Coating device, method for manufacturing separator using same, and separator for lithium secondary battery manufactured thereby

Abstract

The present invention provides a coating device comprising: a coater head; an accommodation chamber which is positioned inside the coater head and accommodates a coating solution; an ultrasonic wave generation unit which is positioned inside the coater head and applies ultrasonic waves to the coating solution accommodated in the accommodation chamber; and a coating bar which transfers the coating solution from the accommodation chamber onto at least one surface of a substrate transferred in one direction.

Description

Coating device, method for manufacturing a separator using the same, and separator for lithium secondary batteries manufactured thereby

[0001] The present invention relates to a coating device, a method for manufacturing a separator using the same, and a separator for a lithium secondary battery manufactured thereby.

[0002]

[0003] In general, a separator is interposed between the cathode and the anode of a lithium secondary battery that can repeat charging and discharging to prevent short circuits between the cathode and the anode. The separator can be manufactured by using only a porous polymer substrate, or by applying and drying a slurry-like coating solution containing inorganic particles and a binder polymer to at least one surface of the porous polymer substrate to form an inorganic coating layer. The inorganic coating layer of the separator improves the mechanical and thermal stability of the separator, and coats the surface of the separator with inorganic particles to improve performance while maintaining ionic conductivity. The inorganic coating layer mainly plays a role in increasing mechanical strength and securing ionic conductivity while maintaining a porous structure.

[0004]

[0005] According to one aspect of the present invention, the present invention provides a coating device capable of manufacturing a separation membrane by controlling the properties of a coating solution using ultrasonic waves, and a method for manufacturing a separation membrane using the same.

[0006] According to another aspect of the present invention, a coating device capable of maintaining or reducing the viscosity of a coating solution and the particle size of inorganic particles by irradiating ultrasonic waves to a coating solution that has not been transferred or whose properties have changed over time, and a method for manufacturing a separation membrane using the same are provided.

[0007] According to another aspect of the present invention, the present invention provides a coating device capable of recycling a coating solution that is not transferred onto a substrate while maintaining the quality of the coating solution constant, and a method for manufacturing a separation membrane using the same.

[0008] According to another aspect of the present invention, the present invention can provide a separation membrane having excellent surface roughness characteristics by breaking up agglomeration of inorganic particles and a binder to lower the span value of the inorganic particles.

[0009] The technical problems to be solved by the present invention are not limited to the problems described above, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

[0010]

[0011] According to one aspect of the present invention, a coating device according to the following embodiment and a method for manufacturing a separator using the same and a separator for a lithium secondary battery manufactured thereby are provided.

[0012] According to a first embodiment, a coating device is provided, comprising: a coater head; a receiving chamber located inside the coater head and containing a coating liquid; an ultrasonic generator located inside the coater head and applying ultrasonic waves to the coating liquid contained in the receiving chamber; and a coating bar for transferring the coating liquid from the receiving chamber onto at least one surface of a substrate being transported in one direction.

[0013] According to a second embodiment, in the first embodiment, the ultrasonic generator may be located inside the receiving chamber.

[0014] According to a third embodiment, in any one of the first to second embodiments, the ultrasonic generator may be located on the inner wall of the receiving chamber.

[0015] According to a fourth embodiment, in any one of the first to third embodiments, a coating liquid tank may be further included, which is located outside the coater head and supplies the coating liquid to the receiving chamber through a transfer pipe.

[0016] According to a fifth embodiment, in any one of the first to fourth embodiments, the coater head may further include a recovery unit located on the outer surface thereof, which coats at least one surface of the substrate and transfers and receives the remaining coating liquid along the outer surface of the coater head.

[0017] According to a sixth embodiment, in the fifth embodiment, it may further include a first recovery conduit located inside the coater head and connecting the recovery section and the receiving chamber.

[0018] According to a seventh embodiment, in any one of the first to eighth embodiments, the coating solution tank may be located outside the coater head and supplying the coating solution to the receiving chamber through a transfer conduit; a recovery unit located on the outer surface of the coater head and transferring the remaining coating solution along the outer surface of the coater head to receive it after coating at least one surface of the substrate; and a second recovery conduit connecting the recovery unit and the coating solution tank.

[0019] According to the eighth embodiment, in any one of the first to seventh embodiments, the ultrasonic generator may have a sensor unit inside so as to control whether or not to generate ultrasonic waves according to an external signal.

[0020] According to a ninth embodiment, a method for manufacturing a separation membrane using a coating device including a coater header is provided, comprising the steps of: supplying a coating solution including a binder polymer, inorganic particles, and a solvent to a receiving chamber included in the coater head (S10); applying ultrasonic waves to the coating solution received in the receiving chamber using an ultrasonic generator located inside the coater head (S20); and transferring the coating solution applied with ultrasonic waves onto at least one surface of a substrate being transported in one direction using a coating bar provided in the coater head (S30).

[0021] According to the tenth embodiment, in the ninth embodiment, the ultrasonic waves may have a frequency of 20 kHz to 100 kHz.

[0022] According to the eleventh embodiment, in any one of the ninth to tenth embodiments, after the step (S30), a step (S40) of transferring the coating liquid onto at least one surface of the substrate using a recovery unit installed on the outer surface of the coater head and recovering the remaining coating liquid may be further included.

[0023] According to the 12th embodiment, in the 11th embodiment, after the step (S40), the step (S50) of applying ultrasonic waves to the coating liquid recovered in the receiving chamber through the recovery unit may be further included.

[0024] According to the 13th embodiment, in any one of the 9th to 12th embodiments, the viscosity of the coating liquid in the step (S10) may be in the range of about 10 cps to 50 cps at 25°C.

[0025] According to a 14th embodiment, a method for manufacturing a separation membrane using a coating device including a coater head is provided, comprising the steps of (P1) supplying a coating solution including a binder polymer, inorganic particles, and a solvent to a receiving chamber included in the coater head; (P2) transferring the coating solution onto at least one surface of a substrate being transported in one direction using a coating bar installed on a part of the coater head; (P3) transferring the coating solution onto at least one surface of the substrate using a recovery unit installed on an outer surface of the coater head and recovering the remaining coating solution; and (P4) applying ultrasonic waves to the coating solution recovered in the receiving chamber through the recovery unit.

[0026] According to a 15th embodiment, a separator for a lithium secondary battery is provided, comprising: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, wherein the surface roughness (Ra) of the inorganic coating layer is 0.12 ㎛ or less, the span value of the inorganic particles is 1.35 or less, and the span value is calculated by the following equation 1.

[0027] SPAN value = (particle diameter of inorganic particles (D) 90 ) - particle size of inorganic particles (D 10 )) / Particle diameter of inorganic particles (D 50 ) … Equation (1)

[0028] According to the 16th embodiment, in the 15th embodiment, the inorganic coating layer is formed by a coating solution in which inorganic particles and a binder polymer are mutually disintegrated by ultrasonic waves, and the coating solution may be manufactured by any one of the 9th to 14th embodiments.

[0029] According to the 17th embodiment, in any one of the 15th to 16th embodiments, the particle diameter (D) of the inorganic particles50 ) may be 1.0 ㎛ to 1.3 ㎛.

[0030]

[0031] A coating device according to one embodiment of the present invention can control the particle size and viscosity of a coating liquid and control the particle size of inorganic particles by including an ultrasonic generator.

[0032] A coating device according to one embodiment of the present invention can recycle coating liquid that has not been transferred onto a substrate, and can maintain the particle size of particles contained in the recycled coating liquid at a constant level and maintain or reduce the viscosity of the coating liquid by using an ultrasonic generator.

[0033] A coating device according to one embodiment of the present invention can recycle coating liquid that has not been transferred onto a substrate, and can apply ultrasonic waves to the coating liquid received in a receiving chamber until just before the coating liquid is transferred onto the substrate, thereby maintaining the particle size of particles contained in the coating liquid constant and maintaining or reducing the viscosity of the coating liquid.

[0034] A method for manufacturing a separation membrane according to one embodiment of the present invention can manufacture a separation membrane by applying ultrasonic waves to a coating solution to control the particle size of inorganic particles contained in the coating solution and controlling the viscosity of the coating solution.

[0035] A method for manufacturing a separation membrane according to one embodiment of the present invention can recycle a coating liquid that has not been transferred onto a substrate, and by applying ultrasonic waves to the recycled coating liquid, the particle size of particles contained in the recycled coating liquid can be maintained constant, and the viscosity of the coating liquid can be maintained or reduced.

[0036] A method for manufacturing a separation membrane according to one embodiment of the present invention can recycle a coating solution that has not been transferred onto a substrate, and can apply ultrasonic waves to the coating solution received in a receiving chamber until just before the coating solution is transferred onto the substrate, thereby maintaining the particle size of particles contained in the coating solution constant and maintaining or reducing the viscosity of the coating solution.

[0037] A separation membrane according to one embodiment of the present invention may have excellent particle size distribution and surface roughness characteristics of inorganic particles.

[0038] However, the effects that can be obtained through the present invention are not limited to the effects described above, and other technical effects that are not mentioned can be clearly understood by those skilled in the art from the description of the invention described below.

[0039]

[0040] The following drawings attached to this specification illustrate embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0041] Figure 1 schematically illustrates the structure of a coating device according to one embodiment of the present invention.

[0042] Figure 2 schematically illustrates the structure of a coating device according to one embodiment of the present invention.

[0043] FIG. 3 schematically illustrates the structure of a coating device according to one embodiment of the present invention, and specifically schematically illustrates a coating device further including a coating liquid tank.

[0044] FIG. 4 schematically illustrates the structure of a coating device according to one embodiment of the present invention, and specifically schematically illustrates a coating device further including a recovery section.

[0045] FIG. 5 schematically illustrates the structure of a coating device according to one embodiment of the present invention, specifically schematically illustrating a coating device further including a recovery unit and a coating liquid tank.

[0046] Figure 6 schematically illustrates a flow chart of a method for manufacturing a separation membrane according to one embodiment of the present invention.

[0047] Figure 7 schematically illustrates a flow chart of a method for manufacturing a separation membrane according to another embodiment of the present invention.

[0048] Figures 8a to 8c are photographs of the surface of the separation membrane according to the examples and comparative examples observed using a confocal scanning microscope.

[0049] Figure 8a is a photograph of the surface of the separation membrane of Comparative Example 1 observed using a confocal scanning microscope.

[0050] Figure 8b is a photograph of the surface of the membrane of Comparative Example 2 observed using a confocal scanning microscope.

[0051] Figure 8c is a photograph of the surface of the membrane of Example 1 observed using a confocal scanning microscope.

[0052]

[0053] In some of the accompanying drawings, corresponding components are designated by the same reference numerals. Those skilled in the art will appreciate that the drawings illustrate elements simply and clearly and are not necessarily drawn to scale. For example, to facilitate understanding of various embodiments, the dimensions of some elements depicted in the drawings may be exaggerated relative to other elements. Furthermore, elements of known technology that are useful or essential in commercially feasible embodiments may often not be depicted so as not to obscure the spirit of various embodiments of the present invention.

[0054]

[0055] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0056] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0057] Justice

[0058] Throughout this specification, when it is said that a part "includes" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0059] Throughout the present specification, the particle diameter (or particle size) can be measured using a laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and when the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle diameters at points where the number of particles is 10%, 50%, and 90% of the cumulative distribution according to the particle diameter in the measuring device, D is calculated, respectively. 10 , D 50 and D 90 can be measured.

[0060] Throughout this specification, the term “primary particle” means a particle that has no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM).

[0061] Throughout this specification, a 'secondary particle' is a particle formed by agglomeration of the above primary particles.

[0062] Throughout this specification, a 'single particle' is a particle that exists independently of the secondary particles and has no apparent grain boundary.

[0063] Throughout this specification, when the term “particle” is used, it may mean one or all of a single particle, a secondary particle, or a primary particle.

[0064]

[0065] In the manufacture of separators for electrochemical devices such as lithium secondary batteries, a slurry-state coating solution can be applied to a porous polymer substrate using a device such as a separator coater, followed by drying to form an inorganic coating layer. Meanwhile, various methods for applying a slurry-state coating solution to a substrate include dip coating, which simultaneously coats both sides; gravure coating, which coats one side first and then the opposite side; and die coating, which primarily uses a slit die structure to spread the liquid over a wide area.

[0066] Dip coating and gravure coating are relatively simple coating processes. However, since the coating solution is exposed to air in large quantities during the coating process, the solvent may evaporate, increasing the viscosity of the coating solution or causing solutes in the coating solution to coagulate with each other, thereby degrading the coating solution quality. Furthermore, die coating, while less exposed to air and thus free of the aforementioned problems, has the drawback of difficulty in maintaining uniform coating thickness and the inability to recycle coating solution that is not transferred to the substrate.

[0067] The present invention provides a coating device and a method for manufacturing a separation membrane capable of recycling a coating solution that is not transferred onto a substrate, maintaining a constant particle size of particles contained in the recycled coating solution using an ultrasonic generator, and maintaining or reducing the viscosity of the coating solution.

[0068] Hereinafter, the present invention will be described in more detail with the attached drawings.

[0069]

[0070] <Coating device>

[0071] The present invention provides a coating device.

[0072] Figure 1 schematically illustrates the structure of a coating device according to one embodiment of the present invention.

[0073] According to one aspect of the present invention, a coating device (1) of the present invention comprises: a coater head (100); a receiving chamber (110) located inside the coater head (100) and containing a coating liquid; an ultrasonic generator (120) located inside the coater head (100) and applying ultrasonic waves to the coating liquid contained in the receiving chamber (110); and a coating bar (130) that transfers the coating liquid from the receiving chamber (110) onto at least one surface of a substrate (2) transported in one direction.

[0074] The above substrate (2) is illustrated in FIG. 1 for reference, but should not be construed as limiting the coating device (1) of the present invention. According to one embodiment, the substrate (2) may be a porous polymer substrate for manufacturing a separator for a secondary battery. In addition, the coating solution may be a slurry-like coating solution containing a binder polymer, inorganic particles, and a solvent. By coating such a coating solution on at least one surface of the substrate (2), a separator including an inorganic coating layer on the porous polymer substrate can be manufactured. The coating device (1) of the present invention is thus suitable for use in separator coating.

[0075] In one embodiment of the present invention, the coating device (1) can receive a coating liquid from the outside and store the coating liquid in a receiving chamber (110), and the coating liquid contained in the receiving chamber (110) can be transferred onto at least one surface of a substrate (2) through contact with a coating bar (130) so that the coating liquid applied to the coating bar (130) is transferred in one direction. Meanwhile, in order for the coating liquid to be in contact with the coating bar (130) in the receiving chamber (110), an auxiliary device (not shown) for pushing up the coating liquid so that the position where the coating liquid is stored is positioned close to the coating bar (130) may be additionally provided inside the receiving chamber (110).

[0076]

[0077] In one embodiment of the present invention, the ultrasonic generator (120) is a device capable of generating ultrasonic waves within the receiving chamber (110), and there are no particular limitations on its type and shape. The ultrasonic generator (120) of the present invention converts an electrical signal into a mechanical signal by a piezoelectric element, and the mechanical signal is amplified by a metal material such as a vibrator to generate vibrations having an ultrasonic frequency in a solvent (medium). The generated ultrasonic waves generate, for example, microbubbles in the solvent (medium), and when the microbubbles disappear, very high pressure and high temperature are generated. The energy generated at this time can be transferred to the solute.

[0078] In one embodiment of the present invention, the ultrasonic generator (120) generates ultrasonic waves having a frequency of about 20 kHz to 100 kHz, or a frequency of about 20 kHz to 60 kHz, or a frequency of about 20 kHz to 40 kHz to cause vibrations in the solvent of the coating solution, and energy is generated as microbubbles are created and destroyed by the vibrations, and the energy can deagglomerate the agglomerates between the inorganic particles and the binder polymer in the coating solution. The ultrasonic generator (120) can also help to uniformly disperse the solid matter in the coating solution in the solvent. For example, the ultrasonic generator (120) is configured to be capable of generating ultrasonic waves that can exhibit a disintegrating effect of the inorganic particles by separating the agglomerated inorganic particles.

[0079]

[0080] In one embodiment of the present invention, there is no limitation on the location of the ultrasonic generator (120) as long as it can generate vibrations having an ultrasonic frequency in the solvent.

[0081] In one embodiment of the present invention, the ultrasonic generator (120) may be positioned inside the receiving chamber (110). When the ultrasonic generator (120) is positioned inside the receiving chamber (110), the area that the ultrasonic generator (120) faces the coating liquid is larger, thereby generating more microbubbles in the coating liquid per hour. For example, since the ultrasonic generator (120) is positioned inside the receiving chamber (110), ultrasonic waves can be directly applied to the coating liquid received in the receiving chamber (110). The coating liquid can receive ultrasonic waves until just before being transferred to the coating bar (130), so that the ultrasonic generator (120) positioned inside the coater head (100), for example, inside the receiving chamber (110), has the advantage of a clear ultrasonic wave application effect.

[0082] In one embodiment of the present invention, as long as the ultrasonic generator (120) can be positioned inside the receiving chamber (110), there are no limitations on its shape and means. For example, the ultrasonic generator (120) may be attached to the inner wall of the receiving chamber (110) and may extend to the central portion of the receiving chamber (110).

[0083] FIG. 2 schematically illustrates the structure of a coating device (1) according to one embodiment of the present invention. In one embodiment shown in FIG. 2, the ultrasonic generator (120) may be positioned on the inner wall of the receiving chamber (110). As illustrated in FIG. 2, the ultrasonic generator (120) may be positioned on the inner wall of the receiving chamber (110) so that a vibrator that directly generates vibrations may be exposed so as to come into contact with the coating liquid. In this way, when the ultrasonic generator (120) is positioned on the inner wall of the receiving chamber (110), the area where the ultrasonic generator (120) comes into contact with the coating liquid is small, so that corrosion of the ultrasonic generator (120) due to microbubbles generated and extinguished by vibration can be reduced. Meanwhile, in the present embodiment, the ultrasonic generator (120) is located on the inner wall of the receiving chamber (110), but in another embodiment, the ultrasonic generator (120) may be located on the outer wall of the receiving chamber (110).

[0084] In one embodiment of the present invention, the ultrasonic generator (120) may have a sensor unit (not shown) inside to control whether or not to generate ultrasonic waves based on an external signal. The sensor unit may control whether or not to generate ultrasonic waves. For example, depending on the type of inorganic particles and binder polymers, ultrasonic irradiation may not be necessary when initially supplying the coating solution, but when ultrasonic irradiation is required for recycled coating solutions, the sensor unit may be used to control whether or not to generate ultrasonic waves.

[0085]

[0086] FIG. 3 schematically illustrates the structure of a coating device according to one embodiment of the present invention, and schematically illustrates a coating device (1) further including a coating liquid tank (200).

[0087] As illustrated in FIG. 3, in one embodiment of the present invention, the coating device (1) may further include a coating liquid tank (200). The coating liquid tank (200) may be located outside the coater head (100) and configured to supply the coating liquid to the receiving chamber (110) through a transfer pipe (210).

[0088] In one embodiment of the present invention, the coating solution tank (200) may be equipped with an impeller (not shown) for stirring the coating solution. In this case, the coating solution located within the coating solution tank (200) may be stirred by the impeller. As a result, the inorganic particles and binder polymers within the coating solution may exist within the coating solution without agglomerating with each other.

[0089] In one embodiment of the present invention illustrated in FIG. 3, the coating device (1) may further include a first pressure pump (220). The first pressure pump (220) may be provided in the transfer pipe (210) to provide pressure so that the coating liquid is transferred to the coater head (100). The first pressure pump (220) may be configured to control whether or not the coating liquid is supplied from the coating liquid tank (200) to the coater head (100) by controlling opening and closing, and the first pressure pump (220) may be configured to control the speed of the coating liquid supplied from the coating liquid tank (200) to the coater head (100) by controlling pressure. In addition, the first pressure pump (220) may also apply pressure to the coating liquid so that the coating liquid can easily come into contact with the coating bar (130).

[0090]

[0091] FIG. 4 schematically illustrates the structure of a coating device (1) according to one embodiment of the present invention, and schematically illustrates a coating device (1) further including a recovery unit (140).

[0092] In one embodiment of the present invention, the coating device (1) may further include a recovery unit (140). The recovery unit (140) may be positioned on the outer surface of the coater head (100) and configured to coat at least one surface of the substrate (not shown, see 2 of FIG. 1) and transfer and receive the remaining coating liquid along the outer surface of the coater head (100). For this purpose, the coater head (100) may have an inclined slope formed on its outer surface.

[0093] In one embodiment of the present invention, the coating liquid is transferred from the receiving chamber (110) to the substrate through the coating bar (130). However, if the coating liquid is excessively applied to the coating bar (130), the coating liquid is not entirely transferred to the substrate but flows down the outer surface of the coater head (100). In this case, if the outer surface of the coater head (100) is inclined, the coating liquid may flow down along the surface of the coater head (100) and be collected in the recovery unit (140).

[0094] Meanwhile, in one embodiment of the present invention, if the coating liquid is excessively applied to the coating bar (130), the coating liquid may fall back to the coater head (100) due to gravity or the like even after being transferred to a substrate moving to the right in FIG. 4, for example. In this case, the coating liquid may flow down along the inclined outer surface of the coater head (100) and collect in the recovery unit (140). To prepare for this case, the internal space of the recovery unit (140) located at the rear of the coater head (100), for example, on the right in FIG. 4, may be larger than the internal space of the recovery unit (140) located at the front of the coater head (100), for example, on the left in FIG. 4.

[0095] In the present specification, the front side of the coater head (100) means the outer surface of the coater head (100) close to before the substrate being transported in one direction (e.g., to the right) comes into contact with the coating bar (130), and the rear side of the coater head (100) means the outer surface of the coater head (100) close to after the substrate being transported in one direction comes into contact with the coating bar (130).

[0096]

[0097] In one embodiment of the present invention, the coating device (1) may further include a first recovery conduit (141). The first recovery conduit (141) may be located inside the coater head (100) and configured to connect the recovery unit (140) and the receiving chamber (110). The coating liquid collected in the recovery unit (140) may be transferred to the receiving chamber (110) through the first recovery conduit (141) to recycle the coating liquid. In this case, the recycled coating liquid may generate microbubbles in the coating liquid by the ultrasonic generator (120), thereby deagglomerating solutes in the coating liquid or reducing the viscosity of the coating liquid. In addition, the solvent of the coating liquid may evaporate in an air atmosphere when the coating liquid is transferred to a substrate, and thus, the solutes, i.e., inorganic particles and binder polymers, may coagulate with each other. For example, primary particles of inorganic particles and binder polymers may aggregate to form secondary particles. At this time, the aggregated inorganic particles and binder polymers may be deagglomerated by ultrasonic waves in a receiving chamber (110) by the recovery unit (140) and the first recovery conduit (141).

[0098] In one embodiment of the present invention, the internal space of the recovery unit (140) may be formed with an inclined portion, thereby connecting to the recovery unit below. The inclined portion may be a curved surface with or without an internal angle. The inclined portion may facilitate the transport of the coating liquid to the recovery conduit, and may prevent the coating liquid from accumulating inside.

[0099]

[0100] The coater head (100) is an open type rather than a sealed type, so that the inorganic particles and binder polymer in the coating solution may re-agglomerate when the solvent evaporates due to exposure to air during the coating process. If the coating solution is recycled while still containing the re-agglomerated inorganic particles or binder polymer, there is a risk of quality deterioration. For example, the re-agglomerated inorganic particles have a large particle size, which adversely affects the quality of the membrane. In the present invention, the coating solution collected in the recovery unit (140) is transferred to the receiving chamber (110), and the re-agglomerated inorganic particles or binder polymer are de-agglomerated using the ultrasonic generator (120), so that the coating solution can be used in a state close to that before recycling. Even if the inorganic particles re-agglomerate due to exposure to air, they can be applied to a substrate after being de-agglomerated by the ultrasonic generator (120), so that a membrane can be manufactured using inorganic particles having a small particle size, that is, fine particles close to the original state.

[0101] In one embodiment of the present invention, the coating device (1) may further include a second pressure pump (142) that provides pressure so that the coating liquid contained in the recovery unit (140) is transferred to the receiving chamber (110).

[0102] In one embodiment of the present invention, there is no limitation on the position, shape, and type of the second pressure pump (142) provided, as long as the second pressure pump (142) can provide pressure so that the coating liquid contained in the recovery unit (140) is transferred to the receiving chamber (110).

[0103] In one embodiment of the present invention, as illustrated in FIG. 4, the second pressure pump (142) may be provided in the first recovery conduit (141). In this case, the second pressure pump (142) may control the opening and closing of the pump to control whether or not the coating liquid is recovered from the recovery unit (140) to the receiving chamber (110), and the second pressure pump (142) may control the pressure to control the speed of the coating liquid supplied from the recovery unit (140) to the receiving chamber (110). In addition, the second pressure pump (142) may apply pressure to the coating liquid so that the coating liquid can easily come into contact with the coating bar (130).

[0104] In the coating device (1) of FIG. 4, the first recovery conduit (141) is located inside the coater head (100), and since the recovery section (140) and the receiving chamber (110) can be connected over a short distance, there is an advantage in that the coating liquid recovered for reuse can be quickly transferred to the receiving chamber (110).

[0105] FIG. 5 schematically illustrates the structure of a coating device (1) according to one embodiment of the present invention, and schematically illustrates a coating device further including a recovery unit (140) and a coating liquid tank (200).

[0106] In one embodiment of the present invention, the coating device (1) further includes a coating solution tank (200), and the coating solution tank (200) is located outside the coater head (100) and may be configured to supply the coating solution to the receiving chamber (110) through a transfer conduit (210). The coating device (1) may further include a recovery unit (140) located on the outer surface of the coater head (100) and configured to transfer and receive the remaining coating solution after coating at least one surface of the substrate along the outer surface of the coater head (100), and may further include a second recovery conduit (143) connecting the recovery unit (140) and the coating solution tank (200). In this case, the coating solution collected in the recovery unit (140) may be moved to the coating solution tank (200) through the second recovery conduit (143) to recycle the coating solution. At this time, the recycled coating liquid may be stirred by an impeller or the like of the coating liquid tank (200) to pulverize the solutes in the coating liquid or reduce the viscosity of the coating liquid. In addition, the recycled coating liquid may be mixed with other coating liquids in the coating liquid tank (200) and transferred to the receiving chamber (110) through a transfer pipe (210), and the solutes in the coating liquid may be deagglomerated again by the ultrasonic generator (120) of the receiving chamber (110) or the viscosity of the coating liquid may be reduced.

[0107] In the coating device (1) of FIG. 5, the coating liquid recovered for reuse can be circulated through the coating liquid tank (200), which is a difference from the coating device (1) of FIG. 4. Since the coating liquid collected in the recovery unit (140) can be transferred to the receiving chamber (110) after being stirred by an impeller or the like of the coating liquid tank (200), even if the coagulation becomes severe or the degree of dispersion within the coating liquid changes during the transfer of the coating liquid, it is stirred with other coating liquids in the coating liquid tank (200) to be homogenized and then transferred to the receiving chamber (110), which has the advantage of maintaining a constant quality of the coating liquid.

[0108]

[0109] In one embodiment of the present invention, the third pressure pump (144) may be further included to provide pressure so that the coating liquid contained in the recovery unit (140) is transferred to the coating liquid tank (200).

[0110] In one embodiment of the present invention, there is no limitation on the position, shape, and type of the third pressure pump (144) provided, as long as the third pressure pump (144) can provide pressure so that the coating liquid contained in the recovery unit (140) is transferred to the coating liquid tank (200).

[0111] In one embodiment of the present invention, as illustrated in FIG. 5, the third pressure pump (144) may be provided in the second recovery conduit (143). In this case, the third pressure pump (144) can control whether or not the coating liquid is recovered from the recovery unit (140) to the coating liquid tank (200) by controlling the opening and closing of the pump, and the third pressure pump (144) can control the speed of the coating liquid supplied from the recovery unit (140) to the coating liquid tank (200) by controlling the pressure.

[0112]

[0113] In one embodiment of the present invention, the coating bar (130) is not limited in type and shape, as long as it can transfer the coating liquid from the receiving chamber onto at least one surface of a substrate being transported in one direction. For example, the coating bar (130) may be a wire bar in which wire or the like is wound around a cylindrical bar, or a cylindrical bar without a wire wound around it. According to one embodiment, the coating bar (130) may be a Mayer bar.

[0114]

[0115] <Method for manufacturing a separation membrane>

[0116] The present invention provides a method for manufacturing a separation membrane.

[0117] Figure 6 schematically illustrates a flow chart of a method for manufacturing a separation membrane according to one embodiment of the present invention.

[0118] Referring to FIG. 6, a method for manufacturing a separation membrane according to one embodiment of the present invention includes a step (S10) of supplying a coating solution including a binder polymer, inorganic particles, and a solvent to a receiving chamber included in the coater head; a step (S20) of applying ultrasonic waves to the coating solution received in the receiving chamber using an ultrasonic generator located inside the coater head; and a step (S30) of transferring the coating solution applied with ultrasonic waves onto at least one surface of a substrate being transported in one direction using a coating bar provided in the coater head.

[0119] In addition, referring to FIG. 6, in one embodiment of the present invention, the method for manufacturing a separation membrane may further include, after the step (S30), a step (S40) of transferring a coating solution onto at least one surface of the substrate using a recovery unit installed on the outer surface of the coater head and recovering the remaining coating solution.

[0120] In addition, referring to FIG. 6, in one embodiment of the present invention, the method for manufacturing a separation membrane may further include, after the step (S40), a step (S50) of applying ultrasonic waves to the coating liquid recovered in the receiving chamber through the recovery unit.

[0121] Below, the manufacturing method of the separation membrane is explained step by step.

[0122]

[0123] First, the method for manufacturing the separation membrane of the present invention supplies a coating solution containing a binder polymer, inorganic particles, and a solvent to the receiving chamber (110) of the coating device (1) (step S10).

[0124] In one embodiment of the present invention, a coating solution may be prepared by adding a binder polymer and inorganic particles to a solvent and mixing them. The solids content of the coating solution may be in the range of about 5% to 40% by weight relative to 100% by weight of the coating solution.

[0125] In one embodiment of the present invention, the method of supplying the coating solution to the receiving chamber (110) is not limited, but for example, the coating solution may be supplied by pouring it into the receiving chamber (110), or the prepared coating solution may be first supplied to the coating solution tank (200), and then the coating solution may be supplied to the receiving chamber (110) through a separate transport conduit (210).

[0126]

[0127] In a separator manufactured by a method for manufacturing a separator according to an embodiment of the present invention, the binder polymer can improve mechanical properties such as flexibility and elasticity of the finally formed separator, and faithfully performs the role of a binder that connects and stably fixes inorganic particles, thereby contributing to preventing deterioration of the mechanical properties of the separator. According to one embodiment, the glass transition temperature (T) of the binder polymer g ) can exist within a range of approximately -200°C to 200°C.

[0128] In addition, the binder polymer does not necessarily need to have ion-conducting capability, but if a polymer having ion-conducting capability is used, the performance of the lithium secondary battery can be further improved. Therefore, the binder polymer may have a high dielectric constant as much as possible. In fact, since the degree of salt dissociation in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the binder polymer, the better the degree of salt dissociation in the electrolyte. The dielectric constant of the binder polymer can be used in the range of about 1.0 to 100 (measurement frequency = 1 kHz), and for example, can be about 10 or more.

[0129] In one embodiment of the present invention, the binder polymer can exhibit a high degree of swelling by being gelled when impregnated with a liquid electrolyte. The solubility index of the binder polymer, i.e., the Hildebrand solubility parameter, is about 15 MPa. 1 / 2 Up to 45 MPa 1 / 2 or about 15 MPa 1 / 2 Up to 25 MPa 1 / 2 and about 30 MPa 1 / 2 Up to 45 MPa 1 / 2 It may be a range. In one embodiment of the present invention, when hydrophilic polymers having a large number of polar groups are used rather than hydrophobic polymers such as polyolefins, the above-described solubility index range can be satisfied.

[0130] In one embodiment of the present invention, the inorganic particles are filled and in contact with each other and are bound to each other by the binder polymer, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles may become an empty space to form pores. The binder polymer may attach the inorganic particles to each other so that the particles can maintain a state of being bound to each other, for example, the binder polymer may connect and fix the inorganic particles. In addition, the pores of the separator are pores formed by the interstitial volume between the inorganic particles becoming an empty space, and this may be a space defined by the inorganic particles substantially meeting each other in a closed packed or densely packed structure by the inorganic particles.

[0131] In one embodiment of the present invention, any binder polymer commonly used in the relevant technical field can be used without limitation. The above binder polymers include, for example, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl Cellulose (carboxyl methyl cellulose), or two or more of these.

[0132] The above binder polymer may be a particulate binder or a soluble binder. The particulate binder is a binder polymer that does not dissolve in a solvent. The binder polymer is a soluble binder, meaning that the binder polymer dissolves in a solvent. The solvent may be an aqueous solvent or an oil-based solvent.

[0133]

[0134] In one embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. For example, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the applied electrochemical device (e.g., Li / Li). + There are no particular limitations as long as no oxidation and / or reduction reaction occurs at 0 to 5 V as a standard. When inorganic particles with a high dielectric constant are used as inorganic particles, the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte can be increased, thereby improving the ionic conductivity of the electrolyte.

[0135] For the reasons mentioned above, the inorganic particles may include high-k inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2 or mixtures thereof.

[0136] Inorganic particles may be used that have lithium ion transfer capability, for example, inorganic particles that contain lithium element but do not store lithium but have the function of transferring lithium ions. Non-limiting examples of inorganic particles that have lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li). x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li2O-9Al2O3-38TiO2-39P2O5, etc. (LiAlTiP) x O y Series Glass (0 <x < 4, 0 < y < 13), 리튬란탄티타네이트(Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li 3 N ), etc. x N y , 0 < x < 4, 0 < y < 2), SiS2 series glasses such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 글래스(Li x P y S z , 0 < x < 3, 0< y < 3, 0 < z < 7) or mixtures thereof.

[0137] Average particle diameter (D) of inorganic particles (single particles) 50 ) has no special limitations, but in order to form a coating layer of uniform thickness and an appropriate porosity, it may be in the range of about 0.1 ㎛ to 1.5 ㎛, or 1.0 ㎛ to 1.3 ㎛, or 1.05 ㎛ to 1.2 ㎛. When the average particle diameter of the inorganic particles is in the above range, the dispersibility is not reduced, and the thickness of the formed inorganic coating layer does not increase.

[0138] In one embodiment of the present invention, the inorganic particles may be included in a range of about 10 wt% to 90 wt% based on 100 wt% of the solid content of the coating liquid.

[0139]

[0140] In one embodiment of the present invention, the solvent may be an aqueous solvent or an oil-based solvent.

[0141] In one embodiment of the present invention, the aqueous solvent may be water or an aqueous solvent containing water. Furthermore, when drying speed and temperature are limited, methanol, ethanol, isopropyl alcohol, or the like, which have a lower boiling point than water, may be used together.

[0142] In one embodiment of the present invention, the organic solvent is cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and ethylbenzene; ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane and ethylcyclohexane; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitrile such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; amides such as N-methylpyrrolidone and N,N-dimethylformamide. , and the organic solvent may include acetone in consideration of the advantage in the drying process.

[0143] In one embodiment of the present invention, the organic solvent may be used alone, or a mixed solvent of two or more thereof may be used. Among these, a solvent with a low boiling point and high volatility can be removed in a short time and at a low temperature. For example, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, or N-methylpyrrolidone, or a mixed solvent thereof, may be used.

[0144]

[0145] Afterwards, ultrasonic waves are applied to the coating solution (step S20).

[0146] There is no limitation on the method of applying ultrasonic waves to the coating solution, but for example, ultrasonic waves can be applied to the coating solution by an ultrasonic generator (120).

[0147]

[0148] In one embodiment, the ultrasound may have a frequency of about 20 kHz to 100 kHz, or about 20 kHz to 60 kHz, or about 20 kHz to 40 kHz. The ultrasound having the above frequency range causes vibration in the solvent of the coating solution, and energy is generated as microbubbles are created and destroyed by the vibration, and the physical bond between the inorganic particles and the binder polymer in the coating solution is separated by the energy, so that the agglomeration between the inorganic particles and the binder polymer can be deagglomerated. Meanwhile, the closer the frequency of the ultrasound is to the lower limit of the above-described range, the stronger the degree of deagglomeration between the inorganic particles and the binder polymer can be, and the closer the frequency of the ultrasound is to the upper limit of the above-described range, the more easily the degree of deagglomeration between the inorganic particles and the binder polymer can be controlled.

[0149]

[0150] In one embodiment of the present invention, in the step (S10), before the ultrasonic waves are applied, the binder polymer has a first particle size, the inorganic particles have a second particle size, and the coating liquid to which the ultrasonic waves are applied includes a binder polymer having a first a particle size and an inorganic particle having a second a particle size, and the first a particle size may be about 70% or less of the first particle size, or the second a particle size may be about 70% or less of the second particle size.

[0151] In one embodiment of the present invention, the binder polymer may be a particulate binder, and the particulate binder polymer may mean one or all of single particles, secondary particles, and primary particles of the binder polymer. In addition, the first particle diameter may mean the diameter of any binder polymer, for example, D of the binder polymer. 10 Diameter, D 50 Diameter and D 90 It could mean diameter.

[0152] In one embodiment of the present invention, in the step (S10), the binder polymer having the first particle size may have the 1a particle size as ultrasound is applied to the coating liquid, and the 1a particle size may be about 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less of the first particle size. For example, in one embodiment of the present invention, the binder polymer may be in the form of secondary particles in which binder polymers having the first particle size are aggregated together before the ultrasound is applied, and as ultrasound is applied, the secondary particles may deagglomerate into binder polymer primary particles, thereby including the binder polymer having the 1a particle size.

[0153] In one embodiment of the present invention, the inorganic particles may mean any one or all of a single particle, a secondary particle, and a primary particle of an inorganic substance. The second particle size may mean the diameter of any inorganic particle, for example, D of the inorganic particle. 10 Diameter, D 50 Diameter and D 90 It could mean diameter.

[0154] In one embodiment of the present invention, in the step (S10), the inorganic particles having the second particle size may have the seconda particle size as ultrasound is applied to the coating liquid, and the seconda particle size may be about 90% or less, 80% or less, 70% or less, 60% or less, or 50% or less of the second particle size. For example, in one embodiment of the present invention, the inorganic particles may be in the form of secondary particles in which binder polymers having the second particle size are aggregated together before the ultrasound is applied, and as the ultrasound is applied, the secondary particles may deagglomerate into inorganic particle secondary particles, thereby including inorganic particles having the seconda particle size.

[0155] In one embodiment of the present invention, when the coating liquid includes a soluble binder polymer, only the particle size of the inorganic particles can be reduced by ultrasonic waves.

[0156]

[0157] Next, the coating liquid to which the ultrasonic waves have been applied is transferred onto at least one surface of a substrate that is transported in one direction (step S30).

[0158] The above substrate may be a porous polymer substrate for manufacturing a separator for a secondary battery. The porous substrate may electrically insulate the positive and negative electrodes, prevent short circuits due to electrode contact, and provide a path for lithium ions to move. For example, the porous substrate may be a polymer film or nonwoven fabric comprising one or more polymer resins selected from, but not limited to, polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous substrate may be formed of, but is not limited to, a single layer of polymer film or nonwoven fabric, and may be formed of multiple layers.

[0159]

[0160] In one embodiment of the present invention, after the step (S30), the step (S40) may further include a step of transferring the coating liquid onto at least one surface of the substrate and recovering the remaining coating liquid. The coating liquid contained in the receiving chamber (110) may contact the coating bar (130) and be transferred onto at least one surface of the substrate through which the coating liquid applied to the coating bar (130) is conveyed in one direction. Meanwhile, if the coating liquid is excessively applied to the coating bar (130), the coating liquid may not be completely transferred onto the substrate, but may flow onto the outer surface of the coater head (100) and may flow down along the inclined surface of the coater head (100) and be collected in the recovery unit (140). At this time, the coating liquid collected in the recovery unit (140) may be transferred back to the coating liquid tank (200) or to the receiving chamber (110), thereby transferring the coating liquid onto at least one surface of the substrate and recovering the remaining coating liquid.

[0161]

[0162] In one embodiment of the present invention, (S50) may further include a step of applying ultrasonic waves to the recovered coating liquid. As described above, the recovered coating liquid may be directly transferred to the receiving chamber (110) or transferred to the coating liquid tank (200) and then transferred back to the receiving chamber (110) depending on the embodiment of the coating device (1). Meanwhile, when the coating liquid is exposed to an air atmosphere for a long time, the solvent may evaporate, and thus the solute in the coating liquid may coagulate or the viscosity of the coating liquid may change. At this time, by applying ultrasonic waves to the recovered coating liquid as described above, the solute may decoagulate due to the generation and disappearance of microbubbles, and the viscosity of the coating liquid may also change.

[0163]

[0164] In one embodiment of the present invention, the viscosity of the coating liquid may be in the range of about 10 cps to 50 cps at 25°C. At this time, the viscosity of the coating liquid may be measured, for example, using a Brookfield viscometer (DV2T viscometer, 1000 rpm, spindle 63) at 25°C. At this time, the viscosity of the coating liquid may refer to the viscosity of the coating liquid accommodated in the receiving chamber (110). The receiving chamber (110) may contain the recovered coating liquid, but the viscosity of the coating liquid in the receiving chamber (110) may be maintained constant by the ultrasonic generator (120). Meanwhile, in one embodiment of the present invention, the viscosity of the coating liquid remaining after transferring the coating liquid onto at least one surface of the substrate may increase as the solvent evaporates, but as described above, by applying ultrasonic waves to the coating liquid, the viscosity of the coating liquid may be lowered again.

[0165]

[0166] In one embodiment of the present invention, the binder polymer of the recovered coating liquid has a third particle size larger than the first particle size, the inorganic particles of the recovered coating liquid have a fourth particle size larger than the second particle size, and the third and fourth particle sizes may be reduced by ultrasonic waves in the step (S50).

[0167] In one embodiment of the present invention, the recovered coating liquid may be formed by the binder polymer, inorganic particles, or two or more thereof coagulating with each other to form aggregates by evaporation of the solvent, and the aggregates may be separated by ultrasonic waves in the step (S50).

[0168]

[0169] In one embodiment of the present invention, the recovered coating liquid may have a binder polymer having a third particle size due to the binder polymer in the form of secondary particles agglomerating with each other as the solvent evaporates, or the binder polymer in the form of secondary particles agglomerating with each other and increasing in diameter. In this case, when ultrasonic waves are applied to the recovered coating liquid, the agglomerated binder polymer may deagglomerate and return to the form of primary binder polymer, thereby reducing the third particle size and separating the binder polymer aggregates.

[0170] In one embodiment of the present invention, the recovered coating liquid may have inorganic particles in the form of primary particles of the second particle size aggregate with each other as the solvent evaporates to form inorganic particles in the form of secondary particles of the fourth particle size, or inorganic particles in the form of secondary particles of the second particle size aggregate with each other to increase in diameter, thereby forming inorganic particles having the fourth particle size. At this time, when ultrasonic waves are applied to the recovered coating liquid, the aggregated inorganic particles may deagglomerate to become binder polymers in the form of primary particles again, so that the fourth particle size may be reduced and the aggregates of the inorganic particles may be separated.

[0171] In one embodiment of the present invention, in the recovered coating liquid, the inorganic particles and the binder polymer may each or a combination thereof aggregate to form aggregates, and the aggregates may be separated by applying ultrasonic waves to the recovered aggregates.

[0172]

[0173] The coating solution from which the aggregates are separated through ultrasonic application in the above step (S50) can be reused. This coating solution can be mixed with the coating solution used in the above step (S10) or supplied to the receiving chamber (110) to be used for continuous application on the substrate.

[0174] According to the method for manufacturing a membrane of the present invention, re-agglomerated inorganic particles or binder polymers can be de-agglomerated using an ultrasonic generator, and the coating solution can be reused in a state close to that prior to recycling. Even if the inorganic particles re-agglomerate due to exposure to air, they can be de-agglomerated by the ultrasonic generator and then applied to a substrate, thereby enabling the manufacture of a membrane using small particle sizes, or fine particles of inorganic particles. If the coating solution is recycled while still containing re-agglomerated inorganic particles or binder polymers, there is a risk of quality degradation. According to the present invention, re-agglomerated inorganic particles can be broken down to restore them to fine particles, which can then be used in the manufacture of a membrane. A membrane manufactured using this method can have a high level of safety by including a high-quality inorganic coating layer. In addition, since the coating solution can be recycled, the unit cost of manufacturing the membrane can be reduced.

[0175]

[0176] Figure 7 schematically illustrates a flow chart of a method for manufacturing a separation membrane according to another embodiment of the present invention.

[0177] Referring to FIG. 7, a method for manufacturing a separation membrane according to another embodiment of the present invention includes the steps of (P1) supplying a coating solution including a binder polymer, inorganic particles, and a solvent to a receiving chamber included in the coater head using a coating device including a coater head; (P2) transferring the coating solution onto at least one surface of a substrate being transported in one direction using a coating bar installed on a part of the coater head; (P3) transferring the coating solution onto at least one surface of the substrate using a recovery unit installed on an outer surface of the coater head and recovering the remaining coating solution; and (P4) applying ultrasonic waves to the coating solution recovered in the receiving chamber through the recovery unit.

[0178] That is, the method for manufacturing a separation membrane according to another embodiment of the present invention is different from the method for manufacturing a separation membrane according to the above-described embodiment in that ultrasonic waves are not irradiated to the initial coating liquid, but ultrasonic waves are applied to the coating liquid recovered through the recovery unit.

[0179] The above-mentioned binder polymer, inorganic particles, and solvent are replaced with those described above.

[0180] In one embodiment of the present invention, after the step (P4), a step of transferring a coating solution to which ultrasonic waves are applied onto at least one surface of a porous polymer substrate may be further included.

[0181]

[0182] Separator for lithium secondary batteries

[0183] The present invention provides a separator for a lithium secondary battery.

[0184] The separator for a lithium secondary battery of the present invention comprises: a porous polymer substrate; and an inorganic coating layer formed on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, wherein the surface roughness (Ra) of the inorganic coating layer is 0.12 ㎛ or less, the span value of the inorganic particles is 1.35 or less, and the span value is calculated by the following equation 1:

[0185] SPAN value = (particle diameter of inorganic particles (D) 90 ) - particle size of inorganic particles (D 10 )) / Particle diameter of inorganic particles (D 50 ) … Equation (1)

[0186] In one embodiment of the present invention, the inorganic coating layer is formed by mixing a plurality of inorganic particles and a binder polymer. By coating the porous polymer substrate with the inorganic coating layer containing inorganic particles in this manner, the heat resistance and mechanical properties of the separator can be further improved.

[0187] In one embodiment of the present invention, the thickness of the inorganic coating layer may be in the range of 0.5 µm to 5 µm, 0.6 µm to 2 µm, or 0.8 µm to 1.8 µm based on the thickness formed on either side of the porous polymer substrate.

[0188] In one embodiment of the present invention, the SPAN value may be 1.35 or less, 1.33 or less, or 1.3 or less. When the SPAN value satisfies the numerical range, the quality of the separator may be better, such as having a low surface roughness of the separator.

[0189] In one embodiment of the present invention, the SPAN value may be 0 or greater.

[0190] In one embodiment of the present invention, the surface roughness (Ra) of the inorganic coating layer may be 0.12 μm or less or 0.115 μm or less. When the surface roughness of the inorganic coating layer satisfies the above-described range, the adhesion of the electrode-separator may be further improved.

[0191] Meanwhile, in one embodiment of the present invention, there is no limitation on the method for measuring surface roughness (Sa). For example, the surface roughness can be measured using a roughness measuring device (e.g., a surface profiler) or a confocal laser scanning microscope (CLSM). For example, the surface roughness can be measured by enlarging a predetermined scanning area at a magnification of 50 times using a confocal laser scanning microscope, and the average value can be used after measuring 10 times per sample. Examples of the confocal laser scanning microscope that can be used include OLS 5100 and OLS4100 from Olympus, but are not limited thereto. The magnification of the confocal laser microscope can be adjusted to 10 times, 50 times, 100 times, 1000 times, 2000 times, 5000 times, etc.

[0192] In one embodiment of the present invention, the inorganic coating layer may be formed by a coating solution in which inorganic particles and a binder polymer are mutually disintegrated by ultrasonic waves, and the coating solution may be manufactured by the method described above.

[0193] In one embodiment of the present invention, the particle diameter (D) of the inorganic particles 50 ) may be 1.0 ㎛ to 1.3 ㎛ or 1.05 ㎛ to 1.2 ㎛. The particle diameter (D of the inorganic particles 50 ) If the above-described range is satisfied, the thickness of the coating layer can be more easily controlled.

[0194]

[0195] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0196]

[0197] <Comparative Example 1>

[0198] Aluminum oxide (Al2O3, D) as inorganic particles 50 : 600 nm, Sumitomo Corporation) and polymethylmethacrylate (D) as a particle-type acrylic binder 50 : 200 nm, Toyo-ink Co., Ltd.) was added to water at room temperature to prepare a coating solution. The viscosity of the coating solution was 20 cps at 25°C. In addition, the particle size D of the inorganic particles in the coating solution 10 Silver 0.6 ㎛ D 50 is 1.3㎛, D 90 was 2.4 ㎛, and the span value was 1.38.

[0199] Afterwards, the coating solution was applied on one side of a porous polymer substrate (porosity 40%, thickness 9 ㎛) made of polyethylene, and then dried at a temperature of 65°C for 30 seconds to manufacture a separator having an inorganic coating layer formed thereon.

[0200]

[0201] <Comparative Example 2>

[0202] Aluminum oxide (Al2O3, D) as inorganic particles 50 : 600 nm, Sumitomo Corporation) and polymethylmethacrylate (D) as a particle-type acrylic binder 50 : 200 nm, Toyo-ink Co.) was added to water at room temperature to prepare a coating solution, and then left in an air atmosphere for 30 minutes to prepare a coating solution. At this time, the viscosity of the coating solution was 60 cps at 25°C, and the particle size D 10 Silver 0.7 ㎛ D 50 is 2.5 ㎛, D 90It was confirmed that the silver was 4.2 ㎛ and the span value was 1.40.

[0203] Afterwards, the coating solution was applied on one side of a porous polymer substrate (porosity 40%, thickness 9 ㎛) made of polyethylene, and then dried at a temperature of 65°C for 30 seconds to manufacture a separator having an inorganic coating layer formed thereon.

[0204]

[0205] <Example 1>

[0206] Aluminum oxide (Al2O3, D) as inorganic particles 50 : 600 nm, Sumitomo Corporation) and polymethylmethacrylate (D) as a particle-type acrylic binder 50 : 200 nm, Toyo-ink Co.) was added to water at room temperature to prepare a coating solution, and then left in an air atmosphere for 30 minutes. Then, an ultrasonic wave with a frequency of 20 kHz was applied to the coating solution using an ultrasonic generator to prepare an ultrasonic-applied coating solution. At this time, the viscosity of the coating solution was 15 cps at 25°C, and the particle size D 10 Silver 0.5 ㎛ D 50 is 1.1 ㎛, D 90 It was confirmed that the silver was 1.9 ㎛ and the span value was 1.27.

[0207] Afterwards, the coating solution was applied on one side of a porous polymer substrate (porosity 40%, thickness 9 ㎛) made of polyethylene, and then dried at a temperature of 65°C for 30 seconds to manufacture a separator having an inorganic coating layer formed thereon.

[0208]

[0209] Experimental Example 1

[0210] [Viscosity measurement]

[0211] The viscosity of the coating solution of the examples and comparative examples was measured at 25°C using a Brookfield viscometer (DV2T viscometer, 1000 rpm, spindle 63).

[0212] [Diameter D10, D50, D90 Measurement and SPAN Value Derivation]

[0213] The inorganic particles and binder polymers of the examples and comparative examples were dispersed in a dispersion medium and then introduced into a laser diffraction particle size measuring device (Mastersizer 3000) for measurement. The particle size values ​​thus derived were converted into span values ​​using Equation 1 below and summarized in Table 1 below.

[0214] SPAN value = (particle diameter of inorganic particles (D) 90 ) - particle size of inorganic particles (D 10 )) / Particle diameter of inorganic particles (D 50 ) … Equation (1)

[0215] Viscosity D 10 D 50 D 90 Span value comparison example 120 cps 0.6 ㎛ 1.3 ㎛ 2.4 ㎛ 1.38 Comparative example 260 cps 0.7 ㎛ 2.5 ㎛ 4.2 ㎛ 1.40 Exemplary example 115 cps 0.5 ㎛ 1.1 ㎛ 1.9 ㎛ 1.27

[0216] Through a comparison of the above comparative examples and examples, it was confirmed that when left in an air atmosphere, the agglomeration of inorganic particles and binder particles accelerates, the viscosity increases, and when ultrasonic waves are applied to a coating solution with an increased span value, the agglomeration of inorganic particles and binder polymers is broken down, the viscosity decreases, and the distribution, i.e., the dispersion, of the inorganic particles is small. That is, it was confirmed that through the application of ultrasonic waves, the coating solution recovers its viscosity close to the state before exposure to air, or rather, the viscosity is lowered and the particle size of the inorganic particles is further reduced compared to the initial coating solution. This is judged to be the result of the inorganic particles and binder polymers being agglomerated due to physical and chemical properties even before exposure to air, but such agglomeration is effectively broken down by the application of ultrasonic waves.

[0217]

[0218] Experimental Example 2

[0219] [Surface observation and surface roughness (Ra) measurement]

[0220] The surfaces of the membranes of the examples and comparative examples are shown in Figs. 8a to 8c using a confocal scanning microscope (OLS 5100 from Olympus). The surfaces of the membranes were measured 10 times at 50x magnification to determine the average roughness, which is shown in Table 2 below. Specifically, Fig. 8a is a photograph of the surface of the membrane of Comparative Example 1 observed using a confocal scanning microscope, Fig. 8b is a photograph of the surface of the membrane of Comparative Example 2 observed using a confocal scanning microscope, and Fig. 8c is a photograph of the surface of the membrane of Example 1 observed using a confocal scanning microscope.

[0221] Surface roughness (Ra) Comparative example 10.1065 ㎛ Comparative example 20.1898 ㎛ Example 10.1108 ㎛

[0222] As a result of comparing the above comparative examples and examples, it was confirmed that when left in an air atmosphere, the agglomeration of inorganic particles and binder particles was accelerated, and the surface roughness of comparative example 2 increased compared to comparative example 1. Thereafter, as a result of applying ultrasonic waves to the coating solution as in example 1, the agglomeration of inorganic particles and binder polymers was broken up, and it was confirmed that the separator manufactured with the coating solution of example 1 exhibited a surface roughness value similar to that in the initial state.

[0223] Through the experimental results according to the above examples and comparative examples, it was confirmed that when ultrasonic waves were applied to a coating solution containing inorganic particles and a binder polymer as in one aspect of the present invention, the particle size of the inorganic particles decreased and the span value (dispersity) decreased.

[0224] Accordingly, it was confirmed that a separation membrane having excellent surface roughness characteristics can be manufactured when an inorganic coating layer is formed using a coating solution to which ultrasonic waves are applied.

[0225] In addition, according to another aspect of the present invention, it was confirmed that even when a coating solution containing inorganic particles and a binder polymer is left in an air atmosphere or the coating solution that is not transferred to a porous polymer substrate is reused, the properties of the coating solution can be restored to a level identical to or similar to the initial state by applying ultrasonic waves.

[0226]

[0227] Although the present disclosure has been described above with reference to embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes to the various embodiments of the present disclosure may be made without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. Cotter head; A receiving chamber located inside the above coater head and containing a coating liquid; An ultrasonic generator located inside the coater head and applying ultrasonic waves to the coating liquid contained in the receiving chamber; and A coating device comprising a coating bar for transferring the coating liquid from the receiving chamber onto at least one surface of a substrate being transported in one direction.

2. In claim 1, The above ultrasonic generator is a coating device located inside the receiving chamber.

3. In claim 1, The above ultrasonic generator is a coating device located on the inner wall of the receiving chamber.

4. In claim 1, A coating device further comprising a coating liquid tank located outside the coater head and supplying the coating liquid to the receiving chamber through a conveying conduit.

5. In claim 1, Located on the outer surface of the above cotter head, A coating device further comprising a recovery unit for coating at least one side of the above-described substrate and transporting the remaining coating liquid along the outer surface of the coater head to receive it.

6. In claim 5, Located inside the above cotter head, A coating device further comprising a first recovery conduit connecting the recovery unit and the receiving chamber.

7. In claim 1, A coating liquid tank located outside the above coater head and supplying the coating liquid to the receiving chamber through a transfer pipe; A recovery unit located on the outer surface of the coater head, which coats at least one side of the substrate and transfers and receives the remaining coating liquid along the outer surface of the coater head; and A coating device further comprising a second recovery conduit connecting the recovery unit and the coating liquid tank.

8. In claim 1, The above ultrasonic generator is a coating device having a sensor section inside so that it can control whether to generate ultrasonic waves according to an external signal.

9. A method for manufacturing a separation membrane using a coating device including a coater head, A step (S10) of supplying a coating solution containing a binder polymer, inorganic particles, and a solvent to a receiving chamber included in the coater head; A step (S20) of applying ultrasonic waves to the coating liquid contained in the receiving chamber using an ultrasonic generator located inside the coater head; and A method for manufacturing a separation membrane, comprising a step (S30) of transferring the coating solution applied with ultrasonic waves onto at least one surface of a substrate being transported in one direction using a coating bar provided on the coater head.

10. In claim 9, The above ultrasonic wave is a method for manufacturing a separation membrane having a frequency of 20 kHz to 100 kHz.

11. In claim 9, After the above step (S30), A method for manufacturing a separation membrane further comprising a step (S40) of transferring a coating solution onto at least one surface of the substrate using a recovery unit installed on the outer surface of the coater head and recovering the remaining coating solution.

12. In claim 11, After the above step (S40), A method for manufacturing a separation membrane further comprising a step (S50) of applying ultrasonic waves to the coating liquid recovered in the receiving chamber through the recovery unit.

13. In claim 9, A method for manufacturing a separation membrane, wherein the viscosity of the coating solution in the above step (S10) is within a range of 10 cps to 50 cps at 25°C.

14. A method for manufacturing a separation membrane using a coating device including a coater head, A step (P1) of supplying a coating solution containing a binder polymer, inorganic particles and a solvent to a receiving chamber included in the coater head; A step (P2) of transferring a coating liquid onto at least one surface of a substrate being transported in one direction using a coating bar installed on a part of the coater head; A step (P3) of transferring a coating liquid onto at least one side of the substrate using a recovery unit installed on the outer surface of the coater head and recovering the remaining coating liquid; and A method for manufacturing a separation membrane, comprising a step (P4) of applying ultrasonic waves to a coating liquid recovered in the receiving chamber through the recovery unit.

15. Porous polymer substrate; and An inorganic coating layer formed on at least one surface of the porous polymer substrate and including inorganic particles and a binder polymer, The surface roughness (Ra) of the above-mentioned inorganic coating layer is 0.12 ㎛ or less, The span value of the above inorganic particles is 1.35 or less, The above span value is calculated by the following equation 1: SPAN value = (particle diameter of inorganic particles (D) 90 ) - particle size of inorganic particles (D 10 )) / Particle diameter of inorganic particles (D 50 ) … Equation (1) 16. In claim 15, The above inorganic coating layer is formed by a coating solution in which inorganic particles and binder polymers are mutually disintegrated by ultrasonic waves. The above coating solution is a separator for a lithium secondary battery manufactured according to claim 9.

17. In claim 15, The particle size of the above inorganic particles (D 50 ) is a separator for a lithium secondary battery, characterized in that it has a thickness of 1.0 ㎛ to 1.3 ㎛.

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