A flexible gradient fiber membrane and a preparation method and application thereof

Abstract

The application discloses a flexible gradient fiber membrane and a preparation method and application thereof, and compared with the prior art, the flexible gradient fiber membrane can be used as an air positive electrode without adhesive, a zinc-air battery assembled by using the flexible gradient fiber membrane has high power density and excellent battery durability, and has the advantages of being lighter and thinner, and as a flexible positive electrode and a diaphragm composite material of a lithium-sulfur battery, the flexible gradient fiber membrane has excellent polysulfide chemical adsorption capacity and unique chemical catalytic properties, so that the lithium-sulfur battery has high capacity, high coulomb efficiency and excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of energy storage material preparation technology, specifically relating to a flexible gradient fiber membrane, its preparation method, and its application. Background Technology

[0002] With the increasing depletion of non-renewable energy sources such as oil, natural gas, and coal, the development and application of clean energy are receiving growing attention. Currently, solar, tidal, wind, and wave energy are considered renewable energy sources, but they are intermittent, thus requiring energy storage and conversion devices to store and release energy. To date, several energy-related devices have been explored and developed, including potassium-ion batteries, metal-based batteries, sulfur-based batteries, and supercapacitors. Among the energy systems explored, lithium-sulfur batteries have demonstrated high theoretical specific capacity (1675 mA h g⁻¹) and high energy density (2600 W h kg⁻¹). -1 With low-cost batteries, these devices hold promise as our next generation of energy storage equipment.

[0003] However, lithium-sulfur batteries currently face many defects and problems. On the positive electrode side, sulfur and the discharge product lithium polysulfides have poor electronic conductivity, which greatly hinders electron transfer during charge and discharge. Furthermore, lithium polysulfide intermediates dissolve in the organic electrolyte and migrate towards the negative electrode, leading to rapid capacity decay and short lifespan. In addition, the volume expansion of long-chain lithium polysulfides often disrupts the microstructure of the positive electrode material, resulting in capacity decay. Simultaneously, the growth of lithium dendrites on the anode side can cause microstructural intrusion, leading to battery safety issues.

[0004] To address these issues, increasing research focuses on the microstructure of cathode materials, modifying them to improve conductivity and suppress polysulfide shuttle effects, aiming to enhance the electrochemical stability of lithium-sulfur batteries. In recent years, additive manufacturing technologies, such as electrospinning, and the emergence of three-dimensional porous materials, such as metal-organic frameworks, have sparked a new wave of exploration in electrode materials. On the cathode side, electrospun fiber membranes offer a simple and low-cost method for preparing stable fibrous frameworks, achieving high specific surface area and numerous active sites. In lithium-sulfur batteries, the high specific surface area and abundant catalytically active sites of nitrogen-doped carbon framework fiber membranes can suppress polysulfide shuttle effects, resulting in better reaction kinetics and electrochemical stability. Furthermore, nitrogen-doped carbon framework fiber membranes, when applied to the air cathode of zinc-air batteries, also provide excellent catalytic activity in terms of reaction kinetics, without the need for additional binders / additives. Additionally, fiber membranes prepared by electrospinning, after simple modification, can also be used as battery separators. The ultrathin thickness of the separator effectively reduces ion transport distance. In lithium-sulfur batteries, electrospun polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) fiber membranes can improve interfacial issues within the battery due to their excellent mechanical properties and thermal stability. In zinc-air batteries, PVDF fiber membranes prepared by electrospinning can also be used as hydrophobic-permeable layers, replacing expensive commercially available waterproof and breathable separators. Therefore, composite flexible fiber membranes with an integrated design concept have the potential to be applied to different types of high-performance batteries. However, these strategies only address a small part of the battery assembly and do not provide a complete integrated solution for the battery.

[0005] Therefore, developing an integrated flexible gradient fiber membrane with multiple battery functions is of significant practical importance. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention aims to solve the problem of how to improve the electrochemical performance of batteries.

[0007] To achieve the above objectives, the present invention provides a flexible gradient fiber membrane, its preparation method and application, specifically including the following two optional structures.

[0008] The first type of flexible gradient fiber membrane includes a Co-NC layer and a PVDF layer, wherein the fiber diameter of the PVDF layer is 500 nm and the fiber diameter of the Co-NC layer is 5 μm.

[0009] The preparation method of this flexible gradient fiber membrane specifically includes the following steps:

[0010] S1. Co-NC layers were prepared by electrospinning, chemical bath deposition and chemical vapor deposition.

[0011] S2. The PVDF layer is prepared by electrospinning.

[0012] S3. Load Li2S6 onto the Co-NC layer, and then stack the PVDF layer on the Co-NC layer to obtain a flexible gradient fiber membrane.

[0013] Preferably, step S1 specifically includes the following steps:

[0014] S11. Dissolve cobalt nitrate hexahydrate and polyacrylonitrile in N,N-dimethylformamide, and stir at 20-30℃ for at least 10 hours to obtain a mixed solution.

[0015] S12. Using a syringe, draw up the mixed solution obtained in step S11 and prepare a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 10-15kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.4-0.8ml / h.

[0016] S13. Using a chemical bath deposition method, the PAN / Co fiber membrane obtained in step S12 is immersed in an aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole, and a sheet-like Co-MOF organometallic framework is grown in situ to obtain the PAN / Co-MOF fiber membrane.

[0017] S14. Using chemical vapor deposition, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace, pre-oxidized in air at 250°C, and then carbonized at 800°C by argon gas to obtain Co-NC conductive fiber membrane.

[0018] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0019] Preferably, step S2 specifically includes the following steps:

[0020] S21. Pour vinylidene fluoride powder into a mixture of acetone and N,N-dimethylformamide, and stir at 60-80°C for at least 10 hours to obtain a mixed solution.

[0021] S22: The mixed solution obtained in S21 is drawn up using a syringe, and a PVDF layer is prepared by electrospinning. The parameters of the electrospinning method are as follows: voltage is 15-16kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.5-1ml / h.

[0022] The present invention also provides the application of this flexible gradient fiber membrane in zinc-air batteries.

[0023] Compared with existing technologies, Co-NC / PVDF bilayer gradient fiber membranes can also be used as binder-free air cathodes, and the assembled zinc-air batteries achieve high power density and excellent battery durability, while also being lighter and thinner.

[0024] The second type of flexible gradient fiber membrane includes a Co-NC layer, a PVDF layer and a PAN layer arranged sequentially from top to bottom. The fiber diameter of the PVDF layer is 500 nm, the fiber diameter of the Co-NC layer is 5 μm, and the fiber diameter of the PAN layer is 200 nm.

[0025] The preparation method of this flexible gradient fiber membrane specifically includes the following steps:

[0026] S1. Co-NC layers were prepared by electrospinning, chemical bath deposition and chemical vapor deposition.

[0027] S2. The PVDF layer is prepared by electrospinning.

[0028] S3. The PAN layer is prepared by electrospinning and high-temperature oxidation.

[0029] S4. Load Li2S6 onto the Co-NC layer, and then stack the PVDF layer and PAN layer sequentially on the Co-NC layer to obtain a flexible gradient fiber membrane.

[0030] Preferably, step S1 specifically includes the following steps:

[0031] S11. Dissolve cobalt nitrate hexahydrate and polyacrylonitrile in N,N-dimethylformamide, and stir at 20-30℃ for at least 10 hours to obtain a mixed solution.

[0032] S12. Using a syringe, draw up the mixed solution obtained in step S11 and prepare a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 10-15kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.4-0.8ml / h.

[0033] S13. Using a chemical bath deposition method, the PAN / Co fiber membrane obtained in step S12 is immersed in an aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole, and a sheet-like Co-MOF organometallic framework is grown in situ to obtain the PAN / Co-MOF fiber membrane.

[0034] S14. Using chemical vapor deposition, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace, pre-oxidized in air at 250°C, and then carbonized at 800°C by argon gas to obtain Co-NC conductive fiber membrane.

[0035] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0036] Preferably, step S2 specifically includes the following steps:

[0037] S21. Pour vinylidene fluoride powder into a mixture of acetone and N,N-dimethylformamide, and stir at 60-80°C for at least 10 hours to obtain a mixed solution.

[0038] S22: Using a syringe, the mixed solution obtained in S21 is drawn up, and a PVDF layer is prepared by electrospinning. The parameters of the electrospinning method are as follows: voltage 15-16kV, distance from syringe needle to collector 10-15cm, syringe injection speed 0.5-1ml / h; and / or,

[0039] Preferably, step S3 specifically includes the following steps:

[0040] S31. Pour polyacrylonitrile powder into N,N-dimethylformamide solution and stir at 20-30℃ for at least 10 hours to obtain a mixed solution;

[0041] S32. Using a syringe, draw up the mixed solution obtained in step S31 and prepare a polyacrylonitrile fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 16-18kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.4-1ml / h.

[0042] S33. The polyacrylonitrile fiber membrane obtained in step S32 is pre-oxidized using a muffle furnace to obtain the PAN layer. The parameters of the pre-oxidation treatment are as follows: temperature is 250℃, and heating rate is 2.5-6.5℃ / min.

[0043] This invention also provides the application of this flexible gradient fiber membrane in lithium-sulfur batteries.

[0044] Compared to existing technologies, this gradient fiber membrane offers diverse applications and advantages in various battery systems. In lithium-sulfur batteries, a SA-Co-NC / PVDF / PAN three-layer fiber membrane constructs a highly polar, strongly adsorbed, flexible, self-supporting sulfur cathode material. Due to the advantages of the gradient three-layer structure, the prepared lithium-sulfur full cell exhibits excellent electrochemical performance, particularly in capacity and cycle stability. Furthermore, the multifunctionality of the gradient layers enables the full cell to maintain high initial capacity and excellent cycle stability even under high sulfur loading, while also possessing ultra-thin thickness and ideal flexibility. Attached Figure Description

[0045] Figure 1 These are electron microscope images of the Co-NC layers obtained in Examples 1 and 2 of this invention;

[0046] Figure 2 These are electron microscope images of the PVDF layers obtained in Examples 1 and 2 of this invention.

[0047] Figure 3 This is an electron microscope image of the PAN layer obtained in Example 2 of the present invention;

[0048] Figure 4 The figures show the chemical performance of Application Example 1 and Application Example 2 of this invention in lithium-sulfur batteries;

[0049] Figure 5 The diagram shows the chemical performance of application examples 3 and 4 of the present invention in a zinc-air battery. Detailed Implementation

[0050] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0052] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0053] The specific implementation of the flexible gradient electrode of the present invention can be divided into two types. The first type of flexible gradient fiber membrane includes a Co-NC layer and a PVDF layer. The fiber diameter of the PVDF layer is 500 nm, and the fiber diameter of the Co-NC layer is 5 μm. The preparation method specifically includes the following steps: S1, the Co-NC layer is prepared by electrospinning, chemical bath deposition and chemical vapor deposition; S2, the PVDF layer is prepared by electrospinning; S3, Li2S6 is loaded on the Co-NC layer, and then the PVDF layer is stacked on the Co-NC layer to obtain the flexible gradient fiber membrane.

[0054] In this specific embodiment, step S1 specifically includes the following steps: S11, dissolving cobalt nitrate hexahydrate and polyacrylonitrile in N,N-dimethylformamide, and stirring at 20-30°C for at least 10 hours to obtain a mixed solution; S12, using a syringe to draw up the mixed solution obtained in step S11, and preparing a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage of 10-15kV, distance from syringe needle to collector of 10-15cm, and syringe injection speed of 0.4-0.8ml / h;

[0055] S13. Using a chemical bath deposition method, the PAN / Co fiber membrane obtained in step S12 is immersed in an aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole to grow a sheet-like Co-MOF organometallic framework in situ, thereby obtaining a PAN / Co-MOF fiber membrane; S14. Using a chemical vapor deposition method, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace, pre-oxidized in air at 250°C, and then subjected to high-temperature carbonization treatment by argon gas to obtain a Co-NC conductive fiber membrane;

[0056] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0057] In this specific embodiment, step S2 specifically includes the following steps: S21, pour vinylidene fluoride powder into a mixture of acetone and N,N-dimethylformamide, and stir at 60-80°C for at least 10 hours to obtain a mixed solution; S22: use a syringe to draw up the mixed solution obtained in S21, and prepare a PVDF layer by electrospinning. The parameters of the electrospinning method are as follows: voltage is 15-16kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.5-1ml / h.

[0058] The present invention also provides the application of this flexible gradient fiber membrane in zinc-air batteries.

[0059] The second type of flexible gradient fiber membrane includes a Co-NC layer, a PVDF layer, and a PAN layer arranged sequentially from top to bottom. The fiber diameter of the PVDF layer is 500 nm, the fiber diameter of the Co-NC layer is 5 μm, and the fiber diameter of the PAN layer is 200 nm. The preparation method specifically includes the following steps: S1, preparing the Co-NC layer by electrospinning, chemical bath deposition, and chemical vapor deposition; S2, preparing the PVDF layer by electrospinning; S3, preparing the PAN layer by electrospinning and high-temperature oxidation; S4, loading Li2S6 onto the Co-NC layer, and then stacking the PVDF layer and the PAN layer sequentially on the Co-NC layer to obtain the flexible gradient fiber membrane.

[0060] In this specific embodiment, step S1 specifically includes the following steps: S11, dissolving cobalt nitrate hexahydrate and polyacrylonitrile in N,N-dimethylformamide, and stirring at 20-30°C for at least 10 hours to obtain a mixed solution; S12, using a syringe to draw up the mixed solution obtained in step S11, and preparing a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage of 10-15kV, distance from syringe needle to collector of 10-15cm, and syringe injection speed of 0.4-0.8ml / h;

[0061] S13. Using a chemical bath deposition method, the PAN / Co fiber membrane obtained in step S12 is immersed in an aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole to grow a sheet-like Co-MOF organometallic framework in situ, thereby obtaining a PAN / Co-MOF fiber membrane; S14. Using a chemical vapor deposition method, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace, pre-oxidized in air at 250°C, and then subjected to high-temperature carbonization treatment by argon gas to obtain a Co-NC conductive fiber membrane;

[0062] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0063] In this specific embodiment, step S2 specifically includes the following steps: S21, pour vinylidene fluoride powder into a mixture of acetone and N,N-dimethylformamide, and stir at 60-80°C for at least 10 hours to obtain a mixed solution; S22: use a syringe to draw up the mixed solution obtained in S21, and prepare a PVDF layer by electrospinning. The parameters of the electrospinning method are as follows: voltage is 15-16kV, distance from syringe needle to collector is 10-15cm, and syringe injection speed is 0.5-1ml / h.

[0064] In this specific embodiment, step S3 specifically includes the following steps: S31, pouring polyacrylonitrile powder into an N,N-dimethylformamide solution and stirring at 20-30℃ for at least 10 hours to obtain a mixed solution; S32, using a syringe to draw up the mixed solution obtained in step S31, and preparing a polyacrylonitrile fiber membrane by electrospinning, wherein the parameters of the electrospinning method are as follows: voltage 16-18kV, distance from syringe needle to collector 10-15cm, and syringe injection speed 0.4-1ml / h; S33, using a muffle furnace to pre-oxidize the polyacrylonitrile fiber membrane obtained in step S32 to obtain a PAN layer, wherein the parameters of the pre-oxidation treatment are as follows: temperature 250℃, and heating rate 2.5-6.5℃ / min.

[0065] The present invention also provides the application of this flexible gradient fiber membrane in lithium-sulfur batteries.

[0066] The technical effects of the present invention will be described below with reference to specific embodiments.

[0067] Example 1

[0068] This embodiment provides a flexible gradient fiber membrane, comprising a Co-NC layer and a PVDF layer, which is prepared by the following method:

[0069] S11. Dissolve 0.35g of cobalt nitrate hexahydrate and 1g of polyacrylonitrile in 11ml of N,N-dimethylformamide, and stir at 25℃ for 18h to obtain a mixed solution.

[0070] S12. Using a syringe, draw up the mixed solution obtained in step S11 and prepare a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 12kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 0.5ml / h.

[0071] S13. First, prepare an aqueous solution of cobalt nitrate hexahydrate and an aqueous solution of dimethylimidazole. The mass of the solute in the cobalt nitrate hexahydrate aqueous solution is 1.455 g, and the volume of the solution is 60 ml. The mass of the solute in the dimethylimidazole aqueous solution is 4.105 g, and the volume of the solution is 60 ml. Stir the dimethylimidazole aqueous solution and the cobalt nitrate hexahydrate aqueous solution separately, and then mix and stir for 30 s. Using the chemical bath deposition method, immerse the PAN / Co fiber membrane obtained in step S12 in the aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole and let it stand for 4 hours to grow a sheet-like Co-MOF organometallic framework in situ. Then, rinse the surface with deionized water and dry it in a vacuum drying oven at 40 ℃ to obtain the PAN / Co-MOF fiber membrane.

[0072] S14. Using chemical vapor deposition, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace and pre-oxidized in air at 250°C for 60 min. Then, argon gas is introduced to perform high-temperature carbonization at 800°C for 120 min to obtain the Co-NC conductive fiber membrane.

[0073] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0074] S21. Pour 1g of vinylidene fluoride powder into a mixture containing 5.27g of acetone and 5.86g of N,N-dimethylformamide, and stir at 80°C for 12 hours to obtain a mixed solution.

[0075] S22: The mixed solution obtained in S21 is drawn up using a syringe, and a PVDF layer is prepared by electrospinning. The parameters of the electrospinning method are as follows: voltage is 16kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 1ml / h.

[0076] S3. Load Li2S6 onto the Co-NC layer, and then stack the PVDF layer on the Co-NC layer to obtain a flexible gradient fiber membrane.

[0077] Example 2

[0078] This embodiment provides a flexible gradient fiber membrane comprising a Co-NC layer, a PVDF layer, and a PAN layer arranged sequentially from top to bottom. The specific surface area of ​​the flexible gradient fiber membrane is XX. The preparation method of the flexible gradient fiber membrane specifically includes the following steps:

[0079] S11. Dissolve 0.35g of cobalt nitrate hexahydrate and 1g of polyacrylonitrile in 11ml of N,N-dimethylformamide, and stir at 25℃ for 18h to obtain a mixed solution.

[0080] S12. Using a syringe, draw up the mixed solution obtained in step S11 and prepare a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 12kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 0.5ml / h.

[0081] S13. First, prepare an aqueous solution of cobalt nitrate hexahydrate and an aqueous solution of dimethylimidazole. The mass of the solute in the cobalt nitrate hexahydrate aqueous solution is 1.455 g, and the volume of the solution is 60 ml. The mass of the solute in the dimethylimidazole aqueous solution is 4.105 g, and the volume of the solution is 60 ml. Stir the dimethylimidazole aqueous solution and the cobalt nitrate hexahydrate aqueous solution separately, and then mix and stir for 30 s. Using the chemical bath deposition method, immerse the PAN / Co fiber membrane obtained in step S12 in the aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole and let it stand for 4 hours to grow a sheet-like Co-MOF organometallic framework in situ. Then, rinse the surface with deionized water and dry it in a vacuum drying oven at 40 ℃ to obtain the PAN / Co-MOF fiber membrane.

[0082] S14. Using chemical vapor deposition, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace and pre-oxidized in air at 250°C for 60 min. Then, argon gas is introduced to perform high-temperature carbonization at 800°C for 120 min to obtain the Co-NC conductive fiber membrane.

[0083] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0084] S21. Pour 1g of vinylidene fluoride powder into a mixture containing 5.27g of acetone and 5.86g of N,N-dimethylformamide, and stir at 80°C for 12 hours to obtain a mixed solution.

[0085] S22: The mixed solution obtained in S21 is drawn up using a syringe, and a PVDF layer is prepared by electrospinning. The parameters of the electrospinning method are as follows: voltage is 16kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 1ml / h.

[0086] S31. Pour 1g of polyacrylonitrile powder into 10ml of N,N-dimethylformamide solution and stir at 25℃ for 12h to obtain a mixed solution;

[0087] S32. Using a syringe, draw up the mixed solution obtained in step S31 and prepare a polyacrylonitrile fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 18kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 0.5ml / h.

[0088] S33. The polyacrylonitrile fiber membrane obtained in step S32 is pre-oxidized using a muffle furnace to obtain the PAN layer. The parameters of the pre-oxidation treatment are as follows: temperature is 250℃, duration is 90min, and heating rate is 5℃ / min.

[0089] S4. Load Li2S6 onto the Co-NC layer, and then stack the PVDF layer and PAN layer sequentially on the Co-NC layer to obtain a flexible gradient fiber membrane.

[0090] Example 3

[0091] This embodiment provides a fiber membrane, comprising an NC layer and a PVDF layer, and its preparation method specifically includes the following steps:

[0092] S1. Dissolve 0.35g zinc nitrate hexahydrate and 1g polyacrylonitrile in 11ml N,N-dimethylformamide and stir thoroughly at 25℃ for 18h to obtain a mixed solution.

[0093] S2. Use a syringe to draw up the solution prepared in S1 and perform electrospinning to prepare PAN / Zn fiber membrane. The electrospinning parameters are: voltage 12kV, distance from syringe needle to collector 10cm, and syringe injection speed 0.5ml / h.

[0094] S3. First, prepare an aqueous solution of zinc nitrate hexahydrate and an aqueous solution of dimethylimidazole. The mass of the solute in the zinc nitrate hexahydrate aqueous solution is 1.487 g, and the volume of the solution is 60 ml. The mass of the solute in the dimethylimidazole aqueous solution is 4.105 g, and the volume of the solution is 60 ml. Stir the dimethylimidazole aqueous solution and the zinc nitrate hexahydrate aqueous solution separately, and then mix and stir for 30 s. Using a chemical bath deposition method, immerse the prepared PAN / Co fiber membrane in the mixed aqueous solution of zinc nitrate hexahydrate and dimethylimidazole and let it stand in situ for 4 h to grow a sheet-like Zn-MOF organometallic framework in situ. Then, rinse the surface with deionized water and dry it in a vacuum drying oven at 40 ℃ to obtain the PAN / Zn-MOF fiber membrane.

[0095] S4. Using chemical vapor deposition, the PAN / Zn-MOF fiber membrane obtained in step S3 is placed in a tube furnace and pre-oxidized in air at 250°C for 60 min. Then, argon gas is introduced for high-temperature carbonization at 800°C for 120 min to obtain the NC conductive fiber membrane.

[0096] S5. Pour 1g of vinylidene fluoride powder into a mixture containing 5.27g of acetone and 5.86g of N,N-dimethylformamide, and stir at 80°C for 12 hours to obtain a mixed solution.

[0097] S6: The mixed solution prepared in S21 is drawn up using a syringe, and a PVDF layer is prepared by electrospinning. The parameters of the electrospinning method are as follows: voltage is 16kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 1ml / h.

[0098] S7. Load Li2S6 onto the NC layer, and then stack the PVDF layer on the NC layer to obtain a fiber membrane.

[0099] Example 4

[0100] This embodiment provides a fiber membrane, including a Co-NC layer and a PAN layer, and its preparation method specifically includes the following steps:

[0101] S11. Dissolve 0.35g of cobalt nitrate hexahydrate and 1g of polyacrylonitrile in 11ml of N,N-dimethylformamide, and stir at 25℃ for 18h to obtain a mixed solution.

[0102] S12. Using a syringe, draw up the mixed solution obtained in step S11 and prepare a PAN / Co fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 12kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 0.5ml / h.

[0103] S13. First, prepare an aqueous solution of cobalt nitrate hexahydrate and an aqueous solution of dimethylimidazole. The mass of the solute in the cobalt nitrate hexahydrate aqueous solution is 1.455 g, and the volume of the solution is 60 ml. The mass of the solute in the dimethylimidazole aqueous solution is 4.105 g, and the volume of the solution is 60 ml. Stir the dimethylimidazole aqueous solution and the cobalt nitrate hexahydrate aqueous solution separately, and then mix and stir for 30 s. Using the chemical bath deposition method, immerse the PAN / Co fiber membrane obtained in step S12 in the aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole and let it stand for 4 hours to grow a sheet-like Co-MOF organometallic framework in situ. Then, rinse the surface with deionized water and dry it in a vacuum drying oven at 40 ℃ to obtain the PAN / Co-MOF fiber membrane.

[0104] S14. Using chemical vapor deposition, the PAN / Co-MOF fiber membrane obtained in step S13 is placed in a tube furnace and pre-oxidized in air at 250°C for 60 min. Then, argon gas is introduced to perform high-temperature carbonization at 800°C for 120 min to obtain the Co-NC conductive fiber membrane.

[0105] S15. The Co-NC conductive fiber membrane obtained in step S14 is placed in a 0.2-1.0 mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washed with deionized water and dried to obtain the Co-NC layer.

[0106] S21. Pour 1g of polyacrylonitrile powder into 10ml of N,N-dimethylformamide solution and stir at 25℃ for 12h to obtain a mixed solution;

[0107] S22. Using a syringe, draw up the mixed solution obtained in step S31 and prepare a polyacrylonitrile fiber membrane by electrospinning. The parameters of the electrospinning method are as follows: voltage is 18kV, distance from syringe needle to collector is 10cm, and syringe injection speed is 0.5ml / h.

[0108] S23. The polyacrylonitrile fiber membrane obtained in step S32 is pre-oxidized using a muffle furnace to obtain the PAN layer. The parameters of the pre-oxidation treatment are as follows: temperature is 250℃, duration is 90min, and heating rate is 5℃ / min.

[0109] S24. Load Li2S6 onto the Co-NC layer, and then stack the PAN layer on the Co-NC layer to obtain a flexible gradient fiber membrane.

[0110] Scanning electron microscope images of the Co-NC layers obtained in Examples 1, 2, and 4 are shown below. Figure 1 As shown, from Figure 1 Scanning electron microscope (SEM) images show that the sheet-like nanosheets on the Co-NC layer are uniformly arranged, with a single fiber diameter of about 5 μm. At the same time, the overall specific surface area of ​​the material increases, and the catalytic sites of metallic Co are also enriched.

[0111] Scanning electron microscope images of the PVDF layers obtained in Examples 1, 2, and 3 are shown below. Figure 2 As shown, from Figure 2 According to the scanning electron microscope (SEM) images, the PVDF fiber membrane has a uniform fiber distribution, with the diameter of a single fiber being around 500 nm.

[0112] Scanning electron microscope images of the PAN layers obtained in Examples 2 and 4 are shown below. Figure 3 As shown, from Figure 3 According to the scanning electron microscope (SEM) images, the fibers in the PAN layer are evenly distributed, and the fiber diameter is about 200 nm.

[0113] Application Example 1

[0114] The flexible gradient fiber membrane prepared in Example 2 was used in lithium-sulfur batteries as a self-supporting carrier for the positive electrode and separator of lithium-sulfur batteries.

[0115] Application Example 2

[0116] The flexible gradient fiber membrane prepared in Example 4 was used in lithium-sulfur batteries as a self-supporting carrier for the positive electrode and separator of lithium-sulfur batteries.

[0117] To investigate the electrochemical performance of the three-layer gradient material in lithium-sulfur batteries, the cycle performance of symmetric batteries from Application Example 1 and Application Example 2 was tested. The results are as follows: Figure 4As shown, at a current density of 0.5 A / g, the battery exhibits significant advantages in cycle stability. The battery in Application Example 1 demonstrates a high initial discharge capacity of 1124 mAh / g and maintains a high capacity of 1123 mA h / g after 100 cycles with extremely low capacity decay and a stable coulombic efficiency above 99.95%, corresponding to a significant reduction in capacity decay. In contrast, the battery in Application Example 2 has an initial discharge capacity of 542 mA / h at the same current density, and a capacity of 716 mA h / g after approximately 100 cycles. It can be seen that the high capacity, high coulombic efficiency, and excellent cycle stability demonstrate the highly efficient synergy of the three-layer flexible gradient fiber membrane.

[0118] Application Example 3

[0119] The flexible gradient fiber membrane prepared in Example 1 was used in a zinc-air battery as a self-supporting carrier for the positive electrode and hydrophobic separator of the zinc-air battery.

[0120] Application Example 4

[0121] The fiber membrane prepared in Example 3 was used in a zinc-air battery as a self-supporting carrier for the positive electrode and hydrophobic separator of the zinc-air battery.

[0122] To investigate the electrochemical performance of the bilayer gradient material in a zinc-air battery, the constant current cycling performance of Application Example 3 and Application Example 4 was tested, and the results are as follows: Figure 5 As shown. At 1mA / cm 2 At the specified current density, the initial charge-discharge voltage difference of the Co-NC / PVDF-based battery in Application Example 3 was significantly smaller than that of the NC / PVDF-based battery in Application Example 4 (1.09V < 1.33V). Furthermore, after more than 2500 cycles (250h), the full charge-discharge voltage difference of the battery in Application Example 3 was 0.85V, while that of Application Example 4 was 1.54V. After a final 5000 cycles (500h), the charge-discharge voltage difference of Application Example 3 did not show a significant increase, while the battery in Application Example 4 had already failed.

[0123] Clearly, the Co-NC flexible fiber membrane exhibits a stronger electrolyte adsorption capacity than the NC membrane due to its large specific surface area for loading active sites. Conversely, the NC fiber membrane, lacking metallic Co and a high specific surface area, has insufficient electrolyte adsorption capacity. The unique dual-gradient Co-NC / PVDF air cathode material demonstrates excellent performance in aqueous zinc-air batteries.

[0124] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A flexible gradient fiber membrane, characterized in that, The flexible gradient fiber membrane comprises, from top to bottom, a Co-N-C layer, a PVDF layer and a PAN layer, the fiber diameter of the PVDF layer is 500 nm, the fiber diameter of the Co-N-C layer is 5 microns, and the preparation method of the flexible gradient fiber membrane specifically comprises the following steps: S1, using electrospinning method, chemical water bath deposition method and high temperature annealing method to prepare Co-N-C layer; S2, using electrospinning method to prepare PVDF layer; S3, using electrospinning method and high temperature oxidation method to prepare PAN layer; S4, loading Li2S6 on the Co-N-C layer, then stacking the PVDF layer and the PAN layer on the Co-N-C layer in turn to obtain the flexible gradient fiber membrane; The step S1 specifically comprises the following steps: S11, dissolving cobalt nitrate hexahydrate and polyacrylonitrile in N,N-dimethylformamide, stirring at 20-30℃ for at least 10 hours to obtain a mixed solution; S12, using a syringe to suck the mixed solution prepared in step S11, and preparing a PAN / Co fiber membrane by electrospinning method, the parameters of the electrospinning method are as follows: the voltage is 10-15kV, the distance between the syringe needle and the collector is 10-15cm, and the injection speed of the syringe is 0.4-0.8ml / h; S13, using chemical water bath deposition method, immersing the PAN / Co fiber membrane prepared in step S12 in a mixed aqueous solution of cobalt nitrate hexahydrate and dimethylimidazole, and growing Co-MOF organic metal framework in situ to obtain PAN / Co-MOF fiber membrane; S14, using high temperature annealing method, placing the PAN / Co-MOF fiber membrane prepared in step S13 into a tube furnace, first performing pre-oxidation treatment at 250℃ in air, and then performing high temperature carbonization treatment at 800℃ in argon to obtain Co-N-C conductive fiber membrane; S15, placing the Co-N-C conductive fiber membrane prepared in step S14 into 0.2-1.0mol / L hydrochloric acid aqueous solution for etching for 2-8 hours, then washing with deionized water and drying to obtain Co-N-C layer; The step S2 specifically comprises the following steps: S21, pouring polyvinylidene fluoride powder into a mixed solution of acetone and N,N-dimethylformamide, stirring at 60-80℃ for at least 10 hours to obtain a mixed solution; S22, using a syringe to suck the mixed solution prepared in S21, and preparing a PVDF layer by electrospinning method, the parameters of the electrospinning method are as follows: the voltage is 15-16kV, the distance between the syringe needle and the collector is 10-15cm, and the injection speed of the syringe is 0.5-1ml / h; The step S3 specifically comprises the following steps: S31, pouring polyacrylonitrile powder into N,N-dimethylformamide solution, stirring at 20-30℃ for at least 10 hours to obtain a mixed solution; S32, using a syringe to suck the mixed solution prepared in step S31, and preparing a polyacrylonitrile fiber membrane by electrospinning method, the parameters of the electrospinning method are as follows: the voltage is 18kV, the distance between the syringe needle and the collector is 10cm, and the injection speed of the syringe is 0.5ml / h; S33, using a muffle furnace to pre-oxidize the polyacrylonitrile fiber film prepared in step S32 to obtain a PAN layer, and the pre-oxidation parameters are as follows: a temperature of 250 DEG C, a duration of 90 min, and a temperature rising speed of 5 DEG C / min.

2. Use of the flexible gradient fiber membrane according to claim 1 in a lithium-sulfur battery.

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