Sodium-ion negative electrode sheet, preparation method thereof, and sodium-ion battery

Abstract

This application relates to a sodium-ion negative electrode sheet and its preparation method, as well as a sodium-ion battery. The preparation method includes: mixing a negative electrode active material, a conductive agent, a binder, and a solvent to obtain a mixed slurry; coating the mixed slurry onto the surface of a conductive substrate to obtain an initial negative electrode sheet; and spraying an aqueous sodium salt solution onto the surface of the initial negative electrode sheet to form a target negative electrode sheet. By uniformly depositing sodium salt by spraying a sodium salt solution onto the surface of the initial negative electrode sheet, the spray method can better control the amount of sodium salt adhering to the negative electrode, and the sodium salt is only on the surface of the negative electrode sheet, without affecting the conductivity of the electrode sheet. Furthermore, the sodium salt adhering to the surface can achieve pre-sodiumification of the negative electrode, reducing the contact area between the negative electrode and the electrolyte, thereby reducing the consumption of sodium ions by the negative electrode during the formation of the SEI film, improving the charge-discharge efficiency and reversible capacity of the negative electrode, and achieving a significant increase in the energy density of the sodium-ion battery.

Description

Technical Field

[0001] This application relates to the field of new energy battery technology, and in particular to a sodium-ion negative electrode sheet and its preparation method, and a sodium-ion battery. Background Technology

[0002] With the booming development of the new energy sector, lithium-ion batteries have been widely used in energy storage, automobiles, power tools, mobile digital devices, and many other fields. However, the rapidly increasing market demand for lithium-ion batteries has led to a severe shortage of lithium resources, causing a sharp rise in lithium salt prices, which is detrimental to the sustainable and healthy development of the industry. Sodium, an element in the same group as lithium, is abundant, inexpensive, and shares similar physicochemical properties with lithium. The research and development of sodium-ion batteries can, to some extent, alleviate the battery development problems caused by lithium resource shortages. Furthermore, sodium-ion batteries exhibit superior performance in low-temperature discharge, high-rate charging, and safety, compensating for the inherent shortcomings of lithium-ion batteries.

[0003] However, the sodium-ion batteries currently in use generally suffer from low charge and discharge efficiency, especially the initial charge and discharge efficiency, due to the excessive consumption of sodium ions during the formation of the SEI (Solid Electrolyte Interphase) film at the negative electrode. This results in significant capacity loss at the negative electrode and low reversible capacity. Summary of the Invention

[0004] Therefore, it is necessary to address the problem of low charge and discharge efficiency in existing sodium-ion batteries due to excessive sodium ion consumption during the formation of the SEI film at the negative electrode, and to provide a sodium-ion negative electrode sheet, its preparation method, and a sodium-ion battery.

[0005] A method for preparing a sodium-ion negative electrode includes:

[0006] The negative electrode active material, conductive agent, binder and solvent are mixed to obtain a mixed slurry;

[0007] The mixed slurry is coated on the surface of a conductive substrate to obtain an initial negative electrode sheet;

[0008] A sodium salt aqueous solution is sprayed onto the surface of the initial negative electrode to form the target negative electrode.

[0009] In one embodiment, the step of spraying an aqueous sodium salt solution onto the surface of the initial negative electrode to form the target negative electrode includes:

[0010] A sodium salt aqueous solution is sprayed onto the surface of the initial negative electrode to obtain a negative electrode coated with a sodium salt aqueous solution.

[0011] The negative electrode sheet coated with sodium salt aqueous solution is dried to obtain the target negative electrode sheet.

[0012] In one embodiment, the diameter of the sprayed sodium salt aqueous solution is 1µm-20µm.

[0013] In one embodiment, the drying temperature for drying the negative electrode sheet coated with sodium salt aqueous solution is 80°C-120°C.

[0014] In one embodiment, the sodium salt additive in the sodium salt aqueous solution includes at least one of Na2CO3, NaHCO3, NaCl, NaF, Na2S, and Na2SO4.

[0015] In one embodiment, the concentration of the sodium salt aqueous solution is 0.1 mol / L to 6 mol / L.

[0016] In one embodiment, the negative electrode active material accounts for 90%-97% by weight, the conductive agent accounts for 0.5%-5% by weight, and the binder accounts for 2.5%-5% by weight.

[0017] In one embodiment, the conductive substrate is copper foil or aluminum foil.

[0018] In one embodiment, a sodium-ion negative electrode is provided, which is prepared based on the above-described method for preparing a sodium-ion negative electrode.

[0019] In one embodiment, a sodium-ion battery is provided, including the sodium-ion negative electrode sheet described above.

[0020] The aforementioned sodium-ion negative electrode sheet and its preparation method, as well as the sodium-ion battery, achieve uniform deposition of sodium salt by spraying an aqueous sodium salt solution onto the surface of the initial negative electrode sheet. This spraying method allows for better control of the amount of sodium salt adhering to the negative electrode, and the sodium salt remains only on the surface of the negative electrode sheet, without affecting its conductivity. Furthermore, the surface-adhered sodium salt enables pre-sodiumization of the negative electrode, reducing the contact area between the negative electrode and the electrolyte. This, in turn, reduces the consumption of sodium ions during the formation of the SEI film (solid electrolyte interface film), improving the charge / discharge efficiency and reversible capacity of the negative electrode, and significantly increasing the energy density of the sodium-ion battery. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for preparing a sodium-ion negative electrode sheet in one embodiment;

[0022] Figure 2 This is a schematic diagram of the structure of a sodium ion negative electrode in one embodiment;

[0023] Figure 3 This is a schematic diagram of the sodium ion negative electrode sheet in another embodiment;

[0024] Figure 4 This is a flowchart of the method for fabricating a target negative electrode sheet in one embodiment;

[0025] Figure 5 This is a schematic diagram showing the sodium salt adhesion on the surface of the target negative electrode sheet prepared in Example 1;

[0026] Figure 6 This is a schematic diagram showing the sodium salt adhesion on the surface of the target negative electrode sheet prepared in Example 2;

[0027] Figure 7 This is a schematic diagram showing the sodium salt adhesion on the surface of the target negative electrode sheet prepared in Example 3;

[0028] Figure 8 This is a schematic diagram showing the sodium salt adhesion on the surface of the target negative electrode sheet prepared in Example 4;

[0029] Figure 9 This is a schematic diagram showing the sodium salt adhesion on the surface of the target negative electrode sheet prepared in Comparative Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0032] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0033] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0034] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0035] As described in the background section, with the booming development of the new energy field, lithium-ion batteries have been widely used in energy storage, automobiles, power tools, mobile digital devices, and many other fields. However, the current market demand for lithium-ion batteries is growing rapidly, leading to a severe shortage of lithium resources and a sharp rise in lithium salt prices, which is detrimental to the sustainable and healthy development of the industry. Sodium, an element in the same group as lithium, is abundant, inexpensive, and shares similar physicochemical properties with lithium. The research and development of sodium-ion batteries can, to some extent, alleviate the battery development problems caused by the lithium resource shortage. Furthermore, sodium-ion batteries exhibit superior performance in low-temperature discharge, high-rate charging, and safety, compensating for the shortcomings of lithium-ion batteries.

[0036] However, currently used sodium-ion batteries generally suffer from low charge-discharge efficiency, especially in the initial charge-discharge cycle, due to the excessive consumption of sodium ions during the formation of the SEI (Solid Electrolyte Interphase) film at the negative electrode. This results in significant capacity loss and low reversible capacity. While existing technologies employ methods to attach organic or inorganic salts to the negative electrode during fabrication—such as adding sodium salt as an additive to the negative electrode slurry or immersing the negative electrode in a sodium salt solution—these methods struggle to control the amount of sodium salt adhering to the negative electrode. This can easily lead to a thick layer of sodium salt coating, hindering sodium ion migration. Furthermore, sodium salts have poor electronic conductivity; if incorporated into the negative electrode slurry, they will affect the conductivity between the negative electrode material and the conductive substrate, as well as between the negative electrode material particles.

[0037] Based on this, this application proposes a sodium-ion negative electrode and its preparation method. By uniformly depositing sodium salt by spraying an aqueous sodium salt solution onto the surface of the initial negative electrode, the spraying method can effectively control the amount of sodium salt adhering to the negative electrode. Moreover, the sodium salt is only on the surface of the negative electrode and does not affect the conductivity of the electrode. Furthermore, the sodium salt adhering to the surface can achieve pre-sodiumification of the negative electrode, reducing the contact area between the negative electrode and the electrolyte, thereby reducing the consumption of sodium ions during the formation of the SEI film (solid electrolyte interface film), improving the charge-discharge efficiency and reversible capacity of the negative electrode, and achieving a significant increase in the energy density of sodium-ion batteries.

[0038] In one embodiment, such as Figure 1As shown, a method for preparing a sodium-ion negative electrode sheet is provided, including the following steps 102 to 106.

[0039] Step 102: Mix the negative electrode active material, conductive agent, binder and solvent to obtain a mixed slurry.

[0040] The negative electrode active material is a material capable of intercalating and releasing sodium ions, and can be one or more of carbon-based, titanium-based, alloy-based, and organic-based negative electrode materials. In this embodiment, a carbon-based negative electrode material is selected as the negative electrode active material, such as one or more of graphite, soft carbon, and hard carbon. Soft carbon can be selected from carbon microspheres, metallurgical coke, pitch-derived carbon, mesoporous soft carbon, nitrogen-sulfur co-doped porous soft carbon nanosheets, etc.; hard carbon can be selected from resin carbon, phenolic resin-based hard carbon, hollow carbon nanowires, orange peel hard carbon, and oxygen-sulfur co-doped hard carbon, etc.

[0041] It is understood that there are no particular limitations on the conductive agents and binders in the mixed slurry used to fabricate the negative electrode sheet, and commonly used conductive agents and binders in this field can be used. For example, the conductive agent can be one or more of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene. The binder can be one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber (SBR). The solvent can be deionized water or N-methylpyrrolidone (NMP solvent).

[0042] Specifically, when preparing the mixed slurry required for the negative electrode sheet, the corresponding negative electrode active material, conductive agent, and binder need to be weighed from the prepared materials according to their mass proportions, thoroughly ground, and then added to an appropriate amount of solvent. The mixture is then carried out in a vacuum mixer or disperser to form a stable and uniform mixed slurry.

[0043] The specific weight percentages of the negative electrode active material, conductive agent, and binder are not fixed and can be selected according to specific implementation methods. In one embodiment, the weight percentage of the negative electrode active material is 90%-97%, the weight percentage of the conductive agent is 0.5%-5%, and the weight percentage of the binder is 2.5%-5%. Specifically, the specific weight percentages of the negative electrode active material, conductive agent, and binder can be: 94% negative electrode active material, 1.5% conductive agent, and 4.5% binder; 95% negative electrode active material, 1% conductive agent, and 4% binder; or 93.5% negative electrode active material, 1.5% conductive agent, and 4% binder.

[0044] Step 104: Coat the surface of the conductive substrate with the mixed slurry to obtain the initial negative electrode sheet.

[0045] The conductive substrate serves as a carrier for the coated slurry. Due to its conductivity, it connects the negative electrode active materials coated on the substrate, thus collecting and outputting the current generated by all the negative electrode active materials. Therefore, the conductive substrate needs to have good conductivity and good chemical and electrochemical stability. In one embodiment, the conductive substrate is copper foil or aluminum foil. In this embodiment, copper foil is used as the conductive substrate for fabricating the negative electrode sheet. Specifically, it can be electrolytic copper foil or composite copper foil made from polymer materials such as PET (Polyethylene Terephthalate) as the base material to improve battery safety.

[0046] Specifically, the mixed slurry is uniformly coated onto the surface of a conductive substrate, and then dried. For example, the conductive substrate coated with the mixed slurry is placed in a drying oven for vacuum drying. Afterwards, it can undergo cold pressing, cutting, and other steps to obtain the initial negative electrode sheet for later use. The mixed slurry can be coated onto the conductive substrate using a slurry-drawing method, and the coating thickness can be determined according to the specific implementation method. Furthermore, the temperature and duration of vacuum drying can also be selected according to the specific implementation method, aiming to ensure that the mixed slurry coated on the conductive substrate surface has no residual moisture. The size and shape of the initial negative electrode sheet can be determined according to the final shape of the sodium-ion battery to be manufactured, and are not limited thereto.

[0047] In addition, when uniformly coating the mixed slurry onto the surface of the conductive substrate, the appropriate method can be used, depending on the requirements of the final sodium-ion battery to be manufactured. Figure 2 The method shown involves coating a mixed slurry onto one side of a conductive substrate to create an initial negative electrode sheet with a mixed slurry layer on one side; alternatively, a method such as... Figure 3 The method shown involves coating the mixed slurry onto the surfaces of opposite sides of a conductive substrate to create an initial negative electrode sheet with a mixed slurry layer on both sides.

[0048] Step 106: Spray an aqueous solution of sodium salt onto the surface of the initial negative electrode to form the target negative electrode.

[0049] The sodium salt aqueous solution is a solution containing one or more sodium salt additives, which can be obtained by mixing and dissolving one or more sodium salt additives in water. The sodium salt additives in the sodium salt aqueous solution are sodium-containing organic or inorganic salts that are readily soluble in water and insoluble or slightly soluble in organic solvents. In one embodiment, the sodium salt additives in the sodium salt aqueous solution may include at least one of Na₂CO₃, NaHCO₃, NaCl, NaF, Na₂S, and Na₂SO₄. For example, it may include two sodium salt additives: Na₂CO₃ and NaCl; it may include three sodium salt additives: Na₂CO₃, NaHCO₃, and NaCl; it may include four sodium salt additives: Na₂CO₃, NaHCO₃, NaF, and NaCl; or it may include four sodium salt additives: Na₂CO₃, NaF, Na₂S, and Na₂SO₄.

[0050] It is understood that the concentration of the sodium salt aqueous solution will vary depending on the proportion of different sodium salt additives mixed together. In one embodiment, the concentration of the sodium salt aqueous solution can be 0.1-6 mol / L. For example, mixing two sodium salt additives, Na2CO3 and NaCl, in a 1:1 ratio yields a sodium salt aqueous solution with a concentration of 1.5 mol / L; mixing three sodium salt additives, Na2CO3, NaHCO3, and NaCl, in a 0.5:0.5:1 ratio yields a sodium salt aqueous solution with a concentration of 1.0 mol / L; mixing four sodium salt additives, Na2CO3, NaHCO3, NaF, and NaCl, in a 0.25:0.25:0.5:1 ratio yields a sodium salt aqueous solution with a concentration of 2.0 mol / L; and mixing four sodium salt additives, Na2CO3, NaF, Na2S, and Na2SO4, in a 0.5:1:0.25:0.25 ratio yields a sodium salt aqueous solution with a concentration of 1.0 mol / L.

[0051] Specifically, after mixing the sodium salt aqueous solution, the sodium salt aqueous solution can be sprayed onto the surface of the initial negative electrode sheet using a sprayer to form the target negative electrode sheet. In one embodiment, such as Figure 4 As shown, step 106 includes steps 202 to 204.

[0052] Step 202: Spray the sodium salt aqueous solution onto the surface of the initial negative electrode to obtain a negative electrode coated with sodium salt aqueous solution.

[0053] Specifically, the mixed sodium salt solution can be poured into the sprayer first, and the sprayer parameters can be adjusted to control the diameter of the sprayed sodium salt solution droplets. In addition, the flow rate and time during the spraying process can be controlled to ensure that the amount of sodium salt on the surface of the initial negative electrode sheet per square meter meets the preset sodium salt amount value, and finally the negative electrode sheet with the sodium salt solution sprayed is obtained.

[0054] The preset sodium salt amount is a sodium salt adhesion amount that ensures the migration effect of sodium ions between the positive and negative electrodes without affecting the conductivity of the negative electrode. For example, the preset sodium salt amount can be selected between 1 and 50g, specifically 10g, 15g, 20g, 30g, or 40g. The sodium salt amount per square meter of the initial negative electrode surface meets the preset sodium salt amount, which can be expressed as the difference between the initial sodium salt amount per square meter of the initial negative electrode surface and the preset sodium salt amount, which is less than or equal to a preset error, where the preset error can be a value close to zero. In addition, in one embodiment, the diameter of the sodium salt aqueous solution spray obtained by adjusting the sprayer parameters in the above process can be 1µm-20µm, and in a specific embodiment, 5µm can be selected.

[0055] Step 204: Dry the negative electrode sheet coated with sodium salt aqueous solution to obtain the target negative electrode sheet.

[0056] Specifically, the negative electrode sheet coated with sodium salt aqueous solution is placed in a drying oven for vacuum drying to obtain the final target negative electrode sheet. In one embodiment, the drying temperature for drying the negative electrode sheet coated with sodium salt aqueous solution can be 80℃-120℃. For example, in a specific implementation, 100℃ can be selected as the negative electrode baking temperature after spraying. The drying time for the negative electrode sheet coated with sodium salt aqueous solution is not limited, and can be determined to ensure that the target negative electrode sheet is completely dry.

[0057] The above-mentioned method for preparing sodium-ion negative electrode involves uniformly depositing sodium salt by spraying an aqueous sodium salt solution onto the surface of the prepared initial negative electrode. This spraying method allows for better control of the amount of sodium salt adhering to the negative electrode, and the sodium salt remains only on the surface of the negative electrode, without affecting its conductivity. Furthermore, the surface-adhered sodium salt achieves pre-sodiumification of the negative electrode, reducing the contact area between the negative electrode and the electrolyte. This reduces the consumption of sodium ions during the formation of the SEI film (solid electrolyte interface film), improving the charge / discharge efficiency and reversible capacity of the negative electrode, and significantly increasing the energy density of sodium-ion batteries.

[0058] In one embodiment, a sodium-ion negative electrode sheet is provided, prepared based on the preparation method of the sodium-ion negative electrode sheet provided in any of the above embodiments. In this embodiment, by uniformly depositing sodium salt by spraying an aqueous sodium salt solution onto the surface of the prepared initial negative electrode sheet, the prepared sodium-ion negative electrode sheet not only does not affect the conductivity of the negative electrode sheet, but also reduces the contact area between the negative electrode and the electrolyte, thereby reducing the consumption of sodium ions by the negative electrode during the formation of the SEI film (solid electrolyte interface film), improving the charge and discharge efficiency and reversible capacity of the negative electrode, and achieving a significant increase in the energy density of the sodium-ion battery.

[0059] In one embodiment, a sodium-ion battery is provided, including the aforementioned sodium-ion negative electrode sheet. Specifically, the sodium-ion negative electrode sheet included in the sodium-ion battery provided in this application is prepared by uniformly depositing sodium salt by spraying an aqueous sodium salt solution onto the surface of a prepared initial negative electrode sheet. This not only does not affect the conductivity of the negative electrode sheet, but also reduces the contact area between the negative electrode and the electrolyte, thereby reducing the consumption of sodium ions by the negative electrode during the formation of the SEI film (solid electrolyte interface film), improving the charge-discharge efficiency and reversible capacity of the negative electrode, and achieving a significant increase in the energy density of the sodium-ion battery.

[0060] In addition to the aforementioned sodium-ion negative electrode, the sodium-ion battery provided in this application also includes a positive electrode, an electrolyte, and a separator. The positive electrode, electrolyte, and separator can all be made from conventional sodium-ion battery materials in the art, either commercially available or prepared in-house. Since these are all known technologies, they will not be described in detail here. The assembly of the sodium-ion battery is also a conventional assembly method in the art and will not be described in detail here either. The form of the sodium-ion battery provided in this application is not unique; it can be a button cell, or it can be designed as a thin-film, flat, cylindrical, or stacked cell, etc., depending on the requirements.

[0061] The present invention will be further described in detail below with reference to the embodiments.

[0062] Example 1: A commonly used hard carbon material for the negative electrode was selected and mixed with a conductive agent, a binder, and a solvent in a specific ratio to form a slurry. This included: 94% hard carbon by weight, 1.5% conductive carbon black (conductive agent) by weight, 2% sodium carboxymethyl cellulose (binder 1) by weight, 2.5% styrene-butadiene rubber (binder 2) by weight, and an appropriate amount of deionized water (solvent). The slurry was uniformly coated onto copper foil and dried to form an initial negative electrode sheet. A sodium salt solution was then sprayed onto the initial negative electrode sheet, and dried at 100°C to form the target negative electrode sheet. In Example 1, the sodium salt additives in the sodium salt solution included two types: Na₂CO₃ and NaCl, in a weight ratio of 1:1, and the sodium salt aqueous solution concentration was 1.5 mol / L. The sprayer was adjusted to control the droplet diameter to approximately 5 μm, and the amount of sodium salt sprayed per square meter of negative electrode sheet was controlled to be 10 g by adjusting the sprayer flow rate and spraying time. Take a small piece of the target negative electrode and observe the sodium salt adhesion on its surface using a scanning electron microscope, such as... Figure 5 As shown.

[0063] Example 2: A commonly used hard carbon material in the field of aero-electrode composition was selected as the negative electrode active material. It was mixed with a conductive agent, a binder, and a solvent in a specific ratio to form a slurry. This included: 94% hard carbon by weight, 1.5% conductive carbon black (conductive agent) by weight, 2% sodium carboxymethyl cellulose (binder 1) by weight, 2.5% styrene-butadiene rubber (binder 2) by weight, and an appropriate amount of deionized water (solvent). The slurry was uniformly coated onto copper foil and dried to form an initial negative electrode sheet. A sodium salt solution was then sprayed onto the initial negative electrode sheet, and the sheet was dried at 100°C to form the target negative electrode sheet. In this Example 2, the sodium salt additives in the sodium salt solution included Na₂CO₃, NaHCO₃, and NaCl in a weight ratio of 0.5:0.5:1, and the sodium salt aqueous solution concentration was 1.0 mol / L. The sprayer was adjusted to control the droplet diameter to approximately 5 μm, and the amount of sodium salt sprayed per square meter of negative electrode sheet was controlled by the sprayer's flow rate and spraying time to achieve a total of 15 g of sodium salt. Take a small piece of the target electrode and observe the sodium salt adhesion on its surface using a scanning electron microscope, such as... Figure 6 As shown.

[0064] Example 3: A commonly used hard carbon material for the negative electrode was selected as the active material, and a mixed slurry was prepared with a conductive agent, a binder, and a solvent according to the specified ratio. This included: 94% hard carbon by weight, 1.5% conductive carbon black (conductive agent) by weight, 2% sodium carboxymethyl cellulose (binder 1) by weight, 2.5% styrene-butadiene rubber (binder 2) by weight, and an appropriate amount of deionized water (solvent). The slurry was uniformly coated onto copper foil and dried to form an initial negative electrode sheet. A sodium salt solution was then sprayed onto the initial negative electrode sheet, and dried at 100°C to form the target negative electrode sheet. In this Example 3, the sodium salt additives in the sodium salt solution included four types: Na₂CO₃, NaHCO₃, NaF, and NaCl, in a weight ratio of 0.25:0.25:0.5:1, and the sodium salt aqueous solution concentration was 2.0 mol / L. The sprayer was adjusted to control the droplet diameter to approximately 5 μm, and the amount of sodium salt sprayed per square meter of negative electrode sheet was controlled to be 15 g by adjusting the sprayer flow rate and spraying time. Take a small piece of the target electrode and observe the sodium salt adhesion on its surface using a scanning electron microscope, such as... Figure 7 As shown.

[0065] Example 4: A commonly used hard carbon material for the negative electrode was selected and mixed with a conductive agent, a binder, and a solvent in a specific ratio to form a slurry. This included: 94% hard carbon by weight, 1.5% conductive carbon black (conductive agent) by weight, 2% sodium carboxymethyl cellulose (binder 1) by weight, 2.5% styrene-butadiene rubber (binder 2) by weight, and an appropriate amount of deionized water (solvent). The slurry was uniformly coated onto copper foil and dried to form an initial negative electrode sheet. A sodium salt solution was then sprayed onto the initial negative electrode sheet, and dried at 100°C to form the target negative electrode sheet. In this Example 4, the sodium salt additives in the sodium salt solution included four types: Na₂CO₃, NaF, Na₂S, and Na₂SO₄, in a weight ratio of 0.5:1:0.25:0.25, and the sodium salt aqueous solution concentration was 1.0 mol / L. The sprayer was adjusted to control the droplet diameter to approximately 5 μm, and the amount of sodium salt sprayed per square meter of negative electrode sheet was controlled to be 15 g by adjusting the sprayer flow rate and spraying time. Take a small piece of the target electrode and observe the sodium salt adhesion on its surface using a scanning electron microscope, such as... Figure 8 As shown.

[0066] Comparative Example 1: The process for preparing the initial negative electrode in Comparative Example 1 is the same as in Examples 1-4, except that a sodium salt aqueous solution was not sprayed onto the prepared initial negative electrode; the initial negative electrode was directly used as the target negative electrode. Similarly, a small piece of the electrode was taken and its surface condition was observed using a scanning electron microscope. Figure 9 As shown.

[0067] Furthermore, coin cells were fabricated using the target negative electrode sheets prepared in Examples 1-4 and Comparative Example 1, respectively. The charging and discharging capacities of each coin cell were then tested, the charging and discharging efficiencies were calculated, and the reversible capacity (i.e., the discharge capacity) was compared, as shown in the table below.

[0068]

[0069] As can be seen from the table above, the coin cells made using the target negative electrode sheets prepared in Examples 1-4 all exhibit significantly higher initial discharge capacity, lower capacity loss, and higher initial efficiency than Comparative Example 1 after the first charge-discharge cycle. This demonstrates that uniformly depositing sodium salt by spraying an aqueous sodium salt solution onto the surface of the sodium-ion negative electrode sheet can achieve the goal of not affecting the conductivity of the negative electrode sheet, reducing the contact area between the negative electrode and the electrolyte, thereby reducing the consumption of sodium ions during the formation of the SEI film (solid electrolyte interface film), and improving the charge-discharge efficiency and reversible capacity of the negative electrode, thus achieving a significant increase in the energy density of sodium-ion batteries. Furthermore, by selecting different types, proportions, solution concentrations, and spraying parameters using the preparation method provided in this application, the charge-discharge efficiency of sodium-ion batteries can be significantly improved under different schemes, and all of these should fall within the scope of protection of this application.

[0070] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0071] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a sodium-ion negative electrode, characterized in that, include: The negative electrode active material, conductive agent, binder and solvent are mixed to obtain a mixed slurry; The mixed slurry is coated onto the surface of a conductive substrate to obtain an initial negative electrode sheet; A sodium salt aqueous solution is sprayed onto the surface of the initial negative electrode to obtain a negative electrode coated with the sodium salt aqueous solution. The sodium salt aqueous solution is an inorganic sodium salt aqueous solution. The sodium salt additives in the sodium salt aqueous solution include Na₂CO₃ and NaCl; or the sodium salt additives in the sodium salt aqueous solution include Na₂CO₃, NaHCO₃, and NaCl; or the sodium salt additives in the sodium salt aqueous solution include Na₂CO₃, NaHCO₃, NaF, and NaCl; or the sodium salt additives in the sodium salt aqueous solution include Na₂CO₃, NaF, Na₂S, and Na₂SO₄. The concentration of the sodium salt aqueous solution is 0.1 mol / L-6 mol / L, and the diameter of the spray droplets is 5 μm. During the spraying process, the spray flow rate and time of the sodium salt aqueous solution are controlled by adjusting the sprayer parameters to ensure that the amount of sodium salt on the surface of the initial negative electrode per square meter meets a preset sodium salt content value, which is 1-50 g. The negative electrode sheet coated with sodium salt aqueous solution is dried to obtain the target negative electrode sheet.

2. The method for preparing the sodium-ion negative electrode according to claim 1, characterized in that, The negative electrode active material is selected from one or more carbon-based negative electrode materials selected from graphite, soft carbon, and hard carbon.

3. The method for preparing the sodium-ion negative electrode sheet according to claim 2, characterized in that, The conductive agent is one or more of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene.

4. The method for preparing the sodium-ion negative electrode sheet according to claim 2, characterized in that, The drying temperature for drying the negative electrode sheet coated with sodium salt aqueous solution is 80℃-120℃.

5. The method for preparing the sodium-ion negative electrode sheet according to claim 2, characterized in that, The adhesive is one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

6. The method for preparing a sodium-ion negative electrode sheet according to any one of claims 1 to 5, characterized in that, The negative electrode active material accounts for 90%-97% by weight, the conductive agent accounts for 0.5%-5% by weight, and the binder accounts for 2.5%-5% by weight.

7. The method for preparing a sodium-ion negative electrode sheet according to any one of claims 1 to 5, characterized in that, The conductive substrate is copper foil or aluminum foil.

8. A sodium-ion negative electrode, characterized in that, The sodium-ion negative electrode sheet was prepared according to the preparation method of any one of claims 1-7.

9. A sodium-ion battery, characterized in that, Including the sodium ion negative electrode sheet as described in claim 8.

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