Separator for electrochemical device including organic / inorganic composite porous coating layer and electrochemical device including the same

Abstract

An electrochemical device separator is proposed, which includes a porous polymer substrate and an organic / inorganic composite porous coating formed on at least one side of the polymer substrate, the organic / inorganic composite porous coating including particulate binder polymers and first inorganic particles, the particulate binder polymers including hybrid polymer particles of a fluorine-based polymer and an acrylic polymer and acrylic polymer particles, the particle size D50(a) of the acrylic polymer particles being in the range of 1 µm to 7 µm, the particle size D50(b) of the inorganic particles being in the range of 200 nm to 800 nm, a / b being in the range of 2 to 15, and the particle size D50 of the hybrid polymer particles being smaller than the particle size D50 of the acrylic polymer particles.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2022-0064640, filed on May 26, 2022, the entire contents of which are incorporated herein by reference for all purposes. The present disclosure relates to an electrochemical device separator having improved compression resistance, adhesion in a dry state (dry adhesion), and adhesion in an electrolyte-impregnated state (wet adhesion), and to an electrochemical device including the same. BACKGROUND

[0002] An electrochemical device, such as a lithium secondary battery, is generally mainly composed of a cathode, a separator, an anode, and an electrolyte solution. The electrochemical device is a high-density energy storage device capable of charging and discharging by reversible conversion between chemical energy and electrical energy, and is widely used for small electronic devices, such as mobile phones, notebook computers, etc. Recently, the application of the electrochemical device is rapidly expanding to hybrid electric vehicles (HEV), plug-in EVs, electric bicycles, and energy storage systems (ESS) to cope with environmental problems, high oil prices, energy efficiency, and energy storage.

[0003] In the manufacture and use of such electrochemical devices, ensuring the safety thereof is an important issue. Specifically, the separator commonly used in the electrochemical device, which is made of a porous polymer substrate, shows an extreme thermal shrinkage behavior at high temperatures or the like due to its material properties and manufacturing process properties, thereby causing internal short-circuit. Recently, in order to ensure the safety of the lithium secondary battery, a separator in which a mixture of inorganic particles and a binder polymer is coated on a porous polymer substrate to form an organic / inorganic composite porous coating has been developed.

[0004] Generally, the electrode assembly is manufactured by a lamination process in which the separator and the electrode are combined by heat and pressure, and the higher the heat and pressure applied in the process, the higher the binding force between the electrode and the separator. Recently, since the processing speed is increased for the purpose of improving productivity, the time for applying heat to the separator is shortened. However, due to high pressure, the organic / inorganic composite porous coating extrudes the porous polymer substrate, thereby reducing the thickness and causing deformation of the pore structure. When the inorganic particles are locally aggregated or formed into protrusions, the porous polymer substrate can be damaged, and thus there is a problem that dielectricity deterioration of the separator can occur.

[0005] On the other hand, when an electrode assembly is formed by laminating an electrode and a separator having an organic / inorganic composite porous coating, there is a high risk that the electrode and the separator can be separated due to insufficient adhesion, and in this case, inorganic particles that are deintercalated during the separation process can act as a local defect in the device. Therefore, a separator in which an acrylic polymer binder is applied to the organic / inorganic composite porous coating to improve the adhesion between the electrode and the separator is proposed, but when the acrylic polymer binder is used, dry adhesion is improved, but there is a problem that wet adhesion is reduced after application to a battery due to problems such as swelling or dissolution of the acrylic polymer binder by the electrolyte. SUMMARY

[0006] TECHNICAL PROBLEM

[0007] An object of the present disclosure is to provide a separator for an electrochemical device in which a phenomenon of a decrease in dielectricity of the separator, such as a decrease in thickness of a porous polymer substrate or deformation of a pore structure due to high pressure applied when laminating a separator having an organic / inorganic composite porous coating on at least one side of the porous polymer substrate and an electrode, is improved, and at the same time, the adhesion to the electrode can be improved under both dry and wet conditions.

[0008] Further, another object of the present disclosure is to provide an electrochemical device including a separator having the above-described properties.

[0009] Other objects and advantages of the present disclosure will be understood by the following description. On the other hand, it will be readily understood that the objects and advantages of the present disclosure can be achieved by the means or methods described in the claims and combinations thereof.

[0010] TECHNICAL SOLUTION

[0011] A first aspect of the present disclosure relates to a separator for an electrochemical device,

[0012] The separator includes a porous polymer substrate and an organic / inorganic composite porous coating formed on at least one side of the polymer substrate,

[0013] wherein the organic / inorganic composite porous coating contains a particulate binder polymer and first inorganic particles,

[0014] The particulate binder polymer contains hybrid polymer particles of a fluorine-based polymer and an acrylic polymer and acrylic polymer particles,

[0015] The particle size D50(a) of the acrylic polymer particles is in the range of 1 μm to 7 μm,

[0016] The particle size D50 (b) of the first inorganic particles is in the range of 200 nm to 800 nm, and a / b is 2 to 15,

[0017] The particle size D50 of the hybrid polymer particles is smaller than the particle size D50 of the acrylic polymer particles.

[0018] A second aspect of the present disclosure is that, in the first aspect, the particle size D50 (a) of the acrylic polymer particles is in the range of 2 μm to 6 μm, and the particle size D50 (b) of the first inorganic particles is in the range of 300 nm to 700 nm, and a / b is 5 to 12.

[0019] A third aspect of the present disclosure is that, in the first aspect or the second aspect, the particle size D50 of the acrylic polymer particles is 4 to 20 times larger than the particle size D50 of the hybrid polymer particles.

[0020] A fourth aspect of the present disclosure is that, in any one of the first aspect to the third aspect, the average particle diameter (D50) of the hybrid polymer particles is in the range of 100 nm to 500 nm.

[0021] A fifth aspect of the present disclosure is that, in any one of the first aspect to the fourth aspect, the mixing weight ratio of the hybrid polymer particles and the acrylic polymer particles is 8:2 to 2:8.

[0022] A sixth aspect of the present disclosure is that, in any one of the first aspect to the fifth aspect, the Tg of the acrylic polymer included in the hybrid polymer particles is 10°C or more lower than the Tg of the acrylic polymer included in the acrylic polymer particles.

[0023] A seventh aspect of the present disclosure is that, in the sixth aspect, the Tg of the acrylic polymer included in the hybrid polymer particles is 10°C to 30°C, and the Tg of the acrylic polymer included in the acrylic polymer particles is 30°C to 50°C.

[0024] An eighth aspect of the present disclosure is that, in any one of the first aspect to the seventh aspect, the fluorine-based polymer is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and other polymerizable monomers, or a mixture of two or more thereof.

[0025] A ninth aspect of the present disclosure is that, in the eighth aspect, the monomer is at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene, and fluoroethylene.

[0026] The tenth aspect of the present disclosure is: in the eighth aspect, the fluorine-based polymer is a copolymer of vinylidene fluoride and hexafluoropropylene.

[0027] The eleventh aspect of the present disclosure is: in the eighth aspect, the content of the monomer is 1 to 20% by weight of the copolymer.

[0028] The twelfth aspect of the present disclosure is: in any one of the first aspect to the eleventh aspect, the acrylic polymer constituting the hybrid polymer particles and the acrylic polymer constituting the acrylic polymer particles each independently contains a (meth)acrylic acid alkyl ester repeating unit having an alkyl group of 1 to 18 carbon atoms.

[0029] The thirteenth aspect of the present disclosure is: in any one of the first aspect to the twelfth aspect, the organic / inorganic composite porous coating further contains a non-particulate acrylic polymer.

[0030] The fourteenth aspect of the present disclosure is: in the thirteenth aspect, the Tg of the non-particulate acrylic polymer is 0°C or lower.

[0031] The fifteenth aspect of the present disclosure is: in any one of the first aspect to the fourteenth aspect, the organic / inorganic composite porous coating contains second inorganic particles different from the first inorganic particles, and the particle size D50 of the second inorganic particles is smaller than the particle size D50 of the first inorganic particles.

[0032] The sixteenth aspect of the present disclosure is: in the fifteenth aspect, the particle size (D50) of the second inorganic particles is in the range of 100 to 500 nm.

[0033] The seventeenth aspect of the present disclosure is: in the fifteenth aspect, the first inorganic particles are alumina, and the second inorganic particles are boehmite.

[0034] The eighteenth aspect of the present disclosure is: in any one of the first aspect to the seventeenth aspect, the organic / inorganic composite porous coating contains the particulate binder polymer in an amount of 1 to 30% by weight based on the total weight of the organic / inorganic composite porous coating.

[0035] The nineteenth aspect of the present disclosure is: in any one of the first aspect to the eighteenth aspect, the organic / inorganic composite porous coating is formed by coating a slurry in which the particulate binder polymer and the inorganic particles are dispersed in an aqueous dispersion medium on at least one surface of the porous polymer substrate and drying.

[0036] The twentieth aspect of the present disclosure relates to an electrochemical device, wherein the electrochemical device includes an anode, a cathode, and a separator interposed between the anode and the cathode, wherein the separator is according to any one of the first aspect to the nineteenth aspect.

[0037] The twenty-first aspect of the present disclosure is that, in the twentieth aspect, the electrochemical device is a lithium secondary battery.

[0038] Advantageous effects

[0039] According to the present disclosure, the organic / inorganic composite porous coating of the separator includes acrylic polymer particles and first inorganic particles, wherein the particle size D50(a) of the acrylic polymer particles is in the range of 1 μm to 7 μm, and the particle size D50(b) of the first inorganic particles is in the range of 200 nm to 800 nm, and a / b is 2 to 15. Since the particle size D50 of the acrylic polymer particles is at least 2 times larger than the particle size D50 of the first inorganic particles, it helps that the inorganic particles of the organic / inorganic composite porous coating are less likely to cause damage to the porous polymer substrate even when a high pressure is applied during the lamination process with the electrode, and improves the thickness reduction and deformation of the pore structure of the porous polymer substrate.

[0040] Further, according to the present disclosure, the organic / inorganic composite porous coating of the separator includes hybrid polymer particles of a fluorine-based polymer and an acrylic polymer, the particle size D50 of the hybrid polymer particles being smaller than the particle size D50 of the acrylic polymer particles. Since the fluorine-based polymer included in the hybrid polymer particles is insoluble in the electrolyte, the hybrid polymer particles maintain their shape even when immersed in the electrolyte, even while including the acrylic polymer. Therefore, the separator of the present disclosure maintains the adhesion to the electrode without significantly losing the adhesion to the electrode even in a wet state. On the other hand, the acrylic polymer particles also help to maintain the adhesion of the separator to the electrode in a dry state.

[0041] Therefore, in a roll-to-roll continuous process of manufacturing an electrode assembly by laminating an electrode and the separator of the present disclosure, there is an effect of improving the dielectric deterioration of the separator and improving the shape stability and processability of the electrode assembly. Further, by using an electrode assembly including the separator to manufacture a battery, a high bonding force can be maintained between the separator and the electrode even in a state of being immersed with an electrolyte, thereby improving the interface resistance characteristics. Further, since the binder polymer particles maintain a high adhesion force in a dry state or a wet state, the inorganic particles included in the organic / inorganic composite porous coating do not separate and are well fixed, so that the morphological stability of the separator can be improved. Therefore, there is an effect of improving the thermal stability and dielectric characteristics of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which are included to provide a further understanding of the principles of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and together with the detailed description serve to explain the principles of the present disclosure. In the drawings:

[0043] Figure 1 is a schematic view showing a cross section of a separator according to one embodiment of the present disclosure;

[0044] Figure 2 is an SEM image of a surface of the separator of Example 1 before impregnation with electrolyte; and

[0045] Figure 3 is an SEM image of a cross section of the separator according to Example 1. DETAILED DESCRIPTION

[0046] The terms or words used in the present specification and claims should not be interpreted as being common meanings or dictionary meanings, but should be interpreted as meanings and concepts within the technology to which the present application pertains based on the principle that the inventor can appropriately define the terms to best describe his or her application. Accordingly, it should be understood that the configurations described in the embodiments described herein are merely the most preferred embodiments of the present disclosure and do not represent all technical ideas of the present disclosure. Accordingly, it should be understood that various equivalents and modifications of the present disclosure can be made by those skilled in the art in the light of the present disclosure.

[0047] Figure 1 is a schematic view showing a cross section of a separator 10 for an electrochemical device according to one embodiment of the present disclosure.

[0048] In the present disclosure, the separator 10 includes a porous polymer substrate 1 and an organic / inorganic composite porous coating layer 3 formed on at least one side of the polymer substrate. Although Figure 1 The organic / inorganic composite porous coating layer 3 is shown as being formed on both side surfaces of the porous polymer substrate 1, but the organic / inorganic composite porous coating layer 3 can be formed on only one side surface of the porous polymer substrate 1.

[0049] The organic / inorganic composite porous coating layer 3 contains a particulate binder polymer and first inorganic particles 9. The particulate binder polymer contains hybrid polymer particles 5 of a fluorine-based polymer and an acrylic polymer and acrylic polymer particles 7.

[0050] As Figure 1As shown, the organic / inorganic composite porous coating layer 3 includes acrylic polymer particles 7 and first inorganic particles 9, and the particle size D50(a) of the acrylic polymer particles 7 is in the range of 1 pm to 7 pm, the particle size D50(b) of the first inorganic particles 9 is in the range of 200 nm to 800 nm, and a / b is 2 to 15.

[0051] Since the particle size D50 of the acrylic polymer particles 7 is at least twice as large as the particle size D50 of the first inorganic particles 9, it helps that the first inorganic particles 9 of the organic / inorganic composite porous coating layer 3 are less likely to cause damage to the porous polymer substrate 1 even when a high pressure is applied during the lamination process with the electrode layer, and the thickness reduction and deformation of the pore structure of the porous polymer substrate 1 are improved. If a / b is less than 2, the compression resistance can be insufficient, and if a / b exceeds 15, the electrical resistance can be too high. When the particle size D50(a) of the acrylic polymer particles 7 is less than 1 pm, there is a risk that the adhesion can be reduced, and when the particle size exceeds 7 pm, there can be a risk that the electrical resistance can be excessively increased. When the particle size D50(b) of the first inorganic particles 9 is less than 200 nm, the dispersibility in the slurry can be reduced, and when the particle size D50(b) of the first inorganic particles 9 is greater than 800 nm, the thickness of the organic / inorganic composite porous coating layer can be excessively increased or the pores can be too large. In this regard, the particle size D50(a) of the acrylic polymer particles can be 1 pm to 6 pm, more specifically 2 pm to 6 pm, and even more specifically 3 pm to 5 pm. Further, the particle size D50(b) of the first inorganic particles can be in the range of 300 nm to 700 nm, more specifically 400 nm to 600 nm. a / b can be 3 to 13, more specifically 5 to 12, and even more specifically 6 to 11.

[0052] On the other hand, the acrylic polymer particles 7 also help to maintain the adhesion of the separator to the electrode in the dry state.

[0053] Further, according to the present disclosure, the organic / inorganic composite porous coating layer 3 of the separator 10 includes hybrid polymer particles 5 of a fluorine-based polymer and an acrylic polymer, and the particle size D50 of the hybrid polymer particles 5 is smaller than the particle size D50 of the acrylic polymer particles 7. Since the fluorine-based polymer included in the hybrid polymer particles 5 is insoluble in the electrolyte, the hybrid polymer particles 5 maintain their shape even when wetted in the electrolyte even though the acrylic polymer is included at the same time. Therefore, the separator 10 of the present disclosure maintains the adhesion to the electrode without significantly losing the adhesion to the electrode even in the wet state.

[0054] On the other hand, by adjusting the particle size D50 of the hybrid polymer particles 5 to be smaller than the particle size D50 of the acrylic polymer particles 7, movement to the surface layer during the coating formation process is promoted, as shown in Figure 1 The organic / inorganic composite porous coating layer 3 has a composition profile that is non-uniform in the thickness direction, in which the content ratio of the hybrid polymer particles 5 / acrylic polymer particles 7 present on the surface portion opposite the surface in contact with the porous polymer substrate 1 is greater than the content ratio of the hybrid polymer particles 5 / acrylic polymer particles 7 present in the interior of the organic / inorganic composite porous coating layer 3. Thus, when wetted with an electrolyte, the adhesion of the separator 10 to the electrode can be further improved.

[0055] Thus, when the hybrid polymer particles 5 and / or the acrylic polymer particles 7 have a composition profile that is non-uniform in the thickness direction in the form described above, the polymer particles are present more on the surface portion opposite the surface in contact with the porous polymer substrate 1 than in the interior of the organic / inorganic composite porous coating layer 3. Thus, the dry / wet adhesion to the electrode is further increased due to the adhesion force characteristics of the polymer particles present on the surface. Furthermore, resistance to external stimuli such as peeling and scratching is increased, and the lamination characteristics of the electrode are improved. Thus, very excellent characteristics can be exhibited in the battery assembly process (e.g., winding and lamination). Furthermore, since the porosity is improved due to the increase in inorganic particles to the interior, excellent ion conduction characteristics can be exhibited, thereby contributing to the improvement of battery performance. In this regard, the particle size D50 of the acrylic polymer particles 7 can be 4 to 20 times larger than the particle size D50 of the hybrid polymer particles 5, and the particle size D50 of the hybrid polymer particles 5 can be in the range of 100 nm to 500 nm, but is not limited thereto.

[0056] Furthermore, the mixed weight ratio of the hybrid polymer particles 5 and the acrylic polymer particles 7 can be 8:2 to 2:8, but is not limited thereto.

[0057] In the specification of the present disclosure, the "composition profile in the thickness direction is non-uniform, in which the content ratio of the hybrid polymer particles / acrylic polymer particles present on the surface portion opposite to the surface in contact with the polymer substrate is greater than the content ratio of the hybrid polymer particles / acrylic polymer particles present in the interior of the organic / inorganic composite porous coating", in which if the content ratio of the hybrid polymer particles / acrylic polymer particles present on the surface portion opposite to the surface in contact with the polymer substrate of the organic / inorganic composite porous coating is greater than the content ratio of the hybrid polymer particles / acrylic polymer particles present in the interior of the porous coating, it should be understood to include any aspect. For example, it should be understood to mean to include all of: forming the porous coating such that the content ratio of the hybrid polymer particles / acrylic polymer particles linearly decreases from the surface of the porous coating to the porous substrate, forming the porous coating such that the content ratio of the hybrid polymer particles / acrylic polymer particles nonlinearly decreases from the surface of the porous coating to the porous substrate, and forming the porous coating such that the content ratio of the hybrid polymer particles / acrylic polymer particles discontinuously decreases from the surface of the porous coating to the porous substrate, and the like.

[0058] The organic / inorganic composite porous coating 3 can have a composition profile in the thickness direction that is non-uniform, in which the content of the hybrid polymer particles 5 present on the surface portion opposite to the surface in contact with the porous polymer substrate 1 is greater than the content of the hybrid polymer particles 5 present in the interior of the organic / inorganic composite porous coating 3. Further, the organic / inorganic composite porous coating 3 can have a composition profile in the thickness direction that is non-uniform, in which the content of the acrylic polymer particles 7 present on the surface portion opposite to the surface in contact with the porous polymer substrate 1 is greater than the content of the acrylic polymer particles 7 present in the interior of the organic / inorganic composite porous coating 3.

[0059] As described above, in a roll-to-roll continuous process of manufacturing an electrode assembly by laminating an electrode and the separator 10 of the present disclosure, there is an effect of improving the dielectric deterioration of the separator 10 and improving the shape stability and processability of the electrode assembly. Further, since a high bonding force can be maintained between the separator 10 and the electrode even when a battery is manufactured using an electrode assembly including the separator 10 and impregnated with an electrolyte, the interface resistance characteristics are improved. Further, since the binder polymer particles maintain a high adhesion force under dry conditions or wet conditions, the first inorganic particles 9 included in the organic / inorganic composite porous coating 3 do not separate and are well fixed. Therefore, it is possible to improve the shape stability of the separator 10. Therefore, there is an effect of improving the thermal stability and dielectric characteristics of the battery.

[0060] According to one specific embodiment of the present disclosure, the porous polymer substrate 1 is capable of providing a moving path for lithium ions while preventing a short circuit by electrically insulating the anode and the cathode, and can be used without particular limitation as long as it is generally used as a separator polymer substrate of an electrochemical device. As an example of the separator substrate, for example, a porous polymer film or a nonwoven fabric including at least one polymer resin among polyolefins such as polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate can be used.

[0061] In the present disclosure, the thickness of the polymer substrate can be 3 μm to 50 μm. Although the range of the separator substrate is not particularly limited to the aforementioned range, if the thickness is too thin compared to the lower limit described above, the mechanical properties are reduced, and the separator can be easily damaged during the use of the battery. Meanwhile, the pore size and the porosity present in the separator substrate are also not particularly limited, but can be 0.01 μm to 50 μm and 10% by volume to 95% by volume, respectively.

[0062] The organic / inorganic composite porous coating layer 3 is made by mixing a plurality of the first inorganic particles 9 and the particulate binder polymer. Since the porous polymer substrate 1 is coated with the organic / inorganic composite porous coating layer 3 including the first inorganic particles 9, the heat resistance and the mechanical properties of the separator 10 can be further improved. According to one preferred embodiment of the present disclosure, the organic / inorganic composite porous coating layer 3 is disposed on both sides of the porous polymer substrate 1. As described above, by forming the organic / inorganic composite porous coating layer 3 on both sides of the porous polymer substrate 1, the wet adhesion and the dry adhesion between the cathode and the separator and between the anode and the separator can be improved.

[0063] The organic / inorganic composite porous coating layer 3 can have a microporous structure due to the interstitial volume between the first inorganic particles 9 and the particulate binder polymer constituting it. The first inorganic particles 9 serve as a kind of spacer capable of maintaining the physical shape of the organic / inorganic composite porous coating layer 3. The interstitial volume refers to a space defined by the substantially surface contact with the first inorganic particles 9 and the particles of the particulate binder polymer. Further, since the first inorganic particles 9 generally have a characteristic that does not change its physical properties even at a high temperature of 200℃ or more, the separator 10 has excellent heat resistance by the organic / inorganic composite porous coating layer 3. In the present disclosure, the thickness of the organic / inorganic composite porous coating layer 3 can be in the range of 1 μm to 50 μm, 2 μm to 30 μm, or 2 μm to 20 μm, based on the thickness formed on either side of the porous polymer substrate 1.

[0064] In the present disclosure, the particulate polymer refers to a binder polymer that is added in the form of particles to a dispersion medium to form the organic / inorganic composite porous coating layer 3 and remains the added particle shape after coating and drying, and is distinguished from a "non-particulate" binder polymer defined as being transformed into a film-like form losing the particle phase during drying at the time of forming the coating layer regardless of whether it is dissolved in a solvent or not. That is, in the present disclosure, "particles" are defined as substantially maintaining the same shape of the added particles, and the shape is generally a circular particle, but is not limited thereto. As such, since the polymer particles remain in the form of particles, they are hardly permeated into the pores of the porous polymer substrate, thereby contributing to improvement in clogging of the pores of the polymer substrate.

[0065] In one embodiment of the present disclosure, the particulate binder polymer can be present in an amount of about 90% by weight or more or about 99% by weight or more, based on the binder component present in the organic / inorganic composite porous coating layer 3. In the present specification, the particulate binder polymer can be referred to as a polymer particle, a resin particle, or a binder particle. The particulate binder polymer forms the organic / inorganic composite porous coating layer 3 having a layered structure through adhesion between the first inorganic particles 9 and mutual adhesion between the first inorganic particles 9 and the porous polymer substrate 1.

[0066] The hybrid polymer particle 5 can be prepared with reference to, for example, WO 2020 / 263936, and can be incorporated with the references of the present disclosure.

[0067] The fluorine-based polymer included in the hybrid polymer particle is an electrolyte-insoluble polymer that is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and other polymerizable monomers, or a mixture of two or more thereof.

[0068] The polymerizable monomer other than vinylidene fluoride can include at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene, and fluoroethylene, but is not limited thereto. In particular, the fluorine-based polymer can be a copolymer of vinylidene fluoride and hexafluoropropylene. The content of vinylidene fluoride and other polymerizable monomers can be 1 to 20% by weight of the copolymer, but is not limited thereto.

[0069] In the present disclosure, the content of the comonomer in the PVDF-based polymer can be measured using a 1H-NMR method by Varian 500 MHz. For the detailed measurement method, see Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. For the confirmation of the NMR spectrum, a suitable device such as Bruker Avance III HD 700Mhz NMR or Varian 500 MHz NMR can be used.

[0070] The acrylic polymer constituting the hybrid polymer particle and the acrylic polymer constituting the acrylic polymer particle can each independently include a (meth)acrylic acid alkyl ester repeating unit having an alkyl group of 1 to 18 carbon atoms, but are not limited thereto.

[0071] In one embodiment of the present disclosure, the Tg of the acrylic polymer included in the hybrid polymer particle can be 10°C or more lower than the Tg of the acrylic polymer included in the acrylic polymer particle. Since the lower the Tg of the acrylic polymer, the better the adhesion, the lower the Tg of the acrylic polymer included in the hybrid polymer particle, the higher the dry / wet adhesion of the hybrid polymer particle to the electrode.

[0072] More specifically, the Tg of the acrylic polymer included in the hybrid polymer particle can be 10°C to 30°C, and the Tg of the acrylic polymer included in the acrylic polymer particle can be 30°C to 50°C. Although the acrylic polymer included in the hybrid polymer particle has a low Tg, due to the mixed fluorine-based polymer, the particulate form can be maintained even at room temperature. In addition, when the Tg of the acrylic polymer included in the acrylic polymer particle is selected to be higher than or equal to room temperature, the particle shape can be maintained at room temperature, thereby exhibiting electrode adhesion during lamination with the electrode layer.

[0073] The glass transition temperature (Tg) of the acrylic polymer can be 40°C or lower.

[0074] More specifically, the acrylic polymer contains a carboxylate as a repeating unit, and can be preferably a (meth)acrylate. Specific examples of such (meth)acrylate can include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, and the like, and can be at least one selected from among them. Among these, at least one selected from among methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is preferable, and methyl (meth)acrylate is particularly preferable.

[0075] The organic / inorganic composite porous coating layer can contain the particulate binder polymer in an amount of 1 to 30% by weight of the organic / inorganic composite porous coating layer, but is not limited thereto.

[0076] The organic / inorganic composite porous coating layer can further contain a non-particulate acrylic polymer. The non-particulate acrylic polymer is an acrylic polymer that is not soluble in an aqueous dispersion medium but does not maintain a particulate form, for example, an acrylic polymer having a low Tg of 0°C or less. The non-particulate acrylic polymer can improve the adhesion of the organic / inorganic composite porous coating layer to the electrode and the binding force between the inorganic particles and between the inorganic particles and the polymer substrate. The non-particulate acrylic polymer can be added in an amount of 10% by weight or less, based on the total weight of the binder polymer contained in the organic / inorganic composite porous coating layer, but is not limited thereto.

[0077] Meanwhile, the first inorganic particles contained in the organic / inorganic composite porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as they are electrochemically stable within the operating voltage range of the electrochemical device to which they are applied (for example, based on Li / Li +The oxidation reaction and / or the reduction reaction can not occur (e.g., the potential is 0 V to 5 V). In particular, when the first inorganic particles having ion transportability are used, the performance can be improved by increasing the ion conductivity in the electrochemical device. In addition, when inorganic particles having a high dielectric constant are used as the first inorganic particles, the ion conductivity of the electrolyte can be improved by promoting an increase in the degree of dissociation of an electrolyte salt (e.g., a lithium salt) in the liquid electrolyte.

[0078] For the above reasons, the first inorganic particles can include inorganic particles having a high dielectric constant of 5 or more or 10 or more, inorganic particles having lithium ion transportability, or a mixture thereof. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3alone, Pb(Zr,Ti)O3(PZT), Pb(Mg 1-x La x Zr 1-y Ti y O3(PLZT, where 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, aluminum oxide (Al2O3), boehmite, SiC, TiO2, etc., or a mixture of two or more thereof. In addition, when the above high dielectric constant inorganic particles are mixed with inorganic particles having lithium ion transportability, their synergistic effect can be doubled.

[0079] Non-limiting examples of inorganic particles having lithium ion transportability 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), glass based on (LiAlTiP) x O y (0 < x < 4, 0 < y < 13), such as 14Li2O-9Al2O3-38TiO2-39P2O5, 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), such as Li 3.25Ge 0.25 P 0.75 S4, lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2) such as Li3N, a glass based on SiS2(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) such as Li3PO4-Li2S-SiS2, a glass based on P2S5(Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) such as LiI-Li2S-P2S5, etc., or a mixture thereof.

[0080] Meanwhile, the organic / inorganic composite porous coating layer can further include second inorganic particles having a particle size D50 smaller than the particle size D50 of the first inorganic particles and different from the first inorganic particles. By mixing these second inorganic particles, the packing density of the porous coating layer can be improved, thereby further improving the heat resistance. In this regard, the particle size D50 of the second inorganic particles can be in the range of 100 nm to 500 nm.

[0081] As the second inorganic particles, the above-described first inorganic particles can be used. In particular, alumina can be used as the first inorganic particles, and boehmite can be used as the second inorganic particles.

[0082] In the organic / inorganic composite porous coating layer, the content ratio of the inorganic particles is determined in consideration of the thickness, pore size, and porosity of the finally prepared organic / inorganic composite porous coating layer, but based on 100 wt% of the porous coating layer, the inorganic particles can be included in the range of 70 wt% to 99 wt%. When the content of the inorganic particles is less than 70 wt%, the heat resistance can be reduced. On the other hand, when the content of the inorganic particles is too large, the amount of the binder is relatively too small, and thus the adhesion of the porous coating layer can be reduced.

[0083] On the other hand, in one embodiment of the disclosure, the separator including the organic / inorganic composite porous coating layer can be prepared by mixing binder particles and inorganic particles with an aqueous dispersion medium to prepare a slurry for forming a coating layer, and then coating the slurry on at least one side surface of a polymer substrate.

[0084] As the coating method, dip coating, die coating, roll coating, comma coating, or a mixture thereof can be employed.

[0085] In one embodiment of the present disclosure, the aqueous dispersion medium can include at least one of water and an alcohol having 1 to 5 carbon atoms. For example, the aqueous dispersion medium can include a mixture of water and isopropyl alcohol. By using the aqueous dispersion medium in the above production method, the binder particles are dispersed while maintaining the particle shape in the aqueous dispersion medium without dissolving in the dispersion medium. For this reason, the binder particles can be maintained in a particle state in the prepared organic / inorganic composite porous coating layer, and do not enter the pores of the polymer substrate.

[0086] On the other hand, in one embodiment of the present disclosure, it is preferable to control the slurry for forming the coating layer such that the concentration of solids (not including the dispersion medium) is in the range of 20 to 50% by weight. By controlling the concentration of solids, the average particle diameter, and the content ratio of the injected binder particles to be in the above ranges, it is advantageous to obtain the separator of the present disclosure having the organic / inorganic composite porous coating layer having a composition profile unevenness.

[0087] On the other hand, the separator of the present disclosure can be applied to an electrochemical device. The electrochemical device can include an anode and a cathode, and the separator can be interposed between the anode and the cathode. The electrochemical device includes all devices that perform electrochemical reactions, and specific examples thereof include primary batteries, secondary batteries, fuel cells, solar cells, or capacitors of all kinds. In particular, lithium ion secondary batteries among secondary batteries are preferred: including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

[0088] In one specific embodiment, the electrochemical device can be manufactured according to the conventional method known in the art according to the present disclosure. According to one embodiment of the present disclosure, the electrochemical device can be configured by a method of interposing the above-described separator between the cathode and the anode.

[0089] That is, the separator prepared by the above-described method is interposed between the anode and the cathode, and manufactured into an electrode assembly through a lamination process of applying heat and / or pressure to bond the separator. In one embodiment of the present disclosure, the lamination process can be performed by a roll press device including a pair of pressure rollers. That is, the anode, the separator, and the cathode are sequentially stacked and placed between the pressure rollers to achieve interlayer bonding. In this case, the lamination process can be performed by a method of hot pressing.

[0090] The electrochemical device can be manufactured by loading the electrode assembly assembled by laminating the anode, the separator, and the cathode into a battery case, and then injecting an electrolyte.

[0091] In one embodiment of the present disclosure, the electrode is not particularly limited, and the electrode active material can be prepared in a form adhered to an electrode current collector according to a conventional method known in the art. As a non-limiting example of the cathode active material in the electrode active material, a conventional cathode active material that can be used for a cathode of a conventional electrochemical device can be used, and particularly, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium intercalation material such as a composite oxide formed by a combination thereof is preferred. As a non-limiting example of the anode active material, a conventional anode active material that can be used for an anode of a conventional electrochemical device can be used. And particularly, lithium metal or a lithium alloy; a lithium adsorption material such as carbon, petroleum coke, activated carbon, graphite, or other carbon is preferred. Non-limiting examples of the cathode current collector include a foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the anode current collector include a foil made of copper, gold, nickel, or a copper alloy, or a combination thereof.

[0092] The electrolyte solution that can be used in the present disclosure is a salt having the same structure as A + B - , and A + includes an ion formed of an alkali metal cation such as Li + , Na + , K + , or a combination thereof, or B - includes PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - , or a combination thereof. In the electrolyte, the salt can be dissolved or dissociated in an organic solvent including or consisting of a mixture of the following: 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), and gamma butyrolactone (γ-butyrolactone), but is not limited thereto.

[0093] The electrolyte injection can be performed at an appropriate stage in the battery manufacturing process depending on the manufacturing process of the final product and the required physical properties. That is, the electrolyte can be applied before assembling the battery or in the final stage of assembling the battery. As a method for applying the electrode assembly of the present disclosure to a battery, in addition to the general winding method, a lamination, stacking, and folding method of separators and electrodes is also possible.

[0094] Embodiment

[0095] Hereinafter, examples will be given to describe the present disclosure in detail. However, the embodiments according to the present disclosure can be modified in various other forms, and the scope of the present disclosure should not be interpreted as being limited to the embodiments described below. The embodiments of the present disclosure are provided to more completely explain the present disclosure to those having ordinary skill in the art.

[0096] Example 1

[0097] 8.2 parts by weight of hybrid polymer particles [Arkema, LBG4330LX, D50: 300 nm, hybrid polymer particles in which a copolymer in which VDF and HFP are polymerized in a molar ratio of 95:5 is mixed with a copolymer of ethyl acrylate and methyl methacrylate (Tg 20℃) at a weight ratio of 7:3], 8.2 parts by weight of acrylic polymer particles [D50: 5 μm, copolymer of styrene and butyl acrylate (Tg 40℃)], 80 parts by weight of inorganic particles (Al2O3, D50: 500 nm) were added to water and dispersed to prepare a dispersion (35% by weight of solid concentration) for forming a porous coating layer.

[0098] Next, a polyethylene material separator substrate (porosity 40%, thickness 9 μm) was prepared, the dispersion was coated on both sides of the separator substrate by bar coating using a doctor blade, and then dried using a hot air gun with hot air at 50℃ to form a porous coating layer having a thickness of 12 μm based on the thickness of one side. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al2O3 (a / b) was 10.

[0099] Figure 2 is an SEM image of the surface of the separator of Example 1 before impregnation with electrolyte, and Figure 3 is an SEM image of a cross-section of the separator according to Example 1.

[0100] Example 2

[0101] A porous coating layer was formed in the same manner as in Example 1, except that the content of the hybrid polymer particles was 10.2 parts by weight, the content of the acrylic polymer particles was 10.2 parts by weight, and the content of the inorganic particles was changed to 75 parts by weight, to prepare a dispersion (35% by weight of solid concentration) for forming a porous coating layer. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 10.

[0102] Example 3

[0103] A porous coating layer was formed in the same manner as in Example 1, except that 0.9 parts by weight of a non-particulate acrylic polymer [Toyochem CSB130, particle size 150 nm, Tg-30°C] was added to water based on the solid content. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 10.

[0104] Example 4

[0105] A porous coating layer was formed in the same manner as in Example 1, except that 80 parts by weight of inorganic particles (Al203, D50: 500 nm) and boehmite (D50: 300 nm) were added in a weight ratio of 85:15 instead of 80 parts by weight of inorganic particles (Al203, D50: 500 nm). The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 10.

[0106] Comparative Example 1

[0107] A porous coating layer was formed in the same manner as in Example 1, except that a dispersion (35% by weight of solid concentration) for forming a porous coating layer was prepared by changing the content of the acrylic polymer particles to 16.4 parts by weight without adding the hybrid polymer particles. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 10.

[0108] Comparative Example 2

[0109] A porous coating layer was formed in the same manner as in Example 1, except that a dispersion (35% by weight of solid concentration) for forming a porous coating layer was prepared by changing the content of the hybrid polymer particles to 16.4 parts by weight without adding the acrylic polymer particles. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 0.

[0110] Comparative Example 3

[0111] A porous coating layer was formed in the same manner as in Example 1, except that 8.2 parts by weight of acrylic polymer particles having a small particle size D50 [copolymer of styrene and butyl acrylate (Tg 40°C) (D50: 0.9 μm)] were added instead of 8.2 parts by weight of the acrylic polymer particles having a D50 of 5 μm in Example 1. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 1.8.

[0112] Comparative Example 4

[0113] A porous coating layer was formed in the same manner as in Example 1, except that 8.2 parts by weight of acrylic polymer particles having a small particle size D50 [copolymer of styrene and butyl acrylate (Tg 40°C) (D50: 0.4 μm)] were added instead of 8.2 parts by weight of the acrylic polymer particles having a D50 of 5 μm in Example 1. The particle size D50 of the acrylic polymer particles / a particle size D50 of the first inorganic particles Al203 (a / b) was 0.8.

[0114] Measurement of average particle size D50

[0115] D50 can be defined as the particle size based on 50% of the particle size distribution, and is measured using a laser diffraction method.

[0116] Measurement of Tg

[0117] Tg of a 25 mg sample was measured using DSC under a nitrogen atmosphere at a temperature elevation rate of 10°C / minute in the range from room temperature to 300°C.

[0118] Production of wet adhesion test samples

[0119] The separators and cathode layers obtained in each of the examples and comparative examples were laminated, immersed in 1.0 g of electrolyte (content ratio of ethylene carbonate:methyl ethyl carbonate = 7:3, LiPF61M), and left to stand at room temperature for 24 hours. Thereafter, a test sample was prepared by lamination using a hot press. At this time, pressure was applied at 70°C and 5 kgf for 5 minutes. The size of the test sample was 2 cm x 6 cm.

[0120] The cathode was prepared as follows. LiNi 0.8 Co 0.1 Mn 0.1 O2, PVdF, and carbon black were mixed in a weight ratio of 97.0:1.5:1.5 and dispersed in 2-methyl-2-pyrrolidone to prepare a cathode slurry, coated on an aluminum current collector, and then dried and roll-pressed to prepare a cathode.

[0121] Production of dry adhesion test samples

[0122] The separators and anode obtained in each of the examples and comparative examples were laminated using a hot press to prepare test samples. At this time, pressing was performed at 6.5 MPa at 60°C for 1 second. The size of the test sample was 2.5 cm x 6 cm.

[0123] The anode was prepared as follows. Graphite, SBR, and CMC were mixed in a weight ratio of 89.2:10:0.8 and dispersed in distilled water to prepare an anode slurry, coated on a copper current collector, and then dried and roll-pressed to prepare an anode.

[0124] Measurement of adhesion to electrode

[0125] Using each of the test samples prepared above, the wet adhesion and dry adhesion of the separators were evaluated, and the results are summarized in Table 1 below. After preparing each of the test samples, the test samples were left to stand at room temperature for 1 hour and then the adhesion was measured. The adhesion was measured using a tensile testing machine (UTM device) by peeling at an angle of 180° (for dry) and 90° (for wet).

[0126] [Table 1]

[0127]

[0128] As can be seen in Table 1, in Comparative Example 1, the dry adhesion is high and the wet adhesion is low, and thus when applied to an actual battery, the battery performance can be degraded. Comparative Example 2 has a problem in that the adhesion is reduced during the electrode assembly manufacturing process due to low dry adhesion. Comparative Examples 3 and 4 have low compression resistance, and thus the thickness of the porous polymer substrate can be reduced due to high pressure applied when the separator and the electrode are laminated, and thus the dielectricity of the separator can be degraded, for example, deformation of the pore structure. On the other hand, according to the embodiments, the separator exhibits good levels of wet adhesion and dry adhesion, thereby exhibiting excellent electrochemical effects in the electrode assembly manufacturing process and battery operation.

[0129] [Explanation of reference numerals]

[0130] 1: porous polymer substrate

[0131] 3: organic / inorganic composite porous coating layer

[0132] 5: hybrid polymer particles

[0133] 7: acrylic polymer particles

[0134] 9: first inorganic particles

[0135] 10: separator

Claims

1. An electrochemical device separator comprising a porous polymer substrate and an organic / inorganic composite porous coating layer formed on at least one side of the polymer substrate, wherein the organic / inorganic composite porous coating layer comprises particulate binder polymers and first inorganic particles, the particulate binder polymers comprise hybrid polymer particles of a fluorine-based polymer and an acrylic polymer and acrylic polymer particles, a particle size D50"a" of the acrylic polymer particles is in a range of 1 pm to 7 pm, a particle size D50"b" of the first inorganic particles is in a range of 200 nm to 800 nm, a / b is 2 to 15, and a particle size D50 of the hybrid polymer particles is less than a particle size D50 of the acrylic polymer particles.

2. The separator according to claim 1, wherein the particle size D50"a" of the acrylic polymer particles is in a range of 2 pm to 6 pm, and the particle size D50"b" of the first inorganic particles is in a range of 300 nm to 700 nm, and a / b is 5 to 12.

3. The separator according to claim 1, wherein the particle size D50 of the acrylic polymer particles is 4 to 20 times larger than the particle size D50 of the hybrid polymer particles.

4. The separator according to claim 1, wherein the particle size D50 of the hybrid polymer particles is in a range of 100 nm to 500 nm.

5. The separator according to claim 1, wherein the hybrid polymer particles and the acrylic polymer particles are mixed at a weight ratio of 8:2 to 2:

8.

6. The separator according to claim 1, wherein a Tg of the acrylic polymer included in the hybrid polymer particles is 10°C or more lower than a Tg of the acrylic polymer included in the acrylic polymer particles.

7. The separator according to claim 6, wherein the Tg of the acrylic polymer included in the hybrid polymer particles is in a range of 10°C to 30°C, and the Tg of the acrylic polymer included in the acrylic polymer particles is in a range of 30°C to 50°C.

8. The separator according to claim 1, wherein the fluorine-based polymer is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride with other polymerizable monomers, or a mixture of two or more thereof.

9. The separator according to claim 8, wherein the monomer includes at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3 dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene, and fluoroethylene.

10. The separator according to claim 8, wherein the fluorine-based polymer is a copolymer of vinylidene fluoride with hexafluoropropylene.

11. The separator according to claim 8, wherein a content of the monomer is 1 to 20% by weight of the copolymer.

12. The separator according to claim 1, wherein the acrylic polymer constituting the hybrid polymer particles and the acrylic polymer constituting the acrylic polymer particles each independently comprises (meth)acrylic alkyl ester repeating units having an alkyl group of 1 to 18 carbon atoms.

13. The separator according to claim 1, wherein the organic / inorganic composite porous coating layer further comprises a non-particulate acrylic polymer.

14. The separator according to claim 13, wherein the non-particulate acrylic polymer has a Tg of 0°C or lower.

15. The separator according to claim 1, wherein the organic / inorganic composite porous coating layer comprises second inorganic particles different from the first inorganic particles, and the particle size D50 of the second inorganic particles is smaller than the particle size D50 of the first inorganic particles.

16. The separator according to claim 15, wherein the particle size D50 of the second inorganic particles is in the range of 100 to 500 pm.

17. The separator according to claim 15, wherein the first inorganic particles are alumina, and the second inorganic particles are boehmite.

18. The separator according to claim 1, wherein the organic / inorganic composite porous coating layer comprises the particulate binder polymer in an amount of 1 to 30% by weight, based on the total weight of the organic / inorganic composite porous coating layer.

19. The separator according to claim 1, wherein the organic / inorganic composite porous coating layer is formed by coating and drying a slurry in which the particulate binder polymer and the inorganic particles are dispersed in an aqueous dispersion medium on at least one surface of the porous polymer substrate.

20. An electrochemical device comprising an anode, a cathode, and a separator interposed between the anode and the cathode, wherein the separator is the separator according to any one of claims 1 to 19.

21. The electrochemical device according to claim 20, wherein the electrochemical device is a lithium secondary battery.

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