Ceramic coated separator for secondary battery, secondary battery including same, and method for manufacturing ceramic coated separator for secondary battery

Abstract

One embodiment of the present invention provides a coated separator for a secondary battery comprising: a separator substrate made of a porous polymer resin; and a coating layer coated on at least one surface of the separator substrate, wherein the coating layer comprises inorganic particles and a binder polymer, and the inorganic particles are ceramic particles. The invention also relates to a secondary battery and a method for manufacturing a ceramic coated separator for a secondary battery, wherein the same is utilized as a separator for a lithium secondary battery to improve thermal stability, ion conductivity, and high-speed charge / discharge performance.

Description

Technology Field

[0001] The present invention relates to a ceramic-coated separator for a secondary battery, a secondary battery including the same, and a method for manufacturing a ceramic-coated separator for a secondary battery. More specifically, the invention relates to a secondary battery and a method for manufacturing a ceramic-coated separator for a secondary battery, wherein ceramic particles and a binder polymer are coated on the surface of the separator and the same is utilized as a separator for a lithium secondary battery to improve thermal stability, ion conductivity, and high-speed charge / discharge performance. Background Technology

[0003] Recently, as climate change caused by the use of fossil fuels has emerged as a critical global issue, interest in eco-friendly energy is surging. Amidst this trend, rechargeable batteries are one of the fields attracting attention as a sustainable energy storage technology. In the past, lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, and all-solid-state batteries were used; however, currently, rechargeable lithium-ion batteries (LIBs) are widely utilized in most electronic devices. Lithium is the lightest of all metals and possesses a high energy density reaching 160 Wh / kg, which is twice that of nickel-cadmium batteries and six times that of lead-acid batteries. Furthermore, it has a low standard reduction potential of -3.04 V (vs. H₂ / Pt), allowing it to provide high voltage.

[0004] In lithium-ion batteries, the separator is a key component that prevents direct contact between the anode and cathode while allowing lithium ions to move freely. Separators generally possess fine pores ranging in size from 0.01 to 1 μm and must block the flow of electrons to prevent internal short circuits, while simultaneously serving as a pathway for lithium ion movement. The primary materials currently used for separators are polyolefin-based polyethylene (PE) and polypropylene (PP), which offer the advantages of low cost and excellent mechanical properties. However, polyolefin-based separators have the disadvantage of lacking thermal stability due to their low melting temperatures. Safety can be ensured when the temperature of the LIB rises, as the separator blocks the pores and triggers a "shut-down" phenomenon to prevent ion movement. However, if the temperature continues to rise even after the shut-down, a melt-down occurs, leading to a massive movement of lithium ions between the electrodes and potentially increasing the risk of explosion. Generally, the melting point of polyolefin materials ranges from 135 to 165°C. Therefore, if the separator shrinks or ruptures as the temperature of the LIB rises, it becomes difficult to maintain battery stability; thus, to solve this problem, the development of a separator capable of maintaining its structure even at high temperatures is essential.

[0005] In addition, polyolefin separators are hydrophobic, resulting in low affinity with the electrolyte of lithium-ion batteries and poor impregnation. Consequently, the electrolyte does not permeate uniformly, which can lead to reduced ion conductivity and consequently decrease battery performance. To address this issue, a technology has been developed to apply a ceramic coating to the surface of the separator. Ceramic-coated separators offer superior high-temperature stability compared to conventional separators and have the advantage of improving ion conductivity due to their high affinity with the electrolyte. Generally, they are manufactured by coating a slurry, which is a mixture of ceramic particles and a polymer binder, onto the surface of the separator and then drying it.

[0006] Alumina (Al₂O₃) is the most widely used material for ceramic coatings, while zirconia (ZrO₂) and silica (SiO₂) are also being studied. Since ceramic particles possess a high specific surface area and hydrophilicity, they can improve wettability to the electrolyte and enhance the charge and discharge performance of batteries. Currently, battery manufacturers are commercializing and applying ceramic composite separators; representative examples include LG Energy Solution's SRS (Safety-Reinforcing Separator), Samsung SDI's SFL (Safety Functional Layer), and Panasonic's HRL (Heat Resistance Layer). These ceramic-coated separators offer improved heat resistance, mechanical strength, and electrolyte impregnation compared to conventional polyolefin separators, leading to their widespread application in high-capacity and large-scale batteries.

[0007] In conclusion, lithium-ion batteries play an essential role in the energy storage industry and are undergoing continuous development. In particular, secondary battery technology that simultaneously satisfies high energy density and safety is becoming increasingly important, and accordingly, ceramic-coated separators have established themselves as a core research field. This invention was developed to meet these technical demands and aims to present a new technology capable of overcoming the limitations of existing technologies. The problem to be solved

[0009] The present invention has been devised to solve the aforementioned problems, and one embodiment of the present invention provides a coating separator for a secondary battery.

[0010] In addition, another embodiment of the present invention provides a method for manufacturing a coating separator for a secondary battery.

[0011] In addition, another embodiment of the present invention provides a lithium secondary battery.

[0012] However, the technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0014] As a technical means for achieving the aforementioned technical problem, one aspect of the present invention provides a coated separator for a secondary battery, comprising: a separator substrate made of a porous polymer resin; and a coating layer coated on at least one surface of the separator substrate; wherein the coating layer comprises inorganic particles and a binder polymer, and the inorganic particles are ceramic particles.

[0015] The above binder polymer is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinylacetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate It may be one or more mixtures selected from the group consisting of cellulose acetate propionate, carboxymethylcellulose, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, and pullulan.

[0016] The ceramic particles may be one or more inorganic compounds selected from AlF₃, Al₂O₃, SiO₂, ZnO, TiO₂, HfO₂, Ga₂O₃, CeO₂, MgO, NiO, Y₂O₃, CaO, SrTiO₃, SnO₂, ZrO₂, SiC, SiC₂, ZnS, and Zeolite.

[0017] The ceramic particles are one-dimensional nanostructures, and the nanostructures may have the form of nanorods, nanowires, nanofibers, nanotubes, needle-shaped, or a combination thereof.

[0018] The average length of the ceramic particles may be 0.1 to 5 μm, and the average diameter may be 100 to 500 nm.

[0019] The aspect ratio of the ceramic particles may be 5 to 6.

[0020] As a result of X-ray diffraction (XRD) analysis of the above ceramic particles, the 2θ value was 18.2 o to 20.2 o It indicates the first peak having a maximum peak at, and the 2θ value is 21.1 o to 23.1 o It shows a second peak with a maximum peak at, and the 2θ value is 34.4 o to 36.4 o A third peak having a maximum peak can be shown.

[0021] The thickness of the coating layer may be 5 to 25 μm.

[0023] Another aspect of the present invention is,

[0024] The present invention provides a method for manufacturing a coating separator for a secondary battery, comprising the steps of: preparing a mixed solution comprising an inorganic particle precursor, a first solvent, and a second solvent; adding a fluorinating agent to the mixed solution to precipitate inorganic particles; washing and drying the inorganic particles to obtain them; preparing a coating solution comprising the obtained inorganic particles, a binder polymer, and a third solvent; applying the coating solution onto at least one surface of a porous polymer substrate; and drying the coating solution to form a coating layer.

[0025] The porous polymer substrate may be formed from any one selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, or a mixture of two or more of these.

[0026] In the step of preparing the above mixed solution; wherein the moles of the first solvent and the second solvent

[0027] The ratio can be 3:1 to 6:1.

[0028] In the step of precipitating the above inorganic particles; the fluorinating agent may be one or more fluorinating agents selected from HF, NH₄HF₂, NH₄F, KF, and NaF.

[0029] In the step of preparing the coating solution, the weight ratio of the inorganic particles to the binder polymer may be 2:1 to 6:1.

[0030] The step of precipitating the above inorganic particles; may involve stirring the above mixed solution at a speed of 400 to 600 rpm for 0.3 to 1 hour at a temperature of 10 to 100 ℃.

[0032] Another aspect of the present invention is,

[0033] The present invention provides a lithium secondary battery characterized by including a coating separator for a secondary battery. Effects of the invention

[0035] According to one embodiment of the present invention, shrinkage of the membrane was suppressed even at high temperatures compared to conventional polypropylene membranes, and thanks to the characteristics of the one-dimensional nanostructure, the shape could be maintained even at high temperatures.

[0036] In addition, according to one embodiment of the present invention, the surface structure of the separator is optimized due to the ceramic coating, and the ion conductivity is improved by increasing the electrolyte impregnation. This helps lithium ions move smoothly, thereby enhancing the performance of the battery.

[0037] Furthermore, according to one embodiment of the present invention, the separator of the present invention maintains stable performance even at high charge and discharge speeds, and the capacity retention rate is improved compared to conventional ceramic-coated separators. Through this, the possibility of applying it to batteries requiring high output and fast charging has been confirmed.

[0038] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0040] FIG. 1 is a schematic diagram showing the steps for manufacturing a coating separator for a secondary battery according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a polypropylene (PP) separator coated with AlF3 nanorods according to one embodiment of the present invention. Figure 3 shows the manufacturing process of an AlF3 nanorod coated separator according to an embodiment of the present invention. Figure 4 shows the SEM analysis results of ceramic particles of a comparative example and an example according to one embodiment of the present invention. Figure 4 shows an SEM image of AlF3 nanorods, (b) AlF3 nanorods formed at a low temperature, (c) AlF3 nanorods formed at a high temperature, (d) AlF3 nanorods when the batch number of samples is tripled, (e) AlF3 nanorods when IPA is changed to ethanol, and (f) AlF3 nanoparticles. FIG. 5 shows the SEM and TEM analysis results of ceramic particles and a separator membrane according to an embodiment of the present invention. FIG. 5 shows (a) an SEM image of AlF3 nanorods after high-temperature heating, (b) a TEM image of AlF3 nanorods, (c) an SEM image of an AlF3-coated separator membrane, and (d) an SEM image of a cross- section of an AlF3-coated separator membrane. FIG. 6 shows the SEM and TEM analysis results of ceramic particles and a separation membrane of a comparative example according to one embodiment of the present invention. FIG. 6 (a) is an SEM image of Al2O3, (b) is a TEM image of Al2O3, (c) is an SEM image of an Al2O3-coated separation membrane, and (d) is an SEM image of a cross- section of an Al2O3-coated separation membrane. FIG. 7 shows the XRD analysis results of ceramic particles of a comparative example and an example according to one embodiment of the present invention. FIG. 7 (a) is the XRD analysis result of AlF3 nanoparticles, and (b) is the XRD analysis result of AlF3 nanorods. Figure 8 shows the particle size distribution of AlF3 nanorods of an example according to one embodiment of the present invention. FIG. 9 shows the thermogravimetric analysis results of an α-AlF3 nanorod of an example according to one embodiment of the present invention. FIG. 10 shows a digital photograph of a separator after heat shrinkage evaluation of a comparative example and an example according to one embodiment of the present invention. FIG. 11 shows the MD thermal shrinkage rate of the separation membranes of the comparative example and the example according to one embodiment of the present invention. FIG. 12 shows a digital photograph of a separator undergoing a wettability test of a comparative example and an example according to one embodiment of the present invention. FIG. 13 shows the Nyquist plot of the AC impedance spectrum of a symmetric cell of a comparative example and an example according to one embodiment of the present invention. FIG. 14 shows a graph of the initial charge and discharge voltage change of a full cell of a comparative example and an example according to one embodiment of the present invention, measured under 0.1C conditions. FIG. 15 shows the C-rate performance of a full cell of a comparative example and an example according to one embodiment of the present invention. FIG. 16 shows the results of evaluating long-term performance changes while charging and discharging full cells of a comparative example and an example according to one embodiment of the present invention at a rate of 0.2C. FIG. 17 shows the results of evaluating long-term performance changes while charging and discharging full cells of a comparative example and an example according to one embodiment of the present invention at a rate of 0.5C. FIG. 18 shows the electrochemical impedance spectrum of a cell after 100 cycles of charging and discharging at 0.2C of a comparative example and an example according to one embodiment of the present invention. FIG. 19 shows the results of evaluating long-term performance changes while charging and discharging a full cell at a rate of 0.2C at 60°C of a comparative example and an example according to one embodiment of the present invention. Specific details for implementing the invention

[0041] The present invention will be described in more detail below. However, the present invention may be implemented in various different forms and is not limited by the embodiments described herein, and is defined only by the claims set forth below.

[0042] The terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0043] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0044] The present invention will be described below with reference to the attached drawings. In order to clearly explain the invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0046] The first aspect of the present invention is,

[0047] A coating separator for a secondary battery is provided, comprising: a separator substrate made of a porous polymer resin; and a coating layer coated on at least one surface of the separator substrate; wherein the coating layer comprises inorganic particles and a binder polymer, and the inorganic particles are ceramic particles.

[0049] Hereinafter, a coating separator for a secondary battery according to the first aspect of the present invention will be described in detail.

[0051] In one embodiment of the present invention, the binder polymer is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinylacetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose It may be one or more mixtures selected from the group consisting of cellulose acetate propionate, carboxymethylcellulose, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, and pullulan. In one preferred embodiment of the present invention, the binder polymer may be polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene.

[0052] In one embodiment of the present invention, the ceramic particles may be one or more inorganic compounds selected from AlF₃, Al₂O₃, SiO₂, ZnO, TiO₂, HfO₂, Ga₂O₃, CeO₂, MgO, NiO, Y₂O₃, CaO, SrTiO₃, SnO₂, ZrO₂, SiC, SiC₂, ZnS, and Zeolite. In a preferred embodiment of the present invention, the ceramic particles may be AlF₃. AlF₃ can have high ionic conductivity and chemical and electrochemical stability due to strong and stable Al-F bonds. When AlF₃ is coated on a separator, AlF₃ having fluorine groups does not react with a fluorinating agent, thereby providing chemical stability. AlF₃ has a total of five phases: α-, β-, η-, κ-, and τ-AlF₃. The α-phase has a perovskite structure, is the most stable at room temperature, crystallizes into a rhombohedral structure, and is thermodynamically stable at room temperature. Additionally, α-AlF₃ is a dielectric compound with a low refractive index, a wide band gap of 10.8 eV, and strong Lewis acidity. More preferably, the ceramic particles may be α-AlF₃.

[0053] In one embodiment of the present invention, the ceramic particles are one-dimensional nanostructures, and the nanostructures may have the form of nanorods, nanowires, nanofibers, nanotubes, needle-shaped structures, or a combination thereof. In a preferred embodiment of the present invention, the nanostructures may have the form of nanorods. Nanorods have an anisotropic structure and exhibit improved performance compared to spherical particles, which is mainly because the electric field is strengthened as surface plasmon excitation increases due to an increase in the aspect ratio. Additionally, because they have an anisotropic structure, they are difficult to align uniformly when randomly arranged, resulting in a lower density. The one-dimensional nanostructures have excellent thermal conductivity and thermal stability, making them advantageous in various high-temperature applications. Among multidimensional nanostructures, nanorods, which are one-dimensional structures, have the advantages of a large surface area, fast charge transport capability, and applicability to flexible substrates. Furthermore, due to their anisotropic structure, nanorods stack randomly when arranged, resulting in a large number of empty spaces and consequently exhibiting high permeability. Thanks to these characteristics, nanorods can play an important role in various advanced materials and electronic device applications.

[0054] In one embodiment of the present invention, the average length of the ceramic particles may be 0.1 to 5 μm and the average diameter may be 79 to 756 nm. For example, the average length may preferably be 0.65 to 4 μm and more preferably 1 to 3 μm. The average diameter may preferably be 100 to 500 nm and more preferably 198 to 472 nm. If the average length and average diameter of the ceramic particles are below the ranges described above, the coating layer may become thin, making it difficult to sufficiently improve the thermal stability of the separator, and the ceramic layer may become excessively dense, resulting in a lack of pores and consequently a decrease in ion conductivity. If the ranges described above are exceeded, it may be difficult to form a uniform coating on the surface of the separator, the surface may become rough, and cracks in the coating layer may occur, leading to a decrease in the mechanical strength of the separator and an uneven contact with the electrolyte.

[0055] In one embodiment of the present invention, the aspect ratio of the ceramic particles may be 3.75 to 8.82. For example, the aspect ratio may preferably be 4.5 to 7.35, and more preferably 5 to 6. If the range is below the above range, pores may not be sufficiently formed due to particles with a small aspect ratio, and the electrolyte may not easily penetrate into the coating layer, which may reduce ion conductivity. If the range is exceeded, the particles may become entangled with each other to form a network structure, which may make it difficult to achieve a uniform coating, result in an uneven pore distribution, and weaken the durability of the coating layer.

[0056] In one embodiment of the present invention, the X-ray diffraction (XRD) analysis result of the ceramic particles shows that the 2θ value is 18.2 o to 20.2 o It indicates the first peak having a maximum peak at, and the 2θ value is 21.1 oto 23.1 o It shows a second peak with a maximum peak at, and the 2θ value is 34.4 o to 36.4 o A third peak having a maximum peak can be shown at. In one preferred embodiment of the present invention, the 2θ value is 18.7 o to 19.7 o It shows the first peak having a maximum peak at, and 21.6 o to 22.6 o It shows a second peak with a maximum peak at 34.9 o to 35.9 o A third peak having a maximum peak can be represented. The first peak corresponds to the Miller index (1 1 0), the second peak corresponds to the Miller index (1 0 1), and the third peak corresponds to the Miller index (2 1 1).

[0057] In one embodiment of the present invention, the thickness of the coating layer may be 3 to 30 μm. For example, the thickness may preferably be 5 to 25 μm, and more preferably 7.5 to 12 μm. If the thickness is less than the above range, the insulation between the anode and the cathode is reduced, an internal short circuit may occur, and the separator may be easily torn even by minor physical damage. If the thickness exceeds the above range, the ion conductivity may decrease, the charging and discharging speed of the battery may be reduced, and the internal resistance may increase, thereby reducing battery efficiency.

[0058] In one embodiment of the present invention, the pore size of the coating layer may be 0.1 to 10 μm, and the porosity may be 10 to 50%. If the pore size of the coating layer is below the above range, the electrolyte may not penetrate sufficiently, causing the ion mobility to slow down and the internal resistance to increase, which may exacerbate the degradation of battery performance. If it exceeds the above range, the risk of lithium dendrite growth increases, raising the likelihood of an internal short circuit and potentially reducing the safety of the battery. If the porosity of the coating layer is below the above range, the electrolyte may not penetrate sufficiently into the separator, which may increase internal resistance and degrade battery charge / discharge performance. If it exceeds the above range, the mechanical strength of the separator may be weakened, which may increase the risk of an internal short circuit.

[0060] The second aspect of the present invention is,

[0061] The present invention provides a method for manufacturing a coating separator for a secondary battery, comprising the steps of: preparing a mixed solution comprising an inorganic particle precursor, a first solvent, and a second solvent; adding a fluorinating agent to the mixed solution to precipitate inorganic particles; washing and drying the inorganic particles to obtain them; preparing a coating solution comprising the obtained inorganic particles, a binder polymer, and a third solvent; applying the coating solution onto at least one surface of a porous polymer substrate; and drying the coating solution to form a coating layer.

[0063] Detailed explanations have been omitted for parts that overlap with the first aspect of the present invention, but the content described in the first aspect of the present invention may be applied equally even if such explanations are omitted in the second aspect.

[0065] Hereinafter, a method for manufacturing a coating separator for a secondary battery according to the second aspect of the present invention will be described in detail.

[0067] First, FIG. 1 is a schematic diagram showing the steps for manufacturing a coating separator for a secondary battery according to one embodiment of the present invention. Referring to FIG. 1, the steps for manufacturing a coating separator for a secondary battery according to the present invention include: adding a fluorinating agent to a mixed solution containing an inorganic particle precursor and a solvent (Fig. 1a); precipitating inorganic particles while stirring the mixed solution (Fig. 1b); centrifuging the mixed solution (Fig. 1c); preparing a coating solution by drying the washed inorganic particles in an oven and then mixing them with a binder polymer and a solvent (Fig. 1d); and coating the coating solution onto the separator (Fig. 1e). Additionally, FIG. 2 is a schematic diagram showing AlF3 nanorods coated on a polypropylene (PP) separator according to one embodiment of the present invention.

[0068] In one embodiment of the present invention, the porous polymer substrate may be formed from any one selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, or a mixture of two or more of these. In a preferred embodiment of the present invention, the porous polymer substrate may be polypropylene.

[0069] In one embodiment of the present invention, in the step of preparing the mixed solution, the molar ratio of the first solvent to the second solvent may be 3 to 6:1. The first solvent may be an aqueous solvent or a glycol, and preferably may be distilled water (DW), deionized water (DI water), or ethylene glycol (propylene glycol). The second solvent may be an alcohol, and preferably may be isopropyl alcohol, ethyl alcohol, or methanol. In a preferred embodiment of the present invention, the molar ratio of the first solvent to the second solvent may be 3.7 to 5:1, and more preferably may be 4 to 4.8:1. If the ratio of the first solvent exceeds the range described above, spherical inorganic particles or aggregated clumps may be formed, and the polarity of the solvent may increase, leading to excessive crystal growth. If the ratio of the second solvent exceeds the range described above, the hydration reaction may be restricted, and nanorods, which are one-dimensional nanostructures, may not be formed, the possibility of irregular particle formation may increase, and the reaction rate may be slowed down.

[0070] In one embodiment of the present invention, in the step of precipitating the inorganic particles; the fluorinating agent may be one or more fluorinating agents selected from HF, NH₄HF₂, NH₄F, KF, and NaF. In a preferred embodiment of the present invention, the fluorinating agent may be HF.

[0071] In one embodiment of the present invention, in the step of preparing the coating solution, the weight ratio of the inorganic particles to the binder polymer may be 2 to 6:1. For example, the weight ratio of the inorganic particles to the binder polymer may preferably be 3 to 5:1. If the ratio of the inorganic particles exceeds the above-described range, the bonding force between particles weakens, causing the coating layer to detach easily, and if external pressure or mechanical deformation is applied, the coating layer may detach from the separator or crack may occur. If the ratio of the binder polymer exceeds the above-described range, the ion conductivity may decrease, the impregnation of the electrolyte may decrease due to an excessive amount of binder, and the thermal stability of the coating layer may decrease as the effect of the inorganic particles is reduced.

[0072] In one embodiment of the present invention, the step of precipitating the inorganic particles may involve stirring the mixed solution at a speed of 400 to 600 rpm for 0.3 to 1 hour at a temperature of 10 to 150 ℃. In a preferred embodiment of the present invention, the temperature may be 10 to 100 ℃, and more preferably 10 to 80 ℃. If the temperature is below the above range, the size of the inorganic particles may become excessively large, it may be difficult to form a uniform coating on the surface of the separator, the surface of the separator may become rough, and cracks in the coating layer may occur. If the temperature exceeds the above range, the size of the inorganic particles may become very small, the coating layer may become excessively dense and lack pores, and consequently, the ion conductivity may decrease and battery performance may be degraded.

[0074] The third aspect of the present invention is,

[0075] The present invention provides a lithium secondary battery characterized by including a coating separator for a secondary battery.

[0077] Detailed explanations have been omitted for parts that overlap with the first and second aspects of the present invention; however, the contents described for the first and second aspects of the present invention may be applied equally to the third aspect even if such explanations are omitted.

[0079] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0081] Example: AlF 3 Manufacturing of nanorod-coated separators and secondary batteries

[0082] 1) Fabrication of AlF3 nanorod coated separator

[0083] To synthesize α-AlF3 nanorods, 7.035 g of Al(NO3) in a Teflon beaker 3· Stir 9H2O with 125 ml of IPA and 123 ml of distilled water. Then, add 2040 µl of HF to create a total solution of 300 ml. Upon addition of HF, a white powder precipitates immediately at room temperature, and the solution is stirred with a stirrer at 500 rpm for 30 minutes. Next, centrifuge the solution, and wash the precipitated powder twice with IPA. Finally, dry the precipitated powder in a circulation oven at 50 ℃ for 3 hours. After this process, 1.7 g of α-AlF 3· 3H2O nanorods are obtained.

[0084] A T-max 16 μm separator from Xiamen was used. The generated AlF3 was mixed with a 10 wt% Poly(vinylidene fluoride-co-hexafluoropropylene) - Acetone solution in an 8:2 wt% ratio, and the resulting solution was double-sided coated onto a Polypropylene (PP) separator using a doctor blade. The manufacturing process of the AlF3 nanorod coated separator is shown in Figure 3.

[0086] 2) Preparation of symmetric cells

[0087] A stainless steel / separator / stainless steel symmetric cell was fabricated using an AlF3 nanorod coated separator.

[0089] 3) Full cell manufacturing

[0090] A full cell was fabricated using an NCM 622-based anode and a Natural Graphite-based cathode. During this process, an AlF3 nanorod coated separator was laminated, and 2032 type coin cells were assembled in an argon glove box. As the electrolyte, 1M LiPF6 in EC (Ethylene Carbonate) / DMC (Dimethyl Carbonate) = 3 / 7, VC 5%, PS 1%, SN 1% (ENCHEM, Korea) was used, and the coin cells were aged at 45°C for 2 hours after assembly.

[0092] Comparative Example 1: AlF 3 Manufacturing of nanoparticle-coated separators and secondary batteries

[0093] AlF₃ was prepared in the same manner as in the example, except that the molar ratio of distilled water to IPA was changed to 9:1, and a separator coating was performed, and a secondary battery was manufactured using this.

[0095] Comparative Example 2: Al 2 O 3 Manufacturing of coating separators and secondary batteries

[0096] Separator coating was performed in the same manner as in the example, except that Al2O3 was used instead of AlF₃, and a secondary battery was manufactured using this.

[0098] Comparative Example 3: Preparation of Polypropylene (PP) Separator and Secondary Battery

[0099] A secondary battery was manufactured using the same method as in the example, except that ceramic particles were not coated on the polypropylene (PP) separator.

[0101] Experimental Example 1: Evaluation of Structure, Morphology, and Membrane Characteristics of Ceramic Particles

[0102] Experimental Example 1-1: Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) Analysis Results of Ceramic Particles and Ceramic-Coated Separator Membranes

[0103] To observe the microstructure of AlF₃, Field emission-Scanning Electron Microscope (FE-SEM, HITACHI, Regulus8100) and Field emission-Transmission Electron Microscope (FE-TEM, FEI, Tecnai G2 F20 X-Twin) were analyzed, and the results are shown in Figures 4 to 6.

[0104] Figure 4 shows the SEM analysis results of ceramic particles of Comparative Example 1 and Example, where Figure 4(a) shows AlF3 nanorods, (b) shows AlF3 nanorods formed at low temperature, (c) shows AlF3 nanorods formed at high temperature, (d) shows AlF3 nanorods when the batch number of samples was tripled, (e) shows AlF3 nanorods when IPA was changed to ethanol, and (f) shows an SEM image of AlF3 nanoparticles. From Figure 4(a), it was confirmed that nanorods with a morphological length of 1.882 μm, a height of 320 nm, and an aspect ratio of 5.88 were formed. Temperature affects the degree of supersaturation because solubility changes with temperature. In addition, temperature affects the particle size during nanorod formation; accordingly, experiments were conducted to form nanorods at low and high temperatures of 10°C and 80°C, which was verified through the formation of nanorods in Figures 4(b) and 4(c). In (b), nanorods were formed with a length of 2.009 μm and a height of 378 nm, and in (c), nanorods were formed with a length of 1.325 μm, a height of 264 nm, and aspect ratios of 5.31 and 5.01, respectively. α-AlF3·H2O is more soluble in water than IPA, and the supersaturation of α-AlF3·H2O is likely higher in solutions rich in IPA. Furthermore, the sample batch size was tripled, and upon examining Figure 4(d), the formation of nanorods similar in size to those in Figure 4(a) was confirmed, demonstrating that mass production is also possible. IPA does not play an active role in the chemical reaction, which can be confirmed by the fact that when the experiment was conducted by replacing IPA with ethanol and checking Figure 4(e), nanorods with similar particle sizes were obtained.

[0105] Figure 5 shows the SEM and TEM analysis results of the ceramic particles and separator membrane of the example. Figure 5(a) shows an SEM image of AlF3 nanorods after high-temperature heating, (b) shows a TEM image of AlF3 nanorods, (c) shows an SEM image of the AlF3-coated separator membrane, and (d) shows an SEM image of the cross-section of the AlF3-coated separator membrane. Figure 5(a) shows α-AlF3 nanorod particles after heating at 300°C. Figure 5(b) is a TEM image of α-AlF3 nanorods, confirming nanorods with a length of 1.882 μm and a height of 320 nm, and observing that the outer surface of the nanorods is amorphous through a high-energy electron beam. Figure 5(c) is an SEM image of the separator membrane coated with AlF3 nanorods, and it was confirmed that the membrane has a random arrangement in the cross-sectional image of the separator membrane after coating with AlF3 nanorods. This random arrangement creates many empty spaces, allowing ions to pass through smoothly, which maintains the number of lithium ions passing through the separator. In addition, the morphology of the separator affects characteristics such as thermal shrinkage, electrolyte wettability, porosity, ion conductivity, and battery performance. Figure 5(d) is a cross-sectional view of the separator after coating with AlF3 nanorods, showing that it is coated to a thickness of about 10 µm.

[0106] Figure 6 shows the SEM and TEM analysis results of the ceramic particles and membrane of Comparative Example 2, where (a) is an SEM image of Al2O3, (b) is a TEM image of Al2O3, (c) is an SEM image of the Al2O3-coated membrane, and (d) is an SEM image of the cross-section of the Al2O3-coated membrane.

[0108] Experimental Example 1-2: X-ray Diffraction (XRD) Analysis Results of Ceramic Particles

[0109] X-ray diffraction (XRD, Rigaku Smart Lab X-ray diffractometer) imaging was performed to observe the composition of the ceramic particles of Example and Comparative Example 1. Figure 7 (a) shows the XRD analysis results of AlF3 nanoparticles, and (b) shows the XRD analysis results of AlF3 nanorods. The crystal phase of the material obtained through XRD showed peaks of (1 1 0), (1 0 1), (2 1 1), (1 3 1), and (4 0 1) at positions 19.2°, 22.1°, 35.4°, 49.6°, and 49.6°, respectively, and it was confirmed that they matched the XRD peaks of α-AlF3·H2O.

[0111] Experimental Example 1-3: Particle Size Analysis (PSA) Results of Ceramic Particles

[0112] Particle Size Analysis (PSA, Malvern, Nano ZS) was performed to confirm the microstructure size of the AlF3 nanorods in the example. Dynamic light scattering is a technique that measures the size or distribution of molecules and particles in the smaller than 1 μm size range using the latest technology for particles smaller than 1 nm. It is used to analyze particles dispersed or dissolved in a liquid. As laser light is scattered at various angles, the velocity of Brownian motion is calculated accordingly, and the particle size is calculated using the Stokes-Einstein relationship.

[0113]

[0114] Here, dH is the hydrodynamic radius, k is the Boltzmann constant, T is the temperature, η is the viscosity of the solvent, and D is the diffusion coefficient. The results of the PSA are shown in Fig. 8, and the average size of the AlF3 nanorods was measured to be approximately 800 μm. This is because the direction in which the laser light scatters on the nanorods changes continuously, and as a result, the size of the AlF3 nanorod particles is most frequently measured when they are illuminated diagonally.

[0116] Experimental Example 1-4: Thermogravimetry Analysis (TGA) Results of Ceramic Particles

[0117] Thermogravimetric analysis (TA, Q500) was performed to analyze the thermal stability of the AlF3 nanorods of the example. Thermogravimetric analysis (TGA) is a technique that measures the mass of a material as a function of temperature or time while the sample is subjected to temperature in a controlled atmosphere. The TGA graph is shown in Fig. 9. Mass loss can generally be classified into volatile components such as absorbed moisture and residual solvent that evaporate between the ambient temperature and 300°C. Sudden weight loss occurs in the temperature range of 100 to 140°C. Then, the weight gradually decreases until the temperature reaches 300°C. Through this, it can be confirmed that α-AlF3 is formed from which the trihydrate (3H2O) has disappeared from α-AlF3·3H2O.

[0119] Experimental Example 1-5: Evaluation of Thermal Shrinkage of Separator Membrane

[0120] To evaluate the thermal shrinkage of polypropylene membranes and ceramic-coated membranes, the polypropylene membrane of Comparative Example 3, the polypropylene membrane coated with Al2O3 of Comparative Example 2, the polypropylene membrane coated with AlF3 nanoparticles of Comparative Example 1, and the polypropylene membrane coated with AlF3 nanorods of the Example were cut into uniform sizes (3 cm x 3 cm), heated at 130, 140, and 150 ℃ for 30 minutes, and the results were analyzed. Figure 10 shows a digital photograph of the membrane after the thermal shrinkage evaluation, and Figure 11 shows the MD thermal shrinkage rate of the membrane. Polypropylene membranes exhibited the highest thermal shrinkage rates of 4%, 8%, and 18% at temperatures of 130, 140, and 150 ℃, respectively; AlF3 nanorod membranes showed thermal shrinkage rates of 0%, 4%, and 8%, respectively; AlF3 nanoparticle membranes showed thermal shrinkage rates of 0%, 8%, and 12%, respectively; and Al2O3 membranes showed thermal shrinkage rates of 0%, 8%, and 8%, respectively. All coated membranes exhibited lower thermal shrinkage rates than non-coated membranes, which can be attributed to the heat-resistant material coated on the surface of the membranes. It is believed that the ceramic coating layer formed with a PVdF binder effectively suppressed the thermal shrinkage of the polypropylene membrane supporting the membrane. These results suggest that ceramic-coated membranes prevent deformation of the membrane caused by meltdown at high temperatures.

[0122] Experimental Example 1-6: Evaluation of Membrane Wetness

[0123] To test the wettability of the non-coated polypropylene separator of Comparative Example 3 and the ceramic-coated separator of Example and Comparative Example 2, LiPF6 electrolyte was filled into a Petri dish. Then, the polypropylene separator coated on both sides with AlF3 nanorods or Al2O3, respectively, and the non-coated separator were set up, and the height to which the electrolyte was absorbed was measured. Figure 12 shows a digital photograph of the separator undergoing the wettability test. The non-coated separator exhibited low wettability of less than 2 mm, while the AlF3 nanorod and Al2O3 coated separators showed impregnation of approximately 18 mm and 13 mm, respectively. The wettability of the AlF3 nanorod coated separator was measured to be the highest. Since the non-coated PP separator is hydrophobic, the hydrophilic electrolyte could not penetrate it, and the wettability was improved by coating it with ceramic. Furthermore, observing that the coated portion did not peel off during the wettability test, it is expected to possess chemical stability. The excellent wettability of these ceramic coatings is even more pronounced when the electrolyte components are highly polar, such as ethylene carbonate (EC) and propylene carbonate (PC).

[0125] Experimental Example 1-7: Evaluation of Ionic Conductivity of Secondary Battery

[0126] The ionic conductivity of the battery was measured using AC impedance (EIS, Biologic, VSP). The AC impedance of a stainless steel / separator / stainless steel symmetric cell fabricated using the polypropylene separator of Comparative Example 3, the polypropylene separator coated with Al2O3 of Comparative Example 2, and the polypropylene separator coated with AlF3 of the Example was measured. The measurement conditions were performed by applying an AC amplitude of 5 mV in a frequency range from 100 kHz to 10 mHz. Figure 13 shows the AC impedance spectrum of the symmetric cell as a Nyquist plot. The real part, the x-axis, represents resistance, and the imaginary part, the y-axis, represents capacitance and inductance; in this case, the intercept value on the x-axis is the bulk resistance (Rb). Bulk resistance is a complex resistance caused by the electrolyte or separator, etc. If the electrolyte is kept the same and the influence of other factors is excluded, it changes due to the influence of the separator. Ionic conductivity can be calculated using the following equation. σ represents ionic conductivity, L represents the thickness of the separator, Rb represents the bulk resistance, and A represents the area of ​​the separator. The area of ​​each separator is 283.529 cm². 2 am.

[0127]

[0128] As a result of the ion conductivity test, the ion conductivity of the AlF3 nanorod is 0.398 mS·cm. -1 The ionic conductivity of Al2O3 is 0.301 mS·cm -1 The ionic conductivity of the non-coated polypropylene separator is 0.930 mS·cm -1 It was calculated as.

[0130] Experimental Example 2: Evaluation of Electrochemical Characteristics of a Unit Cell

[0131] Cell formation was performed by charging and discharging at 0.1C at a voltage of 3.0–4.2V using a battery test system (Wonatech, WBCS 3000L). This process enabled the cells to be activated and perform electrical functions. For cycle performance testing, two of the three cells were charged and discharged for 200 cycles at 0.2C and 500 cycles at 0.5C, respectively, while the remaining one underwent a rate test. After running 100 cycles of 0.2C charging and discharging, electrochemical impedance spectroscopy (EIS, Biologic, VSP) measurements were performed at frequencies ranging from 100k to 10MHz. Subsequently, one full cell each was fabricated using an AlF3-coated separator and a non-coated separator, and a 0.2C cycle test was conducted at a temperature of 60°C. Figure 14 shows a graph of the initial charge and discharge voltage change of a full cell measured under 0.1C conditions.

[0133] Experimental Example 2-1: Rate capability test

[0134] For Examples and Comparative Examples 1 to 3, each coin pool cell manufactured with a separator was charged and discharged three times in sections at 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C. Figure 15 shows the C-rate performance of the full cell, and it was confirmed that at rates of 0.1, 0.2, 0.5, 1, 2, and 3C, the AlF3 nanorods had capacities of 2.75, 2.66, 2.51, 2.37, 2.06, and 1.72 mAh, the AlF3 nanoparticles had capacities of 2.3, 2.25, 2.03, 1.67, 1.08, and 0.34 mAh, the Al2O3 coated separator had capacities of 2.88, 2.77, 2.58, 2.30, 1.67, and 0.92 mAh, and the non-coated separator had capacities of 2.92, 2.81, 2.67, 2.47, 1.69, and 1.32 mAh. At high rates of 2C and 3C, the capacities of coin cells fabricated with separators coated with AlF₃ nanorods were measured to be the highest, at 2.06 and 1.72 mAh, respectively. This is related to the characteristics of LIBs, where high-rate performance improves due to the higher porosity of the separator. The one-dimensional nanoporous samples exhibited much better rate capacities, and both samples recovered 0.1 C capacity. Capacity recovery to 0.1 C capacity was confirmed for each sample after the rate test.

[0136] Experimental Example 2-2: Cycle test

[0137] For Examples and Comparative Examples 1 to 3, the cycle test was conducted at room temperature, and measurements were taken by performing 300 cycles and 500 cycles of charging and discharging at 0.2C and 0.5C, respectively. FIG. 16 shows the results of evaluating long-term performance changes while charging and discharging a full cell at a rate of 0.2C, and FIG. 17 shows the results of evaluating long-term performance changes while charging and discharging at a rate of 0.5C. The initial capacities were measured as 2.772 mAh for non-coated 0.2C, 2.573 mAh for 0.5C, 2.653 mAh for AlF3 nanorods 0.2C, 2.480 mAh for 0.5C, 1.972 mAh for AlF3 nanoparticles 0.2C, 2.230 mAh for 0.5C, 3.100 mAh for Al2O3 0.2C, and 2.917 mAh for 0.5C, respectively, and the discharge capacity of the assembled cells decreases with increasing internal resistance. During observation, the coated separators exhibited better discharge capacities compared to the non-coated PP separator. This improvement may be due to the coating particles reducing pore size and mitigating the self-discharge current of the battery.

[0139] Experimental Example 2-3: Electrochemical Impedance Spectroscopy (EIS)

[0140] For Examples and Comparative Examples 1 to 3, AC impedance measurements were performed to demonstrate the electrochemical performance of the separator in more detail. The electrochemical impedance spectroscopy (EIS) of the Full-Cell after formation was measured. Figure 18 shows the electrochemical impedance spectrum (EIS) of the cell after 100 charge-discharge cycles at 0.2C. Bulk resistance is the measured value of the resistance loaded on the electrolyte and the separator, and was measured without significant difference among the four Full-Cells. The charge-transfer resistance of the AlF3 nanorods Full-Cell was improved compared to the AlF3 nanoparticle Full-Cell, and as a result, it appears that the impedance of the Full-Cell decreased because the electrolyte wettability of the AlF3 nanorod coated separator is superior.

[0142] Experimental Example 2-4: High temperature cycle test

[0143] For Example and Comparative Example 3, the cycle test was conducted at 60°C, and measurements were taken after performing 100 cycles of charge-discharge at 0.2C for each. Figure 19 shows the results of evaluating long-term performance changes while charging and discharging a full cell at 60°C at a rate of 0.2C. The performance improvement of the coated separator is evident in both the better capacity retention compared to the reference cell during the cycling test period. Cells fabricated with a separator coated with AlF3 nanorods and a non-coated separator showed 100-cycle capacity retention rates of approximately 84.45% and 81.72%, respectively. Operating a battery at high temperatures accelerates performance degradation and shortens the cell's life cycle. It can be confirmed that using a separator coated with AlF3 nanorods can extend the life cycle.

[0145] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0146] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A separation membrane substrate made of a porous polymer resin; and a coating layer coated on at least one surface of the separation membrane substrate; wherein the coating layer comprises inorganic particles and a binder polymer, wherein the inorganic particles are ceramic particles, and the ceramic particles are AlF₃, and as a result of X-ray diffraction (XRD) analysis of the ceramic particles, the 2θ value is 18.2 o to 20.2 o It indicates the first peak having a maximum peak at, and the 2θ value is 21.1 o to 23.1 o It shows a second peak with a maximum peak at, and the 2θ value is 34.4 o to 36.4 o A coating separator for a secondary battery, characterized by exhibiting a third peak having a maximum peak at Claim 2 ◈Claim 2 was abandoned upon payment of the registration fee.◈ In Claim 1, the binder polymer is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinylacetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate A coating separator for a secondary battery, characterized by being one or more mixtures selected from the group consisting of butyrate (Cellulose Acetate Butyrate), Cellulose Acetate Propionate, Carboxylmethylcellulose, Cyanoethylpullulan, Cyanoethylpolyvinylalcohol, Cyanoethylcellulose, Cyanoethylsucrose, and Pullulan. Claim 3 delete Claim 4 A coating separator for a secondary battery according to claim 1, wherein the ceramic particles are one-dimensional nanostructures, and the nanostructures have the form of nanorods, nanowires, nanofibers, nanotubes, needle-shaped structures, or a combination thereof. Claim 5 A coating separator for a secondary battery according to claim 1, characterized in that the average length of the ceramic particles is 0.1 to 5 μm and the average diameter is 100 to 500 nm. Claim 6 A coating separator for a secondary battery according to claim 1, characterized in that the aspect ratio of the ceramic particles is 5 to 6. Claim 7 delete Claim 8 A coating separator for a secondary battery according to claim 1, characterized in that the thickness of the coating layer is 5 to 25 μm. Claim 9 The method comprises the steps of: preparing a mixed solution comprising an inorganic particle precursor, a first solvent, and a second solvent; adding a fluorinating agent to the mixed solution to precipitate inorganic particles; washing and drying the inorganic particles to obtain them; preparing a coating solution comprising the obtained inorganic particles, a binder polymer, and a third solvent; applying the coating solution onto at least one surface of a porous polymer substrate; and drying the coating solution to form a coating layer; wherein the inorganic particles are ceramic particles, the ceramic particles are AlF₃, and the X-ray diffraction (XRD) analysis results of the ceramic particles show a 2θ value of 18.2 o to 20.2 o It indicates the first peak having a maximum peak at, and the 2θ value is 21.1 o to 23.1 o It shows a second peak with a maximum peak at, and the 2θ value is 34.4 o to 36.4 o A method for manufacturing a coating separator for a secondary battery, exhibiting a third peak having a maximum peak. Claim 10 ◈Claim 10 was abandoned upon payment of the registration fee.◈ A method for manufacturing a coating separator for a secondary battery, wherein the porous polymer substrate according to Claim 9 is formed from any one selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, or a mixture of two or more of these. Claim 11 A method for manufacturing a coating separator for a secondary battery, characterized in that, in the step of preparing the mixed solution according to claim 9, the molar ratio of the first solvent to the second solvent is 3:1 to 6:

1. Claim 12 ◈Claim 12 was abandoned upon payment of the registration fee.◈ A method for manufacturing a coating separator for a secondary battery, wherein, in the step of precipitating the inorganic particles according to Claim 9, the fluorinating agent is one or more fluorinating agents selected from HF, NH₄HF₂, NH₄F, KF, and NaF. Claim 13 A method for manufacturing a coating separator for a secondary battery, characterized in that, in the step of preparing the coating solution according to claim 9, the weight ratio of the inorganic particles to the binder polymer is 2:1 to 6:

1. Claim 14 A method for manufacturing a coating separator for a secondary battery, wherein, in claim 9, the step of precipitating the inorganic particles is characterized by stirring the mixed solution at a speed of 400 to 600 rpm for 0.3 to 1 hour at a temperature of 10 to 100 ℃. Claim 15 A lithium secondary battery characterized by including a coating separator for a secondary battery according to claim 1.

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