A low-expansion silicon-carbon negative electrode material, a preparation method therefor, and an application thereof

Abstract

This invention pertains to lithium-ion battery anode materials, specifically disclosing a low-expansion silicon-carbon anode material, its preparation method, and its applications. The preparation method includes the following steps: dissolving an organic carbon source A, an organic silicon source, and a metal salt in solvent A, followed by a hydrothermal reaction to obtain SiO2-MeO2. x -C complex; wherein Me is selected from at least one of nickel, cobalt, manganese, iron, zinc, tin, titanium, tantalum, niobium, magnesium, aluminum, lead, scandium, vanadium, germanium, molybdenum, zirconium, and copper, and x is a positive number satisfying the valence of Me; SiO2-MeO x The -C complex was carbon-coated to obtain SiO2-MeO x -C@C complex; SiO2-MeO x The -C@C composite is subjected to pyrolysis and reduction at high temperature to obtain the low-expansion silicon-carbon anode material Si-Me-C@C. The low-expansion silicon-carbon anode material prepared by this invention has advantages such as structural stability and excellent cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a low-expansion silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and energy storage technologies, the energy density of traditional lithium-ion batteries has approached its limit of 300 Wh / kg, necessitating the development of novel electrode materials to achieve breakthroughs. Against this backdrop, silicon-based anode materials, with their theoretical specific capacity of up to 4200 mAh / g, suitable operating potential, and abundant natural resource reserves, have become a focus of attention for both academia and industry.

[0003] However, silicon materials face three major challenges in practical applications: first, poor intrinsic conductivity leads to sluggish electrochemical reaction kinetics; second, the approximately 300% volume expansion during lithiation causes electrode structure damage; and finally, particle pulverization during cycling significantly reduces battery life. To address these issues, current research focuses on optimization in three dimensions: (1) reducing absolute volume change through nano-sizing; (2) constructing porous structures to reserve expansion space; and (3) developing silicon-carbon composite material systems. In silicon-carbon composite materials, silicon provides lithium storage capacity, while the carbon matrix not only enhances the conductive network but also effectively inhibits silicon particle agglomeration and buffers mechanical stress. This synergistic design significantly improves the cycling stability of the silicon-carbon composite anode, opening a new path for the practical application of high-energy-density batteries.

[0004] Patent CN116262615B uses a nitrogen-containing alkaline carbon source matrix as the carbon source and prepares a core-shell composite material of silica-coated carbon spheres through the hydrolysis of tetraethyl orthosilicate. A magnesothermic reduction reaction is then performed to obtain NC@Si nanospheres. Although this slightly improves the material's volume expansion and intrinsic electronic conductivity, the direct contact between silicon and the electrolyte exacerbates side reactions, resulting in poor material cycling performance. Furthermore, the silicon prepared by magnesothermic reduction is prone to agglomeration and growth, leading to poor performance. The production process is difficult to control, poses safety hazards, and is costly, making it unsuitable for large-scale production. Patent CN111082014A addresses the problem of poor silicon-carbon mixing uniformity leading to weak bonding. It uses carbon nanotubes as a substrate, loads silica onto the substrate through tetraethyl orthosilicate hydrolysis, and then converts the silica into elemental silicon through high-temperature reduction. Finally, it mixes with pitch and undergoes high-temperature pyrolysis to enhance the bonding between silicon and carbon. The addition of asphalt does indeed improve the bonding strength between silicon particles and carbon nanotubes, thus improving the reversible capacity and cycle stability of the silicon-carbon anode material. However, the silicon-carbon anode material of this invention has an excessively large specific surface area, which leads to more side reactions during cycling and faster reversible capacity decay. Furthermore, the material does not provide space for the volume change of silicon particles. After the silicon expands, it breaks through the outer carbon layer, causing the silicon to directly contact the electrolyte. The continuously generated SEI film leads to poor cycle performance.

[0005] Therefore, given the current problems of poor structural stability, easy expansion and pulverization, and low capacity retention of silicon-carbon anode materials, it is particularly important to develop a silicon-carbon anode material with stable structure and excellent cycle performance. Summary of the Invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a low-expansion silicon-carbon anode material, its preparation method and application. The low-expansion silicon-carbon anode material prepared by the present invention has the advantages of stable structure and excellent cycle performance.

[0007] To achieve the above objectives, the present invention provides a method for preparing a low-expansion silicon-carbon anode material, comprising the following steps:

[0008] S1. Organic carbon source A, organosilicon source, and metal salt are dissolved in solvent A, and then subjected to a hydrothermal reaction to obtain SiO2-MeO. x -C complex; wherein Me is selected from at least one of nickel, cobalt, manganese, iron, zinc, tin, titanium, tantalum, niobium, magnesium, aluminum, lead, scandium, vanadium, germanium, molybdenum, zirconium, and copper, and x is a positive number that satisfies the valence of Me;

[0009] S2, SiO2-MeO x The -C complex was carbon-coated to obtain the SiO2-MeOx-C@C complex;

[0010] S3. The SiO2-MeOx-C@C composite is pyrolyzed and reduced at high temperature to obtain the low-expansion silicon-carbon anode material Si-Me-C@C.

[0011] According to one aspect of the present invention, in step S1, the organic carbon source A includes at least one of glucose, sucrose, citric acid, urea, polyethylene glycol, asphalt, phenolic resin, carboxymethyl cellulose, polyvinylpyrrolidone, polyaniline, polypyrrole, and polyvinylidene fluoride; the organosilicon source includes at least one of tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the metal salt includes at least one of sulfate, nitrate, chloride, acetate, citrate, and oxalate; and the molar ratio of the organic carbon source, organosilicon source, and metal salt is 1-9:1-9:0.05-2.

[0012] According to one aspect of the present invention, in step S1, the solvent A includes at least one of water, ethanol, and acetone; the content of the solvent in the hydrothermal reaction system is 30-90 wt%.

[0013] According to one aspect of the present invention, in step S1, a catalyst is further added to the hydrothermal reaction system, the catalyst being an acid or a base; the acid adjusts the pH of the solution to 1-5, including at least one of hydrochloric acid, sulfuric acid, nitric acid, and oxalic acid; the base adjusts the pH of the solution to 8-11, including at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0014] According to one aspect of the present invention, in step S1, a dispersant is further added to the hydrothermal reaction system, the dispersant including at least one of carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, gelatin, gum arabic, and acrylic acid-maleic anhydride copolymer; the content of the dispersant in the hydrothermal reaction system is 1-10 wt%.

[0015] According to one aspect of the present invention, in step S1, the hydrothermal reaction is carried out at a temperature of 60-220°C for a time of 1-48 hours; after the reaction, the product is washed, filtered, and dried to obtain SiO2-MeO. x -C complex.

[0016] According to one aspect of the present invention, in step S2, the carbon coating method includes at least one of chemical vapor deposition, physical vapor deposition, atomic layer deposition, organic carbon source liquid phase wet coating, and organic carbon source solid phase dry coating.

[0017] The organic carbon source solution in the liquid-phase wet coating process has a viscosity of 10~4000 mPa·s and is composed of organic carbon source B and solvent B. The organic carbon source B includes at least one of glucose, sucrose, citric acid, cellulose, dopamine salt, formaldehyde, phenolic resin, asphalt, coal tar, xylenol, resorcinol, polyacrylonitrile, polypyrrole, polyaniline, and polythiophene, with a concentration of 5~75 wt%. The solvent B includes at least one of water, ethanol, acetone, and NMP.

[0018] According to one aspect of the present invention, in step S3, the temperature of the high-temperature reaction is 750-1300°C, the time is 4-48 hours, and the protective gas is at least one of nitrogen, helium, and argon.

[0019] Based on the same inventive concept, this invention also provides a low-expansion silicon-carbon anode material prepared by any of the above-described preparation methods, wherein the C content in Si-Me-C@C is 20-80 wt%, the Me content in Si-Me-C@C is 0.1-1 wt%, the carbon coating thickness in Si-Me-C@C is 0.1-5 μm, and the specific surface area of ​​Si-Me-C@C is 1-20 m². 2 / g.

[0020] Based on the same inventive concept, the present invention also provides a low-expansion silicon-carbon anode material prepared by any of the above-described preparation methods, or the application of the above-described low-expansion silicon-carbon anode material in lithium-ion batteries.

[0021] The beneficial effects of this invention are:

[0022] (1) In this invention, organic carbon source, organosilicon and metal salt are hydrolyzed in a synergistic manner. Due to the steric hindrance effect of hydrothermal carbon and the effect of dispersant, the silica and metal oxide formed by hydrolysis have extremely small particle size and are highly dispersed in the carbon matrix. The amorphous state and small particle size of hydrolyzed silica give it high reactivity, which can be carbon reduced at a lower temperature and transformed into nano-silicon, while avoiding the problem of simultaneous generation of silicon carbide at higher temperatures.

[0023] (2) The silicon in the silicon-carbon anode material of the present invention is obtained by reducing silicon dioxide carbon. It is highly dispersed in the carbon matrix, with extremely small particle size, small self-volume effect, high reversible capacity, and excellent structural stability. During the high-temperature reduction process, silicon dioxide becomes silicon element, shrinks in volume, and consumes carbon around the particles. Therefore, there are sufficient pores between silicon particles and carbon for silicon to expand and contract, which improves cycle stability. Due to the presence of silicon dioxide and metal oxides, they play a template role. Therefore, the amorphous carbon inside the material has a porous structure, similar to a sponge, which can further alleviate the volume effect of silicon, limit the volume change of silicon to the particles, and ensure that the silicon-carbon particles do not expand as a whole. After the metal oxide is reduced, in-situ doped metal quantum dots are obtained, which can improve the electronic conductivity of the material and significantly improve the rate performance. The outer dense carbon layer reduces the specific surface area of ​​the material, isolates the contact between silicon and electrolyte, significantly improves the first efficiency, reduces side reactions, and improves the cycle capacity retention rate.

[0024] (3) In the preparation method of the present invention, the reduction of silicon dioxide and metal oxide, the pyrolysis of internal amorphous carbon and the pyrolysis of external carbon coating are carried out simultaneously. The process flow is short and it is convenient for large-scale production. The dispersion distribution of silicon and metal doping can be achieved in one step. The unique structural design of the low-expansion silicon-carbon anode material proposed in this patent endows the material with high reversible capacity, excellent cycle performance, excellent rate performance and stable structure. Si-Me-C@C can achieve a structure and performance similar to CVD silicon-carbon. It has a porous elastic structure inside, and Si nanoparticles are embedded in it, which can internally relieve the stress effect of silicon. However, the cost is much lower than that of CVD silicon-carbon anode. It is a silicon-carbon anode material with great application prospects. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the low-expansion silicon-carbon anode material of the present invention;

[0026] Figure 2 This is a comparison chart of the cycle performance of Embodiment 1 and Comparative Example 1 of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Carbon coating; 2. Amorphous carbon; 3. Nano-Si particles; 4. Porosity; 5. Metal. Detailed Implementation

[0029] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0030] To address the problems of poor structural stability, easy expansion and pulverization, and low capacity retention in existing silicon-carbon anode materials, the inventors of this application provide a method for preparing a low-expansion silicon-carbon anode material, comprising the following steps:

[0031] S1. Organic carbon source A, organosilicon source, and metal salt are dissolved in solvent A, and then subjected to a hydrothermal reaction to obtain SiO2-MeO. x -C complex; wherein Me is selected from at least one of nickel, cobalt, manganese, iron, zinc, tin, titanium, tantalum, niobium, magnesium, aluminum, lead, scandium, vanadium, germanium, molybdenum, zirconium, and copper, and x is a positive number that satisfies the valence of Me;

[0032] S2, SiO2-MeO x -C complexes are carbon-coated to obtain SiO2-MeO x -C@C complex;

[0033] S3, SiO2-MeO x The -C@C composite is pyrolyzed and reduced at high temperature to obtain the low-expansion silicon-carbon anode material Si-Me-C@C.

[0034] In some specific implementation schemes, in step S1, the organic carbon source A includes at least one of glucose, sucrose, citric acid, urea, polyethylene glycol, asphalt, phenolic resin, carboxymethyl cellulose, polyvinylpyrrolidone, polyaniline, polypyrrole, and polyvinylidene fluoride; the organosilicon source includes at least one of tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the metal salt includes at least one of sulfate, nitrate, chloride, acetate, citrate, and oxalate; and the molar ratio of the organic carbon source, organosilicon source, and metal salt is 1-9:1-9:0.05-2.

[0035] In some specific implementations, in step S1, solvent A includes at least one of water, ethanol, and acetone; the content of the solvent in the hydrothermal reaction system is 30-90 wt%.

[0036] In some specific implementations, in step S1, a catalyst is also added to the hydrothermal reaction system, and the catalyst is an acid or a base; the acid adjusts the pH of the solution to 1-5, including at least one of hydrochloric acid, sulfuric acid, nitric acid, and oxalic acid; the base adjusts the pH of the solution to 8-11, including at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0037] In some specific implementation schemes, in step S1, a dispersant is also added to the hydrothermal reaction system. The dispersant includes at least one of carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, gelatin, gum arabic, and acrylic acid-maleic anhydride copolymer. The content of the dispersant in the hydrothermal reaction system is 1-10 wt%.

[0038] In some specific implementations, in step S1, the hydrothermal reaction temperature is 60-220℃ and the time is 1-48h; after the reaction, the product is washed, filtered, and dried to obtain SiO2-MeO. x -C complex.

[0039] It should be noted that in step S1, SiO2-MeO x The -C complex is spherical or near-spherical with a particle size of 1-30 μm. During the hydrothermal reaction, the organic carbon source, organosilicon source, and metal salt are simultaneously hydrolyzed to yield carbon matrix C, silicon dioxide SiO2, and metal oxide MeO, respectively. x SiO2 and MeO during hydrolysis x Due to the steric hindrance of the carbon matrix, nucleation is difficult, resulting in particle sizes as small as 2-100 nm. SiO2 particles are small and amorphous, exhibiting high reactivity, thus they can be reduced by carbon at relatively low temperatures. Furthermore, the presence of a dispersant allows SiO2 to react with MeO2. x The particles do not agglomerate but are dispersed within the carbon spheres obtained from the hydrolysis of the organic carbon source.

[0040] In some specific implementations, in step S2, the carbon coating method includes at least one of chemical vapor deposition, physical vapor deposition, atomic layer deposition, organic carbon source liquid phase wet coating, and organic carbon source solid phase dry coating.

[0041] The organic carbon source solution in the liquid-phase wet coating process has a viscosity of 10~4000 mPa·s and is composed of organic carbon source B and solvent B. The organic carbon source B includes at least one of glucose, sucrose, citric acid, cellulose, dopamine salt, formaldehyde, phenolic resin, asphalt, coal tar, xylenol, resorcinol, polyacrylonitrile, polypyrrole, polyaniline, and polythiophene, with a concentration of 5~75 wt%. The solvent B includes at least one of water, ethanol, acetone, and NMP.

[0042] It should be noted that solvent B removal methods include at least one of natural evaporation, heating and stirring to evaporate to dryness, baking or spray drying.

[0043] In some specific implementations, in step S3, the temperature of the high-temperature reaction is 750-1300℃, the time is 4-48h, and the protective gas is at least one of nitrogen, helium, and argon.

[0044] It should be noted that, as Figure 1 As shown, in step S3, the role of the high-temperature reaction is: (1) SiO2-MeO x -C@C particles' outer organic carbon source undergoes high-temperature pyrolysis to become a dense carbon coating layer 1, and the internal hydrothermal carbon further undergoes pyrolysis to become amorphous carbon 2; (2) the internal amorphous carbon 2 is reduced to SiO2 and MeO at high temperature. x They are transformed into nano-Si particles (3) and Me (metal 5), respectively. Simultaneously, the reduction process consumes SiO2 and MeO2. x Contact with amorphous carbon, as well as SiO2 and MeO x When it transforms into Si and Me, the volume shrinks, so voids 4 are generated between the amorphous carbon and Si and Me; the void volume around Si is 2-4 times the volume of Si particles, reserving space for the expansion of Si; the metal 5 obtained by reduction can greatly improve the electronic conductivity of the material in the internal amorphous carbon, thus improving the rate performance.

[0045] The present invention also provides a low-expansion silicon-carbon anode material prepared by any of the above-described preparation methods, wherein the C content in Si-Me-C@C is 20-80 wt%, the Me content in Si-Me-C@C is 0.1-1 wt%, the carbon coating thickness in Si-Me-C@C is 0.1-5 μm, and the specific surface area of ​​Si-Me-C@C is 1-20 m². 2 / g.

[0046] The present invention also provides a low-expansion silicon-carbon anode material prepared by any of the above-described preparation methods, or the application of the above-described low-expansion silicon-carbon anode material in lithium-ion batteries.

[0047] The following examples and comparative models further illustrate this point.

[0048] Example 1

[0049] A method for preparing a low-expansion silicon-carbon anode material includes the following steps:

[0050] (1) Sucrose, tetraethoxysilane, and ferric nitrate were mixed in a molar ratio of 9:3:0.1 and dissolved in 100 ml of a mixed solvent of ethanol and water (volume ratio of ethanol to water is 1:1) (the content of the mixed solvent in the hydrothermal reaction system is 50 wt%). 5 wt% of polyacrylic acid was added as a dispersant, and hydrochloric acid was added to adjust the pH to 2. The mixture was then hydrothermally reacted at 80℃ for 12 h to obtain SiO2-MeO x -C complex; wherein, the above hydrothermal reaction system includes sucrose, tetraethoxysilane, ferric nitrate, mixed solvent and dispersant;

[0051] (2) For SiO2-MeO x The -C complex was subjected to liquid-phase wet coating with an organic carbon source. Glucose was dissolved in deionized water at a mass fraction of 10 wt%, and spray-dried to obtain SiO2-MeO2. x -C@C;

[0052] (3) For SiO2-MeO x -C@C underwent high-temperature pyrolysis and reduction, held at 900℃ for 6 hours under a nitrogen protective atmosphere, and then cooled and ground to obtain the final low-expansion silicon-carbon anode material Si-Me-C@C. The material has a carbon content of 40 wt% and a specific surface area of ​​7 m². 2 / g.

[0053] Example 2

[0054] A method for preparing a low-expansion silicon-carbon anode material includes the following steps:

[0055] (1) Citric acid, tetraethoxysilane, and cobalt sulfate were mixed in a molar ratio of 8:3.5:0.15 and dissolved in 150 ml of a mixed solvent of ethanol and water (volume ratio of ethanol to water is 2:1) (the content of the mixed solvent in the hydrothermal reaction system is 45 wt%). 3 wt% of carboxymethyl cellulose was added as a dispersant, and sulfuric acid was added to adjust the pH to 1.5. The mixture was then hydrothermally reacted at 100℃ for 8 h to obtain SiO2-MeO x -C complex; wherein the above hydrothermal reaction system includes citric acid, tetraethoxysilane, cobalt sulfate, mixed solvent and dispersant;

[0056] (2) For SiO2-MeO x The -C complex was subjected to a liquid-phase wet coating with an organic carbon source. PVP was dissolved in NMP at a mass fraction of 25 wt%, and the solvent was evaporated to obtain SiO2-MeO2.x -C@C;

[0057] (3) For SiO2-MeO x -C@C underwent high-temperature pyrolysis and reduction, held at 1050℃ for 10 hours under an argon protective atmosphere, and then cooled and ground to obtain the final low-expansion silicon-carbon anode material Si-Me-C@C. The material has a carbon content of 55 wt% and a specific surface area of ​​4.7 m². 2 / g.

[0058] Example 3

[0059] A method for preparing a low-expansion silicon-carbon anode material includes the following steps:

[0060] (1) Phenolic resin, tetramethoxysilane, and zinc chloride were mixed in a molar ratio of 9:4:0.2 and dissolved in 200 ml of a mixed solvent of ethanol and water (volume ratio of ethanol to water is 1:1) (the content of the mixed solvent in the hydrothermal reaction system is 55 wt%). 1 wt% polyvinylpyrrolidone was added as a dispersant, and ammonia was added to adjust the pH to 11. The mixture was then hydrothermally reacted at 115℃ for 12 h to obtain SiO2-MeO x -C complex; wherein, the above hydrothermal reaction system includes phenolic resin, tetramethoxysilane, zinc chloride, mixed solvent and dispersant;

[0061] (2) For SiO2-MeO x The -C complex was subjected to a liquid-phase wet coating with an organic carbon source. Phenolic resin was dissolved in ethanol (40 wt%), and the solvent was evaporated to obtain SiO2-MeO2. x -C@C;

[0062] (3) For SiO2-MeO x -C@C underwent high-temperature pyrolysis and reduction, held at 950℃ for 20 hours under an argon protective atmosphere, and then cooled and ground to obtain the final low-expansion silicon-carbon anode material Si-Me-C@C. The material has a carbon content of 61wt% and a specific surface area of ​​3.5 m². 2 / g.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that tetraethoxysilane was replaced with nano-silicon, and other experimental conditions were controlled to be the same as in Example 1 to ensure that the nano-silicon particle size, silicon content, carbon content, and specific gravity were the same in the final material.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 2 is that the temperature for high-temperature pyrolysis and reduction in step (3) is 700°C. Other experimental conditions are controlled in the same way as in Example 2.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 3 is that zinc chloride is not added in step (1), and other experimental conditions are controlled in the same way as in Example 3.

[0069] Comparative Example 4

[0070] The difference between this comparative example and Example 1 is that the amount of 25wt% sucrose added in step (1) is reduced, and the amount of 25wt% glucose added in step (2) is increased to ensure that the carbon content of the final material is the same; other experimental conditions are controlled to be the same as in Example 1.

[0071] Performance testing and results analysis:

[0072] The silicon-carbon anode materials prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to coin cell performance tests, with an electrode areal density of 2 mg / cm². -2 The electrolyte solute is LiPF6, and the solvents are EC, DMC, and DEC in a volume ratio of 0.3:0.3:0.4. The solute concentration is 1 mol / L. -1 Half-cell testing was performed, including charge-discharge tests between 0.01 and 1.5 V (at a current density of 50 mAg). -1 The first three charge-discharge tests were performed (cycle testing was conducted at a current density of 200 mA g⁻¹), and the electrochemical performance is shown in Table 1. The comparison graph of the cycle performance between Example 1 and Comparative Example 1 is shown below. Figure 2 As shown.

[0073] Table 1:

[0074]

[0075] From Table 1 and Figure 2As can be seen from the comparison between Example 1 and Comparative Example 1, when using nano-silicon as raw material, compared with using tetraethoxysilane as raw material, the shortcomings of the prepared silicon-carbon anode are: there are no gaps between the nano-silicon and the amorphous carbon matrix inside the particles. During charge and discharge, the nano-silicon expands, causing the particles to break and pulverize, resulting in a sharp decline in cycle performance. The performance results are shown in Table 1. Although the two materials have the same initial reversible capacity due to the same silicon content, the cycle capacity retention rate of the silicon-carbon anode material prepared with nano-silicon decreases sharply due to structural defects. As can be seen from the comparison between Example 2 and Comparative Example 2, due to the lower temperature of high-temperature pyrolysis and reduction, the reaction of carbon reducing SiO2 is slower, and SiO2 is not completely converted into nano-silicon. SiO2, SiOx and nano-Si coexist in the material. Therefore, as can be seen from Table 1, the initial reversible capacity and initial efficiency of the silicon-carbon anode material prepared at 700℃ are lower. Furthermore, due to the insufficient carbon reduction process, the gaps between silicon and the amorphous carbon matrix are narrower, which cannot completely resist the volume effect of silicon, so the cycle performance of the material is also poor. Comparing Example 3 and Comparative Example 3, it can be seen that the material without zinc chloride lacks internal metal quantum dopants, resulting in lower electronic conductivity and affecting the rate performance. Table 1 shows that the material without zinc chloride has a slightly lower initial reversible capacity at 0.1 C than the material with zinc chloride, and their 0.5 C cycle capacity retention is also basically the same. However, the material without zinc chloride has poorer rate performance, so its reversible capacity at 0.5 C is significantly lower than that with zinc chloride. Comparing Example 1 and Comparative Example 4, reducing the amount of organic carbon source during hydrothermal treatment results in less hydrothermal carbon, which is insufficient in terms of steric hindrance for the SiO2 generated by the hydrolysis of organosilicon. This easily leads to uneven SiO2 distribution and particle growth, meaning that the resulting nano-silicon is unevenly distributed and has a large particle size. Both of these situations severely affect the material's reversible capacity and cycle performance. Table 1 shows that the silicon-carbon anode material prepared by reducing the amount of sucrose has a lower cycle capacity retention because the internal nano-silicon particles are large and easily pulverize during charge and discharge, making it difficult to achieve full capacity utilization.

[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a low-expansion silicon-carbon anode material, characterized in that, Includes the following steps: S1. Organic carbon source A, organosilicon source, and metal salt are dissolved in solvent A, and then subjected to a hydrothermal reaction to obtain SiO2-MeO. x -C complex; wherein Me is selected from at least one of nickel, cobalt, manganese, iron, zinc, tin, titanium, tantalum, niobium, magnesium, aluminum, lead, scandium, vanadium, germanium, molybdenum, zirconium, and copper, and x is a positive number satisfying the valence of Me; the organic carbon source A includes at least one of glucose, sucrose, citric acid, urea, polyethylene glycol, asphalt, phenolic resin, carboxymethyl cellulose, polyvinylpyrrolidone, polyaniline, polypyrrole, and polyvinylidene fluoride; the organosilicon source includes at least one of tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the metal salt includes at least one of sulfate, nitrate, chloride, acetate, citrate, and oxalate; the molar ratio of the organic carbon source, organosilicon source, and metal salt is 1-9:1-9:0.05-2; S2, SiO2-MeO x -C complexes are carbon-coated to obtain SiO2-MeO x -C@C complex; S3, SiO2-MeO x The -C@C composite is subjected to pyrolysis and reduction at high temperature to obtain a low-expansion silicon-carbon anode material Si-Me-C@C; wherein the high temperature reaction is 750-1300℃ for 4-48h, and the protective gas is at least one of nitrogen, helium, and argon.

2. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In step S1, solvent A includes at least one of water, ethanol, and acetone; the content of the solvent in the hydrothermal reaction system is 30-90 wt%.

3. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In step S1, a catalyst is also added to the hydrothermal reaction system. The catalyst is an acid or a base. The acid adjusts the pH of the solution to 1-5 and includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and oxalic acid. The base adjusts the pH of the solution to 8-11 and includes at least one of sodium hydroxide, potassium hydroxide, and ammonia.

4. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In step S1, a dispersant is also added to the hydrothermal reaction system. The dispersant includes at least one of carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, gelatin, gum arabic, and acrylic acid-maleic anhydride copolymer. The content of the dispersant in the hydrothermal reaction system is 1-10 wt%.

5. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In step S1, the hydrothermal reaction is carried out at a temperature of 60-220℃ for 1-48 hours. After the reaction, the product is washed, filtered, and dried to obtain SiO2-MeO. x -C complex.

6. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In step S2, the carbon coating method includes at least one of chemical vapor deposition, physical vapor deposition, atomic layer deposition, organic carbon source liquid phase wet coating, and organic carbon source solid phase dry coating. The organic carbon source solution in the liquid-phase wet coating process has a viscosity of 10~4000 mPa·s and is composed of organic carbon source B and solvent B. The organic carbon source B includes at least one of glucose, sucrose, citric acid, cellulose, dopamine salt, formaldehyde, phenolic resin, asphalt, coal tar, xylenol, resorcinol, polyacrylonitrile, polypyrrole, polyaniline, and polythiophene, with a concentration of 5~75 wt%. The solvent B includes at least one of water, ethanol, acetone, and NMP.

7. A low-expansion silicon-carbon anode material prepared by the preparation method according to any one of claims 1-6, characterized in that, The Si-Me-C@C has a C content of 20-80 wt%, a Me content of 0.1-1 wt%, a carbon coating thickness of 0.1-5 μm, and a specific surface area of ​​1-20 m². 2 / g.

8. The application of the low-expansion silicon-carbon anode material prepared by any one of the preparation methods according to claims 1-6 or the low-expansion silicon-carbon anode material according to claim 7 in lithium-ion batteries.

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