Preparation method and application of tin-iron sulfide composite material constructed by carbon confinement

Abstract

The invention relates to the field of sodium ion batteries, and discloses a preparation method and application of a tin-iron sulfide composite material constructed in a carbon confinement range. According to the preparation method, an oxidized hydroxyl ferric stannate precursor is prepared through a mechanochemical reaction, a carbon composite structure is constructed through secondary ball milling, and finally the tin-iron sulfide carbon composite material is obtained through gas-phase vulcanization. The method is simple in preparation, realizes solvent-free production in the preparation process, and has the advantages of environmental protection, high yield and the like; the finally obtained tin-iron sulfide carbon composite material shows excellent cycle performance and rate capability when being used as a sodium-ion battery negative electrode material.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a preparation method and application of a carbon-confined tin-iron sulfide composite material. Background Art

[0002] In recent years, the massive consumption of fossil fuels has caused significant pollution and damage to the environment. As global demand for energy 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 widely used commercial electrochemical energy storage devices, but the scarcity and uneven global distribution of lithium resources have limited their large-scale application. Against this backdrop, sodium-ion batteries, due to their abundant resources, low cost, and similar operating principles, are considered one of the most promising alternatives to lithium-ion batteries. Sodium-ion batteries hold broad promise in the field of electrochemical energy storage and are expected to play an important role in the future.

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

[0004] Researchers have proposed several strategies to solve the above problems, such as nanostructure design, carbon material composite, and heterojunction construction. Among them, Chinese patent CN114068904A provides a carbon-coated tin-based sulfide composite material, its preparation method and application. Specifically, the invention first obtains a nano-spherical tin dioxide precursor by hydrolysis of stannate, and coats a layer of polydopamine on its surface, and then obtains a carbon-coated tin sulfide composite material through carbonization and sulfurization treatment. The carbon-coated structure designed by the invention effectively suppresses the volume change of tin-based sulfide during the charge and discharge process, and at the same time improves the electrical conductivity of the material. This material is applied to sodium ion battery negative electrode materials, which significantly improves the rate performance and cycle stability of the material. However, in this technical solution, a long hydrolysis reaction will lead 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 a preparation method thereof. This method first obtains a ZnSn(OH)6 precursor through a coprecipitation reaction under alkaline conditions, then disperses the precursor in a buffer solution and compounds it with dopamine hydrochloride to obtain a ZnSn(OH)6@C intermediate. Finally, high-temperature carbonization and vapor-phase sulfurization are performed to obtain a zinc-tin binary sulfide / carbon nanocubic composite material ZnS / SnS2@C. This heterojunction design exerts the synergistic effect of multiple components and significantly improves the electrochemical performance of the material. Currently, the processes used to prepare bimetallic sulfide carbon composite materials are mainly hydrothermal and coprecipitation methods, but both preparation methods have harsh conditions, are time-consuming, cause significant environmental pollution, and have complex preparation processes. Therefore, it is still necessary to explore an efficient and environmentally friendly synthesis method to prepare bimetallic sulfide carbon composite electrode materials with high specific capacity. Summary of the Invention

[0005] In response to the above-mentioned technical problems, the present invention provides a method for preparing a carbon-confined tin-iron sulfide composite material and its application. The present invention prepares an oxidized hydroxy-iron stannate precursor through a mechanochemical reaction, realizes the construction of a carbon composite structure through secondary ball milling, and finally obtains a tin-iron sulfide-carbon composite material through vapor phase sulfidation. The method is simple to prepare, reduces the use of solvents in the preparation process, and has the advantages of being green, environmentally friendly, and having high yields. The tin-iron sulfide-carbon composite material finally obtained exhibits excellent cycle performance and rate performance when used as a negative electrode material for sodium ion batteries.

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

[0007] (1) Iron salt and tin salt are placed in a ball mill, and an oxidized hydroxystannate iron precursor is obtained through a mechanochemical reaction and subsequent washing.

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

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

[0010] Tin-iron bimetallic sulfide has a high sodium storage capacity, and iron disulfide has a narrow band gap (0.7eV), which can form a built-in electric field with tin disulfide having a wide band gap (2.1eV), thereby promoting interfacial reaction kinetics and ion transport. The bimetallic heterogeneous interface provides more sodium storage sites, which makes the sodium storage capacity of tin-iron bimetallic sulfide higher. At the same time, the built-in electric field formed reduces the resistance to ion diffusion and accelerates the transmission of ions. Therefore, it is expected to obtain high-performance sodium storage negative electrode materials by using a mechanochemical method to prepare tin-iron sulfide and composite it with a carbon material. The present invention adopts a mechanochemical method to prepare an oxidized hydroxyl stannate iron precursor, and mixes it with a carbon material by ball milling, and finally obtains a tin-iron sulfide carbon composite material by gas phase sulfidation. The present invention adopts a mechanochemical method to prepare an oxidized hydroxyl stannate iron precursor. The preparation method of this method is simple, the synthesis process is green and environmentally friendly, and can avoid the problems of traditional hydrothermal and coprecipitation synthesis methods, reduce the reaction solvent, shorten the reaction time, and is conducive to large-scale production.

[0011] Specifically, during the first ball milling process in step (1), the main reactions that occur are divided into two stages. First, the raw material particles are broken and evenly mixed under the action of mechanical force; second, the mechanical force causes the iron ions and stannate ions to react to form a relatively uniformly sized oxidized hydroxystannate iron precursor. During the second ball milling process, the resulting precursor is ball milled and mixed with the carbon material to uniformly distribute the oxidized hydroxystannate iron precursor on the carbon matrix. Subsequently, through vapor phase sulfurization, the precursor reacts with the sulfur source to form a tin-iron bimetallic sulfide material, resulting in a composite material having tin-iron bimetallic sulfide particles uniformly grown on the carbon matrix.

[0012] In summary, the composite obtained by the present invention has the following advantages when used as a sodium ion negative electrode material: (1) the composite of carbon materials not only improves the electrical conductivity of the material, but also plays a role in the spatial confinement effect of carbon materials, effectively alleviates the volume change of sulfide materials during the charge and discharge process, and enhances the structural stability of the material; (2) the introduction of bimetallic sulfide to construct a heterojunction generates a large amount of lattice mismatch, distortion and defects on the heterojunction interface, which is a good choice for Na + The composite material provides abundant active sites for the transport of ions and also promotes ion transport; (3) When used as the negative electrode of sodium ion batteries, it has excellent cycle and rate performance.

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

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

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

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

[0017] The second stage: without changing the ball-to-material ratio, some large ball milling beads are replaced with small ball milling beads of the same mass, the crushed raw material particles are mixed and refined, and the reaction is promoted; the mass ratio of large and small ball milling beads is (2.5:7.5) to (3.5:6.5), the ball milling time is 2 to 4 hours, and the rotation speed is 300 to 500 rpm.

[0018] In the preparation process using the ball milling process of the second scheme, the main reaction process is as follows: large ball milling beads are placed together with the metal salt raw material in a ball mill jar. The metal salt raw material is broken into smaller particles by the mechanical force of the large ball milling beads at a high speed. When the size of the raw material particles is broken to roughly the same, most of the large ball milling beads are replaced with small ball milling beads. The specific surface area of the ball milling beads is increased, and the ball milling is performed again to further mix and refine the broken material particles. The reaction during the ball milling process mainly occurs on the surface of the ball milling beads. When the ball milling beads collide with each other, the contact surface generates high temperature. The energy generated will induce a chemical reaction between the tin salt and the iron salt. At the same time, the crystal water in the raw materials contains hydroxyl groups, making it easier for the materials to react, achieving synthesis between the reaction materials. Compared with the first scheme, the material particles obtained by the second scheme are smaller in nanometer size and do not agglomerate.

[0019] Preferably, in step (1), in order to obtain the iron oxidized hydroxystannate precursor, the present invention found that the molar ratio of tin salt to iron salt is very critical. If the iron salt is too much compared to the tin salt, the reaction will produce by-products; if the iron salt is too little compared to the tin salt, the excess tin salt will hydrolyze to produce tin oxide, affecting the successful synthesis of the iron oxidized hydroxystannate precursor. Ultimately, the present invention found that the best effect was achieved when the molar ratio of iron salt to tin salt was controlled in the range of 1: (1-2).

[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 very critical. If the carbon source is introduced during the ball milling stage of step (1), the introduced carbon source will exhibit a negative charge due to the presence of surface oxygen-containing functional groups (such as carboxyl and hydroxyl groups). 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 oxidized hydroxyl stannate iron precursor particles. The tin salt that does not participate in the reaction generates tin oxide byproducts during the ball milling and water washing process. On the other hand, if the carbon source is too much than the precursor, the precursor will be completely wrapped, and agglomeration will occur between the particles, affecting the efficiency of ball milling. If the carbon source is too little than the precursor, the dispersion of the carbon source in the material is limited, resulting in an incomplete conductive carbon matrix, which affects electron transport. Finally, the present invention found that the best effect was achieved when the carbon source was introduced into the carbon source during the second ball milling in step (2) and the mass ratio of the precursor to the carbon source was controlled in the range of (0.5 to 2.5):1.

[0021] Preferably, in step (3), in order to obtain a tin-iron sulfide-carbon composite material with excellent performance after heat treatment and sulfurization, the present invention limits the mass ratio of the intermediate product to sulfur powder to 1: (2-8). When the mass ratio of the intermediate product to sulfur powder is too low, sulfur residue will result, causing environmental pollution problems. When the mass ratio of the intermediate product to sulfur powder is too high, it will lead to insufficient reaction, reduce the yield of the target product, and also affect its performance.

[0022] Preferably, in step (1), the tin salt is sodium stannate trihydrate or potassium stannate trihydrate; and 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° C., and the holding time is 1-3 hours; and 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 present invention has the following beneficial effects:

[0029] (1) The present invention prepares the iron oxidized hydroxystannate precursor by ball milling mechanochemical method, which avoids the problems of long time cycle and large amount of solvent consumption in traditional hydrothermal method, coprecipitation method and other synthetic materials. The synthesis process is simple, efficient, green and environmentally friendly, with high yield, and can be used for large-scale industrial production.

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

[0031] (3) The present invention uses iron oxidized hydroxystannate as a precursor to derive bimetallic sulfide, forming a heterojunction between the two-phase components. The resulting built-in electric field reduces the ion diffusion barrier, accelerates ion transmission, and significantly improves sodium storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the X-ray diffraction pattern of the final product prepared in Example 3 of the present 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 1 is a cycle performance diagram of Example 1 of the present invention and Comparative Example 1;

[0036] Figure 5 1 is a rate performance diagram of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

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

[0038] Example 1

[0039] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride, and 30 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0040] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 5 h at a speed of 400 rpm to obtain a precursor;

[0041] (3) 300 mg of the precursor, 150 mg of Super P, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0042] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 300 rpm to obtain an intermediate;

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

[0044] Example 2

[0045] (1) 3 mmol of potassium stannate trihydrate, 2 mmol of ferric nitrate nonahydrate, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0046] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 6 h at a speed of 400 rpm to obtain a precursor;

[0047] (3) 200 mg of the precursor, 100 mg of acetylene black, and 10 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0048] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 500 rpm to obtain an intermediate;

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

[0050] Example 3

[0051] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of ferrous sulfate heptahydrate, and 25 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0052] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 6 h at a speed of 600 rpm to obtain a precursor;

[0053] (3) 300 mg of the precursor, 200 mg of Ketjen black, and 30 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0054] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 5 h at a speed of 300 rpm to obtain an intermediate;

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

[0056] Example 4

[0057] (1) 3 mmol of sodium stannate trihydrate, 2 mmol of ferric nitrate nonahydrate, and 15 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0058] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 4 h at a speed of 400 rpm to obtain a precursor;

[0059] (3) 200 mg of the precursor, 250 mg of Super P, and 15 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0060] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 2 h at a speed of 300 rpm to obtain an intermediate;

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

[0062] Example 5

[0063] (1) 3 mmol of potassium stannate trihydrate, 1.5 mmol of anhydrous ferric chloride, and 25 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0064] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 7 h at a speed of 300 rpm to obtain a precursor;

[0065] (3) 200 mg of the precursor, 300 mg of Ketjen black, and 40 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0066] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 4 h at a speed of 500 rpm to obtain an intermediate;

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

[0068] Example 6

[0069] (1) 2 mmol of potassium stannate trihydrate, 1 mmol of ferrous sulfate heptahydrate, and 40 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0070] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 4 h at a speed of 300 rpm to obtain a precursor;

[0071] (3) 500 mg of the precursor, 200 mg of acetylene black, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0072] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 300 rpm to obtain an intermediate;

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

[0074] Example 7

[0075] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride, 25 g of large (20 mm diameter) agate milling beads, and 5 g of small (5 mm diameter) agate milling beads were added to a ball mill;

[0076] (2) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 2 h at a speed of 400 rpm;

[0077] (3) After step (2) is completed, the ball milling beads in step (1) are replaced with 9 g of large (20 mm diameter) agate ball milling beads and 21 g of small (5 mm diameter) agate ball milling beads, and the ball milling is continued for another 3 h at a speed of 400 rpm;

[0078] (4) 300 mg of the precursor, 150 mg of Super P, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0079] (5) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 300 rpm to obtain an intermediate;

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

[0081] Comparative Example 1

[0082] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride, and 30 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0083] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 5 h at a speed of 400 rpm to obtain a precursor;

[0084] (3) 300 mg of the precursor, 100 mg of Super P, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0085] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 300 rpm to obtain an intermediate;

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

[0087] Comparative Example 2

[0088] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of ferrous sulfate heptahydrate, and 25 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0089] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 600 rpm to obtain a precursor;

[0090] (3) 300 mg of the precursor, 200 mg of Ketjen black, and 30 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0091] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 2 h at a speed of 300 rpm to obtain an intermediate;

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

[0093] Comparative Example 3

[0094] (1) 3 mmol of sodium stannate trihydrate, 0.5 mmol of ferric nitrate nonahydrate, and 15 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0095] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 4 h at a speed of 400 rpm to obtain a precursor;

[0096] (3) 200 mg of the precursor, 250 mg of Super P, and 15 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0097] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 2 h at a speed of 300 rpm to obtain an intermediate;

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

[0099] Comparative Example 4

[0100] (1) 2 mmol of sodium stannate trihydrate, 2 mmol of anhydrous ferric chloride, and 30 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0101] (2) The ball mill jar was transferred to a planetary ball mill and assembled, and then ball milled for a total of 5 h at a speed of 400 rpm to obtain a precursor;

[0102] (3) 300 mg of the precursor, 650 mg of Super P, and 20 g of agate milling beads with a diameter of 10 mm were added to a ball mill;

[0103] (4) The ball mill was transferred into a planetary ball mill and assembled, and then ball milled for a total of 3 h at a speed of 300 rpm to obtain an intermediate;

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

[0105] Performance Testing

[0106] The final product obtained in each embodiment and comparative example is mixed with a conductive agent (Super P) and a binder (PVDF) in a mass ratio of 7:2:1. The product and the conductive agent are first mixed in a fixed ratio, ground several times, and then evenly mixed. A fixed ratio of PVDF is added and a suitable amount of solvent N-methylpyrrolidone (NMP) is used to make a homogeneous slurry. The slurry is then evenly coated on the current collector (copper foil). After drying at a constant temperature of 60°C for 12 hours, a 12 mm pole piece is punched out by a slicer as an electrode. Glass fiber is used as a diaphragm, a metal sodium sheet is used as a counter electrode, and 1.0 mol L -1A half-cell was assembled using NaPF6 as the solute and diglyme as the solvent. The cell was assembled in an argon-filled glove box, following the order of the cathode shell, prepared electrode, separator, electrolyte, sodium metal sheet, nickel foam, and anode shell. The assembled sodium-ion half-cell was allowed to rest for 24 hours before electrochemical testing was performed under constant temperature.

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

[0108] Figure 2 The scanning electron microscope image of the final product prepared in Example 4 of the present invention shows that the final product is evenly dispersed without obvious agglomeration, and the particle size is 40 to 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. Figure 2 (Example 4) More flaky materials can be seen stacking. This is because the raw materials in Comparative Example 3 contain more tin salt than iron salt, resulting in residual tin salt, which hydrolyzes to form tin oxide during ball milling and water washing. After vapor phase sulfidation, more flaky SnS2 is generated, resulting in the stacking distribution of the material.

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

[0111] Figure 5 The rate performance diagram of Example 1 of the present invention and Comparative Example 1 is shown. In Example 1, the sodium ion battery is at 0.2Ag. -1 , 0.5Ag -1 , 1Ag -1 , 2Ag -1 , 5Ag -1 and returns 0.2Ag -1 The reversible specific capacities at current densities of 701.1 mAh g -1 , 613.6mAh g -1、579.5mAh g -1 、541.1mAh g -1 、420.0mAh g -1 、657.1mAh g -1 , compared with Comparative Example 1, it exhibits excellent rate performance.

[0112] The capacities at the 50th cycle and the first cycle coulombic efficiencies of the embodiments 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 1Ag -1 At a current density of , the capacity of the half-cell at 50 cycles and the coulombic efficiency of the first cycle. Comparing Example 1 with Comparative Example 1 and Comparative Example 4, it can be seen that the ratio of the precursor to the carbon source has a significant effect on the performance of the material. If there is too much carbon source (Comparative Example 4), the material will be severely agglomerated, and the carbon matrix will not be loaded with enough effective active substances, resulting in a lower capacity of the battery. If there is too little carbon source (Comparative Example 1), the sulfide cannot be confined, the sulfide material grows, and the diffusion resistance is increased. The volume changes greatly during the charge and discharge process, affecting the cycle stability. Comparing Example 4 with Comparative Example 3, it can be seen that the ratio of metal salts has an important influence on the structure and performance of the material. If the proportion of stannate is too high (Comparative Example 3), the stannate will undergo a self-hydrolysis reaction to generate tin oxide during the ball milling reaction, which affects the synthesis of oxidized hydroxy iron stannate, such as Figure 3 As shown, the composite material grows more SnS2 flake structures, and the synthesis of bimetallic sulfides is also affected, which in turn affects the performance of the material.

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

[0119] Table 2

[0120]

[0121] Test with voltage window of 0.01~3V

[0122] Table 2 shows the capacity of each embodiment and comparative example at different current densities. Comparing Example 3 with Comparative Example 2, it can be seen that the ball milling time has a great influence on the performance of the material. In the first ball milling of Comparative Example 2, when the ball milling time is short, the raw materials are not completely refined, resulting in insufficient contact reaction and mixing of tin salt and iron salt, which will affect the synthesis and dispersion of the precursor material. In the second ball milling, if the ball milling time is too short, the carbon source and precursor material will not be evenly mixed, and the obtained product will be seriously agglomerated, affecting the performance of the material. When the ball milling time is set longer in Example 3, the raw materials can be fully mixed and refined, and can be evenly dispersed. Comparing Example 6 with Example 1, it can be seen that the vulcanization conditions have an important influence on the performance of the material. When the vulcanization temperature is low (Example 6), the sulfur powder cannot completely sublimate and react with the material during the gas phase vulcanization process, but is adsorbed on the surface of the material in the form of physical adsorption. The relative proportion of active substances is low, which also limits the capacity of the material. The best vulcanization can be achieved within the range of 500-600°C. Comparing Example 7 with Example 1, it can be seen that the different ball milling stage settings in the first ball milling reaction have a certain impact on the material properties. In Example 7, which adopts the second solution, the two-stage ball milling refines the material, resulting in a more complete reaction and a more uniform dispersion of the final product, resulting in superior electrochemical performance.

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

[0124] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a carbon-confined tin-iron sulfide composite material, characterized in that The following steps are involved: (1) mixing an iron salt and a tin salt, ball milling the mixture, and washing the mixture to obtain an oxidized hydroxystannate iron precursor, wherein the molar ratio of the iron salt to the tin salt is 1:(1-2); (2) mixing an oxidized hydroxystannate iron precursor with a carbon source, performing secondary ball milling, and washing to obtain a carbon-composite oxidized hydroxystannate iron intermediate, wherein the mass ratio of the oxidized hydroxystannate iron precursor to the carbon source is (0.5-2.5):1; (3) The carbon-composite oxidized hydroxyl iron stannate intermediate and the sulfur source are heat-treated under an inert atmosphere to obtain a composite material having tin iron sulfide nanoparticles uniformly grown on a carbon matrix, i.e., a carbon-confined tin iron sulfide composite material; the mass ratio of the carbon-composite oxidized hydroxyl iron stannate intermediate to the sulfur source is 1:(2-8).

2. The preparation method according to claim 1, wherein: In step (1), The mass ratio of the total mass of the iron salt and the tin salt to the mass of the ball milling beads is 1:(10-40); The diameter of the ball milling beads used in the ball milling is 8 to 12 mm; The ball milling time is 4 to 7 hours, and the rotation speed is 300 to 600 rpm.

3. The preparation method according to claim 1, wherein: In step (1), the ball milling includes the following stages: The first stage: mainly using large ball milling beads to crush the material particles; the total mass ratio of iron salt and tin salt to ball milling beads is 1: (10-40), the diameter of large ball milling beads is 15-25 mm, the diameter of small ball milling beads is 3-7 mm, the mass ratio of large and small ball milling beads is (7.5:2.5) to (8.5:1.5), the ball milling time is 1-2 hours, and the rotation speed is 400-600 rpm; The second stage: without changing the ball-to-material ratio, some large ball milling beads are replaced with small ball milling beads of the same mass, the crushed raw material particles are mixed and refined, and the reaction is promoted; the mass ratio of large and small ball milling beads is (2.5:7.5) to (3.5:6.5), the ball milling time is 2 to 4 hours, and the rotation speed is 300 to 500 rpm.

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

5. The preparation method according to claim 1, wherein: In step (1), the tin salt is sodium stannate trihydrate or potassium stannate trihydrate.

6. The preparation method according to claim 1, wherein: In step (2), the carbon source is Super P, Ketjen black or acetylene black.

7. The preparation method according to claim 1, wherein: In step (2), the mass ratio of the oxidized hydroxystannate iron precursor to the ball milling beads is 1: (10-40), the ball milling time is 2-5 hours, and the rotation speed is 200-600 rpm.

8. The preparation method according to claim 1, wherein: In step (3), the sulfur source is sulfur powder, thiourea or thioacetamide.

9. The preparation method according to claim 1, wherein: In step (3), the heat treatment temperature is 500-600° C., and the holding time is 1-3 hours; the inert atmosphere is nitrogen or argon.

10. Use of the carbon-confined tin-iron sulfide composite material obtained by the preparation method according to any one of claims 1 to 9 as a negative electrode material for sodium ion batteries.

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