Preparation method of carbon-confined tin-iron-sulfide composite material and application thereof

Abstract

The application belongs to the field of sodium ion batteries, and discloses a preparation method of a carbon-confined tin-iron sulfide composite material and application thereof. The application prepares an iron hydroxyl stannate oxide precursor through a mechanical chemical reaction, realizes construction of a carbon composite structure through secondary ball milling, and finally obtains a tin-iron sulfide carbon composite material through gas phase sulfuration. The method has the advantages of simple preparation, solvent-free production in the preparation process, green environmental protection, high yield and the like. The tin-iron sulfide carbon composite material obtained finally has excellent cycle performance and rate performance when used as a negative electrode material of a sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a method for preparing a carbon-confined tin-iron sulfide composite material and its application. Background Technology

[0002] In recent years, the massive consumption of fossil fuels has caused enormous pollution and damage to the environment. As global energy demand continues to expand, people are increasingly replacing traditional energy sources with recyclable new energy materials to address environmental degradation and the energy crisis. Lithium-ion batteries are commercially widely used electrochemical energy storage devices, but the scarcity and uneven global distribution of lithium resources limit their large-scale application. Against this backdrop, sodium-ion batteries, with their abundant resources, low cost, and similar working principle to lithium-ion batteries, are considered one of the most promising alternatives. Sodium-ion batteries have broad prospects in the field of electrochemical energy storage and are expected to play a significant role in the future.

[0003] In the entire sodium storage system, the anode material directly affects the electrochemical performance of the sodium-ion battery. Among anode materials, tin-based sulfides have attracted widespread attention from researchers due to their abundant raw material resources, high specific capacity, and unique layered structure. However, tin-based sulfides still have some problems in practical applications, such as low intrinsic conductivity, large volume changes during charge and discharge, and slow ion kinetics.

[0004] Researchers have proposed several strategies to address these issues, such as nanostructure design, carbon material composites, and heterostructure construction. Among them, Chinese patent CN114068904A provides a carbon-coated tin-based sulfide composite material, its preparation method, and its application. Specifically, this invention first obtains a nanosphere-shaped tin dioxide precursor through stannate hydrolysis, then coats its surface with a layer of polydopamine, followed by carbonization and sulfidation treatments to obtain a carbon-coated tin sulfide composite material. The carbon-coated structure designed in this invention effectively suppresses the volume change of tin-based sulfides during charge and discharge, while simultaneously improving the material's conductivity. This material, applied to sodium-ion battery anode materials, significantly improves the material's rate performance and cycle stability. However, in this technical solution, the prolonged hydrolysis reaction leads to increased energy consumption and reduced production efficiency during the reaction process. Chinese patent CN114920283A discloses a zinc-tin binary sulfide / carbon nanocubic composite material and its preparation method. This method first yields a ZnSn(OH)6 precursor through a co-precipitation reaction under alkaline conditions. Then, the precursor is dispersed in a buffer solution and complexed with dopamine hydrochloride to obtain a ZnSn(OH)6@C intermediate. Finally, high-temperature carbonization and gas-phase sulfidation are performed to obtain a zinc-tin binary sulfide / carbon nanocubic composite material, ZnS / SnS2@C. This heterojunction design leverages the synergistic effect of multiple components, significantly improving the material's electrochemical performance. Currently, the main processes for preparing bimetallic sulfide carbon composite materials are hydrothermal and co-precipitation methods. However, both methods are demanding, time-consuming, and environmentally polluting, and the preparation processes are complex. Therefore, it is still necessary to explore an efficient and environmentally friendly synthesis method to prepare high-specific-capacity bimetallic sulfide carbon composite electrode materials. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing carbon-confined tin-iron sulfide composite materials and their applications. This invention prepares an iron stannate oxidized precursor via a mechanochemical reaction, constructs the carbon composite structure through secondary ball milling, and finally obtains the tin-iron sulfide carbon composite material via gas-phase sulfidation. This method is simple to prepare, reduces solvent usage, and has advantages such as being environmentally friendly and having high yield. The resulting tin-iron sulfide carbon composite material exhibits excellent cycle performance and rate performance when used as a negative electrode material in sodium-ion batteries.

[0006] The specific technical solution of this invention is: a method for preparing a carbon-confined tin-iron sulfide composite material, comprising the following steps:

[0007] (1) Iron salts and tin salts are placed in a ball mill jar and the precursor of ferric hydroxystannate is obtained through mechanochemical reaction and subsequent washing.

[0008] (2) The precursor of oxidized hydroxystannate iron is mixed with carbon source by ball milling for a second time to obtain intermediate product.

[0009] (3) The intermediate product and sulfur source were heat-treated under an inert protective atmosphere to obtain a composite material in which tin-iron bimetallic sulfide particles were uniformly grown on a carbon matrix.

[0010] Tin-iron bimetallic sulfides possess high sodium storage capacity. Iron disulfide, with its narrow band gap (0.7 eV), can form an internal electric field with tin disulfide, which has a wide band gap (2.1 eV), thereby promoting interfacial reaction kinetics and ion transport. The bimetallic heterostructure provides more sodium storage sites, resulting in a higher sodium storage capacity for tin-iron bimetallic sulfides. Simultaneously, the formed internal electric field reduces the resistance to ion diffusion and accelerates ion transport. Therefore, preparing tin-iron sulfides using a mechanochemical method and compositing them with carbon materials holds promise for obtaining high-performance sodium storage anode materials. This invention uses a mechanochemical method to prepare an iron hydroxystannate precursor, which is then ball-milled and uniformly mixed with carbon materials. Finally, a gas-phase sulfidation process is performed to obtain a tin-iron sulfide carbon composite material. This invention uses a mechanochemical method to prepare the iron hydroxystannate precursor. This method is simple, environmentally friendly, and avoids the problems of traditional hydrothermal and co-precipitation methods. It reduces the amount of solvent used in the reaction, shortens the reaction time, and facilitates large-scale production.

[0011] Specifically, in the first ball milling process of step (1), the main reaction occurs in two stages. First, the raw material particles are crushed and uniformly mixed under mechanical force. Second, under mechanical force, iron ions and stannate ions react to generate a relatively uniformly sized precursor of ferric hydroxystannate oxide. In the second ball milling process, the obtained precursor is ball-milled and mixed with carbon material, so that the ferric hydroxystannate oxide precursor is uniformly distributed on the carbon matrix. Subsequently, after gas-phase sulfidation, the precursor reacts with the sulfur source to generate a tin-iron bimetallic sulfide material, resulting in a composite material with tin-iron bimetallic sulfide particles uniformly grown on the carbon matrix.

[0012] In summary, the composite material obtained in this invention has the following advantages when used as a sodium-ion anode material: (1) The composite of carbon materials not only improves the conductivity of the material, but also leverages the spatial confinement effect of carbon materials, effectively mitigating the volume change of sulfide materials during charging and discharging, and enhancing the structural stability of the material; (2) The introduction of bimetallic sulfides to construct heterojunctions generates a large number of lattice mismatches, distortions, and defects at the heterojunction interface, providing a suitable anode material for sodium ions. + The transport provides abundant active sites and also promotes ion transport; (3) When the composite material is used as the negative electrode of sodium-ion battery, it has excellent cycle and rate performance.

[0013] Preferably, in step (1), the ball mill of the present invention includes two optional solutions:

[0014] The first option is a more conventional one-step ball milling: the total mass ratio of the iron salt and tin salt to the mass of the grinding beads is 1:(10-40); the diameter of the grinding beads used in the ball milling is 8-12 mm; the ball milling time is 4-7 hours, and the rotation speed is 300-600 rpm.

[0015] More preferably, the ball milling includes the following two stages:

[0016] The first stage: using large grinding balls to crush the material particles; the total mass ratio of iron salts and tin salts to the mass of grinding balls is 1:(10-40), the diameter of the large grinding balls is 15-25mm, the diameter of the small grinding balls is 3-7mm, the mass ratio of large to small grinding balls is (7.5:2.5) to (8.5:1.5), the grinding time is 1-2 hours, and the rotation speed is 400-600 rpm;

[0017] Second stage: Without changing the ball-to-material ratio, some of the large grinding balls are replaced with small grinding balls of the same mass to mix and refine the crushed raw material particles and promote the reaction. The mass ratio of large to small grinding balls is (2.5:7.5) to (3.5:6.5), the grinding time is 2 to 4 hours, and the rotation speed is 300 to 500 rpm.

[0018] In the preparation process using the second ball milling method described above, the main reaction process is as follows: Large grinding balls and metal salt raw materials are placed together in a ball mill jar. The metal salt raw material is broken into smaller particles by the mechanical force of the large grinding balls at high speed. When the particle size is roughly the same, most of the large grinding balls are replaced with smaller ones, increasing the specific surface area of ​​the grinding balls. Ball milling is then performed again to further mix and refine the broken material particles. During ball milling, the reaction mainly occurs on the surface of the grinding balls. High temperatures are generated at the contact surfaces when the grinding balls collide with each other. The energy generated induces a chemical reaction between tin and iron salts. Simultaneously, the crystal water in the raw materials contains hydroxyl groups, making it easier for the materials to react and achieve synthesis. Compared to the first method, the second method yields material particles with smaller nanoscale sizes and no agglomeration.

[0019] Preferably, in step (1), in order to obtain the precursor of ferric hydroxystannate, the present invention found that the molar ratio of tin salt to iron salt is crucial. If there is too much iron salt compared to tin salt, byproducts will be generated in the reaction; if there is too little iron salt compared to tin salt, the excess tin salt will hydrolyze to obtain tin oxide, affecting the successful synthesis of the ferric hydroxystannate precursor. Ultimately, the present invention found that controlling the molar ratio of iron salt to tin salt in the range of 1:(1~2) yields the best results.

[0020] Preferably, in step (2), in order to obtain an intermediate product with an ideal structure, the present invention finds that the mixing method and ratio of the precursor and the carbon source are crucial. If the carbon source is introduced in the ball milling stage of step (1), the introduced carbon source will exhibit a negative charge due to the presence of oxygen-containing functional groups (such as carboxyl groups and hydroxyl groups) on the surface. During the ball milling process, the surface electronegativity is further enhanced due to mechanical friction and oxidation. At this time, the carbon source will preferentially combine with the positively charged iron salt, resulting in carbon coating on the outside of the iron, hindering the full contact between the tin salt and the iron salt, resulting in an incomplete reaction process, and the inability to generate stable ferric stannate oxide precursor particles. The tin salt that does not participate in the reaction will generate tin oxide byproducts during the ball milling and water washing process. On the other hand, if there is too much carbon source compared to the precursor, it will completely coat the precursor, causing agglomeration between particles and affecting the efficiency of ball milling. If there is too little carbon source compared to the precursor, the dispersion of the carbon source in the material will be limited, resulting in an incomplete conductive carbon matrix and affecting electron transport. Ultimately, this invention found that introducing the carbon source into the second ball milling in step (2), while controlling the mass ratio of the precursor to the carbon source within the range of (0.5 to 2.5):1, yields the best results.

[0021] Preferably, in step (3), in order to obtain a high-performance tin-iron sulfide carbon composite material after heat treatment and sulfidation, the present invention limits the mass ratio of intermediate product to sulfur powder to 1:(2-8). When the mass ratio of intermediate product to sulfur powder is too low, sulfur residue will occur, causing environmental pollution problems. On the other hand, if the mass ratio of intermediate product to sulfur powder is too high, the reaction will be incomplete, reducing the yield of the target product and affecting its performance.

[0022] Preferably, in step (1), the tin salt is sodium stannate trihydrate or potassium stannate trihydrate; the iron salt is anhydrous ferric chloride, ferrous sulfate heptahydrate or ferric nitrate nonahydrate.

[0023] Preferably, in step (2), the carbon source is any one of Super P, Ketjen Black, or acetylene black.

[0024] Preferably, in step (2), the ball milling time is 2 to 5 hours and the rotation speed is 200 to 600 rpm.

[0025] Preferably, in step (3), the sulfur source is sulfur powder, thiourea, or thioacetamide.

[0026] Preferably, in step (3), the heat treatment temperature is 500-600℃ and the holding time is 1-3h; the inert protective atmosphere is nitrogen or argon.

[0027] The tin-iron sulfide carbon composite material obtained by the above method is used as a negative electrode material for sodium-ion batteries.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) The present invention prepares the precursor of ferric hydroxystannate by ball milling mechanochemical method, avoiding the problems of long synthesis time and large solvent consumption of traditional hydrothermal method and coprecipitation method. The synthesis process is simple, efficient, green and environmentally friendly, and has a high yield, and can be used for large-scale industrial production.

[0030] (2) The present invention uses ball milling to uniformly mix the precursor material and carbon source, and gas phase sulfidation to realize the in-situ conversion of intermediate product into tin-iron bimetallic sulfide. The introduction of carbon source not only improves the electrical conductivity of the material, but also plays a spatial confinement effect as a carbon framework network, avoiding the agglomeration of bimetallic sulfide particles, effectively alleviating the volume change of the material during the insertion / extraction process, enhancing the structural stability of the material, and improving the cycle and rate performance of the electrode material.

[0031] (3) In this invention, a bimetallic sulfide is derived from ferric hydroxystannate as a precursor. A heterojunction is formed between the two phase components, and the resulting built-in electric field reduces the ion diffusion barrier, accelerates ion transport, and significantly improves sodium storage performance. Attached Figure Description

[0032] Figure 1 The X-ray diffraction pattern of the final product prepared in Example 3 of this invention;

[0033] Figure 2 This is a scanning electron microscope image of the final product prepared in Example 4 of the present invention;

[0034] Figure 3 This is a scanning electron microscope image of the final product prepared in Comparative Example 3 of the present invention;

[0035] Figure 4 The diagram shows the cycle performance of Embodiment 1 and Comparative Example 1 of the present invention;

[0036] Figure 5 This is a rate performance diagram of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0037] The present invention will be further described in detail below through embodiments, but the present invention is not limited to the following examples.

[0038] Example 1

[0039] (1) Take 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride and 30g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0040] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 5 hours at a speed of 400 rpm to obtain the precursor.

[0041] (3) Take 300mg of precursor, 150mg of Super P and 20g of agate grinding beads with a diameter of 10mm and add them into the grinding jar.

[0042] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 300 rpm to obtain the intermediate.

[0043] (5) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0044] Example 2

[0045] (1) Take 3 mmol potassium stannate trihydrate, 2 mmol ferric nitrate nonahydrate and 20g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0046] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 6 hours at a speed of 400 rpm to obtain the precursor.

[0047] (3) Take 200mg of precursor, 100mg of acetylene black and 10g of agate grinding beads with a diameter of 10mm and add them together into the grinding jar.

[0048] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 500 rpm to obtain the intermediate.

[0049] (5) The intermediate product and thioacetamide were heat-treated at 600°C for 2 hours under an argon atmosphere in a mass ratio of 1:3 to obtain tin disulfide / iron disulfide carbon composite material.

[0050] Example 3

[0051] (1) Take 2 mmol of sodium stannate trihydrate, 2 mmol of ferrous sulfate heptahydrate and 25g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0052] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 6 hours at a speed of 600 rpm to obtain the precursor.

[0053] (3) Take 300mg of precursor, 200mg of Ketjen black and 30g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0054] (4) Transfer the ball mill jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 5 hours at a speed of 300 rpm to obtain the intermediate.

[0055] (5) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under an argon atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0056] Example 4

[0057] (1) Take 3 mmol sodium stannate trihydrate, 2 mmol ferric nitrate nonahydrate and 15g agate grinding beads with a diameter of 10mm and put them into the grinding jar together;

[0058] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain the precursor.

[0059] (3) Take 200mg of precursor, 250mg of Super P and 15g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0060] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 2 hours at a speed of 300 rpm to obtain the intermediate.

[0061] (5) The intermediate product and thioacetamide were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:5 to obtain tin disulfide / iron disulfide carbon composite material.

[0062] Example 5

[0063] (1) Take 3 mmol of potassium stannate trihydrate, 1.5 mmol of anhydrous ferric chloride and 25 g of agate grinding beads with a diameter of 10 mm and put them into the grinding jar;

[0064] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 7 hours at a speed of 300 rpm to obtain the precursor.

[0065] (3) Take 200mg of precursor, 300mg of Ketjen black and 40g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0066] (4) Transfer the ball mill jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 4 hours at a speed of 500 rpm to obtain the intermediate.

[0067] (5) The intermediate product and thiourea were heat-treated at 500°C for 1 hour under an argon atmosphere in a mass ratio of 1:6 to obtain tin disulfide / iron disulfide carbon composite material.

[0068] Example 6

[0069] (1) Take 2 mmol of potassium stannate trihydrate, 1 mmol of ferrous sulfate heptahydrate and 40g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0070] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 4 hours at a speed of 300 rpm to obtain the precursor.

[0071] (3) Take 500mg of precursor, 200mg of acetylene black and 20g of agate grinding beads with a diameter of 10mm and add them into the grinding jar.

[0072] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 300 rpm to obtain the intermediate.

[0073] (5) The intermediate product and sulfur powder were heat-treated at 400°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0074] Example 7

[0075] (1) Take 2 mmol sodium stannate trihydrate, 2 mmol anhydrous ferric chloride, 25g large (20mm in diameter) agate grinding ball and 5g small (5mm in diameter) agate grinding ball and put them into the grinding jar together;

[0076] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly, then perform ball milling for a total time of 2 hours at a speed of 400 rpm;

[0077] (3) After step (2) is completed, replace the grinding balls in step (1) with 9g large (20mm in diameter) agate grinding balls and 21g small (5mm in diameter) agate grinding balls, and then grind for 3 hours at a speed of 400rpm.

[0078] (4) Take 300mg of precursor, 150mg of Super P and 20g of agate grinding beads with a diameter of 10mm and add them into the grinding jar.

[0079] (5) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 300 rpm to obtain the intermediate.

[0080] (6) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0081] Comparative Example 1

[0082] (1) Take 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride and 30g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0083] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 5 hours at a speed of 400 rpm to obtain the precursor.

[0084] (3) Take 300mg of precursor, 100mg of Super P and 20g of agate grinding beads with a diameter of 10mm and add them into the grinding jar;

[0085] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 300 rpm to obtain the intermediate.

[0086] (5) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0087] Comparative Example 2

[0088] (1) Take 2 mmol of sodium stannate trihydrate, 2 mmol of ferrous sulfate heptahydrate and 25g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0089] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 600 rpm to obtain the precursor.

[0090] (3) Take 300mg of precursor, 200mg of Ketjen black and 30g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0091] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 2 hours at a speed of 300 rpm to obtain the intermediate.

[0092] (5) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under an argon atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0093] Comparative Example 3

[0094] (1) Take 3 mmol sodium stannate trihydrate, 0.5 mmol ferric nitrate nonahydrate and 15 g of agate grinding beads with a diameter of 10 mm and put them into the grinding jar;

[0095] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 4 hours at a speed of 400 rpm to obtain the precursor.

[0096] (3) Take 200mg of precursor, 250mg of Super P and 15g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0097] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 2 hours at a speed of 300 rpm to obtain the intermediate.

[0098] (5) The intermediate product and thioacetamide were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:5 to obtain tin disulfide / iron disulfide carbon composite material.

[0099] Comparative Example 4

[0100] (1) Take 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride and 30g of agate grinding beads with a diameter of 10mm and put them into the grinding jar.

[0101] (2) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total duration of 5 hours at a speed of 400 rpm to obtain the precursor.

[0102] (3) Take 300mg of precursor, 650mg of Super P and 20g of agate grinding beads with a diameter of 10mm and add them to the grinding jar.

[0103] (4) Transfer the grinding jar into the planetary ball mill and complete the assembly. Then, perform ball milling for a total time of 3 hours at a speed of 300 rpm to obtain the intermediate.

[0104] (5) The intermediate product and sulfur powder were heat-treated at 500°C for 2 hours under a nitrogen atmosphere in a mass ratio of 1:4 to obtain tin disulfide / iron disulfide carbon composite material.

[0105] Performance testing

[0106] The final products obtained in each embodiment and comparative example were mixed with a conductive agent (Super P) and a binder (PVDF) in a mass ratio of 7:2:1. First, the product and conductive agent were mixed in a fixed ratio, and after multiple grindings and uniform mixing, a fixed proportion of PVDF was added, along with an appropriate amount of solvent N-methylpyrrolidone (NMP) to form a homogeneous slurry. This slurry was then smoothly coated onto a current collector (copper foil), dried at 60°C for 12 hours, and then punched out 12mm electrode sheets using a slicing machine. Glass fiber was used as the diaphragm, sodium metal sheet as the counter electrode, and 1.0 mol L... -1A half-cell was assembled using NaPF6 as the solute and diethylene glycol dimethyl ether as the solvent. Assembly was performed in an argon-filled glove box, proceeding from bottom to top in the following order: positive electrode shell, prepared electrode, separator, electrolyte, sodium metal sheet, nickel foam, and negative electrode shell. The assembled sodium-ion half-cell was allowed to stand for 24 hours before electrochemical testing was conducted under constant temperature conditions.

[0107] Figure 1 The X-ray diffraction pattern of the final product prepared in Example 3 of this invention shows that both hexagonal tin disulfide (JCPDS No. 23-0677) and cubic iron disulfide (JCPDS No. 42-1340) are present. A broad diffraction peak exists near 25°. However, due to the high intensity of the SnS2 product peak, the intensity of the amorphous carbon peak is not obvious. The product has good crystallinity, indicating that the tin disulfide / iron disulfide carbon composite material was successfully synthesized.

[0108] Figure 2 The image shown is a scanning electron microscope image of the final product prepared in Example 4 of this invention. It can be seen that the product is uniformly dispersed, with no obvious agglomeration, and the particle size is 40-80 nm.

[0109] Figure 3 This is a scanning electron microscope image of the final product prepared in Comparative Example 3 of the present invention, for comparison. Figure 2 (Example 4) More sheet-like materials can be seen stacked. This is because the raw materials of Comparative Example 3 contain more tin salts than iron salts, resulting in excess tin salts. During ball milling and water washing, tin oxide is generated by hydrolysis. After gas-phase sulfidation, more sheet-like SnS2 is generated, causing the materials to stack and distribute.

[0110] Figure 4 The diagram shows the cycle performance of Example 1 and Comparative Example 1 of the present invention. The difference between Example 1 and Comparative Example 1 is that the ratio of precursor to carbon source in step (2) is different (the carbon source is relatively less in Comparative Example 1). By comparison, it can be seen that the ratio of precursor to carbon source has a great influence on the performance of composite material. A reasonable amount of carbon source can better exert the sodium storage performance of active material.

[0111] Figure 5 The figures show the rate performance of Example 1 and Comparative Example 1 of the present invention. In Example 1, the sodium-ion battery was tested at 0.2 Ag. -1 0.5Ag -1 1Ag -1 2Ag -1 5Ag -1 And return 0.2Ag -1 The reversible specific capacity at the given current density is 701.1 mAh g. -1 613.6mAh g -1579.5mAh g -1 541.1mAh g -1 420.0mAh g -1 657.1mAh g -1 Compared with Comparative Example 1, it exhibits superior rate performance.

[0112] The capacity and coulomb efficiency at the 50th cycle of the examples and comparative examples are shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] *Current density is 1Ag -1 (Voltage window is 0.01~3V) test.

[0117] Table 1 summarizes the examples and comparative examples in 1 Ag. -1 The capacity of the half-cell at 50 cycles and the coulombic efficiency of the first cycle were compared at a current density. Example 1, compared with Comparative Examples 1 and 4, shows that the ratio of precursor to carbon source has a significant impact on the material's performance. Excessive carbon source (Comparative Example 4) causes severe material agglomeration, and the carbon matrix fails to load sufficient effective active material, resulting in a low battery capacity. Insufficient carbon source (Comparative Example 1) prevents confinement of sulfides, leading to sulfide material growth, increased diffusion resistance, and significant volume changes during charge and discharge, affecting cycle stability. Example 4, compared with Comparative Example 3, shows that the metal salt ratio has a significant impact on the material's structure and performance. Excessive stannate ratio (Comparative Example 3) causes stannate to undergo self-hydrolysis during ball milling, generating tin oxide, which affects the synthesis of ferric hydroxystannate. Figure 3 As shown, the composite material exhibits a large number of SnS2 lamellar structures, which affects the synthesis of bimetallic sulfides and consequently impacts the material's performance.

[0118] The rate discharge capacity of each embodiment and comparative example is shown in Table 2.

[0119] Table 2

[0120]

[0121] Test with a voltage window of 0.01 to 3V

[0122] Table 2 shows the capacity of each embodiment and comparative example at different current densities. A comparison of Example 3 and Comparative Example 2 shows that the ball milling time has a significant impact on the material's performance. In the first ball milling of Comparative Example 2, a shorter milling time resulted in incomplete refinement of the raw materials, leading to insufficient contact and mixing of tin and iron salts, which affected the synthesis and dispersion of the precursor materials. In the second ball milling, an excessively short milling time resulted in uneven mixing of the carbon source and precursor materials, leading to severe product agglomeration and affecting the material's performance. In Example 3, a longer milling time allowed for thorough mixing and refinement of the raw materials, resulting in uniform dispersion. A comparison of Example 6 and Example 1 shows that the sulfidation conditions have a significant impact on the material's performance. At a lower sulfidation temperature (Example 6), the sulfur powder cannot completely sublimate and react with the material during gas-phase sulfidation; instead, it is adsorbed onto the material surface via physical adsorption. The relatively low proportion of active substances also limits the material's capacity. Optimal sulfidation can be achieved within the range of 500-600℃. Comparing Example 7 with Example 1, it can be seen that different ball milling stages in the first ball milling reaction have a certain impact on the material properties. In Example 7, which uses the second approach, the two-stage ball milling refines the material, allows for a more complete reaction, and results in a more uniformly dispersed final product, thus leading to superior electrochemical performance.

[0123] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-confined tin-iron sulfide composite material, characterized in that... Includes the following steps: (1) Iron salt and tin salt are mixed, ball-milled, and washed to obtain ferric hydroxystannate precursor, wherein the molar ratio of iron salt to tin salt is 1:(1~2). (2) The precursor of ferric hydroxystannate is mixed with a carbon source and subjected to secondary ball milling for 2-5 h. After washing, carbon composite ferric hydroxystannate intermediate is obtained. The mass ratio of the precursor of ferric hydroxystannate to the carbon source is (0.5-2.5):

1. (3) The carbon-composite iron stannate oxide intermediate and the sulfur source are heat-treated in an inert atmosphere at a temperature of 500~600 ℃ to obtain a composite material in which tin iron sulfide nanoparticles are uniformly grown on a carbon matrix, namely, a carbon-confined tin iron sulfide composite material; the mass ratio of the carbon-composite iron stannate oxide intermediate to the sulfur source is 1:(2~8). The ball milling in step (1) includes the following stages: First stage: using large grinding balls as the main material, the material particles are crushed. The total mass ratio of iron salt and tin salt to the mass of grinding balls is 1:(10~40). The diameter of the large grinding balls is 15~25 mm, the diameter of the small grinding balls is 3~7 mm, and the mass ratio of large to small grinding balls is (7.5:2.5)~(8.5:1.5). The ball milling time is 1~2 h, and the rotation speed is 400~600 rpm. Second stage: without changing the ball-to-material ratio, some of the large grinding balls are replaced with small grinding balls of the same mass. The crushed raw material particles are mixed and refined, and the reaction is promoted. The mass ratio of large to small grinding balls is (2.5:7.5)~(3.5:6.5). The ball milling time is 2~4 h, and the rotation speed is 300~500 rpm.

2. The preparation method according to claim 1, characterized in that: In step (1), the iron salt is anhydrous ferric chloride, ferrous sulfate heptahydrate, or ferric nitrate nonahydrate.

3. The preparation method according to claim 1, characterized in that: In step (1), the tin salt is sodium stannate trihydrate or potassium stannate trihydrate.

4. The preparation method according to claim 1, characterized in that: In step (2), the carbon source is Super P, Ketjen Black or acetylene black.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of the oxidized ferric stannate precursor to the ball milling beads is 1:(10~40), and the rotation speed is 200~600 rpm.

6. The preparation method according to claim 1, characterized in that: In step (3), the sulfur source is sulfur powder, thiourea or thioacetamide.

7. The preparation method according to claim 1, characterized in that: In step (3), the heat treatment holding time is 1 to 3 hours; the inert atmosphere is nitrogen or argon.

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