Method and apparatus for manufacturing separators, and separators manufactured thereby

Abstract

This disclosure relates to a method and apparatus for manufacturing a separator, and the separator obtained therefrom. The method for manufacturing a separator according to embodiments of this disclosure includes applying a solvent for pore impregnation to a porous polymer substrate before applying a slurry for forming a porous coating to the porous polymer substrate. In this way, a separator exhibiting small deviations in physical properties between a porous coating formed on the top surface of the porous polymer substrate and a porous coating formed on the back surface of the porous polymer substrate can be provided.

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for manufacturing a separator that can be used in electrochemical devices such as lithium secondary batteries, and the separator obtained therefrom.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0081079, filed in Korea on July 1, 2020, the disclosure of which is incorporated herein by reference. Background Technology

[0003] Lithium-ion secondary batteries include a separator inserted between the positive and negative electrodes to prevent physical contact and electrical short circuits between them. Such separators frequently utilize polyolefin-based porous polymer substrates. In addition, separators with a porous coating comprising inorganic particles and a binder polymer disposed on at least one surface of the porous polymer substrate are frequently used to prevent thermal shrinkage of the porous polymer substrate and increase adhesion to the electrodes.

[0004] Here, the method of applying a porous coating to a porous polymer substrate can be broadly classified into two methods depending on the time interval between coating the two surfaces of the substrate: a simultaneous coating method that coats both surfaces of the porous polymer substrate without time interval (e.g., dip coating), and a sequential coating method that coats one surface of the porous polymer substrate and then coats the other surface at predetermined time intervals (e.g., slot die coating).

[0005] The simultaneous coating method is advantageous because the slurry for forming the porous coating is applied simultaneously to both surfaces of the porous polymer substrate, resulting in small variations in the physical properties of the porous coatings applied to the porous polymer substrate. However, this simultaneous coating method is limited in terms of productivity and requires a large space, and therefore its use has recently decreased.

[0006] To increase productivity and improve space efficiency, sequential coating methods have recently been used. However, in sequential coating methods, the porous coating is applied to one surface of the porous polymer substrate separately from the other surface. Therefore, discrepancies in the physical properties of the resulting porous coatings exist. When the top surface of the porous polymer substrate exhibits physical properties different from those of the back surface, defective products are produced during the battery assembly process.

[0007] In these cases, this disclosure relates to providing a method for reducing the deviation of physical properties between porous coatings formed when two surfaces of a porous polymer substrate are coated at a time interval. Summary of the Invention

[0008] Technical issues

[0009] This disclosure is designed to address problems in the related art, and therefore relates to providing a separator that exhibits significantly reduced deviations in physical properties between the two surfaces of a porous polymer substrate and does not lead to the generation of defective products during subsequent battery assembly processes.

[0010] This disclosure also relates to a method for manufacturing a separator that exhibits reduced deviations in physical properties between porous coatings formed on two surfaces of a porous polymer substrate.

[0011] In addition, this disclosure relates to providing an apparatus for manufacturing partitions using the methods mentioned above.

[0012] Technical solution

[0013] In one aspect of this disclosure, a partition is provided according to any of the following embodiments.

[0014] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising:

[0015] Porous polymer substrate;

[0016] A first porous coating, comprising inorganic particles and a binder polymer, is formed on one surface of the porous polymer substrate; and

[0017] A second porous coating, comprising the inorganic particles and the binder polymer, is formed on another surface of the porous polymer substrate.

[0018] The first and second porous coatings exhibit a physical property deviation of ±100gf / 15mm in terms of peel strength, and

[0019] The first porous coating and the second porous coating show a physical property deviation of ±50gf / 25mm in terms of lamination strength.

[0020] According to the second embodiment, a partition as defined in the first embodiment is provided.

[0021] The adhesive polymers mentioned above include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyetylexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, or two or more of these.

[0022] In another aspect of this disclosure, a method for manufacturing a separator for a lithium secondary battery is provided according to any of the following embodiments.

[0023] According to a third embodiment, a method for manufacturing a separator for a lithium secondary battery as described in the first embodiment is provided, comprising the following steps:

[0024] (S1) Apply the solvent for pore impregnation to one surface of the porous polymer substrate;

[0025] (S2) A slurry comprising inorganic particles, an organic solvent, and a binder polymer soluble in the organic solvent for forming a porous coating is applied to another surface of the porous polymer substrate;

[0026] (S3) Apply the slurry for forming the porous coating to the surface of the porous substrate mentioned in step (S1); and

[0027] (S4) The product of drying step (S3) is used to obtain a separator having a first porous coating on one surface of the porous polymer substrate and a second porous coating on the other surface of the porous polymer substrate.

[0028] According to the fourth embodiment, a method for manufacturing a partition as defined in the third embodiment is provided.

[0029] Steps (S2) and (S3) are performed sequentially at a time interval.

[0030] According to the fifth embodiment, a method for manufacturing a partition as defined in the third or fourth embodiment is provided.

[0031] The application step is performed using a one-sided coating process.

[0032] According to the sixth embodiment, a method for manufacturing a partition as defined in the fifth embodiment is provided.

[0033] The single-sided coating process is implemented using a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

[0034] According to the seventh embodiment, a method for manufacturing a partition as defined in any of the third to sixth embodiments is provided.

[0035] The solvent used for pore impregnation is the same as the organic solvent, or is miscible with the adhesive polymer and has a low boiling point.

[0036] According to the eighth embodiment, a method for manufacturing a partition as defined in any of the third to seventh embodiments is provided.

[0037] The solvent used for pore impregnation has a boiling point lower than the melting point of the porous polymer substrate.

[0038] According to the ninth embodiment, a method for manufacturing a partition as defined in the eighth embodiment is provided.

[0039] The solvent used for pore impregnation has a boiling point of 10°C or higher and 300°C or lower.

[0040] According to the tenth embodiment, a method for manufacturing a partition as defined in the eighth embodiment is provided.

[0041] The solvent used for pore impregnation includes acetone, methyl ethyl ketone, tetrahydrofuran, methyl isobutyl ketone, dimethyl sulfoxide, 1-methyl-2-pyrrolidone, dimethylformanide, or two or more thereof.

[0042] According to the eleventh embodiment, a method for manufacturing a partition as defined in any of the third to tenth embodiments is provided.

[0043] The organic solvent mentioned herein includes any one of the following compounds selected from acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, and cyclohexane, or a mixture of two or more thereof.

[0044] According to the twelfth embodiment, a method for manufacturing a partition as defined in any of the third to eleventh embodiments is provided.

[0045] Step (S1) includes applying the solvent for pore impregnation to the interior of the pores of the porous polymer substrate.

[0046] According to the thirteenth embodiment, a method for manufacturing a partition as defined in any of the third to twelfth embodiments is provided.

[0047] Step (S4) includes drying the solvent used for pore impregnation and the organic solvent.

[0048] According to the fourteenth embodiment, a method for manufacturing a partition is provided as defined in any of the third to thirteenth embodiments.

[0049] The solids content (solvent-free solute content) in the slurry used to form the porous coating is 30% by weight or less based on 100% by weight of the slurry used to form the porous coating.

[0050] According to the fifteenth embodiment, a method for manufacturing a partition as defined in any of the third to fourteenth embodiments is provided.

[0051] The drying step is carried out at a relative humidity of 20% to 80%.

[0052] According to the sixteenth embodiment, a method for manufacturing a partition as defined in any of the third to fifteenth embodiments is provided.

[0053] The composition of the slurry used to form the porous coating in step (S2) is the same as that in step (S3).

[0054] In another aspect of this disclosure, a partition coating apparatus according to the following embodiments is provided.

[0055] According to the seventeenth embodiment, a partition coating apparatus is provided for implementing the method of manufacturing a partition as defined in any of the third to sixteenth embodiments, comprising:

[0056] (a) A porous polymer substrate supply roller configured to supply a porous polymer substrate;

[0057] (b) A solvent application unit for pore impregnation configured to apply a solvent for pore impregnation to one surface of the porous polymer substrate;

[0058] (c) A first coating unit configured to apply a slurry for forming a porous coating to another surface of the porous polymer substrate;

[0059] (d) is a second coating unit configured to apply a slurry for forming a porous coating to the surface of the porous polymer substrate mentioned in (b);

[0060] (e) Two or more rotating rollers configured to transmit the separator by friction while in contact with at least one surface of the porous polymer substrate; and

[0061] (f) A drying unit configured to dry a porous polymer substrate having two porous coatings applied to its two surfaces.

[0062] Beneficial effects

[0063] According to embodiments of the present disclosure, a separator can be provided that shows a small deviation in physical properties between a porous coating formed on the top surface of a porous polymer substrate and a porous coating formed on the back surface of a porous polymer substrate.

[0064] A method for manufacturing a separator that reduces the deviation of physical properties between porous coatings is also provided. Specifically, a method for manufacturing a separator exhibiting small deviations in physical properties between porous coatings is provided by applying a solvent for pore impregnation to one surface of a porous polymer substrate such that the pores in the porous polymer substrate can be impregnated by the solvent, coating both surfaces of the porous polymer substrate at time intervals, and simultaneously drying the porous coatings. Attached Figure Description

[0065] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the following disclosure, are used to provide a further understanding of the technical features of the present disclosure; therefore, the present disclosure should not be construed as limited to the drawings.

[0066] Figure 1 This is a schematic diagram illustrating an apparatus for manufacturing separators for lithium secondary batteries based on a conventional sequential coating process.

[0067] Figure 2 This is a schematic diagram illustrating an apparatus for manufacturing a separator for a lithium secondary battery according to an embodiment of the present disclosure. Detailed Implementation

[0068] In the following description, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its common or dictionary meaning, but should be interpreted based on its meaning and concept in relation to the technical aspects of the present disclosure, on the basis of allowing the inventors to appropriately define the terminology for the best interpretation.

[0069] In electrochemical devices such as lithium-ion batteries, separators prevent physical contact and electrical short circuits between the positive and negative electrodes. Polyolefin-based porous polymer substrates are frequently used for these separators. In addition, separators with a porous coating comprising inorganic particles and a binder polymer disposed on at least one surface of the porous polymer substrate are also frequently used to prevent thermal shrinkage of the porous polymer substrate and increase adhesion to the electrodes.

[0070] Methods for forming porous coatings can be broadly categorized into simultaneous coating methods and sequential coating methods. Recently, porous coatings have been primarily applied to porous polymer substrates via sequential coating methods because simultaneous coating methods exhibit low productivity and low space efficiency.

[0071] Figure 1 This is a schematic diagram illustrating an apparatus 100 for manufacturing separators for lithium-ion secondary batteries based on a conventional sequential coating process. (Refer to...) Figure 1An apparatus 100 for manufacturing separators for lithium secondary batteries according to related technologies includes a porous polymer substrate supply roller 110 configured to supply a porous polymer substrate 10, a first porous coating unit 120 configured to apply a first porous coating, a second porous coating unit 130 configured to apply a second porous coating, a rotary roller 140, and a drying unit 150. A problem with the sequential coating process using this apparatus is that, since the porous coating is first applied to one surface of the porous polymer substrate and then to another surface, there is a difference in physical properties between the porous coating formed on the top surface of the porous polymer substrate and the porous coating formed on the back surface of the porous polymer substrate.

[0072] The inventors of this disclosure have conducted extensive research to provide a partition capable of solving the problems mentioned above, and a method and apparatus for manufacturing it.

[0073] In one aspect of this disclosure, a partition is provided.

[0074] Specifically, a separator for a lithium secondary battery is provided, comprising:

[0075] Porous polymer substrate;

[0076] A first porous coating, comprising inorganic particles and a binder polymer, is formed on one surface of the porous polymer substrate; and

[0077] A second porous coating, comprising the inorganic particles and the binder polymer, is formed on another surface of the porous polymer substrate.

[0078] The first and second porous coatings exhibit a physical property deviation of ±100gf / 15mm in terms of peel strength, and

[0079] The first porous coating and the second porous coating show a physical property deviation of ±50gf / 25mm in terms of lamination strength.

[0080] Here, the adhesion between the porous polymer substrate and the porous coating is referred to as the peel strength (Ps) and the adhesion between the electrode and the outermost surface facing the electrode (the porous coating in the case of this disclosure) is referred to as the lamination strength (Ls).

[0081] Here, the peel strength is determined as follows: The separator is cut into 15mm × 100mm dimensions. Double-sided adhesive tape is attached to the glass plate, and the porous coating surface of the separator is attached to the tape. Then, the ends of the separator are mounted to a UTM instrument (LLOYD Instrument LF Plus), and forces are applied at 180° and 300mm / min. The force required to separate the porous coating from the porous polymer substrate is measured.

[0082] The term "deviation of physical properties in terms of peel strength" refers to the difference between "peel strength between the second porous coating and the porous polymer substrate" and "peel strength between the first porous coating and the porous polymer substrate," and can be calculated according to the following formula:

[0083] The deviation of physical properties in terms of peel strength = (peel strength between the second porous coating and the porous polymer substrate) - (peel strength between the first porous coating and the porous polymer substrate)

[0084] Lamination strength can be measured as follows. The separators are cut to dimensions of 25 mm × 100 mm. The separators are stacked with electrodes, and this stack is inserted into a 100 μm thick PET film and adhered using a flatbed press. Here, the flatbed press is heated and pressurized at 60°C for 1 second at a pressure of 6.5 MPa. The ends of the separators attached to the electrodes are mounted to a UTM instrument (LLOYD Instrument LF Plus), and forces are applied at 180° and 300 mm / min. The force required to separate the electrodes from the outermost surface (the porous coating in the case of this disclosure) is measured. Here, the electrodes can be either negative or positive.

[0085] The term "deviation of physical properties in terms of lamination strength" refers to the difference between "the bond strength between the second porous coating and the electrode facing the second porous coating" and "the bond strength between the first porous coating and the electrode facing the first porous coating," and can be calculated according to the following formula:

[0086] Regarding lamination strength, the deviation of physical properties = (bond strength between the second porous coating and the electrode) - (bond strength between the first porous coating and the electrode)

[0087] While there are no particular limitations on the thickness of the porous coating, it can range from 1 μm to 15 μm, particularly from 1.5 μm to 10 μm. Furthermore, there are no particular limitations on the porosity of the porous coating, but it is preferably between 35% and 85%.

[0088] In particular, the porous polymer substrate can be a porous polymer film substrate or a porous polymer nonwoven mesh substrate.

[0089] The porous polymer membrane substrate can be a porous polymer membrane comprising a polyolefin such as polyethylene or polypropylene. This polyolefin porous polymer membrane substrate achieves a shut-off function at temperatures ranging from 80°C to 150°C.

[0090] In this document, polyolefin-based porous polymer membranes may be formed from polymers, either alone or in combination of two or more of them, including polyolefin polymers such as polyethylene, polypropylene, polybutene, or polypentene, which contain high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0091] In addition, porous polymer membrane substrates can be obtained by molding various polymers other than polyolefins, such as polyesters, into a membrane shape. Furthermore, porous polymer membrane substrates can have a stacked structure of two or more membrane layers, wherein each membrane layer can be formed by a polymer, including the polymers mentioned above such as polyolefins or polyesters, alone or in combination of two or more of them.

[0092] In addition to the polyolefins mentioned above, porous polymer membrane substrates and porous polymer nonwoven substrates can also be formed from polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, or polyethylene naphthalene, either alone or in combination.

[0093] While there are no particular restrictions on the thickness of the porous polymer substrate, it can range from 1 μm to 100 μm, particularly from 5 μm to 50 μm. Furthermore, while there are no particular restrictions on the size and porosity of the pores present in the porous polymer substrate, the pore size can range from 0.01 μm to 50 μm and the porosity from 20% to 75%, respectively.

[0094] There are no particular restrictions on the inorganic particles used, as long as they are electrochemically stable. That is, there are no particular restrictions on the inorganic particles that can be used in this paper, as long as they are within the operating voltage range of the applicable electrochemical device (e.g., based on Li / Li). + It should not cause oxidation and / or reduction in the 0-5V range. In particular, when using inorganic particles with high dielectric constants, the ionic conductivity of the electrolyte can be improved by increasing the degree of dissociation of electrolyte salts such as lithium salts in the liquid electrolyte.

[0095] For the reasons mentioned above, inorganic particles can be inorganic particles with a dielectric constant of 5 or greater, inorganic particles with lithium-ion transport capability, or a combination thereof.

[0096] Inorganic particles with a dielectric constant of 5 or greater can be selected from Al2O3, SiO2, ZrO2, AlO(OH), TiO2, BaTiO3, Pb(Zr) x Ti 1-x O3(PZT, where 0 < x < 1), Pb 1-x La x Zr 1-y Ti y O3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg) 1 / 3 Nb 2 / 3 Any one of the following groups: O3-xPbTiO3 (PMN-PT, where 0 < x < 1), hafnium oxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZO3, and SiC, or a mixture of two or more of them.

[0097] Inorganic particles with lithium-ion transport capabilities can be selected from lithium phosphate (Li3PO4) and lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O yBase glass (1 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), 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 (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), and P2S5-based glass (Li x P y S z Any one of the groups consisting of 0 < x < 3, 0 < y < 3, 0 < z < 7, or a mixture of two or more of them.

[0098] In addition, there are no particular limitations on the average particle diameter of the inorganic particles. However, the inorganic particles preferably have an average particle diameter of 0.001 μm to 10 μm in order to form a coating with uniform thickness and provide suitable porosity. The average particle diameter of the inorganic particles is preferably 100 nm to 2 μm, more preferably 150 nm to 1 μm.

[0099] The binder polymer used to form the porous coating has high solubility in the solvent used with respect to it. For example, the binder polymer has a solubility of 5% by weight or more based on the organic solvent. Referring to the binder polymer used according to this disclosure, the effects of this disclosure can only be clearly described when the binder polymer is dissolved in the organic solvent, since the solvent used for pore impregnation is applied in advance to prevent the binder polymer from dissolving in the organic solvent and penetrating into the porous polymer substrate.

[0100] Any adhesive polymer commonly used in the art to form porous coatings may be used without particular limitation, provided that it meets the above description regarding solubility. In particular, a glass transition temperature (T0) of -200°C to 200°C may be used. g The polymer is used because this binder polymer improves the mechanical properties of the resulting porous coating, such as flexibility and elasticity. This binder polymer acts as a binder that connects and stabilizes the inorganic particles, thus helping to prevent a decline in the mechanical properties of the separator with the porous coating.

[0101] In addition, the binder generally does not need to be ionicly conductive. However, the performance of the electrochemical device can be further improved when using polymers with ionic conductivity. Therefore, binder polymers with the highest possible dielectric constant can be used. In fact, since the degree of dissociation of salt in an electrolyte depends on the dielectric constant of the solvent used for the electrolyte, binder polymers with higher dielectric constants can improve the degree of salt dissociation in the electrolyte. Binder polymers can have dielectric constants (measured at a frequency of 1 kHz) ranging from 1.0 to 100, particularly 10 or higher.

[0102] In addition to the functions mentioned above, the adhesive polymer is also characterized by its gelation upon impregnation with a liquid electrolyte, thus exhibiting a high degree of swelling. Therefore, the adhesive polymer has a strength of 15 MPa. 1 / 2 up to 45MPa 1 / 2 or 15MPa 1 / 2 Up to 25MPa 1 / 2 and 30MPa 1 / 2 up to 45MPa 1 / 2 The solubility parameter (Hildebrand solubility parameter) is used. Therefore, hydrophilic polymers with multiple polar groups can be used more frequently compared to hydrophobic polymers such as polyolefins. When the solubility parameter is less than 15 MPa... 1 / 2 or greater than 45MPa 1 / 2 At that time, the adhesive polymer was difficult to swell using conventional liquid electrolytes for batteries.

[0103] Non-limiting examples of adhesive polymers may include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, and cellulose acetate propionate. Propionate, cyanoethyl pullullan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullullan, and carboxyl methyl cellulose.

[0104] In another aspect of this disclosure, a method is provided for manufacturing a separator that exhibits small deviations in physical properties in terms of peel strength and lamination strength.

[0105] According to embodiments of this disclosure, a method for manufacturing a partition is provided, comprising the following steps:

[0106] (S1) Apply the solvent for pore impregnation to one surface of the porous polymer substrate;

[0107] (S2) A slurry comprising inorganic particles, an organic solvent, and a binder polymer soluble in the organic solvent for forming a porous coating is applied to another surface of the porous polymer substrate;

[0108] (S3) Apply the slurry for forming the porous coating to the surface of the porous substrate mentioned in step (S1); and

[0109] (S4) The product of drying step (S3) is used to obtain a separator having a first porous coating on one surface of the porous polymer substrate and a second porous coating on the other surface of the porous polymer substrate.

[0110] The method will be explained in more detail below.

[0111] First, a solvent for pore impregnation is applied to one surface of a porous polymer substrate, such that the interior of the pores of the porous polymer substrate can be impregnated with the solvent for pore impregnation (S1).

[0112] According to related technologies, a slurry for forming a porous coating is directly applied to one surface of a porous polymer substrate, and then the slurry for forming the porous coating is immediately applied to another surface of the porous polymer substrate. The inventors of this disclosure have discovered a problem that occurs in this configuration. The problem is that the binder polymer in the slurry first penetrates into the pores of the porous polymer substrate, resulting in a difference in the amount of binder polymer compared to the amount in the slurry for forming the porous coating subsequently applied to the other surface. This is believed to be due to the difference in the amount of binder polymer in the slurry to be coated being drawn into the surface of the earlier-coated porous polymer substrate. As a result, a problem arises where there are differences in the physical properties between one surface (e.g., the top surface) and the other surface (e.g., the back surface) of the porous polymer substrate.

[0113] In contrast, according to the embodiments of this disclosure, the solvent for pore impregnation is first applied to the porous polymer substrate. Therefore, the interior of the pores in the porous polymer substrate is impregnated with the solvent for pore impregnation. Specifically, even when the solvent for pore impregnation is applied to one surface of the porous polymer substrate, the solvent does not only penetrate into the pores near that surface, but rather into all the pores present throughout the entire porous polymer substrate. Therefore, even when the slurry for forming the porous coating is applied to the porous polymer substrate, a smaller amount of the binder polymer in the slurry penetrates into the pores of the porous polymer substrate. As a result, the deviation in physical properties between the first and second porous coatings can be reduced.

[0114] This application is carried out through a sequential coating process. For example, it can be implemented using a slotdie coater, spray coater, gravure roll coater, or DM coater. Sequential coating processes are advantageous because, compared to simultaneous coating processes, the solvent used for pore impregnation can be supplied in only the amount needed to impregnate the interior of the pores of the porous polymer substrate. That is, it is important to control the amount of solvent used for pore impregnation that penetrates into the pores of the porous polymer substrate to reduce deviations in physical properties between the first and second porous coatings. Specifically, it is preferable to control the amount of solvent used for pore impregnation to fill the pores of the porous polymer substrate. However, a typical example of simultaneous coating processes, namely dip coating, has the problem that it cannot control the amount as described above. At the same time, sequential coating processes are less constrained by space than dip coating processes, which are a typical example of simultaneous coating processes, and can be designed with longer drying areas, thus providing high coating rates and improved productivity in terms of time and cost efficiency.

[0115] Here, the slot die coating process includes forming coating beads from a coating solution supplied via a slot die between a lip and a porous polymer substrate, and coating the coating beads onto the porous polymer substrate. Specifically, the slot die coating process involves coating the entire surface of the substrate with a composition supplied via the slot die, and is advantageous because the coating thickness can be controlled depending on the flow rate supplied via a metering pump.

[0116] The spray coating process involves spraying a coating solution onto a porous polymer substrate using compressed air.

[0117] Gravure coating involves transferring a coating solution through small wells or cells engraved on the surface of a cylinder.

[0118] DM (direct metering) coating process involves transferring coating solution through small wells or cells engraved on the surface of a cylinder using a DM coating machine.

[0119] Here, the solvent used for pore impregnation can be the same as the organic solvent contained in the slurry used to form the porous coating. Alternatively, the solvent used for pore impregnation can be miscible with the binder polymer in the slurry used to form the porous coating and have a low boiling point. Specifically, the solvent used for pore impregnation can have a boiling point lower than the melting point of the porous polymer substrate.

[0120] For example, the solvent used for pore impregnation may have a boiling point of 10°C or higher, 20°C or higher, 30°C or higher, or 40°C or higher, and 300°C or lower, 250°C or lower, 200°C or lower, or 150°C or lower. When the boiling point of the solvent used for pore impregnation is within the above-defined range, the problem of premature solvent evaporation before the application of the slurry can be prevented. In addition, it is advantageous that the boiling point of the solvent used for pore impregnation is not higher than the melting point of the porous polymer substrate, thus providing a high drying rate.

[0121] According to embodiments of this disclosure, the solvent used for pore impregnation may vary depending on the porous polymer substrate used herein. For example, when the porous polymer substrate is a polyolefin-based porous polymer membrane, the solvent used for pore impregnation may have a boiling point of 30°C or higher, or 40°C or higher, and 150°C or lower, or 130°C or lower. Non-limiting examples of solvents include acetone, methyl ethyl ketone, tetrahydrofuran (THF), methyl isobutyl ketone, or two or more of these.

[0122] According to embodiments of this disclosure, when the porous polymer substrate is a porous nonwoven substrate such as polyethylene terephthalate, the solvent used for impregnating the pores may have a boiling point of 30°C or higher, or 40°C or higher, and 260°C or lower, or 230°C or lower. Non-limiting examples of solvents include acetone, methyl ethyl ketone, tetrahydrofuran, methyl isobutyl ketone, dimethyl sulfoxide, 1-methyl-2-pyrrolidone, dimethylformamide, or two or more of these.

[0123] Next, a slurry for forming a porous coating, comprising inorganic particles, an organic solvent, and a binder polymer soluble in the organic solvent, is applied to another surface of the porous polymer substrate (S2). Here, the term "another surface" refers to the remaining surface of the porous polymer substrate that was not coated with the solvent for pore impregnation in step (S1). The surface of the porous polymer substrate coated with the solvent for pore impregnation requires time to dry any excess solvent remaining on that surface. Furthermore, when the slurry for forming the porous coating is immediately applied to the surface of the porous polymer substrate coated with the solvent for pore impregnation, the slurry concentration may change due to excess solvent remaining on that surface after pore impregnation. Therefore, in step (S2) following step (S1), the slurry for forming the porous coating is applied to the other surface of the porous polymer substrate that was not coated with the solvent for pore impregnation.

[0124] Here, the slurry used to form the porous coating is applied via a sequential coating process. Specifically, a single-sided coating process advantageous for sequential coating can be used. For example, the slurry used to form the porous coating can be applied using a slot die coater, a spray coater, a gravure roll coater, or a direct metering (DM) coater.

[0125] Refer to the above description of inorganic particles and adhesive polymers.

[0126] The organic solvents used for porous coatings according to this disclosure preferably have solubility parameters similar to those of the adhesive polymer to be used, and have a low boiling point. This is because such solvents promote homogeneous mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include any one of acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, and cyclohexane, or mixtures of two or more of these.

[0127] In addition to inorganic particles and binder polymers, the slurry used to form the porous coating may further include dispersants and other additives.

[0128] Here, the slurry used to form the porous coating can be prepared by solvents of a binder polymer in an organic solvent, adding inorganic particles thereto, and dispersing the inorganic particles thereto. The inorganic particles can be added after being pre-crushed to a predetermined average particle diameter. Alternatively, the inorganic particles can be added to the binder polymer solution, then crushed and dispersed, while controlling them to have a predetermined diameter using a ball milling process or similar.

[0129] Here, the slurry used to form the porous coating preferably has a solids content (solvent-free solute content) of 30% by weight or less based on 100% by weight of the slurry. In particular, the solids content is preferably 10% to 30% by weight, or 15% to 25% by weight. Within the ranges defined above, the deviation in physical properties between the first and second porous coatings can be reduced. Due to the increased solids content, the absolute amount of binder that penetrates into the pores when the binder solution in the same volume of slurry penetrates into the pores increases, and therefore the two surfaces exhibit an increased deviation in physical properties. Therefore, it is important to apply a minimum solids content. When the solids content is too low, it may not be possible to coat to the desired coating thickness. In addition, the deviation in physical properties may be reduced due to the reduced solids content. However, when the solids content is too low, it may not be possible to obtain heat shrinkage, adhesion to the electrodes (lamination strength), and adhesion between the porous polymer substrate and the porous coating (peel strength) at levels equal to or similar to those according to related technologies. Meanwhile, when the solid content is within the above-defined range, a thick coating may be obtained.

[0130] Next, a slurry for forming a porous coating is applied to one surface of a porous polymer substrate (S3).

[0131] Here, the term "a surface" refers to the surface of the porous polymer substrate coated with a solvent for pore impregnation in step (S1), which is different from the surface coated with a slurry for forming a porous coating in step (S2).

[0132] The slurry used to form the porous coating is the same as the slurry used in step (S2) to form the porous coating. Therefore, the resulting separator can exhibit reduced deviations in physical properties between the first and second porous coatings formed on the two surfaces of the porous polymer substrate.

[0133] Here, steps (S2) and (S3) are performed at a time interval. This is because the present disclosure is intended to address problems that occur in sequential coating processes.

[0134] Then, the product obtained from step (S3) is dried (S4). In this way, the separator can have a first porous coating on one surface of the porous polymer substrate and a second porous coating on the other surface of the porous polymer substrate.

[0135] Step (S4) can be carried out by drying both the solvent and the organic solvent used for pore impregnation.

[0136] The separator according to embodiments of this disclosure is used in a lithium-ion secondary battery. The lithium-ion secondary battery includes a separator that interrupts the physical contact between the positive and negative electrodes to prevent internal short circuits. Furthermore, the lithium-ion secondary battery has a structure in which a liquid electrolyte is injected into pores formed in the separator, and lithium ions are transported through the liquid electrolyte. Therefore, the separator for a lithium-ion secondary battery according to embodiments of this disclosure should have pores in the separator to provide high ionic conductivity and low resistance.

[0137] According to embodiments of this disclosure, after step (S4), both the solvent and the organic solvent used for pore impregnation are dried to form pores in the resulting partition.

[0138] Furthermore, in the method according to the embodiments of this disclosure, drying is performed for the first time in step (S4). When the drying step is performed after step (S1) or step (S2), the solvent used for pore impregnation or the organic solvent in the slurry used to form the porous coating is dried, and therefore the technical problem of this disclosure cannot be solved.

[0139] The porous coating is dried using a dryer such as an oven. For example, the drying step can be carried out at a temperature of 30°C to 200°C for 5 minutes or longer, particularly 1 hour or longer and 24 hours or less.

[0140] Furthermore, according to embodiments of this disclosure, the porous coating is dried under humidified conditions. For example, the porous coating is dried at a relative humidity of 20% or greater, 30% or greater, 35% or greater, or 40% or greater, and 80% or less, 75% or less, or 70% or less.

[0141] In this way, in the porous coating, inorganic particles are bonded together by a binder polymer, while they stack up and come into contact with each other, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles becomes an empty space to form pores.

[0142] In other words, the adhesive polymer binds inorganic particles together, thus maintaining their bonded state. For example, the adhesive polymer connects and fixes inorganic particles together. Furthermore, the pores in the porous coating are formed by interstitial volumes between the inorganic particles, which become vacant spaces. These spaces can be defined by inorganic particles that are substantially facing each other in a closely packed or densely packed structure.

[0143] In another aspect of this disclosure, a partition coating apparatus for implementing the above-described method for manufacturing partitions is provided.

[0144] Specifically, the identification of partition manufacturing includes:

[0145] (a) A porous polymer substrate supply roller configured to supply a porous polymer substrate;

[0146] (b) A solvent application unit for pore impregnation configured to apply a solvent for pore impregnation to one surface of the porous polymer substrate;

[0147] (c) A first coating unit configured to apply a slurry for forming a porous coating to another surface of the porous polymer substrate;

[0148] (d) is a second coating unit configured to apply a slurry for forming a porous coating to the surface of the porous polymer substrate mentioned in (b);

[0149] (e) Two or more rotating rollers configured to transmit the separator by friction while in contact with at least one surface of the porous polymer substrate; and

[0150] (f) A drying unit configured to dry a porous polymer substrate having two porous coatings applied to its two surfaces.

[0151] When the two surfaces of a porous polymer substrate are sequentially coated and then dried using this device, the deviation in physical properties between the first and second porous coatings can be reduced.

[0152] Figure 2 This is a schematic diagram illustrating an apparatus for manufacturing a separator for a lithium secondary battery according to an embodiment of this disclosure. (Refer to...) Figure 2 An apparatus 200 for manufacturing separators for lithium secondary batteries according to embodiments of the present disclosure includes a porous polymer substrate supply roller 110, a first coating unit 120, a second coating unit 130, a rotating roller 140, a drying unit 150, and a solvent application unit 160 for pore impregnation.

[0153] The porous polymer substrate supply roller 110 continuously supplies the porous polymer substrate to the solvent application unit 160 for pore impregnation.

[0154] The solvent application unit 160 for pore impregnation applies solvent for pore impregnation to a surface of a porous polymer substrate 10 supplied from a porous polymer substrate supply roller 110.

[0155] The first coating unit 120 and the second coating unit 130 each apply a slurry for forming a porous coating onto the porous polymer substrate 10 through a single-sided coating process.

[0156] The rotating roller 140 can transfer a porous polymer substrate coated with a slurry for forming a porous coating on one surface by friction while in contact with at least one surface of the porous polymer substrate.

[0157] The drying unit 150 dries the organic solvent contained in the slurry used to form a porous coating, which is applied to both surfaces of the porous polymer substrate under humidification conditions, so that a porous coating including multiple pores can be formed on both surfaces of the porous polymer substrate. In addition, the drying unit 150 dries the solvent used for pore impregnation to form pores in the porous polymer substrate.

[0158] In another aspect of this disclosure, an electrochemical device is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator described above according to the embodiments of this disclosure.

[0159] Electrochemical devices include any device that performs an electrochemical reaction, and specific examples include all types of primary cells, secondary cells, fuel cells, solar cells, or capacitors such as supercapacitors. In particular, lithium secondary cells, including lithium metal secondary cells, lithium-ion secondary cells, lithium polymer secondary cells, or lithium-ion polymer batteries, are preferred among secondary cells.

[0160] There are no particular limitations on the positive and negative electrodes used in conjunction with the separator according to this disclosure, and they can be obtained by incorporating electrode active materials into the electrode current collector using methods generally known in the art. Non-limiting examples of positive electrode active materials include conventional positive electrode active materials that can be used as positive electrodes in conventional electrochemical devices. In particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides containing combinations thereof are preferred. Non-limiting examples of negative electrode active materials include conventional negative electrode active materials that can be used as negative electrodes in conventional electrochemical devices. In particular, materials such as lithium metal or lithium alloys (which intercalate lithium), carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials are preferred. Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0161] The electrolyte that can be used in the electrochemical device according to this disclosure is having A+ B - Salts of structure, in which A + Including, for example, Li + Na + K + alkali metal cations such as B, or combinations thereof, - Including PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Anions such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), or combinations thereof, are present in organic solvents, including but not limited to these.

[0162] Depending on the manufacturing process of the final product and the desired properties of the final product, electrolyte injection can be performed at an appropriate step during the process used to manufacture the battery. That is, electrolyte injection can be performed before battery assembly or as a final step in battery assembly.

[0163] The embodiments will then be described in more detail so that this disclosure can be readily understood. However, the following embodiments may be embodied in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0164] Comparative Example 1

[0165] First, polyvinylidene fluoride (PVDF), serving as the binder polymer, is introduced into acetone, serving as the solvent, and dissolved therein at 50°C for approximately 4 hours to prepare a binder polymer solution. Next, aluminum hydroxide (Al(OH)3) (particle size: 500 nm), serving as inorganic particles, is introduced into the binder polymer solution. Here, the weight ratio of inorganic particles to binder polymer is controlled at 70:30 to prepare a slurry for forming a porous coating. Furthermore, the solids content in the slurry (solvent-free solids content) is 30% by weight based on 100% by weight of the slurry.

[0166] The slurry for forming the porous coating was applied at a rate of 120 m / min to one surface of a 9 μm thick polyethylene porous membrane (porosity: 35%) using a direct metering (DM) coating process in a horizontal coating machine. Then, the slurry for forming the porous coating was applied at a rate of 120 m / min to the other surface of a porous polymer substrate that was not coated with the slurry for forming the porous coating. Afterward, the porous polymer substrate with the slurry for forming the porous coating coated on both surfaces was dried at 50°C at 40% relative humidity to obtain a separator with a first porous coating and a second porous coating on each of its two surfaces. The test results are shown in Table 1 below.

[0167] Example 1

[0168] First, acetone, used as a solvent for pore impregnation, is applied to a surface of a 9 μm thick polyethylene porous membrane (porosity: 35%) at a rate of 120 m / min using a direct metering (DM) coating process in a horizontal coating machine.

[0169] Next, the slurry described below is applied to the other surface of the porous polymer substrate at a rate of 120 m / min using a DM coating process in a horizontal coating machine. The slurry is prepared as follows: Polyvinylidene fluoride (PVDF), as the binder polymer, is introduced into acetone, as the solvent, and dissolved therein at 50°C for approximately 4 hours to prepare a binder polymer solution. Next, aluminum hydroxide (Al(OH)3) (particle size: 500 nm), as inorganic particles, is introduced into the binder polymer solution. Here, the weight ratio of inorganic particles to binder polymer is controlled at 70:30 to prepare the slurry for forming the porous coating. Furthermore, the solids content (solvent-free solids content in the slurry) is 30% by weight based on 100% by weight of the slurry.

[0170] The slurry is then applied to one surface of the aforementioned porous polymer substrate at a rate of 120 m / min using a slot die coating process in a horizontal coating machine.

[0171] Subsequently, a porous polymer substrate coated with a slurry for forming a porous coating on both surfaces was dried at 50°C with a relative humidity of 40% to obtain a separator with a first porous coating and a second porous coating on each of its two surfaces. The test results are shown in Table 1 below.

[0172] Examples 2 to 5

[0173] The separators were obtained in the same manner as in Example 1, except that the solids content in the slurry was controlled at 25 wt%, 20 wt%, 15 wt%, and 10 wt%, instead of 30 wt%. The test results are shown in Table 1 below.

[0174] [Table 1]

[0175]

[0176]

[0177] As can be seen from Table 1, when Comparative Example 1 is compared with Examples 1 to 5, the spacers show equal or similar values ​​in terms of air permeability, heat shrinkage rate, adhesion between the porous polymer substrate and the porous coating, and adhesion between the spacer and the electrode. However, compared with the values ​​corresponding to the deviations in physical properties in terms of adhesion between the porous polymer substrate and the porous coating and adhesion between the spacer and the electrode, Comparative Example 1 shows a deviation of up to about 50 times in physical properties. In contrast, Examples 1 to 5 show small deviations in physical properties between the first porous coating and the second porous coating.

[0178] Meanwhile, it can be seen from Examples 1 to 5 that a lower solids content provides a smaller deviation in physical properties.

[0179] 1) Methods for measuring thickness

[0180] The thickness of each partition in Comparative Example 1 and Examples 1 to 5 was determined using a thickness gauge (Mitutoyo Co., VL-50S-B).

[0181] 2) Methods for determining air permeability

[0182] The air permeability of each partition in Comparative Example 1 and Examples 1 to 5 was determined according to JIS P-8117 using a Gurley type air permeability tester. Here, air permeability was measured as the passage of 100 cc of air through a partition with a diameter of 28.6 mm and an area of ​​645 mm². 2 The time required.

[0183] 3) Methods for determining heat shrinkage rate

[0184] The heat shrinkage rate of each partition in Comparative Example 1 and Examples 1 to 5 was calculated using the formula (initial length - length after heat shrinkage at 150°C for 30 minutes) / (initial length) × 100.

[0185] 4) Determination of adhesion (peel strength) between the porous polymer substrate and the porous coating.

[0186] Each separator according to Comparative Example 1 and Examples 1 to 5 was cut to a size of 15 mm × 100 mm. Double-sided adhesive tape was attached to a glass plate, and the porous coated surface of the separator was attached to the tape. Then, the ends of the separators were mounted to a UTM instrument (LLOYD Instrument LF Plus), and forces were applied at 180° and 300 mm / min. The force required to separate the porous coating from the porous polymer substrate was measured.

[0187] 5) Determination of adhesion (lamination strength) between the electrode and the separator.

[0188] The negative electrode was obtained as described below and cut to a size of 25 mm × 100 mm. Each separator according to Comparative Example 1 and Examples 1 to 5 was cut to a size of 25 mm × 100 mm. The prepared separators were stacked with the negative electrode, the stack was inserted between 100 μm thick PET films and adhered using a flat press. Here, the flat press was heated and pressurized at 60°C for 1 second at a pressure of 6.5 MPa. The adhered separators and negative electrodes were attached to a glass slide using double-sided tape. The ends of the separators (10 mm or less from the end of the adhered surface) were peeled off and attached to the 25 mm × 100 mm PET film using single-sided tape so that they could be connected longitudinally. The glass slide was then mounted to the lower fixture of the UTM instrument (LLOYDInstrument LF Plus), and the PET film adhered to the separators was mounted to the upper fixture of the UTM instrument. Force was then applied at a rate of 180° and 300 mm / min. The force required to separate the negative electrode from the porous coating facing the negative electrode is measured.

[0189] Here, the negative electrode is prepared as follows. First, artificial graphite, carbon black, carboxymethyl cellulose (CMC), and binder are mixed with water in a weight ratio of 95.8:1:1:2.2 to obtain a negative electrode slurry. This negative electrode slurry is coated onto a copper (Cu) foil to a thickness of up to 50 μm to form a thin electrode plate, which is then dried at 135°C for 3 hours or longer, and then pressed to obtain the negative electrode.

[0190] [Figure Labels]

[0191] 100: Equipment for the conventional manufacture of partitions

[0192] 200: Equipment for manufacturing partitions according to this disclosure

[0193] 110: Porous polymer substrate supply roller

[0194] 120: First Coating Unit

[0195] 130: Second Coating Unit

[0196] 140: Rotating roller

[0197] 150: Drying unit

[0198] 160: Solvent application unit for pore impregnation

[0199] 170: Partition winding roller

[0200] 10: Porous polymer substrate

[0201] 20: Partition

Claims

1. A separator for a lithium secondary battery, comprising: Porous polymer substrate; A first porous coating formed on one surface of the porous polymer substrate and comprising inorganic particles and a binder polymer; A second porous coating is formed on the other surface of the porous polymer substrate and includes the inorganic particles and the binder polymer; The first and second porous coatings exhibit a deviation of ±100 gf / 15 mm in terms of physical properties with respect to peel strength. This deviation refers to the difference between the peel strength between the second porous coating and the porous polymer substrate and the peel strength between the first porous coating and the porous polymer substrate. The first and second porous coatings exhibit a deviation of ±50 gf / 25 mm in terms of physical properties with respect to lamination strength. This deviation refers to the difference between the "bond strength between the second porous coating and the electrode facing the second porous coating" and the "bond strength between the first porous coating and the electrode facing the first porous coating." The separator for the lithium secondary battery is manufactured by a method comprising the following steps: (S1) Apply the solvent for pore impregnation to one surface of the porous polymer substrate; (S2) A slurry comprising inorganic particles, an organic solvent, and a binder polymer soluble in the organic solvent for forming a porous coating is applied to another surface of the porous polymer substrate; (S3) Apply the slurry for forming the porous coating to the surface of the porous polymer substrate mentioned in step (S1); and (S4) The product of drying step (S3) yields a separator with a first porous coating on one surface of the porous polymer substrate and a second porous coating on the other surface of the porous polymer substrate. Steps (S2) and (S3) are performed sequentially at a time interval.

2. The partition according to claim 1, wherein the adhesive polymer comprises polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, ethylhexyl acrylate, butyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or two or more thereof.

3. A method for manufacturing a separator for a lithium secondary battery as defined in claim 1, comprising the following steps: (S1) Apply the solvent for pore impregnation to one surface of the porous polymer substrate; (S2) A slurry comprising inorganic particles, an organic solvent, and a binder polymer soluble in the organic solvent for forming a porous coating is applied to another surface of the porous polymer substrate; (S3) Apply the slurry for forming the porous coating to the surface of the porous polymer substrate mentioned in step (S1); and (S4) The product of drying step (S3) yields a separator with a first porous coating on one surface of the porous polymer substrate and a second porous coating on the other surface of the porous polymer substrate. Steps (S2) and (S3) are performed sequentially at a time interval.

4. The method of claim 3, wherein the application step is performed by a one-sided coating process.

5. The method according to claim 4, wherein the single-sided coating process is carried out by using a slot die coater, a spray coater, a gravure roller coater, or a DM coater.

6. The method of claim 3, wherein the solvent used for pore impregnation is the same as the organic solvent.

7. The method of claim 3, wherein the solvent for pore impregnation has a boiling point lower than the melting point of the porous polymer substrate.

8. The method of claim 7, wherein the solvent for pore impregnation has a boiling point of 10°C or higher and 300°C or lower.

9. The method of claim 7, wherein the solvent for pore impregnation comprises acetone, methyl ethyl ketone, tetrahydrofuran, methyl isobutyl ketone, dimethyl sulfoxide, 1-methyl-2-pyrrolidone, dimethylformamide, or two or more thereof.

10. The method of claim 3, wherein the organic solvent comprises any one of the following compounds selected from acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, and cyclohexane, or a mixture of two or more thereof.

11. The method of claim 3, wherein step (S1) comprises applying the solvent for pore impregnation to the interior of the pores of the porous polymer substrate.

12. The method of claim 3, wherein step (S4) comprises drying the solvent for pore impregnation and the organic solvent.

13. The method of claim 3, wherein the solids content in the slurry for forming the porous coating is 30% by weight or less of 100% by weight of the slurry for forming the porous coating.

14. The method of claim 3, wherein the drying step is performed at a relative humidity of 20% to 80%.

15. The method according to claim 3, wherein the composition of the slurry for forming the porous coating in step (S2) is the same as the composition of the slurry for forming the porous coating in step (S3).

16. A separator coating apparatus for implementing the method of manufacturing the separator as defined in any one of claims 3 to 15, comprising: (a) A porous polymer substrate supply roller configured to supply a porous polymer substrate; (b) A solvent application unit for pore impregnation configured to apply a solvent for pore impregnation to one surface of the porous polymer substrate; (c) A first coating unit configured to apply a slurry for forming a porous coating to another surface of the porous polymer substrate; (d) is a second coating unit configured to apply a slurry for forming a porous coating to the surface of the porous polymer substrate mentioned in (b); (e) Two or more rotating rollers configured to transmit the separator by friction while in contact with at least one surface of the porous polymer substrate; and (f) A drying unit configured to dry a porous polymer substrate having two porous coatings applied to its two surfaces.

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