Composite diaphragm, preparation method and application thereof, and lithium-sulfur battery

Abstract

The invention relates to the technical field of membrane materials, in particular to a composite membrane, a preparation method and application thereof and a lithium-sulfur battery, the composite membrane comprises a matrix membrane and a composite layer arranged on the surface of the matrix membrane, and the composite layer contains an SCM-36 molecular sieve and a conductive material; the composite layer of the composite diaphragm contains the SCM-36 molecular sieve, so that the cycling stability and the capacity of the lithium battery (such as a lithium-sulfur battery) can be improved when the composite diaphragm is used for the lithium battery (such as the lithium-sulfur battery).

Description

Technical Field

[0001] The present invention relates to the technical field of membrane materials, and particularly to a composite separator, a preparation method and application thereof, and a lithium-sulfur battery. Background Art

[0002] Lithium-sulfur batteries have the advantages of high specific capacity (1675 mAh / g) and energy density (2600 Wh / kg) in the next-generation secondary battery system, and can be used as an ideal alternative to future lithium-ion batteries to meet the requirements for high-energy-density batteries in electric vehicles, drones, aerospace, etc. In addition, the sulfur cathode of lithium-sulfur batteries also has the advantages of rich reserves, low price, and environmental friendliness.

[0003] However, the commercial application of current lithium-sulfur batteries still faces many challenges, such as the low ionic / electronic conductivity of sulfur and the discharge product lithium sulfide, the large volume change of the sulfur cathode during charge and discharge, and the "shuttle effect" caused by polysulfides. Among them, the side reaction inside the battery - the "shuttle effect" is the biggest obstacle restricting its application. Specifically, the shuttle effect means that a series of sulfur-containing intermediate products are generated during the charge and discharge process of lithium-sulfur batteries. Among them, long-chain polysulfides (Li2S x , 2 < x ≤ 8) are easily soluble in conventional electrolytes, and under the action of the concentration gradient and electric field, they pass through the separator and chemically react with the lithium anode, resulting in the loss of active substances and the corrosion of the lithium anode, thereby causing the reduction of battery capacity and the decline of cycle performance. Therefore, inhibiting the shuttle effect is one of the most effective strategies to improve the performance of lithium-sulfur batteries.

[0004] Currently, the prior art has modified ordinary separators to inhibit the shuttle effect of lithium-sulfur batteries. Commonly used separator modification materials include porous carbon, inorganic compounds, metal-organic framework materials, etc., but they have problems such as limited effect, complex synthesis process, and high cost. In order to improve the electrochemical performance of lithium-sulfur batteries to meet the requirements of new energy electric vehicles and large-capacity energy storage systems for higher-energy-density batteries, the development of separators with excellent performance is a key topic一直在研究的重点课题 in this field. Summary of the Invention

[0005] In view of the above problems of the prior art, the present invention provides a composite separator, a preparation method and application thereof, and a lithium-sulfur battery; the composite separator is used for lithium batteries and can improve the capacity and cycle performance of lithium-sulfur batteries.

[0006] To achieve the above object, in the first aspect of the present invention, a composite separator is provided, which includes: a base film and a composite layer disposed on the surface of the base film, and the composite layer contains SCM-36 molecular sieve and a conductive material.

[0007] In the second aspect of the present invention, a preparation method of the composite separator of the present invention is provided, and the method includes:

[0008] S1. Disperse the SCM-36 molecular sieve and conductive material in a solvent to prepare a slurry;

[0009] S2. Coat the slurry onto the surface of the substrate film and remove the solvent.

[0010] A third aspect of the present invention provides an application of the composite separator described herein in a lithium battery.

[0011] A fourth aspect of the present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator comprises the composite separator described in the present invention.

[0012] Through the above technical solution, the composite layer of the composite membrane of the present invention contains SCM-36 molecular sieve, which can improve the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries) when used in lithium batteries (e.g., lithium-sulfur batteries). Attached Figure Description

[0013] Figure 1 This is the XRD pattern of the SCM-36 molecular sieve in Example 1;

[0014] Figure 2 This is a SEM image of the SCM-36 molecular sieve in Example 1;

[0015] Figure 3 This is the first charge-discharge curve of the lithium-sulfur battery in Example 1 at 0.5C;

[0016] Figure 4 This is a cycle test diagram of the lithium-sulfur battery in Example 1 at 0.5C. 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] In the context of this specification, the structure of the sample was determined by X-ray diffraction (XRD), which was measured using an X-ray powder diffractometer with a Cu-Kα ray source and a nickel filter. In the context of this specification, including the examples and comparative examples below, the X-ray powder diffractometer used for analyzing the phases of the sample was a Panalytical XPERPRO type X-ray powder diffractometer, with a Cu-Kα ray source. Nickel filter, 2θ scanning range 2~50°, operating voltage 40kV, current 40mA, scanning rate 10° / min.

[0019] In the context of this specification, in the XRD data of molecular sieves, w, m, s, and vs represent diffraction peak intensities, where w is weak, m is moderate, s is strong, and vs is very strong, as is well known to those skilled in the art. Generally, w is less than 20%; m is 20%–40% (inclusive); s is 40%–70% (exclusive); and vs is greater than or equal to 70% (inclusive).

[0020] The first aspect of the present invention provides a composite membrane, the composite membrane comprising: a base membrane and a composite layer disposed on the surface of the base membrane, the composite layer containing SCM-36 molecular sieve and conductive material.

[0021] In this invention, the SCM-36 molecular sieve has the illustrative chemical composition "mSiO2·nAl2O3", where m / n≥5.

[0022] According to a preferred embodiment of the present invention, the SCM-36 molecular sieve has the X-ray diffraction pattern shown in the table below.

[0023]

[0024]

[0025] (a) = ±0.3°, (b) varies with 2θ. The composite layer of the composite membrane of the present invention contains SCM-36 molecular sieve with a crystalline structure, which can improve the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries) when used in lithium batteries.

[0026] In this invention, SCM-36 molecular sieves with the aforementioned X-ray diffraction pattern and the illustrative chemical composition "mSiO2·nAl2O3" and m / n ≥ 5 can achieve the purpose of this invention; the range of selectable m / n is relatively wide, for example, 10, 15, 20, 25, 30, 40, 50, 60, 65, 70, 75, 80, 90, 100, 200, etc. According to a preferred embodiment of this invention, m / n = 5-80, preferably m / n = 10-60; this is beneficial to improving the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries).

[0027] According to a preferred embodiment of the present invention, the SCM-36 molecular sieve further comprises at least one diffraction peak in the X-ray diffraction pattern shown in the table below.

[0028]

[0029] (a) = ±0.3°, (b) varies with 2θ.

[0030] According to a preferred embodiment of the present invention, the SCM-36 molecular sieve has a nanosheet morphology and the thickness of the crystal is <30 nanometers, for example, it can be 2 nanometers, 5 nanometers, 8 nanometers, 10 nanometers, 12 nanometers, 15 nanometers, 28 nanometers, 20 nanometers, 25 nanometers, or 28 nanometers; preferably 2-25 nanometers, more preferably 7-20 nanometers; which is beneficial to improving the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries).

[0031] In this invention, the SCM-36 molecular sieve has a microporous structure. According to a preferred embodiment of the invention, the micropore size of the SCM-36 molecular sieve is 0.20-0.75 nanometers, for example, 0.30 nanometers, 0.40 nanometers, 0.50 nanometers, 0.60 nanometers, or 0.70 nanometers; preferably 0.30-0.70 nanometers, more preferably 0.5-0.65 nanometers; which is beneficial for improving the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries).

[0032] In this invention, the SCM-36 molecular sieve has a microporous structure. According to a preferred embodiment of the invention, the micropore volume of the SCM-36 molecular sieve is 0.05-0.35 cm³. 3 / gram, preferably 0.08-0.30 cm 3 / gram.

[0033] In this invention, the SCM-36 molecular sieve has a microporous structure. According to a preferred embodiment of this invention, the specific surface area of ​​the SCM-36 molecular sieve is 300-700 m². 2 / gram, preferably 300-600 meters 2 / gram.

[0034] In this invention, the mass ratio of SCM-36 molecular sieve to conductive material can be selected over a wide range. According to a preferred embodiment of this invention, the mass ratio of SCM-36 molecular sieve to conductive carbon material is (1-20):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, ... 20:1 or any value between them.

[0035] In this invention, there are no special requirements for the type of conductive material; commonly used conductive materials can be used. According to some embodiments of the invention, the conductive material is selected from one or more carbon-based conductive materials. Preferably, the conductive carbon material is selected from at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjen black.

[0036] In this invention, the composite layer is disposed on one or both sides of the substrate film.

[0037] In this invention, the thickness of the composite layer refers to the thickness of the composite layer located on one side of the substrate film. The thickness of the composite layer can be selected from a wide range, for example, the thickness of the composite layer can be 1-50 μm. According to a preferred embodiment of this invention, the thickness of the composite layer is 1-30 μm. For example, the thickness of the composite layer can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 23 μm, 25 μm, 27 μm or any value between them, which is beneficial to improving the cycle stability and capacity of lithium batteries (e.g., lithium-sulfur batteries).

[0038] In this invention, there are no special requirements for the material of the substrate membrane; conventional substrate membrane materials in the art can achieve the objectives of this invention. According to a preferred embodiment of this invention, the material of the substrate membrane is selected from at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride. In this embodiment, a three-layer composite membrane (PP / PE / PP) of polyethylene and polypropylene, brand name: Celgard 2325, is used as an example, but this does not limit the scope of the invention.

[0039] According to a preferred embodiment of the present invention, the composite layer further contains a binder; preferably, the mass ratio of SCM-36 molecular sieve to binder is (4-20):1, for example, the mass ratio of SCM-36 molecular sieve to binder can be 4:1, 4.5:1, 5:1, 5.5:1, ... 20:1 or any value between them.

[0040] In this invention, there are no special requirements for the adhesive; commonly used adhesives can be used. According to some embodiments of the invention, the adhesive is selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber, and polyacrylate. Polyvinylidene fluoride is used as an example in the implementation of this invention, but this does not limit the scope of the invention.

[0041] As long as a composite membrane with the aforementioned characteristics of this invention can be prepared, there are no special requirements for the preparation method of the composite membrane. This is an illustrative example and does not limit the scope of this invention. According to a preferred embodiment of this invention, a method for preparing the composite membrane of this invention is provided, the method comprising:

[0042] S1. Disperse the SCM-36 molecular sieve and conductive carbon material in a solvent to prepare a slurry;

[0043] S2. Coat the slurry onto the surface of the substrate film, and then remove the solvent.

[0044] In this invention, the solvent is used only for preparing the slurry, and the range of solvent types is relatively wide. According to some embodiments of the invention, in step S1, the solvent is selected from at least one of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. N-methylpyrrolidone is used as an example in the implementation of this invention, but this does not limit the scope of the invention.

[0045] According to some embodiments of the present invention, step S1 further includes dispersing the binder in a solvent to prepare a slurry.

[0046] According to a preferred embodiment of the present invention, in step S1, SCM-36 molecular sieve is first mixed with conductive carbon material to obtain a mixture, and then the obtained mixture is dispersed with a binder in a solvent to prepare a slurry.

[0047] In this invention, the coating method can be a conventional method in the art. According to some embodiments of the present invention, in step S2, the coating is achieved by at least one of the following methods: casting, blade coating, spraying, spin coating, gravure roller coating, and slot extrusion.

[0048] A third aspect of the present invention provides an application of the composite separator described herein in a lithium battery.

[0049] A fourth aspect of this invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, wherein the separator comprises the composite separator described in this invention. The composite layer of the composite separator of this invention contains an SCM-36 molecular sieve with a crystalline structure, which, when used in lithium batteries (e.g., lithium-sulfur batteries), can improve the cycle stability and capacity of the lithium battery (e.g., lithium-sulfur battery).

[0050] In the context of this specification, specific surface area refers to the total area per unit mass of sample.

[0051] In the context of this specification, pore volume refers to the volume of pores per unit mass of porous material. Micropore volume refers to the volume of all micropores (generally referring to pores with a diameter less than 2 nanometers) per unit mass of molecular sieve. The pore structure parameters of the material, such as total pore volume, micropore volume, total specific surface area, and external specific surface area, are obtained by measuring the nitrogen physical adsorption-desorption isotherm of the molecular sieve using a physical adsorption instrument (such as the TriStar 3000 physical adsorption instrument from Micron Instruments, Inc.), and then calculating using the BET method and t-plot method. The experimental conditions for nitrogen physical adsorption-desorption are: measurement temperature -169℃, and the molecular sieve pre-treated under vacuum at 300℃ for 10 hours before measurement.

[0052] In the context of this specification, the term "crystal thickness" refers to the average sum of the thicknesses of all plate-like crystals within a randomly selected field of view when observing SCM-36 molecular sieves at 100,000x magnification using a transmission electron microscope. This operation is repeated 10 times. The average of the sums of these 10 averages is taken as the crystal thickness.

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0054] 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.

[0055] In this invention, the assembly and performance testing processes of the lithium-sulfur battery are as follows:

[0056] 1. Assembly of lithium-sulfur battery samples:

[0057] Preparation of the positive electrode: Sublimed sulfur, conductive carbon material Ketjen black, and binder polyvinylidene fluoride are mixed in a weight ratio of 6:3:1, and N-methylpyrrolidone is added to form a positive electrode slurry; the positive electrode slurry is coated on aluminum foil and dried to obtain the positive electrode.

[0058] Assemble 2025 coin cells in an argon glove box with a water oxygen content of less than 0.1 ppm: Assemble in the following order: positive electrode shell, positive electrode, separator, lithium anode, nickel foam, and anode shell, and add 100 μL of electrolyte.

[0059] The electrolyte used is a mixed solution of 1,3-dioxolane / ethylene glycol dimethyl ether (DOL / DME, volume ratio 1:1) containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and 0.2 mol / L lithium nitrate.

[0060] 2. The capacity and cycle performance of the lithium-sulfur battery samples prepared as described above were tested by constant current charge-discharge testing.

[0061] The lithium-sulfur battery samples were tested at 0.1C (1C = 1675 mA g) within a voltage range of 1.7-2.7V. -1 The lithium-sulfur battery samples were cycled twice at 0.2C, and then further cycled 100 times at 0.5C or 200 times at 1.0C. The specific capacity was recorded after the first cycle at 0.5C and after the 100th cycle; the specific capacity was recorded after the first cycle at 1.0C and after the 200th cycle. The capacity retention rate after 100 cycles at 0.5C was calculated according to the following formula (1); the capacity retention rate after 200 cycles at 1.0C was calculated according to the following formula (2).

[0062] Formula (1): Capacity retention rate after 100 cycles = Specific capacity of the 100th cycle / Specific capacity of the 1st cycle × 100%.

[0063] Formula (2): Capacity retention rate after 200 cycles = Specific capacity of the 200th cycle / Specific capacity of the 1st cycle × 100%.

[0064] In the following examples, the SCM-36 molecular sieve was purchased from Sinopec (Shanghai) Petrochemical Research Institute Co., Ltd., see CN115959681A.

[0065] In the following examples, the micropore size, micropore volume, and specific surface area of ​​SCM-36 molecular sieve were obtained by testing with a multi-station fully automated specific surface area and porosity analyzer.

[0066] In the following examples, the content of silicon oxide, aluminum oxide, or non-silicon, non-aluminum element oxides in SCM-36 molecular sieves was measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0067] Example 1

[0068] S1. Grind and mix 0.35g of SCM-36 molecular sieve and 0.1g of graphene oxide in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide is 3.5:1; disperse the mixture with 0.05g of polyvinylidene fluoride in N-methylpyrrolidone, stir and mix evenly to obtain a coating slurry;

[0069] The chemical composition of the SCM-36 molecular sieve is “mSiO2·nAl2O3”, where m / n = 20.

[0070] The XRD pattern of SCM-36 molecular sieve is shown below. Figure 1 As shown, the SCM-36 molecular sieve has the X-ray diffraction pattern shown in Table A-1.

[0071] Table A-1

[0072]

[0073] The scanning electron microscope image of the SCM-36 molecular sieve is as follows: Figure 2 As shown, the SCM-36 molecular sieve has a nanosheet morphology and the thickness of the crystal is 15 nanometers.

[0074] The SCM-36 molecular sieve has a micropore size of 0.59 nanometers and a micropore volume of 0.10 centimeters. 3 / gram; specific surface area is 380 m² 2 / gram;

[0075] S2. The coating slurry is uniformly coated on one side of the polyethylene / polypropylene matrix film using a scraping method, and then dried to remove the solvent, resulting in a composite battery separator with a composite layer uniformly distributed on one side of the polymer matrix film, wherein the thickness of the composite layer is 10 μm.

[0076] Performance testing of composite battery separator: Based on the description of the test methods above, lithium-sulfur battery samples were assembled using the prepared composite battery separator and their performance was tested. The specific test results are shown in Table 1.

[0077] Example 2

[0078] S1. Grind and mix 0.20g of SCM-36 molecular sieve and 0.20g of graphene oxide in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide is 1:1; disperse the mixture with 0.02g of polyvinylidene fluoride in N-methylpyrrolidone, stir and mix evenly to obtain a coating slurry;

[0079] The chemical composition of the SCM-36 molecular sieve is “mSiO2·nAl2O3”, where m / n = 15.

[0080] The SCM-36 molecular sieve has an X-ray diffraction pattern as shown in Table A-2.

[0081] Table A-2

[0082]

[0083] The morphology of the SCM-36 molecular sieve and Figure 2 Similarly, this indicates that the SCM-36 molecular sieve has a nanosheet morphology and the thickness of the crystal is 7 nanometers;

[0084] The SCM-36 molecular sieve has a micropore size of 0.58 nanometers and a micropore volume of 0.10 centimeters. 3 / gram; specific surface area is 372 cubic meters. 2 / gram;

[0085] S2. The coating slurry is uniformly coated on one side of the polyethylene / polypropylene matrix film using a scraping method, and then dried to remove the solvent, resulting in a composite battery separator with a composite layer uniformly distributed on one side of the polymer matrix film, wherein the thickness of the composite layer is 3μm.

[0086] Performance testing of composite battery separator: Based on the description of the test methods above, lithium-sulfur battery samples were assembled using the prepared composite battery separator and their performance was tested. The specific test results are shown in Table 1.

[0087] Example 3

[0088] S1. Grind and mix 0.20g of SCM-36 molecular sieve and 0.02g of graphene oxide in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide is 10:1; disperse the mixture with 0.05g of polyvinylidene fluoride in N-methylpyrrolidone, stir and mix evenly to obtain a coating slurry;

[0089] The chemical composition of the SCM-36 molecular sieve is “mSiO2·nAl2O3”, where m / n = 50.

[0090] The SCM-36 molecular sieve has an X-ray diffraction pattern as shown in Table A-3.

[0091] Table A-3

[0092]

[0093] The morphology of the SCM-36 molecular sieve and Figure 2 Similarly, this indicates that the SCM-36 molecular sieve has a nanosheet morphology and the thickness of the crystal is 20 nanometers;

[0094] The SCM-36 molecular sieve has a micropore size of 0.61 nanometers and a micropore volume of 0.13 centimeters. 3 / gram; specific surface area is 401 cubic meters. 2 / gram;

[0095] S2. The coating slurry is uniformly coated on one side of the polyethylene / polypropylene matrix film using a scraping method, and then dried to remove the solvent, resulting in a composite battery separator with a composite layer uniformly distributed on one side of the polymer matrix film, wherein the thickness of the composite layer is 25μm.

[0096] Performance testing of composite battery separator: Based on the description of the test methods above, lithium-sulfur battery samples were assembled using the prepared composite battery separator and their performance was tested. The specific test results are shown in Table 1.

[0097] Example 4

[0098] Compared with Example 1, the difference is that the thickness of the composite layer is 40 μm; the other conditions are the same as in Example 1.

[0099] Example 5

[0100] Compared with Example 1, the difference is that 0.35g of SCM-36 molecular sieve and 0.70g of graphene oxide were ground and mixed in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide was 1:2; the other conditions were the same as in Example 1.

[0101] Example 6

[0102] Compared with Example 1, the difference is that 0.35g of SCM-36 molecular sieve and 0.018g of graphene oxide were ground and mixed in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide was 19:1; the other conditions were the same as in Example 1.

[0103] Example 7

[0104] S1. Grind and mix 0.35g of SCM-36 molecular sieve and 0.1g of graphene oxide in a mortar to obtain a mixture, wherein the mass ratio of SCM-36 molecular sieve to graphene oxide is 3.5:1; disperse the mixture with 0.05g of polyvinylidene fluoride in N-methylpyrrolidone, stir and mix evenly to obtain a coating slurry;

[0105] The chemical composition of the SCM-36 molecular sieve is “mSiO2·nAl2O3”, where m / n = 67.

[0106] The SCM-36 molecular sieve has the X-ray diffraction pattern shown in Table A-4.

[0107] Table A-4

[0108]

[0109] The scanning electron microscope image of the SCM-36 molecular sieve and Figure 2 Similarly, this indicates that the SCM-36 molecular sieve has a nanosheet morphology and the thickness of the crystal is 12 nanometers;

[0110] The SCM-36 molecular sieve has a micropore size of 0.74 nanometers and a micropore volume of 0.17 centimeters. 3 / gram; specific surface area is 379 cubic meters. 2 / gram;

[0111] S2. The coating slurry is uniformly coated on one side of the polyethylene / polypropylene matrix film using a scraping method, and then dried to remove the solvent, resulting in a composite battery separator with a composite layer uniformly distributed on one side of the polymer matrix film, wherein the thickness of the composite layer is 10 μm.

[0112] Performance testing of composite battery separator: Based on the description of the test methods above, lithium-sulfur battery samples were assembled using the prepared composite battery separator and their performance was tested. The specific test results are shown in Table 1.

[0113] Comparative Example 1

[0114] Compared with Example 1, the difference is that SCM-36 molecular sieve is not used in the preparation of the membrane, and 0.1g of graphene oxide is replaced with 0.45g of graphene oxide; the other conditions are the same as in Example 1.

[0115] Comparative Example 2

[0116] Compared with Example 1, the difference is that the molecular sieve used in the preparation of the diaphragm is SCM-14 molecular sieve; the other conditions are the same as in Example 1.

[0117] Table 1

[0118]

[0119] 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 combining the 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 composite diaphragm, characterized in that, The composite membrane includes a base membrane and a composite layer disposed on the surface of the base membrane, wherein the composite layer contains SCM-36 molecular sieve and conductive material.

2. The composite diaphragm according to claim 1, wherein, The SCM-36 molecular sieve has the illustrative chemical composition "mSiO2·nAl2O3", where m / n ≥ 5; and / or The SCM-36 molecular sieve has the X-ray diffraction pattern shown in the table below. (a) = ±0.3°, (b) varies with 2θ.

3. The composite diaphragm according to claim 2, wherein, In the SCM-36 molecular sieve, m / n = 5-80, preferably m / n = 10-60; Preferably, the SCM-36 molecular sieve further has at least one diffraction peak included in the X-ray diffraction patterns shown in the table below. (a) = ±0.3°, (b) varies with 2θ.

4. The composite diaphragm according to any one of claims 1-3, wherein, The SCM-36 molecular sieve has a nanosheet morphology, with crystal thickness ranging from 2 to 25 nanometers; and / or The SCM-36 molecular sieve has a micropore size of 0.20-0.75 nm, preferably 0.30-0.70 nm; and / or The SCM-36 molecular sieve has a micropore volume of 0.05-0.35 cm³. 3 / gram; and / or The specific surface area of ​​the SCM-36 molecular sieve is 300-700 m². 2 / gram.

5. The composite separator according to any one of claims 1-4, wherein, The mass ratio of SCM-36 molecular sieve to conductive material is 0.5-20:1, preferably 1-10:1; and / or The conductive material is selected from one or more carbon-based conductive materials, preferably from at least one of graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, acetylene black, Super P, and Ketjen black; and / or The thickness of the composite layer is 1-50 μm, preferably 1-30 μm; and / or The material of the substrate membrane is selected from at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile, polyethylene terephthalate, polytetrafluoroethylene, and polyvinylidene fluoride.

6. The composite separator according to any one of claims 1-5, wherein, The composite layer also contains a binder; preferably, the mass ratio of SCM-36 molecular sieve to binder is 4-20:

1. Preferably, the adhesive is selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, styrene-butadiene rubber, and polyacrylate.

7. The method for preparing the composite separator according to any one of claims 1-6, characterized in that, The method includes: S1. Disperse the SCM-36 molecular sieve and conductive material in a solvent to prepare a slurry; S2. Coat the slurry onto the surface of the substrate film and remove the solvent.

8. The preparation method according to claim 7, wherein, In step S1, the solvent is selected from at least one of deionized water, anhydrous ethanol, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; Preferably, step S1 further includes dispersing the binder in a solvent to prepare a slurry; Preferably, in step S2, the coating is achieved by at least one of the following methods: casting, scraping, spraying, spin coating, gravure roller coating, and slot extrusion.

9. The application of the composite separator according to any one of claims 1-6 in lithium batteries.

10. A lithium-sulfur battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator includes the composite separator as described in any one of claims 1-6.

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