Sodium supplement diaphragm and preparation method thereof, sodium ion battery

Abstract

The present application relates to a sodium-supplemented diaphragm and a preparation method thereof, and a sodium-ion battery. The sodium-supplemented diaphragm includes a diaphragm substrate, a sodium-supplemented coating and an adhesive layer. The sodium-supplemented coating is coated on at least one side of the diaphragm substrate, and the adhesive layer is coated on the sodium-supplemented coating. The sodium-supplemented coating includes a sodium-supplemented additive, a first conductive agent, a first dispersant and a first binder. The adhesive layer includes a second binder, a second conductive agent and a second dispersant. The mass ratio of the second binder, the second conductive agent and the second dispersant is (60~95): (1~25): (3~20); the thickness of the adhesive layer is 0.3μm~5μm. The present application forms a strong bond between the diaphragm and the pole piece by setting an adhesive layer, effectively suppressing the generation of solid and gas residues after the sodium-supplemented agent reacts, the adverse effects on the interface contact between the diaphragm and the pole piece, and the problem of poor battery cycle stability.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a sodium-supplementing diaphragm and a preparation method thereof, and a sodium-ion battery. Background Art

[0002] Sodium-ion batteries have been widely used in energy storage and other fields because of their abundant resources, low prices, and wide distribution. However, during the first charge and discharge process, sodium-ion batteries have side reactions on the positive electrode side that consume some active sodium, and on the negative electrode side, the formation of the SEI film also consumes some active sodium. Therefore, the energy density of sodium-ion batteries is reduced, resulting in low coulombic efficiency of sodium-ion batteries during the first charge and discharge, which hinders the industrialization of sodium-ion batteries.

[0003] In order to improve the energy density and first coulombic efficiency of sodium-ion batteries, it is particularly important to pre-sodiumize sodium-ion batteries. Traditional treatment methods mainly include: (1) short-circuit pre-sodium method, by dripping electrolyte to directly short-circuit the negative electrode sheet and the sodium sheet, applying a certain pressure to assemble into a short-circuit half-cell, and then assembling the pre-sodiumized negative electrode sheet into the full battery. This method is complex and difficult to apply on a large scale. (2) direct pre-sodiumization method with metallic sodium, adding metal directly to the negative electrode material or the positive electrode material. Since metallic sodium is very active, the safety of this method is difficult to guarantee. (3) adding a sodium supplement to the positive electrode, mixing the sodium supplement with the positive electrode slurry to form a slurry, and coating it on the current collector to form a positive electrode sheet. This method produces residual solids and gases after the reaction, which will cause serious damage to the positive electrode structure. And (4) sodium supplementation of the diaphragm, by transferring the sodium supplement agent and the conductive agent to the surface of the base film through slurry coating. However, this method is prone to adversely affect the interface contact between the diaphragm and the electrode due to the generation of solid and gas residues after the sodium supplement agent reacts, resulting in a decrease in the cycle performance of the battery. Summary of the invention

[0004] Based on this, in order to solve the above problems, the present application provides a sodium-supplementing diaphragm and a preparation method thereof, and a sodium-ion battery to solve the above technical problems.

[0005] The first aspect of the present application provides a sodium-supplementing diaphragm, which comprises a diaphragm substrate, a sodium-supplementing coating and a bonding layer, wherein at least one side of the diaphragm substrate is coated with the sodium-supplementing coating, and the bonding layer is coated on the sodium-supplementing coating;

[0006] The sodium supplement coating comprises a sodium supplement additive, a first conductive agent, a first dispersant and a first binder;

[0007] The bonding layer includes a second bonding agent, a second conductive agent and a second dispersant, and the mass ratio of the second bonding agent, the second conductive agent and the second dispersant is (60-95): (1-25): (3-20);

[0008] The thickness of the bonding layer is 0.3μm ~5μm.

[0009] In some embodiments, the mass ratio of the second binder, the second conductive agent, and the second dispersant is (65-90): (5-20): (8-15).

[0010] In some embodiments, the mass ratio of the sodium-supplementing additive, the first conductive agent, the first dispersant, and the first binder in the sodium-supplementing coating is (70-95): (1-20): (0.5-15): (0.5-10).

[0011] In some embodiments, the sodium supplement additive includes one or more of NaN3, Na2S, Na3P, NaCrO2, Na2NiO2, Na2CO3, NaNO2, Na2C2O4, Na2C4O4, Na2C6O6, Na2C6H2O6, EDTA-4Na, and DTPA-5Na.

[0012] In some embodiments, the second binder and the first binder are the same or different and are independently selected from one or more of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, sodium alginate, styrene-acrylic emulsion, polyurethane, carboxymethyl cellulose, polyvinyl alcohol, polytetrafluoroethylene, polyvinyl acetate, methacrylic acid, ethacrylic acid, ethyl acrylate, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate.

[0013] In some embodiments, the second conductive agent and the first conductive agent are the same or different and are independently selected from one or more of carbon black, acetylene black, Ketjen black, graphene, and carbon nanotubes.

[0014] In some embodiments, the second dispersant is the same as or different from the first dispersant, and is independently selected from one or more of polyvinyl pyrrolidone, sodium polyacrylate, polyethylene glycol, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, polymethacrylate, sodium hexametaphosphate, polyacrylate ammonium copolymer, and polyvinyl alcohol.

[0015] In some embodiments, the second binder, the second conductive agent, and the second dispersant are the same as the first binder, the first conductive agent, and the first dispersant, respectively.

[0016] The second aspect of the present application provides a method for preparing the sodium supplementation diaphragm provided in the first aspect, comprising the following steps:

[0017] S1, mixing a sodium supplement additive, a first conductive agent, a first dispersant, and a first binder, and adding the mixture to a first solvent to prepare a first slurry;

[0018] The mass ratio of the sodium supplement additive, the first conductive agent, the first dispersant, and the first binder is (70-95): (1-20): (0.5-15): (0.5-10); and the solid content of the first slurry is 15%-65%;

[0019] S2, coating the first slurry on at least one side of the surface of the diaphragm substrate, and drying to obtain a sodium-replenishing coating on the diaphragm substrate;

[0020] S3, mixing a second binder, a second conductive agent, and a second dispersant, and adding the mixture to a second solvent to prepare a second slurry;

[0021] The mass ratio of the second binder, the second conductive agent and the second dispersant is (60-95): (1-25): (3-20); and the solid content of the second slurry is 10%-65%;

[0022] S4, coating the second slurry on the sodium-supplementing coating prepared in step S2, and drying to form a bonding layer to prepare a sodium-supplementing diaphragm.

[0023] A third aspect of the present application provides a sodium ion battery, which includes a positive electrode plate, a negative electrode plate, and a sodium-supplementing diaphragm as provided in the first aspect above.

[0024] In the present application, a bonding layer is provided in the sodium supplement diaphragm, and the bonding layer forms a strong bond between the diaphragm and the pole piece, which can effectively inhibit the generation of solid and gas residues after the sodium supplement agent reacts, the adverse effects on the interface contact between the diaphragm and the pole piece, and the problem of poor battery cycle stability. At the same time, the provision of the bonding layer can not only control the sodium supplement coating to slowly and continuously provide additional sodium ions to the battery, ensuring the sustainability of sodium supplementation, but also improve the heat resistance of the diaphragm, as well as the wettability and liquid retention capacity of the electrolyte, which helps to further maintain the battery cycle and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process of preparing a sodium-supplementing diaphragm in one embodiment of the present application. DETAILED DESCRIPTION

[0026] References to embodiments of the present application will now be provided in detail, one or more embodiments of which are described below. Each embodiment is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0027] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0028] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0029] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0030] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100~150 nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0031] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0034] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0035] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0036] The first aspect of the present application provides a sodium-supplementing diaphragm, which comprises a diaphragm substrate, a sodium-supplementing coating and a bonding layer, wherein at least one side of the diaphragm substrate is coated with the sodium-supplementing coating, and the bonding layer is coated on the sodium-supplementing coating;

[0037] The sodium supplement coating comprises a sodium supplement additive, a first conductive agent, a first dispersant and a first binder;

[0038] The adhesive layer includes a second adhesive, a second conductive agent and a second dispersant.

[0039] It is understandable that the mass ratio of each substance in the bonding layer is extremely important for the sodium supplementation diaphragm. When the content of the dispersant is too little, it will cause the problem of local aggregation between the second bonding agent and the second conductive agent, which will cause abnormal conditions such as particles to appear on the surface of the film layer coated with the bonding layer, seriously affecting the uniformity of the distribution of the bonding layer. When the content of the dispersant is too much, the content of the second bonding agent and the second conductive agent will be reduced accordingly, which will cause the bonding performance, ion transmission performance and liquid absorption and retention performance of the bonding layer to decrease.

[0040] Therefore, in some embodiments, the mass ratio of the second binder, the second conductive agent, and the second dispersant in the adhesive layer is (60-95): (1-25): (3-20).

[0041] Furthermore, the mass ratio of the second binder, the second conductive agent and the second dispersant is (65-90): (5-20): (8-15).

[0042] Furthermore, the mass ratio of the second binder, the second conductive agent and the second dispersant is 75:15:10.

[0043] It is understandable that the thickness of the bonding layer also has an extremely important effect on the sodium supplementation diaphragm. When the thickness of the bonding layer is too thin, it cannot effectively suppress the generation of solid and gas residues after the sodium supplementation agent reaction, which has an adverse effect on the interface contact between the diaphragm and the pole piece. When the thickness of the bonding layer is too thick, it is not conducive to the rapid transmission of sodium ions, resulting in excessive interface polarization, which in turn affects the battery cycle performance.

[0044] Therefore, in some embodiments, the thickness of the adhesive layer is 0.3 μm to 5 μm, including but not limited to 0.3 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, and 5 μm.

[0045] In some of the embodiments, the separator substrate can be selected from a polyethylene (PE) separator prepared by a wet process, a polypropylene (PP) separator prepared by a dry process, a non-woven PE separator, a non-woven PP separator or a non-woven polyethylene terephthalate PET separator.

[0046] It should be noted that the choice of the diaphragm substrate is not particularly limited in the present application. Without violating the overall inventive concept of the present application, any known diaphragm substrate can be applied to the present application. The above is merely an illustrative example and not a limitation on the scope of protection.

[0047] In some embodiments, the sodium supplement additive includes one or more of NaN3, Na2S, Na3P, NaCrO2, Na2NiO2, Na2CO3, NaNO2, Na2C2O4, Na2C4O4, Na2C6O6, Na2C6H2O6, EDTA-4Na, and DTPA-5Na.

[0048] In some embodiments, the first binder includes one or more of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, sodium alginate, styrene-acrylic emulsion, polyurethane, carboxymethyl cellulose, polyvinyl alcohol, polytetrafluoroethylene, polyvinyl acetate, methacrylic acid, ethacrylic acid, ethyl acrylate, polyvinylidene fluoride-hexafluoropropylene copolymer, and polymethyl methacrylate.

[0049] In some of these embodiments, the second binder and the first binder can be the same or different.

[0050] In some embodiments, the first conductive agent includes one or more of carbon black (super-P), acetylene black, Ketjen black, graphene, and carbon nanotubes.

[0051] In some embodiments, the second conductive agent and the first conductive agent may be the same or different.

[0052] In the present application, by adding a second conductive agent to the bonding layer, not only can the electron transmission capacity be increased, but more importantly, the second conductive agent has a large specific surface area, and its large specific surface area can better absorb and retain liquid in the bonding layer, further accelerate the ion transmission of sodium ions between the bonding layers, and reduce the polarization of the interface.

[0053] In some embodiments, the first dispersant includes one or more of polyvinyl pyrrolidone, sodium polyacrylate, polyethylene glycol, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, polymethacrylate, sodium hexametaphosphate, polyacrylic acid ammonium salt copolymer, and polyvinyl alcohol.

[0054] In some of these embodiments, the second dispersant and the first dispersant can be the same or different.

[0055] In some embodiments, the sodium-replenishing coating further comprises a first solvent, and the bonding layer further comprises a second solvent.

[0056] Illustratively, the first solvent includes one or more of deionized water, N-methylpyrrolidone, ethyl acetate, ethanol, isopropanol, dimethylformamide, cyclohexane, and tetrahydrofuran.

[0057] In some of these embodiments, the second solvent and the first solvent can be the same or different.

[0058] In some embodiments, the second binder, the second conductive agent, and the second dispersant are respectively the same as the first binder, the first conductive agent, and the first dispersant.

[0059] Further, the second binder includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polymethyl methacrylate (PMMA).

[0060] In the present application, by setting the second binder, the second conductive agent and the second dispersant to be the same as the first binder, the first conductive agent and the first dispersant, respectively, it is ensured that solvents of the same polarity are used in the bonding layer and the sodium-supplementing coating, and then when the bonding layer is coated, it is ensured that there is a smaller surface tension between it and the sodium-supplementing coating, so that the bonding layer and the sodium-supplementing coating have better wettability, thereby ensuring that the bonding layer has a good film surface when coated.

[0061] The sodium-supplementing diaphragm provided in the present application can effectively avoid the damage to the positive electrode plate structure caused by directly adding sodium-supplementing additives to the positive electrode material, does not affect the processing performance of the positive electrode plate, and improves the battery stability; at the same time, the sodium-supplementing additives in the sodium-supplementing diaphragm can provide an additional sodium source for the battery, which is beneficial to improving the energy density and first coulombic efficiency of the battery.

[0062] In the present application, a bonding layer is provided in the sodium supplement diaphragm, and the bonding layer forms a strong bond between the diaphragm and the pole piece, which can effectively inhibit the generation of solid and gas residues after the sodium supplement agent reacts, the adverse effects on the interface contact between the diaphragm and the pole piece, and the problem of poor battery cycle stability. At the same time, the provision of the bonding layer can not only control the sodium supplement coating to slowly and continuously provide additional sodium ions to the battery, ensuring the sustainability of sodium supplementation, but also improve the heat resistance of the diaphragm, as well as the wettability and liquid retention capacity of the electrolyte, which helps to further maintain the battery cycle and rate performance.

[0063] like Figure 1 As shown, the second aspect of the present application provides a method for preparing the sodium supplementing diaphragm provided in the first aspect, comprising the following steps:

[0064] S1, mixing a sodium supplement additive, a first conductive agent, a first dispersant, and a first binder, and adding the mixture to a first solvent to prepare a first slurry;

[0065] The mass ratio of the sodium supplement additive, the first conductive agent, the first dispersant, and the first binder is (70-95): (1-20): (0.5-15): (0.5-10); and the solid content of the first slurry is 15%-65%;

[0066] S2, coating the first slurry on at least one side of the surface of the diaphragm substrate, and drying to obtain a sodium-replenishing coating on the diaphragm substrate;

[0067] S3, mixing a second binder, a second conductive agent, and a second dispersant, and adding the mixture to a second solvent to prepare a second slurry;

[0068] The mass ratio of the second binder, the second conductive agent and the second dispersant is (60-95): (1-25): (3-20), and the solid content of the second slurry is 10%-65%;

[0069] S4, coating the second slurry on the sodium-supplementing coating prepared in step S2, and drying to form a bonding layer to prepare a sodium-supplementing diaphragm.

[0070] In some embodiments, in steps S2 and S4, the first slurry coated on at least one side of the surface of the diaphragm substrate is dried at 50° C. to 90° C.

[0071] A third aspect of the present application provides a sodium ion battery, which includes a positive electrode plate, a negative electrode plate, and a sodium-supplementing diaphragm as provided in the first aspect above.

[0072] Specifically, the positive electrode sheet, the negative electrode sheet, and the sodium-supplementing diaphragm are wound or stacked to form a bare battery, and the battery is formed and divided into different capacities; thus, a sodium-ion battery capable of continuously replenishing sodium through the sodium-supplementing diaphragm is obtained.

[0073] The present application will be further described below with reference to specific embodiments and comparative examples.

[0074] Example 1

[0075] Preparation of sodium supplementation membrane

[0076] S1. Weigh the sodium supplement additive Na2CO3, the first conductive agent super-P, the first dispersant sodium polyacrylate, and the first binder polyvinylidene fluoride according to a mass ratio of 85:5:3:7, stir and mix them evenly to obtain a first mixture, add the first mixture into the first solvent N-methylpyrrolidone to obtain a first slurry; wherein the solid content of the first slurry is 45%.

[0077] S2. Coat the first slurry on one side of a polyethylene (PE) diaphragm, and dry it at 50°C to obtain a sodium-replenishing coating on the diaphragm substrate; wherein the thickness of the polyethylene (PE) diaphragm is 9 μm, and the thickness of the sodium-replenishing coating is 3 μm.

[0078] S3. Weigh the second binder polyvinylidene fluoride, the second conductive agent super-P, and the second dispersant sodium polyacrylate according to a mass ratio of 75:15:10, stir and mix them evenly to obtain a second mixture, add the second mixture into the second solvent N-methylpyrrolidone to obtain a second slurry; the solid content of the second slurry is 45%.

[0079] S4, coating the second slurry on the surface of the sodium-supplementing coating obtained in step S2, drying the coating at 50°C, forming a bonding layer on the surface of the sodium-supplementing coating, and obtaining a sodium-supplementing diaphragm, wherein the thickness of the bonding layer is 1 μm.

[0080] Example 2

[0081] Preparation of sodium supplementation membrane

[0082] S1. Weigh the sodium supplement additive Na2CO3, the first conductive agent super-P, the first dispersant sodium polyacrylate, and the first binder polyvinylidene fluoride according to a mass ratio of 85:5:3:7, stir and mix them evenly to obtain a first mixture, add the first mixture into the first solvent N-methylpyrrolidone to obtain a first slurry; wherein the solid content of the first slurry is 45%.

[0083] S2. Coat the first slurry on one side of a polyethylene (PE) diaphragm, and dry it at 50°C to obtain a sodium-replenishing coating on the diaphragm substrate; wherein the thickness of the polyethylene (PE) diaphragm is 9 μm, and the thickness of the sodium-replenishing coating is 3 μm.

[0084] S3. Weigh the second binder PVDF-HFP, the second conductive agent super-P, and the second dispersant sodium polyacrylate according to a mass ratio of 80:10:10, stir and mix them evenly to obtain a second mixture, add the second mixture into the second solvent N-methylpyrrolidone to obtain a second slurry; wherein the solid content of the second slurry is 44%.

[0085] S4, coating the second slurry on the surface of the sodium-supplementing coating obtained in step S2, drying the coating at 50°C, forming a bonding layer on the surface of the sodium-supplementing coating, and obtaining a sodium-supplementing diaphragm, wherein the thickness of the bonding layer is 1 μm.

[0086] Example 3

[0087] Preparation of sodium supplementation membrane

[0088] S1. Weigh the sodium supplement additive Na2CO3, the first conductive agent super-P, the first dispersant sodium polyacrylate, and the first binder polyvinylidene fluoride according to a mass ratio of 85:5:3:7, stir and mix them evenly to obtain a first mixture, add the first mixture into the first solvent N-methylpyrrolidone to obtain a first slurry; wherein the solid content of the first slurry is 45%.

[0089] S2. Coat the first slurry on one side of a polyethylene (PE) diaphragm, and dry it at 50°C to obtain a sodium-replenishing coating on the diaphragm substrate; wherein the thickness of the polyethylene (PE) diaphragm is 9 μm, and the thickness of the sodium-replenishing coating is 3 μm.

[0090] S3. Weigh the second binder polyvinylidene fluoride, the second conductive agent super-P, and the second dispersant sodium polyacrylate in a mass ratio of 60:20:20, stir and mix them evenly to obtain a second mixture, add the second mixture into the second solvent N-methylpyrrolidone to obtain a second slurry; the solid content of the second slurry is 46%.

[0091] S4, coating the second slurry on the surface of the sodium-supplementing coating obtained in step S2, drying the coating at 50°C, forming a bonding layer on the surface of the sodium-supplementing coating, and obtaining a sodium-supplementing diaphragm, wherein the thickness of the bonding layer is 1 μm.

[0092] Example 4

[0093] Preparation of sodium supplementation membrane

[0094] S1. Weigh the sodium supplement additive Na2CO3, the first conductive agent super-P, the first dispersant sodium polyacrylate, and the first binder polyvinylidene fluoride according to a mass ratio of 85:5:3:7, stir and mix them evenly to obtain a first mixture, add the first mixture into the first solvent N-methylpyrrolidone to obtain a first slurry; wherein the solid content of the first slurry is 45%.

[0095] S2. Coat the first slurry on one side of a polyethylene (PE) diaphragm, and dry it at 50°C to obtain a sodium-replenishing coating on the diaphragm substrate; wherein the thickness of the polyethylene (PE) diaphragm is 9 μm, and the thickness of the sodium-replenishing coating is 3 μm.

[0096] S3. Weigh the second binder polyvinylidene fluoride, the second conductive agent super-P, and the second dispersant sodium polyacrylate according to a mass ratio of 95:2:3, stir and mix them evenly to obtain a second mixture, add the second mixture into the second solvent N-methylpyrrolidone to obtain a second slurry; the solid content of the second slurry is 40%.

[0097] S4, coating the second slurry on the surface of the sodium-supplementing coating obtained in step S2, drying the coating at 50°C, forming a bonding layer on the surface of the sodium-supplementing coating, and obtaining a sodium-supplementing diaphragm, wherein the thickness of the bonding layer is 1 μm.

[0098] Example 5

[0099] The difference between this embodiment and the embodiment 1 is that in step S4 , the thickness of the bonding layer is 3 μm, and the rest is the same as the embodiment 1.

[0100] Example 6

[0101] The difference between this embodiment and the embodiment 1 is that in step S4 , the thickness of the bonding layer is 0.3 μm, and the rest is the same as the embodiment 1.

[0102] Example 7

[0103] The difference between this embodiment and the embodiment 1 is that in step S4 , the thickness of the bonding layer is 5 μm, and the rest is the same as the embodiment 1.

[0104] Example 8

[0105] The difference between this embodiment and embodiment 1 is that in step S1, the sodium supplement additive Na2CO3, the first conductive agent super-P, the first dispersant sodium polyacrylate, and the first binder polyvinylidene fluoride are weighed according to a mass ratio of 80:8:4:8, and the rest is the same as embodiment 1.

[0106] Example 9

[0107] The difference between this embodiment and embodiment 1 is that in step S1, the sodium supplement additive is Na2S, and the rest is the same as embodiment 1.

[0108] Comparative Example 1

[0109] The difference between this comparative example and Example 1 is that in step S3 , the second binder polyvinylidene fluoride, the second conductive agent super-P, and the second dispersant sodium polyacrylate are weighed according to a mass ratio of 40:30:30, and the rest is the same as Example 1.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is that in step S3, the second binder polyvinylidene fluoride, the second conductive agent super-P, and the second dispersant sodium polyacrylate are weighed according to a mass ratio of 98:1:1, and the rest is the same as Example 1.

[0112] Comparative Example 3

[0113] The difference between this comparative example and Example 1 is that in step S4 , the thickness of the bonding layer is 0.1 μm, and the rest is the same as Example 1.

[0114] Comparative Example 4

[0115] The difference between this comparative example and Example 1 is that in step S4 , the thickness of the bonding layer is 7 μm, and the rest is the same as Example 1.

[0116] Comparative Example 5

[0117] The difference between this comparative example and Example 1 is that in step S3, the second binder polyvinylidene fluoride and the second dispersant sodium polyacrylate are weighed according to a mass ratio of 75:10, and the rest is the same as Example 1, that is, no conductive agent is added to the adhesive layer.

[0118] Comparative Example 6

[0119] The difference between this comparative example and Example 1 is that in step S3, the second binder polyvinylidene fluoride and the second conductive agent super-P are weighed according to a mass ratio of 75:15, and the rest is the same as Example 1, that is, no dispersant is added to the adhesive layer.

[0120] Comparative Example 7

[0121] The difference between this comparative example and Example 1 is that step S3 and step S4 are omitted, that is, no adhesive layer is provided in the sodium supplementing diaphragm, and the rest is the same as Example 1.

[0122] Comparative Example 8

[0123] The difference between this comparative example and Example 8 is that step S3 and step S4 are omitted, that is, no bonding layer is provided in the sodium supplementing diaphragm, and the rest is the same as Example 8.

[0124] Comparative Example 9

[0125] The difference between this comparative example and Example 9 is that step S3 and step S4 are omitted, that is, no bonding layer is provided in the sodium supplementing diaphragm, and the rest is the same as Example 9.

[0126] Preparation of sodium ion batteries:

[0127] Preparation of positive electrode: NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, PVDF and super-P were dispersed in NMP in a mass ratio of 9.5:0.2:0.3 to prepare a positive electrode active slurry, which was then coated on an aluminum foil with a thickness of 13 μm, and the positive electrode sheet was obtained by drying, rolling and punching.

[0128] Preparation of negative electrode sheet: Hard carbon, SBR, CMC and super-P are dispersed in water in a mass ratio of 9.5:0.15:0.15:0.2 to prepare a negative electrode active slurry, which is then coated on a copper foil with a thickness of 13 μm, and then dried, rolled and punched to obtain a negative electrode sheet.

[0129] The positive electrode sheet, the negative electrode sheet, and the sodium supplement diaphragm prepared in the above embodiments and comparative examples are wound or laminated to form a bare cell, and the battery is packaged, injected, formed, and divided into different volumes to obtain a sodium ion battery. The adhesive layer in the sodium supplement diaphragm is arranged close to one side of the positive electrode sheet.

[0130] Test Case

[0131] The sodium ion battery obtained by using the sodium supplement diaphragm prepared by the above embodiment and comparative example was tested for the first coulombic efficiency, initial specific capacity and cycle life. Among them, the formation step: constant current charging at 0.33C, the cut-off voltage is 4V, constant voltage charging at 4V, the cut-off current is 0.05C, and the capacity obtained at this time is the first formation charging capacity; the capacity division step: constant current discharge at 0.33C, the cut-off voltage is 1.5V, and the capacity obtained at this time is the first capacity division discharge capacity.

[0132] The first coulomb efficiency test method is to divide the first divided capacity discharge capacity by the first formation charge capacity. The test results are shown in Table 1 below.

[0133] The initial specific capacity is the value obtained by dividing the first capacity-dividing discharge capacity of the positive electrode of the battery by the active mass of the positive electrode after the capacity-dividing. The test results are shown in Table 1 below.

[0134] The cycle life is the ratio of the capacity after 1000 cycles to the initial capacity. The cycle cut-off voltage range is 1.5-3.95V, and the charge and discharge current is 0.5C. The test results are shown in Table 1 below.

[0135] Table 1

[0136]

[0137] By comparing Examples 1-4 and Comparative Examples 1-2, it can be seen that only when the mass ratio of each substance in the bonding layer and the mass proportion of the second dispersant are within an appropriate range, the prepared sodium ion battery has both good first coulombic efficiency and cycle life.

[0138] By comparing Example 1 with Comparative Examples 5-7; Example 8 with Comparative Example 8; and Example 9 with Comparative Example 9, it can be seen that the use of the bonding layer provided in the present application improves the cycle life of the sodium ion battery.

[0139] By comparing Examples 1, 5-7 and Comparative Examples 3-4, it can be seen that when the thickness of the bonding layer is too thin, the generation of solid and gaseous residues after the sodium supplementation agent reaction cannot be effectively suppressed, which has an adverse effect on the interface contact between the diaphragm and the electrode. When the thickness of the bonding layer is too thick, it is not conducive to the rapid transmission of sodium ions, resulting in excessive interface polarization, which in turn affects the battery cycle performance.

[0140] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A sodium supplementing membrane, characterized in that: It comprises a diaphragm substrate, a sodium-supplementing coating and a bonding layer, wherein at least one side of the diaphragm substrate is coated with the sodium-supplementing coating, and the bonding layer is coated on the sodium-supplementing coating; The sodium supplement coating comprises a sodium supplement additive, a first conductive agent, a first dispersant and a first binder, wherein the mass ratio of the sodium supplement additive, the first conductive agent, the first dispersant and the first binder in the sodium supplement coating is (70-95): (1-20): (0.5-15): (0.5-10); The bonding layer includes a second bonding agent, a second conductive agent and a second dispersant, wherein the mass ratio of the second bonding agent, the second conductive agent and the second dispersant is (60-95): (1-25): (3-20); The thickness of the bonding layer is 0.3 μm to 3 μm; The second binder, the second conductive agent, and the second dispersant are respectively the same as the first binder, the first conductive agent, and the first dispersant; The sodium supplement additive includes one or more of Na2S and Na2CO3; The second binder and the first binder are selected from one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

2. The sodium supplement membrane according to claim 1, characterized in that: The mass ratio of the second binder, the second conductive agent and the second dispersant is (65-90): (5-20): (8-15).

3. The sodium supplementation membrane according to claim 1 or 2, characterized in that: The second conductive agent and the first conductive agent are selected from one or more of carbon black, acetylene black, Ketjen black, graphene, and carbon nanotubes.

4. The sodium supplementation membrane according to claim 1 or 2, characterized in that: The second dispersant and the first dispersant are selected from one or more of polyvinyl pyrrolidone, sodium polyacrylate, polyethylene glycol, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, polymethacrylate, sodium hexametaphosphate, polyacrylic acid ammonium salt copolymer, and polyvinyl alcohol.

5. A method for preparing a sodium supplementing diaphragm according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, mixing a sodium supplement additive, a first conductive agent, a first dispersant, and a first binder, and adding the mixture to a first solvent to prepare a first slurry; The mass ratio of the sodium supplement additive, the first conductive agent, the first dispersant, and the first binder is (70-95): (1-20): (0.5-15): (0.5-10); and the solid content of the first slurry is 15%-65%; S2, coating the first slurry on at least one side of the surface of the diaphragm substrate, and drying to obtain a sodium-replenishing coating on the diaphragm substrate; S3, mixing a second binder, a second conductive agent, and a second dispersant, and adding the mixture to a second solvent to prepare a second slurry; The mass ratio of the second binder, the second conductive agent and the second dispersant is (60-95): (1-25): (3-20); and the solid content of the second slurry is 10%-65%; S4, coating the second slurry on the sodium-supplementing coating prepared in step S2, and drying to form a bonding layer to prepare a sodium-supplementing diaphragm.

6. A sodium ion battery, characterized in that: The sodium ion battery comprises a positive electrode sheet, a negative electrode sheet and a sodium supplementing diaphragm as described in any one of claims 1 to 4.

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