A double-sided anisotropic separator and its preparation method and application

Abstract

The present invention provides a double-sided anisotropic separator and its preparation method and application. The double-sided anisotropic separator of the present invention includes a substrate separator, a conductive layer, and a non-conductive layer, and the conductive layer and the non-conductive layer are respectively located on different sides of the substrate separator; the conductive layer includes at least one of the following conductive materials: transition metal carbon / nitride, conductive carbon material, metal sulfide, conductive polymer material, etc.; the non-conductive layer includes at least one of the following non-conductive materials: metal-organic framework MOF, covalent organic framework COF, non-conductive polymer, etc. When the double-sided anisotropic separator of the present invention is applied in an energy storage device, the shuttle effect of soluble intermediate products generated during charge and discharge can be prevented by the conductive layer and the non-conductive layer on both sides, which is beneficial to improving the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical power sources, and relates to a preparation method and application of a double-sided anisotropic separator, in particular to a double-sided anisotropic separator with an effect of inhibiting the shuttle effect of soluble intermediates, and its preparation method and application. Background Art

[0002] Due to the excessive consumption of fossil fuels and serious environmental pollution problems, there is an urgent need for a green and low-cost energy storage system to meet the growing energy demand. Currently, alkali metal-sulfur batteries are considered to be one of the most promising next-generation energy storage devices because of their advantages such as high theoretical energy density, non-toxic, environmentally friendly, and low cost.

[0003] However, the defects they themselves have seriously restrict the development of high-energy metal-sulfur batteries. These defects include: 1) poor electron conductivity of sulfur and its discharge products, resulting in low utilization rate of active materials and slow reaction kinetics; 2) the generated intermediate polysulfides are extremely soluble in the electrolyte, migrate through the separator to the negative electrode region and react with metallic lithium, resulting in low Coulomb efficiency and poor cycle life. Therefore, improving conductivity and inhibiting the shuttle effect of soluble intermediates are crucial in the research of metal-sulfur batteries. Currently, various strategies have been studied to further improve the performance of the battery for these problems of lithium-sulfur batteries, including the structural design of the positive electrode, electrolyte optimization, separator modification, and protection of the lithium negative electrode, etc. Among them, the separator is one of the important components of the battery, mainly used as an electronic insulator to prevent short circuits and provide a transmission channel for lithium ions. Currently, commercial separators usually have poor affinity with the electrolyte, and are generally polymer membranes with a large number of nanopores, and the sizes of these pores are much larger than those of polysulfides. Therefore, soluble lithium polysulfides can freely diffuse through the separator and react with the lithium negative electrode, resulting in the degradation of the lithium negative electrode. Traditional commercial separators cannot block the shuttle effect of intermediate polysulfides, resulting in problems such as poor Coulomb efficiency of the battery and continuous attenuation of capacity. Summary of the Invention

[0004] The present invention provides a double-sided anisotropic separator, including a substrate separator, a conductive layer, and a non-conductive layer, and the conductive layer and the non-conductive layer are respectively located on different sides of the substrate separator. That is, the substrate separator is located between the conductive layer and the non-conductive layer.

[0005] According to an embodiment of the present invention, the substrate separator is selected from polyethylene and / or polypropylene.

[0006] According to an embodiment of the present invention, the conductive layer includes at least one of the following conductive materials: transition metal carbon / nitride, conductive carbon material, metal sulfide, conductive polymer material, etc.

[0007] Preferably, the transition metal carbon / nitride is selected from MXene materials. The MXene materials in the present invention are selected from the MXene materials known in the technical field, such as Ti3C2-MXene, Ti2C-MXene, Ti2N-MXene, Cr2C-MXene, Ta4C3-MXene, Ti3CN X -MXene, Ta4C3-MXene, Nb4C3-MXene, Nb2C-MXene, V2C-MXene, Mo2TiC2-MXene, Mo2C-MXene, V4C3-MXene, etc., at least one of them.

[0008] Preferably, the conductive carbon material is selected from at least one of carbon nanotubes, graphene, reduced graphene oxide, etc.

[0009] Preferably, the metal sulfide is selected from at least one of VS2, TiS2, Co2S2, CoS2, WS2, etc.

[0010] Preferably, the conductive polymer material is selected from at least one of polypyrrole, polyphenylene sulfide, phthalocyanine compounds, polyaniline, polythiophene, etc.

[0011] Exemplarily, the conductive layer is selected from Ti3C2 MXene.

[0012] According to an embodiment of the present invention, the non-conductive layer includes at least one of the following non-conductive materials: metal-organic framework MOF, covalent organic framework COF, non-conductive polymer, etc.

[0013] Preferably, the metal-organic framework MOF is selected from the MOF materials known in the technical field. Preferably, the MOF material is a porous material. Exemplarily, the metal-organic framework MOF is selected from at least one of Cu-TCPP, trimer chromium MOF (MIL-100(Cr)), MIL-101(Cr), MIL-100(Fe), MIL-125, Cu-BTC, ZIF-67, ZIF-8, UiO-66, Cu-TCPP, etc.

[0014] Preferably, the covalent organic framework COF is selected from at least one of CTF-1, COF-1, COF-5, COF-102, COF-103, COF-303, etc.

[0015] Preferably, the non-conductive polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride, polyisoprene, polymethyl methacrylate, etc.

[0016] Exemplarily, the non-conductive layer is selected from Cu-TCPP.

[0017] According to an embodiment of the present invention, the average thickness of the conductive layer is 0.1 - 10 μm, preferably 0.5 - 1 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0018] According to an embodiment of the present invention, the average thickness of the non - conductive layer is 1 - 10 μm, preferably 0.5 - 1 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0019] According to an embodiment of the present invention, the average thickness of the substrate separator is 5 - 25 μm, such as 5 μm, 10 μm, 15 μm, 20 μm, 25 μm.

[0020] According to an exemplary embodiment of the present invention, the double - sided anisotropic separator includes a substrate separator, a conductive layer, and a non - conductive layer. The conductive layer and the non - conductive layer are respectively located on different sides of the substrate separator. The conductive layer is a Ti3C2 MXene layer, and the non - conductive layer is a Cu - TCPP layer.

[0021] According to an embodiment of the present invention, the conductive layer and the non - conductive layer are respectively attached to different sides of the substrate separator by vacuum filtration.

[0022] According to an embodiment of the present invention, the double - sided anisotropic separator has the effect of suppressing the shuttle effect of soluble intermediates (such as lithium polysulfide). The inventors found that the conductive layer attached to the substrate separator, as an expandable electrode, improves sulfur utilization; at the same time, the conductive layer can also adsorb soluble intermediates (such as lithium polysulfide) generated during charge and discharge through physical or chemical actions. On the other hand, the non - conductive layer attached to the substrate separator also has the ability to adsorb soluble intermediates (such as lithium polysulfide), and at the same time, the non - conductive layer has the effect of blocking the shuttle effect of soluble intermediates (such as lithium polysulfide). It can be seen that the separator of the present invention can not only effectively improve sulfur utilization, but also achieve dual adsorption of soluble intermediates.

[0023] The present invention also provides a method for preparing the above - mentioned double - sided anisotropic separator. The preparation method includes attaching a conductive layer and a non - conductive layer to different sides of a substrate separator by vacuum filtration. Among them, the substrate separator, the conductive layer, and the non - conductive layer have the meanings as described above.

[0024] According to an embodiment of the present invention, the method for preparing the double-sided anisotropic separator comprises the following steps:

[0025] (1) Using a substrate separator as the first filter membrane;

[0026] (2) Attaching a dilution of a conductive material to the first filter membrane by vacuum filtration, and drying to form a conductive layer, thereby obtaining a separator comprising a conductive layer;

[0027] (3) Using the separator comprising a conductive layer obtained in step (2) as the second filter membrane, attaching a dilution of a non-conductive material to the second filter membrane by vacuum filtration, and drying to form a non-conductive layer, wherein the conductive layer and the non-conductive layer are respectively attached to different sides of the substrate separator, thereby obtaining the double-sided anisotropic separator;

[0028] Or,

[0029] (2’) Attaching a dilution of a non-conductive material to the first filter membrane by vacuum filtration, and drying to form a non-conductive layer, thereby obtaining a separator comprising a non-conductive layer;

[0030] (3’) Using the separator comprising a non-conductive layer obtained in step (2’) as the second filter membrane, attaching a dilution of a conductive material to the second filter membrane by vacuum filtration, and drying to form a conductive layer, wherein the conductive layer and the non-conductive layer are respectively attached to different sides of the substrate separator, thereby obtaining the double-sided anisotropic separator.

[0031] According to an embodiment of the present invention, in step (1), the first filter membrane is washed by a method known in the art. Exemplarily, the washing is performed using ethanol, preferably ethanol solution with a mass fraction of 75%.

[0032] According to an embodiment of the present invention, in step (2) or (3’), the dilution of the conductive material or the dilution of the non-conductive material is a homogeneous solution. For example, before vacuum filtration, ultrasonic treatment is further required.

[0033] In step (2’) or (3), the dilution of the non-conductive material is a homogeneous solution. For example, before vacuum filtration, ultrasonic treatment is further required.

[0034] Preferably, the time of the ultrasonic treatment is greater than 0 and not more than 30 minutes, preferably 10 - 20 minutes, for example, it is 15 minutes.

[0035] According to an embodiment of the present invention, the concentration of the dilution of the conductive material and / or the dilution of the non-conductive material is 0.0001 mg / mL - 10 mg / mL.

[0036] According to an embodiment of the present invention, in steps (2), (2'), (3), and (3'), draining needs to be performed before drying. The draining in the present invention can be carried out by using methods known in the art.

[0037] Preferably, the draining time is 0 - 30 minutes, more preferably 10 - 15 minutes, for example, 10 minutes.

[0038] Preferably, the draining further includes washing. The present invention does not specifically limit the washing, and methods known in the art can be used. Exemplarily, ethanol is used for washing.

[0039] According to an embodiment of the present invention, in step (2), (2'), (3), or (3'), the drying conditions include: heating at 10 - 60°C for 1 - 48 h. Exemplarily, the drying conditions include heating at 40°C for 24 h.

[0040] Preferably, the drying is carried out under vacuum conditions.

[0041] According to an exemplary embodiment of the present invention, the method for preparing the double-sided anisotropic separator includes the following steps:

[0042] (1) Using a PP separator as the first filter membrane and washing it with ethanol;

[0043] (2) Preparing a Cu-TCPP dilution solution, ultrasonicating it evenly, subjecting the Cu-TCPP dilution solution to vacuum filtration and attaching it to the first filter membrane, draining and drying to obtain a Cu-TCPP / PP separator;

[0044] (3) Using the Cu-TCPP / PP separator as the second filter membrane;

[0045] (4) Preparing a MXene dilution solution, ultrasonicating it evenly, subjecting the MXene dilution solution to vacuum filtration and attaching it to the second filter membrane, draining and drying to obtain a Cu-TCPP / PP / MXene separator;

[0046] Preferably, in step (2), the concentration of the dilution solution is 0.03 mg / mL.

[0047] Preferably, in steps (2) and (4), the ultrasonic time is 15 min.

[0048] Preferably, in steps (2) and (4), the draining time is 10 min.

[0049] Preferably, in steps (2) and (4), the drying conditions are 50°C and drying for 12 h.

[0050] Preferably, in step (4), the concentration of the dilution solution is 2.5 mg / μL.

[0051] Preferably, in steps (2) and (4), the drying conditions are 40 °C for 24 h, preferably carried out under vacuum conditions.

[0052] The present invention also provides an application of the above double-sided anisotropic separator in energy storage devices.

[0053] According to an embodiment of the present invention, the energy storage device is selected from alkali metal-sulfur / selenium energy storage devices.

[0054] Preferably, the alkali metal-sulfur / selenium energy storage device is selected from any one of lithium-sulfur batteries, lithium-selenium batteries, sodium-sulfur batteries, sodium-selenium batteries, etc.

[0055] The present invention also provides a lithium-sulfur battery, which contains the double-sided anisotropic separator.

[0056] According to an embodiment of the present invention, the lithium-sulfur battery further includes: a negative electrode, a positive electrode, and an electrolyte. In the present invention, the negative electrode, the positive electrode, and the electrolyte are not specifically limited, and materials known in the art can be selected.

[0057] According to an embodiment of the present invention, in the lithium-sulfur battery, the side of the double-sided anisotropic separator close to the positive electrode is a conductive layer, and the side close to the negative electrode is a non-conductive layer.

[0058] According to an exemplary scheme of the present invention, the negative electrode is selected from metallic lithium.

[0059] According to an exemplary scheme of the present invention, the positive electrode is selected from at least one of S / CMK-3 and S / conductive carbon black.

[0060] According to an exemplary scheme of the present invention, the electrolyte is 1.0 moL / L of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) with a volume ratio of 1:1, and the additive is 2% by mass of lithium nitrate (LiNO3).

[0061] According to an exemplary scheme of the present invention, the specific capacity of the lithium-sulfur battery after 30 cycles at a rate of 0.1C is 845.4 mAh·g -1 .

[0062] According to an exemplary scheme of the present invention, the specific capacity of the lithium-sulfur battery after 100 cycles at a rate of 0.5C is 687.0 mAh·g -1 .

[0063] Advantages of the present invention:

[0064] (1) The double-sided anisotropic separator of the present invention attaches functional materials with different properties as the conductive layer and the non-conductive layer to different sides of the substrate separator, and utilizes the adsorption capacity of the conductive layer and the non-conductive layer for soluble intermediates (such as polysulfides) to inhibit the shuttle effect of alkali metal-sulfur / selenium energy storage devices (such as lithium-sulfur batteries). Among them, the conductive layer not only stores and disperses sulfur particles as an expandable electrode, which is beneficial to the rapid transfer of electrons, can effectively improve the conductivity and utilization rate of the sulfur cathode, but also can block the shuttle of polysulfides through chemical or physical actions; the non-conductive layer has insulation properties and is conducive to ion conduction, and can also block the diffusion of polysulfides through chemical / physical actions. Thus, the double-sided anisotropic separator not only has the properties of the substrate separator itself, but also the conductive layer and the non-conductive layer together constitute a double adsorption effect, inhibiting the shuttle effect of soluble intermediates, thereby improving the cycle stability and service life of the battery.

[0065] (2) By controlling the thicknesses of the conductive layer and the non-conductive layer, the present invention can prepare double-sided anisotropic separators with different thicknesses. The double-sided anisotropic separator prepared by the present invention has the characteristics of ultra-thin and controllable thickness. The double-sided anisotropic separator of the present invention can effectively solve the problem that the thickness and mass of the separator account for a large proportion in the battery, which is beneficial to further improving the energy density of the battery.

[0066] (3) When the double-sided anisotropic separator of the present invention is applied in an energy storage device, especially in an alkali metal-sulfur / selenium energy storage device, through the double adsorption effect of the double-sided anisotropic separator of the present invention, the shuttle effect of soluble intermediates generated during the charge and discharge process of the energy storage device can be inhibited, and the cycle performance of the energy storage device can be improved.

[0067] (4) The preparation method of the double-sided anisotropic separator of the present invention is simple, the conditions are controllable, the cost is low, it is environmentally friendly, and it can be prepared in large quantities, having good development potential.

[0068] (5) By utilizing the different conductivities of the conductive layer and the non-conductive layer located on different sides of the separator, the side close to the positive electrode has high conductivity, while the side close to the negative electrode has insulation properties, thereby improving the cycle performance and cycle stability of the energy storage device. Description of the Drawings

[0069] Figure 1 It is a scanning electron microscope picture of the cross-section of the double-sided anisotropic separator in Example 1.

[0070] > Figure 2 It is a cycle curve graph of the lithium-sulfur batteries assembled in Example 1 and Comparative Examples 1-3 at a rate of 0.1C.

[0071] Figure 3 It is a cycle curve graph of the lithium-sulfur batteries assembled in Example 1 and Comparative Examples 1-3 at a rate of 0.5C. Detailed implementation manners

[0072] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0073] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products or can be prepared by known methods.

[0074] In the following embodiments, unless specifically stated, the ethanol refers to an ethanol solution with a mass fraction of 75%.

[0075] Preparation examples

[0076] (1) Synthesis of MXene

[0077] 5 g of Ti3AlC2 powder was immersed in 100 mL of 9 mol / L HCl solution (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) with 5 g of LiF (Sigma Aldrich) at room temperature for 24 hours. The obtained powder was washed several times with deionized water. Then, it was ultrasonicated for 1 h and centrifuged at 3500 r / min for 60 min to remove large particles. A black Ti3C2T x MXene colloidal supernatant was obtained, and then MXene powder was obtained by freeze-drying.

[0078] After diluting the MXene powder with ethanol, an MXene suspension was obtained, and the concentration of MXene was 0.02 mg / mL.

[0079] (II) Synthesis of Cu-TCPP

[0080] Cu(NO3)2·3H2O (1.85 mg, 0.0075 mmol), trifluoroacetic acid (1.0 M × 5 μL), and PVP (5.0 mg) were dissolved in a mixed solution of 6 mL of N,N-dimethylformamide (DMF) and absolute ethanol (V:V = 3:1). Then, TCPP (2.0 mg, 0.0025 mmol) dissolved in a mixture of 2 mL of DMF and ethanol (volume ratio = 3:1) was added dropwise under stirring. After that, the solution was ultrasonicated for 5 minutes. The vial was heated to 80 °C and then the reaction was maintained for 3 hours. The obtained red nanosheets were washed three times with ethanol and collected by centrifugation at 8000 revolutions per minute for 10 minutes to obtain the Cu-TCPP product.

[0081] After diluting Cu-TCPP with ethanol, a Cu-TCPP suspension was obtained. In the Cu-TCPP suspension, the concentration of Cu-TCPP was 0.5 mg / mL.

[0082] Example 1

[0083] (I) Preparation of double-sided anisotropic separator

[0084] (1) Take 300 μL of Cu-TCPP suspension, dilute it with ethanol to 5 mL, shake well and sonicate for 10 min to obtain a Cu-TCPP dilution. Use a PP separator as the first filter membrane, and subject the Cu-TCPP dilution to vacuum filtration to adhere it to the first filter membrane. After drying, wash it several times with ethanol, remove the separator with the Cu-TCPP layer attached, and place it in an oven at 50 °C for 12 h to dry, obtaining a Cu-TCPP / PP separator.

[0085] (2) Use the Cu-TCPP / PP separator obtained in step (1) as the second filter membrane (with the side of the Cu-TCPP layer facing down), and then add 1 mL of MXene dilution for vacuum filtration to adhere it to the first filter membrane. After drying, wash it several times with ethanol, remove the separator with the Cu-TCPP layer and MXene layer attached, and place it in a vacuum oven at 40 °C for 24 h to obtain the MXene / PP / Cu-TCPP double-sided anisotropic separator.

[0086] Figure 1 Figure 15 is a scanning electron microscope of the cross-section of the double-sided anisotropic separator in Example 1. It can be seen from Figure 1 that the double-sided anisotropic separator presents a three-layer stacked structure. From top to bottom, it is a non-conductive layer, a substrate separator, and a conductive layer. The average thickness of the conductive layer and non-conductive layer on both sides of the substrate separator is about 0.5 - 1 μm. The conductive materials and non-conductive materials on both sides can adhere to the polypropylene substrate separator relatively evenly and tightly to form the conductive layer and non-conductive layer. The double-sided anisotropic separator includes a conductive MXene layer and an insulating Cu-TCPP modified layer, which are located on different sides of the substrate separator.

[0087] (II) Assembly of lithium-sulfur battery

[0088] Cut the double-sided anisotropic separator prepared in this example into a separator disc with a diameter of 19 mm. The negative electrode is a lithium metal sheet, the positive electrode is S / CMK-3, the electrolyte is 1.0 moL / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) with a volume ratio of 1:1, and the additive is 2% lithium nitrate (LiNO3) by mass fraction. Assemble a lithium-sulfur battery in an Ar-filled glove box, where the MXene layer of the double-sided anisotropic separator is close to the positive electrode and the Cu-TCPP layer is close to the negative electrode.

[0089] Comparative Example 1

[0090] Prepare a blank lithium-sulfur battery

[0091] The blank lithium-sulfur battery adopts the preparation method of the assembled lithium-sulfur battery in Example 1, except that the double-sided anisotropic separator is replaced with a polypropylene substrate separator without a conductive layer and a non-conductive layer.

[0092] Comparative Example 2

[0093] (I) Preparation of MXene / PP separator

[0094] The preparation method is the same as that in Example 1, except that only a separator with a single-sided MXene layer is obtained by vacuum filtration, denoted as MXene / PP separator.

[0095] (II) Preparation of MXene / PP lithium-sulfur battery

[0096] The preparation method of the MXene / PP lithium-sulfur battery is the same as that of the lithium-sulfur battery assembled in Example 1, except that the double-sided anisotropic separator is replaced with MXene / PP separator.

[0097] Comparative Example 3

[0098] (I) Preparation of Cu-TCPP / PP separator

[0099] The preparation method is the same as that in Example 1, except that only a separator with a single-sided Cu-TCPP layer is obtained by vacuum filtration, denoted as Cu-TCPP / PP separator.

[0100] (II) Preparation of Cu-TCPP / PP lithium-sulfur battery

[0101] The preparation method of the Cu-TCPP / PP lithium-sulfur battery is the same as that of the lithium-sulfur battery assembled in Example 1, except that the double-sided anisotropic separator is replaced with Cu-TCPP / PP separator.

[0102] Test Example 1

[0103] Electrochemical tests were carried out on the lithium-sulfur batteries.

[0104] The lithium-sulfur batteries in Examples 1-3 and the blank lithium-sulfur battery in Comparative Example 1 were respectively subjected to constant current charge and discharge tests using a charge and discharge instrument. The test temperature was 25 °C, the test current density was 0.1C, and the charge and discharge interval was 1.7-2.8V.

[0105] Figure 2 The cycle curves of the lithium-sulfur batteries in Comparative Examples 1-3 and the lithium-sulfur battery in Example 1 at a rate of 0.1C are shown. The discharge specific capacity of the lithium-sulfur battery assembled with the blank separator dropped to 651.84 mAh·g after 30 cycles. -1 The discharge specific capacity of the full battery assembled with MXene / PP separator was 762.5 mAh·g after 30 cycles. -1, the discharge specific capacity of the full cell assembled with the Cu-TCPP / PP separator after 30 cycles is 790.1 mAh·g -1 , the discharge specific capacity of the full cell assembled with the double-sided anisotropic separator of Example 1 after 30 cycles is 845.4 mAh·g -1 , which is better than the cycling performance of the blank lithium-sulfur battery. The cycling retention rate of the lithium-sulfur battery of Example 1 is 67.2%, while the cycling retention rates of the blank lithium-sulfur batteries of Comparative Examples 1-3 are 55.1%, 64.6%, and 67.1% respectively.

[0106] Figure 3 are the cycling curves of the blank lithium-sulfur battery and the lithium-sulfur battery of Example 1 at a rate of 0.5C. After testing, at a rate of 0.5C, the discharge specific capacity of the battery assembled with the blank separator drops to 479.6 mAh·g after 100 cycles -1 , the discharge specific capacity of the full cell assembled with the MXene-modified separator after 100 cycles is 604.9 mAh·g -1 , the discharge specific capacity of the full cell assembled with the Cu-TCPP-modified separator after 100 cycles is 519.5 mAh·g -1 , the specific capacity of the full cell assembled with the modified separator after 100 cycles is about 687.0 mAh·g -1 , which is better than the cycling performance of the blank lithium-sulfur battery.

[0107] Example 2

[0108] In the preparation of the double-sided anisotropic separator of this example, the addition amounts of the Cu-TCPP suspension and the MXene dilution are 2 mL and 4 mL respectively, and the rest is the same as in Example 1. The average thickness of the modified layers on both sides of the double-sided anisotropic separator of this example is about 2 microns.

[0109] The lithium-sulfur battery of this example has the same preparation method as the lithium-sulfur battery assembled in Example 1, except that the double-sided anisotropic separator of Example 1 is replaced with the double-sided anisotropic separator of this example.

[0110] It can be seen from Example 2 that by increasing the addition amounts of the Cu-TCPP suspension and the MXene dilution, the thickness of the modified layers on both sides increases. However, due to the relatively large thickness on both sides, the modified layers on both sides will partially fall off during the suction filtration process, resulting in a decrease in the electrochemical performance compared to Example 1. After testing, at a rate of 0.1C, the specific capacity of the full cell assembled with the double-sided anisotropic separator after 30 cycles is about 71,200 mAh·g -1 . The cycling retention rate of the lithium-sulfur battery of this example is 66.3%.

[0111] Example 3

[0112] In the preparation of the double-sided anisotropic separator of this embodiment, the addition amounts of the Cu-TCPP suspension and the MXene diluent are 100 μL and 200 μL respectively, and the rest is the same as in Embodiment 1. The average thickness of both sides of the prepared double-sided anisotropic separator is about 0.3 micrometers.

[0113] The preparation method of the lithium-sulfur battery of this embodiment is the same as that of the lithium-sulfur battery assembled in Embodiment 1, except that the double-sided anisotropic separator of Embodiment 1 is replaced with the double-sided anisotropic separator of this embodiment.

[0114] It can be seen from Embodiment 3 that by reducing the addition amounts of the Cu-TCPP suspension and the MXene diluent, the thickness of the modification layers on both sides decreases. However, due to the reduction of the modification materials on both sides, the adsorption capacity for polysulfides is weakened, so the cycle stability is lower than that of Embodiment 1. After testing, at a rate of 0.1C, the specific capacity of the full battery assembled with the double-sided anisotropic separator is about 689.7 mAh·g -1 . The cycle retention rate of the lithium-sulfur battery of this embodiment is 61.2%.

[0115] Embodiment 4

[0116] In the preparation of the double-sided anisotropic separator of this embodiment, the drying time is shortened from 10 min to 2 min, and the rest is the same as in Embodiment 1.

[0117] The preparation method of the lithium-sulfur battery of this embodiment is the same as that of the lithium-sulfur battery assembled in Embodiment 1, except that the double-sided anisotropic separator of Embodiment 1 is replaced with the double-sided anisotropic separator of this embodiment.

[0118] It can be seen from Embodiment 4 that due to the shortening of the drying time, the modification layer is likely to fall off, which is not conducive to the long-term cycle of the battery. After testing, at a rate of 0.1C, the specific capacity of the full battery assembled with the double-sided anisotropic separator is about 746.7 mAh·g -1 . The cycle retention rate of the lithium-sulfur battery of this embodiment is 65.7%.

[0119] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A double-sided anisotropic diaphragm, characterized in that: The double-sided anisotropic diaphragm comprises a substrate diaphragm, a conductive layer and a non-conductive layer, wherein the conductive layer and the non-conductive layer are respectively located on different sides of the substrate diaphragm; The conductive layer is made of MXene material; The non-conductive layer is a metal organic framework MOF.

2. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The substrate separator is selected from polyethylene and / or polypropylene.

3. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The MXene material is selected from Ti3C2-MXene, Ti2C-MXene, Ti2N-MXene, Cr2C-MXene, Ta4C3-MXene, Ti3CN X -MXene, Ta4C3-MXene, Nb4C3-MXene, Nb2C-MXene, V2C-MXene, Mo2TiC2-MXene, Mo2C-MXene, V4C3-MXene, at least one of the group consisting of:

4. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The metal organic framework MOF is a porous material; The metal organic framework MOF is selected from at least one of Cu-TCPP, trimer chromium MOF, MIL-101 (Cr), MIL-100 (Fe), MIL-125, Cu-BTC, ZIF-67, ZIF-8, UiO-66, and Cu-TCPP.

5. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The average thickness of the conductive layer is 0.1-10 μm; The average thickness of the non-conductive layer is 1-10 μm; The average thickness of the substrate separator is 5-25 μm.

6. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The average thickness of the conductive layer is 0.5-1 μm; The average thickness of the non-conductive layer is 0.5-1 μm.

7. The double-sided anisotropic diaphragm according to claim 1, characterized in that: The double-sided anisotropic diaphragm includes a substrate diaphragm, a conductive layer and a non-conductive layer, wherein the conductive layer and the non-conductive layer are respectively located on different sides of the substrate diaphragm, the conductive layer is a Ti3C2 MXene layer, and the non-conductive layer is a Cu-TCPP layer.

8. The method for preparing a double-sided anisotropic separator according to any one of claims 1 to 7, characterized in that: The preparation method comprises attaching a conductive layer and a non-conductive layer on different sides of a substrate membrane by a reduced pressure filtration method.

9. The preparation method according to claim 8, characterized in that The preparation method of the double-sided anisotropic diaphragm comprises the following steps: (1) Using the substrate membrane as the first filter membrane; (2) The diluted liquid of the conductive material is attached to the first filter membrane by vacuum filtration, and a conductive layer is formed after drying to obtain a diaphragm containing the conductive layer; (3) Using the diaphragm containing the conductive layer in step (2) as the second filter membrane, the diluted liquid of the non-conductive material is attached to the second filter membrane by vacuum filtration, and the non-conductive layer is obtained after drying, and the conductive layer and the non-conductive layer are respectively attached to different sides of the substrate diaphragm to obtain the double-sided anisotropic diaphragm; or, (2') allowing the diluted solution of the non-conductive material to adhere to the first filter membrane by vacuum filtration, and forming a non-conductive layer after drying, thereby obtaining a diaphragm including the non-conductive layer; (3') The membrane containing the non-conductive layer in step (2') is used as the second filter membrane, and the diluted liquid of the conductive material is attached to the second filter membrane by vacuum filtration, and a conductive layer is formed after drying. The conductive layer and the non-conductive layer are respectively attached to different sides of the substrate membrane to obtain the double-sided anisotropic membrane.

10. The preparation method according to claim 9, characterized in that In step (2) or (3'), the dilution liquid of the conductive material is a uniform solution; in step (2') or (3), the dilution liquid of the non-conductive material is a uniform solution; It is also necessary to drain before the drying.

11. The preparation method according to claim 6, characterized in that The preparation method of the double-sided anisotropic diaphragm comprises the following steps: Use PP membrane as the first filter membrane and wash it with ethanol; Prepare a Cu-TCPP dilution solution, perform ultrasonic homogenization, filter the Cu-TCPP dilution solution under reduced pressure and attach it to the first filter membrane, drain and dry it to obtain a Cu-TCPP / PP membrane; Cu-TCPP / PP membrane was used as the second filter membrane; A MXene dilution solution was prepared and homogenized by ultrasonication. The MXene dilution solution was filtered under reduced pressure and attached to a second filter membrane. After drying, a Cu-TCPP / PP / MXene double-sided anisotropic diaphragm was obtained.

12. Use of the double-sided anisotropic diaphragm according to any one of claims 1 to 7 in energy storage devices.

13. A lithium-sulfur battery, characterized in that: The lithium-sulfur battery comprises the double-sided anisotropic separator according to any one of claims 1 to 7; In the lithium-sulfur battery, the side of the double-sided anisotropic separator close to the positive electrode is a conductive layer, and the side close to the negative electrode is a non-conductive layer.

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