Green low-energy low-expansion silicon-carbon negative electrode and preparation method and application thereof
The low-expansion silicon-carbon anode prepared by hydrolysis reaction of organosilicon and carbon source solutions and multi-stage heat treatment solves the problems of structural stability and cycle performance of silicon-carbon anode materials, realizing high-capacity and low-energy-consumption silicon-carbon anode materials suitable for lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN SMART VALLEY NEW ENERGY TECHNOLOGY RESEARCH INSTITUTE CO LTD
- Filing Date
- 2025-07-24
- Publication Date
- 2026-05-19
AI Technical Summary
Existing silicon-carbon anode materials suffer from poor structural stability, are prone to expansion and pulverization, and have low capacity retention, making it difficult to meet the needs of commercial applications.
A colloidal silica precipitate is generated by hydrolysis of an organosilicon source and an organic carbon source solution. After two stages of heat treatment and carbon coating, a porous Si-C composite is formed. The outer carbon coating layer is dense, forming a structurally stable low-expansion silicon-carbon anode.
A silicon-carbon anode material with high reversible capacity, excellent cycle performance and low energy consumption has been achieved, which has commercial application prospects. The porous structure alleviates volume changes, reduces side reactions, and improves first efficiency and cycle stability.
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Figure CN120809792B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon-carbon anode materials for lithium-ion batteries, specifically to a green, low-energy-consumption, low-expansion silicon-carbon anode, its preparation method, and its applications. Background Technology
[0002] With the booming development of the new energy industry, electric vehicles and energy storage systems are placing higher demands on battery performance. The energy density of current commercial lithium-ion batteries is approaching the theoretical upper limit of 300Wh / kg, making the development of new electrode materials an urgent industry need. Under this trend, silicon-based anode materials, with their ultra-high theoretical specific capacity of 4200mAh / g, suitable charge and discharge potentials, and abundant availability in the Earth's crust, have rapidly become a research hotspot.
[0003] However, the industrial application of silicon anodes still faces key bottlenecks: insufficient conductivity of the material itself restricts electron transport speed; the huge volume expansion (about 300%) during charging and discharging easily causes electrode structure failure; and the material pulverization problem caused by repeated cycling seriously affects battery life. To solve these problems, researchers have adopted three innovative strategies: (1) using silicon nanoscale design to reduce the absolute deformation of the material; (2) constructing a porous structure with buffer space; and (3) developing a composite system based on carbon materials—through the synergistic effect of silicon and carbon, the high capacity characteristics of silicon are maintained, while the carbon framework is used to improve conductivity, prevent particle aggregation, and alleviate mechanical stress. These breakthroughs have significantly improved the cycling performance of the electrode, laying an important foundation for the industrialization of the next generation of high-energy-density silicon-carbon anodes.
[0004] Patent CN106058207A introduces a mixture of silicon tetrachloride gas and reducing carrier gas into a reaction chamber containing carbon material. The silicon tetrachloride gas is reduced to elemental silicon, which is then deposited onto the carbon material to form a silicon-carbon composite material. While this method uses inexpensive raw materials and is simple, the difficulty in controlling the porosity of the carbon matrix leads to uneven silicon deposition, uneven stress distribution within the material during charging and discharging, and easy pulverization of the material structure, resulting in poor cycle performance. Furthermore, the high temperature required for directly reducing silicon tetrachloride with a reducing gas increases energy consumption, hindering large-scale application. Patent CN107394176A addresses the technical problem of battery performance degradation caused by the detachment of silicon material from the current collector due to silicon volume changes. It employs electroplating, using silicon tetrachloride as the silicon source, to electrodeposit silicon onto the surface of a three-dimensional carbon material, followed by heat treatment to directly obtain a silicon-carbon negative electrode sheet. Although this invention alleviates the problem of structural pulverization during cycling of silicon-based anodes to some extent, the direct contact between silicon particles and electrolyte, as well as the large specific surface area of the material, lead to low initial efficiency, numerous side reactions, and low cycle capacity retention, resulting in limited practical application value.
[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, excellent cycle performance, and commercial application prospects. Summary of the Invention
[0006] In view of the above-mentioned shortcomings, the present invention provides a green, low-energy-consumption, low-expansion silicon-carbon anode, its preparation method and application. The green, low-energy-consumption, low-expansion silicon-carbon anode prepared by the present invention has the advantages of stable structure, excellent cycle performance and commercial application prospects.
[0007] To achieve the above objectives, the present invention provides a method for preparing a green, low-energy-consumption, low-expansion silicon-carbon anode, comprising the following steps:
[0008] S1. Add the organosilicon source to the organic carbon source solution A. After hydrolysis, dry the solution to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C.
[0009] S2. The common precipitate H2SiO3-C is subjected to two stages of heat treatment, then cooled and ground to obtain a porous Si-C composite.
[0010] S3. The Si-C composite is coated with carbon, then pyrolyzed, cooled and ground to obtain a low-expansion silicon-carbon anode Si-C@C.
[0011] According to one aspect of the present invention, in step S1, the organosilicon source includes at least one of silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide, and hexachlorosilane; the organic carbon source solution A includes organic carbon source A and solvent A, wherein the mass fraction of organic carbon source A in the organic carbon source solution A is 5-60 wt%; 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 molar ratio of the organosilicon source to the organic carbon source is 1-10:2-15; and the solvent A includes deionized water.
[0012] According to one aspect of the invention, solvent A further includes at least one of ethanol, acetone, NMP, and toluene.
[0013] According to one aspect of the present invention, in step S1, the drying temperature is 40-100°C and the time is 1-6 hours.
[0014] According to one aspect of the present invention, in step S2, the two-stage heat treatment is carried out under a protective atmosphere, the protective atmosphere including at least one of nitrogen, helium, argon, and a hydrogen-argon mixture; the two-stage heat treatment includes a low-temperature holding treatment and a high-temperature holding treatment; the low-temperature holding treatment is performed at a temperature of 300-700°C for 1-4 hours; the high-temperature holding treatment is performed at a temperature of 750-1350°C for 6-48 hours.
[0015] According to one aspect of the present invention, in step S3, 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 B in the organic carbon source liquid-phase wet coating includes organic carbon source B and solvent B, the mass fraction of organic carbon source B in the organic carbon source solution B is 20-75 wt%, and the viscosity of the organic carbon source solution B is 100-4000 mPa; 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; the solvent B includes at least one of water, ethanol, acetone, and NMP.
[0016] According to one aspect of the present invention, in step S3, the carbon coating process is as follows: the Si-C composite is mixed evenly with the organic carbon source solution B to obtain a slurry; after removing solvent B from the slurry, it is dried; wherein the solid content of the slurry is 10-80 wt%.
[0017] According to one aspect of the present invention, in step S3, the pyrolysis temperature is 500-1100°C and the time is 1-24h; the protective atmosphere for the pyrolysis includes at least one of nitrogen, helium, and argon.
[0018] Based on the same inventive concept, this invention also provides a green, low-energy-consumption, low-expansion silicon-carbon anode prepared by any of the above-mentioned preparation methods, wherein the carbon content in the low-expansion silicon-carbon anode Si-C@C is 20wt%-80wt%; the outer carbon coating layer of the low-expansion silicon-carbon anode Si-C@C is uniform and dense, with a carbon coating thickness of 0.1-3μm and a specific surface area of 1-20m². 2 / g.
[0019] Based on the same inventive concept, this invention also provides the application of the above-mentioned green, low-energy-consumption, low-expansion silicon-carbon anode in lithium-ion batteries.
[0020] The beneficial effects of this invention are:
[0021] (1) In the preparation method of the present invention, the silica mixed with the organic carbon source at the molecular level has extremely small particle size due to the steric hindrance effect of organic carbon, and is highly dispersed in the carbon matrix. The amorphous state and small particle size of silica give it high reactivity, and it can be carbon reduced at a lower temperature to transform into nano-Si particles, while avoiding the problem of simultaneous generation of silicon carbide at higher temperatures.
[0022] (2) In the preparation method of the present invention, when silica is dehydrated and condensed to form silica, the organic carbon source is simultaneously pyrolyzed, and the water vapor produced by dehydration overflows to realize the pore-forming process of the carbon matrix; the temperature continues to rise, and the carbon in situ reduces silica to silicon, which shrinks in volume and consumes the carbon around the particles. Therefore, there are sufficient pores between the silicon particles and carbon for the expansion and contraction of silicon, which improves the cycle stability; the silicon is obtained by reducing silica to carbon, and is highly dispersed in the carbon matrix with extremely small particle size, small self-volume effect, high reversible capacity, and excellent structural stability; at the same time, the carbon matrix in the Si-C composite is a porous structure, similar to the effect of a sponge, which can further alleviate the volume effect of silicon, limit the volume change within the large particles, and ensure that the silicon-carbon particles as a whole do not expand; the outer coating layer reduces the material specific surface area, isolates the contact between silicon and electrolyte, significantly improves the first efficiency, reduces side reactions, and improves the cycle capacity retention rate;
[0023] (3) In the preparation method of the present invention, organosilicon sources such as silicon tetrachloride and silicon tetrafluoride are dropped into the organic carbon source solution, and the solvent is consumed by hydrolysis. The organic carbon source and silicic acid are simultaneously precipitated, reducing the energy consumption of solvent drying. Hydrogen chloride and hydrogen fluoride gases can be recycled and reacted with low-cost metallurgical micron silicon powder to prepare the process raw materials organosilicon sources - silicon tetrachloride and silicon tetrafluoride. The production process of the present invention has no emissions, and the process is green, environmentally friendly and low cost. The low-expansion silicon-carbon anode material proposed in the present invention has a unique structural design that endows the material with high reversible capacity, excellent cycle performance, excellent rate performance and stable structure. Si-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, but the cost is far lower than that of CVD silicon-carbon anode. It is a silicon-carbon anode material with great application prospects. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the structure of the low-expansion silicon-carbon anode of the present invention;
[0025] Figure 2 This is a comparison chart of the cycling performance of Embodiment 1 and Comparative Example 1 of the present invention.
[0026] Explanation of reference numerals in the attached figures:
[0027] 1. Carbon coating layer; 2. Amorphous carbon; 3. Nano-sized Si particles; 4. Porosity; 5. Porosity within the carbon matrix; Detailed Implementation
[0028] 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.
[0029] To address the problems of poor structural stability, easy expansion and pulverization, and low capacity retention of current silicon-carbon anode materials, the inventors of this application provide a green, low-energy-consumption, low-expansion silicon-carbon anode preparation method, comprising the following steps:
[0030] S1. Add the organosilicon source to the organic carbon source solution A. After hydrolysis, dry the solution to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C.
[0031] S2. The common precipitate H2SiO3-C is subjected to two stages of heat treatment, then cooled and ground to obtain a porous Si-C composite.
[0032] S3. The Si-C composite is coated with carbon, then pyrolyzed, cooled and ground to obtain a low-expansion silicon-carbon anode Si-C@C.
[0033] It should be noted that in step S1, depending on the type of organosilicon source, the way the organosilicon source is added to the organic carbon source solution A for mixing is also different, including at least one of the following mixing methods: gas introduction, slow droplet addition of liquid, direct mixing of liquid, and direct addition of solid powder.
[0034] It should be noted that when the organosilicon source is added to the organic carbon source solution A, it will spontaneously undergo a hydrolysis reaction with water to generate a silicic acid gel precipitate. The hydrolysis reaction consumes water and releases a large amount of heat, so all or most of the solvent is consumed during the hydrolysis reaction. At this time, the organic carbon source will precipitate simultaneously and coexist with the gel silicic acid precipitate, and the two can reach a molecular-level mixed state.
[0035] In some specific implementations, in step S1, the organosilicon source includes at least one of silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide, and hexachlorosilane; the organic carbon source solution A includes organic carbon source A and solvent A, wherein the mass fraction of organic carbon source A in the organic carbon source solution A is 5-60 wt%; 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 molar ratio of the organosilicon source to the organic carbon source is 1-10:2-15; and the solvent A includes deionized water.
[0036] In some specific embodiments, solvent A further includes at least one of ethanol, acetone, NMP, and toluene.
[0037] It should be noted that deionized water in solvent A is mandatory, while ethanol, acetone, NMP, and toluene are not mandatory.
[0038] In some specific implementations, in step S1, the drying temperature is 40-100℃ and the time is 1-6h.
[0039] It should be noted that in step S1, since most of the solvent has been consumed in the hydrolysis process, the drying temperature is lower, 40-100℃, and the drying time is shorter, 1-6h, which greatly reduces energy consumption; and the lower drying temperature can prevent the silica from agglomerating, which is convenient for the subsequent preparation of small-particle-size nano-silicon.
[0040] In some specific implementations, in step S2, the two-stage heat treatment is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, argon, and a hydrogen-argon mixture; the two-stage heat treatment includes a low-temperature holding treatment and a high-temperature holding treatment; the low-temperature holding treatment is performed at a temperature of 300-700℃ for 1-4 hours; the high-temperature holding treatment is performed at a temperature of 750-1350℃ for 6-48 hours.
[0041] It should be noted that, as Figure 1As shown, during the low-temperature insulation treatment, the precipitate H2SiO3-C undergoes the following changes: H2SiO3 dehydrates and condenses to transform into amorphous SiO2, and the organic carbon source pyrolyzes to transform into amorphous carbon 2. Since the two are in a molecular-level mixed state in the precipitate, the generated SiO2 is uniformly dispersed in the amorphous carbon 2. Moreover, thanks to the steric hindrance effect of the organic carbon source or amorphous carbon on the H2SiO3 to SiO2 transformation reaction, SiO2 is difficult to grow after nucleation, so the particle size of SiO2 is extremely small, ranging from 20 to 100 nm. During the dehydration of colloidal H2SiO3, a large number of water molecules escape and play a pore-forming role in the pyrolysis process of the organic carbon source. The amorphous carbon obtained by pyrolysis has a porous structure, and the low-temperature insulation treatment process yields a porous SiO2-C complex.
[0042] It should be noted that, as Figure 1 As shown, the SiO2-C composite undergoes the following changes during the high-temperature insulation treatment: Due to the small particle size and amorphous morphology of SiO2, its reactivity is high. Amorphous carbon reduces SiO2 at high temperature, transforming it into nano-Si particles 3. The reduction process consumes amorphous carbon 2 in contact with SiO2, and the volume of SiO2 shrinks when it transforms into Si particles 3, thus creating voids 4 between amorphous carbon 2 and Si particles 3. The volume of the voids around Si is 2-4 times the volume of the Si particles, reserving space for the expansion of Si. The high-temperature insulation treatment yields a porous (voids 5 within the carbon matrix) Si-C composite with a material specific gravity of 100-1000 μm. 2 / g.
[0043] In some specific implementations, in step S3, 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.
[0044] It should be noted that, as Figure 1 As shown, the purpose of carbon coating in step S3 is to form a dense carbon coating layer 1 on the surface of the porous Si-C composite, thereby reducing the specific surface area of the material while retaining the porous structure of the Si-C composite.
[0045] In some specific embodiments, the organic carbon source solution B in the liquid-phase wet coating of the organic carbon source includes organic carbon source B and solvent B. The mass fraction of organic carbon source B in the organic carbon source solution B is 20-75 wt%, and the viscosity of the organic carbon source solution B is 100-4000 mPa. 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. The solvent B includes at least one of water, ethanol, acetone, and NMP.
[0046] In some specific implementations, in step S3, the carbon coating process is as follows: the Si-C composite is mixed evenly with the organic carbon source solution B to obtain a slurry; after removing solvent B from the slurry, it is dried; wherein the solid (Si-C composite + organic carbon source) content of the slurry is 10-80 wt%.
[0047] In some specific implementations, in step S3, the pyrolysis temperature is 500-1100℃ and the time is 1-24h; the protective atmosphere for the pyrolysis includes at least one of nitrogen, helium, and argon.
[0048] This invention also provides a green, low-energy-consumption, low-expansion silicon-carbon anode prepared by any of the above-mentioned methods, wherein the carbon content in the low-expansion silicon-carbon anode Si-C@C is 20 wt%-80 wt%; the outer carbon coating layer of the low-expansion silicon-carbon anode Si-C@C is uniform and dense, with a carbon coating thickness of 0.1-3 μm and a specific surface area of 1-20 m². 2 / g.
[0049] This invention also provides the application of the aforementioned green, low-energy-consumption, low-expansion silicon-carbon anode in lithium-ion batteries.
[0050] The following examples and comparative models further illustrate this point.
[0051] Example 1
[0052] A method for preparing a green, low-energy-consumption, low-expansion silicon-carbon anode includes the following steps:
[0053] (1) Silicon tetrafluoride gas was slowly introduced into a glucose aqueous solution (45 wt%) to carry out a hydrolysis reaction. The product was dried at 60°C for 4 h to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C; wherein the molar ratio of silicon tetrafluoride to glucose was 2:5.
[0054] (2) The precipitate H2SiO3-C was heated at 600℃ for 2 hours under a nitrogen atmosphere, then heated to 1100℃ for 4 hours. After cooling, it was ground to obtain a porous Si-C composite with a specific surface area of 354 m². 2 / g;
[0055] (3) A 55 wt% sucrose solution was used to perform liquid-phase carbon coating on the Si-C composite. The viscosity of the sucrose solution was 550 mPas. The solid content (Si-C composite + organic carbon source) in the sucrose solution after adding the Si-C composite was 65 wt%. The uniformly mixed solution was spray-dried and then pyrolyzed at 700℃ for 6 h under an argon atmosphere. After cooling, it was ground to obtain a low-expansion silicon-carbon anode material Si-C@C, which contained 52 wt% carbon and had a specific surface area of 5.6 m².2 / g.
[0056] Example 2
[0057] A method for preparing a green, low-energy-consumption, low-expansion silicon-carbon anode includes the following steps:
[0058] (1) Silicon tetrachloride liquid was slowly added dropwise to sucrose aqueous solution (35 wt%) to carry out hydrolysis reaction. The product was dried at 55°C for 5 h to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C; wherein the molar ratio of silicon tetrafluoride to sucrose was 5:4.
[0059] (2) The precipitate H2SiO3-C was heated at 660℃ for 3 hours under a nitrogen atmosphere, then heated to 1150℃ for 6 hours. After cooling, it was ground to obtain a porous Si-C composite with a specific surface area of 257 m². 2 / g;
[0060] (3) A 45 wt% asphalt solution was used to perform liquid-phase carbon coating on the Si-C composite. The solution viscosity was 350 mPas. The solid content (Si-C composite + organic carbon source) in the asphalt solution after adding the Si-C composite was 60 wt%. The uniformly mixed solution was spray-dried, then kept at 750℃ for 3 h under an argon atmosphere. After cooling, it was ground to obtain a low-expansion silicon-carbon anode material Si-C@C, which contained 46 wt% carbon and had a specific surface area of 4.3 m². 2 / g.
[0061] Example 3
[0062] A method for preparing a green, low-energy-consumption, low-expansion silicon-carbon anode includes the following steps:
[0063] (1) Silicon tetraiodide solid powder was slowly added to citric acid aqueous solution (35 wt%), and the mixture was stirred to carry out hydrolysis reaction. The product was dried at 75°C for 8 hours to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C; wherein the molar ratio of silicon tetraiodide to citric acid was 3:8.
[0064] (2) The precipitate H2SiO3-C was kept at 550℃ for 6 hours under a nitrogen atmosphere, then heated to 1250℃ and kept at that temperature for 8 hours. After cooling, it was ground to obtain a porous Si-C composite with a specific surface area of 406 m². 2 / g;
[0065] (3) A 35 wt% glucose solution was used to perform liquid-phase carbon coating on the Si-C composite. The solution viscosity was 204 mPas. The solid content (Si-C composite + organic carbon source) in the glucose solution after adding the Si-C composite was 50 wt%. The uniformly mixed solution was spray-dried and then kept at 800℃ for 2 hours under a nitrogen atmosphere. After cooling, it was ground to obtain a low-expansion silicon-carbon anode material Si-C@C, which contained 57 wt% carbon and had a specific surface area of 3.8 m². 2 / g.
[0066] Comparative Example 1
[0067] The difference between this comparative example and Example 1 is that in step (1), nano-silicon is used directly instead of silicon tetrafluoride, there is no hydrolysis step, and the nano-silicon is dried under the same conditions after being mixed evenly with the organic carbon source solution. Other steps and parameters are the same as in Example 1.
[0068] Comparative Example 2
[0069] The difference between this comparative example and Example 2 is that the concentration of the asphalt solution in step (3) is 15 wt% and the viscosity is 75 mPa. Other steps and parameters are the same as in Example 1.
[0070] Comparative Example 3
[0071] The difference between this comparative example and Example 3 is that step (2) only involves high-temperature heat preservation, and the heat preservation time is extended to 14 hours. Other steps and parameters are the same as in Example 1.
[0072] Performance testing and results analysis:
[0073] The negative electrode materials prepared in Examples 1-3 and Comparative Example 103 were subjected to coin cell performance tests. The electrode areal density was 2 mg cm⁻², the electrolyte solute was LiPF₆, and the solvents were EC, DMC, and DEC in a volume ratio of 0.3:0.3:0.4, with a solute concentration of 1 mol L⁻¹. Half-cell tests were performed, with charge-discharge tests conducted between 0.01 and 1.5 V (at a current density of 50 mA g⁻¹). -1 The first three charge-discharge tests were conducted at a current density of 200 mA g. -1 (Cyclic testing was conducted), and the electrochemical performance is shown in Table 1. The comparison graph of the cyclic performance between Example 1 and Comparative Example 1 is shown below. Figure 1 As shown.
[0074] Table 1:
[0075]
[0076] Depend on Figure 1Comparing with Example 1 and Comparative Example 1 in Table 1, it can be seen that although the two materials in Example 1 and Comparative Example 1 have the same initial reversible capacity due to the same silicon content, the cycle capacity retention rate of the silicon-carbon anode material prepared by nano-silicon decreases sharply due to structural defects. Furthermore, the lack of solvent consumption during hydrolysis significantly increases the energy consumption of the drying process, which is detrimental to reducing production costs. This indicates that when using nano-silicon as a raw material, compared to using silicon tetrafluoride, the shortcomings of the prepared silicon-carbon anode are: there are no voids between the nano-silicon particles and the amorphous carbon matrix, and the amorphous carbon lacks a porous structure formed by water vapor overflow; during charge and discharge, the nano-silicon expands, leading to particle breakage and pulverization, resulting in a sharp decline in cycle performance.
[0077] As can be seen from the comparison between Example 2 and Comparative Example 2 in Table 1, the silicon-carbon anode material coated with the low-viscosity organic carbon source solution has poor cycle performance. This indicates that as the viscosity of the organic carbon source solution decreases, a large amount of organic carbon enters the pores of the amorphous carbon, destroying the porous structure inside the material. This weakens the material's ability to resist the expansion of nano-silicon particles, thus reducing cycle performance.
[0078] As can be seen from the comparison between Example 3 and Comparative Example 3 in Table 1, the initial reversible capacity of Example 3 and Comparative Example 3 is basically the same, but the cycle capacity retention rate of the material with only high-temperature heat treatment is low. This indicates that the material with only high-temperature heat treatment lacks a low-temperature holding process. The dehydration condensation of silicic acid into SiO2, the overflow of water vapor, and the pyrolysis of the organic carbon source are all completed under the heating condition. The process is too violent, so the SiO2 particles formed are larger (resulting in larger nano-silicon particles in the final material). The amorphous carbon obtained by pyrolysis has too large pores and a lower specific surface area. Therefore, the material with only high-temperature heat treatment is not as stable as the material with two-stage heat treatment during cycling.
[0079] 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 green, low-energy-consumption, low-expansion silicon-carbon anode, characterized in that, Includes the following steps: S1. An organosilicon source is added to an organic carbon source solution A. After hydrolysis, the solution is dried to obtain a co-precipitate of colloidal silicic acid and organic carbon source, H2SiO3-C. The organosilicon source includes at least one of silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide, and hexachlorosilane. The organic carbon source solution A includes organic carbon source A and solvent A, with the mass fraction of organic carbon source A in solution A being 5-60 wt%. 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 molar ratio of the organosilicon source to the organic carbon source is 1-10:2-15. Solvent A includes deionized water. S2. The co-precipitate H2SiO3-C is subjected to two-stage heat treatment, followed by cooling and grinding to obtain a porous Si-C composite. The two-stage heat treatment is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, argon, and a hydrogen-argon mixture. The two-stage heat treatment includes a low-temperature holding treatment and a high-temperature holding treatment. The low-temperature holding treatment is performed at 300-700℃ for 1-4 hours; the high-temperature holding treatment is performed at 750-1350℃ for 6-48 hours. S3. The Si-C composite is coated with carbon, then pyrolyzed, cooled and ground to obtain a low-expansion silicon-carbon anode Si-C@C.
2. The method for preparing the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 1, characterized in that, Solvent A further includes at least one of ethanol, acetone, NMP, and toluene.
3. The method for preparing the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 1, characterized in that, In step S1, the drying temperature is 40-100℃ and the time is 1-6h.
4. The method for preparing the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 1, characterized in that, In step S3, 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 B in the organic carbon source liquid-phase wet coating includes organic carbon source B and solvent B, the mass fraction of organic carbon source B in the organic carbon source solution B is 20-75 wt%, and the viscosity of the organic carbon source solution B is 100-4000 mPa; 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; the solvent B includes at least one of water, ethanol, acetone, and NMP.
5. The method for preparing the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 4, characterized in that, In step S3, the carbon coating process is as follows: the Si-C composite is mixed evenly with the organic carbon source solution B to obtain a slurry; after removing solvent B from the slurry, it is dried; wherein the solid content of the slurry is 10-80 wt%.
6. The method for preparing the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 1, characterized in that, In step S3, the pyrolysis temperature is 500-1100℃ and the time is 1-24h; the protective atmosphere for the pyrolysis includes at least one of nitrogen, helium, and argon.
7. A green, low-energy-consumption, low-expansion silicon-carbon anode prepared by the preparation method according to any one of claims 1-6, characterized in that, The carbon content in the low-expansion silicon-carbon anode Si-C@C is 20wt%-80wt%; the outer carbon coating layer of the low-expansion silicon-carbon anode Si-C@C is uniform and dense, with a carbon coating thickness of 0.1-3μm and a specific surface area of 1-20m². 2 / g.
8. The application of the green, low-energy-consumption, low-expansion silicon-carbon anode prepared by any of the preparation methods according to claims 1-6, or the green, low-energy-consumption, low-expansion silicon-carbon anode according to claim 7, in lithium-ion batteries.