Metal-doped silicon-carbon negative electrode material and preparation method thereof

Abstract

The present invention provides a metal-doped silicon-carbon anode material and a preparation method thereof. The preparation method comprises the following steps: separately preparing a modified amorphous carbon material and a metal silane precursor, wherein the modified amorphous carbon material has a particle size of 7-8 μm and an internal pore size of 0.1-10 nm; placing the modified amorphous carbon material in a chemical vapor deposition reactor, introducing nitrogen gas, raising the temperature to 500-700°C, then introducing a composite gas, and performing a deposition reaction for 100-800 minutes to obtain a pre-product, wherein the composite gas includes the metal silane precursor, a doping auxiliary gas, and acetylene gas, and the doping auxiliary gas is used to control the growth of the deposit; and heating the pre-product to 750-850°C for 10-30 minutes, cooling it to 500-600°C, introducing acetylene gas again, and maintaining the temperature for 30-300 minutes to obtain the metal-doped silicon-carbon anode material. This effectively improves electrochemical performance and cycle life.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a metal-doped silicon-carbon negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, owing to their long cycle life and high energy density, have become the most important energy storage technology for electric vehicles and electronic devices. However, the low theoretical capacity of traditional graphite anodes in lithium-ion batteries no longer meets the market demand for high-energy-density lithium-ion batteries. Consequently, industry and academic research are turning their attention to silicon-based anode materials, which offer high industrial feasibility. However, these materials suffer from two major limitations: large volume expansion (>300% during lithium insertion and extraction) and poor electronic conductivity. After years of research and development, silicon-based anode materials have evolved into third-generation silicon-carbon anodes. These materials exhibit significantly improved expansion compared to first-generation milled silicon and offer even more pronounced advantages in cycle and first-efficiency compared to second-generation silicon-oxygen anodes. Despite these significant capacity and expansion advantages, third-generation silicon-carbon anodes exhibit poor rate performance. Improving the rate performance of third-generation silicon materials and developing silicon anode materials with high specific capacity and long cycle life remain pressing challenges in the lithium battery field.

[0003] Current approaches to improving the dynamics of silicon-carbon materials all have drawbacks. For one thing, while doping and modification of porous carbon substrates can reduce some internal resistance in localized areas, the overall electron transport network is not effectively constructed due to insufficient contact between silicon and carbon, resulting in limited reduction in the overall system's internal resistance. Furthermore, silicon undergoes dramatic volume changes during charge and discharge. This expansion-contraction effect destroys the microstructure of the carbon substrate. Even if the conductivity of the carbon substrate is improved, it cannot fundamentally alleviate problems such as interface fracture and particle shedding, affecting long-term cycle stability.

[0004] On the other hand, regarding the modification method of the outer coating layer, the interface bonding between the coating layer and the base material is not strong enough or the chemical properties do not match, which will cause peeling or microcracks during the cycle, leading to problems such as electrolyte infiltration and solid electrolyte interface (SEI) instability, thereby resulting in poor battery cycle life and electrochemical performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a metal-doped silicon-carbon negative electrode material and a preparation method thereof, aiming to solve the problems of poor electrochemical performance and cycle life of batteries.

[0006] To solve the above technical problems, the present invention is implemented as follows: the present invention provides a method for preparing a metal-doped silicon-carbon negative electrode material for making a lithium-ion battery, the steps comprising:

[0007] S1. Preparing a modified amorphous carbon material and a metal silane precursor respectively, wherein the particle size of the modified amorphous carbon material is 7-8 μm, and the internal pore size of the modified amorphous carbon material is 0.1-10 nm;

[0008] S2. Placing the modified amorphous carbon material in a chemical vapor deposition reactor, introducing nitrogen and heating the reactor to 500-700° C., then introducing a composite gas, and performing a deposition reaction for 100-800 minutes to obtain a pre-product, wherein the composite gas includes the metal silane precursor, a doping auxiliary gas, and acetylene gas, and the doping auxiliary gas is used to control the growth of the deposit;

[0009] S3. The pre-product is heated to 750-850° C. for 10-30 minutes, cooled to 500-600° C., acetylene gas is introduced again, and the temperature is kept at this temperature for 30-300 minutes to obtain a metal-doped silicon-carbon negative electrode material.

[0010] In some embodiments, step S1 includes:

[0011] S1.1. Disperse the amorphous carbon powder in deionized water, ultrasonicate it in an ultrasonic cleaner for 10 minutes, transfer it to a reactor, add concentrated nitric acid, and react under pressure at a temperature of 120°C for 2 hours. After the reaction, filter or collect the product by centrifugation, wash it with deionized water until the pH of the filtrate reaches 7, and then dry it in an oven at 80°C for 12 hours to obtain etching carbon powder.

[0012] S1.2. The etching carbon powder was mixed with solid potassium hydroxide in a mass ratio of 1:3, and then placed in a tube furnace under a nitrogen atmosphere and heated to 800°C at a heating rate of 5°C / min. The mixture was kept warm for 2 hours. After cooling, the mixture was repeatedly washed with dilute hydrochloric acid until the pH was neutral, and dried at 100°C for 12 hours to obtain a modified amorphous carbon material.

[0013] S1.3. Add the silane component and the metal component to anhydrous toluene, stir for 10 to 30 minutes, then add the catalyst, heat to 110°C, keep warm for 12 hours, cool to room temperature, and then perform rotary evaporation to remove anhydrous toluene. Dissolve in a small amount of ethyl acetate for purification, and dry at 60°C to constant weight to obtain a metal silane precursor.

[0014] In some embodiments, in step S1.3, the silane component includes at least one of methyltriethoxysilane, tetraethoxysilane, and diethoxydimethylsilane, and the metal component includes at least one of tetraethoxygermanium, triethoxyarsenic, tetraethoxytin, triethoxyantimony, and triethoxygallium. Calculated by molar ratio, the silane component: the metal component = (5~20): 1, and the catalyst includes at least one of p-toluenesulfonic acid, dilute hydrochloric acid, and trifluoroacetic acid. The catalyst accounts for 1~2% of the total mass of the silane component and the metal component.

[0015] In some embodiments, step S2 includes:

[0016] S2.1, placing the modified amorphous carbon material in a chemical vapor deposition reactor in a nitrogen atmosphere, heating to 500-700°C at a heating rate of 5-10°C / min;

[0017] S2.2, maintaining the temperature, stopping the nitrogen flow, vaporizing the metallosilane precursor, mixing it with the auxiliary doping gas and acetylene gas to form a composite gas, and then introducing it into the chemical vapor deposition reactor containing the modified amorphous carbon material, and setting the deposition reaction duration to 100 to 800 minutes;

[0018] S2.3. Continue to introduce the composite gas, raise the temperature to 750-850°C, keep warm for 10-30 minutes, and cool to obtain a pre-product.

[0019] In some embodiments, in step S2.2, the flow rate of nitrogen is 0.5-20 L / min, the flow rate of the composite gas is 0.5-15 L / min, and the auxiliary doping gas includes at least one of hydrogen fluoride, hydrogen chloride, and ammonia.

[0020] In some embodiments, in step S2.2, the molar ratio of the metal silane precursor: the auxiliary doping gas: the acetylene gas is (10-20): 1: (5-10), and the density of the auxiliary doping gas is 1.52-1.54 g / cm 3 The density of the acetylene gas is 0.5~1.57g / cm 3 .

[0021] In some embodiments, step S3 includes:

[0022] S3.1. Continue heating the pre-product in the chemical vapor deposition reactor at a recommended heating rate of 10-20°C / min to rapidly raise the temperature to 800-900°C and hold for 10-30 minutes.

[0023] S3.2. Cool down to 500-600°C, introduce acetylene gas at a flow rate of 0.5-10 L / min, and keep warm for 30-300 minutes. After heating is completed, stop introducing acetylene gas, continue to maintain nitrogen protection, and slowly cool down to room temperature to obtain a metal-doped silicon-carbon negative electrode material.

[0024] The present invention provides a metal-doped silicon-carbon negative electrode material, which is prepared by the above-mentioned preparation method of a metal-doped silicon-carbon negative electrode material, wherein the metal-doped silicon-carbon negative electrode material comprises a modified amorphous carbon material, a metal silane precursor, a doping auxiliary gas and acetylene gas; wherein,

[0025] The modified amorphous carbon material is used as a carrier for depositing a metal silane precursor;

[0026] The metal silane precursor is used to improve the specific capacity and electrochemical performance of the metal-doped silicon-carbon negative electrode material;

[0027] The doping auxiliary gas is used to enhance the cycle stability of the metal-doped silicon-carbon negative electrode material;

[0028] The acetylene gas is used to form a carbon coating layer.

[0029] Compared with the prior art, the metal-doped silicon-carbon negative electrode material and its preparation method in the present invention have the following advantages:

[0030] Modifying the internal pores of the amorphous carbon material allows for uniform dispersion of the active material in the negative electrode, while providing ample diffusion channels for lithium ions and reducing local concentration gradients, thereby facilitating uniform intercalation and deintercalation of lithium ions. Uniform dispersion of metal doping is achieved by chemical vapor deposition (CVD) of a composite gas containing a metallosilane precursor. Metal doping can form a continuous conductive network in silicon-carbon materials, reducing electron transport resistance and improving overall conductivity. This is crucial for reducing internal resistance and accelerating electron transfer during charge and discharge. Metal doping can improve the interfacial bonding between silicon and carbon, alleviate structural damage caused by the drastic volume changes of silicon during charge and discharge, ensure the mechanical integrity and interfacial stability of the electrode material during long-term cycling, and thus improve cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a SEM image of the metal-doped silicon-carbon negative electrode material in Example 1 of the present invention;

[0032] Figure 2 This is an overlay diagram of element distribution of the metal-doped silicon-carbon negative electrode material in Example 1 of the present invention;

[0033] Figure 3 This is a distribution diagram of the germanium element in the metal-doped silicon-carbon negative electrode material in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The present invention provides a method for preparing a metal-doped silicon-carbon negative electrode material for making a lithium-ion battery, comprising the following steps:

[0036] S1. Prepare a modified amorphous carbon material and a metal silane precursor respectively, wherein the particle size of the modified amorphous carbon material is 7-8 μm, and the internal pore size of the modified amorphous carbon material is 0.1-10 nm.

[0037] Step S1 includes:

[0038] S1.1. Disperse the amorphous carbon powder in deionized water and ultrasonically treat it in an ultrasonic cleaner for 10 minutes. Transfer the powder to a reactor and add concentrated nitric acid. The reaction temperature is 120°C and the reaction is carried out for 2 hours. After the reaction is completed, filter or collect the product by centrifugation, wash it with deionized water until the pH of the filtrate reaches 7, and then dry it in an oven at 80°C for 12 hours to obtain etching carbon powder. The concentration of concentrated nitric acid should be 68-70%.

[0039] Concentrated nitric acid oxidizes amorphous carbon powder at 120°C, generating oxidized functional groups such as carboxyl and hydroxyl groups on the carbon surface. This process creates fine etching on the carbon surface, increasing surface roughness and activity, and providing favorable conditions for subsequent chemical activation. Ultrasonic treatment in deionized water ensures full dispersion of the carbon powder, improving the uniformity of the reaction and ensuring that each particle surface receives a uniform etching treatment. The resulting etched carbon powder has a higher surface energy and an improved primary pore structure, laying the foundation for subsequent potassium hydroxide activation and ensuring that the modified carbon material has the desired particle size (7-8μm) and initial pore structure.

[0040] In one embodiment, the etching carbon powder can be immersed in a solution containing 30% hydrogen peroxide to promote the introduction of more oxidizing functional groups (such as quinones or peroxides) and improve red oxygen reduction properties. This step helps form a surface gradient functional layer, which serves as a buffer interface for subsequent metal silicon deposition.

[0041] S1.2. Mix the etching carbon powder and solid potassium hydroxide in a mass ratio of 1:3, place it in a tubular furnace in a nitrogen atmosphere and heat it to 800°C at a heating rate of 5°C / min, keep it warm for 2 hours, cool it down, wash it repeatedly with dilute hydrochloric acid until the pH is neutral, and dry it at 100°C for 12 hours to obtain a modified amorphous carbon material.

[0042] Etching carbon powder and potassium hydroxide were mixed in a 1:3 mass ratio and heated at 800°C (heating rate 5°C / min) for 2 hours under nitrogen. Gases generated during the reaction accumulate locally in the closed system, producing tiny bubbles. These localized high-pressure impacts disrupt the local structure of the carbon material, etching micropores into the carbon powder surface. At high temperatures, potassium hydroxide reacts with carbon to produce intermediates such as potassium carbonate, along with gases such as carbon dioxide and water vapor. These reaction products form pores within the carbon particles. Subsequently, washing with dilute hydrochloric acid removes residual metal salts and byproducts, preserving the internal pores generated by potassium hydroxide activation. This process results in a modified carbon material that not only maintains the original particle size but also features internal pores concentrated in the 0.1-10 nm range, enhancing both specific surface area and pore connectivity. The resulting modified amorphous carbon material exhibits a more active surface and a uniform pore structure, facilitating uniform adhesion and atomic-scale deposition of precursors during subsequent deposition, effectively improving the overall electrochemical activity and ion transport efficiency of the anode material.

[0043] In order to judge whether the particle size of the modified amorphous carbon material meets the requirements, a scanning electron microscope (SEM) or a dynamic light scattering instrument (DLS) is used.

[0044] Take a sample of the prepared modified amorphous carbon material and observe it under a SEM. Count the particle diameters across multiple fields of view. Confirm that the average particle size is within the 7-8 μm range. If the average particle size is below 7 μm or above 8 μm, adjust the chemical etching or activation treatment conditions (such as reaction time, temperature, or potassium hydroxide ratio) to correct the particle size distribution.

[0045] In order to determine whether the internal pore size of the modified amorphous carbon material meets the requirements, a nitrogen adsorption-desorption experiment was carried out using BET (specific surface area and pore size distribution tester).

[0046] Perform a BET test on the sample and analyze the pore size distribution data. Check that the internal pore size distribution is primarily within the 0.1-10 nm range. If the pore size distribution deviates significantly from the 0.1-10 nm range, it indicates that the pore structure is not adequately controlled during the etching or activation process. In this case, parameters such as etching concentration, temperature, or activation time may need to be readjusted.

[0047] If the above test results all meet the predetermined requirements, the next process step is entered; if the above test results do not meet the requirements, the deviation is recorded and fed back to step S1.1, and the reaction parameters are adjusted and the modification process is repeated until the target parameters are reached.

[0048] In one embodiment, if SEM statistics show an average particle size of 6.5 μm (lower than the target of 7 μm), the acid etching time is shortened from 2 hours to 1.5 hours, or the concentrated nitric acid concentration is reduced from 68% to 60%, and the preparation is repeated and the particle size change is observed until the average particle size reaches 7-8 μm.

[0049] If the BET test shows an average pore size of 15 nm (exceeding the target upper limit of 10 nm), reduce the ratio of potassium hydroxide to carbon powder from 1:3 to 1:2, or shorten the holding time from 2 hours to 1.5 hours. Subsequent testing will confirm whether the pore size distribution has been adjusted to the range of 0.1 to 10 nm.

[0050] S1.3. The silane component and the metal component are added to anhydrous toluene to determine whether the particle size of the modified amorphous carbon material meets the requirements. After stirring for 10-30 minutes, the catalyst is added, the temperature is raised to 110°C, the temperature is maintained for 12 hours, and the anhydrous toluene is removed by rotary evaporation after cooling to room temperature. The precursor is dissolved in a small amount of ethyl acetate for purification and dried at 60°C to constant weight to obtain a metallosilane precursor. In step S1.3, the silane component includes at least one of methyltriethoxysilane, tetraethoxysilane, and diethoxydimethylsilane, and the metal component includes at least one of tetraethoxygermanium, triethoxyarsenic, tetraethoxytin, triethoxyantimony, and triethoxygallium. The molar ratio of silane component to metal component is (5-20):1. The catalyst includes at least one of p-toluenesulfonic acid, dilute hydrochloric acid, and trifluoroacetic acid. The catalyst accounts for 1-2% of the total mass of the silane component and the metal component.

[0051] The silane component and the metal component are added to anhydrous toluene and stirred under an inert atmosphere for 10–30 minutes to ensure thorough mixing and uniform dispersion of the components in the solvent. After the catalyst is added, the temperature is raised to 110°C and maintained for 12 hours. Under the action of the catalyst, a condensation reaction occurs between the silane component and the metal component, generating a molecularly uniform metallosilane precursor. The molar ratio of silane to metal is controlled to be (5–20):1, with the silane component predominating, ensuring a stable silicon skeleton, while the metal component is introduced as a dopant. After the reaction, the precursor is cooled to room temperature, the anhydrous toluene is removed by rotary evaporation, and the product is dissolved in a small amount of ethyl acetate for purification. Finally, it is dried at 60°C to constant weight to obtain the metallosilane precursor. The precursor molecule contains both silicon and metal functional groups, and covalent bonds are formed through the condensation reaction, achieving uniform molecular bonding between the metal and silicon. The resulting metallosilane precursor exhibits high volatility (facilitating subsequent vapor deposition), while its chemical structure lays the foundation for atomic-scale deposition during chemical vapor deposition. Precise control of the molar ratio of the silane component to the metal component and the amount of catalyst used ensures efficient precursor reaction and structural stability, thereby enhancing the uniformity and functionality of the metal, silicon, and carbon three-phase composite structure during subsequent deposition.

[0052] S2. Place the modified amorphous carbon material in a chemical vapor deposition reactor, introduce nitrogen and heat it to 500-700°C, then introduce a composite gas, and perform the deposition reaction for 100-800 minutes to obtain a pre-product, wherein the composite gas includes a metal silane precursor, a doping auxiliary gas, and acetylene gas, and the doping auxiliary gas is used to regulate the growth of the deposit.

[0053] Step S2 includes:

[0054] S2.1. Place the modified amorphous carbon material in a chemical vapor deposition reactor in a nitrogen atmosphere and heat it to 500-700°C at a heating rate of 5-10°C / min.

[0055] During the preheating process, the temperature is evenly increased, allowing the substrate surface to reach an optimal activation state, facilitating subsequent precursor decomposition and uniform deposition. Nitrogen protection prevents oxidation of the carbon substrate at high temperatures, ensuring that surface functional groups and pore structure are not destroyed. This ensures substrate surface activity and structural stability, creating an ideal thermal environment for subsequent deposition. The controlled heating rate helps avoid structural stress and unevenness caused by excessive temperature gradients.

[0056] S2.2. Maintain the temperature, stop introducing nitrogen, vaporize the metal silane precursor, mix it with the auxiliary doping gas and acetylene gas to form a composite gas, and then introduce it into the chemical vapor deposition reactor containing the modified amorphous carbon material. The deposition reaction duration is set at 100~800 minutes; the flow rate of nitrogen is 0.5~20L / min, the flow rate of the composite gas is 0.5~15L / min, and the auxiliary doping gas includes at least one of hydrogen fluoride, hydrogen chloride, and ammonia. According to the molar ratio, metal silane precursor: auxiliary doping gas: acetylene gas = (10~20): 1: (5~10), and the density of the auxiliary doping gas is 1.52~1.54g / cm 3 The density of acetylene gas is 0.5~1.57g / cm 3 .

[0057] Through heating and carrier gas delivery, the metallosilane precursor volatilizes into a gaseous state in anhydrous toluene and mixes with auxiliary doping gas and acetylene gas in a preset molar ratio to ensure molecular-level uniformity. The trace addition of auxiliary doping gas regulates the reaction interface energy, modulates the nucleation and growth rate, and helps form deposits with uniform size and few defects. At 500-700°C, the vaporized metallosilane precursor decomposes, while acetylene is deposited to form an auxiliary carbon layer, together forming a composite deposit of metal, silicon, and carbon on the carbon substrate. This achieves atomically uniform deposition of metal and silicon on the substrate, while the auxiliary doping gas regulates the growth of the deposit, ensuring that the grain size and morphology of the deposited layer meet the desired design. The participation of acetylene improves the density and conductivity of the deposited layer, providing a guarantee for subsequent electrochemical performance.

[0058] In one embodiment, to ensure that the thickness of the deposited layer formed on the modified amorphous carbon material remains within a preset thickness, a calculation formula is obtained from multiple experimental experiences:

[0059]

[0060] in, (nm) is the deposition thickness, and the preset thickness can be 200~600 nm. (dimensionless) is the deposition efficiency, which is obtained by comparing the actual measured deposition thickness with the ideal thickness calculated theoretically. is a composite constant whose unit is determined by the units of the terms in the equation. is the length (nm), and are dimensionless, The unit is Pa, The unit is K, The unit is mL / min, The unit is min, then The units of need to be compensated so that the entire right-hand side expression has length units, which is . The value needs to be obtained by fitting experimental data. It is a process constant and its specific value depends on the reaction system and equipment design. Through preliminary experiments, the deposition thickness measured by other known parameters can be reversed. and is fixed for use in subsequent processes. (dimensionless) is the mole fraction of the metallosilane precursor, representing the molar proportion of the metallosilane precursor in the gas mixture, such as 0.05-0.2 (i.e., 5%-20%), depending on the desired deposition rate and the composition of the final deposited layer. (Pa) In a CVD reactor, the specific pressure depends on the process design. It is directly measured by a pressure sensor inside the reactor and is regulated and maintained stable by equipment such as the gas supply system and vacuum pump. (K) is the absolute temperature. For step S2.2, the temperature is controlled at 500-700°C, which is approximately 773-973 K in absolute temperature and is measured by a temperature sensor (thermocouple, infrared thermometer, etc.) in the reactor. (mL / min) is the gas flow rate obtained by the flow meter. In step S2.2, the composite gas flow rate is set in the range of 0.5 to 15 L / min. (min) is the deposition time, which is set between 100 and 800 minutes.

[0061] Using the formula, engineers can set the reaction parameters (such as the mole fraction of metal silane precursor) Total pressure ,temperature , flow rate and deposition time ) Estimated thickness of sedimentary layer This allows process developers to more precisely design the deposition process, ensuring that the deposited layer achieves the desired thickness (a target range of 200-600 nm is possible). Each parameter in the formula (temperature, pressure, flow rate, time, etc.) directly reflects its impact on the deposition rate and final thickness. For example, the square root relationship between temperature and flow rate indicates that increasing both temperature and flow rate increases the deposition rate, but the effect is nonlinear. This relationship facilitates fine-tuning and optimizing deposition conditions in practice. Furthermore, by adjusting the mole fraction of the metallosilane precursor and the deposition time, the thickness and uniformity of the deposited layer can be precisely controlled while ensuring sufficient chemical reaction. This formula provides theoretical support for online monitoring and feedback control. By measuring the deposited thickness in real time (for example, using online optical measurement or cross-sectional analysis), the actual thickness can be compared with the predicted value, and process parameters (such as flow rate and temperature) can be adjusted to achieve precise control and stable production. In the preparation of metal-doped silicon-carbon anode materials, the thickness and uniformity of the deposited layer directly affect the interface quality, ion transport efficiency, and electronic conductivity. By precisely controlling the deposition thickness, an ideal composite structure can be formed, thereby reducing internal resistance, improving electrochemical reaction kinetics, and improving cycle stability and rate performance.

[0062] S2.3. Continue to introduce the composite gas, raise the temperature to 750-850°C, keep warm for 10-30 minutes, and cool to obtain a pre-product.

[0063] Under high-temperature conditions of 750-850°C, the metal silicon decomposition products in the deposited layer undergo further partial crystallization and interface fusion, forming a more regular grain boundary structure. High-temperature treatment helps eliminate the internal stress formed during the deposition process, strengthens interlayer bonding, and promotes the interdiffusion of metal, silicon, and carbon phases, making the composite structure more compact. Through high-temperature insulation treatment, the internal grain size of the pre-product is more uniform, the interface structure is more stable, and the electrochemical performance and structural durability of the overall deposit are improved. This step helps to form an ideal nanocomposite layer, laying the foundation for the subsequent practical application of negative electrode materials.

[0064] In one embodiment, before step S3, the pre-product is further processed to increase the silicon content and improve the specific surface area of ​​the metal-doped silicon-carbon negative electrode material.

[0065] Mix the resulting pre-product, siloxane precursor, and magnesium powder in a suitable ratio to form a mixture. The mass ratio is: pre-product: siloxane precursor: magnesium powder = 1:1:1 (this ratio can be optimized based on the target silicon content). Thoroughly mix to ensure uniform contact between the components.

[0066] The mixture was placed in a quartz boat in a tube furnace and heated at a rate of 5°C / min to 650-700°C under an inert nitrogen atmosphere (nitrogen flow rate of 50 mL / min). The temperature was maintained within this temperature range for 2 hours. The siloxane precursor was converted to silicon through a magnesium thermal reduction reaction, and the resulting magnesium oxide was intercalated into the mixture. After the reaction, the mixture was allowed to cool naturally to room temperature. The cooled product was treated with dilute hydrochloric acid to dissolve the generated magnesium oxide and unreacted magnesium, and then repeatedly washed with deionized water until the pH of the washing solution reached neutral. The washed product was then dried at 100°C for 12 hours. The siloxane precursor included at least one of methyltrimethoxysilane, methyltriethoxysilane, and methyltrichlorosilane.

[0067] The siloxane precursor is hydrolyzed and condensed to form (CH3SiO 1-5 )n network-structured siloxane material, with magnesium powder acting as a reducing agent to reduce the silicon-oxygen bonds in the siloxane precursor to elemental silicon. The pre-product's existing deposited layer contains some metallic silicon and a carbon network. By adding the siloxane precursor and magnesium powder, additional silicon can be introduced into the existing composite structure, effectively reinforcing the pre-product with silicon. Under inert nitrogen protection, the magnesium powder and the siloxane precursor are heated to 650-700°C at a rate of 5°C / min, whereupon a magnesium-thermal reduction reaction occurs between the magnesium powder and the siloxane precursor. The resulting silicon is dispersed throughout the mixture, increasing the silicon content of the pre-product. Furthermore, since silicon is often generated in a porous form, the overall composite material's microstructure becomes more hierarchical and interconnected.

[0068] The siloxane precursor is converted into silicon through a magnesium thermal reduction reaction, which makes up for the silicon deficiency in the pre-product. The newly generated porous silicon forms a tight composite with the modified amorphous carbon material, which not only improves the conductive network, but also provides more active interfaces for subsequent deposition, promoting charge transfer and lithium ion diffusion. The magnesium oxide generated during the magnesium thermal reduction process will be temporarily embedded in the mixture, and local gas generation will produce pores. The magnesium oxide and residual magnesium are then washed away with dilute hydrochloric acid. After repeated washing, a large number of uniform and interconnected pores will remain on the surface and inside of the product. After the porous silicon and the original modified amorphous carbon material are composited, the specific surface area of ​​the overall material is greatly increased, which is conducive to the infiltration of the electrolyte and the rapid transmission of lithium ions. The high specific surface area and good pore structure provide more ion transmission channels, reduce the interfacial impedance, and have a positive effect on both cycle performance and rate performance.

[0069] By mixing a siloxane precursor, magnesium powder, and pre-product in a 1:1:1 mass ratio, a solid-state reduction method is organically combined with a CVD deposition pre-product, resulting in material benefits in both chemical composition and microstructure. This process not only increases the effective silicon content but also leverages the pore formation caused by high-temperature reduction to further enhance the overall composite's kinetic properties. The resulting composite exhibits a higher silicon content, a richer pore structure, and an optimized composite interface, which helps alleviate stress caused by silicon volume changes during charge and discharge, improving the material's cycling stability. The high specific surface area and uniform composite structure promote rapid lithium ion transport and efficient electron conduction, thereby enhancing the rate capability and cycle life of the anode material. By incorporating a magnesium-thermal reduction method of the siloxane precursor and magnesium powder into the pre-product treatment, using methyltrimethoxysilane, methyltriethoxysilane, or methyltrichlorosilane as the silicon source, and carrying out the reduction reaction at 650-700°C under nitrogen, not only does it significantly increase the silicon content in the pre-product, but it also forms a large number of microporous structures during the acid washing and drying processes, thereby increasing the specific surface area of ​​the composite. This treatment method enables the final metal-doped silicon-carbon negative electrode material to have better electrochemical kinetics and cycle stability, which is of great significance to improving the overall performance of the battery.

[0070] S3. The pre-product is heated to 750-850°C for 10-30 minutes, cooled to 500-600°C, acetylene gas is introduced again, and the temperature is kept at this temperature for 30-300 minutes to obtain a metal-doped silicon-carbon negative electrode material.

[0071] Step S3 includes:

[0072] S3.1. Continue heating the pre-product in the chemical vapor deposition reactor at a recommended heating rate of 10-20°C / min. Rapidly raise the temperature to 800-900°C and maintain it for 10-30 minutes.

[0073] Under high-temperature conditions of 800-900°C, the metal-silicon mixture in the pre-product undergoes further partial crystallization and interfacial reconstruction, enhancing atomic diffusion and strengthening the interface between the metal and silicon. High-temperature conditions help eliminate internal defects and stresses generated during the deposition process, forming a more regular, dense grain and interface structure. Annealing promotes interdiffusion between the metal and silicon and grain reorganization, improving the crystallinity and interfacial bonding of the composite deposited layer. High-temperature insulation significantly reduces internal stress and crystal defects, thereby improving the uniformity of the subsequently deposited carbon coating. The strengthened grain boundaries help improve the material's stability under dynamic thermal shock, supporting subsequent applications such as rapid charging and discharging in extremely cold environments.

[0074] S3.2. Cool down to 500-600°C, introduce acetylene gas at a flow rate of 0.5-10 L / min, and keep warm for 30-300 minutes. After heating is completed, stop introducing acetylene gas, continue to maintain nitrogen protection, and slowly cool down to room temperature to obtain a metal-doped silicon-carbon negative electrode material.

[0075] At 500-600°C, acetylene gas partially pyrolyzes to produce active carbon atoms or carbon clusters. These active species aggregate on the surface of the pre-product, gradually forming a uniform carbon coating. The carbon coating fills tiny defects on the pre-product surface while forming a continuous, dense covering, which helps improve electronic conductivity and the mechanical stability of the overall structure. The formed carbon coating effectively prevents the external environment (such as the electrolyte) from corroding the internal metallic silicon structure, improving the cycling stability of the material. The uniform and dense carbon layer facilitates electron transport, reduces interfacial impedance, and enhances the electrochemical performance of the negative electrode material. The carbon coating, through its thermal conductivity, helps to quickly dissipate local heat during rapid charge and discharge, thereby improving the thermal stability of the material under extreme conditions.

[0076] The present invention provides a metal-doped silicon-carbon negative electrode material, which is prepared by a method for preparing a metal-doped silicon-carbon negative electrode material. The metal-doped silicon-carbon negative electrode material includes a modified amorphous carbon material, a metal silane precursor, a doping auxiliary gas, and acetylene gas; wherein,

[0077] The modified amorphous carbon material is used as a support for depositing metal silane precursors;

[0078] Metallosilane precursors are used to improve the specific capacity and electrochemical performance of metal-doped silicon-carbon anode materials;

[0079] Doping auxiliary gas is used to enhance the cycle stability of metal-doped silicon-carbon anode materials;

[0080] Acetylene gas is used to form the carbon coating.

[0081] Example 1:

[0082] 1500g of modified amorphous carbon material with a particle size D50 of 8um was added to a chemical vapor deposition reactor, nitrogen was introduced at a flow rate of 14L / min, the temperature in the furnace was raised to 520°C, methyltriethoxysilane and tetraethoxygermanium with a molar ratio of 10:1 were introduced at a flow rate of 3L / min, and acetylene gas was introduced at the same time, and the gas introduction time was set to 500min. The temperature was raised to 800°C, kept warm for 20 minutes, and cooled to obtain a pre-product. Subsequently, nitrogen was introduced into the chemical vapor deposition reactor at a heating rate of 14L / min, the temperature was raised to 850°C, kept warm for 20 minutes, and then cooled to 550°C. Acetylene gas was introduced at a flow rate of 3L / min, and the acetylene gas ventilation time was set to 200min. After cooling, a metal-doped silicon-carbon negative electrode material was obtained.

[0083] Comparative Example 1:

[0084] Compared with Example 1, the difference is that only methyltriethoxysilane is introduced during the silane deposition stage.

[0085] Table 1: Electrical experimental data:

[0086] .

[0087] Metal-doped silicon-carbon anode material, conductive carbon black, and binder CMC were weighed and added to deionized water to form a homogenous slurry. The solids ratio of metal-doped silicon-carbon anode material: conductive carbon black: binder CMC was 95:1.5:3.5. Samples were prepared using a homogenizer at 2000 rpm for 20 minutes. The slurry was sieved and evenly coated onto copper foil. The resulting electrode was then dried in a 90°C vacuum drying oven. The dried electrode sheet was roller-pressed and cut into circular electrodes of a desired size. The electrode mass was recorded. In an argon-filled glove box, a lithium metal sheet was used as the counter electrode. The resulting electrode, separator, and gasket were assembled into button cells. A dedicated silicon-carbon electrolyte was used as the electrolyte.

[0088] After subjecting Example 1 and Comparative Example 1 to charge and discharge cycles, the experimental data obtained are shown in Table 1, which shows that the metal-doped silicon-carbon negative electrode material after being doped with metal has excellent cycle performance, effectively improving the charging efficiency and service life of the lithium-ion battery.

[0089] Figure 1 This is a scanning electron microscope (SEM) image showing the appearance, size, and surface characteristics of a single particle of metal-doped silicon-carbon anode material. The particle is generally polyhedral or blocky, with a relatively flat surface and distinct corners, indicating certain crystallization or sintering characteristics.

[0090] Figure 2 Based on SEM images, elemental composition analysis is performed using energy dispersive spectroscopy (EDS). The distribution information of multiple elements (such as Si, C, O, and Ge) is superimposed on a single image. The color or grayscale distribution allows for intuitive visualization of the distribution uniformity and relative content of each element on the particle surface and within. As can be seen from the image, elements such as Si, C, O, and Ge appear to be distributed throughout the particle, indicating that these elements have been successfully incorporated into the material during the preparation process.

[0091] Figure 3 This is a distribution map of germanium. Each bright spot or grayscale point on the map represents the presence and intensity of the element in a local area. This point cloud distribution shows that germanium is evenly distributed in the particle, with no obvious enriched areas or localized depletion, indicating relatively uniform doping.

[0092] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a metal-doped silicon-carbon negative electrode material for making a lithium-ion battery, characterized in that the steps include: S1. Preparing a modified amorphous carbon material and a metal silane precursor respectively, wherein the particle size of the modified amorphous carbon material is 7-8 μm, and the internal pore size of the modified amorphous carbon material is 0.1-10 nm; Step S1 includes: S1.

3. Add the silane component and the metal component to anhydrous toluene, stir for 10-30 minutes, then add the catalyst, heat to 110°C, keep warm for 12 hours, cool to room temperature, and then remove anhydrous toluene by rotary evaporation. Dissolve in a small amount of ethyl acetate for purification, and dry at 60°C to constant weight to obtain a metallosilane precursor. The silane component includes at least one of methyltriethoxysilane, tetraethoxysilane, and diethoxydimethylsilane; the metal component includes at least one of tetraethoxygermanium, triethoxyarsenic, tetraethoxytin, triethoxyantimony, and triethoxygallium; the molar ratio of the silane component to the metal component is (5-20):1; the catalyst includes at least one of p-toluenesulfonic acid, dilute hydrochloric acid, and trifluoroacetic acid; and the catalyst accounts for 1-2% of the total mass of the silane component and the metal component; S2. Placing the modified amorphous carbon material in a chemical vapor deposition reactor, introducing nitrogen and heating the reactor to 500-700° C., then introducing a composite gas, and performing a deposition reaction for 100-800 minutes to obtain a pre-product, wherein the composite gas includes the metal silane precursor, a doping auxiliary gas, and acetylene gas, and the doping auxiliary gas is used to control the growth of the deposit; Step S2 includes: S2.1, placing the modified amorphous carbon material in a chemical vapor deposition reactor in a nitrogen atmosphere, heating to 500-700°C at a heating rate of 5-10°C / min; S2.2, maintaining the temperature, stopping the introduction of nitrogen, vaporizing the metallosilane precursor, mixing it with an auxiliary doping gas and acetylene gas to form a composite gas, and then introducing it into the chemical vapor deposition reactor containing the modified amorphous carbon material, wherein the deposition reaction duration is set to 100 to 800 minutes, and the auxiliary doping gas includes at least one of hydrogen fluoride, hydrogen chloride, and ammonia; S2.

3. Continue to introduce the composite gas, raise the temperature to 750-850°C, maintain the temperature for 10-30 minutes, and cool to obtain a pre-product; S3. The pre-product is heated to 750-850° C. for 10-30 minutes, cooled to 500-600° C., acetylene gas is introduced again, and the temperature is kept at this temperature for 30-300 minutes to obtain a metal-doped silicon-carbon negative electrode material.

2. The method for preparing a metal-doped silicon-carbon negative electrode material according to claim 1, characterized in that: Step S1 further includes: S1.

1. Disperse the amorphous carbon powder in deionized water, ultrasonicate it in an ultrasonic cleaner for 10 minutes, transfer it to a reactor, add concentrated nitric acid, and react under pressure at a temperature of 120°C for 2 hours. After the reaction, filter or collect the product by centrifugation, wash it with deionized water until the pH of the filtrate reaches 7, and then dry it in an oven at 80°C for 12 hours to obtain etching carbon powder. S1.

2. Mix the etching carbon powder with solid potassium hydroxide in a mass ratio of 1:3, place it in a tubular furnace in a nitrogen atmosphere and heat it to 800°C at a heating rate of 5°C / min, keep it warm for 2 hours, cool it down, and repeatedly wash it with dilute hydrochloric acid until the pH is neutral, and dry it at 100°C for 12 hours to obtain a modified amorphous carbon material.

3. The method for preparing a metal-doped silicon-carbon negative electrode material according to claim 1, characterized in that: In step S2.2, the flow rate of nitrogen is 0.5-20 L / min, and the flow rate of the composite gas is 0.5-15 L / min.

4. The method for preparing a metal-doped silicon-carbon negative electrode material according to claim 1, characterized in that: In step S2.2, the molar ratio of the metal silane precursor: the auxiliary doping gas: the acetylene gas is (10-20): 1: (5-10), and the density of the auxiliary doping gas is 1.52-1.54 g / cm 3 The density of the acetylene gas is 0.5~1.57g / cm 3 .

5. The method for preparing a metal-doped silicon-carbon negative electrode material according to claim 1, characterized in that: Step S3 includes: S3.

1. Continue heating the pre-product in the chemical vapor deposition reactor at a recommended heating rate of 10-20°C / min to rapidly raise the temperature to 800-900°C and hold for 10-30 minutes. S3.

2. Cool down to 500-600°C, introduce acetylene gas at a flow rate of 0.5-10 L / min, and keep warm for 30-300 minutes. After heating is completed, stop introducing acetylene gas, continue to maintain nitrogen protection, and slowly cool down to room temperature to obtain a metal-doped silicon-carbon negative electrode material.

6. A metal-doped silicon-carbon negative electrode material, characterized in that: The metal-doped silicon-carbon negative electrode material is prepared by the method for preparing the metal-doped silicon-carbon negative electrode material according to any one of claims 1 to 5, wherein the metal-doped silicon-carbon negative electrode material comprises a modified amorphous carbon material, a metal silane precursor, a doping auxiliary gas, and acetylene gas; wherein, The modified amorphous carbon material is used as a carrier for depositing a metal silane precursor; The metal silane precursor is used to improve the specific capacity and electrochemical performance of the metal-doped silicon-carbon negative electrode material; The doping auxiliary gas is used to enhance the cycle stability of the metal-doped silicon-carbon negative electrode material; The acetylene gas is used to form a carbon coating layer.

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