A method for manufacturing a separator membrane for lithium secondary batteries, a separator membrane for lithium secondary batteries manufactured thereby, and a lithium secondary battery equipped therewith

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 membrane for lithium secondary batteries, a separator membrane for lithium secondary batteries manufactured by the method, and a lithium secondary battery equipped with the separator membrane.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0137543, filed on 24 October 2022, and all content disclosed in the specification and drawings of said application is incorporated herein. [Background technology]

[0003] Recently, interest in energy storage technologies has been growing. In particular, with applications expanding to mobile phones, camcorders and notebook PCs, and even to electric vehicles, efforts to research and develop electrochemical devices are becoming increasingly concrete. Electrochemical devices are one of the most noteworthy fields in this regard, and among them, the development of rechargeable batteries such as lithium-ion batteries is becoming a focal point of interest.

[0004] In the separation membranes that make up such batteries, the basic characteristic is to increase ionic conductivity by increasing the permeability (air permeability) of ions, such as lithium ions, based on high porosity, while separating the positive and negative electrodes and electrically insulating them. As substrates for separation membranes that are commonly used, porous polyolefin substrates made of polyolefin materials such as polyethylene (PE) and polypropylene (PP) are mainly used because they are advantageous for pore formation and have excellent chemical resistance, mechanical properties, and thermal properties.

[0005] However, separation membranes using porous polyolefin substrates suffer from thermal contraction at high temperatures, leading to internal short circuits. During thermal runaway, the polymer separation membrane substrate melts, increasing the risk of ignition. Therefore, to compensate for the heat resistance of the polyolefin substrate, a separation membrane was developed in which an inorganic / organic composite porous coating layer, consisting of a mixture of inorganic particles and binder polymers, is formed on the surface of the porous polyolefin substrate.

[0006] While separation membranes equipped with such inorganic / organic composite porous coating layers exhibit excellent heat resistance, the formation of the inorganic / organic composite porous coating layer involves coating and drying a slurry containing inorganic particles and binder polymers. During this process, the binder polymers penetrate the pores of the porous polyolefin substrate. This results in uneven lithium ion movement, increased resistance, and the deposition of lithium dendrites, among other problems. [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention has been made in view of the above problems, and aims to provide a method for manufacturing a separation membrane for lithium secondary batteries, which has a porous coating layer that improves the pore penetration phenomenon of the porous polyolefin substrate while reinforcing the heat resistance properties of the porous polyolefin substrate.

[0008] Furthermore, in addition to the aforementioned properties, another objective of the present invention is to provide a method for manufacturing a separation membrane for lithium secondary batteries, which is equipped with a porous coating layer capable of inducing uniform movement of lithium ions and thereby reducing resistance.

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

[0010] Furthermore, another objective of the present invention is to provide a lithium secondary battery equipped with a separation membrane having the characteristics described above. [Means for solving the problem]

[0011] According to one aspect of the present invention for achieving the above objectives, a method for manufacturing a separation membrane for lithium secondary batteries is provided as described in the following embodiment.

[0012] The first concrete example is: (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 multiple pores, The present invention relates to a method for producing a separation membrane for a lithium secondary battery, comprising the steps of (S2) drying the result of (S1) to form a porous coating layer of β-chitin nanofibers.

[0013] The second example is: The present invention relates to a method for manufacturing a separation membrane for lithium secondary batteries, 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 load amount of the porous coating layer is 1 to 15 g / m², based on the load amount formed on one surface of the porous polyolefin substrate. 2 This relates to a method for manufacturing a separation membrane for lithium secondary batteries.

[0015] The fourth embodiment is one of the first to third embodiments, This invention relates to a method for producing a separation membrane for lithium secondary batteries, wherein the average diameter of the β-chitin nanofibers is 200 to 2,000 nm.

[0016] The fifth embodiment is one of the first to fourth embodiments, This invention relates to a method for manufacturing a separation membrane for lithium secondary batteries, wherein the porous polyolefin substrate is made of polyethylene.

[0017] The sixth embodiment is 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, a separator for a lithium secondary battery according to the following embodiments is provided.

[0019] The seventh embodiment is a porous polyolefin substrate having a plurality of pores, [[ID=X]]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 embodiment to the ninth embodiment, 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 embodiment to the tenth embodiment, relates to a separator for a lithium secondary battery, wherein the porous polyolefin substrate is made of polyethylene. <(

[0024] Yet another aspect of the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive electrode and the negative electrode, wherein the separator membrane is the separator membrane described in any one of the seventh to eleventh embodiments. [Effects 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 electrospinning.

[0026] β-chitin exhibits excellent heat resistance, maintaining the shape of the porous coating layer made of nanofibers even at 180°C, and improving the heat resistance properties of the substrate, such as suppressing thermal shrinkage of the porous polyolefin substrate. Furthermore, by forming a porous coating layer of β-chitin nanofibers using the electrospinning method, the phenomenon of β-chitin penetrating into the pores of the porous polyolefin substrate is significantly suppressed. This improves problems such as uneven lithium ion movement or increased resistance, and minimizes issues such as the deposition of lithium dendrites.

[0027] Furthermore, β-chitin is a ferroelectric polymer that exhibits ferroelectricity due to functional groups in its molecule and shows a high affinity for lithium ions. Therefore, the porous coating layer of β-chitin nanofibers induces uniform movement of lithium ions, reducing resistance and suppressing the deposition of lithium dendrites. [Brief explanation of the drawing]

[0028] [Figure 1] This is a surface SEM image of the porous coating layer of the separation membrane according to Example 1 of the present invention. [Modes for carrying out the invention]

[0029] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Prior to this, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept appropriate to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best describe the invention.

[0030] One embodiment of the present invention relates to a method for manufacturing a separation membrane for lithium secondary batteries, (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 multiple pores, (S2) The step of drying the result of (S1) to form a porous coating layer of β-chitin nanofibers.

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

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

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

[0034] According to one embodiment, the electrospinning coating is performed by introducing a β-chitin solution as a spinning solution into an electrospinning nozzle adjusted to a temperature of room temperature to 80°C, and then electrospinning while an electric field is formed 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. Subsequently, the β-chitin solution is ejected from the electrospinning nozzle under high voltage and coated onto the porous polyolefin substrate in the form of nanofibers.

[0035] In this case, the porous polyolefin substrate, which is the target of electrospinning and is facing the spinning nozzle, may be positioned parallel to the bottom surface or perpendicular to the bottom surface.

[0036] Next, the result 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 a separate drying device. When a porous coating layer made of β-chitin nanofibers is formed by electrospinning in this way, β-chitin hardly penetrates the pores of the porous polyolefin substrate. In other words, the phenomenon of β-chitin penetrating the pores of the porous polyolefin substrate is greatly suppressed. This improves problems such as uneven lithium ion movement or increased resistance, and minimizes problems such as the deposition of lithium dendrites.

[0038] On the other hand, β-chitin has excellent heat resistance, maintaining the shape of the porous coating layer made of nanofibers even at 180°C. As a result, the porous coating layer of β-chitin nanofibers improves the heat resistance properties of the substrate, such as suppressing the thermal shrinkage of the porous polyolefin substrate. Furthermore, 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 movement of lithium ions, reducing resistance and further suppressing the deposition of lithium dendrites. On the other hand, α-chitin and γ-chitin have lower dielectric properties than β-chitin, so the effect of reducing resistance in the porous coating layer is not as 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 porous coating layers in the form of β-chitin nanofibers intertwine to form a three-dimensional (3D) morphology, and the pore size of the porous coating layer can be adjusted by the average diameter of the β-chitin nanofibers and the load amount of the porous coating layer. The load amount of the porous coating layer is 0.5 to 15 g / m², based on the load amount formed on one surface of the porous polyolefin substrate. 2 This is possible, but not limited to, the porous coating layer. Preferably, the porous coating layer is formed on both sides of the porous polyolefin substrate, and the load amount of the porous coating layer in this case should be 1 to 30 g / m² based on the load amount formed on both sides of the porous polyolefin substrate. 2 It is possible.

[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 surface of the porous polyolefin substrate, but is not limited to this. A porous coating layer in the form of β-chitin nanofibers formed by electrospinning can be easily thinned.

[0041] The method for manufacturing a separation membrane for lithium secondary batteries described above involves forming a porous coating layer of electrospun β-chitin nanofibers on one surface of a porous polyolefin substrate. However, it is of course possible to further form a porous coating layer of electrospun β-chitin nanofibers on the other surface of the porous polyolefin substrate using the method described above, if necessary.

[0042] The separation membrane for lithium secondary batteries manufactured by the method described above comprises a porous polyolefin substrate having multiple pores, and a porous coating layer of electrospun β-chitin nanofibers formed on at least one surface of the porous polyolefin substrate.

[0043] As mentioned above, the thickness of the porous coating layer of such a separation membrane for lithium secondary batteries 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 load amount of the porous coating layer is 0.5 to 15 g / m², based on the load amount formed on one surface of the porous polyolefin substrate. 2 This is possible. Furthermore, the porous polyolefin substrate may 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 separation membrane for lithium secondary batteries mentioned above, if necessary, to improve adhesion to the electrodes.

[0045] According to yet another embodiment of the present invention, a lithium secondary battery is provided that includes the aforementioned separation membrane for lithium secondary batteries.

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

[0047] The following provides a detailed example of the configuration of a lithium-ion secondary battery.

[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 of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Also, 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 adhesion 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 (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; the 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, V2O5, Cu2V2O7; the 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 this formula; the chemical formula LiMn 2-x M xLithium manganese composite oxides represented as 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 part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc. are examples, but are not limited to these.

[0052] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it does not induce chemical changes in the battery and possesses electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material is usually included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0053] The binder plays a role in improving the adhesion between 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used individually or in mixtures of two or more. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0054] The positive electrode can be manufactured by a conventional positive electrode manufacturing method. Specifically, it can be manufactured by applying a composition for forming a positive electrode active material layer, which includes a positive electrode active material and, selectively, a binder and a conductive material, onto a positive electrode current collector, followed by drying and rolling. In this case, the type and content of the positive electrode active material, binder, and conductive material are as described above.

[0055] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or in a mixture of two or more. The amount of solvent used should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness and production yield of the slurry, and that the slurry subsequently has a viscosity that exhibits excellent thickness uniformity when applied for the production of the positive electrode.

[0056] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[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 chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector usually has a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, it is possible to form fine irregularities on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0059] The negative electrode active material layer selectively includes a binder and a conductive material along with the negative electrode active material. The negative electrode active material layer can be manufactured, for example, by coating a negative electrode forming composition containing the negative electrode active material and selectively a binder and a conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0060] As the negative electrode active material, compounds 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, and amorphous carbon; metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metallic oxides that can be doped and dedoped with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. Any one or a mixture of two or more of these can be used. Furthermore, a metallic lithium thin film can be used as the negative electrode active material. In addition, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include 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 carbon such as petroleum or coal tar pitch-derived cokes.

[0061] Furthermore, examples of electrolytes 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 include an organic solvent and a lithium salt.

[0063] As an organic solvent, any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move is not particularly limited. Specifically, the organic solvents 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded directional ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is even more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 may result in excellent electrolyte performance.

[0064] The lithium salt can be used without particular limitation as long as it is a compound capable of supplying lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and enabling effective movement of lithium ions.

[0065] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

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

[0067] The following describes in detail embodiments of the present invention so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in a variety of different forms and is not limited to the embodiments described herein.

[0068] Example 1 A solution was prepared by dissolving β-chitin (Glycosyn,β-chitin) in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) at a concentration of 0.6% by weight. A porous polyethylene separation membrane film (SEMCORP,SV9 original film) with a Gurley time of 65 s / 100cc and a thickness of 9 μm was also prepared.

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

[0070] Next, the same process described above was repeated on the other side of the porous polyethylene separation film, which already had a porous coating layer of β-chitin nanofibers formed on one side, to form another porous coating layer of β-chitin nanofibers on both sides of the porous polyethylene separation film.

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

[0072] Example 2 The separation membrane was prepared 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 Instead of a porous coating layer made of β-chitin nanofibers, an inorganic / organic porous coating layer was formed using the method described below.

[0074] A slurry with a solid content of 18% by weight was prepared by adding alumina with an average particle size of 500 nm and a vinylidene-hexafluoropropylene copolymer in acetone in a weight ratio of 81:19, in which the copolymer was dissolved and the alumina was dispersed.

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

[0076] Comparative Example 2 A separation membrane was produced in the same manner as in Example 1, except that a β-chitin solution was dip-coated on both sides of a 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, Solef 21510, 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 Ratio> The produced separation membrane was left in an oven maintained at 130 °C and 180 °C for 30 minutes, respectively, 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 ratio.

[0080] <Measurement of ER> Each separation membrane according to the examples and comparative examples was cut and placed in a Hoshen 2016 coin cell. The resistance value when impregnated with an electrolytic solution was measured. Using a 1M LiPF6 - ethylene carbonate / ethyl methyl carbonate (weight ratio 3:7) electrolytic solution, the battery resistance was measured by the AC method at 25 °C using EIS (Electrochemical Impedance Spectroscopy).

Table 1

[0081] Furthermore, the separation membrane of Comparative Example 3, which had a porous coating layer made of nanofibers of a vinylidene-hexafluoropropylene copolymer instead of β-chitin, did not significantly enhance the heat resistance properties of the polyolefin substrate.

[0082] On the other hand, the separation film of Comparative Example 4, in which a porous coating layer was formed using α-chitin instead of β-chitin, was found to have higher resistance than the example, particularly in terms of resistance.

Claims

1. (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 multiple pores, A method for producing a separation membrane for a lithium secondary battery, comprising the steps of (S2) drying the result of (S1) to form a porous coating layer of β-chitin nanofibers.

2. The method for producing a separation membrane 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 load amount of the porous coating layer is 1 to 15 g / m², based on the load amount formed on one surface of the porous polyolefin substrate. ２ The method for manufacturing a separation membrane for a lithium secondary battery according to claim 1.

4. A method for producing a separation membrane 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 producing a separation membrane for a lithium secondary battery according to claim 1, wherein the porous polyolefin substrate is made of polyethylene.

6. The method for producing a separation membrane 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 multiple pores, A separation membrane 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 separation membrane 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 load amount of the porous coating layer is 1 to 15 g / m², based on the load amount formed on one surface of the porous polyolefin substrate. ２ The separation membrane for a lithium secondary battery according to claim 7.

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

12. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive electrode and the negative electrode, A lithium secondary battery wherein the separation membrane is the separation membrane described in any one of claims 7 to 11.

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