Preparation process of carbon-silicon coated negative electrode material

Abstract

The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a preparation process of a silicon-carbon coated negative electrode material which takes bamboo wood as a biomass carbon source and is combined with nano silicon and a dual carbon coating technology, and the preparation process comprises the following steps: step a, sol loading, step b, vacuum impregnation, step c, interface bonding, step d, inner layer coating and step e, outer layer coating. A silicon-carbon interface in-situ bonding technology and a double-layer carbon coating technology are utilized, a sol-gel method is adopted to construct a Si-O-C chemical bond on the surface of bamboo-based carbon, molecular-level anchoring of silicon particles (20-50 nm) on the surface of a carbon skeleton is achieved, the interface separation problem of traditional mechanical mixing is solved, meanwhile, inner-layer amorphous carbon (2-3 nm) is generated in cooperation with bamboo wood pyrolysis gas, and the surface of the bamboo-based carbon is separated. Then bamboo vinegar is carbonized to form an outer graphitized carbon shell (5-8nm), and the double carbon layers cooperate to inhibit volume expansion of silicon, so that the problem of volume expansion of silicon is solved, and the first charge-discharge efficiency of the battery and the capacity retention rate after circulation are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials for lithium-ion batteries, and particularly to a preparation process of a silicon-carbon coated anode material using bamboo as a biomass carbon source and combining nano-silicon and double carbon coating technologies. Background Art

[0002] The silicon-carbon coated anode material is a new type of anode material applied in fields such as lithium-ion batteries. Generally, it has silicon as the core and is coated with carbon materials on the outside. Among them, silicon, as the active substance providing high capacity, is the main lithium storage part; the carbon materials play various important roles, such as providing good electrical conductivity and buffering the volume change of silicon during charge and discharge. Common structures of silicon-carbon coated anode materials include core-shell structures, i.e., silicon as the core and carbon as the shell layer; there are also yolk-shell structures, three-dimensional porous structures, etc.

[0003] However, traditional silicon-based anode materials have poor cycling performance due to volume expansion (>200%), and conventional biomass carbon materials have low electrical conductivity and a single pore structure. Existing technologies mostly use mechanical mixing methods to compound silicon and carbon, with weak interfacial bonding force and uneven carbon coating thickness. For example, a modified silicon-carbon anode material and its preparation method disclosed in the Chinese invention patent with patent application number CN202211580546.X specifically disclose that the mixing of silicon source and substrate carbon material is a conventional mechanical mixing.

[0004] In addition, the deposition of graphitized carbon layers requires high temperature (>1100°C), with high energy consumption and easy damage to the substrate structure, and cannot effectively inhibit the volume expansion of silicon. For example, an amorphous carbon-silicon-carbon nanofiber-graphite composite material and its preparation method and application disclosed in the Chinese invention patent with patent application number CNCN202010931540.7 specifically disclose the method of using carbon nanofibers to catalyze chemical vapor deposition of silicon and finally depositing amorphous carbon, which is high-temperature graphitized carbon layer deposition.

[0005] Furthermore, the applicant previously applied for a patent with patent application number 202311791667.3 on December 25, 2023. This patent specifically discloses a silicon-carbon anode material and its preparation method to solve the problems of complicated preparation steps and high production costs of existing silicon-carbon anode materials.

[0006] However, the technical solution previously applied by the applicant is only applicable to consumer electronic batteries that are cost-sensitive and have medium performance requirements. For high-end power batteries such as electric vehicles, which require high cycling and low expansion, the technical solution previously applied by the applicant cannot meet the requirements. Summary of the Invention

[0007] To address the above problems, the present invention provides a preparation process for a carbon-silicon coated anode material. By utilizing the in-situ bonding technology of the silicon-carbon interface and the double-layer carbon coating technology, the sol-gel method is used to construct Si-O-C chemical bonds on the surface of bamboo-based carbon, realizing the molecular-level anchoring of silicon particles (20-50 nm) on the surface of the carbon skeleton, solving the interface separation problem of traditional mechanical mixing. At the same time, the inner amorphous carbon (2-3 nm) is generated by the pyrolysis gas of bamboo, and the outer graphitized carbon shell (5-8 nm) is formed by the carbonization of bamboo vinegar liquid. The double carbon layers synergistically inhibit the volume expansion of silicon, solve the problem of silicon volume expansion, and effectively improve the first charge-discharge efficiency of the battery and the capacity retention rate after cycling.

[0008] To achieve the above object, the present invention provides the following technical solutions: A preparation process for a carbon-silicon coated anode material, comprising the following steps: Step a, sol loading: In a ball mill, nano-silicon powder with a purity > 99% and a particle size of 50-80 nm is ball milled with ethanolamine at a mass ratio of 1:0.3 for 2 h to obtain silicon sol, and the rotation speed of the ball mill is 400 rpm. Step b, vacuum impregnation: In a vacuum furnace, under a vacuum degree of 0.1 Pa, the silicon sol in step a is injected into the pores of bamboo-based carbon and dried at 150 °C. The bamboo-based carbon is crushed to 200 mesh before impregnation, and the silicon loading amount of the bamboo-based carbon after impregnation is 15%. The volume of silicon expands by up to 300% during lithiation / delithiation. An excessive silicon content (> 20%) will cause stress concentration inside the composite material, and the carbon matrix cannot effectively buffer the expansion, resulting in electrode cracking and active material shedding, and the cycle life drops sharply. When the silicon content < 15%, the carbon proportion is too high and the capacity contribution is insufficient (the overall capacity < 1500 mAh / g). Therefore, it is preferred that the silicon loading amount of the bamboo-based carbon after impregnation is 15%. Step c, interface bonding: H 2 / Ar mixed gas is introduced into the vacuum furnace, and heat treatment is carried out at 750 °C for 1 h to form a silicon-carbon composite with Si-O-C bonds. H 2 accounts for 10% of the volume ratio of the mixed gas. Step d, inner layer coating: The silicon-carbon composite is transferred to a tube furnace and bamboo pyrolysis gas is introduced to maintain a slightly positive pressure environment (+3 kPa), and deposition is carried out at 650 °C for 30 min to generate an amorphous carbon layer on the surface of the silicon-carbon composite. The flow rate of the bamboo pyrolysis gas introduced into the deposition reactor is 20-50 mL / min. The bamboo pyrolysis gas stays in the preheating zone (300 °C) for 3-5 seconds to remove light components (such as water and methanol) and activate phenolic substances, and stays in the deposition zone (650 °C) for 2-3 seconds to ensure that the aromatic ring polycondensation reaction is completed (conversion rate > 95%). The bamboo pyrolysis gas is obtained by collecting the gaseous components after removing tar by condensation separation from the gas generated during the gradient carbonization process of bamboo-based carbon. Step e: Outer coating. Using the bamboo vinegar liquid atomization CVD method, deposit for 1 h at 900 °C to form a graphitized carbon shell on the surface of the silicon-carbon composite to obtain the silicon-carbon coated anode material. When this silicon-carbon coated anode material is applied to the anode of a lithium battery, the initial charge-discharge efficiency > 92%. Under the conditions of 1C charge-discharge, the capacity retention rate > 91% after 100 cycles, and the volume expansion rate < 120%.

[0009] Mechanical mixing mixes silicon powder and carbon through physical means such as ball milling, only forming a physical contact interface. During the lithium ion insertion / extraction process, the volume change of silicon (> 300%) causes interface stress concentration, leading to particle peeling and the fracture of the conductive network.

[0010] The sol-gel method is molecular-level bonding. Through the hydrolysis-condensation reaction of a silicon source (such as tetraethyl orthosilicate, TEOS), Si-O-C chemical bonds are in-situ generated on the surface of the bamboo-based carbon. Its reaction path is as follows: Si(OR) 4 +H 2 O Si(OH) 4 +ROH -Si-O-C- (reacting with the hydroxyl groups on the carbon surface).

[0011] This process realizes the chemical bonding of silicon and carbon at the molecular scale, and the interface binding energy is as high as 1.5 - 2.0 J / m² (the mechanical mixing is only van der Waals force, and the binding energy < 0.1 J / m²).

[0012] Moreover, the Si-O-C bonds anchor the silicon particles on the carbon skeleton, restricting their expansion direction, reducing the volume expansion rate from 300% to < 120%. At the same time, the SiO 2 / C composite layer (thickness 5 - 8 nm) has both elasticity (modulus ≈ 50 GPa) and rigidity, further absorbing the expansion stress.

[0013] For double-layer carbon coating, the inner layer of the silicon-carbon coated anode material needs to buffer the volume expansion of silicon and requires flexible amorphous carbon, while the outer layer needs high conductivity and mechanical strength, so graphitized carbon is needed. Most of the existing coating material precursors are pitch, and acetylene black, graphene, carbon nanotubes, starch, lignin, etc. are also used. As a precursor for carbon coating materials, pitch can undergo a carbonization reaction at high temperatures. After mixing it with silicon-based materials and performing heat treatment, pitch can be converted into carbon and coated on the surface of silicon particles. However, the carbonization coating of pitch only forms an amorphous carbon structure and cannot endow the silicon-carbon anode material with high conductivity and mechanical strength. The manufacturing costs of acetylene black, graphene, and carbon nanotubes are high. Moreover, acetylene black, graphene, and carbon nanotubes can only form graphite carbon layers and cannot form the inner amorphous carbon layer, while starch and lignin can generate amorphous carbon but cannot generate the outer graphite carbon layer.

[0014] In addition, even when a double-layer carbon coating is adopted, when the precursors of existing carbon-coated materials combine with bamboo-based carbon, it will lead to many carbon layer defects and poor interfacial bonding force. At the same time, when forming the outer-layer graphitized carbon, high temperature is bound to damage the amorphous carbon layer in the inner chamber.

[0015] In the study of "Research on the Pyrolysis Characteristics of Bamboo", it is recorded that when the temperature of bamboo is rapidly pyrolyzed with a heating rate of 28 °C / s, a residence time of 0.76 s, and a temperature of 500 °C, the yield of the liquid-phase product bamboo tar is 48.5%. The main components are 2,6-dimethoxyphenol and 2-methoxyphenol (guaiacol). At the same time, in the "Method and Process for Extracting a Preparation with Disease Prevention and Yield Increase Functions from Bamboo Vinegar", the component content and ratio in the solution after the bamboo vinegar is filtered through three stages are mentioned. Among them, the content of guaiacol is 8-15 parts. The applicant found through research that phenolic substances (guaiacol) in the pyrolysis gas of bamboo can form an amorphous carbon layer with a thickness of 2-3 nm on the surface of bamboo-based carbon through free radical condensation and deoxygenation reactions at a deposition temperature of 650 °C. This amorphous carbon layer is the amorphous carbon layer. Moreover, the pyrolysis gas of bamboo and bamboo vinegar both originate from the same bamboo pyrolysis process, and their active components (phenols, furans) have excellent chemical compatibility with the bamboo-based carbon skeleton, avoiding the problem of interfacial incompatibility between heterogeneous materials. In addition, the natural vascular bundle pores (5-20 μm) of bamboo-based carbon match the molecular sizes (1-3 nm) of the pyrolysis gas / bamboo vinegar, realizing the directional anchoring growth of the carbon layer.

[0016] Therefore, by selecting the pyrolysis gas of bamboo and bamboo vinegar as precursors, through their component specificity, low-temperature reaction activity, and structural adaptability, the three major pain points of high-temperature requirements, interfacial failure, and high cost in the coating of silicon-carbon anodes with traditional carbon sources are solved. This design based on biomass characteristics provides an innovative path for the industrialization of high specific energy and long-life silicon-carbon anodes.

[0017] Furthermore, the volume expansion rate of silicon is as high as 300%, and elastic materials are needed to disperse stress. The elastic modulus of amorphous carbon (≈100 GPa) is close to that of silicon (≈90 GPa). When the thickness is 2-3 nm, it can effectively absorb the expansion stress (the strain energy density reaches 5-8 J / m³), avoiding interfacial peeling. If it is too thin (<1 nm): it cannot uniformly cover the silicon particles, and local stress concentration leads to cracks; if it is too thick (>5 nm): the stress of the carbon layer itself accumulates, which will instead exacerbate the structural instability; the 2-3 nm thin layer allows lithium ions to pass through quickly (diffusion coefficient > 10 -10 cm² / s). If it is too thick, it will extend the diffusion path (for example, when the thickness is 5 nm, the diffusion coefficient decreases by 30%); the hydroxyl group (-OH) of amorphous carbon reacts with the surface oxide of silicon to form a Si-O-C bond. When the thickness is 2-3 nm, the bond density is the highest (≈10 20(bonds / cm³), the binding energy reaches 1.5 - 2.0 J / m² (when it is too thick, the bond density decreases by 50%). Therefore, it is preferred to form an amorphous carbon layer with a thickness of 2 - 3 nm on the bamboo-based carbon surface.

[0018] Specifically, the reaction process of guaiacol to produce an amorphous carbon layer at 650 °C is as follows: 1. Demethylation and dehydroxylation: The methoxy group (-OCH 3 ) and the hydroxyl group (-OH) of guaiacol break, releasing small molecule gases (such as CO, CH 4 ).

[0019] Reaction formula: C7H8O2 → C6H5O· + CH3· + H2O↑.

[0020] 2. Free radical polycondensation: The generated phenoxy radical (C 6 H 5 O·) forms an amorphous carbon network through aromatic ring cross-linking, accompanied by the release of hydrogen.

[0021] Total reaction formula: C 7 H 8 O 2 Amorphous carbon + CO↑ + CO 2 ↑ + H 2 O↑ + H 2 ↑ + CH 4 ↑.

[0022] At the same time, the applicant found through research that guaiacol in bamboo vinegar produces a graphitized carbon layer through deoxygenation aromatization and graphite microcrystal growth at 900 °C.

[0023] Specifically, the reaction process of guaiacol to produce a graphite carbon layer at 900 °C is as follows: 1. Aromatic ring polycondensation: After the benzene ring is deoxygenated, it polycondenses into polycyclic aromatic hydrocarbons (PAHs), and further forms graphite microcrystals.

[0024] Reaction formula: C 7 H 8 O 2 C 6 H 4 (Aromatic ring) + CO↑ + 2H 2 O↑.

[0025] 2. The oxygen-containing functional groups (-OH, -OCH 3 ) in bamboo vinegar eliminate carbon layer dislocations through in-situ oxidation etching during the deposition process, and high temperature promotes the directional arrangement of sp 2 hybridized carbon. By adjusting H in the carrier gas2 The O partial pressure (controlled at 50 - 100 ppm), by utilizing the adsorption of water molecules on the surface of the carbon layer, induces the preferential growth of carbon hexagonal rings along the (002) crystal plane to form a graphitized structure, and etches sp 3 defects through active oxygen (such as methoxy derivatives in bamboo vinegar liquid), increasing the sp² hybridization rate of the carbon layer to 89 - 92% (only 85% for traditional CVD).

[0026] Overall reaction formula: C 7 H 8 O 2 → graphite microcrystals + CO↑ + CO 2 ↑ + H 2 O↑ + H 2 ↑ + CH 4 ↑.

[0027] Therefore, compared with existing anode materials, the silicon-carbon anode material of the present invention has the following advantages: 1. Synergistically inhibiting silicon volume expansion: The in-situ formed Si-O-C or Si-C chemical bonds tightly anchor silicon particles to the inner-layer carbon, preventing silicon from detaching from the carbon layer during expansion. The bonding interface can withstand a volume change of up to 200% without cracking.

[0028] Furthermore, due to the buffering and restraining effects of the double-layer carbon, the inner-layer amorphous carbon (2 - 3 nm) absorbs the silicon expansion stress through its own flexibility, reducing the mechanical strain transmitted to the outer layer; the outer-layer graphitized carbon (5 - 8 nm), with a high modulus (≈1 TPa) carbon shell, restricts the overall expansion of silicon particles, making the overall volume expansion rate < 120% (traditional silicon-carbon materials > 200%).

[0029] 2. Enhancing interface stability and electron transport: The Si-O-C bond constructs a direct electron channel between silicon and carbon, reducing the interface resistance to 0.5 Ω·cm (traditional physical mixing interface > 2 Ω·cm). The inner-layer carbon provides active sites for bonding with silicon, shortening the lithium-ion diffusion path. The high conductivity (120 S / m) of the outer-layer graphitized carbon forms a continuous conductive network, improving the overall electron transport efficiency.

[0030] 3. Optimizing the stability of the SEI film: Chemical bonding eliminates the gap between silicon and carbon, reducing the direct contact between the electrolyte and silicon, and reducing side reactions (such as silicon oxidation and repeated growth of the SEI film). The inner-layer carbon uniformly coats the silicon surface, forming a dense SEI film substrate; at the same time, the rigid structure of the outer-layer carbon maintains the morphology of the SEI film, preventing it from cracking and falling off during cycling. Experiments show that after 100 cycles, the thickness of the SEI film only increases by 30% (traditional materials increase > 100%).

[0031] 4. Improving lithium-ion diffusion kinetics: Oxygen defects in the Si-O-C bonding layer can serve as preferential paths for lithium-ion transport, with the diffusion coefficient increased to 1×10 -10 cm² / s (traditional interface < 5×10 -11 cm² / s). The inner micropores (1-2 nm) provide a high specific surface area (800-1000 m² / g), increasing the lithium-ion adsorption sites; the outer mesopores (5-50 nm) construct fast ion transport channels, and the capacity retention rate is > 89% at a 3C rate.

[0032] 5. Process synergy: After vacuum impregnation with silica sol, the Si-O-C bonding and the deposition of inner amorphous carbon are synchronously achieved by H 2 / Ar heat treatment, reducing the process steps by 30%. The outer graphitized carbon deposited by bamboo vinegar liquid CVD is further annealed at a high temperature (900 °C) to bond the interface, increasing the interface binding energy to 2.1 J / m² (traditional process < 1.0 J / m²).

[0033] As an improvement, the bamboo-based carbon in step b is made from 2-year-old moso bamboo with a moisture content < 8% (the bamboo green layer of 2-year-old moso bamboo, with a lignin content of 25–30%, avoiding bamboo yellow, low fiber content, and avoiding high ash content in old bamboo). After crushing, it is soaked in 0.5 mol / L NH 4 H 2 PO 4 solution for 12 h with a solid-liquid ratio of 1:10. After soaking, gradient carbonization is used to form bamboo-based carbon. Soaking bamboo powder in 0.5 mol / L NH 4 H 2 PO 4 solution allows phosphorus elements to be embedded in bamboo fibers in the form of (PO 4 ) 3- . In the CO 2 activation stage, phosphides catalyze the C-CO 2 reaction, selectively etching the cellulose chain to form uniform mesopores (pore diameter 50 ± 5 nm), and the contribution of SSA (specific surface area) accounts for more than 60%.

[0034] Among them, the gradient carbonization of bamboo-based carbon includes the following steps: Step s1, in the first stage, the soaked moso bamboo fragments are placed in a carbonization furnace. Under N 2 atmosphere protection, the carbonization furnace is heated to 400 °C at a rate of 5 °C / min and held for 2 h; Step s2, in the second stage, the carbonization furnace is heated to 780 - 820 °C, and CO 2 gas is introduced at a flow rate of 45 - 55 mL / min for activation for 3 h. The bamboo-based carbon is in CO 2The specific surface area in the activation stage is controlled at 800 - 1000 m² / g. The pore size distribution of the bamboo-based carbon is a bimodal structure, with the main peaks located at 1.8 nm and 50 nm. Among them, in the first 1.5 h: CO 2 flow rate is 55 mL / min (rapid pore opening to generate mesopores of 50 nm level). In the subsequent 1.5 h: CO 2 flow rate drops to 45 mL / min, and simultaneously 10% H 2 O (water vapor) is introduced to passivate the reaction interface, inhibit excessive etching, and generate micropores of 1.8 nm level (increase SSA by 200 m² / g and avoid pore wall collapse); Step s3, the third stage: The carbonization furnace is heated to 1100 °C and graphitized for 1 h under Ar atmosphere protection to obtain bamboo-based carbon with a hierarchical porous carbon skeleton.

[0035] Traditional biomass carbonization mostly uses direct carbonization at a single temperature (usually 800 - 1000 °C), resulting in a single pore structure (mainly micropores). Gradient carbonization adopts a three-stage design of "low-temperature pre-carbonization (400 °C) → medium-temperature activation (800 °C) → high-temperature graphitization (1100 °C)", and regulates the decomposition order of the three major components (cellulose, hemicellulose, lignin) of bamboo at the molecular scale: Hemicellulose is preferentially decomposed at 400 °C to form initial pores; At 800 °C, the cellulose skeleton is etched under CO 2 activation to expand the pores to the mesopore range; At 1100 °C, the lignin derivatives are directionally graphitized to construct a conductive network.

[0036] In the hierarchical pores, the micropores (1.8 nm) adsorb silica sol through capillary action, and the mesopores (50 nm) provide space for the expansion of silicon particles, enabling the structure to remain intact when the silicon loading reaches 18% (in the traditional process, cracking occurs when the silicon loading > 15%).

[0037] In addition, by controlling the activation temperature, CO 2 flow rate, activation time, and heating rate, the specific surface area of the bamboo-based carbon in the CO 2 activation stage is controlled at 800 - 1000 m² / g. Specifically, for every 10 °C increase in the activation temperature, the SSA increases by approximately 120 m² / g (high temperature promotes the reaction rate of C + CO 2 → 2CO), for every 5 mL / min increase in the CO 2 flow rate, the SSA increases by 80 m² / g (enhance gas diffusion and expand the activation reaction interface), for every 0.5 h extension of the activation time, the SSA increases by 150 m² / g (prolong the etching time), and slow heating (≤ 5 °C / min) is adopted to fully decompose hemicellulose to form an initial pore network (the concentration of the pore size distribution increases by 30%).

[0038] As an improvement, in step e, the bamboo vinegar liquid atomization CVD method includes the following steps: Step t1: Purify the bamboo vinegar liquid. The crude bamboo vinegar liquid is subjected to vacuum distillation at 80 - 85°C with a vacuum degree of -0.08 MPa, and the intermediate fraction with a pH of 3.2 - 3.8 and a density of 1.18 - 1.22 g / cm³ is collected. The proportion of guaiacol contained in the rectified and purified bamboo vinegar liquid is ≥35%; Step t2: Atomization treatment. Add 0.5 wt% ammonium citrate as a dispersion stabilizer before atomization to prevent the bamboo vinegar liquid from coking. During atomization, an ultrasonic atomizer with a frequency of 1.7 MHz is used to atomize the purified bamboo vinegar liquid into droplets with a particle size of 1 - 3 μm, and the atomization rate is controlled at 0.15 mL / min; Step t3: Deposition reaction. A porous carbon carrier support loaded with a silicon-carbon composite is placed in a horizontal tube furnace. The carrier gas system introduces Ar as the carrier gas into the horizontal tube furnace, and the flow rate is controlled in three ways. The main carrier gas carries the atomized bamboo vinegar liquid with a flow rate of 80 sccm, the dilution gas flow rate is 20 sccm, and the tail blowing gas flow rate is 10 sccm. During the deposition process, the temperature in the horizontal tube furnace is controlled in a temperature gradient. The preheating temperature is 300°C, the deposition reaction temperature is 900°C, the reaction residence time is 2 - 3 seconds, the cooling temperature is 650°C, and the entire deposition reaction time is 1 h to form a graphitized carbon shell with a thickness of 5 - 8 nm, and the ID / IG value of the Raman spectrum is controlled at 0.85 - 1.05.

[0039] The main carrier gas (80 sccm) carries the atomized bamboo vinegar liquid into the reaction chamber. The droplets are evenly transported to the high-temperature reaction zone through gas flow, ensuring the effective decomposition and deposition of the precursor. The flow rate of 80 sccm balances the transport efficiency and avoids turbulence, ensuring the uniform distribution of the precursor in the reaction zone.

[0040] The dilution gas (20 sccm) delays the premature decomposition of the precursor. Concentration dilution reduces the local concentration of the precursor before entering the high-temperature zone and reduces the decomposition reaction during the preheating stage. Thermal buffering, through the physical dilution effect of the dilution gas, slows down the thermal shock of the precursor molecules during the heating process, enabling them to start decomposing only when they reach the reaction zone and improving the deposition uniformity.

[0041] The tail blowing gas (10 sccm) maintains the pressure balance in the reaction chamber. Pressure stability is achieved by supplementing the tail blowing gas at the outlet end to offset the pressure changes caused by the entry of the main carrier gas and the dilution gas, preventing gas flow disorders caused by pressure fluctuations. Flow control optimizes the gas flow path, avoids dead zones or vortices, ensures the uniform passage of the reaction gas through the sample surface, and improves the consistency of the deposited layer.

[0042] Therefore, the ratio of the main carrier gas to the dilution gas (4:1) ensures that the precursor is neither overly diluted during transportation nor preheated and decomposed effectively. The tail gas maintains a stable laminar flow state by fine-tuning the system pressure, reducing deposition defects caused by turbulence.

[0043] In addition, at a preheating temperature of 300 °C, the preliminary pyrolysis and activation of the precursor (atomized droplets of bamboo vinegar) remove light components: low-boiling substances in bamboo vinegar (such as water, acetic acid, etc.) evaporate at 300 °C, preventing them from entering the high-temperature zone to form impurities. Phenolic compounds (such as guaiacol) begin to undergo dehydroxylation reactions to generate reactive intermediates (such as phenoxy radicals), preparing for subsequent reactions. By slowly raising the temperature (the carrier gas drives the droplets through the preheating zone), the instantaneous high-temperature explosion of the droplets is prevented, avoiding uneven carbon source distribution.

[0044] At a reaction temperature of 900 °C, efficient cracking of the carbon source and deposition of the graphitic carbon layer occur. Complete cracking, large molecular phenols in bamboo vinegar undergo aromatic ring polycondensation reactions (C 6 H 5 O· → graphite microcrystals) at 900 °C. Graphitization control, high temperature promotes the directional arrangement of sp² hybridized carbon, combined with H 2 O partial pressure regulation (50 - 100 ppm), achieving low-temperature graphitization (compared to 1100 - 1200 °C in traditional CVD). Defect repair, reactive oxygen species (from the methoxy groups in bamboo vinegar) etch sp³ hybrid defects, improving the crystallinity of the carbon layer (ID / IG value of 0.85 - 1.05).

[0045] At a cooling temperature of 650 °C, slow cooling and structural stabilization of the deposited material occur. Stress release, slow cooling from 900 °C to 650 °C avoids thermal stress cracks in the carbon layer due to rapid cooling. Phase transformation control, during the holding stage at 650 °C, the residual stress in the carbon layer is released through atomic rearrangement, while inhibiting the transformation of amorphous carbon to a disordered structure. Interface strengthening, the interface between the silicon substrate and the carbon layer is further bonded (such as Si - O - C bonds) during the cooling process, enhancing the bonding strength.

[0046] Furthermore, by controlling the deposition temperature, precursor atomization particle size, H 2 O partial pressure in the carrier gas, and deposition time, the ID / IG value of the Raman spectrum is controlled. High temperature promotes the directional arrangement of sp² hybridized carbon, reducing ID / IG; too low a temperature (<850 °C) leads to disorder in the carbon layer, increasing ID / IG. The smaller the atomization particle size, the more uniform the diffusion of carbon source molecules, reducing the aggregation of local defects and lowering the ID / IG value. H 2 O molecules selectively etch sp³ hybrid defects, increasing the sp² content (lowering ID / IG). Too short a deposition time results in a discontinuous carbon layer (many defects, high ID / IG); too long leads to over-graphitization (too low ID / IG).

[0047] In addition, the conductivity of graphitized carbon (≈120 S / m) is 12 times that of amorphous carbon (≈10 S / m). A continuous conductive network can be formed with a thickness of 5-8nm, and the resistivity is <0.1 Ω·cm. Too thin (<3 nm): the conductive network is discontinuous and the local resistance surges; too thick (>10 nm): lithium ion diffusion is hindered and the rate performance decreases. The modulus of graphite carbon (≈1 TPa) requires a thickness of ≥5nm to effectively limit the lateral expansion of silicon particles (the volume expansion rate drops from 300% to <120%). Too thin: insufficient rigidity and the carbon layer is easy to break; too thick: the carbon layer is brittle and easy to break during the cycle. When bamboo vinegar CVD is deposited at 900℃ for 5-8 nm, it can ensure: ID / IG=0.85-1.05 (sp² hybridization rate>90%); defect density <5×10¹ 0 cm⁻² (the defect density increases when it is too thick, ID / IG>1.1), therefore, it is preferred to form a graphitized carbon shell of 5-8nm.

[0048] Gradient carbonization and bamboo vinegar CVD will promote each other. The synergistic mechanism of gradient carbonization and bamboo vinegar CVD includes the following aspects: 1. Structure-function coupling design: 1.1. Pore-carbon layer matching: The hierarchical channels produced by gradient carbonization provide "anchor points" for bamboo vinegar CVD: The mesopores (50 nm) serve as the cavities for the silicon particles, and their opening size (≈20 nm) is just enough to allow the small molecular carbon sources (such as C 2 Fragments) enter and form a continuous coating on the silicon surface; After bonding treatment, the silica sol adsorbed by the micropores (1.8nm) forms an "embedded" interface with the carbon layer of bamboo vinegar liquid, thereby improving the interfacial bonding strength.

[0049] 1.2 Thermodynamic synergy: The high-temperature graphitization stage (1100°C) of gradient carbonization has endowed the bamboo-based carbon skeleton with high thermal stability. Therefore, when bamboo vinegar CVD is deposited at 900°C, the substrate will not undergo structural collapse, ensuring uniform growth of the carbon layer.

[0050] 2. Performance multiplier effect: 2.1. Electrical conductivity-mechanical performance synergy: The high conductivity of the bamboo-based carbon skeleton (120S / m) combined with the high modulus of the bamboo vinegar carbon layer (1TPa) makes the overall resistivity of the composite material less than 0.1Ω·cm, while the compressive strength is greater than 500MPa (traditional silicon-carbon materials ≈200MPa).

[0051] 2.2 Improved dynamic stability: The combined action of the gradient carbonized mesoporous buffer layer and the rigid constraint of the bamboo vinegar liquid carbon layer keeps the lithium ion diffusion coefficient at the order of 10 -10 cm² / s (which drops to 10 -12 cm² / s for conventional materials after cycling).

[0052] The beneficial effects of the present invention are as follows: In summary, the silicon-carbon coated anode material prepared by the present invention has good cycling performance, high cycling stability, and a capacity retention rate of 91.3% (1C charge and discharge) after 100 cycles; it inhibits expansion, has a low volume expansion rate, with the volume expansion rate < 120%, high conductivity, and the overall resistivity of the material < 0.1 Ω·cm; it has low cost, with a bamboo utilization rate > 90% and a 60% reduction in cost compared to petroleum-based carbon sources. It is particularly suitable for the technical field of the preparation of silicon-carbon coated anode materials. Description of the Drawings

[0053] Figure 1 It is a schematic diagram of the preparation process flow of the invention; Figure 2 It is a schematic diagram of the gradient carbonization process of bamboo-based carbon of the present invention; Figure 3 It is a schematic diagram of the bamboo vinegar liquid atomization CVD method of the present invention; Figure 4 It is an electron microscope image of the silicon-carbon coated anode material prepared in Example 1 of the present invention; Figure 5 It is an electron microscope image of the silicon-carbon coated anode material prepared in Comparative Example 1 of the present invention; Figure 6 It is an electron microscope image of the silicon-carbon coated anode material prepared in Comparative Example 2 of the present invention; Figure 7 It is an electron microscope image of the silicon-carbon coated anode material prepared in Comparative Example 3 of the present invention; Figure 8 It is an electron microscope image of the silicon-carbon coated anode material prepared in Comparative Example 4 of the present invention. Detailed Embodiments

[0054] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0055] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0056] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0057] Example 1: As Figures 1 to 3 shown, a preparation process of a carbon-silicon-coated anode material includes the following steps: Step a, sol loading: In a ball mill, nano-silicon powder with a purity > 99% and a particle size of 50 - 80 nm is ball-milled with ethanolamine at a mass ratio of 1:0.3 for 2 h to obtain silica sol, and the rotation speed of the ball mill is 400 rpm. Step b, vacuum impregnation: In a vacuum furnace, under a vacuum degree of 0.1 Pa, the silica sol in step a is injected into the pores of bamboo-based carbon prepared by gradient carbonization, dried at 150 °C. The bamboo-based carbon is crushed to 200 meshes before impregnation, and the silicon loading amount of the bamboo-based carbon after impregnation is 15%. Among them, the specific surface area of the bamboo-based carbon in the activation stage is controlled at 800 m² / g, and the pore size distribution of the bamboo-based carbon is a bimodal structure, with the main peaks located at 1.8 nm and 50 nm. 2 The pore size distribution of the bamboo-based carbon is a bimodal structure, with the main peaks located at 1.8 nm and 50 nm. Step c, interfacial bonding: A H 2 / Ar mixed gas is introduced into the vacuum furnace, and heat treatment is carried out at 750 °C for 1 h to form a silicon-carbon composite with Si-O-C bonds. H 2 accounts for 10% of the volume ratio of the mixed gas. Step d, inner layer coating: The silicon-carbon composite is transferred to a tubular furnace and bamboo pyrolysis gas is introduced, maintaining a slightly positive pressure environment (+3 kPa), depositing at 650 °C for 30 min to generate an amorphous carbon layer on the surface of the silicon-carbon composite. The flow rate of the bamboo pyrolysis gas introduced into the deposition reactor is 20 mL / min, and the bamboo pyrolysis gas stays in the preheating zone (300 °C) for 3 seconds and in the deposition zone (650 °C) for 2 seconds. Step e, outer coating: Using the bamboo vinegar liquid atomization CVD method, the bamboo vinegar liquid with 35% guaiacol content after rectification and purification is atomized into droplets with a particle size of 1 μm by an ultrasonic atomizer with a frequency of 1.7 MHz, and the atomization rate is controlled at 0.15 mL / min. The carrier gas system introduces Ar as the carrier gas into the horizontal tube furnace, and the flow rate is controlled in three ways. The main carrier gas carries the atomized bamboo vinegar liquid with a flow rate of 80 sccm, the dilution gas flow rate is 20 sccm, and the tail blowing gas flow rate is 10 sccm. During the deposition process, the temperature in the horizontal tube furnace is controlled in a temperature gradient. The preheating temperature is 300 °C, the deposition reaction temperature is 900 °C, the reaction residence time is 2 seconds, and the cooling temperature is 650 °C. The entire deposition reaction time is 1 h.

[0058] Example 2: Same as Example 1, the difference from Example 1 is: In step d, the flow rate of bamboo pyrolysis gas is 25 mL / min, and the bamboo pyrolysis gas stays in the preheating zone (300 °C) for 4 seconds and in the deposition zone (650 °C) for 3 seconds; in step e, the bamboo vinegar liquid with 38% guaiacol content is atomized into droplets with a particle size of 2 μm, and the reaction residence time is 3 seconds.

[0059] Example 3: Same as Example 1, the difference from Example 1 is: In step d, the flow rate of bamboo pyrolysis gas is 30 mL / min, and the bamboo pyrolysis gas stays in the preheating zone (300 °C) for 5 seconds and in the deposition zone (650 °C) for 3 seconds, forming an amorphous carbon layer with a thickness of 3 nm on the surface of the bamboo-based carbon; in step e, the bamboo vinegar liquid with 40% guaiacol content is atomized into droplets with a particle size of 3 μm, and the reaction residence time is 3 seconds, generating a graphitized carbon shell with a thickness of 7.5 nm on the surface of the silicon-carbon composite.

[0060] Example 4: Same as Example 1, the difference from Example 1 is: In step d, the flow rate of bamboo pyrolysis gas is 35 mL / min; in step e, the bamboo vinegar liquid with 43% guaiacol content.

[0061] Example 5: Same as Example 2, the difference from Example 2 is: In step d, the flow rate of bamboo pyrolysis gas is 40 mL / min, and in step e, the bamboo vinegar liquid with 45% guaiacol content.

[0062] Example 6: Same as Example 3, the difference from Example 3 is: In step d, the flow rate of bamboo pyrolysis gas is 45 mL / min, and in step e, the bamboo vinegar liquid with 50% guaiacol content.

[0063] Example 7: Same as Example 1, the difference from Example 1 lies in: In step d, the flow rate of bamboo pyrolysis gas is 50 mL / min, and the bamboo pyrolysis gas stays in the preheating zone (300 °C) for 5 seconds and in the deposition zone (650 °C) for 3 seconds; in step e, the bamboo vinegar liquid with a guaiacol proportion of 43% is atomized into droplets with a particle size of 3 μm, and the reaction residence time is 3 seconds.

[0064] Comparative Example 1: Same as Example 1, the difference from Example 1 lies in: In step d, the flow rate of bamboo pyrolysis gas is 19 mL / min; in step e, the bamboo vinegar liquid with a guaiacol proportion of 33%.

[0065] Comparative Example 2: Same as Example 7, the difference from Example 7 lies in: In step d, the flow rate of bamboo pyrolysis gas is 55 mL / min; in step e, the bamboo vinegar liquid with a guaiacol proportion of 60%.

[0066] Comparative Example 3: Same as Example 7, the difference from Example 7 lies in: In step d, the flow rate of bamboo pyrolysis gas is 19 mL / min; in step e, the bamboo vinegar liquid with a guaiacol proportion of 60%.

[0067] Comparative Example 4: Same as Example 1, the difference from Example 1 lies in: The bamboo-based carbon is not subjected to gradient carbonization and is obtained by conventional carbonization means.

[0068] For Examples 1-7 and Comparative Examples 1-3, the thickness of the amorphous carbon layer, surface morphology, thickness of the graphitized carbon shell, volume expansion rate, and guaiacol purification cost of the prepared silicon-carbon anode coating material are tested. At the same time, the silicon-carbon anode coating material is successively passed through the existing electrode sheet making, battery assembly, and battery testing methods, and the initial efficiency and capacity retention rate (under a rated capacitance of 0.1 C) after 100 cycles are tested. The test results are shown in Table 1 below: Table 1 Among them, the capacity retention rate after 100 cycles under a rated capacitance of 0.1 C is measured by the charge-discharge blue battery testing method.

[0069] From the comparison between Example 1 and Comparative Example 1 and Comparative Example 2, and the comparison between Example 7 and Comparative Example 2 and Comparative Example 3, it can be seen that when the flow rate of bamboo pyrolysis gas < 20 mL / min, the concentration of active components (such as phenols and furans) in the pyrolysis gas is insufficient, resulting in too low carbon layer deposition rate (< 0.05 nm / s), and the surface of silicon particles cannot be completely coated. In local areas, silicon directly contacts the electrolyte, triggering intense side reactions (such as silicon oxidation and excessive growth of SEI film). When the flow rate of bamboo pyrolysis gas > 50 mL / min, high-speed airflow induces turbulence, resulting in disordered accumulation of precursor molecules on the substrate surface, forming a loose and porous structure (BET specific surface area < 500 m² / g), and even generating through cracks (crack width > 50 nm visible by SEM).

[0070] Furthermore, from the comparison between Examples 1 - 7 and Comparative Examples 1 - 3, and the comparison between Example 1 and Comparative Example 1 and Comparative Example 2, and the comparison between Example 7 and Comparative Example 2 and Comparative Example 3, it can be seen that when the proportion of guaiacol increases from 35% to 50%, the ID / IG value decreases from 0.95 to 0.84, and the sp² hybridization rate increases from 89% to 93%, the graphitization degree is significantly improved, and the corresponding capacity retention rate is significantly improved, while the volume expansion rate gradually decreases. However, when the proportion of guaiacol is 45%, the capacity retention rate reaches a peak of 93%. When the proportion of guaiacol exceeds 45%, due to too high guaiacol concentration, active carbon fragments (such as C 2 、C 2 free radicals) generated by decomposition at high temperature rapidly nucleate in the gas phase, forming a large number of nano-carbon particles. These particles collide with each other in the airflow and aggregate into clusters, rather than being uniformly deposited on the substrate surface, resulting in a decrease in the effective deposition rate, and then a decrease in the thickness of the graphitized carbon shell. When the thickness of the graphitized carbon shell < 5 nm, the stability of the SEI film decreases (the carbon layer is too thin and prone to rupture), resulting in a slight decrease in the capacity retention rate. Moreover, the increase in the proportion of guaiacol will lead to a significant increase in the purification cost (when the proportion of guaiacol > 50%, multi-stage rectification is required, and the energy consumption increases by more than 2 times). Therefore, the proportion of guaiacol of 45% is the performance-cost inflection point, and the cost performance decreases after exceeding it.

[0071] Also, when the proportion of guaiacol < 35%, at low guaiacol concentration, the modulus of the carbon layer decreases from ≈1 TPa to ≈500 GPa, which cannot effectively limit the expansion of silicon particles, resulting in an increase in the volume expansion rate. At the same time, the Si - O - C bond density between the carbon layer and silicon particles decreases (binding energy < 1.0 J / m²), and interface peeling is likely to occur during the cycling process, leading to rapid capacity decay.

[0072] In addition, from the comparison between Example 1 and Comparative Example 4, it can be seen that bamboo-based carbon provides a stable carbon skeleton for the inner layer coating through gradient carbonization. Therefore, the volume expansion rate, initial efficiency, and capacity retention rate of Example 1 are all better than those of Comparative Example 4.

[0073] In summary, during the preparation process, when the inner layer is coated, the input flow rate of bamboo pyrolysis gas is an important factor determining the performance of the amorphous carbon layer. If the flow rate of bamboo pyrolysis gas is too low, incomplete coverage and out-of-control defects will occur. If the flow rate of bamboo pyrolysis gas is too high, turbulent accumulation and incomplete reaction will be caused. Both will seriously damage the structural integrity and electrochemical performance of the carbon layer.

[0074] When the outer layer is coated, the proportion of guaiacol is an important factor determining the performance of the graphitized carbon shell. Moreover, the combination of the inner layer coating and the outer layer coating effectively inhibits the volume expansion of silicon particles, improves the initial efficiency and capacity retention rate. And the gradient carbonized bamboo-based carbon provides a good bottom load for the inner layer coating, further improving the buffering performance of the amorphous carbon layer against the expansion of silicon particles and further reducing the volume expansion rate.

[0075] Through Figures 4 to 8 , it can be clearly compared that Figure 4 the surface of the silicon-carbon coated negative electrode material in Figures 5 - 7 is smooth and there are no defects, while Figure 8 there are defects on the surface of the silicon-carbon coated negative electrode material in Figures 5 - 7 the surface of the silicon-carbon coated negative electrode material in Figure 8 and Figure 4 is smoother than that of the silicon-carbon coated negative electrode material in Figure 4 , but compared with the surface of the silicon-carbon coated negative electrode material in

[0076] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for preparing a carbon-silicon coated negative electrode material, characterized in that: The following steps are involved: Step a, sol loading, in a ball mill, nano silicon powder with a purity of more than 99% and a particle size of 50-80 nm and ethanolamine at a mass ratio of 1:0.3 are ball-milled for 2 hours to obtain silica sol, and the ball mill speed is 400 rpm; Step b, vacuum impregnation, in a vacuum furnace, at a vacuum degree of 0.1 Pa, injecting the silica sol in step a into the pores of the bamboo-based carbon, drying at 150° C., and crushing the bamboo-based carbon into 200 meshes before impregnation; Step c, interface bonding, introducing H2 / Ar mixed gas into a vacuum furnace, heat treating at 750°C for 1 hour to form a silicon-carbon composite with Si-OC bonds, with H2 accounting for 10% of the volume ratio of the mixed gas; Step d, inner layer coating, transferring the silicon-carbon composite to a tubular furnace, introducing bamboo pyrolysis gas, and depositing at 650° C. for 30 min to form an amorphous carbon layer on the surface of the silicon-carbon composite; Step e, outer layer coating, using bamboo vinegar atomization CVD method, deposition at 900°C for 1h, generating a graphitized carbon shell on the surface of the silicon-carbon composite, and obtaining a silicon-carbon coated negative electrode material. When the silicon-carbon coated negative electrode material is used for the negative electrode of a lithium battery, the first charge and discharge efficiency is greater than 92%, and under 1C charge and discharge conditions, the capacity retention rate after 100 cycles is greater than 91%, and the volume expansion rate is less than 120%.

2. The process for preparing a carbon-silicon coated negative electrode material according to claim 1, characterized in that: The bamboo-based carbon in step b is obtained by crushing 2-year-old bamboo with a moisture content of less than 8%, and soaking it in 0.5 mol / L NH4H2PO4 solution for 12 hours with a solid-liquid ratio of 1:

10. After soaking, a gradient carbonization method is used to form the bamboo-based carbon.

3. The process for preparing a carbon-silicon coated negative electrode material according to claim 2, characterized in that: Gradient carbonization of bamboo-based carbon includes the following steps: Step s1, in the first stage, the soaked bamboo fragments are placed in a carbonization furnace, and under the protection of a N2 atmosphere, the carbonization furnace is heated to 400°C at a rate of 5°C / min and kept warm for 2h; Step s2, the second stage, the carbonization furnace is heated to 780-820°C, and CO2 gas is introduced at a flow rate of 45-55 mL / min for activation for 3 hours; Step s3, the third stage, the carbonization furnace is heated to 1100° C., and graphitization treatment is performed for 1 hour under the protection of Ar atmosphere to obtain bamboo-based carbon with a hierarchical porous carbon skeleton.

4. The process for preparing a carbon-silicon coated negative electrode material according to claim 3, characterized in that: In the step s2, the specific surface area of ​​the bamboo-based carbon in the CO2 activation stage is controlled at 800-1000 m2 / g, and the pore size distribution of the bamboo-based carbon is a bimodal structure, with the main peaks located at 1.8 nm and 50 nm.

5. The process for preparing a carbon-silicon coated negative electrode material according to claim 1, characterized in that: In the step b, the silicon loading of the bamboo-based carbon after impregnation is 15%.

6. The process for preparing a carbon-silicon coated negative electrode material according to claim 1, characterized in that: In the step d, the bamboo pyrolysis gas is obtained by collecting gaseous components from the gas generated in the bamboo-based carbon gradient carbonization process after condensation separation to remove tar.

7. The process for preparing a carbon-silicon coated negative electrode material according to claim 1, characterized in that: In the step d, the phenolic substances in the bamboo pyrolysis gas undergo free radical polycondensation reaction at a deposition temperature of 650°C: C7H8O2 Amorphous carbon + CO↑ + CO2↑ + H2O↑ + H2↑ + CH4↑, An amorphous carbon layer with a thickness of 2-3 nm is formed on the surface of the bamboo-based carbon.

8. The process for preparing a carbon-silicon coated negative electrode material according to claim 1, characterized in that: In the step e, the bamboo vinegar atomization CVD method comprises the following steps: Step t1, bamboo vinegar liquid purification, the crude bamboo vinegar liquid is distilled under reduced pressure at 80-85° C., the vacuum degree is -0.08 MPa, and the middle fraction with pH=3.2-3.8 and density of 1.18-1.22 g / cm³ is collected; Step t2, atomization treatment, using an ultrasonic atomizer with a frequency of 1.7 MHz to atomize the purified bamboo vinegar liquid into droplets with a particle size of 1-3 μm, and the atomization rate is controlled at 0.15 mL / min; Step t3, deposition reaction, the horizontal tube furnace is equipped with a porous carbon carrier support to load the silicon-carbon complex, the carrier gas system introduces Ar as a carrier gas into the horizontal tube furnace, the flow rate is controlled in three ways, the main carrier gas carries atomized bamboo vinegar liquid, the flow rate is 80sccm, the dilution gas flow rate is 20sccm, and the tail gas flow rate is 10sccm. During the deposition process, the temperature gradient in the horizontal tube furnace is controlled, the preheating temperature is 300°C, the deposition reaction temperature is 900°C, the reaction residence time is 2-3 seconds, the cooling temperature is 650°C, the entire deposition reaction time is 1h, and a 5-8nm graphitized carbon shell is formed, and the Raman spectrum ID / IG value is controlled at 0.85-1.

05.

9. The process for preparing a carbon-silicon coated negative electrode material according to claim 8, characterized in that: In the step t1, the proportion of guaiacol contained in the bamboo vinegar liquid after distillation and purification is ≥35%.

10. The process for preparing a carbon-silicon coated negative electrode material according to claim 8, characterized in that: In the step t3, guaiacol in the bamboo vinegar generates graphitized carbon at 900° C. through the following pathway: C7H8O2→graphite microcrystals+CO↑+CO2↑+H2O↑+H2↑+CH4↑.

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