Porous composite ceramic separation membrane, electrochemical device including the same, and method for producing the porous composite ceramic separation membrane

Abstract

The present invention provides a porous composite ceramic separation membrane comprising: a porous ceramic separation membrane substrate including a plurality of inorganic particles and a binder polymer that bonds and fixes the inorganic particles to each other; and a coating layer coated on at least one surface of the porous ceramic separation membrane substrate, the coating layer being formed by mixing binder polymer particles and a plurality of short fibers. The porous composite ceramic separator of the present invention exhibits excellent thermal stability due to the use of a porous ceramic separator substrate, and has an improved tensile strength reduction phenomenon, good resistance characteristics, and properties suitable for assembly into an electrochemical device.

Description

Technical Field

[0001] The present invention relates to a porous composite ceramic separation membrane using a porous ceramic separation membrane substrate mainly made of inorganic particles, an electrochemical element including the same, and a method for manufacturing the porous composite ceramic separation membrane.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0021241 filed on February 18, 2022, and all of the content disclosed in the specification and drawings of the application is incorporated into this application.

Background Art

[0003] Recently, interest in energy storage technology has been increasing. As the application fields expand to include mobile phones, camcorders, laptop computers, and even the energy of electric vehicles, efforts in the research and development of electrochemical elements have become more concrete. Electrochemical elements are the most notable fields in this regard, and in particular, the development of secondary batteries such as rechargeable lithium secondary batteries has attracted attention.

[0004] In the separation membrane constituting such a battery, the basic required characteristics are to separate the positive electrode and the negative electrode and electrically insulate them, while increasing the permeability (porosity) of ions, for example, lithium ions, based on a high porosity to increase the ionic conductivity. As a substrate of a generally used separation membrane, a polymer separation membrane substrate made of polyolefin-based substances such as polyethylene (PE) and polypropylene (PP), which are advantageous for the formation of pores and excellent in chemical resistance, mechanical properties, and thermal properties, is mainly used.

[0005] However, in the separation membrane using a polymer separation membrane substrate, the separation membrane shrinks at high temperatures, resulting in an internal short circuit, and the polymer separation membrane substrate melts during thermal runaway, increasing the risk of ignition. Accordingly, the development of so-called ceramic separation membranes mainly composed of inorganic particles instead of polymer separation membrane substrates has continued.

[0006] Such a ceramic separation membrane has a form in which inorganic particles are substantially in contact with each other, and a binder polymer connects and fixes the inorganic particles to each other. The void space between the inorganic particles is formed as pores, and the membrane functions as a separation membrane. As a result, the ceramic separation membrane has the advantage of very high thermal safety.

[0007] However, the ceramic separation membrane has a problem that its tensile strength is low, and defects occur during assembly into an electrochemical device such as assembly with an electrode.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the problem to be solved by the present invention is to provide a porous composite ceramic separation membrane that exhibits excellent thermal safety by using a porous ceramic separation membrane substrate, improves the phenomenon of tensile strength reduction, and has good resistance characteristics and assembly characteristics for an electrochemical device, and a method for manufacturing the same.

[0009] Another problem to be solved by the present invention is to provide an electrochemical device including a porous composite ceramic separation membrane having the above-described characteristics.

Means for Solving the Problems

[0010] One aspect of the present invention provides a porous composite ceramic separation membrane according to the following embodiments.

[0011] The first embodiment relates to a porous composite ceramic separation membrane including a porous ceramic separation membrane substrate including a plurality of inorganic particles and a binder polymer that connects and fixes the inorganic particles to each other, and a coating layer coated on at least one surface of the porous ceramic separation membrane substrate and formed by mixing binder polymer particles and a plurality of short fibers.

[0012] The second embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in the first embodiment, the binder polymer particles are rubber-based particles or polyacrylate-based particles.

[0013] The third embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in one embodiment of the first or second embodiment, the average particle size of the binder polymer particles is 50 to 1000 nm.

[0014] The fourth embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in any one of the first to third embodiments, the plurality of short fibers have an average length of 0.5 to 10 μm.

[0015] The fifth embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in any one of the first to fourth embodiments, the plurality of short fibers have an average diameter of 200 nm or less.

[0016] The sixth embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in any one of the first to fifth embodiments, the plurality of short fibers are cellulose-based fibers.

[0017] The seventh embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in any one of the first to fifth embodiments, the mixing ratio (weight ratio) of the binder polymer particles to the short fibers is 95:5 to 20:80.

[0018] The eighth embodiment relates to a porous composite ceramic separation membrane, which is characterized in that in any one of the first to sixth embodiments, the thickness of the coating layer is 3 μm or less.

[0019] The ninth embodiment relates to a porous composite ceramic separation membrane, which in any one of the first to seventh embodiments, the inorganic particles contain any one or more selected from the group consisting of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, AlOOH, Al(OH)3, TiO2 and SiC.

[0020] The tenth embodiment relates to a porous composite ceramic separation membrane, which in any one of the first to ninth embodiments, the binder polymer is any one or more selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0021] The 11th embodiment relates to a porous composite ceramic separation membrane, characterized in that, in any one of the 1st to 10th embodiments, the mixing ratio (weight ratio) of the inorganic particles and the binder polymer is 50:50 to 99:1.

[0022] The 12th embodiment relates to a porous composite ceramic separation membrane, characterized in that, in any one of the 1st to 11th embodiments, the tensile strength of the porous composite ceramic separation membrane is 180 kgf / cm 2 or more.

[0023] Another aspect of the present invention provides an electrochemical element according to the following embodiments.

[0024] The 13th embodiment relates to an electrochemical element including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is the porous composite ceramic separation membrane according to any one of the 1st to 12th embodiments.

[0025] The 14th embodiment relates to an electrochemical element, characterized in that, in the 13th embodiment, the electrochemical element is a lithium secondary battery.

[0026] Another aspect of the present invention provides a method for manufacturing a porous composite ceramic separation membrane according to the following embodiments.

[0027] The 15th embodiment relates to a method for manufacturing a porous composite ceramic separation membrane, including: (S1) coating and drying a slurry in which a plurality of inorganic particles are dispersed and a binder polymer is dissolved in a solvent on a support, and peeling off from the support to prepare a porous ceramic separation membrane substrate; and (S2) forming a coating layer by applying and drying an aqueous slurry in which binder polymer particles and a plurality of short fibers are dispersed on at least one surface of the porous ceramic separation membrane substrate.

[0028] The 16th embodiment relates to a method for manufacturing a porous composite ceramic separation membrane, which is characterized in that, in the 15th embodiment, the binder polymer particles are rubber-based particles or polyacrylate-based particles.

[0029] The 17th embodiment relates to a method for manufacturing a porous composite ceramic separation membrane, which is characterized in that, in the 15th or 16th embodiment, the plurality of short fibers are cellulose-based fibers.

[0030] The 18th embodiment relates to a method for manufacturing a porous composite ceramic separation membrane, which is characterized in that, in any one of the 15th to 17th embodiments, the mixing ratio (weight ratio) of the binder polymer particles to the short fibers is 95:5 to 20:80.

Advantages of the Invention

[0031] The porous composite ceramic separation membrane of the present invention exhibits excellent thermal safety by using a porous ceramic separation membrane substrate.

[0032] Also, by forming a coating layer in which particulate binder polymers and fibers are mixed on the surface of the porous ceramic separation membrane substrate, the tensile strength of the ceramic separation membrane is reinforced, thereby improving problems such as wire breakage that may occur during the assembly of the electrochemical element and insulation failure that may occur after lining with the electrode.

[0033] An electrochemical element provided with such a porous composite ceramic separation membrane exhibits good resistance characteristics.

[0034] The following drawings attached to this specification illustrate desirable embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0035]

Figure 1

Embodiments for Carrying Out the Invention

[0036] Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used in this specification and the claims are not to be construed as being limited to their ordinary and dictionary meanings. The inventor himself interprets them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that he can appropriately define the concept of the terms in order to explain the invention in the best way. Therefore, the configurations shown in the embodiments described in this specification are merely the most desirable embodiments of the present invention and do not represent all of the technical ideas of the present invention. It should be understood that there may be various equivalents and modifications that can replace them at the time of this application.

[0037] The porous composite ceramic separation membrane according to one aspect of the present invention A porous ceramic separation membrane substrate including a plurality of inorganic particles and a binder polymer that connects and fixes the inorganic particles to each other, A coating layer that is coated on at least one surface of the porous ceramic separation membrane substrate and is formed by mixing binder polymer particles and a plurality of short fibers.

[0038] FIG. 1 is an example of a cross-sectional view of a porous composite ceramic separation membrane manufactured according to an embodiment of the present invention. The porous composite ceramic separation membrane of the present invention will be described with reference to FIG. 1, but it is not limited thereto.

[0039] <Porous Ceramic Separation Membrane Substrate> The porous composite ceramic separation membrane 10 includes a porous ceramic separation membrane substrate 1 as a separation membrane substrate. In the porous ceramic separation membrane substrate 1, a plurality of inorganic particles 1a form a framework, and the inorganic particles 1a are connected and fixed to each other by a binder polymer (not shown). The binder polymer is located on all or part of the surface of the inorganic particles 1a and performs the above-described functions. As a result, a space between the inorganic particles 1a is formed as a void space through which lithium ions pass.

[0040] Thus, the porous composite ceramic separation membrane 10 of the present invention uses the porous ceramic separation membrane substrate 1 in which the inorganic particles 1a form a framework as a separation membrane substrate without using a polymer separation membrane substrate such as a polyolefin separation membrane substrate, and thus has extremely excellent heat resistance. In addition, since a conventional polymer separation membrane substrate is manufactured through a stretching process, heat shrinkage occurs in a high-temperature environment and causes a short circuit. On the other hand, in the porous ceramic separation membrane substrate 1, since inorganic particles form a framework, almost no heat shrinkage phenomenon occurs.

[0041] The inorganic particles 1a constituting the framework of the porous ceramic separation membrane substrate are not particularly limited as long as they are electrochemically stable. For example, the inorganic particles that can be used in the present invention are not particularly limited as long as no oxidation and / or reduction reaction occurs in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li+).

[0042] Examples of the inorganic particles 1a described above include high dielectric constant inorganic particles having a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectricity, and inorganic particles having lithium ion transfer ability.

[0043] That is, examples of the inorganic particles 1a include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, AlOOH, Al(OH)3, TiO2, and SiC, and one or more of these can be mixed and used.

[0044] In addition, piezoelectric inorganic particles refer to substances that are insulators under normal pressure but have the property of conducting electricity due to changes in their internal structure when a certain pressure is applied. Such piezoelectric inorganic particles have a high dielectric constant value with a dielectric constant of 100 or more. Also, when a certain pressure is applied and they are stretched or compressed, charges are generated. One side becomes positive and the opposite side becomes negative, each becoming charged, resulting in a potential difference between the two sides. When using such piezoelectric inorganic particles, if an internal short circuit occurs between the two electrodes due to an external impact such as local crush or a nail, a potential difference is generated within the particles due to the piezoelectricity of the inorganic particles, and this causes electron movement between the two electrodes, that is, a flow of a minute current, thereby achieving a gentle reduction in the battery voltage and an improvement in safety. Examples of inorganic particles having piezoelectricity include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2) or mixtures thereof, etc., but are not limited thereto.

[0045] Inorganic particles having lithium ion transfer ability refer to inorganic particles that contain lithium elements but have the function of moving lithium ions without storing lithium. Inorganic particles having lithium ion transfer ability can transfer and move lithium ions due to a kind of defect existing inside the particle structure, so the lithium ion conductivity in the battery is improved, thereby improving the battery performance. Examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4, such as lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI - Li2S - P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc., but not limited thereto.

[0046] The particle size of the inorganic particles is not limited, but for the formation of a film with a uniform thickness and an appropriate porosity, it is preferably in the range of 0.001 μm to 10 μm. The pore size of the porous ceramic separation membrane substrate can be controlled by adjusting the particle size of the inorganic particles used and the mixing amount of the binder polymer.

[0047] As the binder polymer constituting the porous ceramic separation membrane substrate 1, any material can be used without limitation as long as it can perform the function of connecting and fixing the inorganic particles 1a to each other. In particular, those with a melting point of, for example, 150 °C or higher, more preferably 200 °C or higher, can be used.

[0048] On the one hand, as the binder polymer, one that gels upon impregnation with the liquid electrolyte can be used. In the case of a polymer with excellent impregnation rate of the electrolyte, the electrolyte injected after the assembly of the battery gels with the binder polymer, improving the wettability of the separator membrane with respect to the electrolyte. In this regard, for example, those having a solubility parameter of 15 MPa 1 / 2 to 45 MPa 1 / 2 can be used.

[0049] Examples of such binder polymers include, but are not limited to, polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. Any one or more selected from the group consisting of these can be used.

[0050] The mixing ratio (weight ratio) of the inorganic particles and the binder polymer constituting the porous ceramic separation membrane substrate is preferably, for example, 50:50 to 99:1, more specifically 60:40 to 99:1.

[0051] <Coating layer> The coating layer 5 of the porous composite ceramic separation membrane 10 is formed by coating at least one surface of the porous ceramic separation membrane substrate 1.

[0052] The coating layer 5 is mixed with binder polymer particles 5b and a plurality of short fibers 5a.

[0053] As described above, since the porous ceramic separation membrane substrate 1 has a form in which the inorganic particles forming the skeleton are connected and fixed by a binder polymer, its tensile strength is low. As a result, there is a problem that defects occur during the assembly into an electrochemical element such as the assembly with an electrode.

[0054] In the present invention, in order to solve such problems, a coating layer 5 in which binder polymer particles 5b and a plurality of short fibers 5a are mixed is formed on at least one surface of the porous ceramic substrate 1.

[0055] By forming such a coating layer 5, the tensile strength of the porous ceramic separation membrane substrate 1 is reinforced, thereby improving problems such as disconnection that may occur during the assembly of the electrochemical element and insulation failure that may occur after lamination with the electrode. Further, since the binder polymer particles 5b are in a particulate form, the phenomenon of an increase in the resistance of the coating layer 5 of the porous composite ceramic separation membrane 10 is improved.

[0056] As the binder polymer particles 5b, any material can be used without limitation as long as it can impart adhesion to the electrode. For example, rubber-based particles or polyacrylate-based particles can be used. Examples of the rubber-based particles include styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, etc. Examples of the polyacrylate-based particles include copolymers of butyl acrylate and ethylhexyl acrylate, copolymers of methyl methacrylate and ethylhexyl acrylate, etc.

[0057] In addition, polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, polycyanoacrylate, etc. can be mentioned, but are not limited thereto.

[0058] The average particle size of the binder polymer particles constituting the coating layer is 50 to 1000 nm, more specifically 100 to 600 nm, and most specifically 200 to 500 nm, but is not limited thereto.

[0059] The average length of the short fibers 5a can be, for example, 0.5 to 10 μm, more specifically 1 to 5 μm, but is not limited thereto. Also, the average diameter of the short fibers 5a is 200 nm or less, specifically 50 nm or less, 1 nm or more, specifically 5 nm or more, and can be 1 nm to 200 nm, specifically 5 to 50 nm, but is not limited thereto.

[0060] These short fibers 5a are formed as a coating layer 5 on the surface of the porous ceramic separation membrane substrate 1. As long as they can reinforce the tensile strength, organic fibers, inorganic fibers, or mixtures thereof can be used. In particular, they can be cellulose-based fibers such as cellulose or modified cellulose obtained by modifying cellulose so that it has a carboxyl group. The mixing ratio (weight ratio) of the binder polymer particles 5b to the short fibers 5a can be 95:5 to 20:80, more specifically 90:10 to 30:70, but is not limited thereto.

[0061] Considering the resistance, the thickness of the coating layer 5 can be formed to be 3 μm or less, more specifically 2 μm or less.

[0062] Thus, the tensile strength of the porous composite ceramic separation membrane 10 including the porous ceramic separation membrane substrate 1 and the coating layer 5 is 180 kgf / cm 2 or more, specifically 180 to 300 kgf / cm 2 and more specifically 200 to 280 kgf / cm 2 but is not limited thereto.

[0063] <Method for manufacturing a porous composite ceramic separation membrane> The porous composite ceramic separation membrane 10 having the above-described configuration can be manufactured as follows, but is not limited thereto.

[0064] A slurry in which a plurality of inorganic particles are dispersed and a binder polymer is dissolved in a solvent is coated and dried on a support, and then peeled off from the support to prepare a porous ceramic separation membrane substrate (step S1).

[0065] Such a method for manufacturing a porous ceramic separation membrane substrate is described in PCT / KR2005 / 002674, and the content of the above international application is incorporated herein by reference.

[0066] First, a slurry in which a plurality of inorganic particles are dispersed and a binder polymer is dissolved in a solvent is produced. That is, after dissolving the above-described binder polymer in an appropriate organic solvent to produce a polymer solution, the inorganic particles are dispersed.

[0067] As the solvent, one having a solubility index similar to the binder polymer to be used and a low boiling point is preferable. This is because mixing can be performed uniformly and then the solvent can be easily removed. Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof.

[0068] The produced polymer solution is added with and dispersed with inorganic particles to produce a slurry. After adding the inorganic particles to the polymer solution, it is preferable to crush the inorganic particles. At this time, the crushing time is appropriately 1 to 20 hours, and the preferable particle size of the crushed inorganic particles is as described above. As the crushing method, a normal method can be used, and in particular, the ball mill method is preferable. The preferable components and mixing ratio of the inorganic particles and the binder polymer are as described above. As the ratio (ratio = I / P) of the inorganic particles I to the binder polymer P increases, the porosity of the porous ceramic separation membrane substrate increases. Also, as the particle size of the inorganic particles increases, the interstitial distance between the inorganic substances increases, so the size of the pores increases. A dispersant can be further added to the slurry as necessary.

[0069] After coating and drying the produced slurry on a support and then peeling it off from the support, a porous ceramic separation membrane substrate can be obtained. At this time, as the support, ordinary sheets or films such as Teflon (registered trademark) sheets can be used, but it is not limited thereto.

[0070] For the step of coating the slurry on the support, ordinary coating methods can be used. In particular, it is preferable to apply by dip coating, die coating, roll coating, comma coating, or a mixed method thereof.

[0071] Next, a coating layer is formed (S2 step) by applying and drying an aqueous slurry in which binder polymer particles and a plurality of short fibers are dispersed on at least one surface of the produced porous ceramic separation membrane substrate.

[0072] The preferable types and compositions of the binder polymer particles and the plurality of short fibers are as described above, and the aqueous slurry is produced by adding and mixing the binder polymer particles and the plurality of short fibers in an aqueous dispersion medium such as water or alcohol and dispersing them.

[0073] For the coating method of the aqueous slurry and the like, the coating method when forming the above-mentioned porous ceramic separation membrane substrate can be used.

[0074] According to still another embodiment of the present invention, an electrochemical element including the porous composite ceramic separation membrane is provided.

[0075] The porous composite ceramic separation membrane produced by the method described above uses a ceramic separation membrane substrate instead of a polymer separation membrane substrate, but is a separation membrane coated with a mixture of binder polymer particles and a plurality of short fibers and having its tensile strength reinforced. By assembling an electrochemical element with this separation membrane interposed between a positive electrode, a negative electrode, and between the positive electrode and the negative electrode, the assembly defect phenomenon is improved.

[0076] The electrochemical device can specifically be a battery or a capacitor, and more specifically can be a lithium secondary battery.

[0077] Hereinafter, the configuration of the lithium secondary battery will be exemplified in more detail.

[0078] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0079] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Further, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and minute irregularities can also be formed on the surface of the positive electrode current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0080] The positive electrode active material layer can contain a known positive electrode active material, a conductive material, and a binder.

[0081] Examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), compounds substituted with one or more transition metals, chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3) of Ni-site type lithium nickel oxide represented by, chemical formula LiMn 2-x M xLithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions, disulfide compounds, Fe2(MoO4)3, etc. are included, but not limited thereto.

[0082] The conductive material is used to impart conductivity to the electrode. In the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing chemical changes. Specific examples include carbon materials such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material can usually be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0083] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One kind alone or a mixture of two or more kinds of these can be used. The binder can be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0084] The positive electrode can be manufactured by a normal positive electrode manufacturing method. Specifically, it can be manufactured by applying a composition for forming a positive electrode active material layer containing a positive electrode active material and optionally a binder or a conductive material onto a positive electrode current collector, and then drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0085] The solvent is a solvent generally used in the art, and examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N - methylpyrrolidone (NMP), acetone, or water, etc. One kind alone or a mixture of two or more kinds of these can be used. The amount of the solvent used is sufficient as long as it dissolves or disperses the positive electrode active material, conductive material, and binder in consideration of the coating thickness of the slurry and the production yield, and then gives a viscosity having excellent thickness uniformity during coating for the production of the positive electrode.

[0086] As another method, the positive electrode can be manufactured by laminating, on a positive electrode current collector, a film obtained by casting the composition for forming the positive electrode active material layer on another support and then peeling the film from the support.

[0087] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0088] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector can usually have a thickness of 3 to 500 μm, and similar to the positive electrode current collector, minute irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0089] The negative electrode active material layer selectively contains a binder or a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer can be manufactured by applying and drying a composition for forming a negative electrode containing a negative electrode active material and selectively a binder or a conductive material on a negative electrode current collector, or by casting the composition for forming a negative electrode on another support and then laminating, on the negative electrode current collector, a film obtained by peeling the film from the support.

[0090] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy, SiO β(0 < β < 2), metal oxides such as SnO₂, vanadium oxides, and lithium vanadium oxides that can be doped and undoped with lithium, composites containing the metal compound and a carbonaceous material such as Si-C composites or Sn-C composites, etc. can be mentioned, and any one or a mixture of two or more of these can be used. Also, a thin film of metallic lithium can be used as the negative electrode active material. Further, as the carbon material, all of low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial 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.

[0091] Also, the binder and the conductive material are the same as those described above for the positive electrode.

[0092] Also, 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-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0093] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0094] As the organic solvent, any solvent can be used without particular limitation as long as it serves as a medium in 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, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC); alcohol solvents such as ethyl alcohol or isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group having a linear, branched or cyclic structure of C2 to C20 and may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a chain carbonate compound having low viscosity (for example, ethylmethylcarbonate, dimethylcarbonate or diethylcarbonate) is more preferred. In this case, the cyclic carbonate and the chain carbonate may be mixed and used at a volume ratio of about 1:1 to about 1:9 for excellent performance of the electrolyte.

[0095] As the lithium salt, any compound can be used without particular limitation as long as it can provide lithium ions used in a lithium secondary battery. Specifically, examples of the lithium salt include 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 in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0096] In addition to the above-described electrolyte constituent components, the electrolyte may further contain one or more additives such as haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. At this time, the additive can be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0097] The electrochemical device according to the present invention is useful in mobile devices such as mobile phones, notebook personal computers, digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0098] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0099] Example 1 〔Manufacture of Porous Ceramic Separation Membrane Substrate〕 After adding polyvinylidene fluoride to NMP and dissolving it, a polymer solution was prepared. Al2O3 powder with a particle size of about 400 nm was added to this polymer solution at a ratio of 8:2 with respect to the polymer content to produce a slurry with a total solid content of 20% by weight. The slurry produced using the doctor blade method was coated on a Teflon (registered trademark) sheet support, dried, and then peeled off from the Teflon (registered trademark) sheet to obtain a porous ceramic separation membrane substrate with a thickness of about 20 μm.

[0100] 〔Formation of Coating Layer〕 The slurry for forming the coating layer of the porous ceramic separation membrane substrate obtained by the above-described method was dip-coated and dried to produce a porous composite ceramic separation membrane with a coating layer formed. The slurry for forming the coating layer was prepared as follows.

[0101] At room temperature, an aqueous dispersion of binder polymer particles [solid content 15% by weight, particulate binder polymer of a copolymer of methyl methacrylate and ethylhexyl acrylate, average particle size 350 nm, Tg 40 °C] and an aqueous dispersion of cellulose short fibers [average length: 3 μm, average diameter 25 nm) (solid content 5% by weight) were uniformly mixed to produce a slurry for forming the coating layer.

[0102] The mixing ratio (weight ratio) of the binder polymer particles and the short fibers in the slurry was 75:25.

[0103] Example 2 A porous composite ceramic separation membrane was produced in the same manner as in Example 1, except that the thickness of the coating layer was changed as shown in Table 1 below.

[0104] Comparative Examples 1 and 2 When preparing the slurry for forming the coating layer, a porous composite ceramic separation membrane was produced in the same manner as in Example 1, except that an aqueous dispersion of cellulose short fibers was not mixed and the thickness of the coating layer was changed as shown in Table 1 below.

[0105]

Table 1

[0106] For the porous composite ceramic separation membranes of the above-described Examples and Comparative Examples, their physical properties and the like were evaluated and shown in Table 2 below.

[0107]

Table 2

[0108] <Measurement of Tensile Strength> After cutting the produced separation membranes of Examples and Comparative Examples to a width of 20 mm (length: 100 mm), the tensile strength was measured using a UTM device under the condition of a speed of 500 mm / sec.

[0109] <Measurement of Electric Resistance> The separation membranes of Examples and Comparative Examples punched out on the lower plate of a coin cell 2032 (diameter: 20 mm, thickness: 3.2 mm) were each placed, and after dropping 1 drop of an electrolytic solution (EC / EMC = 7:3, 1 M LIPF6) using a disposable pipet, a gasket was joined, the upper plate was covered and pressurized to fabricate a coin cell, and the resistance was measured by EIS.

[0110] <Measurement of Dimensional Change Rate> After immersing the separation membrane in the above-described electrolytic solution for 1 hour, the dimensional change rate of the separation membrane was measured using a 3D dimensional measurement device. The dimensional change rate was determined as the average value of the dimensional change rates in the longitudinal and lateral directions.

[0111] <Measurement of Lamination Adhesion Strength> Natural graphite: Conductive material: Binder: Thickener were added in a ratio of 95:1:3:1 by weight to produce a slurry. After that, it was coated on a 20-μm copper current collector with a thickness of 150 μm and dried, and then roll-pressed so that the thickness of the negative electrode became 110 μm. Next, the produced negative electrode and the separator were cut into an area of 2 cm * 2 cm, laminated, placed in PET, and pressed under the conditions of 6 MPa and 10 sec using a hot press device. Then, the adhesive force was measured using a peel tester.

[0112] <Measurement of Initial Capacity and Battery Resistance> The positive electrode active material of NCM111: Conductive material: Binder were added in a ratio of 94:3:3 by weight to produce a slurry. After that, it was coated on a 20-μm aluminum current collector with a thickness of 100 μm and dried, and then roll-pressed so that the thickness of the positive electrode became 70 μm.

[0113] After laminating the positive electrode / separator / negative electrode manufactured by the above method and enclosing it in a pouch, 300 μL of electrolyte was injected to manufacture a monocell (3 cm * 4 cm). After charging and activating it at a 0.1C-rate for 3 hours, 0.33C / 0.33C charge and discharge were performed 3 times to evaluate the battery capacity. After setting SOC50, a 2C, 10-sec pulse was applied to measure the battery resistance at SOC50.

[0114] <Measurement of Insulation Resistance> After roll-laminating a monocell (separator / negative electrode / separator / positive electrode), 5 monocells were stacked to manufacture a laminated cell.

[0115] The insulation resistance of the laminated cell was measured using a Hioki resistance measuring machine, and it was judged as a pass if it exceeded 100 MΩ.

Claims

1. A porous ceramic separation membrane substrate comprising a plurality of inorganic particles forming a skeleton and a binder polymer for connecting and fixing the inorganic particles to each other, and a coating layer coated on at least one surface of the porous ceramic separation membrane substrate and formed by mixing binder polymer particles and a plurality of short fibers.

2. The porous composite ceramic separation membrane according to Claim 1, wherein the binder polymer particles are rubber-based particles or polyacrylate-based particles.

3. The porous composite ceramic separation membrane according to Claim 1, wherein the plurality of short fibers have an average length of 0.5 to 10 μm. The porous composite ceramic separation membrane according to Claim 1.

4. The porous composite ceramic separation membrane according to Claim 1, wherein the plurality of short fibers have an average diameter of 200 nm or less.

5. The porous composite ceramic separation membrane according to Claim 1, wherein the plurality of short fibers are cellulose-based fibers.

6. The porous composite ceramic separation membrane according to Claim 1, wherein the mixing ratio (weight ratio) of the binder polymer particles to the short fibers is 95:5 to 20:

80.

7. The porous composite ceramic separation membrane according to Claim 1, wherein the thickness of the coating layer is 3 μm or less.

8. The inorganic particles are SrTiO ３ , SnO ２ , CeO ２ , MgO, NiO, CaO, ZnO, ZrO ２ , Y ２ O ３ , Al ２ O ３ , AlOOH, Al(OH) ３ , TiO ２ The porous composite ceramic separation membrane according to claim 1, characterized by containing any one or more selected from the group consisting of SiC.

9. The binder polymer is any one or more selected from the group consisting of polyvinylidene fluoride (polyvinylidene fluoride), polyvinylidene fluoride - hexafluoropropylene (polyvinylidene fluoride - co - hexafluoropropylene), polyvinylidene fluoride - trichloroethylene (polyvinylidene fluoride - co - trichloroethylene), polymethyl methacrylate (polymethyl methacrylate), polyethylhexyl acrylate (polyethylhexyl acrylate), polybutyl acrylate (polybutyl acrylate), polyacrylonitrile (polyacrylonitrile), polyvinyl pyrrolidone (polyvinyl pyrrolidone), polyvinyl acetate (polyvinyl acetate), ethylene vinyl acetate copolymer (polyethylene - co - vinyl acetate), polyethylene oxide (polyethylene oxide), polyarylate (polyarylate), cellulose acetate (cellulose acetate), cellulose acetate butyrate (cellulose acetate butyrate), cellulose acetate propionate (cellulose acetate propionate), cyanoethyl pullulan, (cyanoethyl pullulan), cyanoethyl polyvinyl alcohol (cyanoethyl polyvinyl alcohol), cyanoethyl cellulose (cyanoethyl cellulose), cyanoethyl sucrose (cyanoethyl sucrose), pullulan, (pullulan) and carboxymethyl cellulose (carboxymethyl cellulose). The porous composite ceramic separation membrane according to claim 1, characterized in that it is any one or more of them.

10. The porous composite ceramic separation membrane according to claim 1, characterized in that the mixing ratio (weight ratio) of the inorganic particles and the binder polymer is 50:50 to 99:

1.

11. The tensile strength of the porous composite ceramic separation membrane is 180 kgf / cm ２ The porous composite ceramic separation membrane according to claim 1, characterized in that it is 180 kgf / cm or more.

12. In an electrochemical element including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The electrochemical element, wherein the separator is the porous composite ceramic separator according to any one of claims 1 to 11.

13. The electrochemical element according to claim 12, wherein the electrochemical element is a lithium secondary battery.

14. A method for manufacturing a porous composite ceramic separator according to any one of claims 1 to 11, comprising: (S1) Coating and drying a slurry in which a plurality of inorganic particles are dispersed and a binder polymer is dissolved on a support, and peeling from the support to prepare a porous ceramic separator substrate; (S2) Forming a coating layer by applying and drying an aqueous slurry in which binder polymer particles and a plurality of short fibers are dispersed on at least one surface of the porous ceramic separator substrate.

15. The method for manufacturing a porous composite ceramic separator according to claim 14, wherein the binder polymer particles are rubber-based particles or polyacrylate-based particles.

16. The method for manufacturing a porous composite ceramic separator according to claim 14, wherein the plurality of short fibers are cellulose-based fibers.

17. The method for manufacturing a porous composite ceramic separator according to claim 14, wherein a mixing ratio (weight ratio) of the binder polymer particles to the short fibers is 95:5 to 20:80.

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