Separator and manufacturing method thereof, electrode assembly including the same and manufacturing method thereof, and lithium secondary battery including the same

Abstract

The present invention discloses a separator comprising a nonwoven fabric substrate formed by mixing first fibers having an average diameter of 10 μm or more and second fibers having an average diameter of 1 μm or less, and inorganic particles located in pores formed between the fibers of the nonwoven fabric substrate, wherein the melting point of the first fibers is 150°C or less and the D50 of the inorganic particles is 400 nm or less.

Description

[Technical Field]

[0001] The present invention relates to a separator and a method for manufacturing the same, an electrode assembly including the separator and a method for manufacturing the same, and a lithium secondary battery including the separator and the electrode assembly.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0025333 filed on February 24, 2023, and Korean Patent Application No. 10-2023-0179147 filed on December 11, 2023, and the contents disclosed in the specifications and drawings of those applications are incorporated herein in their entirety. [Background technology]

[0003] Recently, interest in energy storage technology has been growing. As its application fields expand to include mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts in the research and development of electrochemical devices are gradually becoming more concrete. Electrochemical devices are the field that has attracted the most attention in this regard, and among them, the development of secondary batteries such as rechargeable lithium secondary batteries is becoming a focus of attention.

[0004] The basic required characteristics of the separator that constitutes such a battery are to separate and electrically insulate the positive and negative electrodes while also increasing the permeability of ions, such as lithium ions, through high porosity, thereby increasing ionic conductivity. The substrate typically used for separators is a porous polyolefin film made from polyolefin materials such as polyethylene (PE) and polypropylene (PP), which are favorable for pore formation and have excellent chemical resistance, mechanical properties, and thermal characteristics.

[0005] However, separators using porous polyolefin films have material properties, as well as manufacturing process properties, particularly those related to stretching, which can cause the separator to thermally shrink at high temperatures, resulting in an internal short circuit. In addition, the polymer separator substrate can melt during thermal runaway, increasing the risk of fire. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a separator that includes a nonwoven fabric substrate and inorganic particles that are filled so as to be located in the pores of the substrate, and that has good insulating properties and adhesive strength to electrodes.

[0007] Another object of the present invention is to provide an electrode assembly including the separator and a method for manufacturing the same.

[0008] It is yet another object of the present invention to provide a lithium secondary battery including the above-mentioned electrode assembly.

[0009] The objects and advantages of the present invention can be realized by the means or methods set forth in the claims and combinations thereof. [Means for solving the problem]

[0010] One aspect of the present invention provides a separator according to the following embodiment.

[0011] The first embodiment is a nonwoven fabric substrate formed by mixing first fibers having an average diameter of 10 μm or more and second fibers having an average diameter of 1 μm or less; and inorganic particles located in pores formed between the fibers of the nonwoven fabric substrate. The separator relates to a separator in which the melting point of the first fibers is 150°C or less, and the D50 of the inorganic particles is 400nm or less.

[0012] The second embodiment is the first embodiment, The separator is characterized in that the mixing weight ratio of the first fibers to the second fibers is 1:9 to 9:1.

[0013] The third embodiment is the first or second embodiment, The separator is characterized in that the first fibers have an average diameter of 10 μm to 30 μm, and the second fibers have an average diameter of 0.1 μm to 1 μm.

[0014] A fourth embodiment is any one of the first to third embodiments, The separator is characterized in that the inorganic particles have a D50 of 30 nm to 400 nm.

[0015] A fifth embodiment is any one of the first to fourth embodiments, The separator is characterized in that the melting point of the first fibers is 50°C to 120°C.

[0016] The sixth embodiment is any one of the first to fifth embodiments, The separator is characterized in that the first fibers are formed from one or more polymers selected from the group consisting of polyamide, polyester, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

[0017] The seventh embodiment is any one of the first to sixth embodiments, The separator is characterized in that the melting point of the second fibers is 200°C or higher.

[0018] The eighth embodiment is any one of the first to seventh embodiments, The separator is characterized in that the second fibers are formed from one or more polymers selected from the group consisting of polyethylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

[0019] The ninth embodiment is any one of the first to eighth embodiments, The separator has a thickness of 10 μm to 30 μm.

[0020] A tenth embodiment is any one of the first to ninth embodiments, The nonwoven fabric substrate has a basis weight of 5 g / m 2 ~30g / m 2 and the basis weight of the inorganic particles is 10 g / m 2 ~50g / m 2 The present invention relates to a separator characterized by:

[0021] An eleventh embodiment is any one of the first to tenth embodiments, The separator has an air permeability of 1 s / 100 cc to 300 s / 100 cc.

[0022] A twelfth embodiment is any one of the first to eleventh embodiments, The separator is characterized in that the inorganic particles have at least a portion of their surfaces coated with a binder polymer.

[0023] Another aspect of the present invention provides a method for manufacturing a separator for a lithium secondary battery according to the following embodiment.

[0024] The thirteenth embodiment is A method for manufacturing a separator for a lithium secondary battery, comprising: forming a nonwoven fabric substrate from a mixture of first fibers and second fibers having different diameters; and providing inorganic particles in pores formed between the first fibers and the second fibers, The average diameter of the first fibers is adjusted to 10 μm or more, and the average diameter of the second fibers is adjusted to 1 μm or less, The present invention relates to a method for manufacturing a separator for a lithium secondary battery, characterized in that a fibrous material having a melting point of 150°C or less is used as the first fiber, and the D50 of the inorganic particles is controlled to 400nm or less.

[0025] The fourteenth embodiment is the thirteenth embodiment, The present invention relates to a method for manufacturing a separator for a lithium secondary battery, wherein the first fibers are formed from one or more polymers selected from the group consisting of polyamide, polyester, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

[0026] The fifteenth embodiment is the thirteenth or fourteenth embodiment, The present invention relates to a method for manufacturing a separator for a lithium secondary battery, characterized in that a fibrous material having a melting point of 200°C or higher is used as the second fiber.

[0027] A sixteenth embodiment is any one of the thirteenth to fifteenth embodiments, The second fibers are formed from one or more polymers selected from the group consisting of polyethylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

[0028] According to yet another aspect of the present invention, there is provided an electrode assembly according to the following embodiment.

[0029] The seventeenth embodiment is: An electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The electrode assembly is characterized in that the separator is a separator according to any one of the first to twelfth embodiments.

[0030] According to yet another aspect of the present invention, there is provided a method for manufacturing an electrode assembly according to the following embodiment.

[0031] The eighteenth embodiment is: Preparing a separator according to any one of the first to twelfth embodiments; and interposing the separator between the positive electrode and the negative electrode, and heating and pressurizing the separator at a temperature of -80°C to +30°C based on the melting point of the first fibers.

[0032] According to yet another aspect of the present invention, there is provided a lithium secondary battery according to the following embodiment.

[0033] The 19th embodiment is: The seventeenth embodiment relates to a lithium secondary battery including an electrode assembly. [Effects of the Invention]

[0034] According to the present invention, the nonwoven fabric substrate is formed from a mixture of fibers having different diameters within a predetermined range, and the melting point of the fibers having a larger diameter and the average particle size of the inorganic particles that fill the pores of the nonwoven fabric are simultaneously controlled, thereby ensuring both adhesive strength to the electrode and insulating properties.

[0035] As a result, when the separator of the present invention is bonded to an electrode by lamination or hot pressing to assemble the electrode structure, the separator adheres well to the electrode interface, so that the rigidity of the battery cell is maintained even after the electrolyte is injected, and the warping or distortion of the battery cell is improved.

[0036] The effects of each component of the present invention will be described in detail below. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, a preferred embodiment 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 claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical concept of the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of terms in order to best explain the invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical concept of the present invention, and therefore, various equivalents and modifications that can be substituted therefor may exist at the time of filing this application.

[0038] Throughout this specification, when a part is described as "comprising" or "having" a certain element, it does not mean that it excludes other elements, but that it may further include or further comprise other elements, unless otherwise specified.

[0039] In this specification, the property of having pores means that an object contains a plurality of pores, and the interconnection structure between the pores allows gaseous and / or liquid fluids to pass from one side of the object to the other side.

[0040] Typically, to increase battery capacity, batteries are manufactured in a stacked configuration by stacking multiple unit cells. For example, in the roll-to-roll process, a pre-manufactured separator is placed in contact with electrodes such as the positive and negative electrodes to manufacture cells, and this process is repeated to continuously manufacture batteries. Therefore, the adhesion between the separator and electrodes is an important factor in the continuous cell manufacturing process, and it is necessary to select separator materials with excellent adhesion to the electrodes.

[0041] When the separator and electrode are in contact with each other, lithium secondary batteries can be manufactured through assembly processes using lamination, heat pressing, etc. This has the advantage of ensuring the hardness of the battery cell even when the electrolyte is injected by closely adhering the electrode interface to the separator. In particular, as the length of the battery cell increases, if the electrodes and separator are not adhered, the alignment of the stacked separator and electrodes may become misaligned, resulting in problems such as warping or distortion of the cell after fabrication.

[0042] Conventional separators are made by coating porous polyolefin with an inorganic material to improve heat resistance, but the polyolefin used as the base material is highly flammable, increasing the risk of fire.

[0043] This invention discloses a separator that uses a nonwoven fabric substrate made from heat-resistant fibers such as polyethylene terephthalate as the base material of the separator, and strengthens its heat resistance by filling the pores formed between the fibers with inorganic particles. Such a separator has a structure similar to a building, with a basic skeleton of rebar (corresponding to the fibers that make up the nonwoven fabric) filled with concrete containing gravel or sand (corresponding to the inorganic particles).

[0044] Such nonwoven fabric substrates have the advantages of relatively simple manufacturing processes and low manufacturing costs, but if the pores are too large, it may be difficult to ensure sufficient insulation with only the inorganic particles located in the pores.

[0045] Meanwhile, because the separator of the present invention is assembled into an electrode structure by bonding to the electrode through a lamination or hot pressing process, the electrode interface and the separator must be in close contact to maintain the rigidity of the battery cell even after the electrolyte is poured in. In particular, as described above, if the electrode and separator are not in close contact, the larger and longer the battery cell becomes, the more likely it is that the stacked separator and electrodes will become misaligned, which can result in warping or distortion of the battery cell after fabrication. Therefore, ensuring adhesion to the electrode is extremely important even for separators in which the pores of the nonwoven fabric substrate are filled with inorganic particles.

[0046] In this specification, the separator has porous properties including a plurality of pores, and serves as a porous ion-conducting barrier that blocks electrical contact between the negative electrode and the positive electrode in the electrochemical device and allows ions to pass through.

[0047] In this specification, the term "nonwoven fabric" refers to a fabric formed by intertwining fibers, rather than a woven fabric woven with warp and weft threads using a loom or a knitted fabric using a knitting machine.

[0048] a nonwoven fabric substrate formed by mixing first fibers having an average diameter of 10 μm or more and second fibers having an average diameter of 1 μm or less; and inorganic particles located in pores formed between the fibers of the nonwoven fabric substrate. The melting point of the first fibers is 150° C. or less, and the average particle size D50 of the inorganic particles is 400 nm or less.

[0049] [Nonwoven fabric base material] When ceramic is coated on a conventional nonwoven fabric, it cannot be used in a lamination process due to its lack of adhesiveness. However, the nonwoven fabric of the present invention has adhesive properties, so it is possible to bond the electrode and separator using a method such as hot melt without forming a separate adhesive layer.

[0050] The nonwoven substrate of the present invention is formed from a mixture of first and second fibers having different average diameters.

[0051] The first fibers have an average diameter of 10 μm or more. Specifically, the average diameter of the first fibers may be 10 μm to 30 μm, more specifically 10 μm to 20 μm, and most specifically 12 μm to 17 μm.

[0052] The first fibers having such a large average diameter increase the surface roughness of the nonwoven fabric, exposing a large amount of the first fibers on the surface of the nonwoven fabric substrate, making it easier for the first fibers to come into contact with the electrodes, and also facilitating the filling of the inorganic particles into the pores of the nonwoven fabric substrate.

[0053] If the average diameter of the first fibers is less than 10 μm, the surface roughness of the nonwoven fabric will be low, and the proportion of the inorganic particles and second fibers exposed on the surface of the nonwoven fabric will increase, which will result in a problem of a reduced proportion of the first fibers exposed on the surface of the nonwoven fabric substrate.

[0054] The melting point of the first fibers is 150°C or less, specifically 50°C to 120°C, more specifically 60°C to 100°C, even more specifically 70°C to 100°C, and most specifically 80°C to 95°C.

[0055] When the separator of the present invention is bonded to an electrode by heating and pressurizing using a lamination or hot press process, the first fibers having the melting point range described above flow by partially melting and are bonded to the electrode interface. As a result, the separator and the electrode are bonded to each other and closely adhere to each other, maintaining the rigidity of the battery cell even after the electrolyte is injected and reducing warping and distortion of the battery cell. In addition, the first fibers may melt and close the pores during thermal runaway of the battery, providing the separator with a shutdown function.

[0056] If the melting point of the first fiber exceeds 150°C, it is difficult to flow the first fiber without affecting the electrodes when heated for thermal bonding. Also, in the event of thermal runaway of the battery, the separator's shutdown temperature becomes excessively high, making it difficult to prevent the battery from catching fire.

[0057] The first fiber may be formed from one or more polymers selected from the group consisting of polyamide, polyester, thermoplastic polyurethane (TPU), and ethylene-vinyl acetate copolymer.

[0058] Specific examples of polyamides include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, thapsic acid, Japanese acid, phellogenic acid, and equisetolic acid. linear diacids such as phthalic acid, isophthalic acid, terephthalic acid, diphenic acid, 2,6-naphthalenedicarboxylic acid, aromatic diacids such as β-propiolactam, γ-butyrolactam, δ-valerolactam, or ε-caprolactam, and methanediamine, ethylenediamine, 1,3-diaminopropane, putrescine, cadaverine, hexamethylenediamine, 1,2-diaminopropyne, 1,4-diaza Examples include compounds produced by reacting diamines such as cycloheptane, PPD (para-phenylenediamine), 1,4-diazacycloheptane, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, dimethyl-4-phenylenediamine, 4,4'-diaminobiphenyl, and 1,8-diaminonaphthalene, and mixtures of two or more of these compounds.

[0059] Specific examples of polyesters include those produced from terephthalic acid or isophthalic acid and 1,4-butadiene, and may further include a tackifying resin, a plasticizing oil, or all of these, to adjust the melting point, or a mixture of two or more of these.

[0060] Specific examples of ethylene-vinyl acetate copolymers include ethylene-vinyl acetate compounds containing 18 parts by weight or more and less than 40 parts by weight of vinyl acetate, or mixtures of two or more of these.

[0061] The second fibers are mixed with the first fibers to form a nonwoven substrate.

[0062] In this specification, the term "mixed" is interpreted to mean not only a state in which the first fiber and the second fiber are homogeneously mixed, but also a state in which the first fiber and the second fiber are heterogeneously mixed so that they are not separated from each other and formed as separate layers.

[0063] The second fibers have an average diameter of 1 μm or less. Specifically, the average diameter of the second fibers may be 0.1 μm to 1 μm, more specifically 0.5 μm to 1 μm, and most specifically 0.6 μm to 0.8 μm. The second fibers, which have an average diameter smaller than that of the first fibers, contribute to ensuring the insulation properties of the separator by controlling the pore size and deviation of the nonwoven fabric substrate to a small value. Furthermore, the second fibers suppress the detachment of inorganic particles located in the pores of the nonwoven fabric substrate. Furthermore, the second fibers prevent the thickness of the nonwoven fabric substrate from becoming excessively thick in order to ensure insulation properties.

[0064] If the average diameter of the second fibers exceeds 1 μm, the functionality of the second fibers may be reduced. In this respect, the mixing weight ratio of the first fibers to the second fibers may be 1:9 to 9:1, specifically 2:8 to 8:2, and most specifically 3:7 to 7:3.

[0065] The second fibers, like the first fibers, may have a melting point of 150°C or less. The second fibers having such a melting point range further improve the adhesive strength of the separator to the electrodes and further strengthen the separator's shutdown function.

[0066] The melting point of the second fibers may be 200°C or higher. When such high-melting-point second fibers are used, even if the first fibers are completely melted due to thermal runaway of the battery, the shape of the separator is maintained by the second fibers, improving heat resistance. The high-melting-point second fibers may be formed from one or more polymers selected from the group consisting of polyethylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, but are not limited to these.

[0067] Considering the functions of the first and second fibers described above, the basis weight of the nonwoven fabric substrate is 5 g / m 2 ~30g / m 2 More specifically, 8 g / m 2 ~25g / m 2 It can be, but is not limited to.

[0068] [Inorganic particles] The pores formed between the fibers of the nonwoven fabric substrate are filled with inorganic particles. The inorganic particles prevent direct contact between the positive and negative electrodes even if the nonwoven fabric substrate melts during thermal runaway, thereby preventing battery explosion. They also contribute to improving the insulating properties of the separator.

[0069] The inorganic particles may have an average particle size D50 of 400 nm or less, specifically 30 nm to 400 nm, more specifically 50 nm to 350 nm, even more specifically 65 nm to 300 nm, and most specifically 70 nm to 290 nm.

[0070] As used herein, "D50" refers to the particle size at 50% of the cumulative particle volume distribution by particle size. D50 can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Malvern MASTERSIZER 3000). When the particles pass through a laser beam, the difference in the diffraction pattern depending on the particle size is measured to calculate the particle size distribution. D50 can be measured by calculating the diameter of the particles at 50% of the cumulative particle volume distribution by particle size measured by the analyzer.

[0071] If the D50 of the inorganic particles exceeds 400 nm, the insulating properties of the separator may be reduced, and the adhesive strength of the separator may be reduced due to an increased proportion of particles exposed on the separator surface. 2 ~50g / m 2 Specifically, 12 g / m 2 ~40g / m 2 and more specifically, 15 g / m 2 ~30g / m 2 It can be, but is not limited to.

[0072] The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are those that are within the operating voltage range (e.g., Li / Li) of the applied electrochemical element. + There are no particular limitations on the dielectric constant as long as oxidation and / or reduction reactions do not occur at a potential of 0 to 5 V relative to the reference potential. In particular, when inorganic particles with a high dielectric constant are used as the inorganic particles, they can contribute to an increase in the degree of dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0073] For the reasons mentioned above, the inorganic particles may include inorganic particles with a high dielectric constant of 5 or more, or 10 or more. Non-limiting examples of inorganic particles with a dielectric constant of 5 or more include BaTiO3, Pb(Zr x , Ti 1-x)O3 (PZT, where 0 < x < 1). Pb 1-x La x Zr 1-y Ti y O3 (PLZT, where 0 < x < 1, 0 < y < 1). (1 - x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x PbTiO3 (PMN - PT, where 0 < x < 1), any one inorganic particle selected from the group consisting of hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, boehmite, Al(OH)3, AlOOH, SiC, and TiO2, or a mixture of two or more thereof may be used.

[0074] Also, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing lithium element but having a function of moving lithium ions without storing lithium can be used. Non - limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y - based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate such as Li 3.25 Ge 0.25 P 0.75 S4 (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x Ny , 0 < x < 4, 0 < y < 2), SiS2-based glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glasses such as LiI-LiS-P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures of two or more of these, etc. can be mentioned.

[0075] The inorganic particles may have at least a portion of their surface coated with a binder polymer, which adheres the inorganic particles to the fibers of the nonwoven fabric and prevents the inorganic particles from falling off. Non-limiting examples of binders include polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloro ethylene, polyvinylidene fluoride-co-chlorotrifluoro ethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. propionate, cyanoethyl pullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or a mixture of two or more thereof.

[0076] The inorganic particles may be positioned in a state where they are substantially in contact with each other, except for the first or second fibers interposed between them. In this case, when a coating layer of a binder polymer is formed on the surface of the inorganic particles, the binder polymer may connect and fix the inorganic particles to each other so that the inorganic particles remain bound to each other.

[0077] As described above, according to one embodiment of the present invention, a method for manufacturing a separator for a lithium secondary battery includes forming a nonwoven fabric substrate from a mixture of first fibers and second fibers having different diameter ranges, and disposing inorganic particles in pores formed between the first fibers and the second fibers, wherein the average diameter of the first fibers is adjusted to 10 μm or more and the average diameter of the second fibers is adjusted to 1 μm or less, and a fibrous material having a melting point of 150°C or less is used as the first fibers, and the D50 of the inorganic particles is simultaneously controlled to 400 nm or less.

[0078] [Separator] The air permeability of the separator comprising the nonwoven fabric substrate and inorganic particles described above may be 1 s / 100 cc to 300 s / 100 cc, specifically 100 s / 100 cc to 300 s / 100 cc, more specifically 140 s / 100 cc to 300 s / 100 cc, and most specifically 150 s / 100 cc to 290 s / 100 cc.

[0079] As used herein, "permeability" refers to the time it takes for 100 cc of air to pass through an object for measuring permeability, such as a separator, and is expressed in units of seconds / 100 cc. This term can be used interchangeably with "transmittance," and is usually expressed as a Gurley value, etc. In one specific embodiment of the present invention, the permeability is measured in accordance with JIS P8117.

[0080] The thickness of the separator may be, but is not limited to, 10 μm to 30 μm, specifically 15 μm to 30 μm, and more specifically 20 to 25 μm.

[0081] [Electrode assembly] A positive electrode, a negative electrode, and the separator interposed between the positive electrode and the negative electrode are assembled into an electrode assembly.

[0082] The structure of the electrode assembly and the method for manufacturing the separator will now be described in more detail.

[0083] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0084] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the surface of the positive electrode current collector may be provided with fine irregularities to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0085] The positive electrode active material layer may include a known positive electrode active material, a conductive material, and a binder.

[0086] Positive electrode active materials include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), as well as compounds substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M xNi-site lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3). 2-x M x Examples of suitable lithium manganese oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0087] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not undergo chemical changes in the battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or 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 powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically contained in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0088] The binder serves to improve adhesion between positive electrode active material particles and 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, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0089] The positive electrode may be fabricated by a conventional method for fabricating a positive electrode. Specifically, the positive electrode may be fabricated by applying a composition for forming a positive electrode active material layer, including a positive electrode active material and, optionally, a binder and a conductive material, to a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0090] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used may be determined in consideration of the coating thickness of the slurry and the production yield, and may be an amount that dissolves or disperses the cathode active material, conductive material, and binder, and provides a viscosity that allows excellent thickness uniformity when applied to produce a cathode.

[0091] Alternatively, the positive electrode can be produced by casting the composition for forming the positive electrode active material layer onto a separate support, peeling the composition from the support, and laminating the resulting film onto a positive electrode current collector.

[0092] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0093] 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 surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0094] The negative electrode active material layer includes a negative electrode active material and, optionally, a binder and a conductive material. For example, the negative electrode active material layer can be fabricated by applying a negative electrode-forming composition including the negative electrode active material and, optionally, the binder and the conductive material to a negative electrode current collector and drying the applied composition, or by casting the negative electrode-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on the negative electrode current collector.

[0095] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, and typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0096] The binder and conductive material may be the same as those described above for the positive electrode.

[0097] The separator may be manufactured by immersing a nonwoven fabric substrate formed by mixing the first fibers and the second fibers having different average diameters into a slurry containing inorganic particles, or by coating the slurry on the nonwoven fabric substrate and drying it.

[0098] A nonwoven fabric substrate formed by mixing first and second fibers having different average diameters can be produced by spinning the first and second fibers using a spinneret in which a nozzle for spinning the first fiber and a nozzle for spinning the second fiber are arranged so as to intersect. The nonwoven fabric substrate can be, but is not limited to, a spunbond nonwoven fabric produced using spunbond equipment or a meltblown nonwoven fabric produced using meltblown equipment.

[0099] The inorganic particle slurry can be prepared by dispersing inorganic particles in an aqueous dispersion medium such as water or an oil-based dispersion medium such as acetone, and optionally by further dispersing a particulate binder polymer in the dispersion medium or by further dissolving a binder polymer that dissolves in the dispersion medium. When a binder polymer is further added, the binder polymer forms a coating layer on the surface of the inorganic particles.

[0100] According to one aspect of the present invention, an electrode assembly can be manufactured by interposing the separator prepared by the above-described method between a positive electrode and a negative electrode and applying heat and pressure. The appropriate heating temperature varies depending on the glass transition temperature (Tg) and melting point (Tm) of the first fibers, and may be a temperature of -80°C to +30°C based on the melting point of the first fibers. Specifically, the heating temperature may be -50°C to +10°C based on the melting point of the first fibers, more specifically, -30°C to +10°C based on the melting point of the first fibers, and most specifically, the heating temperature may be a temperature of 0°C to +10°C based on the melting point of the first fibers.

[0101] That is, when the separator of the present invention is heated and pressurized within the aforementioned temperature range by a lamination or hot press process, some of the first fibers of the separator flow and bond to the electrode, thereby improving adhesion between the electrode interface and the separator, maintaining the rigidity of the battery cell even after injection of the electrolyte, and improving warping or distortion of the battery cell.

[0102] Meanwhile, a lithium secondary battery according to an aspect of the present invention includes the above-described electrode structure.

[0103] The lithium secondary battery includes the electrode structure and electrolyte described above. 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 manufacturing lithium secondary batteries.

[0104] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0105] The organic solvent may be any solvent that functions 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 and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) that have high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, are more preferred. In this case, the cyclic carbonate and the linear carbonate should be mixed in a volume ratio of about 1:1 to about 1:9 to achieve excellent electrolyte performance.

[0106] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may 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. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and enabling efficient lithium ion migration.

[0107] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethyl alcohol amine, cyclic ethers, ethylenediamine, m-glyme (n-glyme), hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0108] The lithium secondary battery according to the present invention is useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0109] While the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein.

[0110] Example 1: First, they created a high-porosity mixed nonwoven fabric composed of a first fiber with a melting point of under 150°C and a second fiber with a melting point of over 200°C. In the case of the nonwoven fabric, the first fiber and second fiber were spun simultaneously using separate nozzles so that they could exist separately. The first fiber, with its low melting point, melts and acts as an adhesive between the electrode and separator, while the second fiber, with its high melting point, does not melt at high temperatures and acts as a support.

[0111] In this example, first and second fibers were melt-spun using a spinneret in which spinning nozzles with different diameters were arranged to intersect, to produce a meltblown nonwoven fabric substrate (porosity 62%) formed by mixing first fibers with an average diameter of 12 μm made of polyester (Chemitech D1531E) polymer with a melting point of 80°C and second fibers with an average diameter of 0.7 μm made of polyethylene terephthalate polymer with a melting point of 260°C. In the produced nonwoven fabric, the mixing ratio of the first and second fibers was 5:5 by weight, and the basis weight of the nonwoven fabric substrate was 10.7 g / m. 2 It was.

[0112] Next, a coating slurry was prepared. Because inorganic particles alone cannot remain bound together within the nonwoven fabric, a polymer binder was added to maintain the inorganic particles' bound state within the nonwoven fabric. For the coating slurry, the binder and inorganic material were added to a solvent and shaken vigorously using a shaker to uniformly disperse the inorganic material and binder in the solution.

[0113] In this example, 20 g of AlOOH (Nabaltec, D50 290 nm), 0.74 g of polyacrylic acid dispersant solution (42% solids), and 20 g of 0.5 mm beads for dispersion were added to 31.1 g of a 95:5 water:ethyl alcohol solution and stirred for 2 hours using a paint shaker to prepare an inorganic particle dispersion. Next, 1.04 g of a 40 wt% water-dispersed acrylic polymer (Toyoink, CSB130) was added to the inorganic particle dispersion as a binder component and shaken to prepare a coating slurry.

[0114] Next, the resulting slurry was impregnated into the nonwoven fabric substrate prepared by the above-mentioned method using a dipping method, followed by drying to produce a separator. To this end, the coating slurry was placed in a container so that the nonwoven fabric was sufficiently immersed, and the prepared nonwoven fabric was impregnated. Through the dipping process in which the nonwoven fabric was immersed in the container filled with the coating slurry and then removed, a separator was produced in which the pores of the nonwoven fabric were filled with inorganic materials and binder.

[0115] The thickness of the produced separator was 21.2 μm, and the basis weight of the inorganic particles in the separator was 25.3 g / m 2 The air permeability of the separator was 159 s / 100 cc.

[0116] Examples 2 to 7 Separators were manufactured in the same manner as in Example 1, except that the types of polymers of the first and second fibers, the corresponding melting points, average diameters, the mixing weight ratio of the first and second fibers, the porosity and basis weight of the nonwoven fabric substrate, the thickness of the separator, the basis weight of the inorganic particles, and the air permeability were changed as shown in Table 1.

[0117] Comparative Examples 1 to 7: Separators were manufactured in the same manner as in Example 1, except that the types of polymers of the first and second fibers, the corresponding melting points, average diameters, the mixing weight ratio of the first and second fibers, the porosity and basis weight of the nonwoven fabric substrate, the thickness of the separator, the basis weight of the inorganic particles, and the air permeability were changed as shown in Table 1.

[0118] <Average fiber diameter> In this specification, the average diameter of the fibers was measured as follows.

[0119] A nonwoven fabric specimen was fixed to a mount for SEM measurement using carbon tape. The surface was then coated with platinum using an ion sputter for 60 seconds. The platinum-coated sample was measured using a field emission scanning electron microscope (FE-SEM) (Hitachi, S-4800) at 10 kV. Using software, the diameter of a single fiber was measured at 10 or more points on a 500x magnification image observed with the FE-SEM, and the average was used to calculate the fiber diameter.

[0120] <Measurement of fiber melting point> The melting point of the fibers herein was measured as follows.

[0121] The "melting points" of the first and second fibers constituting the nonwoven fabric were measured by DSC (differential scanning calorimetry) at a temperature increasing from -30°C to 200°C at a constant rate of 10°C / min, and the temperature at which heat absorption peaks were observed at a specific temperature.

[0122] <D50 measurement of inorganic particles> In this specification, the D50 of inorganic particles is measured using a laser diffraction particle size analyzer.

[0123] Specifically, the D50 of the inorganic particles was measured using a Malvern MASTERSIZER 3000 laser diffraction particle sizer.

[0124] <Basis weight of nonwoven fabric and inorganic particles> In this specification, the basis weights of the nonwoven fabric and inorganic particles were measured as follows.

[0125] The basis weight of nonwoven fabric is 1m 2The weight per unit area was measured, and the basis weight of the inorganic particles in the separator was determined by measuring the basis weight of the separator and then subtracting the basis weight of the nonwoven fabric used.

[0126] <Separator air permeability> In this specification, the air permeability of the separator was measured as follows.

[0127] The air permeability of the separator was measured in accordance with JIS P8117.

[0128] <Evaluation of separator adhesive strength and insulation properties> Adhesion strength evaluation Anode slurry was prepared by mixing natural graphite, carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) with water in a weight ratio of 96:1:2:2. The anode slurry was coated onto copper foil with a capacity of 3.55 mAh / g to form a thin electrode plate, which was then dried at 135°C for at least 3 hours and pressed to prepare an anode.

[0129] The negative electrode was prepared as described above and cut to a size of 25 mm x 100 mm. The separators prepared in the Examples and Comparative Examples were cut to a size of 25 mm x 100 mm. The prepared separator and negative electrode were stacked on top of each other, sandwiched between 100 μm PET films, and then bonded using a flat press. The flat press conditions were heating and pressing at 70°C and a pressure of 600 kgf for 20 seconds. The bonded separator and negative electrode were attached to a glass slide using double-sided tape. The end of the separator's adhesive surface (less than 10 mm from the end of the adhesive surface) was peeled off and attached to a 25 mm x 100 mm PET film using cross-section adhesive tape, connecting it longitudinally. Next, a slide glass was placed in the lower holder of the UTM equipment (LLOYD Instrument LF Plus), and the separator and attached PET film were placed in the upper holder of the UTM equipment. A force was applied to 180° at a measurement speed of 300 mm / min to measure the force required to peel off the negative electrode and the porous coating layer facing the negative electrode.

[0130] Breakdown voltage evaluation The separator samples prepared in the examples and comparative examples were placed between aluminum jigs (upper jig diameter 30 mm, lower jig diameter 50 × 100 mm), and the voltage at which a short circuit occurred was measured using a Hi-pot tester. The measurement conditions were DC, current 0.5 mA, and voltage increase 100 V / s (up to 3 kV).

[0131] [Table 1]

[0132] As can be seen from Table 1, Comparative Example 1, which used a nonwoven fabric made only from the first fibers, had poor insulation properties and it was difficult to control the thickness.

[0133] Comparative Example 2, which used a nonwoven fabric made only from the second fiber, Comparative Examples 3 and 5, which used small-diameter fibers as the first fiber, and Comparative Example 7, which used PP (polypropylene) fibers with a high melting point as the first fiber, all had low adhesive strength.

[0134] Comparative Example 4, in which inorganic particles with a large D50 were used as inorganic particles, and Comparative Example 6, in which fibers with a large diameter were used as the second fibers, had poor insulation properties.

Claims

1. a nonwoven fabric substrate formed by mixing first fibers having an average diameter of 10 μm or more and second fibers having an average diameter of 1 μm or less; and inorganic particles located in pores formed between the fibers of the nonwoven fabric substrate. The separator, wherein the melting point of the first fibers is 150°C or less, and the D50 of the inorganic particles is 400 nm or less.

2. 2. The separator according to claim 1, wherein a mixing weight ratio of the first fibers to the second fibers is 1:9 to 9:

1.

3. 2. The separator according to claim 1, wherein the first fibers have an average diameter of 10 μm to 30 μm, and the second fibers have an average diameter of 0.1 μm to 1 μm.

4. The separator according to claim 1, wherein the inorganic particles have a D50 of 30 nm to 400 nm.

5. 2. The separator according to claim 1, wherein the melting point of the first fibers is 50°C to 120°C.

6. 2. The separator according to claim 1, wherein the first fibers are formed from one or more polymers selected from the group consisting of polyamide, polyester, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

7. The separator according to claim 1 , wherein the second fibers have a melting point of 200° C. or higher.

8. 8. The separator according to claim 7, wherein the second fibers are formed from one or more polymers selected from the group consisting of polyethylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

9. The separator according to claim 1, wherein the separator has a thickness of 10 μm to 30 μm.

10. The nonwoven fabric substrate has a basis weight of 5 g / m ２ ~30g / m ２ and the basis weight of the inorganic particles is 10 g / m ２ ~50g / m ２ The separator according to claim 1 ,

11. 2. The separator according to claim 1, wherein the separator has an air permeability of 1 s / 100 cc to 300 s / 100 cc.

12. The separator according to claim 1 , wherein the inorganic particles have at least a portion of their surfaces coated with a binder polymer.

13. A method for manufacturing a separator for a lithium secondary battery, comprising: forming a nonwoven fabric substrate from a mixture of first fibers and second fibers having different diameter ranges; and providing inorganic particles in pores formed between the first fibers and the second fibers, The average diameter of the first fibers is adjusted to 10 μm or more, and the average diameter of the second fibers is adjusted to 1 μm or less, A method for manufacturing a separator for a lithium secondary battery, comprising using a fibrous material having a melting point of 150° C. or less as the first fibers, and controlling D50 of the inorganic particles to 400 nm or less.

14. 14. The method of claim 13, wherein the first fibers are formed from one or more polymers selected from the group consisting of polyamide, polyester, thermoplastic polyurethane, and ethylene-vinyl acetate copolymer.

15. 15. The method of claim 14, wherein the second fibers are made of a fiber material having a melting point of 200[deg.] C. or higher.

16. 16. The method for manufacturing a separator for a lithium secondary battery according to claim 15, wherein the second fibers are formed from one or more polymers selected from the group consisting of polyethylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

17. An electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrode assembly, characterized in that the separator is the separator according to any one of claims 1 to 12.

18. Providing a separator according to any one of claims 1 to 12; and interposing the separator between the positive electrode and the negative electrode, and heating and pressurizing the separator at a temperature of -80°C to +30°C based on the melting point of the first fibers.

19. A lithium secondary battery comprising the electrode assembly according to claim 17.

Images