Preparation method and application of double-coating-layer sodium ion battery negative electrode material

Abstract

The invention relates to the field of sodium ion batteries, and discloses a preparation method and application of a double-coating-layer sodium ion battery negative electrode material. The preparation method comprises the following steps: 1) uniformly mixing a tin source solution, a graphene dispersion liquid, a carbon nanotube dispersion liquid and soluble carbon, spraying, drying and sintering to obtain an aggregate of graphene / carbon nanotube coated tin powder; (2) crushing the aggregate to obtain graphene / carbon nano tube coated tin powder; and 3) mixing the graphene / carbon nanotube coated tin powder with a gas-phase carbon source in a heated protective atmosphere, and carrying out gas-phase coating to form a carbon coating layer so as to obtain the double-coating-layer sodium ion battery negative electrode material. According to the sodium ion battery negative electrode material prepared by the method, the inner coating layer is the graphene / carbon nanotube, and the outer coating layer is carbon, so that the conductivity of the material can be remarkably improved, and the volume change of the tin-based negative electrode material can be effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the field of sodium-ion batteries, and particularly to a preparation method and application of a negative electrode material for a sodium-ion battery with a double coating layer. Background Art

[0002] In recent years, sodium-ion batteries have developed rapidly due to their low cost advantage, and the battery performance has also been rapidly improved. At the same time, key materials such as sodium-based cathodes and amorphous carbon anodes have become more and more mature and have gradually been widely used. At present, sodium-ion battery products have been widely used in fields such as electric two-wheelers, low-speed vehicles, and energy storage.

[0003] Currently, the negative electrode materials of sodium-ion batteries are generally mainly amorphous carbon, that is, soft carbon and hard carbon. However, the most important problem of amorphous carbon is the relatively low initial Coulomb efficiency. A large amount of active sodium will be consumed during the formation stage, resulting in a decrease in the specific energy of the battery cell, and at the same time, the cost is also increased. In addition, the sodium storage capacity of amorphous carbon is limited, and the specific capacity is only about 300 mAh / g, and the energy density of the battery is relatively low; and the sodium intercalation potential of amorphous carbon is relatively low, close to 0 V, and sodium is likely to be deposited at a high state of charge, resulting in battery failure, and in severe cases, it is likely to cause safety accidents.

[0004] Therefore, a tin-based alloy negative electrode material with a higher sodium storage specific capacity has been developed (for example, CN110212238A discloses a sodium-ion secondary battery with a tin-based negative electrode), and its sodium storage specific capacity can reach 847 mAh / g, which is an ideal negative electrode active material. However, the tin-based alloy negative electrode material also has its disadvantages: relatively poor electrical conductivity, large volume change during charge and discharge, fast specific capacity decay, and it is actually difficult to apply. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a preparation method and application of a negative electrode material for a sodium-ion battery with a double coating layer. In the negative electrode material for a sodium-ion battery prepared by the method of the present invention, the inner coating layer is graphene / carbon nanotubes, and the outer coating layer is carbon, which can not only significantly improve the electrical conductivity of the material, but also effectively inhibit the volume change of the tin-based negative electrode material.

[0006] The specific technical solution of the present invention is as follows: In the first aspect, the present invention provides a preparation method of a negative electrode material for a sodium-ion battery with a double coating layer, which includes the following steps: 1) Mix a tin source solution, a graphene dispersion, a carbon nanotube dispersion, and soluble carbon evenly, and obtain an aggregate of tin powder coated with graphene / carbon nanotubes through spraying, drying, and sintering in a reducing atmosphere.

[0007] 2) Crush the aggregate to obtain tin powder coated with graphene / carbon nanotubes.

[0008] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source under a heated protective atmosphere, and form a carbon coating layer on the surface of the graphene / carbon nanotube-coated tin powder after vapor deposition to obtain a negative electrode material for a sodium-ion battery with a double coating layer.

[0009] Aiming at the disadvantages of existing sodium-ion tin-based alloy negative electrode materials, such as poor conductivity, large volume change during charge and discharge, and rapid specific capacity decay. The present invention first coats a layer of graphene / carbon nanotube composite material on the surface of tin powder by means of wet spray granulation and sintering in a reducing atmosphere; introducing soluble carbon during the spraying process can provide sufficient reaction sites for the reduction of tin; the coating layer formed by the above wet spray granulation-sintering is more complete and uniform, and has a better effect on improving the performance of the negative electrode material. On this basis, the present invention further forms a carbon coating layer on the surface of the graphene / carbon nanotube-coated tin powder by means of chemical vapor deposition, so as to obtain a negative electrode material for a sodium-ion battery with a double-layer coating structure. In the inner coating layer (graphene / carbon nanotube) of the negative electrode material with a double coating layer, graphene with a planar structure and carbon nanotubes with a fibrous structure are combined to form a wire-plane conductive network, which can not only significantly improve the conductivity of the material, but also provide an elastic buffer space to relieve the volume change generated during the insertion / extraction of sodium ions in the negative electrode material, thereby improving the service life of the negative electrode material. The outer carbon coating layer can not only further inhibit the volume expansion of the tin-based negative electrode material, but also improve the compatibility of the material with the electrolyte and form a stable SEI film layer.

[0010] Preferably, in step 1), the mass ratio range of the tin source, graphene, carbon nanotubes, and soluble carbon is 1:(0.01~0.02):(0.01~0.02):(1.8~2.7).

[0011] The present invention needs to strictly control the amounts of graphene, carbon nanotubes, and soluble carbon relative to tin. The present invention finds that when the contents of graphene and carbon nanotubes are too low, a wire-plane conductive network cannot be formed, and the electronic conductivity of the material decreases; while too high will lead to a decrease in the specific capacity of the material and an increase in the agglomeration of the material bulk phase. Soluble carbon is mainly used for the pyrolysis of the carbon source to generate a carbon matrix to disperse metal tin particles, prevent their high-temperature agglomeration, and then form nano-scale uniformly distributed tin particles; at the same time, it also acts as an auxiliary reduction function to reduce part of the tin oxide generated by spray pyrolysis from the bulk phase. Too high or too low content of soluble carbon will have a negative effect on the uniformity of the material bulk phase and the electrochemical performance of the material.

[0012] Preferably, the particle size of the graphene / carbon nanotube-coated tin powder is 2~5 μm.

[0013] The present invention discovers that the particle size of the graphene / carbon nanotube-coated tin powder has a certain influence on the performance of the final material. If the particle size is too large, it will cause the specific capacity of the material to not be fully exerted. At the same time, the contact area between the material and the electrolyte is small, and the rate performance of the material under high current density decreases significantly; conversely, if the particle size is too small, the chemical activity of the material will increase accordingly, and the side reactions will increase after contacting the electrolyte, the polarization will increase, and the electrochemical performance will be reduced.

[0014] Preferably, the carbon coating layer accounts for 2-6 wt% of the dual-coated sodium-ion battery anode material.

[0015] The present invention discovers that the content of the carbon coating layer also has a certain influence on the performance of the final material. If the carbon coating layer is too thick, it will increase the transmission resistance of sodium ions in the anode material, thereby causing the capacity attenuation of the battery. This is because a thicker carbon coating layer will increase the internal resistance of the electrode material and affect the embedding and extraction efficiency of sodium ions in the electrode material. The carbon coating layer can buffer the volume change during the charge and discharge process of the electrode and maintain the structural stability of the electrode. An overly thin carbon coating layer cannot provide sufficient support, which may cause the structure of the electrode material to be damaged during the cycling process, resulting in capacity attenuation. Due to the relatively large ionic radius of sodium ions, the volume will have obvious expansion and contraction during the charge and discharge process of the tin-based anode material. A sufficient carbon coating layer can effectively inhibit this volume change, while an overly thin carbon coating layer cannot effectively control it, which may lead to the damage of the electrode material and the decline of battery performance.

[0016] Preferably, in step 1), the tin source is tin halide; more preferably, it is tin chloride or tin bromide.

[0017] The type of tin source has a certain influence on the spray granulation effect. The present invention discovers that choosing the above-mentioned types of tin halides as the tin source is not only because they can dissolve in water, but also because they can be more uniformly compounded with the graphene dispersion liquid, providing more uniform reaction sites for the generated reduced tin blocks, thereby improving the purity of the material.

[0018] Preferably, in step 1), the soluble carbon is selected from glucose, citric acid, and ascorbic acid.

[0019] The present invention selects the above-mentioned glucose, citric acid, and ascorbic acid as the soluble carbon mainly because the effect of these carbon sources on pyrolyzing to generate carbon matrix to disperse metal tin particles is better, which can prevent the high-temperature agglomeration of metal tin particles, and then form tin particles with a uniform nanoscale distribution; at the same time, these carbon sources can also act as an auxiliary reduction function to reduce a part of the tin oxide generated by spray pyrolysis from the bulk phase.

[0020] Preferably, in step 1), the concentration of the tin source solution is 0.2 - 0.5 mol / L; the concentration of the graphene dispersion is 0.5 - 2 wt%; the concentration of the carbon nanotube dispersion is 0.5 - 2 wt%.

[0021] Preferably, in step 1), the sintering temperature is 800 - 1200 °C, and the time is 8 - 12 h.

[0022] Preferably, in step 1), the atmosphere required for sintering is H 2 / N 2 , where the mass ratio of hydrogen is 1 - 4 wt%, and the optimal is 2 wt%.

[0023] Preferably, in step 3), the gaseous carbon source is selected from methane, ethylene, acetylene, and benzene.

[0024] The above gaseous carbon sources selected in the present invention are all gas molecules with fewer carbon atoms, which is beneficial to deposition on the surface of the tin negative electrode material.

[0025] Preferably, in step 3), the protective atmosphere is selected from argon, nitrogen, helium, neon, krypton, and xenon.

[0026] Preferably, in step 3), the temperature of the gaseous coating is 700 - 900 °C, and the time is 3 - 5 h.

[0027] Preferably, in step 3), the thickness of the carbon coating layer is 50 - 150 nm, and the optimal thickness is 80 - 120 nm.

[0028] In the second aspect, the present invention provides the application of the double-coated sodium-ion battery negative electrode material obtained by the above preparation method in a sodium-ion battery.

[0029] Preferably, the preparation method of the sodium-ion battery includes the following steps: S1. Prepare a positive electrode sheet; S2. Mix the double-coated sodium-ion battery negative electrode material with a binder, a conductive agent, and a solvent uniformly, disperse to obtain a negative electrode slurry, and coat it on a negative electrode current collector to obtain a negative electrode sheet; S3. Assemble the positive electrode sheet, the negative electrode sheet, and a separator into an electric core, and further manufacture a sodium-ion battery.

[0030] More preferably, S1 specifically includes: mixing a sodium-based positive electrode active material with a binder, a conductive agent, and a solvent uniformly, dispersing to obtain a positive electrode slurry, and coating it on a positive electrode current collector to obtain a positive electrode sheet.

[0031] More preferably, S3 specifically includes: winding or laminating the positive electrode sheet, the negative electrode sheet, and the separator to assemble an electric core, baking to remove water, injecting electrolyte, and forming to manufacture a sodium-ion battery.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The method of the present invention can prepare a negative electrode material for a sodium-ion battery with a double-coated structure. The inner coating layer is graphene / carbon nanotubes. The graphene with a planar structure and the carbon nanotubes with a fibrous structure are combined to form a wire-plane conductive network, which can not only significantly improve the conductivity of the material, but also provide an elastic buffer space to relieve the volume change generated during the insertion / extraction process of sodium ions in the negative electrode material, thereby improving the service life of the negative electrode material; and the outer carbon coating layer can further inhibit the volume expansion of the tin-based negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural diagram of a double-coated layer under a high-resolution transmission electron microscope in Example 1.

[0034] Figure 2 It is a schematic diagram of the thickness of the carbon coating layer of the material under a high-resolution transmission electron microscope in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described below in conjunction with the embodiments.

[0036] First, the present invention provides a preparation method for a negative electrode material for a sodium-ion battery with a double-coated layer, which includes the following steps: 1) Mix the tin source solution, graphene dispersion, carbon nanotube dispersion and soluble carbon evenly, and obtain an aggregate of graphene / carbon nanotube-coated tin powder through spraying, drying and sintering in a reducing atmosphere.

[0037] In some preferred embodiments, in step 1), the mass ratio range of the tin source, graphene, carbon nanotubes and soluble carbon is 1:(0.01~0.02):(0.01~0.02):(1.8~2.7).

[0038] In some preferred embodiments, in step 1), the tin source is tin halide; more preferably tin chloride or tin bromide.

[0039] In some preferred embodiments, in step 1), the soluble carbon is selected from glucose, citric acid and ascorbic acid.

[0040] In some preferred embodiments, in step 1), the concentration of the tin source solution is 0.2~0.5 mol / L; the concentration of the graphene dispersion is 0.5~2 wt%; the concentration of the carbon nanotube dispersion is 0.5~2 wt%.

[0041] In some preferred embodiments, in step 1), the atmosphere required for sintering is H 2 / N2 , where the mass proportion of hydrogen is 1~4wt%, and the optimal is 2wt%.

[0042] In some preferred implementation cases, in step 1), the sintering temperature is 800-1200° C., and the sintering time is 8-12 hours.

[0043] 2) crushing the agglomerates to obtain graphene / carbon nanotube-coated tin powder with a particle size of 2-5 μm.

[0044] 3) Mixing the graphene / carbon nanotube coated tin powder with a gaseous carbon source under a heated protective atmosphere, and forming a carbon coating layer on the surface of the graphene / carbon nanotube coated tin powder after gas phase coating to obtain a double-coated sodium ion battery negative electrode material. The carbon coating layer accounts for 2-6wt% of the double-coated sodium ion battery negative electrode material.

[0045] In some preferred implementation cases, in step 3), the thickness of the carbon coating layer is 50-150 nm, and the optimal thickness is 80-120 nm.

[0046] In some preferred implementation cases, in step 3), the gaseous carbon source is selected from methane, ethylene, acetylene and benzene.

[0047] In some preferred implementation cases, in step 3), the protective atmosphere is selected from argon, nitrogen, helium, neon, krypton and xenon.

[0048] In some preferred implementation cases, in step 3), the temperature of the gas phase coating is 700-900° C., and the time is 3-5 hours.

[0049] In a second aspect, the present invention provides the use of the double-coated layer sodium ion battery negative electrode material obtained by the above preparation method in a sodium ion battery.

[0050] In some preferred implementation cases, the method for preparing the sodium ion battery comprises the following steps: S1. Prepare the positive electrode sheet.

[0051] In some more preferred implementation cases, S1 specifically includes: uniformly mixing the sodium-based positive electrode active material with a binder, a conductive agent, and a solvent, dispersing the mixture to obtain a positive electrode slurry, and coating the mixture on a positive electrode current collector to obtain a positive electrode sheet.

[0052] S2. Evenly mix the double-coated sodium ion battery negative electrode material with a binder, a conductive agent, and a solvent, disperse them to obtain a negative electrode slurry, and apply the mixture on a negative electrode current collector to obtain a negative electrode sheet.

[0053] S3. Assemble the positive electrode sheet, negative electrode sheet and separator into a battery cell, and then further make a sodium ion battery.

[0054] In some more preferred embodiments, S3 specifically includes: winding or laminating the positive electrode sheet, negative electrode sheet and separator to assemble into an electrode core, baking to remove water, injecting electrolyte, and forming to produce a sodium-ion battery.

[0055] Specific examples and comparative examples.

[0056] Example 1 (I) Preparation of the negative electrode material for the double-coated sodium-ion battery, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%) and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube and soluble carbon is 1:0.02:0.02:2.5.

[0057] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0058] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) in a heated protective atmosphere (argon), control the inlet gas flow rate to be 80 sccm, and perform gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the negative electrode material for the double-coated sodium-ion battery. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the negative electrode material for the double-coated sodium-ion battery.

[0059] Figure 1 It is the structure diagram of the double-coated layer under high-resolution transmission electron microscopy in Example 1. Figure 2 It is the schematic diagram of the thickness of the material carbon coating layer under high-resolution transmission electron microscopy in Example 1.

[0060] (II) Preparation of the sodium-ion battery, including the following steps: S1. Preparation of the positive electrode sheet: Mix the sodium-based positive electrode active material, binder, conductive agent and solvent evenly, disperse, where the mass ratio of the sodium-based positive electrode active material, binder and conductive agent is 95:3:2 to obtain a positive electrode slurry, and coat it on a positive electrode current collector to obtain a positive electrode sheet.

[0061] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0062] S3. Wind or laminate the positive electrode sheet, the negative electrode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and carry out formation to fabricate a sodium-ion battery.

[0063] Example 2 (compared with Example 1, the only difference is that the tin source is tin bromide, the soluble carbon is glucose, and the gaseous carbon source is ethylene) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin bromide, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (glucose) evenly. After spraying, drying, and sintering in a reducing atmosphere (H 2 / N 2 , with the mass fraction of hydrogen being 2 wt%) at 1000 °C for 10 h, obtain an agglomerate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of the tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0064] 2) Crush the agglomerate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0065] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (ethylene) under a heated protective atmosphere (argon), control the inlet gas flow rate at 80 sccm, and carry out gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0066] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material evenly with a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based positive electrode active material, the binder, and the conductive agent is 95:3:2 to obtain a positive electrode slurry. Coat it on the positive electrode current collector to obtain a positive electrode sheet.

[0067] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0068] S3. Wind or stack the cathode sheet, the anode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and carry out formation to fabricate a sodium-ion battery.

[0069] Example 3 (compared with Example 1, the only difference is that the soluble carbon is citric acid and the gaseous carbon source is benzene) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (citric acid) evenly. After spraying, drying, and sintering in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) at 1000 °C for 10 h, obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0070] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0071] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (benzene) under a heated protective atmosphere (argon), control the inlet gas flow rate to be 80 sccm, and carry out gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0072] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a cathode sheet: Mix the sodium-based cathode active material evenly with a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based cathode active material, the binder, and the conductive agent is 95:3:2 to obtain a cathode slurry. Coat it on the cathode current collector to obtain a cathode sheet.

[0073] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0074] S3. Wind or laminate the positive electrode sheet, the negative electrode sheet, and the separator to assemble an electric core. After baking to remove water, inject electrolyte and perform formation to manufacture a sodium-ion battery.

[0075] Comparative Example 1 (compared with Example 1, the only difference is that the ratio of graphene, carbon nanotubes, and soluble carbon to the tin source is too low) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.005:0.005:1.5.

[0076] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0077] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) in a heated protective atmosphere (argon), control the inlet gas flow rate to 80 sccm, and perform gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0078] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material evenly with a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based positive electrode active material, the binder, and the conductive agent is 95:3:2 to obtain a positive electrode slurry. Coat it on the positive electrode current collector to obtain a positive electrode sheet.

[0079] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coating it on the anode current collector to obtain an anode sheet.

[0080] S3. Wind or laminate the positive electrode sheet, the negative electrode sheet, and the separator to assemble an electric core. After baking to remove water, inject electrolyte and perform formation to manufacture a sodium-ion battery.

[0081] Comparative Example 2 (compared with Example 1, the only difference is that the ratio of graphene, carbon nanotubes, and soluble carbon to the tin source is too high) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , the mass fraction of hydrogen is 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.04:0.04:4.

[0082] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0083] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) under a heated protective atmosphere (argon), control the inlet gas flow rate to 80 sccm, and perform gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0084] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material evenly with a binder, a conductive agent, and a solvent, and disperse. The mass ratio of the sodium-based positive electrode active material, the binder, and the conductive agent is 95:3:2 to obtain a positive electrode slurry. Coating it on the positive electrode current collector to obtain a positive electrode sheet.

[0085] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0086] S3. Wind or laminate the positive electrode sheet, the negative electrode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and carry out formation to fabricate a sodium-ion battery.

[0087] Comparative Example 3 (Compared with Example 1, the only difference is that the particle size of the graphene / carbon nanotube-coated tin powder obtained in Step 2 is too small) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), the graphene dispersion (concentration 1.25 wt%), the carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly. After spraying, drying, and sintering (1000 °C, 10 h) in a reducing atmosphere (H 2 / N 2 , the mass ratio of hydrogen is 2 wt%), obtain an agglomerate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, the graphene dispersion, the carbon nanotube dispersion, and the soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0088] 2) Crush the agglomerate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 1 μm.

[0089] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) in a heated protective atmosphere (argon), control the inlet gas flow rate to 80 sccm, and carry out gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0090] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material evenly with a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based positive electrode active material, the binder, and the conductive agent is 95:3:2 to obtain a positive electrode slurry. Coat it on the positive electrode current collector to obtain a positive electrode sheet.

[0091] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0092] S3. Wind or laminate the anode sheet, the cathode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and carry out formation to fabricate a sodium-ion battery.

[0093] Comparative Example 4 (The difference between Comparative Example 4 and Example 1 is only that: the particle size of the tin powder coated with graphene / carbon nanotubes obtained in Step 2 is too large) (I) Preparation of the double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly. After spraying, drying, and sintering in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) at 1000 °C for 10 h, obtain an aggregate of tin powder coated with graphene / carbon nanotubes. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0094] 2) Crush the aggregate to obtain tin powder coated with graphene / carbon nanotubes with an average particle size of about 10 μm.

[0095] 3) Mix the tin powder coated with graphene / carbon nanotubes with a gaseous carbon source (methane) under a heated protective atmosphere (argon), control the inlet gas flow rate to be 80 sccm, and carry out gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the tin powder coated with graphene / carbon nanotubes to obtain the double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated sodium-ion battery anode material.

[0096] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a cathode sheet: Mix the sodium-based cathode active material evenly with a binder, a conductive agent, and a solvent, and disperse. The mass ratio of the sodium-based cathode active material, the binder, and the conductive agent is 95:3:2 to obtain a cathode slurry. Coat it on the cathode current collector to obtain a cathode sheet.

[0097] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0098] S3. Wind or stack the positive electrode sheet, the negative electrode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and perform formation to fabricate a sodium-ion battery.

[0099] Comparative Example 5 (The difference between Comparative Example 5 and Example 1 is only that: there is only one layer of coating, and there is no outer carbon coating layer) (I) Preparation of the single-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , the mass ratio of hydrogen is 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0100] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0101] (II) Preparation of the sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material evenly with a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based positive electrode active material, the binder, and the conductive agent is 95:3:2 to obtain a positive electrode slurry. Coat it on the positive electrode current collector to obtain a positive electrode sheet.

[0102] S2. Mix the double-coated sodium-ion battery anode material evenly with a binder, a conductive agent, and a solvent, and disperse them to obtain an anode slurry. The mass ratio of the double-coated sodium-ion battery anode material to the binder and the conductive agent is 96:3:1. Coat it on the anode current collector to obtain an anode sheet.

[0103] S3. Wind or stack the positive electrode sheet, the negative electrode sheet, and the separator to assemble a battery cell. After baking to remove water, inject electrolyte and perform formation to fabricate a sodium-ion battery.

[0104] Comparative Example 6 (The difference between Comparative Example 6 and Example 1 is only that: the outer carbon coating layer is too thin) (1) Preparation of the anode material for a dual-coated sodium-ion battery, comprising the following steps: 1) Mix uniformly a tin source solution (tin chloride, concentration: 0.35 mol / L), a graphene dispersion (concentration: 1.25 wt%), a carbon nanotube dispersion (concentration: 1.25 wt%), and soluble carbon (ascorbic acid), spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 ; the mass percentage of hydrogen is 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0105] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0106] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) under a heated protective atmosphere (argon), control the inlet gas flow rate at 50 sccm, and perform gas-phase coating at 800 °C for 40 min. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain the anode material for a dual-coated sodium-ion battery. Among them, the thickness of the carbon coating layer is about 10 - 20 nm, accounting for about 1 wt% of the anode material for a dual-coated sodium-ion battery.

[0107] (2) Preparation of a sodium-ion battery, comprising the following steps: S1. Prepare a positive electrode sheet: Mix uniformly a sodium-based positive electrode active material, a binder, a conductive agent, and a solvent, and disperse them. The mass ratio of the sodium-based positive electrode active material, binder, and conductive agent is 95:3:2 to obtain a positive electrode slurry, and coat it on a positive electrode current collector to obtain a positive electrode sheet.

[0108] S2. Mix uniformly the anode material for a dual-coated sodium-ion battery, a binder, a conductive agent, and a solvent, and disperse them to obtain a negative electrode slurry. The mass ratio of the anode material for a dual-coated sodium-ion battery, binder, and conductive agent is 96:3:1, and coat it on a negative electrode current collector to obtain a negative electrode sheet.

[0109] S3. Wind or stack the positive electrode sheet, negative electrode sheet, and separator to assemble a battery cell, bake to remove water, inject electrolyte, and perform formation to manufacture a sodium-ion battery.

[0110] Comparative Example 7 (compared with Example 1, the only difference is that the outer carbon coating layer is too thick) (1) Preparation of the anode material for a dual-coated sodium-ion battery, comprising the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , with the mass fraction of hydrogen being 2 wt%) at 1000 °C for 10 h to obtain an agglomerate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0111] 2) Crush the agglomerate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0112] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) under a heated protective atmosphere (argon), control the inlet gas flow rate at 300 sccm, and perform gas-phase coating at 800 °C for 5 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain a double-coated sodium-ion battery anode material. Among them, the thickness of the carbon coating layer is about 250 - 300 nm, accounting for about 10 wt% of the double-coated sodium-ion battery anode material.

[0113] (II) Preparation of a sodium-ion battery, including the following steps: S1. Prepare the positive electrode sheet: Mix the sodium-based positive electrode active material, binder, conductive agent, and solvent evenly and disperse them. The mass ratio of the sodium-based positive electrode active material, binder, and conductive agent is 95:3:2 to obtain a positive electrode slurry, and coat it on a positive electrode current collector to obtain a positive electrode sheet.

[0114] S2. Mix the double-coated sodium-ion battery anode material, binder, conductive agent, and solvent evenly and disperse them to obtain a negative electrode slurry. The mass ratio of the double-coated sodium-ion battery anode material, binder, and conductive agent is 96:3:1, and coat it on a negative electrode current collector to obtain a negative electrode sheet.

[0115] S3. Wind or stack the positive electrode sheet, negative electrode sheet, and separator to assemble a battery cell, bake to remove water, inject electrolyte, and perform formation to manufacture a sodium-ion battery.

[0116] Comparative Example 8 (Compared with Example 1, the only difference is that urea is used as the soluble carbon) (I) Preparation of a double-coated sodium-ion battery anode material, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%), and soluble carbon (urea) evenly, spray, dry, and sinter in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) at 1000 °C for 10 h to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion, and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube, and soluble carbon is 1:0.02:0.02:2.5.

[0117] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0118] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (methane) under a heated protective atmosphere (argon), control the inlet gas flow rate to 80 sccm, and perform gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain a double-coated negative electrode material for sodium-ion batteries. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated negative electrode material for sodium-ion batteries.

[0119] (II) Preparation of a sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material, binder, conductive agent, and solvent evenly, disperse them, where the mass ratio of the sodium-based positive electrode active material, binder, and conductive agent is 95:3:2 to obtain a positive electrode slurry, and coat it on a positive electrode current collector to obtain a positive electrode sheet.

[0120] S2. Mix the double-coated negative electrode material for sodium-ion batteries with a binder, conductive agent, and solvent evenly, disperse them to obtain a negative electrode slurry, where the mass ratio of the double-coated negative electrode material for sodium-ion batteries to the binder and conductive agent is 96:3:1, and coat it on a negative electrode current collector to obtain a negative electrode sheet.

[0121] S3. Wind or stack the positive electrode sheet, negative electrode sheet, and separator to assemble a battery cell, bake to remove water, then inject electrolyte and perform formation to manufacture a sodium-ion battery.

[0122] Comparative Example 9 (Compared with Example 1, the only difference is that acetone is used as the gaseous carbon source) (I) Preparation of a double-coated negative electrode material for sodium-ion batteries, including the following steps: 1) Mix the tin source solution (tin chloride, concentration 0.35 mol / L), graphene dispersion (concentration 1.25 wt%), carbon nanotube dispersion (concentration 1.25 wt%) and soluble carbon (ascorbic acid) evenly, spray, dry, and sinter at 1000 °C for 10 h in a reducing atmosphere (H 2 / N 2 , with the mass ratio of hydrogen being 2 wt%) to obtain an aggregate of graphene / carbon nanotube-coated tin powder. Among the tin source solution, graphene dispersion, carbon nanotube dispersion and soluble carbon, the mass ratio of tin source, graphene, carbon nanotube and soluble carbon is 1:0.02:0.02:2.5.

[0123] 2) Crush the aggregate to obtain graphene / carbon nanotube-coated tin powder with an average particle size of about 3 μm.

[0124] 3) Mix the graphene / carbon nanotube-coated tin powder with a gaseous carbon source (acetone) under a heated protective atmosphere (argon), control the inlet gas flow rate to be 80 sccm, and perform gas-phase coating at 800 °C for 3 h. After gas-phase coating, a carbon coating layer is formed on the surface of the graphene / carbon nanotube-coated tin powder to obtain a double-coated negative electrode material for a sodium-ion battery. Among them, the thickness of the carbon coating layer is about 90 - 110 nm, accounting for about 4 wt% of the double-coated negative electrode material for a sodium-ion battery.

[0125] (II) Preparation of a sodium-ion battery, including the following steps: S1. Prepare a positive electrode sheet: Mix the sodium-based positive electrode active material, binder, conductive agent and solvent evenly, disperse them, where the mass ratio of the sodium-based positive electrode active material, binder and conductive agent is 95:3:2 to obtain a positive electrode slurry, and coat it on a positive electrode current collector to obtain a positive electrode sheet.

[0126] S2. Mix the double-coated negative electrode material for a sodium-ion battery with a binder, conductive agent and solvent evenly, disperse them to obtain a negative electrode slurry, where the mass ratio of the double-coated negative electrode material for a sodium-ion battery to the binder and conductive agent is 96:3:1, and coat it on a negative electrode current collector to obtain a negative electrode sheet.

[0127] S3. Wind or stack the positive electrode sheet, negative electrode sheet and separator, assemble them into an electric core, bake to remove water, inject electrolyte, and form the battery to make a sodium-ion battery.

[0128] Performance test: Perform performance tests on the batteries obtained in the above examples and comparative examples, and the results are shown in Table 1.

[0129] Table 1

[0130] From the comparison of the data in the above table, it can be seen that: Compared with Example 1, when the contents of graphene and carbon nanotubes in Comparative Example 1 are too low, a wire-plane conductive network cannot be formed, the electronic conductivity of the material decreases, the internal resistance of the battery increases, the rate performance decreases, and the cycling performance is also affected. Conversely, in Comparative Example 2, the contents of graphene and carbon nanotubes are too high, resulting in a decrease in the specific capacity per gram of the material and an increase in the material cost at the same time.

[0131] Compared with Example 1, in Comparative Example 3, the particle size of the graphene / carbon nanotube-coated tin powder is too small, the chemical activity of the material is correspondingly enhanced, and the side reactions increase after contacting with the electrolyte, affecting the cycling performance of the battery; conversely, in Comparative Example 4, the particle size of the graphene / carbon nanotube-coated tin powder is too large, the contact area of the material decreases, the internal resistance increases, and at the same time, the specific capacity of the material cannot be fully exerted.

[0132] Compared with Example 1, in Comparative Example 5, the negative electrode material has no outer carbon coating layer. The volume change of the material caused by the insertion and extraction of sodium ions is large, the material structure is damaged, and the cycling performance deteriorates.

[0133] Compared with Example 1, in Comparative Example 6, the outer carbon coating layer of the negative electrode material is relatively thin, and the suppression of the volume change of the material during the cycling process is insufficient, affecting the cycling performance of the battery; while in Comparative Example 7, the relatively thick outer carbon coating layer will increase the internal resistance of the electrode material, affect the insertion and extraction efficiency of sodium ions in the electrode material, resulting in an increase in the internal resistance of the battery, and both the rate performance and the cycling performance are affected.

[0134] Compared with Example 1, in Comparative Examples 8 and 9, other types of soluble carbon and gaseous carbon sources are used, and the results show that the cycling, rate, internal resistance, and specific capacity per gram of the material are all affected; this shows that the types of soluble carbon and gaseous carbon sources also have a significant impact on the material performance. The preferred soluble carbon and gaseous carbon sources of the present invention have better performance.

[0135] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0136] The above are only the preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a double-coated layer sodium ion battery negative electrode material, characterized in that include: 1) uniformly mixing a tin source solution, a graphene dispersion, a carbon nanotube dispersion and soluble carbon, spraying, drying and sintering in a reducing atmosphere to obtain agglomerates of graphene / carbon nanotube-coated tin powder; The mass ratio of the tin source, graphene, carbon nanotubes and soluble carbon is 1:(0.01-0.02):(0.01-0.02):(1.8-2.7); 2) crushing the agglomerates to obtain graphene / carbon nanotube-coated tin powder with a particle size of 2-5 μm; 3) The graphene / carbon nanotube coated tin powder is mixed with a gaseous carbon source under a heated protective atmosphere, and a carbon coating layer is formed after gas phase coating to obtain a double-coated layer sodium ion battery negative electrode material; the carbon coating layer accounts for 2-6wt% of the double-coated layer sodium ion battery negative electrode material.

2. The preparation method according to claim 1, characterized in that: In step 1), The tin source is tin halide; The soluble carbon is selected from the group consisting of glucose, citric acid and ascorbic acid.

3. The preparation method according to claim 1 or 2, characterized in that: In step 1), The concentration of the tin source solution is 0.2-0.5 mol / L; The concentration of the graphene dispersion is 0.5-2wt%; The concentration of the carbon nanotube dispersion is 0.5-2 wt %.

4. The preparation method according to claim 1, characterized in that: In step 1), the sintering temperature is 800-1200° C. and the sintering time is 8-12 hours.

5. The preparation method according to claim 1 or 4, characterized in that: In step 1), the reducing atmosphere is a mixed gas of H2 and N2, wherein the mass proportion of hydrogen is 1-4wt%.

6. The preparation method according to claim 1, characterized in that: In step 3), The gas phase carbon source is selected from methane, ethylene, acetylene and benzene; The protective atmosphere is selected from argon, nitrogen, helium, neon, krypton and xenon.

7. The preparation method according to claim 1 or 6, characterized in that: In step 3), the temperature of the gas phase coating is 700-900° C. and the time is 3-5 hours.

8. Application of the double-coated sodium ion battery negative electrode material obtained according to the preparation method according to any one of claims 1 to 7 in sodium ion batteries.

9. The use according to claim 8, characterized in that: The method for preparing the sodium ion battery comprises the following steps: S1, preparing a positive electrode sheet; S2, mixing the double-coated sodium ion battery negative electrode material with a binder, a conductive agent, and a solvent, dispersing them to obtain a negative electrode slurry, and coating the mixture on a negative electrode current collector to obtain a negative electrode sheet; S3. Assemble the positive electrode sheet, negative electrode sheet and separator into a battery cell, and then further make a sodium ion battery.

10. The use according to claim 9, characterized in that: S1 specifically comprises: uniformly mixing the sodium-based positive electrode active material with a binder, a conductive agent, and a solvent, dispersing the mixture to obtain a positive electrode slurry, and coating the mixture on a positive electrode current collector to obtain a positive electrode sheet; S3 specifically includes: winding or stacking the positive electrode sheet, the negative electrode sheet and the separator to assemble into a battery cell, baking to remove water, and then injecting liquid and forming to make a sodium ion battery.

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