Sodium-ion battery negative electrode material and preparation method thereof

Abstract

The present application relates to the technical field of sodium ion battery electrode material, and especially relates to a negative electrode material and a preparation method thereof, mainly comprising the following steps: (1) preparing carbon-coated antimony powder: adding a dispersing agent, carbon black and antimony powder in an aqueous solvent, and obtaining the carbon-coated antimony powder material through dispersion, drying and carbonization processes; (2) graphene compounding and coating: firstly, adding expanded graphite in the aqueous solvent, and after stirring, sanding, homogenizing and drying treatments, compounding the carbon-coated antimony powder and graphene oxide in the aqueous solvent, and obtaining the graphene-antimony composite material through spray drying and carbonization; (3) hard carbon coating: adding the graphene-antimony composite material in a citric acid solution, stirring uniformly, drying and carbonizing to obtain the hard carbon-graphene-antimony composite sodium ion battery negative electrode material. The sodium ion battery composite negative electrode material prepared by the method has the characteristics of good batch stability, high specific capacity, excellent rate performance and long cycle life.

Description

Technical Field

[0001] This invention relates to the technical field of sodium-ion battery electrode materials, and in particular to a negative electrode material and its preparation method. Background Technology

[0002] With the ever-increasing demand for lithium-ion batteries in the new energy market, lithium salts, an indispensable raw material for lithium-ion batteries, have become crucial. Global lithium salt resources are scarce and over-concentrated, with major production areas in South America and Australia. China's share is small, and most lithium salt raw materials are imported. Prices are heavily influenced by mining volume and market demand, which is detrimental to the rapid and stable development of the lithium-ion battery industry. At the same time, the technology for recovering lithium salts from lithium-ion batteries is still immature and has not yet achieved economies of scale, resulting in relatively high costs.

[0003] Sodium-ion batteries and lithium-ion batteries operate on the same principle and their manufacturing processes are compatible. Sodium-ion batteries offer good safety and energy density, excellent high and low temperature performance, low cost, and are environmentally friendly. Their raw material, sodium salt, is widely available, abundant, and inexpensive. However, because sodium ions have a larger radius than lithium ions, they are less likely to embed into the interlayer structure of graphite, therefore graphite materials cannot be used as anodes in sodium-ion batteries. Currently, anodes for sodium-ion batteries mainly consist of amorphous carbon materials, alloy materials, and oxide materials, with hard carbon being the mainstream development direction among amorphous carbon materials. There are currently two production methods for hard carbon: one uses polymer resins or anthracite as raw materials, but this method suffers from high production costs, complex processes, and low capacity and initial efficiency, hindering commercial applications; the other uses biomass as raw material, processing it through crushing, carbonization, and acid washing to obtain hard carbon materials. However, due to the influence of natural environment, climate, and origin, the natural composition of biomass raw materials is complex, making it difficult to guarantee batch stability and hindering large-scale production. Oxide and alloy materials have become a hot topic in sodium-ion battery anode material research due to their high specific capacity, low cost, and abundant and stable raw material sources; however, their intrinsic electron conductivity is poor, and severe volume changes occur during sodium insertion and extraction, resulting in relatively poor rate capability and cycle life. Summary of the Invention

[0004] Therefore, it is necessary to develop a sodium-ion battery anode material and its preparation method that have good batch stability, good conductivity, high specific capacity and long cycle life.

[0005] The first aspect of this invention provides a sodium-ion battery anode material, comprising antimony powder, carbon black, a graphene layer, and a hard carbon layer. The carbon black is loaded onto the surface of the antimony powder through a polymer layer to obtain a carbon-coated antimony powder material. The graphene layer and the hard carbon layer are sequentially coated on the surface of the carbon-coated antimony powder material. When the mass ratio between the antimony powder and the carbon black is 8:1 to 2:1 and the particle size ratio is 3:1 to 20:3, the specific capacity of the anode material is ≥400 mAh / g.

[0006] In one embodiment of the present invention, the mass ratio between antimony powder and carbon black is 3:1, and the particle size ratio is 5:1, and the specific capacity of the negative electrode material is 456mAh / g.

[0007] In one embodiment of the present invention, the mass ratio between antimony powder and carbon black is 4:1, and the particle size ratio is 6:1, and the specific capacity of the negative electrode material is 433mAh / g.

[0008] In one embodiment of the present invention, the mass ratio between antimony powder and carbon black is 5:1, and the particle size ratio is 20:3, and the specific capacity of the negative electrode material is 424 mAh / g.

[0009] In one embodiment of the present invention, the specific surface area of ​​the negative electrode material is 6.0 m². 2 / g, with an average particle size of 12μm.

[0010] In one embodiment of the present invention, the specific surface area of ​​the negative electrode material is 4.8 m². 2 / g, with an average particle size of 15μm.

[0011] In one embodiment of the present invention, the specific surface area of ​​the negative electrode material is 4.2 m². 2 / g, with an average particle size of 10μm.

[0012] In one embodiment of the present invention, the graphene layer comprises graphene microsheets and reduced graphene oxide, wherein the graphene microsheets are mechanically produced graphene, and the mass ratio of the graphene microsheets to the reduced graphene oxide is 16:1 to 5:1, and the particle size ratio is 1:2 to 1:5.

[0013] To achieve the above-mentioned objective, a second aspect of the present invention provides a method for preparing a sodium-ion battery anode material, comprising the following steps:

[0014] (1) Preparation of carbon-coated antimony powder: Dispersant, carbon black and antimony powder are added to an aqueous solvent in a certain mass ratio. Through dispersion, drying and carbonization processes, carbon-coated antimony powder material is obtained.

[0015] (2) Graphene composite and coating: First, a certain amount of expanded graphite is added to an aqueous solvent, and after stirring, sand milling, homogenization and drying, graphene micro-sheets with a few-layer structure are obtained; Second, graphene micro-sheets, carbon-coated antimony powder and graphene oxide are composited in an aqueous solvent in a certain mass ratio, and then spray dried and carbonized to obtain graphene-antimony composite material.

[0016] (3) Hard carbon coating: Graphene-antimony composite material is added to citric acid solution, stirred evenly, dried and carbonized to obtain hard carbon-graphene-antimony composite sodium-ion battery anode material.

[0017] In one embodiment of the present invention, specifically, in step 1, the dispersant is one or both of sodium carboxymethyl cellulose and polyvinylpyrrolidone, with a purity ≥99%; the antimony powder has a particle size of 150-200 nm and a purity ≥99%; the carbon black is one or any combination of SP, Ketjen black, and acetylene black, with a particle size of 30-50 nm and a purity ≥99%; the concentration of the dispersant, carbon black, and antimony powder in the aqueous solvent is 5-15%, wherein the mass percentage of the dispersant is 10-25%, the mass percentage of the carbon black is 10-25%, and the mass percentage of the antimony powder is 50-80%. The carbonization temperature is 450-500℃; the carbonization time is 12-24 h; and the carbonization environment is an inert protective atmosphere, either nitrogen or argon.

[0018] Sodium carboxymethyl cellulose and polyvinylpyrrolidone exhibit excellent dispersibility in aqueous solutions, ensuring the uniform dispersion of carbon black and antimony nanopowder. Furthermore, the amorphous carbon produced after carbonization possesses a porous structure and large interlayer spacing, which helps suppress antimony expansion and prevents particle pulverization during charging and discharging. Simultaneously, the large interlayer spacing facilitates the free intercalation and deintercalation of sodium ions, improving the material's specific capacity. Carbon black has a high specific surface area and abundant microporous structure, exhibiting high oil absorption and strong liquid retention capacity, providing strong support for the rapid transport of sodium ions. It also acts as a conductive link between antimony powder particles, facilitating the construction of a more perfect electronic and ionic conductive network. However, a mass ratio of antimony powder to carbon black of 8:1 to 2:1 and a particle size ratio of 5:1 to 20:3 result in the most ideal electronic and ionic conductive effects. If the carbon black content is too high, its high specific surface area will make dispersion with antimony powder difficult and reduce the stability of the slurry. The resulting material core structure will also become porous, resulting in low material density and a low proportion of active material, further affecting its specific capacity or energy density. If the carbon black content is too low, it will be difficult to build a perfect conductive network, which will have a more serious impact on the specific capacity and rate performance of the antimony powder. In addition, regarding the particle size control of antimony powder and carbon black, the particle size of carbon black must be smaller than that of antimony powder to allow it to achieve uniform loading on the surface of antimony powder. However, if the particle size of carbon black is too small, it will affect the porosity of the material, hindering the free intercalation and deintercalation of sodium ions in the material, thus affecting the rate performance and capacity.

[0019] In one embodiment of the present invention, the dispersant is sodium carboxymethyl cellulose, the carbon black is carbon black SP, the average particle size of the carbon black is 30-50 nm, and the average particle size of the antimony powder is 150-200 nm.

[0020] In one embodiment of the present invention, the mass ratio of antimony powder to carbon black is 3:1, and the particle size ratio is 5:1.

[0021] In one embodiment of the present invention, the mass ratio of antimony powder to carbon black is 4:1, and the particle size ratio is 6:1.

[0022] In one embodiment of the present invention, the mass ratio of antimony powder to carbon black is 5:1, and the particle size ratio is 20:3.

[0023] In one embodiment of the present invention, the concentration of the dispersant, carbon black, and antimony powder in the aqueous solvent in step (1) is 10%.

[0024] In one embodiment of the present invention, the mass percentage of the dispersant in step (1) is 15%, the mass percentage of the carbon black is 17%, and the mass percentage of the antimony powder is 68%.

[0025] In one embodiment of the present invention, the carbonization temperature in step (1) is 480°C and the carbonization time is 16h.

[0026] In one embodiment of the present invention, the carbonization environment described in step (1) is an inert protective atmosphere of nitrogen.

[0027] In step 2, the expanded graphite has a carbon content ≥99%, an ash content ≤1%, and a particle size D. 10 At 5-10 μm, D 50 At 10-20 μm, D 90 The expansion ratio is 200-350 times at a thickness of 20-30 μm; the concentration of the expanded graphite in the aqueous solvent is 2-10%; the number of graphene microsheets is ≤200 layers, and the sheet diameter D is... 50 The graphene microsheets are 2-5 μm in size. The concentrations of the graphene microsheets, carbon-coated antimony powder, and graphene oxide in the aqueous solvent are 5-15%, wherein the mass percentage of the carbon-coated antimony powder is 10-40%, the mass percentage of the graphene microsheets is 50-80%, and the mass percentage of the graphene oxide is 5-10%. The solid content of the graphene oxide in the aqueous solution is 0.5-3%, the carbon content is 60-80%, the oxygen content is 20-60%, and the specific surface area is ≥150 m². 2 / g,D 50 The carbonization depth is 5-10 μm, the number of layers is ≤10; the carbonization temperature is 550-600℃; the carbonization time is 12-24h; and the carbonization environment is an inert protective atmosphere of nitrogen.

[0028] Expanded graphite has a large interlayer spacing, allowing sodium ions to freely intercalate and deintercalate. Under sand milling and high-pressure homogenization, it undergoes varying degrees of exfoliation to form graphene flakes. These graphene flakes provide a good carrier and dispersion for antimony powder materials, forming a sandwich-like layered structure that prevents the free flow and aggregation of nano-antimony powder materials and better limits further expansion. Graphene oxide exhibits excellent dispersion, sheet flexibility, and self-assembly capabilities in aqueous solutions, enabling uniform encapsulation of composite materials. After spraying and carbonization, graphene oxide undergoes reduction to generate reduced graphene oxide. Reduced graphene oxide possesses high purity, low defect content, chemical stability, and good electrical conductivity. To better utilize the encapsulation and conductivity functions of reduced graphene oxide, specific requirements are placed on the amount and particle size of graphene oxide. When the mass ratio of expanded graphite to graphene oxide is 5:1 to 16:1 and the particle size ratio is 1:2 to 1:5, good encapsulation, granulation, and conductivity can be achieved. Graphene oxide has a large specific surface area and is lightweight, but its surface has numerous wrinkles. Excessive addition can reduce the material's tap density, causing difficulties in transportation and processing. Furthermore, after extensive coating, its surface structure becomes dense, reducing gaps and hindering the free insertion and extraction of sodium ions. Simultaneously, if the graphene oxide particle size is too large, sodium ions have difficulty penetrating the graphene coating layer, resulting in significant steric hindrance and a substantial impact on the material's rate performance. Conversely, if the graphene oxide particle size is too small, it is difficult to coat expanded graphite, leading to poor granulation and conductive bridging effects. This results in the carbon-coated antimony powder being exposed outside the graphene layer, exhibiting irregular morphology and negatively affecting the material's consistency and electrical properties.

[0029] In one embodiment of the present invention, in step (2), the mass ratio of the carbon-coated antimony powder, the graphene micro-sheets and the graphene oxide is 3:6:1, and the particle size ratio of the graphene micro-sheets and the graphene oxide is 1:2 to 1:5.

[0030] In one embodiment of the present invention, in step (2), the mass ratio of the carbon-coated antimony powder, the graphene micro-sheets and the graphene oxide is 2:7:1, and the particle size ratio of the graphene micro-sheets and the graphene oxide is 1:2 to 1:5.

[0031] In one embodiment of the present invention, in step (2), the mass ratio of the carbon-coated antimony powder, the graphene micro-sheets and the graphene oxide is 1:8:1 and the particle size ratio of the graphene micro-sheets and the graphene oxide is 1:2 to 1:5.

[0032] In step 3, the concentration of the citric acid solution is 5-15%; the amount of graphene-antimony composite material added is 1-4 times the mass of the citric acid; the carbonization temperature is 500-550℃; the carbonization time is 12-24 hours; and the carbonization environment is an inert protective atmosphere, either nitrogen or argon. The hard carbon-graphene-antimony composite material has a specific surface area of ​​4-7 m². 2 / g,D 50 The particle size is 10-20 μm, the specific capacity is ≥400 mAh / g, and the initial charge / discharge efficiency is ≥80%. Appropriate specific surface area and particle size control play a crucial role in the overall electrical performance of the material. Too large a specific surface area or too small a particle size is detrimental to material dispersion and processing, and will reduce its initial charge / discharge efficiency and tap density; too large a specific surface area or particle size will result in a longer lithium-ion diffusion path, leading to unsatisfactory rate performance. The citric acid in the material is a low-molecular-weight organic compound that, after carbonization, forms amorphous carbon, i.e., a hard carbon structure. It can enhance the adhesion of reduced graphene oxide to the precursor material, preventing its detachment or displacement; at the same time, due to its large interlayer spacing, it can also serve as an ideal sodium storage material. Citric acid accounts for 20-50% of the total mixture. If the amount added is too small, an exposed and uneven hard carbon coating layer will form on the surface of the graphene-antimony composite material, and the structural stability and specific surface area of ​​the material will not be significantly improved; however, if the amount added is too large, it will affect the material's specific capacity and initial charge / discharge efficiency.

[0033] In one embodiment of the present invention, in step (3), the mass ratio of the graphene-antimony composite material to citric acid is 7:3.

[0034] In one embodiment of the present invention, in step (3), the mass ratio of the graphene-antimony composite material to citric acid is 6:3.

[0035] In one embodiment of the present invention, in step (3), the mass ratio of the graphene-antimony composite material to citric acid is 5:3.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The hard carbon-graphene-antimony composite anode material prepared in this invention fully leverages the advantages of each of the three sodium storage materials, maximizing their strengths and minimizing their weaknesses. It exhibits good batch stability, high specific capacity, good rate performance, and long cycle life, solving the problems of poor conductivity and large volume expansion inherent in antimony powder as anode material for sodium-ion batteries, and fully utilizing the high capacity of antimony powder. Firstly, a perfect electron and ion conductive network is constructed on the surface of the antimony powder using nano-carbon black and amorphous carbon. Nano-carbon black has a porous structure, high oil absorption value, and strong liquid absorption capacity, providing a powerful conductive effect for the rapid transport of electrons and sodium ions; the amorphous carbon coating provides the first layer of carbon protection for the antimony powder, preventing the nano-antimony powder particles from expanding and pulverizing. Secondly, by using graphene microsheets as a good carrier for antimony powder, the dispersion in aqueous solvent is enhanced and the aggregation of the antimony nanoparticles is prevented, forming a layered sandwich-like structure. Simultaneously, the use of reduced graphene oxide coating effectively controls the particle morphology and establishes a more efficient 3D conductive network channel, significantly reducing the ohmic resistance and improving the rate performance. The large interlayer spacing of graphene also ensures that sodium ions can freely intercalate and deintercalate, further guaranteeing the high specific capacity of the material. The outer layer of hard carbon further enhances the particle density, preventing the shedding and displacement of reduced graphene oxide and stabilizing the core structure of the material; it also possesses a large interlayer structure, achieving a high sodium storage capacity. The combination of hard carbon, graphene, and antimony—three sodium storage materials—will provide excellent capacity utilization, rate performance, and cycle performance for the anode of sodium-ion batteries. Attached Figure Description

[0038] Figure 1 SEM of hard carbon-graphene-antimony composite material

[0039] Figure 2 The 0.1C initial charge-discharge curves of the materials in Example 1 and Comparative Example 1.

[0040] Figure 3 The 1C cycle performance curves of the materials in Example 1 and Comparative Example 1 are shown. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market. Example 1

[0043] This invention proposes a sodium-ion battery anode material and its preparation method, the steps of which are as follows:

[0044] Preparation of carbon-coated antimony powder:

[0045] In 4.5 kg of pure water solvent, 75 g of sodium carboxymethyl cellulose, 105 g of carbon black SP, and 320 g of antimony powder were added according to a dispersant:carbon black:antimony powder mass ratio of 15%:21%:64%. The mixture was then stirred at high speed to ensure thorough and uniform dispersion. The average particle size of the carbon black was 30 nm, and the average particle size of the antimony powder was 150 nm. The mass ratio of antimony powder to carbon black was 3:1, and the particle size ratio was 5:1.

[0046] Then, it was placed in a 150°C forced-air drying oven to dry thoroughly. The dried powder was then placed in a crucible and sintered in a high-temperature carbon furnace at 480°C in a nitrogen atmosphere for 16 hours, finally obtaining carbon-coated antimony material.

[0047] Graphene composites and coatings:

[0048] First, 500g of expanded graphite was added to 9.5kg of pure water solvent. The expanded graphite had a carbon content ≥99%, an ash content ≤1%, and a particle size D. 10 At 5-10 μm, D 50 At 10-20 μm, D 90 At a thickness of 20-30 μm, the expansion factor is 200-350 times. Few-layer graphene microsheets are obtained through high-speed stirring, sand milling, high-pressure homogenization, and drying. The graphene microsheets have ≤200 layers and a sheet diameter D. 50 The particle size of the grinding balls used in the milling equipment is 0.6-0.8 mm, the ball material is zirconia, the milling speed is 2000 rpm, the milling time is 3 hours, and the slurry temperature in the milling chamber is controlled at 20-45℃; the pressure used in the homogenizing equipment is 900-1000 bar, and the homogenization is carried out 5 times; the drying equipment uses a forced-air drying oven at 150℃ for 48 hours; after drying, the powder is crushed to obtain graphene micro flakes.

[0049] Secondly, in 1 kg of pure water solvent, add 60 g of carbon-coated antimony powder, 120 g of graphene microsheets, and 1 kg of a 2% (w / w) graphene oxide solution. The graphene oxide has a carbon content of 60-80%, an oxygen content of 20-60%, and a specific surface area ≥150 m². 2 / g,D 50The particle size is 5-10 μm, and the number of layers is ≤10. The mass ratio of the carbon-coated antimony powder, the graphene microsheets, and the graphene oxide is 3:6:1, and the particle size ratio of the graphene microsheets to the graphene oxide is 1:2 to 1:5. The graphene-antimony composite material is obtained after high-speed stirring, spray drying, and high-temperature carbonization. The inlet temperature of the spray drying equipment is 195℃, the outlet temperature is 90℃, and the atomization frequency is 50Hz. The spray-dried powder is placed in a crucible and carbonized in a high-temperature carbon furnace at 580℃ in a nitrogen atmosphere for 16 hours, finally obtaining the graphene-antimony composite material.

[0050] (3) Hard carbon coating: In 2.7 kg of pure water solvent, 90 g of citric acid was added to dissolve it completely, and then 210 g of graphene-antimony composite material was added to form an aqueous slurry with a mass concentration of 10%. The mass ratio of the graphene-antimony composite material to citric acid was 7:3. The hard carbon-graphene-antimony composite material was obtained after high-speed stirring, drying and high-temperature carbonization. The drying equipment used a forced-air drying oven at a temperature of 150℃ for 48 h; the fully dried powder was placed in a crucible and sintered in a high-temperature tube furnace at 550℃ in a nitrogen atmosphere for 16 h, finally obtaining a particle size of 12 μm and a specific surface area of ​​6 m². 2 / g of hard carbon-graphene-antimony composite material.

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that:

[0053] In step (1) of this embodiment, 75g of sodium carboxymethyl cellulose, 85g of carbon black SP, and 340g of antimony powder are added to 4.5kg of pure water solvent according to a mass ratio of dispersant: carbon black: antimony powder of 15%:17%:68%. The mass ratio of antimony powder to carbon black is 4:1, the average particle size of the antimony powder is 180nm, the average particle size of the carbon black is 30nm, and the particle size ratio is 6:1.

[0054] In step (2) of this embodiment, 40g of carbon-coated antimony powder, 140g of graphene microsheets, and 1kg of a 2% graphene oxide solution are added to 1kg of pure water solvent. The mass ratio of the carbon-coated antimony powder, the graphene microsheets, and the graphene oxide is 2:7:1, and the particle size ratio of the graphene microsheets to the graphene oxide is between 1:2 and 1:5.

[0055] In step (3) of this embodiment, 100g of citric acid is first added to 2.7kg of pure water solvent to fully dissolve it, and then 200g of graphene-antimony composite material is added to form an aqueous slurry with a mass concentration of 10%. The mass ratio of the graphene-antimony composite material to citric acid is 6:3.

[0056] Everything else was the same as in Example 1, resulting in a mean particle size of 12 μm and a specific surface area of ​​6 m². 2 / g of hard carbon-graphene-antimony composite material.

[0057] Example 3

[0058] The difference between this embodiment and Embodiment 1 is that:

[0059] In step (1) of this embodiment, 75g of sodium carboxymethyl cellulose, 70g of carbon black SP, and 355g of antimony powder are added to 4.5kg of pure water solvent according to a mass ratio of dispersant: carbon black: antimony powder of 15%:14%:71%. The mass ratio of antimony powder to carbon black is 5:1, the average particle size of the antimony powder is 200nm, the average particle size of the carbon black is 30nm, and the particle size ratio is 20:3.

[0060] In step (2) of this embodiment, 20g of carbon-coated antimony powder, 180g of graphene microsheets, and 1kg of a 2% (w / w) graphene oxide solution are added to 1kg of pure water solvent. The mass ratio of the carbon-coated antimony powder, the graphene microsheets, and the graphene oxide is 1:8:1, and the particle size ratio of the graphene microsheets to the graphene oxide is between 1:2 and 1:5.

[0061] In step (3) of this embodiment, 112.5g of citric acid is first added to 2.7kg of pure water solvent to fully dissolve it, and then 187.5g of graphene-antimony composite material is added to form an aqueous slurry with a mass concentration of 10%. The mass ratio of the graphene-antimony composite material to citric acid is 5:3.

[0062] The rest were the same as in Example 1, resulting in a hard carbon-graphene-antimony composite material.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, 75g of sodium carboxymethyl cellulose, 212.5g of carbon black SP and 212.5g of antimony powder are added to 4.5Kg of pure water solvent according to the mass ratio of dispersant: carbon black: antimony powder of 15%:47.5%:47.5%; the mass ratio of antimony powder to carbon black is 1:1.

[0065] The rest were the same as in Example 1, resulting in a hard carbon-graphene-antimony composite material.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that the carbon black used in step (1) of this comparative example has a particle size of 75 nm, and the particle size ratio of the antimony powder to the carbon black is 2:1.

[0068] The rest were the same as in Example 1, resulting in a hard carbon-graphene-antimony composite material.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the graphene oxide sheet diameter D50 selected in step (2) of this comparative example is 2-5 μm. The ratio of the graphene microsheet to the graphene oxide particle size is 1:1.

[0071] The rest were the same as in Example 1, resulting in a hard carbon-graphene-antimony composite material. Comparative Example 4

[0072] The difference between this comparative example and Example 1 is that in step (3) of this comparative example, 200g of citric acid is first added to 2.7Kg of pure water solvent to fully dissolve it, and then 100g of graphene-antimony composite material is added to form an aqueous slurry with a mass concentration of 10%. The mass ratio of the graphene-antimony composite material to citric acid is 1:2.

[0073] The rest were the same as in Example 1, resulting in a hard carbon-graphene-antimony composite material.

[0074] Test case

[0075] The hard carbon-graphene-antimony composite materials obtained in Examples 1-3 and Comparative Examples 1-2 were mixed with SP and PVDF at a mass ratio of 97%:1.5%:1.5% in NMP solvent to form a slurry, where the mass of NMP was 1.5 times the mass of the solids. The slurry was coated onto a 16 μm thick aluminum foil, dried, rolled, and punched into button-type discs. Using sodium foil as the counter electrode, the discs were assembled into a 2032 button cell. The electrolyte used in the battery consisted mainly of sodium hexafluorophosphate (1 mol / L) as the sodium salt and ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as the solvent, in a mass ratio of 1:1:1. The separator was 20 μm thick, a three-layer microporous membrane of polypropylene / polyethylene (PP / PE / PP). The charge / discharge current was tested at 0.6 mA / cm². 2 The charge / discharge cutoff voltage is 0.001V-2.5V. The initial capacity and coulombic efficiency of the coin cell were tested by repeating the above charge / discharge voltage operation until the current increased to 6mA / cm. 2 The battery was subjected to 20 charge / discharge cycles. Additionally, the slurries prepared in Examples 1-3 and Comparative Examples 1-2 were coated onto a PET film, dried, and then cut into φ12mm discs for resistivity testing. The test results are shown in Table 1.

[0076] Table 1. Electrical performance test results of Examples 1-3 and Comparative Examples 1-4

[0077]

[0078] As shown in Table 1 above, the hard carbon-graphene-tin composite anode material prepared using the present invention, tested with coin cells, demonstrates that the composite anode materials prepared in Examples 1-3 exhibit a 0.1C discharge specific capacity of 420-460 mAh / g and an initial efficiency of 88-91%, exhibiting high discharge specific capacity and initial efficiency. The capacity retention rate after 20 cycles at 1C is consistently above 90%, demonstrating good cycle stability. Analysis reveals that in Comparative Example 1, the mass ratio of antimony powder to carbon black is 1:1, resulting in increased carbon black addition compared to Example 1. Due to the high specific surface area of ​​carbon black, dispersion with antimony powder becomes difficult, and the stability of the slurry deteriorates. The resulting material core structure also becomes porous. Furthermore, the carbon black addition ratio in Comparative Example 1 exceeds the range defined in this application, leading to low material density and a low proportion of active material, further affecting its specific capacity or energy density.

[0079] In Comparative Example 2, the carbon black particle size was 75 nm, and the particle size ratio of antimony powder to carbon black was 2:1. The experimental results showed that the battery performance was reduced to varying degrees. The purpose of this scheme is to load carbon black onto the surface of antimony powder and then encapsulate it through a polymer layer to form a stable carbon black loading structure. However, due to the increased carbon black particle size, the loading effect of carbon black around antimony powder is not ideal, making it difficult to form uniform adsorption of carbon black on the surface of antimony powder, resulting in poor dispersion, increased material reaction resistance, and ultimately affecting battery performance.

[0080] In Comparative Example 3, the 1:1 particle size ratio of graphene microsheets to graphene oxide significantly impacts battery life. Analysis suggests that when the amount of reduced graphene oxide added exceeds the designed range, the particle size of the graphene oxide, being similar to that of expanded graphite, makes it difficult to coat the expanded graphite. This results in suboptimal granulation and conductive bridging effects, causing the carbon-coated antimony powder to be exposed outside the graphene layer, exhibiting irregular morphology and affecting material consistency and electrical properties.

[0081] Comparative Example 4 primarily aimed to investigate the effect of varying citric acid content on the performance of the anode material. When the mass ratio of graphene-antimony composite material to citric acid was 1:2, the proportion of hard carbon in the material increased accordingly. Hard carbon, when used as an anode material in sodium-ion batteries, suffers from low capacity and low initial efficiency. Therefore, excessive addition of citric acid would affect the specific capacity and initial efficiency of the material.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a sodium-ion battery anode material, characterized in that, Includes the following steps: (1) Preparation of carbon-coated antimony powder: In an aqueous solvent, a dispersant, carbon black and antimony powder are added in a certain mass ratio. The material is obtained by dispersion, drying and carbonization. The carbonization temperature is 450-500℃ and the carbonization time is 12-24h. (2) Graphene composite and coating: A certain amount of expanded graphite is added to an aqueous solvent, and after stirring, sand milling, homogenization and drying, graphene microsheets with a few-layer structure are obtained; then, the graphene microsheets, carbon-coated antimony powder and graphene oxide are composited in an aqueous solvent in a certain mass ratio, and then spray dried and carbonized to obtain graphene-antimony composite material; the carbonization temperature is 550-600℃ and the carbonization time is 12-24h; (3) Hard carbon coating: Graphene-antimony composite material is added to citric acid solution, stirred evenly, dried and carbonized to obtain hard carbon-graphene-antimony composite sodium-ion battery anode material; the carbonization temperature is 500-550℃; the carbonization time is 12-24h; the carbonization environment is an inert protective atmosphere, either nitrogen or argon.

2. The preparation method according to claim 1, characterized in that, In step (1), the dispersant is one or both of sodium carboxymethyl cellulose and polyvinylpyrrolidone; the average particle size of the antimony powder is 150-200 nm; the carbon black is one or any combination of SP, Ketjen black, and acetylene black, with an average particle size of 30-50 nm; the concentration of the dispersant, carbon black, and antimony powder in the aqueous solvent is 5-15%, wherein the mass percentage of the dispersant is 10-25%, the mass percentage of the carbon black is 10-25%, and the mass percentage of the antimony powder is 50-80%.

3. The preparation method according to claim 1, characterized in that, In step (1), the carbonization environment is an inert protective atmosphere, either nitrogen or argon.

4. The preparation method according to claim 1, characterized in that, In step (2), the expanded graphite has a carbon content ≥99%, an ash content ≤1%, and a particle size D. 10 At 5-10 μm, D 50 At 10-20 μm, D 90 The expansion ratio is 200-350 times at a thickness of 20-30 μm; the concentration of the expanded graphite in the aqueous solvent is 2-10%; the number of graphene microsheets is ≤200 layers, and the sheet diameter D is... 50 At 2-5 μm.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentrations of the graphene microsheets, carbon-coated antimony powder, and graphene oxide in the aqueous solvent are 5-15%, wherein the mass percentage of the carbon-coated antimony powder is 10-40%, the mass percentage of the graphene microsheets is 50-80%, and the mass percentage of the graphene oxide is 5-10%; the solid content of the graphene oxide in the aqueous solution is 0.5-2%, the carbon content of the graphene oxide is 60-80%, the oxygen content is 20-40%, and the specific surface area is ≥150 m². 2 / g,D 50 The carbonization environment is inert and protective, consisting of either nitrogen or argon, with a depth of 5-10 μm and a layer count of ≤10.

6. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the citric acid solution is 5-15%; the amount of graphene-antimony composite material added is 1-4 times the mass of citric acid; and the specific surface area of ​​the hard carbon-graphene-antimony composite material is 4-7 m². 2 / g,D 50 Particle size is 10-20μm, specific capacity is ≥400mAh / g, and initial coulombic efficiency is ≥80%.

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