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

Abstract

(S1) A step of electrospinning a solution in which β-chitin is dissolved in a solvent onto at least one surface of a porous polyolefin substrate having a plurality of pores; and (S2) a step of drying the product of (S1) to form a porous coating layer of β-chitin nanofibers. A method for manufacturing a separator for a lithium secondary battery including these steps is disclosed.

Description

Technical Field

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

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0137543 filed on October 24, 2022, and all of the contents disclosed in the specification and drawings of the application are incorporated into this application.

Background Art

[0003] Recently, interest in energy storage technology has been increasing. In particular, the application fields have expanded to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, and the efforts for research and development of electrochemical devices have been gradually materialized. Electrochemical devices are the most prominent fields in this regard, and among them, the development of secondary batteries such as rechargeable lithium secondary batteries has been becoming the focus of interest.

[0004] In the separator constituting such a battery, its basic characteristic is to increase the ion conductivity by increasing the permeability (air permeability) of ions, for example, lithium ions, based on a high porosity while separating the positive electrode and the negative electrode and electrically insulating them. As a base material of a commonly used separator, a porous polyolefin base material made of a polyolefin-based substance such as polyethylene (PE) or polypropylene (PP), which is advantageous for forming pores and has excellent chemical resistance, mechanical properties, and thermal properties, is mainly used.

[0005] However, in the separation membrane using a porous polyolefin substrate, the separation membrane thermally shrinks at high temperatures, resulting in internal short circuits. During thermal runaway, the polymer separation membrane substrate melts, increasing the risk of ignition. Therefore, in order to supplement the heat resistance of the polyolefin substrate, a separation membrane has been developed in which an inorganic / organic composite porous coating layer composed of a mixture of inorganic particles and a binder polymer is formed on the surface of the porous polyolefin substrate.

[0006] The separation membrane provided with such an inorganic / organic composite porous coating layer has excellent heat resistance characteristics. However, when coating and drying a slurry containing inorganic particles and a binder polymer to form the inorganic / organic composite porous coating layer, a phenomenon occurs in which the binder polymer penetrates into the pores of the porous polyolefin substrate. This causes non-uniform movement of lithium ions, increases resistance, and problems such as precipitation of lithium dendrites occur.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a separation membrane for a lithium secondary battery provided with a porous coating layer in which the heat resistance characteristics of a porous polyolefin substrate are reinforced while the phenomenon of pore penetration of the porous polyolefin substrate is improved.

[0008] Another object of the present invention is to provide a method for manufacturing a separation membrane for a lithium secondary battery provided with a porous coating layer capable of inducing uniform movement of lithium ions and reducing resistance, in addition to the characteristics described above.

[0009] Another object of the present invention is to provide a separation membrane for a lithium secondary battery having the characteristics described above.

[0010] Another object of the present invention is to provide a lithium secondary battery provided with a separation membrane having the characteristics described above.

Means for Solving the Problems

[0011] According to one aspect of the present invention for achieving the above object, there is provided a method for manufacturing a separator for a lithium secondary battery according to the following embodiment.

[0012] The first embodiment is (S1) electrospinning a solution in which β-chitin is dissolved in a solvent on at least one surface of a porous polyolefin substrate having a plurality of pores; (S2) drying the product of (S1) to form a porous coating layer of β-chitin nanofibers, and relates to a method for manufacturing a separator for a lithium secondary battery.

[0013] The second embodiment is relates to a method for manufacturing a separator for a lithium secondary battery, wherein the thickness of the porous coating layer is 0.5 to 10 μm, more specifically 1 to 3 μm, based on the thickness formed on one surface of the porous polyolefin substrate.

[0014] The third embodiment is in the first embodiment or the second embodiment, the loading amount of the porous coating layer is 1 to 15 g / m based on the loading amount formed on one surface of the porous polyolefin substrate 2 and relates to a method for manufacturing a separator for a lithium secondary battery.

[0015] The fourth embodiment is in any one of the first to third embodiments, and relates to a method for manufacturing a separator for a lithium secondary battery, wherein the average diameter of the β-chitin nanofibers is 200 to 2,000 nm.

[0016] The fifth embodiment is in any one of the first to fourth embodiments, and relates to a method for manufacturing a separator for a lithium secondary battery, wherein the porous polyolefin substrate is made of polyethylene.

[0017] The sixth embodiment is in any one of the first to fifth embodiments, The present invention relates to a method for manufacturing a separator for a lithium secondary battery, wherein the solvent is HFIP (1,1,1,3,3,3 - hexafluoro - 2 - propanol).

[0018] According to another aspect of the present invention, there is provided a separator for a lithium secondary battery according to the following embodiments.

[0019] The seventh embodiment is a porous polyolefin substrate having a plurality of pores, and a porous coating layer of electrospun β - chitin nanofibers formed on at least one surface of the porous polyolefin substrate, and relates to a separator for a lithium secondary battery.

[0020] The eighth embodiment is, in the seventh embodiment, relates to a separator for a lithium secondary battery, wherein the thickness of the porous coating layer is 0.5 to 10 μm, more specifically 1 to 3 μm, based on the thickness formed on one surface of the porous polyolefin substrate.

[0021] The ninth embodiment is, in the seventh embodiment or the eighth embodiment, relates to a separator for a lithium secondary battery, wherein the loading amount of the porous coating layer is 0.5 to 15 g / m 2 based on the loading amount formed on one surface of the porous polyolefin substrate.

[0022] The tenth embodiment is, in any one of the seventh to ninth embodiments, relates to a separator for a lithium secondary battery, wherein the average diameter of the β - chitin nanofibers is 200 to 2,000 nm.

[0023] The eleventh embodiment is, in any one of the seventh to tenth embodiments, relates to a separator for a lithium secondary battery, wherein the porous polyolefin substrate is made of polyethylene.

[0024] Still another aspect of the present invention is a lithium secondary battery 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 described in any one of Embodiment 7 to Embodiment 11.

Advantages of the Invention

[0025] According to the present invention, a porous coating layer of β-chitin nanofibers is formed on at least one surface of a porous polyolefin substrate by an electrospinning method.

[0026] β-Chitin has excellent heat resistance and maintains the shape of the porous coating layer composed of nanofibers even at 180°C, improving the heat resistance characteristics of the substrate such as suppressing the thermal shrinkage of the porous polyolefin substrate. Further, by forming a porous coating layer of β-chitin nanofibers by the electrospinning method, the phenomenon of β-chitin penetrating into the pores of the porous polyolefin substrate is significantly suppressed. As a result, problems such as non-uniform movement of lithium ions or an increase in resistance are improved, and problems such as the precipitation of lithium dendrites are minimized.

[0027] In addition, β-chitin is a ferroelectric polymer that exhibits ferroelectricity due to functional groups in the molecule and shows a high affinity for lithium ions. Therefore, the porous coating layer of β-chitin nanofibers induces uniform movement of lithium ions to reduce resistance and also suppresses the precipitation of lithium dendrites.

Brief Description of the Drawings

[0028]

Figure 1

Modes for Carrying Out the Invention

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and the claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors themselves must interpret them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that they can appropriately define the concept of the terms in order to explain the invention in the best way.

[0030] One embodiment of the present invention relates to a method for manufacturing a separator for a lithium secondary battery. (S1) Electrospinning a solution in which β-chitin is dissolved in a solvent onto at least one surface of a porous polyolefin substrate having a plurality of pores; (S2) Drying the product of (S1) to form a porous coating layer of β-chitin nanofibers.

[0031] First, (S1) is to electrospin a solution in which β-chitin is dissolved in a solvent onto at least one surface of a porous polyolefin substrate having a plurality of pores.

[0032] Any porous polyolefin substrate can be used as long as it is a polyolefin substrate commonly used as a separator. For example, polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutylene, polypentene, etc. can be formed into polymers individually or by mixing two or more of these. Such a porous polyolefin substrate exhibits a shutdown function at a temperature of, for example, 80 to 150°C. In this regard, it is desirable that the porous polyolefin substrate be made of polyethylene.

[0033] The solvent for dissolving β-chitin is not limited as long as it can dissolve β-chitin and perform electrospinning. For example, HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) can be used.

[0034] According to one embodiment, the coating by electrospinning is performed by using a solution of β-chitin as a spinning solution, introducing it into an electrospinning nozzle adjusted to a temperature of room temperature to 80°C, and performing electrospinning while forming an electric field between the electrospinning nozzle and a porous polyolefin substrate. For example, the electric field can be formed by applying a voltage of 1 to 30 kV. Thereafter, the β-chitin solution is ejected from the electrospinning nozzle to which a high voltage is applied and coated in the form of nanofibers on the porous polyolefin substrate.

[0035] At this time, the porous polyolefin substrate, which is the target of electrospinning and faces the spinning nozzle, may be positioned in a direction parallel to the bottom surface or in a direction perpendicular to the bottom surface.

[0036] Subsequently, the resultant of (S1) is dried to remove the solvent, thereby forming a porous coating layer of β-chitin nanofibers (S2).

[0037] Most of the solvent can be dried immediately after electrospinning, but it is also possible to completely remove the solvent using another drying device. When forming a porous coating layer made of β-chitin nanofibers by electrospinning in this way, β-chitin hardly penetrates into the pores of the porous polyolefin substrate. That is, the phenomenon of β-chitin penetrating into the pores of the porous polyolefin substrate is significantly suppressed. As a result, problems such as non-uniform movement of lithium ions or an increase in resistance are improved, and problems such as the precipitation of lithium dendrites are minimized.

[0038] On the one hand, β-chitin has excellent heat resistance and can maintain the shape of the porous coating layer composed of nanofibers even at 180°C. As a result, the porous coating layer of β-chitin nanofibers improves the heat resistance characteristics of the substrate, such as suppressing the thermal shrinkage of the porous polyolefin substrate. In addition, β-chitin is a ferroelectric polymer that exhibits ferroelectricity due to the functional groups in its molecule and shows a high affinity for lithium ions. Therefore, the porous coating layer of β-chitin nanofibers induces uniform lithium ion migration to reduce resistance and further suppresses the precipitation of lithium dendrites. On the other hand, α-chitin and γ-chitin have lower dielectric properties than β-chitin, so the effect of reducing the resistance of the porous coating layer is not significant.

[0039] The average diameter of β-chitin nanofibers can be adjusted by the concentration of β-chitin in the solvent and the diameter of the spinning nozzle, and can be, for example, 200 to 2,000 nm. Such a porous coating layer in the form of β-chitin nanofibers becomes intertwined with each other to have a three-dimensional (3D) form, and the pore size of the porous coating layer can be adjusted by the average diameter of the β-chitin nanofibers and the loading amount of the porous coating layer. The loading amount of the porous coating layer can be 0.5 to 15 g / m based on the loading amount formed on one side of the porous polyolefin substrate 2 but is not limited thereto. It is desirable to form the porous coating layer on both sides of the porous polyolefin substrate. At this time, the loading amount of the porous coating layer can be 1 to 30 g / m based on the loading amount formed on both sides of the porous polyolefin substrate 2 and can be.

[0040] The thickness of the porous coating layer can be 0.5 to 10 μm, more specifically 1 to 3 μm, based on the thickness formed on one side of the porous polyolefin substrate, but is not limited thereto. The porous coating layer in the form of β-chitin nanofibers formed by electrospinning is easy to be made into a thin film.

[0041] The above-described method for manufacturing a separator for a lithium secondary battery describes a method of forming a porous coating layer of electrospun β-chitin nanofibers on one surface of a porous polyolefin substrate. Of course, if necessary, a porous coating layer of electrospun β-chitin nanofibers can also be further formed on the other surface of the porous polyolefin substrate by the above-described method.

[0042] The separator for a lithium secondary battery manufactured by the above-described method includes a porous polyolefin substrate having a plurality of pores and a porous coating layer of electrospun β-chitin nanofibers formed on at least one surface of the porous polyolefin substrate.

[0043] As described above, the thickness of the porous coating layer of such a separator for a lithium secondary battery is 0.5 to 10 μm, more specifically 1 to 3 μm, based on the thickness formed on one surface of the porous polyolefin substrate. The average diameter of the β-chitin nanofibers is 200 to 2,000 nm, and the loading amount of the porous coating layer is 0.5 to 15 g / m 2 It can be. Further, the porous polyolefin substrate can be made of polyethylene.

[0044] Of course, a known polymer adhesive layer can be further formed on the surface of the porous coating layer of the separator for a lithium secondary battery described above, if necessary, to improve the adhesion to the electrode.

[0045] According to still another embodiment of the present invention, a lithium secondary battery including the above-described separator for a lithium secondary battery is provided.

[0046] The separator for a lithium secondary battery manufactured by the above-described method is interposed between the positive electrode and the negative electrode, and these positive electrode, negative electrode, and separator are assembled as a lithium secondary battery.

[0047] Hereinafter, the configuration of the lithium secondary battery will be illustrated in detail.

[0048] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0049] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Further, the positive electrode current collector usually has a thickness of 3 to 500 μm, and it is also possible to form fine irregularities on the surface of the positive electrode current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0050] The positive electrode active material layer may contain a known positive electrode active material, a conductive material, and a binder.

[0051] Examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O 4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 ; chemical formula LiNi 1-x M x O 2(Here, M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3.) Nickel-site type lithium nickel oxide represented by; chemical formula LiMn 2-x M x O 2 (Here, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1.) or Li 2 Mn 3 MO 8 (Here, M = Fe, Co, Ni, Cu or Zn.) Lithium manganese composite oxide represented by; a part of Li in the chemical formula is substituted with an alkaline earth metal ion, LiMn 2 O 4 ; Disulfide compound; Fe 2 (MoO 4 ) 3 and the like can be mentioned, but are not limited thereto.

[0052] The conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, it can be used without particular limitation as long as it does not induce a chemical change and has electron conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one of them can be used alone or a mixture of two or more can be used. The conductive material can usually be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0053] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one of them can be used alone or a mixture of two or more can be used. The binder may be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0054] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. Specifically, it can be manufactured by applying a composition for forming a positive electrode active material layer containing a positive electrode active material and optionally a binder and a conductive material onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0055] The solvent may be a solvent commonly used in the art, and examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. Among these, one of them can be used alone or a mixture of two or more can be used. The amount of the solvent used should be such that, considering the coating thickness of the slurry and the manufacturing yield, the positive electrode active material, conductive material, and binder are dissolved or dispersed, and then it has a viscosity that exhibits excellent thickness uniformity during coating for the manufacture of the positive electrode.

[0056] Alternatively, in another method, the positive electrode can be manufactured by laminating, on a positive electrode current collector, a film obtained by casting a composition for forming the positive electrode active material layer on another support and then peeling the film from the support.

[0057] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0058] The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector usually has a thickness of 3 to 500 μm, and similar to the positive electrode current collector, it is also possible to form fine irregularities on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0059] The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer is formed by applying and drying a composition for forming a negative electrode, which contains a negative electrode active material, and selectively a binder and a conductive material, on a negative electrode current collector, or by casting the composition for forming a negative electrode on another support and then laminating, on the negative electrode current collector, a film obtained by peeling the film from the support.

[0060] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphite carbon fiber, amorphous carbon; metallic compounds alloyable with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; SiOβ(0 < β < 2), SnO 2, metal oxides such as vanadium oxide and lithium vanadium oxide that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. may be mentioned, and any one or a mixture of two or more of these can be used. Further, as the negative electrode active material, a thin film of metallic lithium can be used. Also, as the carbon material, all of low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch derived cokes.

[0061] Further, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0062] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0063] As the organic solvent, any solvent can be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are desirable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge and discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more desirable. In this case, the cyclic carbonate and the chain carbonate are preferably mixed and used at a volume ratio of about 1:1 to about 1:9 so that the performance of the electrolyte can be excellent.

[0064] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ), 2 , LiN(C 2 F 5 SO 2 ), 2 , LiN(CF 3 SO 2 ), 2 , LiCl, LiI, or LiB(C 2 O 4 ), 2 etc. can be used. It is desirable to use the lithium salt at a concentration in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it exhibits excellent electrolyte performance and lithium ions can move effectively.

[0065] In addition to the constituent components of the electrolyte, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc., additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included in one or more kinds. At this time, the additive may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0066] The lithium secondary battery according to the present invention is useful in the fields of electric vehicles such as portable devices such as mobile phones, notebook PCs, digital cameras, and hybrid electric vehicles (HEVs).

[0067] Hereinafter, the embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement them. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein.

[0068] Example 1 A solution in which β-chitin (Glycosyn, β-chitin) was dissolved in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) at a concentration of 0.6% by weight was prepared. Also, a porous polyethylene separator film (SEMCORP, SV9 raw satin) having a Gurley time of 65 s / 100cc and a thickness of 9 μm was prepared.

[0069] The prepared β-chitin solution was introduced into an electrospinning nozzle controlled at a temperature of 25°C, and a voltage of 1.5 kV was applied between the electrospinning nozzle and the separation membrane film. While randomly performing electrospinning, it was dried to form a porous coating layer of β-chitin nanofibers on one side of the porous polyethylene separation membrane film.

[0070] Subsequently, the above-described steps were repeated on the other side of the porous polyethylene separation membrane film on which the porous coating layer of β-chitin nanofibers was formed on one side to form a porous coating layer of β-chitin nanofibers on both sides of the porous polyethylene separation membrane film.

[0071] The average diameter, loading amount, and thickness of the porous coating layer of the formed β-chitin nanofibers are shown in Table 1 below, respectively.

[0072] Example 2 A separation membrane was manufactured in the same manner as in Example 1, except that the concentration of β-chitin was changed to 0.4% by weight.

[0073] Comparative Example 1 An inorganic / organic porous coating layer was formed by the following method instead of the porous coating layer of β-chitin nanofibers.

[0074] Alumina with an average particle size of 500 nm and a copolymer of vinylidene-hexafluoropropylene were introduced into acetone at a weight ratio of 81:19 to produce a slurry with a solid content of 18% by weight in which the copolymer was dissolved and the alumina was dispersed.

[0075] The prepared slurry was dip-coated on both sides of the porous polyethylene separation membrane film and then dried to manufacture a separation membrane.

[0076] Comparative Example 2 A separation membrane was manufactured in the same manner as in Example 1, except that the β-chitin solution was dip-coated on both sides of the porous polyethylene separation membrane film and then dried.

[0077] Comparative Example 3 A separation membrane was produced in the same manner as in Example 1, except that a copolymer of vinylidene - hexafluoropropylene (Solvay, Solef21510, acetone) was used instead of the β - chitin solution.

[0078] Comparative Example 4 A separation membrane was produced in the same manner as in Example 1, except that a solution in which α - chitin was dissolved was used instead of β - chitin.

[0079] <Measurement of Thermal Shrinkage Rate> The produced separation membrane was left in an oven maintained at 130 °C and 180 °C for 30 minutes each, and then taken out. The lengths in the MD direction and TD direction before and after being put into the oven were measured to evaluate the thermal shrinkage rate.

[0080] <Measurement of ER> Each separation membrane according to the examples and comparative examples was cut and placed in a Hoshen 2016 coin cell, and the resistance value when impregnated with the electrolyte, which was measured by EIS (Electrochemical Impedance Spectroscopy) at 25 °C using a 1M LiPF 6 - ethylene carbonate / ethyl methyl carbonate (weight ratio 3:7) electrolyte by the AC method to measure the battery resistance.

Table 1

[0081] Also, the separation membrane of Comparative Example 3 having a porous coating layer composed of nanofibers of a copolymer of vinylidene - hexafluoropropylene instead of β - chitin did not have a large reinforcing effect on the heat - resistant characteristics of the polyolefin substrate.

[0082] On the other hand, it can be seen that the separation membrane of Comparative Example 4 in which a porous coating layer was formed using α-chitin instead of β-chitin has a higher resistance than that of the Example, particularly in terms of resistance.

Claims

1. (S1) Electrospinning a solution in which β-chitin is dissolved in a solvent onto at least one surface of a porous polyolefin substrate having a plurality of pores; (S2) Drying the product of (S1) to form a porous coating layer of β-chitin nanofibers. A method for manufacturing a separator for a lithium secondary battery, comprising:

2. The method for manufacturing a separator for a lithium secondary battery according to claim 1, wherein the thickness of the porous coating layer is 0.5 to 10 μm based on the thickness formed on one surface of the porous polyolefin substrate.

3. The loading amount of the porous coating layer is 1 to 15 g / m based on the loading amount formed on one surface of the porous polyolefin substrate. ２ The method for manufacturing a separator for a lithium secondary battery according to claim 1, wherein the loading amount is as described above.

4. The method for manufacturing a separator for a lithium secondary battery according to claim 1, wherein the average diameter of the β-chitin nanofibers is 200 to 2,000 nm.

5. The method for manufacturing a separator for a lithium secondary battery according to claim 1, wherein the porous polyolefin substrate is made of polyethylene.

6. The method for manufacturing a separator for a lithium secondary battery according to claim 1, wherein the solvent is HFIP (1,1,1,3,3,3-hexafluoro-2-propanol).

7. A porous polyolefin substrate having a plurality of pores; A separator for a lithium secondary battery, comprising: a porous coating layer of electrospun β-chitin nanofibers formed on at least one surface of the porous polyolefin substrate.

8. The separator for a lithium secondary battery according to claim 7, wherein the thickness of the porous coating layer is 0.5 to 10 μm based on the thickness formed on one surface of the porous polyolefin substrate.

9. The loading amount of the porous coating layer is 1 to 15 g / m based on the loading amount formed on one surface of the porous polyolefin substrate. ２ The separator for a lithium secondary battery according to claim 7, which is as described above.

10. The separator for a lithium secondary battery according to claim 7, wherein the average diameter of the β-chitin nanofibers is 200 to 2,000 nm.

11. The separator for a lithium secondary battery according to claim 7, wherein the porous polyolefin substrate is made of polyethylene.

12. A lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The lithium secondary battery, wherein the separator is the separator according to any one of claims 7 to 11.

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