the negative electrode active material layer with a concentration of 50 wt% of the remaining components after removing water. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to fabricate a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0128] 3) Lamination process

[0129] The manufactured negative electrode and positive electrode were laminated with the separator of the example and the comparative example 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.

[0130] 4) Electrolyte injection

[0131] The electrode assembly obtained in the lamination process was inserted into a pouch exterior material, and an electrolyte in which 1 M LiPF6 was dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70 was injected to manufacture a lithium secondary battery.

[0132] For the battery manufactured by the method described above, charge and discharge were repeated at a rate of 1C each at 25 °C in the range of 2.5V to 4.25V, and the ratio of the discharge capacity after 500 cycles was derived by calculation.

[0133]

Table 1

Claims

1. (S11) Coating a polymer solution in which a first polymer is dissolved in a solvent on at least one surface of a porous polymer substrate having a plurality of pores, and impregnating the pores of the porous polymer substrate with the polymer solution; (S12) Coating and drying a slurry containing a second polymer on the coated polymer solution; including The first polymer is soluble in a non-aqueous electrolyte in which a lithium salt is dissolved in a carbonate-based organic solvent, and includes one or more selected from the group consisting of polyacrylonitrile (PAN), polylactic acid (PLA), and polyacrylic acid (PAA); The second polymer is insoluble in the non-aqueous electrolyte and includes one or more selected from the group consisting of a PVDF-HFP copolymer, a PVDF-CTFE copolymer, and a PVDF-HFP-CTFE terpolymer. 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, further including a step of drying the polymer solution coated according to the step of S11 before coating the slurry according to the step of S12.

3. The method for manufacturing a separator for a lithium secondary battery according to claim 1 or 2, wherein the first polymer concentration of the polymer solution is 5% by weight to 70% by weight.

4. The method for manufacturing a separator for a lithium secondary battery according to claim 1 or 2, wherein the slurry further includes inorganic particles.

5. A porous polymer substrate having a plurality of closed pores, with the first polymer contained inside the plurality of closed pores; An outer coating layer containing a second polymer disposed on at least one surface of the porous polymer substrate; comprising The first polymer is soluble in a non-aqueous electrolyte in which a lithium salt is dissolved in a carbonate-based organic solvent, and includes one or more selected from the group consisting of polyacrylonitrile (PAN), polylactic acid (PLA), and polyacrylic acid (PAA); The second polymer is insoluble in the non-aqueous electrolyte and includes one or more selected from the group consisting of a PVDF-HFP copolymer, a PVDF-CTFE copolymer, and a PVDF-HFP-CTFE terpolymer. A separator for a lithium secondary battery.

6. Further comprising a coating layer disposed between the porous polymer substrate and the outer coating layer The separation membrane for a lithium secondary battery according to claim 5, wherein the coating layer contains the first polymer.

7. The separation membrane for a lithium secondary battery according to claim 5, wherein the outer coating layer further contains inorganic particles.

8. The separation membrane for a lithium secondary battery according to claim 7, wherein the content ratio of the inorganic particles to the second polymer in the outer coating layer is 50:50 to 99:

1.

9. (S21) Preparing an electrode assembly by laminating the separation membrane for a lithium secondary battery according to any one of claims 5 to 8 with a positive electrode and a negative electrode; (S22) After loading the laminated electrode assembly into a battery case, injecting an electrolytic solution to dissolve the first polymer, thereby opening the closed pores of the porous polymer substrate. A method for manufacturing a lithium secondary battery, comprising the steps.

Images