MIL-121 / Na self-supporting diaphragm with high ionic conductivity as well as preparation method and application of MIL-121 / Na self-supporting diaphragm

Abstract

According to the high-ionic-conductivity MIL-121 / Na self-supporting diaphragm and the preparation method and application thereof, a selective sodium ion transmission channel is constructed through ion exchange, then the flexible high-temperature-resistant diaphragm is prepared through a tape casting method, and the preparation method has the advantages of being simple in reaction in the preparation process, high in operability, high in safety and the like. According to the invention, efficient transmission of sodium ions (the ionic conductivity is 2.27 * 10 <-4 > S / cm) and a double blocking mechanism of polysulfide are realized, the first-circle specific discharge capacity of 1182mAh g <-1 > is realized at the multiplying power of 0.5 C, stable circulation is realized for 400 times, and excellent multiplying power performance and long cycle life are shown.

Description

Technical Field

[0001] This invention belongs to the field of metal-sulfur battery material preparation technology, and provides a high ionic conductivity MIL-121 / Na self-supporting membrane, its preparation method and application. Background Technology

[0002] With the increasing global demand for clean energy, renewable energy sources such as solar and wind power have been developed and utilized. However, the cyclical nature and instability of this energy make energy efficiency a key technology for achieving large-scale application. Lithium-ion batteries are the most widely used energy storage technology, achieving great success in small electronic devices and electric vehicles. However, limited resources and the high cost of lithium restrict the further development of large-scale energy storage.

[0003] Metal-sulfur batteries have garnered significant attention due to their high theoretical energy density and the low cost of sulfur as the cathode. Alkali metal batteries based on lithium, sodium, and potassium anodes, and sulfur-based cathodes, are considered key to next-generation energy storage, particularly lithium-sulfur and sodium-sulfur batteries with their high specific energy. While lithium-sulfur batteries boast twice the theoretical energy density of sodium-sulfur batteries, their sustainable development is hampered by low lithium reserves and rising lithium ore prices. In contrast, developing sodium-sulfur batteries offers high techno-economic value, reducing geoeconomic competition and alleviating resource constraints.

[0004] Room-temperature sodium-sulfur (RT Na-S) batteries are considered strong candidates for next-generation large-scale energy storage systems due to their high theoretical energy density, abundant elemental reserves, and low cost. Compared to lithium-ion batteries, sodium-sulfur batteries show greater potential in terms of resource sustainability; and compared to traditional sodium-sulfur batteries that require high-temperature operation, their room-temperature operating conditions significantly improve safety and practicality, while reducing system complexity and cost. However, the commercial application of RT Na-S batteries still faces three core challenges: Firstly, the intermediate product sodium polysulfide (Na2S) x The dissolution and shuttle effect of (4≤x≤8) in the electrolyte leads to irreversible loss of active material, rapid capacity decay and low coulombic efficiency. Secondly, the insulating properties of sulfur and its discharge products (Na2S2 / Na2S) lead to slow reaction kinetics and low sulfur utilization. Third, the growth of sodium dendrites can puncture the diaphragm and cause safety hazards.

[0005] In these problems, the membrane and electrolyte, as channels and media for ion transport, play a crucial role. They are not only physical barriers separating the positive and negative electrodes, but also key components for regulating ion migration, suppressing side reactions, and stabilizing the electrode interface.

[0006] Currently, glass fiber membranes are the primary type of separator used in room-temperature sodium-sulfur batteries. However, these membranes exhibit low ionic conductivity in room-temperature sodium-sulfur systems, leading to high internal resistance and severe polarization. Furthermore, their micron-sized pores and surface inertness cannot effectively physically block or chemically adsorb polysulfides, failing to suppress the shuttle effect and causing continuous loss of active material and rapid capacity decay. These defects severely restrict the safety and commercial application of these batteries.

[0007] Therefore, it is essential to design and develop a high-performance functional membrane to improve ionic conductivity and effectively suppress polysulfide shuttle effect in order to enhance the chemical performance of metal-sulfur batteries. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a high ionic conductivity MIL-121 / Na self-supporting membrane, its preparation method and application, so as to solve the problems of slow kinetics and low ionic conductivity in metal-sulfur batteries.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a high ionic conductivity MIL-121 / Na self-supporting membrane involves first mixing an inorganic salt and an organic ligand in a hydrothermal reaction to obtain powder I; then, powder I undergoes ion exchange with a solution to obtain powder II; finally, powder II is mixed with a polymer to prepare a sheet, thus obtaining the membrane. The inorganic salt is aluminum nitrate nonahydrate, the organic ligand is pyromellitic acid, and the solution is a 0.5–3 mol / L sodium acetate solution.

[0010] Preferably, the polymer is selected from any one of polyethyleneimine, polyvinylidene fluoride, sodium alginate, vinylidene fluoride-hexafluoropropylene copolymer, and polytetrafluoroethylene; more preferably, it is vinylidene fluoride-hexafluoropropylene copolymer.

[0011] Preferably, the specific steps are as follows: (1) Mixing: Dissolve the inorganic salt and organic ligand in a solvent to obtain a mixed solution; (2) Hydrothermal reaction: The mixed solution obtained in step (1) is subjected to a hydrothermal reaction to obtain the product; (3) Centrifugation: The product obtained in step (2) is centrifuged, washed and dried multiple times to obtain powder I; (4) Ion exchange: Powder I obtained in step (3) is subjected to ion exchange with the solution, and after centrifugation, washing and drying, powder II is obtained; (5) Tablet preparation: Mix powder II with polymer evenly to obtain a mixture, prepare it into tablets, and vacuum dry it to obtain the final product.

[0012] More preferably, in step (1), the mass ratio of inorganic salt, organic ligand and solvent is 3:1:10, and the solvent is selected from deionized water, methanol or N,N-dimethylformamide (DMF), more preferably deionized water.

[0013] Further preferred, in step (2), the hydrothermal reaction conditions are: hydrothermal reaction at 210℃ for 12 to 36 hours, and even more preferred is hydrothermal reaction at 210℃ for 24 hours.

[0014] Further preferred, in step (3), the centrifugation conditions are: centrifugation at 7000-8000 r / min for 1-5 min; after centrifugation, the supernatant is discarded; during washing, deionized water, DMF, and anhydrous ethanol are used in sequence; the drying conditions are: vacuum drying at 80℃ for 12 h.

[0015] More preferably, the centrifugation conditions are: centrifugation at 7000 r / min for 5 min; and washing is performed once each with deionized water, DMF, and anhydrous ethanol.

[0016] More preferably, in step (4), the ratio of powder I to solution is 1g:100mL.

[0017] Further preferably, in step (4), the exchange time is 12 to 24 hours, and even more preferably 24 hours.

[0018] More preferably, in step (5), the mass fraction of the polymer in the mixture is 10-30%, and even more preferably 30%.

[0019] Further preferably, in step (5), the method for preparing the film is selected from any one of rolling, cold pressing, casting, or vacuum filtration; wherein, the rolling method mainly involves continuously rolling the material through a rolling press, and controlling the thickness of the diaphragm by adjusting the pressure; the cold pressing method involves placing the material in a mold and applying pressure through a hydraulic press to form a film; the casting method involves uniformly coating the material onto the surface of the substrate using a casting tool to form a film; the vacuum filtration method involves first pouring the dispersion of the material into a vacuum filtration flask lined with a filter membrane, and then performing vacuum filtration, thereby allowing the film to adhere to the base film. Casting is even more preferred.

[0020] More preferably, in step (5), the vacuum drying conditions are: vacuum drying at 80°C for 12 hours.

[0021] A self-supporting membrane with high ionic conductivity, MIL-121 / Na, is obtained by the aforementioned preparation method.

[0022] The aforementioned application of a high ionic conductivity MIL-121 / Na self-supporting separator in sodium-sulfur batteries.

[0023] The beneficial effects of this invention are: This invention provides a high ionic conductivity MIL-121 / Na self-supporting membrane, its preparation method, and its applications. Inspired by biomembrane ion channels, this invention develops a membrane prepared from a carboxylate-modified metal-organic framework MIL-121 / Na. This material utilizes sub-nanometer charged channels to achieve Na... + Highly efficient selective transport, with an ionic conductivity of 2.27 × 10⁻⁶. -4 S / cm. Its application in room-temperature sodium-sulfur batteries effectively promotes reaction kinetics, showing significant improvement compared to existing sodium-sulfur battery separators. It possesses enormous potential commercial value in metal-sulfur battery systems and is suitable for widespread application.

[0024] This invention constructs a selective sodium ion transport channel through ion exchange, and then prepares a flexible, high-temperature resistant membrane using a casting method. This preparation method has the advantages of simple reaction process, high operability, and high safety. Therefore, this invention can achieve the following effects through simple ion channel construction: (1) Highly efficient suppression of shuttle effect: The -COO- negatively charged functional group in the skeleton can suppress polysulfide anions (S x 2- This generates a strong electrostatic repulsion effect, effectively confining it to the positive side and fundamentally eliminating the shuttle effect.

[0025] (2) Enhanced ionic conductivity and transport number: The abundant -COONa groups in the MIL-121 / Na framework can act as Na + Rapidly transported sites, and blocking anions (such as S) through electrostatic repulsion. x 2- This process significantly increases the sodium ion transference number, reduces polarization, and improves rate performance. Simultaneously, its regular nanopores also act as a size sieve and physical confinement mechanism for polysulfides.

[0026] (3) Promotes uniform deposition and wide electrochemical window: The inherent rigid porous structure of MOF materials helps to homogenize sodium ion flow, inhibit the growth of sodium dendrites, and improve safety. In addition, MIL-121 / Na materials themselves have good chemical and electrochemical stability and can withstand the working potential window of the battery.

[0027] This invention achieves highly efficient sodium ion transport (ionic conductivity 2.27 × 10⁻⁶). -4 A dual blocking mechanism of S / cm and polysulfides achieves 1182 mAh g at 0.5 C rate. -1 It exhibits excellent rate performance and long cycle life, with a high initial discharge specific capacity and stable operation for 400 cycles.

[0028] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 The images show the morphology of the MIL-121 / Na membrane (a) prepared in Example 1 with pyromellitic acid as a ligand and the MIL-121 membrane (b) obtained in Comparative Example 1-1 with pyromellitic acid as a ligand but without ion exchange. Figure 2 The images show the morphology of the MOF membrane (a) prepared in Comparative Examples 1-2 with pyromellitic acid as a ligand and the MOF membrane (b) prepared in Comparative Examples 1-3 with terephthalic acid as a ligand. Figure 3 This is a graph showing the ionic conductivity test results of the MIL-121 / Na membrane with pyromellitic acid as a ligand in Example 2; Figure 4 The graph shows the ionic conductivity test results of the MIL-121 membrane with pyromellitic acid as a ligand in Comparative Example 2-1. Figure 5 The graph shows the ionic conductivity test results of the MOF membrane with pyromellitic acid as a ligand in Comparative Example 2-2. Figure 6 The graph shows the ionic conductivity test results of the MOF membranes with terephthalic acid as ligand in Comparative Examples 2-3.

[0030] Figure 7 The graph shows the electrochemical performance test results of a sodium-sulfur symmetric battery with metallic sodium as both the positive and negative electrodes, which is composed of a MIL-121 / Na membrane with pyromellitic acid as a ligand prepared in Example 1. Figure 8 The figure shows the electrochemical performance test results of a sodium-sulfur symmetric battery with metallic sodium as both the positive and negative electrodes, which is composed of a MIL-121 membrane with pyromellitic acid as a ligand prepared in Comparative Example 1-1 and has metallic sodium as both the positive and negative electrodes. Figure 9 The graph shows the electrochemical performance test results of a sodium-sulfur battery consisting of a positive electrode containing S@C, a metallic sodium negative electrode, and a MIL-121 / Na separator prepared in Example 1 with pyromellitic tetroxide as a ligand; where a is the charge-discharge curve of the battery during the cycle process, and b is the cycle performance graph of the battery. Figure 10The graph shows the electrochemical performance test results of a sodium-sulfur battery consisting of a positive electrode containing S@C, a metallic sodium negative electrode, and a MIL-121 separator prepared in Comparative Example 1-1 with pyromellitic acid as a ligand; where a is the charge-discharge curve of the battery during the cycle process, and b is the cycle performance graph of the battery. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Example 1: A MIL-121 / Na self-supporting membrane with high ionic conductivity using pyromellitic acid as a ligand and its preparation method thereof, specifically including the following steps: Mixing: Inorganic salt aluminum nitrate nonahydrate, organic ligand pyromellitic acid, and deionized water are mixed in a mass ratio of 3:1:10.

[0033] Hydrothermal reaction: The mixed solution obtained in step (1) was subjected to hydrothermal reaction at 210℃ for 24 hours; Centrifugation: The product obtained in step (2) was centrifuged (7000 rpm, 5 min). It was then washed once each with deionized water, DMF, and anhydrous ethanol. Finally, the product was vacuum dried at 80 °C for 12 h to obtain a powder. Ion exchange: The powder obtained in step (3) is mixed with 1M sodium acetate solution at a ratio of 1g:100mL and ion exchange is performed. After centrifugation, washing and drying, the powder is obtained. Sheet preparation: The powder and vinylidene fluoride-hexafluoropropylene copolymer polymer are mixed at a mass ratio of 7:3, and the mixture is prepared into sheets by casting and vacuum drying to obtain the self-supporting diaphragm material. Figure 1 As shown in Figure a.

[0034] Comparative Example 1-1 A self-supporting membrane for MIL-121 with pyromellitic acid as a ligand and its preparation method thereof, specifically including the following steps: Mixing: Inorganic salt aluminum nitrate nonahydrate, organic ligand pyromellitic acid, and deionized water are mixed in a mass ratio of 3:1:10.

[0035] Hydrothermal reaction: The mixed solution obtained in step (1) was subjected to hydrothermal reaction at 210°C for 24 hours; Centrifugation: The product obtained in step (2) was centrifuged (7000 rpm, 5 min). It was then washed once each with deionized water, DMF, and anhydrous ethanol. Finally, the product was vacuum dried at 80 °C for 12 h to obtain a powder. No ion exchange step.

[0036] Preparation: The powder and vinylidene fluoride-hexafluoropropylene copolymer polymer were mixed at a mass ratio of 7:3, and the mixture was prepared by casting and cut into diaphragm discs with a diameter of 19 mm. Vacuum drying yielded the self-supporting diaphragm material. Figure 1 As shown in b.

[0037] Comparative Examples 1-2 A MOF self-supporting membrane with pyromellitic acid as a ligand and its preparation method thereof, specifically including the following steps: Mixing: Inorganic salt aluminum nitrate nonahydrate, organic ligand pyromellitic acid, and deionized water are mixed in a mass ratio of 3:1:10.

[0038] Hydrothermal reaction: The mixed solution obtained in step (1) was subjected to hydrothermal reaction at 210°C for 24 hours; Centrifugation: The product obtained in step (2) was centrifuged (7000 rpm, 5 min). It was then washed once each with deionized water, DMF, and anhydrous ethanol. Finally, the product was vacuum dried at 80 °C for 12 h to obtain a powder. No ion exchange step.

[0039] (5) Sheet preparation: The powder and vinylidene fluoride-hexafluoropropylene copolymer polymer are mixed at a mass ratio of 7:3, and the mixture is prepared by casting and cut into diaphragm discs with a diameter of 19 mm. Vacuum drying yields the self-supporting diaphragm material, such as... Figure 2 As shown in Figure a.

[0040] Comparative Examples 1-3 A MOF self-supporting membrane with terephthalic acid as a ligand and its preparation method thereof, specifically including the following steps: Mixing: Inorganic salt aluminum nitrate nonahydrate, organic ligand terephthalic acid, and deionized water are mixed in a mass ratio of 3:1:10.

[0041] Hydrothermal reaction: The mixed solution obtained in step (1) was subjected to hydrothermal reaction at 210°C for 24 hours; Centrifugation: The product obtained in step (2) was centrifuged (7000 rpm, 5 min). It was then washed once each with deionized water, DMF, and anhydrous ethanol. Finally, the product was vacuum dried at 80 °C for 12 h to obtain a powder. No ion exchange step.

[0042] (5) Sheet preparation: The powder and vinylidene fluoride-hexafluoropropylene copolymer polymer are mixed at a mass ratio of 7:3, and the mixture is prepared by casting and cut into diaphragm discs with a diameter of 19 mm. Vacuum drying yields the self-supporting diaphragm material, such as... Figure 2 As shown in b.

[0043] Example 2 The ionic conductivity test of the MIL-121 / Na membrane with pyromellitic acid as a ligand includes the following steps: (1) Separator: MIL-121 / Na separator with a thickness of 50 micrometers and a diameter of 19 millimeters and ligands of pyromellitic acid (Example 1). (2) Positive and negative electrodes: metal steel sheets with a diameter of 14 mm; (3) Electrolyte: 1M NaClO4 in EC:PC=1:1 Vol% with 5% FEC (NC004 electrolyte); (4) Battery assembly and testing: Assemble a symmetrical battery with a MIL-121 / Na separator in the middle and steel sheets for both the positive and negative electrodes, and perform EIS testing, such as... Figure 3 As shown.

[0044] Comparative Example 2-1 The ionic conductivity test of the MIL-121 membrane with pyromellitic acid as a ligand includes the following steps: (1) Separator: MIL-121 diaphragm with a thickness of 50 micrometers and a diameter of 19 millimeters and pyromellitic acid as ligand (Comparative Example 1-1). (2) Positive and negative electrodes: metal steel sheets with a diameter of 14 mm; (3) Electrolyte: 1M NaClO4 in EC:PC=1:1 Vol% with 5% FEC (NC004 electrolyte); (4) Battery assembly and testing: Assemble a symmetrical battery with a MIL-121 / Na separator in the middle and steel sheets for both the positive and negative electrodes, and perform EIS testing, such as... Figure 4 As shown.

[0045] Comparative Example 2-2 The ionic conductivity test of MOF membranes with pyromellitic acid as a ligand includes the following steps: (1) Separator: MOF separator with a thickness of 50 micrometers and a diameter of 19 millimeters, using pyromellitic acid as a ligand (Comparative Examples 1-2). (2) Positive and negative electrodes: metal steel sheets with a diameter of 14 mm; (3) Electrolyte: 1M NaClO4 in EC:PC=1:1 Vol% with 5% FEC (NC004 electrolyte); (4) Battery assembly and testing: Assemble a symmetrical battery with a MIL-121 / Na separator in the middle and steel sheets for both the positive and negative electrodes, and perform EIS testing, such as... Figure 5 As shown.

[0046] Comparative Examples 2-3 The ionic conductivity test of MOF membranes with terephthalic acid as a ligand includes the following steps: (1) Separator: MOF separator with a thickness of 50 micrometers and a diameter of 19 millimeters, using terephthalic acid as a ligand (Comparative Examples 1-3). (2) Positive and negative electrodes: metal steel sheets with a diameter of 14 mm; (3) Electrolyte: 1M NaClO4 in EC:PC=1:1 Vol% with 5% FEC (NC004 electrolyte); (4) Battery assembly and testing: Assemble a symmetrical battery with a MIL-121 / Na separator in the middle and steel sheets for both the positive and negative electrodes, and perform EIS testing, such as... Figure 6 As shown.

[0047] Performance testing Figure 1 Figures a and b show the morphology of the MIL-121 / Na membrane and the MIL-121 membrane with pyromellitic acid as the ligand, respectively. It can be clearly observed from the figure that the color of the membrane changes from white to yellow after ion exchange, which to some extent indicates the success of ion exchange. Figure 2 Image a shows the morphology of the membrane prepared from MOF synthesized using pyromellitic acid as the organic ligand and aluminum nitrate nonahydrate as the metal salt. Figure 2 Image b shows the morphology of the membrane prepared by MOF synthesized with terephthalic acid as the organic ligand and aluminum nitrate nonahydrate as the metal salt.

[0048] Figure 4 , Figure 5 , Figure 6 Membranes synthesized using pyromellitic acid, pyromellitic acid, and terephthalic acid as ligands to synthesize MOFs showed intrinsic resistivities of 15Ω, 18Ω, and 21Ω, respectively. This leads to the conclusion that, under the same metal salt conditions, the number of carboxyl groups in the organic ligand affects the intrinsic resistivity of the material, further influencing the reaction kinetics of the battery system. As the number of carboxyl groups in the organic ligand decreases, the intrinsic resistivity of the membrane gradually increases, while its ionic conductivity gradually decreases. In the three control experiments, the MIL-121 membrane synthesized using pyromellitic acid as the organic ligand exhibited the highest ionic conductivity. Ion exchange of MIL-121 yielded MIL-121 / Na, containing sodium carboxylate (-COO-Na). + It can ionize to release free sodium ions, and the negatively charged groups can electrostatically attract cations, so in Figure 3 The medium resistance of the MIL121 / Na membrane is only about 8Ω. The reduction from 15Ω to 8Ω means that the conductivity increases by about 2 times after sodium treatment, demonstrating its excellent ionic conductivity (2.2737 × 10⁻⁶). -4 S / cm).

[0049] Therefore, in parallel experiments using pyromellitic acid, pyromellitic acid, and terephthalic acid ligands, the MOF synthesized with pyromellitic acid ligand exhibited superior electrochemical performance. Next, we will further characterize the electrochemical performance of sodium-sulfur batteries assembled using MIL-121 synthesized with pyromellitic acid ligands and MIL-121 / Na MOF materials obtained through ion exchange.

[0050] The deposition / exfoliation behavior of metallic sodium was investigated using Na||Na symmetric cells assembled with different membranes at 0.5 mA cm⁻¹. -2 The current density and 0.5 mAh cm⁻¹ -2 At the area capacity, the electroplating peeling performance of Na||Na batteries with MIL-121 / Na separator and MIL-121 separator were tested respectively. Figure 7 and Figure 8 The comparison shows that the symmetric cell using the MIL-121 / Na separator maintains a stable time-voltage curve for over 1300 hours, while the symmetric cell using the MIL-121 separator ceases operation after approximately 485 hours. In contrast, the symmetric cell using the MIL-121 / Na separator also exhibits an extremely flat and stable polarization overpotential of approximately 37 mV, which can be attributed to the excellent interfacial compatibility and dendrite suppression capabilities of the flexible MIL-121 / Na separator.

[0051] Figure 9 a and Figure 10 Figure a clearly shows the charge-discharge curves of the two battery groups at 0.5 C rate on cycles 1, 5, 10, 100, and 200, more intuitively demonstrating that the battery using the MIL-121 / Na separator exhibits higher reversible capacity and greater capacity retention. Correspondingly, Figure 9 Figure b shows that the initial discharge specific capacity of the MIL-121 / Na battery at a 0.5 C rate is 1182 mAh g. -1 Under the premise that the initial charge-discharge specific capacity is not much different, MIL-121 / Na still has 627 mAh g⁻¹ after 400 cycles. -1 The specific capacity of MIL-121 after cycling is 388 mAh g, compared to the previous value. -1 ( Figure 10 (b)

[0052] In summary, this invention discloses a biomimetic cell membrane-inspired sodium ion channel membrane (MIL-121 / Na) to address key challenges in metal-sulfur batteries. This membrane introduces carboxylate groups into a metal-organic framework, forming ion-selective sub-nanometer channels that enable efficient sodium ion transport. Simultaneously, the material possesses a wide electrochemical window and excellent thermal stability, effectively suppressing sodium dendrite growth and improving interfacial stability. In full-cell testing, batteries based on this membrane exhibit superior rate performance and long cycle life. Symmetrical cell testing further confirms its stable sodium deposition / stripping behavior. This invention provides an innovative membrane design strategy for developing high-performance, high-safety metal-sulfur batteries, especially room-temperature sodium-sulfur batteries, promoting their application in large-scale energy storage and possessing significant potential commercial value, making it suitable for widespread application.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the preparation of a high ionic conductivity MIL-121 / Na self- supporting membrane, characterized in that, The inorganic salt and the organic ligand are mixed to perform a hydrothermal reaction to obtain powder I; then the powder I is ion-exchanged with a solution to obtain powder II; finally, the powder II is mixed with a polymer to prepare a sheet, and the sheet is obtained; wherein the inorganic salt is aluminum nitrate nonahydrate, the organic ligand is pyromellitic acid, and the solution is a 0.5-3 mol / L sodium acetate solution.

2. The production method according to claim 1, characterized by, The polymer is selected from any one of polyethyleneimine, polyvinylidene fluoride, sodium alginate, polyvinylidene fluoride-hexafluoropropylene copolymer, and polytetrafluoroethylene.

3. The preparation method according to claim 1, characterized in that, The specific steps are as follows: (1) mixing: dissolving the inorganic salt and the organic ligand in a solvent to obtain a mixed solution; (2) hydrothermal reaction: performing a hydrothermal reaction on the mixed solution obtained in step (1) to obtain a product; (3) centrifugation: performing multiple centrifugal washing and drying on the product obtained in step (2) to obtain powder I; (4) ion exchange: ion-exchanging the powder I obtained in step (3) with a solution, centrifuging, washing, and drying to obtain powder II; (5) sheet preparation: uniformly mixing the powder II with a polymer to obtain a mixture, preparing a sheet, and vacuum drying to obtain the sheet.

4. The production method according to claim 3, characterized by, In step (1), the mass ratio of the inorganic salt, the organic ligand, and the solvent is 3:1:10, and the solvent is selected from any one of deionized water, methanol, or N,N-dimethylformamide, and is further preferably deionized water.

5. The preparation method according to claim 3, characterized in that, In step (2), the hydrothermal reaction conditions are 210°C for 12-36 h.

6. The preparation method according to claim 3, characterized in that, In step (3), the centrifugation conditions are 7000-8000 r / min for 1-5 min, and the supernatant is discarded after centrifugation; deionized water, DMF, and anhydrous ethanol are used for washing in sequence; and the drying conditions are 80°C vacuum drying for 12 h.

7. The preparation method according to claim 3, characterized in that, In step (4), the dosage ratio of the powder I to the solution is 1 g:100 mL, and the exchange time is 12-24 h.

8. The preparation method according to claim 3, characterized in that, In step (5), the mass fraction of the polymer in the mixture is 10-30%; The method for preparing the sheet is selected from any one of rolling, cold pressing, casting, or suction filtering; The vacuum drying conditions are 80°C vacuum drying for 12 h.

9. A high ionic conductivity MIL-121 / Na self-supporting membrane, characterized in that, obtained by the preparation method of any one of claims 1-8.

10. Use of the MIL-121 / Na self-supporting membrane with high ionic conductivity of claim 9 in a sodium-sulfur battery.

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