Diaphragm and method of manufacturing and use thereof

Abstract

This invention specifically relates to a separator, its preparation method, and its application. The separator comprises a base membrane and a coating. The coating is disposed on at least one surface of the base membrane, and the coating, from the inside out, comprises a ceramic material coating and a binder coating containing carbon fibers. This separator exhibits high thermal stability, mechanical strength, and ionic conductivity, making it particularly suitable for use in batteries, especially in rechargeable batteries. When applied to rechargeable batteries, it can effectively enhance battery performance and safety, and extend battery life.

Description

Technical Field

[0001] This invention relates to a diaphragm, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy technologies, secondary batteries, as key components with great potential for energy storage and conversion, have received increasingly widespread and in-depth attention regarding their performance and safety. Among them, the secondary battery separator plays a crucial role in the entire battery system. Its main function is to accurately separate the positive and negative electrodes, effectively prevent short circuits, and ensure the smooth passage of ions.

[0003] However, traditional secondary battery separators often exhibit numerous defects when faced with harsh conditions such as high temperatures and high-rate charging and discharging. For example, poor thermal stability makes the separator prone to shrinkage or even deformation at high temperatures, greatly increasing the risk of battery short circuits. Furthermore, low ion conductivity leads to increased internal resistance, which not only severely restricts the battery's charging and discharging performance but also increases energy loss, significantly reducing the overall efficiency of the battery and seriously affecting its practical application and safety.

[0004] Therefore, it is necessary to develop a secondary battery separator with excellent thermal stability, mechanical strength and ionic conductivity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, one of the technical problems this invention aims to solve is to provide a novel separator with high thermal stability, mechanical strength, and ionic conductivity, making it particularly suitable for use in batteries, especially in rechargeable batteries.

[0006] To achieve the above objectives, a first aspect of the present invention provides a diaphragm comprising: a base membrane and a coating, wherein the coating is disposed on at least one surface of the base membrane, and the coating comprises, from the inside out, a ceramic material coating and a binder coating containing carbon fibers.

[0007] A second aspect of the present invention provides a method for preparing the diaphragm described herein, the method comprising:

[0008] (1) In the presence of a first solvent, ceramic material is mixed with a surfactant, and the first slurry obtained by mixing is coated on at least one surface of a base film. After drying and plasma cleaning, a base film containing a ceramic material coating is obtained.

[0009] (2) In the presence of a second solvent, the binder is mixed with carbon fiber, and the resulting second slurry is coated on the surface of the ceramic material coating and dried.

[0010] A third aspect of the present invention provides a diaphragm prepared by the preparation method described herein.

[0011] The fourth aspect of the present invention provides the application of the separator described herein in a battery, preferably in a secondary battery, and more preferably in a sodium-ion battery.

[0012] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0013] (1) The diaphragm described in this invention has excellent thermal stability, making it less prone to shrinkage and deformation in high-temperature environments. When applied in batteries, it can effectively prevent battery short circuits and improve battery safety.

[0014] (2) The diaphragm described in this invention has good mechanical strength and can better withstand the volume changes during the charging and discharging process of the battery, thus extending the battery's service life.

[0015] (3) The separator described in this invention has a high ion conductivity. When applied to a battery, it can reduce the battery's internal resistance and improve the battery's charge and discharge performance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the diaphragm prepared in Example 1 of the present invention. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0019] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0020] When this specification uses the prefixes "known to those skilled in the art," "prior art," or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those conventionally used in the art at the time the invention was proposed, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0021] It should be noted that the two or more aspects (or embodiments) disclosed in the context of this specification can be arbitrarily combined with each other, and the resulting technical solutions (such as methods or systems) are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0022] This invention provides a separator comprising: a base membrane and a coating, wherein the coating is disposed on at least one surface of the base membrane, and the coating comprises, from the inside out, a ceramic material coating and a binder coating containing carbon fibers. The separator of this invention exhibits high thermal stability, mechanical strength, and ionic conductivity, making it particularly suitable for applications in batteries, especially in rechargeable batteries.

[0023] In this invention, the carbon fiber content in the diaphragm can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the carbon fiber content is 1-15 wt% based on the total mass of the diaphragm, preferably 3-8 wt%. The diaphragm using the aforementioned preferred carbon fiber content has high thermal stability, mechanical strength, and ionic conductivity.

[0024] In this invention, the thickness of the diaphragm can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the thickness of the diaphragm is 10-50 μm, preferably 20-30 μm.

[0025] In this invention, the transverse tensile strength of the diaphragm can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the transverse tensile strength of the diaphragm is 10-15 MPa, preferably 13-15 MPa.

[0026] In this invention, the longitudinal tensile strength of the diaphragm can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the longitudinal tensile strength of the diaphragm is 10-15 MPa, preferably 13-15 MPa.

[0027] In this invention, the ionic conductivity of the diaphragm can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the ionic conductivity of the diaphragm is 2.2-3.5 S / cm, preferably 2.9-3.3 S / cm.

[0028] The aforementioned preferred separator has the advantages of being able to better withstand volume changes during battery charging and discharging, extending battery life, and improving battery charging and discharging performance.

[0029] In this invention, the base membrane can be selected from a wide range of materials. The following examples are illustrative but do not limit the scope of the invention. According to a preferred embodiment of the invention, the base membrane material is selected from polyacrylonitrile and / or polypropylene, preferably a mixture of polyacrylonitrile and polypropylene. The mass ratio of polyacrylonitrile to polypropylene is not particularly required. According to a preferred embodiment of the invention, the mass ratio of polyacrylonitrile to polypropylene is 1:0.5-5. The separator prepared using the aforementioned preferred base membrane has good thermal stability, making it less prone to shrinkage and deformation under high-temperature environments. When used in batteries, it can effectively prevent battery short circuits and improve battery safety.

[0030] In this invention, the thickness of the base film can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the thickness of the base film is 10-30 μm, preferably 18-22 μm.

[0031] In this invention, the air permeability value of the base membrane can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the air permeability value of the base membrane is 80-250 sec / 100cc, preferably 120-180 sec / 100cc.

[0032] In this invention, the porosity of the base membrane can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the porosity of the base membrane is 30-60%, preferably 40-50%.

[0033] In this invention, the ceramic material coating can be selected from a wide range of types. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the ceramic material is selected from one or more of alumina, boehmite, kaolin, sepiolite, halloysite, and titanium dioxide. Preferably, the ceramic material is selected from a mixture of alumina, boehmite, kaolin, and titanium dioxide, with each component having a content of not less than 10 wt%, and more preferably, a content of 10-70 wt%. The separator prepared using the aforementioned preferred ceramic material has high thermal stability, mechanical strength, and ionic conductivity, making it particularly suitable for applications in batteries, especially in secondary batteries.

[0034] In this invention, the ceramic material coating also includes a surfactant. The range of surfactants that can be selected is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the surfactant is selected from one or more of Span 85, Span 80, Span 65, polyoxyethylene sorbitan hexastearate, and ethylene glycol fatty acid esters, preferably Span 80.

[0035] In this invention, the amount of ceramic material and surfactant can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the mass ratio of ceramic material to surfactant is 1:0.02-0.1, preferably 1:0.04-0.06.

[0036] In this invention, the thickness of the ceramic material coating can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the thickness of the ceramic material coating is 0.1-2 μm, preferably 0.8-1.2 μm.

[0037] In this invention, the size range of the carbon fibers in the carbon fiber-containing binder coating is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the diameter of the carbon fibers is 5-10 μm and the length is 50-200 μm; preferably, the diameter of the carbon fibers is 7.5-9 μm and the length is 100-180 μm. The diaphragm prepared using the aforementioned preferred carbon fiber dimensions exhibits high thermal stability, mechanical strength, and ionic conductivity.

[0038] In this invention, the tensile strength of the carbon fiber can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the tensile strength of the carbon fiber is 3.5-5 GPa.

[0039] In this invention, the tensile modulus of the carbon fiber can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the tensile modulus of the carbon fiber is 200-250 GPa.

[0040] In this invention, there are no special requirements for the pretreatment method of the carbon fiber. Conventional treatment methods in the art can be used in this invention, such as electrochemical treatment of the carbon fiber surface.

[0041] In this invention, the range of types of binders is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the binder is selected from one or more of polyvinylidene fluoride, polyvinylpyrrolidone, and polymethyl methacrylate, preferably a mixture of polyvinylidene fluoride, polymethyl methacrylate, and polyvinylpyrrolidone, with each component having a content of not less than 20 wt%, and more preferably 30-70 wt%. The separator prepared using the aforementioned preferred binder has good mechanical strength and, when applied in a battery, can better withstand volume changes during battery charging and discharging, thus extending the battery's lifespan.

[0042] In this invention, the mass ratio of the binder to the carbon fiber can be selected within a wide range. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of the binder to the carbon fiber is 1:0.3-1, preferably 1:0.5-0.7. The diaphragm prepared using the aforementioned preferred mass ratio of binder to carbon fiber exhibits high thermal stability, mechanical strength, and ionic conductivity.

[0043] In this invention, the thickness of the adhesive coating containing carbon fibers can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the thickness of the adhesive coating containing carbon fibers is 0.1-12 μm, preferably 3-6 μm.

[0044] Membranes possessing the aforementioned features of this invention can all achieve the objectives of this invention. There are no special requirements for their preparation methods. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, this invention provides a method for preparing the membrane described in this invention, the method comprising:

[0045] (1) In the presence of a first solvent, ceramic material is mixed with a surfactant, and the first slurry obtained by mixing is coated on at least one surface of a base film. After drying and plasma cleaning, a base film containing a ceramic material coating is obtained.

[0046] (2) In the presence of a second solvent, the binder is mixed with carbon fiber, and the resulting second slurry is coated on the surface of the ceramic material coating and dried.

[0047] In this invention, the range of types of the first solvent is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the first solvent is selected from one or more of water, anhydrous ethanol, and dimethyl sulfoxide, preferably a mixture of water and anhydrous ethanol. There are no special requirements for the mass ratio of water to anhydrous ethanol. According to a preferred embodiment of the invention, the mass ratio of water to anhydrous ethanol is 1:0.5-2.

[0048] In this invention, the mass ratio of the ceramic material to the first solvent can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of the ceramic material to the first solvent is 1-50:1-100, preferably 20-40:40-80.

[0049] In this invention, the range of types of the second solvent is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the second solvent is selected from one or more of acetone, N-methylpyrrolidone, and N,N-dimethylformamide, preferably a mixture of acetone, N-methylpyrrolidone and N,N-dimethylformamide, with each solvent having a content of not less than 20 wt%, preferably 30-70 wt%.

[0050] In this invention, the mass ratio of the adhesive to the second solvent can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of the adhesive to the second solvent is 0.5-2:1, preferably 1-1.5:1.

[0051] In this invention, there are no special requirements for the drying method described in steps (1) and (2). The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the drying in steps (1) and (2) is vacuum drying. There are no special requirements for the vacuum pressure, which can be selected according to actual needs. For example, the vacuum pressure can be 20-60 kPa.

[0052] According to a preferred embodiment of the present invention, the drying in steps (1) and (2) each includes a first drying and a second drying.

[0053] In this invention, the temperature range for the first drying step is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature for the first drying step is 70-90°C.

[0054] In this invention, the first drying time can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the first drying time is 0.5-1h.

[0055] In this invention, the temperature range for the second drying is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature for the second drying is 90-110°C.

[0056] In this invention, the second drying time can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the second drying time is 0.5-1h.

[0057] In this invention, plasma cleaning is used to improve mechanical interlocking ability and increase adhesion performance. There are no special requirements for the plasma cleaning instrument. Conventional plasma cleaning instruments in the field can be used in this invention, such as vacuum plasma cleaners.

[0058] This invention provides a membrane prepared by the method described herein. The membrane of this invention exhibits high thermal stability, mechanical strength, and ionic conductivity.

[0059] This invention provides the application of the separator described herein in batteries, preferably in secondary batteries, and more preferably in sodium-ion batteries.

[0060] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0061] (1) The diaphragm described in this invention has excellent thermal stability, making it less prone to shrinkage and deformation in high-temperature environments. When applied in batteries, it can effectively prevent battery short circuits and improve battery safety.

[0062] (2) The diaphragm described in this invention has good mechanical strength and can better withstand the volume changes during the charging and discharging process of the battery, thus extending the battery's service life.

[0063] (3) The separator described in this invention has a high ion conductivity. When applied to a battery, it can reduce the battery's internal resistance and improve the battery's charge and discharge performance.

[0064] The present invention will be described in detail below through embodiments. In the following embodiments, the thicknesses of the diaphragm, the ceramic material coating, and the binder coating containing carbon fibers were measured using a membrane thickness tester (Keyence SI-T); the air permeability of the base membrane was measured using a proton exchange membrane air permeability tester; the porosity of the base membrane was measured using a metallographic microscope; and the diameter and length of the carbon fibers were measured using a scanning electron microscope.

[0065] In this invention, the polyacrylonitrile raw material is a commercially available product with brand name XW0125014419010 from Sinopharm Chemical Reagent Co., Ltd.; the polypropylene raw material is a commercially available product with brand name M800E from Shanghai Petrochemical Co., Ltd. Carbon fiber was purchased from Shanghai Petrochemical Co., Ltd. Polyvinylpyrrolidone, polymethyl methacrylate, and polyvinylidene fluoride were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0066] In this invention, a base film is prepared by mixing polyacrylonitrile, polypropylene powder and solvent, degassing and placing the mixture in a film-forming instrument, and then performing plasma cleaning treatment using a vacuum plasma cleaner.

[0067] Example 1

[0068] A base film with a thickness of 10 μm was prepared using polyacrylonitrile, with an air permeability of 80 sec / 100 cc and a porosity of 30%.

[0069] Preparation of ceramic material coating: A mixed ceramic material consisting of 40 wt% alumina, 30 wt% boehmite and 30 wt% kaolin was added to a solvent water and mixed with a surfactant (Span 85). The mass ratio of the mixed ceramic material to the solvent water was 1:10, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.02. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 0.1 μm was obtained and coated on one side of the base film.

[0070] Preparation of the diaphragm: In acetone solvent, polyvinylidene fluoride (PVDF) binder was mixed with carbon fibers that had undergone electrochemical surface oxidation treatment (the tensile strength of the carbon fibers was 3.5 GPa, and the tensile modulus was 200 GPa, the same in the following examples). The carbon fibers had a diameter of 5 μm and a length of 50 μm. The mass ratio of PVDF binder to acetone solvent was 0.5:1, and the mass ratio of PVDF binder to carbon fibers was 1:0.3. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum dried at 80°C and 50 kPa for 0.5 h, followed by vacuum drying at 100°C and 50 kPa for 0.5 h to obtain the diaphragm.

[0071] The membrane has a thickness of 10.2 μm, the binder coating containing carbon fibers has a thickness of 0.1 μm, and the carbon fiber content is 1% by the total mass of the membrane.

[0072] Example 2

[0073] A base membrane with a thickness of 20 μm was made from polypropylene, with an air permeability of 160 sec / 100 cc and a porosity of 45%.

[0074] Preparation of ceramic material coating: A mixed ceramic material of 50 wt% alumina and 50 wt% titanium dioxide was added to anhydrous ethanol and mixed with surfactant (Span 80). The mass ratio of the mixed ceramic material to anhydrous ethanol was 25:50, and the mass ratio of the mixed ceramic material to surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 1 μm was obtained and coated on both sides of the base film.

[0075] Preparation of the diaphragm: Polyvinylpyrrolidone (PVP) binder was mixed with electrochemically surface-oxidized carbon fibers in N-methylpyrrolidone solvent. The carbon fibers had a diameter of 7 μm and a length of 120 μm. The mass ratio of PPV binder to N-methylpyrrolidone solvent was 1:1, and the mass ratio of PPV binder to carbon fibers was 1:0.5. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm.

[0076] A schematic diagram of the diaphragm structure is shown below. Figure 1 As shown, the membrane thickness is 26 μm, the binder coating containing carbon fibers is 5 μm thick, and the carbon fiber content is 5% based on the total mass of the membrane.

[0077] Example 3

[0078] A base film with a thickness of 30 μm was prepared using polyacrylonitrile, with an air permeability of 250 sec / 100 cc and a porosity of 60%.

[0079] Preparation of ceramic material coating: Kaolin ceramic material was added to anhydrous ethanol solvent and mixed with surfactant (Span 65). The mass ratio of mixed ceramic material to anhydrous ethanol solvent was 50:100, and the mass ratio of mixed ceramic material to surfactant was 1:0.08. The mixture was first vacuum dried at 80℃ and 50kPa for 0.5h, and then vacuum dried at 100℃ and 50kPa for 0.5h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 2μm was obtained and coated on one side of the base film.

[0080] Preparation of the diaphragm: In N,N-dimethylformamide solvent, polymethyl methacrylate binder and carbon fibers that have undergone electrochemical surface oxidation treatment were mixed, wherein the carbon fibers had a diameter of 10 μm and a length of 200 μm, the mass ratio of polyvinylidene fluoride to solvent acetone was 2:1, and the mass ratio of polymethyl methacrylate to carbon fibers was 1:1. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm;

[0081] The membrane thickness is 42 μm, the binder coating containing carbon fibers is 10 μm thick, and the carbon fiber content is 10% based on the total mass of the membrane.

[0082] Example 4

[0083] A base film with a thickness of 15 μm was prepared by using a mixture of polyacrylonitrile and polypropylene with a mass ratio of 1:1. The film had an air permeability of 100 sec / 100 cc and a porosity of 35%.

[0084] Preparation of ceramic material coating: A mixed ceramic material consisting of 40 wt% alumina, 30 wt% boehmite and 30 wt% titanium dioxide was added to a solvent (50 wt% water and 50 wt% anhydrous ethanol) and mixed with a surfactant (Span 80). The mass ratio of the mixed ceramic material to the solvent was 10:20, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 0.5 μm was obtained and coated on both sides of the base film.

[0085] Preparation of the diaphragm: Polyvinylidene fluoride (PVDF) binder was mixed with electrochemically surface-oxidized carbon fibers in a solvent (50 wt% acetone, 50 wt% N-methylpyrrolidone). The carbon fibers had a diameter of 6 μm and a length of 80 μm. The mass ratio of PVDF to solvent was 1:1, and the mass ratio of PVDF to carbon fibers was 1:0.5. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum-drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm.

[0086] The membrane thickness is 17.5 μm, the binder coating containing carbon fibers is 2 μm thick, and the carbon fiber content is 2% by the total mass of the membrane.

[0087] Example 5

[0088] A base membrane with a thickness of 25 μm was made from polypropylene, with an air permeability of 200 sec / 100 cc and a porosity of 55%.

[0089] Preparation of ceramic material coating: A mixed ceramic material of 50 wt% kaolin and 50 wt% titanium dioxide was added to a solvent water and mixed with a surfactant (Span 80). The mass ratio of the mixed ceramic material to the solvent water was 30:70, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 1.5 μm was obtained and coated on one side of the base film.

[0090] Preparation of the diaphragm: Polymethyl methacrylate (PMMA) binder was mixed with electrochemically surface-oxidized carbon fibers in N,N-dimethylformamide solvent. The carbon fibers had a diameter of 8 μm and a length of 150 μm. The mass ratio of binder to N,N-dimethylformamide solvent was 1:1, and the mass ratio of binder to carbon fibers was 1:0.5. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum-drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm.

[0091] The membrane thickness is 34.5 μm, the binder coating containing carbon fibers is 8 μm thick, and the carbon fiber content is 7% by the total mass of the membrane.

[0092] Example 6

[0093] A base film with a thickness of 18 μm was prepared by using a mixture of polyacrylonitrile and polypropylene with a mass ratio of 1:1. The film had an air permeability of 120 sec / 100 cc and a porosity of 40%.

[0094] Preparation of ceramic material coating: A mixed ceramic material consisting of 25 wt% alumina, 25 wt% boehmite, 25 wt% kaolin and 25 wt% titanium dioxide was added to a solvent (50 wt% water and 50 wt% anhydrous ethanol) and mixed with a surfactant (Span 80). The mass ratio of the mixed ceramic material to the solvent was 20:40, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 0.8 μm was obtained and coated on both sides of the base film.

[0095] Preparation of the diaphragm: In a solvent (50 wt% N-methylpyrrolidone, 50 wt% N,N-dimethylformamide), a binder (50 wt% polyvinylidene fluoride and 50 wt% polyvinylpyrrolidone) was mixed with electrochemically surface-oxidized carbon fibers. The carbon fibers had a diameter of 7.5 μm and a length of 100 μm. The mass ratio of binder to solvent was 1:1, and the mass ratio of binder to carbon fibers was 1:0.5. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum-drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm.

[0096] The membrane thickness is 21.8 μm, the binder coating containing carbon fibers is 3 μm thick, and the carbon fiber content is 4% by the total mass of the membrane.

[0097] Example 7

[0098] A base film with a thickness of 22 μm was prepared by using polyacrylonitrile and polypropylene in a mass ratio of 1:1. The film had an air permeability of 180 sec / 100 cc and a porosity of 50%.

[0099] Preparation of ceramic material coating: A mixed ceramic material consisting of 40 wt% boehmite, 30 wt% kaolinite and 30 wt% titanium dioxide was added to a solvent (50 wt% water and 50 wt% anhydrous ethanol) and mixed with a surfactant (Span 80). The mass ratio of the mixed ceramic material to the solvent was 40:80, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ and 50 kPa for 0.5 h, and then vacuum dried at 100℃ and 50 kPa for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 1.2 μm was obtained and coated on one side of the base film.

[0100] Preparation of the diaphragm: In a solvent (50 wt% acetone, 50 wt% N,N-dimethylformamide), a binder (50 wt% polyvinylpyrrolidone, 50 wt% polymethyl methacrylate) was mixed with carbon fibers that had undergone electrochemical surface oxidation treatment. The carbon fibers had a diameter of 9 μm and a length of 180 μm. The mass ratio of binder to solvent was 1:1, and the mass ratio of binder to carbon fibers was 1:0.6. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80℃ and 50 kPa for 0.5 h, followed by vacuum-drying at 100℃ and 50 kPa for 0.5 h to obtain the diaphragm.

[0101] The membrane thickness is 29.2 μm, the binder coating containing carbon fibers is 6 μm thick, and the carbon fiber content is 8% by the total mass of the membrane.

[0102] Example 8

[0103] The method steps are the same as in Example 6, except that the adhesive is polyvinylidene fluoride.

[0104] The resulting diaphragm has a thickness of 19.8 μm, and the binder coating containing carbon fibers has a thickness of 1 μm. The carbon fiber content is 1% based on the total mass of the diaphragm.

[0105] Example 9

[0106] The method steps are the same as in Example 6, except that the diameter of the carbon fiber is 5 μm and the length is 50 μm.

[0107] The resulting diaphragm has a thickness of 26.8 μm, and the binder coating containing carbon fibers has a thickness of 8 μm. The carbon fiber content is 9% based on the total mass of the diaphragm.

[0108] Example 10

[0109] The method steps are the same as in Example 6, except that the mass ratio of the binder to the carbon fiber is 1:0.3.

[0110] The resulting diaphragm has a thickness of 29.8 μm, and the binder coating containing carbon fibers has a thickness of 11 μm. The carbon fiber content is 12% based on the total mass of the diaphragm.

[0111] Comparative Example 1

[0112] A base film with a thickness of 18 μm was prepared by using a mixture of polyacrylonitrile and polypropylene with a mass ratio of 1:1. The film had an air permeability of 120 sec / 100 cc and a porosity of 40%.

[0113] Preparation of ceramic material coating: A mixed ceramic material consisting of 25 wt% alumina, 25 wt% boehmite, 25 wt% kaolin and 25 wt% titanium dioxide was added to a solvent (50 wt% water, 50 wt% anhydrous ethanol) and mixed with a surfactant (Span 80). The mass ratio of the mixed ceramic material to the solvent was 20:40, and the mass ratio of the mixed ceramic material to the surfactant was 1:0.05. The mixture was first vacuum dried at 80℃ for 0.5 h, and then vacuum dried at 100℃ for 0.5 h. After cleaning with a vacuum plasma cleaner, a ceramic material coating with a thickness of 0.8 μm was obtained and coated on both sides of the base film.

[0114] Preparation of the diaphragm: A binder (50 wt% polyvinylidene fluoride and 50 wt% polyvinylpyrrolidone) was added to a solvent (50 wt% N-methylpyrrolidone and 50 wt% N,N-dimethylformamide), with a binder-to-solvent mass ratio of 1:1. The resulting slurry was coated onto the surface of a ceramic material coating, and then vacuum-dried at 80°C for 0.5 h, followed by vacuum-drying at 100°C for 0.5 h to obtain the diaphragm.

[0115] The thickness of the diaphragm is 21.8 μm.

[0116] The diaphragms prepared in the above examples and comparative examples were subjected to longitudinal shrinkage rate tests at different temperatures. The test standard was GB / T 1040.3-2006, and the test instrument was a Zwick / Roell Z010. The test results are shown in Table 1.

[0117] Table 1

[0118]

[0119] As can be seen from the results in Table 1, the diaphragm described in this invention has high thermal stability and mechanical strength.

[0120] The separators prepared in the above examples and comparative examples were used to assemble batteries. Na2M[Fe(CN)6] positive electrode, hard carbon negative electrode, EC / PC, and 1M NaClO4 electrolyte were used. The ion conductivity of the assembled batteries was tested, and the test results are shown in Table 2.

[0121] Table 2

[0122]

[0123]

[0124] As can be seen from the results in Table 2, the battery assembled using the separator described in this invention has a high ion conductivity.

[0125] The tensile strength of the diaphragms prepared in the above embodiments and comparative examples was tested according to GB / T 1040.3-2006, and the testing instrument was a Zwick / Roell Z010. The test results are shown in Table 3.

[0126] Table 3

[0127] Example Transverse tensile strength TD (MPa) Longitudinal tensile strength MD (MPa) Example 1 12.5 12.7 Example 2 11.1 10.9 Example 3 12.2 12.4 Example 4 12.9 13.0 Example 5 10.8 11.0 Example 6 13.6 13.8 Example 7 13.3 13.4 Example 8 11.6 11.5 Example 9 10.5 10.4 Example 10 10.1 10.1 Comparative Example 1 9.0 9.3

[0128] As can be seen from the results in Table 3, the diaphragm described in this invention has high mechanical strength.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base membrane and a coating, wherein the coating is disposed on at least one surface of the base membrane, and the coating comprises, from the inside out, a ceramic material coating and a binder coating containing carbon fibers.

2. The diaphragm according to claim 1, wherein, The carbon fiber content is 1-15 wt%, preferably 3-8 wt%, based on the total mass of the diaphragm; and / or The thickness of the diaphragm is 10-50 μm, preferably 20-30 μm; and / or The diaphragm has a transverse tensile strength of 10-15 MPa, preferably 13-15 MPa; and / or The longitudinal tensile strength of the diaphragm is 10-15 MPa, preferably 13-15 MPa; and / or The ionic conductivity of the membrane is 2.2-3.5 S / cm, preferably 2.9-3.3 S / cm.

3. The diaphragm according to claim 1 or 2, wherein, The base film is made of polyacrylonitrile and / or polypropylene, preferably a mixture of polyacrylonitrile and polypropylene, wherein the mass ratio of polyacrylonitrile to polypropylene is 1:0.5-5; and / or The thickness of the base film is 10-30 μm, preferably 18-22 μm; and / or The air permeability of the base membrane is 80-250 sec / 100cc, preferably 120-180 sec / 100cc; and / or The porosity of the base membrane is 30-60%, preferably 40-50%.

4. The diaphragm according to any one of claims 1-3, wherein, In the ceramic material coating The ceramic material is selected from one or more of alumina, boehmite, kaolin, sepiolite, halloysite, and titanium dioxide, preferably a mixture of alumina, boehmite, kaolin, and titanium dioxide, with each component comprising not less than 10 wt%, and more preferably 10-70 wt%; and / or The ceramic material coating further includes a surfactant selected from one or more of Span 85, Span 80, Span 65, polyoxyethylene sorbitan hexastearate, and ethylene glycol fatty acid esters, preferably Span 80; and / or The mass ratio of the ceramic material to the surfactant is 1:0.02-0.1, preferably 1:0.04-0.06; and / or The thickness of the ceramic material coating is 0.1-2 μm, preferably 0.8-1.2 μm.

5. The diaphragm according to any one of claims 1-4, wherein, In the adhesive coating containing carbon fibers, The carbon fiber has a diameter of 5-10 μm and a length of 50-200 μm, preferably a diameter of 7.5-9 μm and a length of 100-180 μm; and / or The tensile strength of the carbon fiber is 3.5-5 GPa; and / or The tensile modulus of the carbon fiber is 200-250 GPa; and / or The adhesive is selected from one or more of polyvinylidene fluoride, polyvinylpyrrolidone, and polymethyl methacrylate, preferably a mixture of polyvinylidene fluoride, polymethyl methacrylate, and polyvinylpyrrolidone, with each component having a content of not less than 20 wt%, and more preferably 30-70 wt%; and / or The mass ratio of the binder to the carbon fiber is 1:0.3-1, preferably 1:0.5-0.7; and / or The thickness of the adhesive coating containing carbon fibers is 0.1-12 μm, preferably 3-6 μm.

6. A method for preparing a diaphragm according to any one of claims 1-5, characterized in that, The method includes: (1) In the presence of a first solvent, ceramic material is mixed with a surfactant, and the first slurry obtained by mixing is coated on at least one surface of a base film. After drying and plasma cleaning, a base film containing a ceramic material coating is obtained. (2) In the presence of a second solvent, the binder is mixed with carbon fiber, and the resulting second slurry is coated on the surface of the ceramic material coating and dried.

7. The preparation method according to claim 6, wherein, The first solvent is selected from one or more of water, anhydrous ethanol, and dimethyl sulfoxide, preferably a mixture of water and anhydrous ethanol, wherein the mass ratio of water to anhydrous ethanol is 1:0.5-2; and / or The mass ratio of the ceramic material to the first solvent is 1-50:1-100, preferably 20-40:40-80; and / or The second solvent is selected from one or more of acetone, N-methylpyrrolidone, and N,N-dimethylformamide, preferably a mixture of acetone, N-methylpyrrolidone, and N,N-dimethylformamide, with each solvent having a content of not less than 20 wt%, preferably 30-70 wt%; and / or The mass ratio of the adhesive to the second solvent is 0.5-2:1, preferably 1-1.5:

1.

8. The preparation method according to claim 6 or 7, wherein, In steps (1) and (2), Each of the drying processes is a vacuum drying process; and / or The drying process includes a first drying and a second drying. Preferably, the drying conditions each include: First drying: temperature 70-90℃, time 0.5-1h; and / or Second drying: temperature 90-110℃, time 0.5-1h.

9. The diaphragm prepared by the preparation method according to any one of claims 6-8.

10. The application of the separator according to any one of claims 1-5, 9 in a battery, preferably in a secondary battery, and more preferably in a sodium-ion battery.

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