Glue coating solution, composite diaphragm, composite diaphragm preparation method and sodium ion battery

Abstract

The present invention relates to the field of sodium ion batteries, and in particular to a coating glue solution, a composite diaphragm, a method for preparing a composite diaphragm, and a sodium ion battery. The coating glue solution includes 3% to 5% by mass of a modified carbon material, 75% to 85% by mass of an organic solvent, and 10% to 22% by mass of polyvinylidene fluoride; the modified carbon material is prepared by coating sodium propargyl sulfonate on the surface of the carbon material, wherein the mass ratio of the carbon material to the sodium propargyl sulfonate is (0.2 to 0.5): (2 to 5). By introducing the modified carbon material into the coating glue solution, a conductive network is formed on the surface of the diaphragm, which promotes electron transfer and reduces the interfacial reaction resistance of the battery cell; and the heat dissipation of the carbon material is utilized to improve the safety of the battery cell; and the coating contains polyvinylidene fluoride, which increases the bonding force between the diaphragm and the positive and negative electrodes, has good wettability and moisture retention to the electrolyte, and improves the cycle life of the battery cell.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a coating adhesive, a composite diaphragm, a method for preparing the composite diaphragm, and a sodium ion battery. Background Art

[0002] Energy shortages caused by the extensive use of chemical fuels have become a global concern, necessitating the development of new energy sources to address energy and environmental crises. Sodium-ion batteries (SIBs) are widely researched due to their long service life, high safety, low theoretical cost, and abundant resources. In SIBs, the separator physically separates the positive and negative electrodes, preventing direct contact and short circuits. It also ensures wettability with the electrolyte, allowing for the rapid passage of solvated sodium ions. The choice and performance of the separator directly impact the overall performance of SIBs, including energy density, cycle life, rate capability, and safety.

[0003] The commonly used diaphragms on the market are polyolefin diaphragms or coated diaphragms, which have the disadvantages of poor thermal stability, poor liquid absorption and retention, and low porosity. Especially when in contact with electrolytes with high dielectric constants such as cyclic carbonates, their wettability is poor, which affects the cycle life and safety of the battery. In coated diaphragms, both the coating slurry and the substrate play a vital role. The substrate provides basic mechanical strength and chemical stability. The coating slurry not only provides thermal stability, mechanical strength, and chemical stability, but also improves the wettability of the electrolyte and the charge and discharge performance of the battery. Therefore, the coating slurry is an important factor influencing the excellence of the diaphragm. Therefore, it is necessary to provide an improved coating slurry and diaphragm material to improve the working performance of sodium ion batteries. Summary of the Invention

[0004] In order to solve the above technical problems, the present application proposes a coating glue solution, a composite diaphragm, a method for preparing the composite diaphragm and a sodium ion battery.

[0005] The specific technical solutions of the present invention are as follows:

[0006] On the one hand, the embodiment of the present application provides a coating glue solution, which includes: 3% to 5% by weight of a modified carbon material, 75% to 85% by weight of an organic solvent, and 10% to 22% by weight of polyvinylidene fluoride;

[0007] The modified carbon material is prepared by coating sodium propargyl sulfonate on the surface of the carbon material. In the modified carbon material, the mass ratio of the carbon material to the sodium propargyl sulfonate is (0.2-0.5): (2-5).

[0008] In a possible implementation manner, the carbon material includes one or more of multi-walled carbon nanotubes, graphene, and conductive carbon black.

[0009] In a possible embodiment, the organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide and dimethyl sulfoxide.

[0010] On the other hand, the present invention also provides a method for preparing a coating adhesive solution, the preparation method comprising:

[0011] Dissolve 2 g to 5 g of sodium propargyl sulfonate in a predetermined volume of deionized water to obtain a sodium propargyl sulfonate solution;

[0012] 0.2 g to 0.5 g of carbon material is added to a sodium propargyl sulfonate solution, dispersed and stirred to obtain a mixed solution, and the mixed solution is filtered, washed, and dried to obtain a modified carbon material;

[0013] The modified carbon material is added into an organic solvent, and the modified carbon dispersion solution is obtained after dispersion treatment and stirring treatment; polyvinylidene fluoride is added into the modified carbon dispersion solution, and the coating adhesive solution is obtained after stirring treatment.

[0014] On the other hand, an embodiment of the present application further provides a composite diaphragm, the composite diaphragm comprising a composite nanofiber membrane and a diaphragm coating coated on at least one side of the composite nanofiber membrane;

[0015] The composite nanofiber membrane is obtained by film-forming a sulfide solid electrolyte and a polymer;

[0016] The diaphragm coating is obtained by coating the above-mentioned adhesive solution, and the thickness of the diaphragm coating is 2μm to 4μm.

[0017] On the other hand, the present invention also provides a method for preparing a composite membrane, the method comprising:

[0018] adding a sulfide solid electrolyte into an organic solvent and dispersing the mixture to obtain a sulfide solid electrolyte dispersion;

[0019] adding the polymer into the sulfide solid electrolyte dispersion, and stirring to obtain a composite spinning solution;

[0020] The composite spinning solution is subjected to film-forming treatment by electrospinning, and a composite nanofiber membrane is obtained after drying.

[0021] The above-mentioned adhesive solution is coated on at least one side of the composite nanofiber membrane, and then dried to obtain a composite membrane.

[0022] In a possible implementation manner, in the composite spinning solution, the mass proportion of the sulfide solid electrolyte is 3% to 5%, the mass proportion of the organic solvent is 75% to 85%, and the mass proportion of the polymer is 10% to 22%.

[0023] In a possible embodiment, the sulfide solid electrolyte is Na3PS4, Na 11 Sn2PS2, Na3SbS4, Na 11.5 Sn2Sb 0.5 Ti 0.5 S 12 、Na 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 At least one of the following: the diameter of the sulfide solid electrolyte is 300nm to 500nm.

[0024] In a possible embodiment, the polymer is one of polyethersulfone, polyetherketone, polyethylene terephthalate, polyamide, polyvinylidene fluoride, polybenzimidazole, polyphenylene sulfide and polyimide.

[0025] In a possible embodiment, the organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide and dimethyl sulfoxide.

[0026] In a possible embodiment, the composite nanofiber membrane has a porosity of 70% to 90% and a thickness of 10 μm to 50 μm.

[0027] On the other hand, an embodiment of the present application further provides a sodium ion battery, which includes the above-mentioned composite diaphragm.

[0028] Based on the above technical solution, the present invention has at least the following beneficial effects:

[0029] 1. Regarding the coating solution, this application introduces a modified carbon material into the coating solution. The modified carbon material is prepared by coating the carbon material surface with sodium propargyl sulfonate (Pys). The coating with sodium propargyl sulfonate improves the dispersion of the carbon material in the coating solution, thereby avoiding local charge differences caused by carbon material agglomeration and ensuring that the introduction of the carbon material does not negatively impact the battery's cycle performance and impedance. Furthermore, the coating solution contains polyvinylidene fluoride, which, when used for separator coating, can increase the adhesion between the separator and the positive and negative electrodes. It also has good wettability and moisture retention with the electrolyte, thereby improving the cycle life of the battery cell.

[0030] 2. For the composite diaphragm, the present application first constructs a composite nanofiber membrane by electrostatic spinning. The fiber membrane prepared by electrostatic spinning has a large porosity, which is conducive to the passage of sodium ions. In the composite nanofiber membrane, the use of sulfide as a solid electrolyte can utilize its own high ionic conductivity and the good wettability with cyclic carbonate to reduce the polarization internal resistance of the battery and improve the cycle life of the battery. Then the above-mentioned coating glue is applied to the surface of the composite nanofiber membrane so that a very small amount of modified carbon material is evenly loaded on the surface of the diaphragm. The conductivity of the carbon material can be utilized to form a conductive network on the surface of the diaphragm to promote electron transmission, thereby reducing the interfacial reaction resistance of the battery, and utilizing the heat dissipation of the carbon material. Under high rate charge and discharge, the heat is dispersed in time, thereby reducing the temperature rise and improving the safety of the battery. The coating contains polyvinylidene fluoride, which can increase the bonding force between the diaphragm and the positive and negative electrodes, has good wettability and moisture retention to the electrolyte, and can improve the cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] Figure 1 It is a flow chart of a method for preparing a coating adhesive provided in an embodiment of the present application.

[0033] Figure 2 It is a schematic flow chart of a method for preparing a composite diaphragm provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] It should be noted that the terms "first", "second", etc. in the description and claims of the embodiments of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this embodiment, unless otherwise specified, "plurality" means two or more. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0036] The embodiments of the present application are described below in combination with the above technical solutions.

[0037] The embodiment of the present application provides a coating glue solution, which includes: 3-5% by weight of a modified carbon material, 75-85% by weight of an organic solvent, and 10-22% by weight of polyvinylidene fluoride;

[0038] The modified carbon material is prepared by coating sodium propargyl sulfonate on the surface of the carbon material. In the modified carbon material, the mass ratio of the carbon material to the sodium propargyl sulfonate is (0.2-0.5): (2-5).

[0039] For example, in the above-mentioned coating glue, the mass ratio of modified carbon material, organic solvent and polyvinylidene fluoride is 3% to 5%: 75% to 85%: 10% to 22%. Excluding other components, the total mass proportion of the three reaches 100%.

[0040] The modified carbon material is obtained by coating sodium propargyl sulfonate on the surface of the carbon material. In the modified carbon material, the mass ratio of the carbon material to the sodium propargyl sulfonate is (0.2-0.5): (2-5).

[0041] It should be noted that the coating glue provided in the embodiment of the present application does not require a dispersant, which may bring advantages such as cost reduction, simplification of the coating glue preparation process, reduction of variables in the production process, and thus improvement of battery product quality.

[0042] In some embodiments, the carbon material includes one or more of multi-walled carbon nanotubes, graphene, and conductive carbon black.

[0043] For example, one or more of multi-walled carbon nanotubes, graphene, and conductive carbon black are used as carbon material raw materials, because these types of carbon materials have good thermal conductivity and heat dissipation, which help to improve the performance of the diaphragm.

[0044] In some embodiments, the organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide and dimethyl sulfoxide.

[0045] For example, the modified carbon material and PVDF are blended by dissolving in an organic solvent. The organic solvent modification can increase the compatibility between the modified carbon material and PVDF, thereby improving the interfacial bonding strength between the two.

[0046] In the embodiment of the present application, polyvinylidene fluoride (PVDF) is doped and blended with a modified carbon material to prepare a coating solution. The coating solution is used for diaphragm coating, so that the surface of the diaphragm can be coated with the coating solution containing the modified carbon material, and the carbon material can be modified so that it can be evenly dispersed in the coating layer, thereby utilizing the conductivity of the carbon material to form a conductive network on the surface of the diaphragm, promoting electron transfer and reducing the interfacial reaction resistance of the battery cell. At the same time, the carbon material has heat dissipation properties, so that it can achieve timely heat dispersion under high-rate charge and discharge, reduce temperature rise, and improve the safety of the battery cell. The modified carbon material is prepared by coating the surface of the carbon material with sodium propargyl sulfonate (Pys) through π-π conjugation, which improves the dispersion of the carbon material, avoids the agglomeration of the carbon material in the coating solution, and allows a very small amount of carbon material to be evenly loaded on the surface of the diaphragm, avoiding the agglomerated carbon material causing uneven load distribution on the surface of the diaphragm, thereby causing local charge differences, affecting cycle performance, and increasing impedance. The coating layer contains PVDF, which can increase the adhesion between the diaphragm and the positive and negative electrodes, has good wettability and moisture retention to the electrolyte, and can improve the cycle life of the battery cell.

[0047] On the other hand, Figure 1 As shown, on the other hand, the embodiment of the present application also provides a method for preparing a coating glue solution, the preparation method comprising:

[0048] S101: dissolving 2 g to 5 g of sodium propargyl sulfonate in a preset volume of deionized water to obtain a sodium propargyl sulfonate solution;

[0049] S103: adding 0.2 g to 0.5 g of the carbon material to the sodium propargyl sulfonate solution, dispersing and stirring to obtain a mixed solution, filtering, washing, and drying the mixed solution to obtain a modified carbon material;

[0050] S105: adding the modified carbon material to an organic solvent, dispersing and stirring to obtain a modified carbon dispersion solution;

[0051] S107: adding polyvinylidene fluoride to the dispersed solution of modified carbon, stirring and obtaining a coating adhesive solution.

[0052] Exemplarily, the preparation process of the coating glue solution includes:

[0053] (1) Preparation of modified carbon materials:

[0054] S101: Dissolve 2 g to 5 g of sodium propargyl sulfonate (Pys) in a preset volume of deionized water to obtain the sodium propargyl sulfonate solution.

[0055] Preferably, the preset volume is 100±5 ml, preferably 100 ml, allowing a certain error range.

[0056] S103: adding 0.2 g to 0.5 g of carbon material to a sodium propargyl sulfonate solution, dispersing and stirring to obtain a mixed solution, filtering, washing and drying the mixed solution to obtain a modified carbon material; wherein the carbon material comprises one or more of multi-walled carbon nanotubes, graphene and conductive carbon black.

[0057] Specifically, it can be understood that the first preset weight can be any value between 2g and 5g, for example, 2, 3, 4, 5, etc. The first preset weight can be any value between 0.2g and 0.5g, for example, 0.2, 0.3, 0.4, 0.5, etc.

[0058] Optionally, the above-mentioned dispersion treatment can be ultrasonic dispersion, and the time is 1h to 2h. Specifically, it can be understood that the dispersion time can be any point value between 1h and 2h, and illustratively, it can be 1, 1.5, 1.8, 2, etc.

[0059] Optionally, the stirring time is 1 hour to 6 hours. Specifically, it can be understood that the stirring time can be any point value between 1 hour and 6 hours. For example, it can be 1, 1.5, 2, 3, etc.

[0060] It should be noted that the specific conditions for filtering, washing and drying are not limited and can be performed according to existing technologies.

[0061] (2) Preparation of glue coating solution:

[0062] S105: Adding the modified carbon material to an organic solvent, dispersing and stirring the modified carbon material to obtain a modified carbon dispersion solution. The organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

[0063] Exemplarily, the dispersion and stirring treatments may be performed by vacuum stirring, specifically under a vacuum degree of -0.08 MPa to -0.1 MPa for 1 to 6 hours. The vacuum degree may be any value between -0.08 MPa and -0.1 MPa, such as -0.08, -0.085, -0.09, or -0.1. The stirring time may be any value between 1 hour and 6 hours, such as 1, 1.5, 2, or 3 hours.

[0064] S107: adding polyvinylidene fluoride to the dispersed solution of modified carbon, stirring and obtaining a coating adhesive solution.

[0065] For example, polyvinylidene fluoride (PVDF) is added to a dispersed solution of modified carbon, and the solution is stirred to obtain a coating adhesive.

[0066] Optionally, the stirring treatment may be performed under vacuum, wherein the stirring treatment is performed under vacuum at a degree of vacuum of -0.08 MPa to -0.1 MPa for 6 to 12 hours. Specifically, the degree of vacuum may be any value between -0.08 MPa and -0.1 MPa, such as -0.08, -0.085, -0.09, or -0.1. The stirring time may be any value between 6 and 12 hours, and may be, for example, 6, 7, 10, or 12 hours.

[0067] In the embodiment of the present application, a modified carbon material is first modified with sodium propargyl sulfonate (Pys) to prepare a modified carbon material, and then a coating solution is prepared by blending the modified carbon material with PVDF. The coating solution is used for diaphragm coating, so that the surface of the diaphragm can be coated with the coating solution containing the modified carbon material, and the modified carbon material can be evenly dispersed in the coating layer. The conductivity of the carbon material can form a conductive network on the surface of the diaphragm, promote electron transfer, and reduce the interfacial reaction resistance of the battery cell. At the same time, the carbon material has heat dissipation properties. Under high-rate charge and discharge, it can disperse heat in time, reduce temperature rise, and improve the safety of the battery cell. The modified carbon material is prepared by coating the surface of the carbon material with sodium propargyl sulfonate (Pys) through π-π conjugation, which improves the dispersion of the carbon material, prevents the carbon material from agglomerating in the coating solution, and allows a very small amount of carbon material to be evenly loaded on the surface of the diaphragm, avoiding the agglomerated carbon material causing uneven load distribution on the surface of the diaphragm, thereby causing local charge differences, affecting cycle performance, and increasing impedance. The coating layer contains PVDF, which can increase the adhesion between the diaphragm and the positive and negative electrodes, has good wettability and moisture retention to the electrolyte, and can improve the cycle life of the battery cell.

[0068] On the other hand, an embodiment of the present application further provides a composite membrane, the composite membrane comprising a composite nanofiber membrane and a membrane coating coated on at least one side of the composite nanofiber membrane;

[0069] The composite nanofiber membrane is obtained by film-forming a sulfide solid electrolyte and a polymer;

[0070] The diaphragm coating is obtained by coating the above-mentioned adhesive solution, and the thickness of the diaphragm coating is 2μm to 4μm.

[0071] The embodiment of the present application uses sulfide solid electrolyte and polymer as raw materials for composite nanofiber membrane, and coats the composite nanofiber membrane with a coating solution prepared by blending modified carbon material and PVDF. This not only utilizes the electrical conductivity and heat dissipation properties of the carbon material to form a conductive network on the surface of the diaphragm, promotes electron transfer, and reduces the interfacial reaction resistance of the battery cell. Under high-rate charge and discharge, it can timely disperse heat, reduce temperature rise, and improve the safety of the battery cell. In addition, it utilizes the high ionic conductivity (>10 -3 S / cm), good mechanical ductility, good interface contact with the electrode, large specific surface area, high surface energy, etc., by adding sulfide solid electrolyte as an inorganic filler to the polymer matrix, the impact strength, tensile strength, heat deformation temperature, etc. of the separator are greatly improved. In addition, the sulfide solid electrolyte has good wettability with cyclic carbonate, which can reduce the polarization internal resistance of the battery cell and increase the cycle life of the battery cell, and can improve the overall ionic conductivity and liquid retention capacity of the separator.

[0072] On the other hand, Figure 2 As shown, the embodiment of the present application also provides a method for preparing a composite diaphragm, the method comprising:

[0073] S201: adding a sulfide solid electrolyte into an organic solvent and dispersing the mixture to obtain a sulfide solid electrolyte dispersion;

[0074] S203: adding the polymer to the sulfide solid electrolyte dispersion, and stirring to obtain a composite spinning solution;

[0075] S205: performing film-forming treatment on the composite spinning solution by electrospinning, and obtaining a composite nanofiber membrane after drying;

[0076] S207: coating the above-mentioned adhesive solution on at least one side of the composite nanofiber membrane, and drying the composite membrane.

[0077] Exemplarily, the preparation process of the composite membrane may include the following steps:

[0078] S201: adding a sulfide solid electrolyte into an organic solvent and dispersing the mixture to obtain a sulfide solid electrolyte dispersion.

[0079] In some embodiments, the sulfide solid electrolyte is Na3PS4, Na 11 Sn2PS2, Na3SbS4, Na 11.5 Sn2Sb 0.5 Ti 0.5 S 12 、Na 2.95 Sb 0.95 W 0.05 S 3.9O 0.1 At least one of the following: the diameter of the sulfide solid electrolyte is 300nm to 500nm.

[0080] In some embodiments, the organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide and dimethyl sulfoxide.

[0081] Optionally, the dispersion treatment may be ultrasonic dispersion for 3 to 6 hours. Specifically, the dispersion time may be any value between 3 and 6 hours, for example, 3, 4, 5, 6, etc.

[0082] It should be noted that the diameter selection of the sulfide solid electrolyte is related to the thickness of the final synthesized composite nanofiber membrane. Different sulfide solid electrolytes will also affect the performance of sodium-ion batteries. The specific material and diameter of the sulfide solid electrolyte can be selected according to the final application of the composite membrane.

[0083] S203: adding the polymer to the sulfide solid electrolyte dispersion, and stirring to obtain a composite spinning solution.

[0084] In some embodiments, the polymer is one of polyethersulfone (PES), polyetherketone (PEEK), polyethylene terephthalate (PET), polyamide (PA), polyvinylidene fluoride (PVDF), polybenzimidazole (PBI), polyphenylene sulfide (PPS), and polyimide (PI).

[0085] Optionally, the stirring time is 12 hours to 24 hours. Specifically, the dispersion time can be any point value between 12 hours and 24 hours, for example, 12, 15, 15, 24, etc.

[0086] It should be noted that in the composite solution, the mass proportion of sulfide solid electrolyte is 3% to 5%, the mass proportion of organic solvent is 75% to 85%, and the mass proportion of polymer is 10% to 22%. The total mass proportion of the three must meet 100%.

[0087] S205: performing film-forming treatment on the composite spinning solution by electrospinning, and obtaining a composite nanofiber membrane after drying.

[0088] For example, electrospinning is an advanced nanofiber manufacturing technology that uses a high-voltage electrostatic field to eject polymer solutions into extremely fine fibers. These fibers, due to their high surface area and porous structure, have broad potential applications in healthcare, filtration, energy, and the environment. This technology allows for precise control of fiber diameter and structure, providing a powerful tool for the development of new high-performance materials.

[0089] In the embodiment of the present application, the composite spun fibers prepared in the above S201 to S202 are subjected to a membrane-forming process by electrospinning technology to obtain a composite spun nanofiber membrane.

[0090] Optionally, the conditions for electrospinning are as follows: a micropump push speed of 0.02 m / min to 1.0 m / min, a syringe needle diameter of 0.025 cm to 0.05 cm, a syringe diameter of 2 cm, a receiving roller speed of 3 m / min to 8 m / min, a needle sweep speed of 5 cm / min to 10 cm / min, a voltage of 15 kV to 25 kV, a distance from the syringe needle to the receiving roller of 10 cm to 20 cm, and an electrospinning time of 5 h to 10 h.

[0091] In some embodiments, the composite nanofiber membrane has a porosity of 70% to 90% and a thickness of 10 μm to 50 μm.

[0092] Specifically, it can be understood that the porosity of the composite nanofiber membrane synthesized using steps S201 to S205 can be any value between 70% and 90%, and can be 70%, 75%, 80%, 85%, 90%, etc. The thickness of the composite nanofiber membrane can be any value between 10 μm and 50 μm, and can be 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm. The specific thickness and porosity can be adjusted based on the mass ratios of the sulfide solid electrolyte, organic solvent, and polymer in the composite spinning solution, as well as the electrospinning conditions.

[0093] S207: coating the above-mentioned adhesive solution on at least one side of the composite nanofiber membrane, and drying the composite membrane.

[0094] Illustratively, the above-mentioned adhesive solution is coated on at least one side of the composite nanofiber membrane, that is, the membrane coating is applied, and the composite membrane is obtained after drying.

[0095] Optionally, the thickness of the diaphragm coating is 2 μm to 4 μm, that is, the coating thickness is 2 μm to 4 μm. Specifically, it can be understood that the coating thickness can be any point value between 2 μm and 4 μm, for example, it can be 2 μm, 3 μm, 4 μm, etc.

[0096] Optionally, the drying temperature is 80° C. to 90° C. Specifically, it can be understood that the drying temperature can be any point value between 80° C. and 90° C., for example, it can be 80° C., 82° C., 84° C., 86° C., 88° C., 90° C., etc.

[0097] Optionally, the coating method may be gravure roller coating, dip coating, narrow coating, spray coating, etc.

[0098] In this embodiment, a composite spinning solution is first prepared using a sulfide solid electrolyte and a polymer, and then the composite spinning solution is prepared into a composite nanofiber membrane through electrospinning technology. Subsequently, a coating glue solution is applied to the composite nanofiber membrane to obtain a composite diaphragm. This composite diaphragm has the following advantages:

[0099] 1. Sulfide solid electrolyte and polymer are used as the raw materials of composite nanofiber membrane, and the composite nanofiber membrane is coated with a coating liquid prepared by blending modified carbon material and PVDF. This fully utilizes the conductivity and heat dissipation properties of carbon materials. It can not only form a conductive network on the surface of the diaphragm, promote electron transfer, and reduce the interfacial reaction resistance of the battery cell, but also can timely disperse heat under high-rate charge and discharge, reduce temperature rise, and improve the safety of the battery cell;

[0100] 2. The coating layer contains PVDF, and the positive electrode of the battery uses PVDF adhesive, which will have a good bonding effect with the coating layer, can increase the bonding force between the diaphragm and the positive and negative electrode sheets, and has good wettability and moisturizing properties to the electrolyte.

[0101] 3. Sulfide solid electrolyte has high ionic conductivity (>10 -3 S / cm), good mechanical ductility, good interface contact with the electrode, large specific surface area, high surface energy, etc., by adding sulfide solid electrolyte as an inorganic filler to the polymer matrix, the impact strength, tensile strength, heat deformation temperature, etc. of the composite nanofiber membrane are greatly improved. In addition, the sulfide solid electrolyte has good wettability with cyclic carbonate, which can reduce the polarization internal resistance of the battery cell and increase the cycle life of the battery cell, and can improve the overall ionic conductivity and liquid retention capacity of the separator.

[0102] 4. The composite nanofiber membrane prepared by electrospinning has good thickness uniformity and high porosity, which is conducive to the passage of sodium ions and can improve the liquid retention capacity of the membrane.

[0103] On the other hand, an embodiment of the present application also provides a sodium ion battery comprising the above-mentioned composite diaphragm.

[0104] Optionally, the sodium ion battery further includes a negative electrode sheet, a sodium ion positive electrode sheet, and a sodium ion electrolyte, and is prepared into a sodium ion battery through processes such as rolling, die-cutting, lamination, assembly, baking, liquid injection, standing, formation, and capacity separation.

[0105] The sodium ion battery provided by the embodiments of the present application has at least the following beneficial effects:

[0106] 1. The surface of the diaphragm is coated with modified carbon material so that the carbon material can be evenly dispersed in the coating layer, promoting electron transmission and reducing the interfacial reaction resistance of the battery cell. At the same time, the carbon material has heat dissipation properties. Under high-rate charge and discharge, it can disperse heat in time, reduce temperature rise, and improve the safety of the battery cell.

[0107] 2. The coating layer contains PVDF, which can increase the bonding force between the diaphragm and the positive and negative electrodes, has good wettability and moisture retention to the electrolyte, and can improve the cycle life of the battery cell.

[0108] 3. Electrospinning is used to construct a composite nanofiber membrane. The high porosity of the electrospun composite nanofiber membrane facilitates the passage of sodium ions. The composite nanofiber membrane contains a sulfide solid electrolyte, which leverages the high ionic conductivity and good wettability of the sulfide solid electrolyte with cyclic carbonates to reduce the polarization internal resistance of the battery cell and improve its cycle life.

[0109] This application also provides a series of examples to further verify the implementation effects of the composite diaphragm and its preparation method, as well as the sodium ion battery in the technical solution of this application. The implementation effects of the technical solution of this application are described in detail below with reference to specific examples.

[0110] Example 1:

[0111] The present invention provides a coating glue solution, and the specific preparation method includes:

[0112] 1. Dissolve 2 g of sodium propargyl sulfonate (Pys) in 100 mL of deionized water to obtain a sodium propargyl sulfonate solution.

[0113] 2. 0.3 g of multi-walled carbon nanotubes was added to the sodium propargyl sulfonate solution, ultrasonically dispersed for 1 h and stirred for 6 h to obtain a mixed solution, which was filtered, washed, and dried to obtain a modified carbon material.

[0114] 3. The modified carbon material was added to N,N-dimethylformamide (DMF) for dispersion, and vacuum stirred at a vacuum degree of -0.09 MPa for 6 hours to obtain a modified carbon dispersion solution.

[0115] 4. Add polyvinylidene fluoride (PVDF) to the dispersed solution of modified carbon and stir it under vacuum at a vacuum degree of -0.09 MPa for 10 hours to obtain a coating adhesive solution.

[0116] In the above process, the mass ratio of the modified carbon material, the organic solvent, and the polyvinylidene fluoride is 3%:75%:22%.

[0117] The present invention provides a composite diaphragm, and the specific preparation method includes:

[0118] 1. A sulfide solid electrolyte Na3PS4 with a diameter of 300 nm was placed in N,N-dimethylformamide (DMF) and ultrasonically dispersed for 6 h to prepare a sulfide solid electrolyte dispersion.

[0119] 2. Dissolve polyethersulfone (PES) powder in sulfide solid electrolyte dispersion and stir for 24 hours to obtain a composite spinning solution.

[0120] Among them, the mass ratio of sulfide solid electrolyte, polymer and organic solvent is 0.5%:20%:79.5%.

[0121] 3. The composite spinning solution was electrospun into a membrane and dried at 80°C for 24 hours to obtain a composite nanofiber membrane. The electrospinning conditions were: a micropump speed of 0.06 m / min, a syringe needle diameter of 0.035 cm, a syringe barrel diameter of 2 cm, a receiving roller speed of 6 m / min, a needle sweep speed of 7 cm / min, a voltage of 20 kV, a distance from the syringe needle to the receiving roller of 15 cm, and an electrospinning time of 8 hours.

[0122] The composite nanofiber membrane prepared by the above process has a porosity of 80% and a thickness of 24 μm.

[0123] 4. The coating glue liquid is evenly coated on one side surface of the composite nanofiber membrane by a coating machine with a coating thickness of 3 μm, and dried at 85° C. to obtain a composite diaphragm.

[0124] The present application also provides a sodium ion battery, the specific preparation method of which includes:

[0125] After the composite diaphragm, negative electrode sheet, sodium ion positive electrode sheet and sodium ion electrolyte are prepared, a sodium ion battery is prepared through processes such as rolling, die cutting, lamination, assembly, baking, liquid injection, standing, formation and capacity separation.

[0126] Example 2:

[0127] The present invention provides a coating glue solution, and the specific preparation method includes:

[0128] 1. Dissolve 3 g of sodium propargyl sulfonate (Pys) in 100 mL of deionized water to obtain a sodium propargyl sulfonate solution.

[0129] 2. 0.2 g of graphene was added to a sodium propargyl sulfonate solution and ultrasonically dispersed for 1 h and stirred for 3 h to obtain a mixed solution. The mixed solution was filtered, washed, and dried to obtain a modified carbon material.

[0130] 3. The modified carbon material was added to N-methylpyrrolidone (NMP) for dispersion, and vacuum stirred for 2 h at a vacuum degree of -0.08 MPa to obtain a modified carbon dispersion solution.

[0131] 4. Add polyvinylidene fluoride (PVDF) to the first mixture and stir under vacuum at a vacuum degree of -0.08 MPa for 6 hours to obtain a coating adhesive solution.

[0132] In the above process, the mass ratio of the modified carbon material, the organic solvent, and the polyvinylidene fluoride is 4%:80%:16%.

[0133] The present invention provides a composite diaphragm, and the specific preparation method includes:

[0134] 1. A sulfide solid electrolyte Na3PS4 with a diameter of 300 nm was ultrasonically dispersed in N-methylpyrrolidone (NMP) for 3 h to prepare a sulfide solid electrolyte dispersion.

[0135] 2. Dissolve polyamide (PA) powder in sulfide solid electrolyte dispersion and stir for 12 hours to obtain a composite spinning solution.

[0136] Among them, the mass ratio of sulfide solid electrolyte, polymer and organic solvent is 0.3%:15%:84.7%.

[0137] 3. The composite spinning solution was electrospun into a membrane and dried at 60°C for 12 hours to obtain a composite nanofiber membrane. The electrospinning conditions were as follows: micropump speed of 0.02 m / min, syringe needle diameter of 0.025 cm, syringe diameter of 2 cm, receiving roller speed of 3 m / min, needle sweep speed of 5 cm / min, voltage of 15 kV, distance from syringe needle to receiving roller of 10 cm, and electrospinning time of 5 hours.

[0138] The composite nanofiber membrane prepared by the above process has a porosity of 70% and a thickness of 12 μm.

[0139] 4. The coating glue liquid is evenly coated on one side surface of the composite nanofiber membrane by a coating machine with a coating thickness of 2 μm, and dried at 80° C. to obtain a composite diaphragm.

[0140] A sodium ion battery provided in this embodiment is prepared using the composite diaphragm obtained above. The specific steps are consistent with those in the aforementioned embodiment 1 and are not described here in detail.

[0141] Example 3:

[0142] The present invention provides a coating glue solution, and the specific preparation method includes:

[0143] 1. Dissolve 5 g of sodium propargyl sulfonate (Pys) in 100 mL of deionized water to obtain a sodium propargyl sulfonate solution.

[0144] 2. Add 0.5 g of conductive carbon black to the mixed solution, ultrasonically disperse for 2 h and stir for 6 h to obtain a mixed solution, filter the mixed solution, wash, and dry to obtain a modified carbon material.

[0145] 3. Add the modified carbon material to dimethyl sulfoxide (DMSO) for dispersion, and stir under a vacuum degree of -0.08 MPa to -0.1 MPa for 1 to 6 hours to obtain a modified carbon dispersion solution.

[0146] 4. Add polyvinylidene fluoride (PVDF) to the dispersed solution of modified carbon and stir it under vacuum at a vacuum degree of -0.1 MPa for 12 hours to obtain the coating glue solution.

[0147] In the above process, the mass ratio of the modified carbon material, the organic solvent, and the polyvinylidene fluoride is 5%:85%:10%.

[0148] The present invention provides a composite diaphragm, and the specific preparation method includes:

[0149] 1. The sulfide solid electrolyte Na with a diameter of 500nm 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 The sulfide solid electrolyte dispersion was prepared by placing it in dimethyl sulfoxide (DMSO) and ultrasonically dispersing it for 6 hours.

[0150] 2. Dissolve polybenzimidazole (PBI) powder in sulfide solid electrolyte dispersion and stir for 24 hours to obtain a composite spinning solution.

[0151] Among them, the weight ratio of sulfide solid electrolyte, polymer and organic solvent is 1%:20%:79%.

[0152] 3. The composite spinning solution was made into a membrane by electrospinning, and dried at 100°C for 24 hours to obtain a composite nanofiber membrane.

[0153] The electrospinning conditions were as follows: micropump pushing speed of 1.0 m / min, syringe needle diameter of 0.05 cm, syringe barrel diameter of 2 cm, receiving roller speed of 8 m / min, needle sweeping speed of 10 cm / min, voltage of 25 kV, distance from syringe needle to receiving roller of 20 cm, and electrospinning time of 10 h.

[0154] The composite nanofiber membrane prepared by the above process has a porosity of 90% and a thickness of 50 μm.

[0155] 4. The coating glue liquid is evenly coated on one side surface of the composite nanofiber membrane by a coating machine with a coating thickness of 4 μm, and dried at 90° C. to obtain a composite diaphragm.

[0156] A sodium ion battery provided in this embodiment is prepared using the composite diaphragm obtained above. The specific steps are consistent with those in the aforementioned embodiment 1 and are not described here in detail.

[0157] Comparative Example 1:

[0158] This comparative example uses a commercial polyethylene diaphragm to prepare a sodium ion battery. The sodium ion battery provided in this comparative example is prepared using a commercial polyethylene diaphragm. The specific steps are consistent with those in the aforementioned Example 1 and will not be repeated here.

[0159] Comparative Example 2:

[0160] In this comparative example, a PVDF-coated diaphragm is used to prepare a sodium ion battery. A sodium ion battery provided in this comparative example is prepared using a commercial polyethylene diaphragm. The specific steps are consistent with those in the aforementioned Example 1 and are not described in detail here.

[0161] PVDF coated diaphragm refers to a diaphragm made by coating polyvinylidene fluoride (PVDF) on a commercial polyethylene diaphragm, which also includes a ceramic coating.

[0162] Comparative Example 3:

[0163] This comparative example provides a coating glue solution, and the specific preparation method includes:

[0164] 1. Dissolve 5 g of sodium propargyl sulfonate (Pys) in 100 mL of deionized water to obtain a sodium propargyl sulfonate solution.

[0165] 2. Add 0.5 g of conductive carbon black to the mixed solution and ultrasonically disperse it for 2 hours. Then stir it for 6 hours, filter the mixed solution, wash it, and dry it to obtain the modified carbon material.

[0166] 3. Add the modified carbon material to dimethyl sulfoxide (DMSO) for dispersion, and stir under a vacuum degree of -0.08 MPa to -0.1 MPa for 1 to 6 hours to obtain a modified carbon dispersion solution.

[0167] The present invention provides a composite diaphragm, and the specific preparation method includes:

[0168] 1. The oxide electrolyte NASICON with a fast ion conductor structure was ultrasonically dispersed in dimethyl sulfoxide (DMSO) for 6 hours to prepare an oxide solid electrolyte dispersion.

[0169] 2. Dissolve polybenzimidazole (PBI) powder in the oxide solid electrolyte dispersion and stir for 24 hours to obtain a composite spinning solution.

[0170] Among them, the mass ratio of oxide solid electrolyte, polymer and organic solvent is 1%:20%:79%.

[0171] 3. The composite spinning solution was electrospun into a membrane and dried at 100°C for 24 hours to obtain a composite nanofiber membrane. The electrospinning conditions were: a micropump speed of 1.0 m / min, a syringe needle diameter of 0.05 cm, a syringe barrel diameter of 2 cm, a receiving roller speed of 8 m / min, a needle sweep speed of 10 cm / min, a voltage of 25 kV, a distance from the syringe needle to the receiving roller of 20 cm, and an electrospinning time of 10 hours.

[0172] The composite nanofiber membrane prepared by the above process has a porosity of 90% and a thickness of 50 μm.

[0173] 4. The coating glue liquid is evenly coated on the composite nanofiber membrane through a coating machine with a coating thickness of 4 μm, and dried at 90°C to obtain a composite diaphragm.

[0174] A sodium ion battery provided in this comparative example is prepared using the composite diaphragm obtained above. The specific steps are consistent with those in the aforementioned Example 1 and will not be repeated here.

[0175] It should be noted that the difference between Comparative Example 3 and Example 3 is only the material difference of the solid electrolyte, and the other raw materials and preparation methods are exactly the same.

[0176] Comparison of the performance parameters of the composite membranes and sodium ion batteries prepared in Examples 1-3 and Comparative Examples 1-3 is shown in Tables 1, 2 and 3.

[0177] Table 1 Comparison of performance of composite diaphragm of Example and diaphragm of comparative example 1

[0178]

[0179] It should be noted that, in the above table, MD represents the thermal shrinkage rate of the diaphragm in the mechanical stretching direction, that is, the longitudinal thermal shrinkage rate, and TD represents the thermal shrinkage rate of the diaphragm perpendicular to the mechanical direction, that is, the transverse thermal stretching rate.

[0180] Thermal shrinkage refers to the rate of dimensional change of the diaphragm under temperature changes, and is used to characterize the dimensional stability of the diaphragm at high temperatures. On the one hand, the thermal shrinkage of the diaphragm is directly related to the safety performance of the battery. For example, when the battery temperature rises to a certain level, if the thermal shrinkage of the diaphragm is too large, it will cause the diaphragm to shrink, causing the positive and negative electrodes to contact, resulting in an internal short circuit in the battery, causing the battery to overheat or even thermal runaway, which may lead to safety accidents such as fire or explosion. On the other hand, the thermal shrinkage of the diaphragm will also affect the performance of the battery. The thermal shrinkage of the diaphragm not only determines its stability in high temperature environments, specifically, diaphragms with high thermal shrinkage are prone to shrinkage and deformation at high temperatures, causing changes in the internal structure of the battery and affecting the thermal stability of the battery; the thermal shrinkage of the diaphragm will also affect the cycle performance of the battery. During the charge and discharge cycle of the battery, the diaphragm will repeatedly experience temperature changes. A diaphragm with a higher thermal shrinkage rate may cause instability in the internal structure of the battery and affect the cycle life of the battery. The thermal shrinkage rate of the diaphragm will also affect its pore structure and the distribution of the electrolyte, thereby affecting the migration of ions and the internal resistance of the battery. Therefore, a diaphragm with a lower thermal shrinkage rate can better maintain its pore structure, which is beneficial to the retention of the electrolyte and the transmission of ions, thereby improving the electrochemical performance of the battery.

[0181] Air permeability is an indicator of a separator's gas permeability and indirectly reflects its ion permeability. The table above uses the Gurley value as the evaluation criterion. This refers to the time it takes for a certain volume of air to pass through a specified area of the separator under a certain pressure when placed in an air permeability tester. The Gurley value is inversely correlated with gas permeability; the lower the Gurley value, the higher the air permeability. In other words, the lower the air permeability value in Table 1, the higher the air permeability of the corresponding separator. Highly permeable separators provide improved ion transport pathways, thereby reducing the battery's internal resistance and improving charge and discharge efficiency. Furthermore, highly permeable separators can better maintain electrolyte distribution, positively impacting battery performance and lifespan.

[0182] Porosity refers to the ratio of the volume of micropores in the separator to the total volume of the separator. Generally speaking, as the permeability of the separator decreases, the porosity of the separator will increase. In other words, the higher the porosity, the better the permeability of the separator, which means that the ability of gas to pass through the separator is stronger. On the other hand, an increase in porosity generally reduces the internal resistance of the battery, because more pores mean that ions can move more freely between the positive and negative electrodes, thereby reducing the resistance to ion transfer and improving the cycle performance of the battery. This is because a separator with a higher porosity can better maintain the distribution of the electrolyte, which helps the battery maintain stable performance during repeated charge and discharge.

[0183] As can be seen from Table 1, the composite membranes prepared in Examples 1-3 of the present application have significantly lower air permeability values compared to the commercial polyethylene membrane of Comparative Example 1 and the PVDF coated membrane of Comparative Example 2. This is because when the porosity of the membrane increases, its air permeability value can be expected to decrease, which means an improvement in air permeability. This proves that the nanofiber membrane prepared by electrospinning has the characteristic of high porosity, thereby improving the air permeability of the composite membrane; it may also have a positive impact on reducing battery internal resistance, improving battery cycle performance, and improving battery charge and discharge stability.

[0184] The composite diaphragms prepared in Examples 1-3 of the present application have significantly reduced thermal shrinkage compared to Comparative Examples 1-2, indicating that the composite diaphragms prepared in the examples of the present application have excellent stability in high temperature environments, proving that the introduction of modified carbon materials into the coating glue used in this application can utilize the heat dissipation of carbon materials to disperse heat in a timely manner and improve the safety of the battery core; further, compared with the composite diaphragm prepared in Example 3 of the present application and the composite diaphragm prepared in Comparative Example 3, it is proved that the addition of sulfide solid electrolyte as an inorganic filler to the polymer matrix greatly increases the thermal deformation temperature of the diaphragm. Therefore, the introduction of modified carbon materials into the coating of the composite diaphragm and the use of sulfide solid electrolyte as an inorganic filler added to the polymer matrix both play an important role in improving the thermal shrinkage rate. The improvement of thermal shrinkage performance not only helps to improve the safety performance of the battery, but also helps to improve the battery performance such as thermal stability and cycle life.

[0185] Table 2 Comparison of performance of composite diaphragm of Example and diaphragm of comparative example 2

[0186]

[0187] The test method for the above peel strength is:

[0188] The positive electrode sheet, the composite separator of the example or the separator of the comparative example, and the negative electrode sheet were stacked in order. The samples were hot-pressed at a pressure of 7 tons and a temperature of 90°C for 60 seconds. The peel strength of the samples was then compared. A higher peel strength value indicates a harder peel, indicating a stronger bond.

[0189] As can be seen from Table 2, the composite diaphragms prepared in Examples 1-3 of the present application have significantly improved peel strength compared with the diaphragm of Comparative Example 1, which means that the adhesion is significantly improved. This shows that the composite diaphragms prepared in the present application contain PVDF in the diaphragm coating, which can increase the adhesion between the diaphragm and the positive and negative electrodes, improve flexibility, and enhance the bonding effect.

[0190] Table 3 Performance comparison of sodium ion batteries prepared in Examples and Comparative Examples

[0191]

[0192] As can be seen from Table 3, the sodium ion batteries prepared in Examples 1-3 of the present application have significantly lower AC resistance and 5C discharge temperature rise than the sodium ion batteries prepared in Comparative Examples 1-2. This shows that the present application uses sodium propargyl sulfonate (Pys) modified carbon materials for coating glue, and then for sodium ion battery diaphragm coating. By utilizing the good conductivity and heat dissipation properties of the carbon materials, a conductive network can be formed on the diaphragm surface, thereby promoting electron transport in the sodium ion battery, reducing the interfacial reaction resistance of the battery cell, and reducing the temperature rise of the battery cell. At the same time, by physically adsorbing and coating the organic sulfonate on the surface of the carbon material, the agglomeration effect of the carbon material is improved, so that a very small amount of carbon material is evenly loaded on the diaphragm surface, avoiding the uneven distribution of the load on the diaphragm surface caused by the agglomerated carbon material, thereby causing local charge differences, affecting cycle performance, and increasing impedance.

[0193] The sodium-ion batteries prepared in Examples 1-3 of the present application showed significant improvements in both the 5C discharge capacity retention rate and the capacity retention rate after 1000 cycles compared to the sodium-ion batteries prepared in Comparative Examples 1-2. This demonstrates that the composite nanofiber membranes constructed by electrospinning in the present application examples have high porosity, which facilitates the passage of sodium ions. The high ionic conductivity of the sulfide solid electrolyte is utilized to reduce the polarization internal resistance of the battery cell and improve the cycle life of the battery cell.

[0194] The sodium ion batteries prepared in Examples 1-3 of the present application have a significantly improved liquid retention coefficient compared to the sodium ion batteries prepared in Comparative Examples 1-2, proving that the composite diaphragm of the sodium electronic battery used in the examples of the present application contains PVDF, which has good wettability and moisture retention to the electrolyte. At the same time, the sulfide solid electrolyte in the composite diaphragm has good wettability with the cyclic carbonate and has ionic conductivity, which can improve the overall ionic conductivity and liquid retention of the diaphragm. The diaphragm of Comparative Examples 1-2 uses the diaphragm in the prior art to prepare sodium ion batteries, without modifying the coating glue, and without using sulfide solid electrolyte to add to the composite spinning solution to prepare a composite diaphragm for sodium ion batteries. Therefore, the performance of the peel strength test, AC internal resistance, 5C discharge capacity retention rate, and capacity retention rate after 1000 cycles are all inferior to the performance of the effect parameters of Examples 1-3 of the present application.

[0195] Furthermore, the composite membrane and sodium ion battery prepared in Example 3 have significantly reduced internal resistance compared to the composite membrane and sodium ion battery prepared in Comparative Example 3, and the 5C discharge capacity retention rate, liquid retention coefficient and capacity retention rate after 1000 cycles are all significantly improved, which shows that the advantage of introducing the sulfide solid electrolyte into the composite membrane and then into the sodium ion battery is to utilize the high ionic conductivity of the sulfide solid electrolyte itself to reduce the polarization internal resistance of the battery cell and increase the cycle life of the battery cell. At the same time, the sulfide solid electrolyte has good wettability with cyclic carbonate and has ionic conductivity itself, which can improve the overall ionic conductivity and liquid retention capacity of the diaphragm.

[0196] In summary, the composite membrane prepared in the embodiment of the present application has a larger porosity than that of the comparative example, is more resistant to high temperatures, and has better liquid absorption and liquid retention properties; the sodium ion battery prepared in the embodiment of the present application has a smaller internal resistance than that of the comparative example, a higher 5C discharge capacity retention rate, a smaller 5C discharge temperature rise, and a higher capacity retention rate after 1000 cycles, that is, it has the advantages of high safety and good cycle performance, and is suitable for high-rate battery application scenarios.

[0197] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0198] It should be noted that all the features recorded in the present invention (including technical features recorded in different embodiments) can be combined arbitrarily under reasonable circumstances, and the new technical solutions formed by the combination are all within the protection scope of the present invention.

[0199] What is described above are only some embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art should understand that the present invention may be subject to various changes and improvements, and any modifications, equivalent substitutions and improvements made in accordance with the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A coating glue for composite diaphragm, characterized in that: The coating glue solution includes: 3% to 5% by weight of modified carbon material, 75% to 85% by weight of organic solvent, and 10% to 22% by weight of polyvinylidene fluoride; The modified carbon material is prepared by coating sodium propargyl sulfonate on the surface of a carbon material. In the modified carbon material, the mass ratio of the carbon material to the sodium propargyl sulfonate is (0.2-0.5):(2-5); the carbon material includes one or more of multi-walled carbon nanotubes, graphene, and conductive carbon black; and the organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

2. A method for preparing the coating glue solution according to claim 1, characterized in that: The preparation method comprises: Dissolve 2 g to 5 g of sodium propargyl sulfonate in a predetermined volume of deionized water to obtain a sodium propargyl sulfonate solution; 0.2 g to 0.5 g of a carbon material is added to the sodium propargyl sulfonate solution, dispersed and stirred to obtain a mixed solution, and the mixed solution is filtered, washed, and dried to obtain a modified carbon material; the carbon material comprises one or more of multi-walled carbon nanotubes, graphene, and conductive carbon black; Adding the modified carbon material to an organic solvent, dispersing and stirring to obtain a modified carbon dispersion solution; Adding polyvinylidene fluoride into the modified carbon dispersion solution and stirring to obtain the coating glue solution.

3. A composite diaphragm, characterized in that: The composite diaphragm comprises a composite nanofiber membrane and a diaphragm coating coated on at least one side of the composite nanofiber membrane; The composite nanofiber membrane is obtained by subjecting a sulfide solid electrolyte and a polymer to a membrane forming process; The diaphragm coating is obtained by coating the adhesive solution according to claim 1, and the thickness of the diaphragm coating is 2 μm to 4 μm.

4. A method for preparing a composite diaphragm according to claim 3, characterized in that: The method comprises: adding a sulfide solid electrolyte into an organic solvent and dispersing the mixture to obtain a sulfide solid electrolyte dispersion; adding a polymer to the sulfide solid electrolyte dispersion, and stirring to obtain a composite spinning solution; Performing a film-forming treatment on the composite spinning solution by electrospinning, and obtaining a composite nanofiber membrane after drying; The adhesive solution as claimed in claim 1 is coated on at least one side of the composite nanofiber membrane, and then dried to obtain the composite membrane.

5. The method for preparing a composite diaphragm according to claim 4, characterized in that: In the composite spinning solution, the mass proportion of the sulfide solid electrolyte is 3% to 5%, the mass proportion of the organic solvent is 75% to 85%, and the mass proportion of the polymer is 10% to 22%.

6. The method for preparing a composite diaphragm according to claim 4, characterized in that: The sulfide solid electrolyte is Na3PS4, Na 11 Sn2PS2, Na3SbS4, Na 11.5 Sn2Sb 0.5 Ti 0.5 S 12 、Na 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 At least one of the following: the diameter of the sulfide solid electrolyte is 300nm to 500nm.

7. The method for preparing a composite diaphragm according to claim 4, characterized in that: The polymer is one of polyethersulfone, polyetherketone, polyethylene terephthalate, polyamide, polyvinylidene fluoride, polybenzimidazole, polyphenylene sulfide and polyimide.

8. The method for preparing a composite diaphragm according to claim 4, characterized in that: The organic solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide and dimethyl sulfoxide.

9. The method for preparing a composite diaphragm according to claim 4, characterized in that: The composite nanofiber membrane has a porosity of 70% to 90% and a thickness of 10 μm to 50 μm.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the composite separator according to claim 3.

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