Negative electrode sheet for sodium-ion battery and sodium-ion battery

Abstract

The application discloses a negative electrode sheet of a sodium ion battery and the sodium ion battery, wherein the negative electrode sheet of the sodium ion battery comprises a current collector, a sodium-philic layer is arranged on the current collector, the sodium-philic layer comprises an active material, a first binder and a first dispersant, the active material comprises at least one of a metal organic framework material and a zeolite imidazolate framework material, MOFs and ZIFs have high porosity, a large specific surface area (≥2000 m 2 / g) and a multi-dimensional framework structure, the high porosity and the multi-dimensional structure can guide the uniform deposition of metallic sodium in the pores, buffer the volume expansion caused by the sodium deposition process, and the large specific surface area can provide more sodium nucleation sites, guide the uniform adhesion of the metallic sodium in the internal pores, and avoid the formation of sodium dendrites.

Description

Technical Field

[0001] This invention relates to the field of sodium battery technology, and more specifically, to the negative electrode sheet of a sodium-ion battery and a sodium-ion battery. Background Technology

[0002] With the rapid development of society and the economy, energy and the environment have become increasingly important concerns. Lithium-ion batteries, as green and environmentally friendly energy storage devices, have been widely used in consumer electronics, energy storage, and electric vehicles due to their advantages such as high energy density, long cycle life, and low pollution. However, the continuous growth in demand for lithium batteries, coupled with lithium resource shortages and rising prices, has severely constrained their development. Sodium shares similar physicochemical properties with lithium. Sodium accounts for approximately 2.3% of the total elemental composition of the Earth's crust, ranking sixth, and its resources are evenly distributed and inexpensive, making it a promising candidate for widespread application in energy storage and low-speed electric vehicles. However, the development of sodium-ion batteries also faces the following problems: because the radius of sodium ions (0.113nm) is larger than that of lithium ions (0.076nm), and the interlayer spacing of graphite anodes (0.334nm) is small, it is difficult to smoothly insert and extract larger sodium ions. The only commercially available anode material is hard carbon (interlayer spacing 0.36-0.38nm). However, the reversible capacity (≤300mAh / g) and initial efficiency (≤85%) of hard carbon anodes are both low. The low reversible capacity of the anode requires more anode material, which increases the weight of the cell. In addition, the initial efficiency of anode materials is lower than that of cathode materials, which means that the specific capacity of cathode materials cannot be fully utilized in the whole cell. This makes the energy density of sodium-ion batteries much lower than that of lithium-ion batteries, thus limiting the large-scale commercial application of sodium-ion batteries.

[0003] Given the current limitations in improving the performance of positive and negative electrode materials for sodium-ion batteries, electrodeless sodium-ion batteries have gradually become a research hotspot to enhance their energy density. Electrodeless sodium-ion batteries utilize only a current collector as the negative electrode. During charging, sodium ions released from the positive electrode deposit onto the current collector to form a sodium metal negative electrode. Because there is no negative electrode active material layer, the mass and volume of the battery cell can be significantly reduced, thereby increasing the battery's energy density. Chinese patent CN113437254A discloses a negative electrode sheet, electrochemical device, and electronic device for a sodium-ion battery. The surface of the negative electrode sheet contains a carbon material coating. A sodium metal layer is formed on the surface of the negative electrode sheet by ion sputtering, resulting in the negative electrode sheet. Finally, it is assembled with a positive electrode sheet, electrolyte, and separator to form an electrodeless sodium-ion battery. The drawbacks of this method are particularly obvious. First, the deposition of sodium metal on the surface of carbon materials causes a huge volume expansion, leading to electrode deformation and affecting cell performance. Second, ion sputtering deposition of sodium metal is inefficient, with a small sputtering area, making it impossible to sputter electrodes with a large area. Furthermore, ion sputtering equipment has a complex structure and the ion gun is expensive, preventing large-scale mass production. Finally, the sodium metal layer formed by ion sputtering does not have a uniform SEI film on its surface. When the negative electrode is assembled with the positive electrode and electrolyte, a dense SEI film forms on the surface of the negative electrode during charging, which consumes active sodium ions, reducing the total amount of active sodium available in the cell and shortening the cell's cycle life. Summary of the Invention

[0004] The purpose of this invention is to provide a negative electrode sheet for a sodium-ion battery and a sodium-ion battery.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a negative electrode sheet for a sodium-ion battery, comprising a current collector, wherein a sodium-loving layer is disposed on the current collector, the sodium-loving layer comprising an active material, wherein the active material comprises at least one of a metal-organic framework structure material and a zeolite imidazole ester framework structure material.

[0006] In an optional implementation, the current collector satisfies at least one of the following conditions (1)-(7): (1) The current collector is an aluminum foil current collector or an aluminum-based composite current collector; (2) The thickness of the current collector is 8-16 μm; (3) The current collector has a dyn value ≥ 37 dyn / cm; (4) The thickness D of the sodium-loving layer is 4-40 μm; (5) Sodium metal is present inside the sodium-loving layer; (6) No metallic sodium was deposited on the surface of the sodium-loving layer; (7) The sodium-loving layer further includes a first binder and a first dispersant, and the mass fraction of the active substance in the sodium-loving layer is ≥95%.

[0007] Another aspect of this application provides a method for processing the negative electrode sheet of a sodium-ion battery according to any of the foregoing embodiments, wherein the raw materials constituting the sodium-loving layer are mixed and stirred with water to form a slurry, the slurry is coated on a current collector and dried to obtain the electrode.

[0008] In an optional embodiment, metallic sodium is deposited inside the sodium-loving layer by electrochemical deposition.

[0009] In an optional embodiment, the step of depositing metallic sodium inside the sodium-loving layer is as follows: Preparation: Under an inert atmosphere, the current collector with a sodium-loving layer, the isolation membrane, and the sodium metal sheet are sequentially stacked and immersed in an electroplating bath containing the first electrolyte. Deposition is performed using a sodium metal sheet as the counter electrode and a current collector with a sodium-loving layer as the working electrode. Direct current is applied to charge the sodium metal sheet, causing sodium ions in the sodium metal sheet to deposit into the pores inside the sodium-loving layer.

[0010] In an optional embodiment, after the deposition step, the electrode sheet with deposited metallic sodium is washed in a solvent and then vacuum dried at 40-60°C to obtain the negative electrode sheet. Preferably, the solvent is at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0011] In an optional embodiment, the charging current density during the deposition step is 0.8-4 mAh / cm³. 2 The total charging time T is 1-300 minutes; Preferably, intermittent charging is used to eliminate polarization, with charging stopped for 4-6 minutes every 5-30 minutes; Preferably, the relationship between the sodium-loving layer thickness and the total charging time satisfies ; Among them, I d This refers to the current density during electroplating, measured in mA / cm². 2 ; t represents the electroplating time, in hours (h). Q represents the theoretical specific capacity of sodium metal, which is 1166 mAh / g. ρ is the density of sodium metal, in g / cm³. 3 ; β is the porosity of the sodium-loving layer, in v%.

[0012] In an optional embodiment, the first electrolyte includes a first sodium salt, a first additive, and a first organic solvent, wherein the first organic solvent includes ethylene carbonate.

[0013] In a second aspect, the present invention provides a sodium-ion battery, comprising a positive electrode, a second electrolyte, and a negative electrode as described in any one of the foregoing embodiments.

[0014] In an optional embodiment, the positive electrode sheet includes a positive electrode active material, a second conductive agent, and a second binder. The positive electrode active material is at least one of a sodium layered transition metal oxide, a polyanionic compound, or a Prussian blue compound. The second electrolyte includes a second sodium salt, a second additive, and a second organic solvent, wherein the second organic solvent includes PC.

[0015] The present invention has the following beneficial effects: The sodium-loving layer in this invention uses metal-organic framework (MOFs) and / or zeolite imidazole ester framework (ZIFs). MOFs and ZIFs have high porosity and a large specific surface area (≥2000 m²). 2 The high porosity and multidimensional structure of sodium ( / g) can guide the uniform deposition of sodium metal in its pores and buffer the volume expansion caused by the sodium deposition process. The huge specific surface area can provide more sodium nucleation sites, guide the uniform attachment of sodium metal in the internal pores, and avoid the formation of sodium dendrites. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the electrode structure in this application.

[0018] Diagram: 1-Negative electrode; 11-Current collector; 12-Sodium-loving layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] This application provides a negative electrode 1 for a sodium-ion battery, such as... Figure 1 As shown, it includes a current collector 11, on which a sodium-loving layer 12 is disposed. The sodium-loving layer 12 includes an active substance, which includes at least one of a metal-organic framework structure material and a zeolite imidazole ester framework structure material.

[0021] MOFs can be selected from IRMOF-3, and ZIFs can be selected from ZIF-8, both of which have high porosity and huge specific surface area (≥2000 m²). 2 The high porosity and multidimensional structure of sodium ( / g) can guide the uniform deposition of sodium metal in its pores and buffer the volume expansion caused by the sodium deposition process. The huge specific surface area can provide more sodium nucleation sites, guide the uniform attachment of sodium metal in the internal pores, and avoid the formation of sodium dendrites.

[0022] In some alternative embodiments, the current collector 11 is an aluminum foil current collector 11 or an aluminum-based composite current collector 11 instead of conventional copper foil, because sodium aluminum does not form an alloy that would cause the aluminum foil to pulverize. Aluminum foil has a lower density than copper foil and costs only 30% of copper foil. Therefore, aluminum foil and aluminum-based current collector 11 are preferred.

[0023] In some optional embodiments, the current collector 11 has a thickness of 8-16 μm; when the thickness is less than 8 μm, the aluminum foil has low tensile strength and is prone to breakage during coating and rolling, which cannot meet the processing requirements; when the aluminum foil thickness exceeds 16 μm, the electrode weight increases, resulting in a decrease in the energy density of the battery cell.

[0024] In some alternative embodiments, the current collector 11 has a dyn value ≥37 dyn / cm, which enables the coating on the current collector 11 to have good adhesion, thereby avoiding the problems of bulging and wrinkling caused by coating edge shrinkage during gravure coating, as well as the problem of uneven sodium deposition and the formation of sodium dendrites.

[0025] In some optional embodiments, the thickness D of the sodium-loving layer 12 is 4-40 μm. When the thickness is less than 4 μm, the coating process of the sodium-loving layer 12 is difficult. When the thickness exceeds 40 μm, the weight increases, which affects the energy density of the battery cell.

[0026] In some alternative embodiments, metallic sodium is present inside the sodium-loving layer 12, the mass fraction of the metallic sodium is 50-95%, and metallic sodium is not deposited on the surface of the sodium-loving layer 12; In some optional embodiments, the sodium-loving layer 12 further includes a first binder and a first dispersant, wherein the mass fraction of the active substance in the sodium-loving layer 12 is ≥95%. The selection of the binder and dispersant in this embodiment can refer to existing technologies; for example, the first binder can be selected from polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, polyethylene oxide, and polyvinylidene fluoride, and the first dispersant can be selected from polyvinylpyrrolidone.

[0027] Another embodiment of this application provides a method for processing a negative electrode sheet 1 of a sodium-ion battery, wherein the raw materials constituting the sodium-loving layer 12 are mixed with water and stirred to form a slurry, the slurry is coated on the current collector 11 and dried to obtain the product; In some preferred embodiments, the metallic sodium is deposited inside the sodium-loving layer 12 by electrochemical deposition. Pre-depositing metallic sodium in the pores inside MOFs and / or ZIFs is essentially pre-sodiumization, which can improve the cell's initial coulombic efficiency and cycle performance.

[0028] In some alternative embodiments, the step of depositing metallic sodium inside the sodium-loving layer 12 is as follows: Preparation: Under an inert atmosphere, the current collector 11 with a sodium-loving layer 12, the separator and the sodium metal sheet are sequentially stacked and immersed in an electroplating bath containing the first electrolyte. Deposition is performed using a sodium metal sheet as the counter electrode and a current collector 11 with a sodium-loving layer 12 as the working electrode. Direct current is applied to charge the sodium metal sheet, causing sodium ions in the sodium metal sheet to deposit into the pores inside the sodium-loving layer 12.

[0029] The inert atmosphere can be argon or helium. Compared with ion sputtering, electrochemical deposition is lower in cost and higher in efficiency, and the area of ​​the negative electrode is not limited, making it more suitable for large-scale manufacturing.

[0030] In some alternative embodiments, after the deposition step, the electrode sheet with deposited metallic sodium is cleaned in a solvent and then vacuum dried at 40-60°C to obtain the negative electrode sheet 1. Adding an electrode cleaning process can prevent sodium salt from crystallizing on the surface of the negative electrode sheet 1 and deteriorating the cell performance.

[0031] In some preferred embodiments, the solvent is at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0032] In some optional embodiments, the charging current during the deposition step is 0.8-4 mAh / cm². 2 The total charging time T is 1-300 minutes.

[0033] By depositing metallic sodium into the sodium-loving layer 12 and charging it with a small current in an electrolyte environment, electrochemical and concentration polarization are eliminated. At the same time, by controlling the magnitude of the charging current and the charging time, sodium ions can be uniformly deposited inside the sodium-loving layer 12 without being deposited on the surface of the sodium-loving layer 12, thus avoiding the formation of sodium dendrites.

[0034] Specifically, the maximum amount of metallic sodium deposited is related to the thickness of the sodium-loving layer 12. This application uses scanning electron microscopy to observe the surface of the sodium-loving layer 12 and ensures that metallic sodium is deposited in the pores inside MOFs and ZIFs by controlling the current and time of electrochemical deposition.

[0035] In some preferred embodiments, intermittent charging is employed to eliminate polarization. Charging is stopped for 4-6 minutes every 5-30 minutes. This low-current intermittent charging effectively eliminates electrochemical and concentration polarization. Simultaneously, controlling the charging current and charging time ensures uniform deposition of sodium ions within the sodium-loving layer 12, preventing the formation of sodium dendrites. Compared to continuous charging, intermittent charging more effectively eliminates electrochemical and concentration polarization, resulting in more uniform sodium deposition.

[0036] In some preferred embodiments, the relationship between the thickness of the sodium-loving layer 12 and the total charging time satisfies ; Among them, I d This refers to the current density during electroplating, measured in mA / cm². 2 ; t represents the electroplating time, in hours (h). Q represents the theoretical specific capacity of sodium metal, which is 1166 mAh / g. ρ is the density of sodium metal, in g / cm³. 3 ; β is the porosity of the sodium-loving layer 12, in v%.

[0037] At this point, pre-sodiumization is achieved without causing metallic sodium to deposit on the surface of the sodium-loving layer 12.

[0038] In some optional embodiments, the first electrolyte includes a first sodium salt, a first additive, and a first organic solvent. The first organic solvent includes ethylene carbonate, whose high dielectric constant promotes the dissociation of the sodium salt, reducing it on the sodium metal surface to form a stable solid electrolyte interphase (SEI) film, thereby increasing electrode stability. The formation of the SEI film can prevent the continued consumption of sodium ions in the positive electrode active material after subsequent assembly with the positive electrode sheet into a battery cell, thus improving the initial efficiency. The first sodium salt and the first additive can refer to existing technologies, and may include, for example, sodium hexafluorophosphate, VC, DTD, TMSP, and PST.

[0039] In a second aspect, the present invention provides a sodium-ion battery, comprising a positive electrode, a second electrolyte, and a negative electrode 1 as described in any one of the foregoing embodiments.

[0040] In some optional embodiments, the positive electrode includes a positive active material, a second conductive agent, and a second binder. The positive active material is at least one of a sodium layered transition metal oxide, a polyanionic compound, or a Prussian blue-like compound. The second electrolyte includes a second sodium salt, a second additive, and a second organic solvent, the second organic solvent of which includes PC. The positive electrode, separator, and negative electrode 1 are stacked in a Z-shape, and after assembly, electrolyte injection, formation, and capacity testing, a sodium-ion battery is obtained. The second electrolyte, a cyclic carbonate, is pure PC, which has a relatively low viscosity, improving the low-temperature performance and cycle performance of the cell. Furthermore, the solvent in the second electrolyte does not contain EC, avoiding gas generation in the cell due to EC decomposition during high-temperature storage, thus improving high-temperature storage performance. The second sodium salt and the second additive can refer to existing technologies, and may include sodium hexafluorophosphate, VC, DTD, TMSP, and PST, etc.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example (1) Preparation of positive electrode sheet Dissolve 2 wt% polyvinylidene fluoride adhesive thoroughly in N A uniformly dispersed positive electrode slurry was prepared by adding 3 wt% carbon black conductive agent and 95 wt% sodium layered transition metal oxide (NFM) positive electrode active material to methylpyrrolidone. The positive electrode slurry was then uniformly coated onto the surface of carbon-coated aluminum foil, dried, rolled, and die-cut.

[0043] (2) Preparation of negative electrode plate 1 S1. Prepare a uniformly dispersed slurry by mixing 97wt% IRMOF-3 and / or ZIF-8 with 2wt% binder, 1wt% dispersant and deionizer, apply it evenly to the surface of aluminum foil, dry it, roll it, and die-cut it.

[0044] S2. The above-mentioned negative electrode 1 is placed in an electroplating tank containing the first electrolyte, and sodium metal is electrochemically deposited. After washing and drying, a negative electrode 1 without a negative electrode structure is obtained. The first electrolyte includes A:EMC:DEC=30wt%:40wt%:15%, 12wt% sodium hexafluorophosphate, 0.5wt% VC, 0.5wt% DTD, 1wt% TMSP, and 1wt% PST.

[0045] (3) Preparation of the second electrolyte B:EMC:DEC=30wt%:40wt%:15%, 12wt% sodium hexafluorophosphate, 0.5wt% VC, 0.5wt% DTD, 1wt% TMSP, 1wt% PST.

[0046] (4) Preparation of full cells The above-mentioned positive electrode, separator and negative electrode 1 are stacked in a Z-shaped stacking manner, and after assembly, liquid injection, formation and capacity testing, a sodium-ion battery is obtained.

[0047] The examples and comparative examples all use sodium-ion batteries prepared according to the above preparation method, and their specific parameters are shown in the table below.

[0048]

[0049] In this context, " / " indicates that the content of the substance is 0.

[0050] Performance testing: (1) Observe whether there is sodium metal deposition on the surface of MOFs and / or ZIFs by scanning electron microscopy (SEM).

[0051] (2) Battery performance testing Initial efficiency and cycle count: Under 25°C conditions, the batteries prepared in the examples and comparative examples were charged to 4V at a rate of 0.1C and discharged to 1V at a rate of 0.1C. Full charge and discharge cycle tests were conducted until the battery capacity retention rate was less than or equal to 80% of the initial capacity. The initial discharge efficiency and cycle count were recorded.

[0052] High-temperature storage: Store at 60℃ for 7 days and observe whether the battery cells show signs of gas expansion.

[0053] The sodium-ion batteries obtained in each embodiment and comparative example were tested, and the results are shown in the table below.

[0054]

[0055] According to the test results of Examples 1 to 4, 13 and Comparative Examples 1 and 2, when the thickness of the sodium-loving layer 12 is in the range of 4 to 40 μm, the initial coulombic efficiency of the battery is high and the cycle life at room temperature is good. However, when the thickness of the sodium-loving layer 12 is less than 4 μm, the processing technology is difficult, defects appear on the surface of the negative electrode 1, and when metallic sodium is electrochemically deposited, the sodium-loving layer 12 cannot effectively buffer the huge volume expansion caused by the deposition of metallic sodium, and the framework cannot completely accommodate the deposited sodium metal, resulting in sodium dendrite growth, low coulombic efficiency and short cycle life. When the thickness of the sodium-loving layer 12 exceeds 40 μm, the energy density of the battery decreases, and the effect of improving the energy density of sodium-ion batteries without a negative electrode structure cannot be achieved. Moreover, the cycle life is poor due to more side reactions. Preferably, the thickness of the sodium-loving layer 12 is 4 to 40 μm.

[0056] According to the test results of Examples 2, 4, 5 and Comparative Example 3, when the active material of the sodium-loving layer 12 is a combination of MOFs and ZIFs, its coulombic efficiency and cycle life are significantly improved compared with the use of MOFs or ZIFs alone or without active material. Compared with single materials, the combination of MOFs and ZIFs can play a greater role. Its porosity and specific surface area are larger, and the framework structure is richer. Therefore, it can reduce / suppress the volume expansion caused by sodium metal deposition, making the structure of the negative electrode 1 more stable. The huge specific surface area can provide more sodium nucleation sites, guide the uniform attachment of sodium metal in the internal pores, and avoid the formation of sodium dendrites. Therefore, the coulombic efficiency and cycle life are comprehensively improved in the first stage.

[0057] Based on the test results of Examples 6 to 11 and Comparative Examples 4 to 5, it can be seen that when the thickness of the sodium-loving layer 12 is constant, and the deposition current density is 0.8 mAh / cm², 2 Up to 4mAh / cm 2 Within the specified range, the deposition time is determined by ensuring that metallic sodium is not deposited on the surface of the sodium-loving layer 12 (observed by SEM). Lower electrodeposition currents result in slightly improved coulombic efficiency and cycle life. When the current density is less than 0.8 mAh / cm³... 2 At this point, the sodium deposition efficiency is too low; when the current density is greater than 4 mAh / cm³, the deposition efficiency is too low. 2 Sodium dendrites tend to form on the surface of the sodium-loving layer 12, leading to gas generation during high-temperature storage and poor cycle life. Therefore, the magnitude of the current during electrodeposition has a significant impact on battery performance. By controlling the appropriate current density, electrochemical polarization and concentration polarization can be eliminated, allowing sodium ions to be uniformly deposited within the pores of the sodium-loving layer 12, preventing sodium dendrite formation, and improving battery performance.

[0058] Based on the test results of Examples 10 and 11 and Comparative Examples 6 and 7, it can be seen that when the deposition current is constant, a deposition time that is too short results in insufficient deposition of metallic sodium in the pores inside the sodium-loving layer 12, while a deposition time that is too long causes metallic sodium to be deposited on the surface of the sodium-loving layer 12, and also leads to gas generation during high-temperature storage. The test results of Example 5 and Comparative Example 11 show that, compared with non-intermittent charging, intermittent charging results in higher initial efficiency and better cycle stability. If the charging interval is too short, the depolarization effect is not obvious, which reduces the initial efficiency and cycle stability; if the interval is too long, it affects the efficiency.

[0059] Based on the test results of Example 2 and Comparative Examples 8 to 10, it is evident that when both the first and second electrolytes use PC or EC-based solvents, or when the first electrolyte solvent is PC and the second electrolyte solvent is EC, gas generation occurs in the battery cell during high-temperature storage. When the first electrolyte solvent is PC, a stable solid electrolyte membrane (SEI) cannot be formed on the sodium metal surface, resulting in poor electrode stability. When the second electrolyte solvent is EC, gas generation in the battery cell occurs due to the decomposition of EC during high-temperature storage, both of which lead to poor battery performance.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sodium-ion battery, characterized in that, The device includes a positive electrode, a second electrolyte, and a negative electrode. The negative electrode includes a current collector, on which a sodium-loving layer is disposed. The sodium-loving layer includes an active material, which is IRMOF-3 and / or ZIF-8. The sodium-loving layer also includes a first binder and a first dispersant. The mass fraction of the active material in the sodium-loving layer is ≥95%. The negative electrode sheet is processed as follows: the raw materials that make up the sodium-loving layer are mixed with water and stirred to form a slurry, the slurry is coated on the current collector and dried to obtain the negative electrode sheet; The sodium-loving layer has metallic sodium deposited inside by electrochemical deposition, while no metallic sodium is deposited on the surface of the sodium-loving layer. The thickness of the sodium-loving layer is 4-40 μm. The steps for depositing metallic sodium inside the sodium-loving layer are as follows: Preparation: Under an inert atmosphere, the current collector with a sodium-loving layer, the separator and the sodium metal sheet are sequentially stacked and immersed in an electroplating bath containing a first electrolyte; the first electrolyte includes a first sodium salt, a first additive and a first organic solvent, wherein the first organic solvent includes ethylene carbonate. Deposition: Using a sodium metal sheet as the counter electrode and a current collector with a sodium-loving layer as the working electrode, a direct current is applied for charging, causing sodium ions from the sodium metal sheet to deposit into the pores inside the sodium-loving layer; during the deposition step, the charging current density is 0.8-4 mAh / cm³. 2 The total charging time is 50-300 minutes; The positive electrode sheet includes a positive electrode active material, a second conductive agent, and a second binder. The positive electrode active material is at least one of sodium layered transition metal oxide, polyanionic compound, or Prussian blue compound. The second electrolyte includes a second sodium salt, a second additive, and a second organic solvent. The second organic solvent includes PC but does not include EC.

2. The sodium-ion battery according to claim 1, characterized in that, The negative electrode sheet satisfies at least one of the following conditions (1)-(4): (1) The current collector is an aluminum foil current collector or an aluminum-based composite current collector; (2) The thickness of the current collector is 8-16 μm; (3) The dyne value of the current collector is ≥37 dyn / cm; (4) The sodium-loving layer contains metallic sodium, and the mass fraction of the metallic sodium is 50-95%.

3. The sodium-ion battery according to claim 1, characterized in that, After the deposition step, the electrode sheet with deposited metallic sodium is placed in solvent A for cleaning, and then vacuum dried at 40-60℃ to obtain the negative electrode sheet.

4. The sodium-ion battery according to claim 3, characterized in that, Solvent A is at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

5. The sodium-ion battery according to claim 1, characterized in that, Intermittent charging is used to eliminate polarization, with charging stopped for 4-6 minutes every 5-30 minutes.

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