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

Abstract

The invention provides a metal doped silicon carbon negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: a modified amorphous carbon material and a metal silane precursor are respectively prepared, the particle size of the modified amorphous carbon material is 7-8 [mu] m, and the internal pore size of the modified amorphous carbon material is 0.1-10 nm; the modified amorphous carbon material is placed in a chemical vapor deposition reactor, nitrogen is introduced, the temperature is increased to 500-700 DEG C, then composite gas is introduced, the deposition reaction is carried out for 100-800 minutes, a pre-product is obtained, the composite gas comprises a metal silane precursor, doping auxiliary gas and acetylene gas, and the doping auxiliary gas is used for regulating and controlling growth of sediments; and heating the pre-product to 750-850 DEG C for 10-30 minutes, cooling the pre-product to 500-600 DEG C, introducing acetylene gas again, and keeping the temperature for 30-300 minutes to obtain the metal-doped silicon-carbon negative electrode material. Therefore, the electrochemical performance and the cycle life are effectively improved.

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 have developed into the most important energy storage technology for electric vehicles and electronic devices due to their long cycle life and high energy density. However, lithium-ion batteries can no longer meet the market demand for high-energy lithium-ion batteries due to the low theoretical capacity of traditional graphite negative electrodes. Therefore, the industry and scholars have turned their attention to silicon-based negative electrode materials with high industrial feasibility. Silicon-based materials have two major problems: one is the large volume expansion (>300% during lithium insertion and extraction), and the other is poor electronic conductivity. After years of research and development, silicon-based negative electrode materials have been iterated to the third generation of new silicon carbon, which has significantly improved expansion compared to the first generation of ground silicon, and has more obvious advantages in cycle and first effect compared to the second generation of silicon oxygen. Although the third generation of silicon carbon has obvious advantages in capacity and expansion, its rate performance is poor. How to effectively improve the rate performance of the third generation of silicon materials and obtain silicon negative electrode materials with high specific capacity and long cycle life is an urgent problem to be solved in the current lithium battery field.

[0003] At present, the methods for improving the dynamics of silicon-carbon materials have defects. On the one hand, although the doping modification of porous carbon substrates can reduce some internal resistance in local areas, the overall electron transmission network has not been effectively constructed due to insufficient contact between silicon and carbon, resulting in limited reduction in the internal resistance of the entire system. In addition, silicon undergoes drastic volume changes during charging and discharging. This expansion-contraction effect will destroy 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, thus 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 the battery.

[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: S1. Prepare a modified amorphous carbon material and a metal silane precursor respectively. Among them, 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; S2. Place the modified amorphous carbon material in a chemical vapor deposition reactor, introduce nitrogen gas and heat up to 500 - 700 °C, then introduce a composite gas, and carry out a deposition reaction for 100 - 800 minutes to obtain a pre-product. Among them, 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; S3. Heat the pre-product to 750 - 850 °C for a duration of 10 - 30 minutes, cool down to 500 - 600 °C, and introduce acetylene gas again, and keep the temperature for 30 - 300 minutes to obtain a metal-doped silicon-carbon anode material.

[0007] In some embodiments, step S1 includes: S1.1. Disperse amorphous carbon powder in deionized water, ultrasonically treat it in an ultrasonic cleaner for 10 minutes, transfer it to a reaction kettle, add concentrated nitric acid, the reaction temperature is 120 °C, carry out the reaction under pressure conditions for 2 hours. After the reaction ends, filter or centrifuge to collect the product, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 80 °C for 12 hours to obtain etched carbon powder; S1.2. Mix the etched carbon powder and solid potassium hydroxide in a mass ratio of 1:3, then place it in a tube furnace under a nitrogen atmosphere and heat it to 800 °C, with a heating rate of 5 °C / min, keep the temperature 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; S1.3. Add a silane component and a metal component to anhydrous toluene, stir for 10 - 30 minutes, then add a catalyst, heat up to 110 °C, keep the temperature for 12 hours, cool it down to room temperature, then carry out rotary evaporation to remove anhydrous toluene, dissolve it in a small amount of ethyl acetate for purification, and dry it at 60 °C to constant weight to obtain a metal silane precursor.

[0008] In some embodiments, in step S1.3, the silane component includes at least one of methyltriethoxysilane, tetraethoxysilane, and diethoxydimethylsilane, the metal component includes at least one of tetraethoxygeranium, triethoxyarsenic, tetraethoxytin, triethoxystibine, 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.

[0009] In some embodiments, step S2 includes: S2.1. Place the modified amorphous carbon material in a chemical vapor deposition reactor under a nitrogen atmosphere, heat it to 500 - 700 °C at a heating rate of 5 - 10 °C / min; S2.2. Maintain the temperature, stop introducing nitrogen, vaporize the metal silane precursor and mix it with an auxiliary doping gas and acetylene gas to form a composite gas, and then introduce the composite gas into the chemical vapor deposition reactor containing the modified amorphous carbon material. The deposition reaction duration is set at 100 - 800 minutes; S2.3. Continuously introduce the composite gas, raise the temperature to 750 - 850 °C, keep it warm for 10 - 30 minutes, and obtain a pre - product after cooling.

[0010] 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.

[0011] In some embodiments, in step S2.2, calculated by molar ratio, the metal silane precursor: the auxiliary doping gas: the acetylene gas = (10 - 20):1:(5 - 10), the density of the auxiliary doping gas is 1.52 - 1.54 g / cm 3 , and the density of the acetylene gas is 0.5 - 1.57 g / cm 3 .

[0012] In some embodiments, step S3 includes: S3.1. Continuously heat the pre - product in the chemical vapor deposition reactor, with a recommended heating rate of 10 - 20 °C / min, quickly raise the temperature to 800 - 900 °C, and keep it warm for 10 - 30 minutes; S3.2. Cool down to 500 - 600 °C, introduce acetylene gas with a flow rate of 0.5 - 10 L / min, keep it warm for 30 - 300 minutes, stop introducing acetylene gas after heating is completed, continue to maintain nitrogen protection, and slowly cool down to room temperature to obtain a metal - doped silicon - carbon anode material.

[0013] The present invention provides a metal - doped silicon - carbon anode material, which is prepared by the preparation method of a metal - doped silicon - carbon anode material as described above. The metal - doped silicon - carbon anode material includes 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 the metal silane precursor; The metal silane precursor is used to improve the specific capacity and electrochemical performance of the metal - doped silicon - carbon anode material; The doped auxiliary gas is used to enhance the cycle stability of the metal-doped silicon-carbon anode material; The acetylene gas is used to form a carbon coating layer.

[0014] Compared with the prior art, a metal-doped silicon-carbon anode material and its preparation method in the present invention have the beneficial effects that: The internal pores of the modified amorphous carbon material enable the active substances to be evenly dispersed in the anode, and at the same time provide sufficient diffusion channels for lithium ions, reducing the local concentration gradient, which is beneficial to the uniform insertion and extraction of lithium ions. By chemically vapor depositing (CVD) a composite gas containing a metal silane precursor, the uniform dispersion of metal doping is achieved. Metal doping can form a continuous conductive network in the silicon-carbon material, reducing the electron transfer resistance and improving the overall conductivity. This is crucial for reducing the internal resistance and accelerating the electron transfer speed during charge and discharge. Metal doping can improve the interfacial bonding between silicon and carbon, alleviate the structural damage problem caused by the drastic volume change of silicon during charge and discharge, ensure the mechanical integrity and interfacial stability of the electrode material during long-term cycling, and thus improve the cycle life. Description of the Drawings

[0015] Figure 1 is the SEM image of the metal-doped silicon-carbon anode material in Example 1 of the present invention; Figure 2 is the elemental distribution overlay image of the metal-doped silicon-carbon anode material in Example 1 of the present invention; Figure 3 is the germanium element distribution image of the metal-doped silicon-carbon anode material in Example 1 of the present invention. Detailed Embodiments

[0016] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] The present invention provides a preparation method of a metal-doped silicon-carbon anode material for manufacturing a lithium-ion battery, and the steps include: 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.

[0018] Step S1 includes: S1.1. Disperse amorphous carbon powder in deionized water, ultrasonically treat it in an ultrasonic cleaner for 10 minutes, transfer it to a reaction kettle, add concentrated nitric acid, react at a temperature of 120 °C for 2 hours. After the reaction, filter or centrifuge to collect the product, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 80 °C for 12 hours to obtain etched carbon powder. The concentration of concentrated nitric acid is 68 - 70%.

[0019] The concentrated nitric acid oxidizes the amorphous carbon powder at 120 °C, generating oxidation functional groups such as carboxyl and hydroxyl groups on the carbon surface. This process can form fine etching on the carbon surface, increasing the surface roughness and activity, providing favorable conditions for subsequent chemical activation. By ultrasonically treating in deionized water, it ensures the full dispersion of carbon powder, improves the uniformity of the reaction, and enables each particle surface to receive uniform etching treatment. The obtained etched carbon powder has a higher surface energy and an improved primary pore structure, laying a foundation for subsequent potassium hydroxide activation and ensuring that the modified carbon material has the required particle size (7 - 8 μm) and preliminary pore structure.

[0020] In one embodiment, the etched carbon powder can be soaked in a solution containing 30% hydrogen peroxide to promote the introduction of more oxidizing functional groups (such as quinones or peroxides), improving the redox characteristics. This step helps to form a surface gradient functional layer as a buffer interface during subsequent metal silicon deposition.

[0021] S1.2. Mix the etched carbon powder and solid potassium hydroxide in a mass ratio of 1:3, then place it in a tubular furnace under a nitrogen atmosphere and heat it to 800 °C at a heating rate of 5 °C / min, hold for 2 hours, cool it, 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.

[0022] Mix the etched carbon powder and potassium hydroxide in a mass ratio of 1:3 and heat them at 800 °C (heating rate 5 °C / min) for 2 hours under nitrogen protection. During the reaction process, the generated gas will locally accumulate in the closed system, resulting in a phenomenon of tiny bubbles. These local high-pressure impact forces will damage the local structure of the carbon material, thereby etching out fine pores on the surface of the carbon powder. At high temperatures, potassium hydroxide reacts with carbon to form intermediate products such as potassium carbonate, and at the same time, gases (such as carbon dioxide and water vapor) are generated. These reaction products form pores inside the carbon particles. Subsequently, through washing with dilute hydrochloric acid, the residual metal salts and by-products in the carbon are removed, and the internal pores generated by the activation of potassium hydroxide are retained. This process enables the modified carbon material to not only possess the stability of the original particle size but also have internal pores mainly concentrated in the range of 0.1 - 10 nm, enhancing the specific surface area and pore connectivity. The obtained modified amorphous carbon material has a more active surface and a uniform pore structure, which is conducive to the uniform attachment of the precursor and atomic-level deposition during the subsequent deposition process, effectively improving the overall electrochemical reaction activity and ion transport efficiency of the anode material.

[0023] To determine 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.

[0024] Take the sample of the prepared modified amorphous carbon material and conduct SEM observation to count the particle diameters in multiple fields of view. Confirm whether the average particle size is in the range of 7 - 8 μm. If the average particle size is less than 7 μm or greater than 8 μm, the chemical etching or activation treatment conditions (such as reaction time, temperature, or the ratio of potassium hydroxide) need to be adjusted to correct the particle size distribution.

[0025] To determine whether the internal pore size of the modified amorphous carbon material meets the requirements, a nitrogen adsorption - desorption experiment is carried out using a BET (specific surface area and pore size distribution tester).

[0026] Conduct a BET test on the sample and analyze the pore size distribution data. Check whether the internal pore size is mainly distributed in the range of 0.1 - 10 nm. If the pore size distribution significantly deviates from the range of 0.1 - 10 nm, it indicates that the pore structure regulation in the etching or activation process is insufficient. At this time, parameters such as etching concentration, temperature, or activation time need to be readjusted.

[0027] If the above test results all meet the predetermined requirements, proceed to the next process; if the above test results do not meet the requirements, record the deviation situation and feedback it to step S1.1. After adjusting the reaction parameters, perform the modification treatment again until the target parameters are achieved.

[0028] In one embodiment, if the SEM statistics show that the average particle size is 6.5 μm (lower than the target of 7 μm), the acid etching time is shortened from the original 2 hours to 1.5 hours, or the concentration of concentrated nitric acid is reduced from 68% to 60%. After re-preparation, observe the change in particle size until the average particle size reaches 7 - 8 μm.

[0029] If the BET test shows that the average pore size is 15 nm (exceeding the upper target limit of 10 nm), the ratio of potassium hydroxide to carbon powder is reduced from 1:3 to 1:2, or the heat preservation time is shortened from 2 hours to 1.5 hours. Confirm whether the pore size distribution is adjusted to the range of 0.1 - 10 nm through subsequent detection.

[0030] S1.3. Add the silane component and the metal component to anhydrous toluene to determine whether the particle size of the modified amorphous carbon material meets the requirements. After stirring for 10 - 30 minutes, add a catalyst, heat up to 110 °C, keep warm for 12 hours, cool to room temperature, then perform rotary evaporation to remove anhydrous toluene, dissolve in a small amount of ethyl acetate for purification, and dry to constant weight at 60 °C to obtain a metal silane 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 tetraethoxy germanium, triethoxy arsenic, tetraethoxy tin, triethoxy antimony, and triethoxy gallium. Calculated by molar ratio, silane component: 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.

[0031] The silane component and the metal component are added to anhydrous toluene, and stirred for 10 - 30 minutes under an inert atmosphere to ensure that each component is fully mixed and uniformly dispersed in the solvent. After adding the catalyst, 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 to form a molecular-level homogeneous metal silane precursor. Among them, the molar ratio is controlled such that the silane component to the metal component is (5 - 20):1, that is, the silane component dominates to ensure the formation of a stable silicon skeleton, while the metal component is introduced in a doped form. After the reaction is completed, it is cooled to room temperature, and anhydrous toluene is removed by rotary evaporation, then dissolved in a small amount of ethyl acetate for purification, and finally dried to a constant weight at 60 °C to obtain the metal silane precursor. The precursor molecule contains both silicon and metal functional groups, and covalent bonds are formed through a condensation reaction, achieving a homogeneous combination of metal and silicon at the molecular level. The obtained metal silane precursor has good volatility (facilitating subsequent chemical vapor deposition), and its chemical structure lays the foundation for atomic-level deposition during the subsequent chemical vapor deposition process. The molar ratio of the silane component to the metal component and the amount of the catalyst are precisely controlled to ensure the high efficiency and stable structure of the precursor reaction, thereby improving the homogeneity and functionality of the metal, silicon, and carbon three-phase composite structure during the subsequent deposition process.

[0032] S2. Place the modified amorphous carbon material in a chemical vapor deposition reactor, introduce nitrogen gas and heat up to 500 - 700 °C, then introduce the composite gas, and carry out the deposition reaction for 100 - 800 minutes to obtain a pre-product. Among them, the composite gas includes the metal silane precursor, the doping auxiliary gas, and acetylene gas, and the doping auxiliary gas is used to regulate the growth of the deposit.

[0033] Step S2 includes: S2.1. Place the modified amorphous carbon material in a chemical vapor deposition reactor under a nitrogen atmosphere, and heat up to 500 - 700 °C at a heating rate of 5 - 10 °C / min.

[0034] During the preheating process, the temperature rises evenly to bring the substrate surface to the optimal activation state, which helps the subsequent decomposition of the precursor and uniform deposition. The nitrogen protection prevents the carbon substrate from being oxidized at high temperatures, ensuring that the surface functional groups and pore structure are not damaged. Ensuring the surface activity and structural stability of the substrate creates an ideal thermal environment for subsequent deposition, and the controlled heating rate helps to avoid structural stress and inhomogeneity caused by too large a temperature gradient.

[0035] 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. Calculated by 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 .

[0036] Through heating and carrier gas delivery, the metal silane precursor volatilizes into a gaseous state in anhydrous toluene, and is mixed with auxiliary doping gas and acetylene gas in a preset molar ratio to ensure molecular uniformity. The trace addition of auxiliary doping gas regulates the reaction interface energy, adjusts the nucleation and growth rate, and helps to form deposits with uniform size and fewer defects. At 500~700℃, the vaporized metal silane precursor decomposes, and acetylene is deposited to form an auxiliary carbon layer, which together forms a composite deposit of metal, silicon and carbon on the carbon substrate. Atomic-level uniform deposition of metal and silicon on the substrate is achieved, and at the same time, the auxiliary doping gas regulates the growth of the deposit, so that the grain size and morphology of the deposited layer meet the expected design. The participation of acetylene improves the density and conductivity of the deposited layer, providing a guarantee for subsequent electrochemical performance.

[0037] In one embodiment, in order to ensure that the thickness of the deposited layer generated on the modified amorphous carbon material remains within a preset thickness, a calculation formula is obtained from multiple experimental experiences:

[0038] 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 combined constant whose units are 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 and belongs to a process constant. The specific value depends on the reaction system and equipment design. Through preliminary experiments, using the deposition thickness measured with other known parameters, the value is deduced and fixedly used in subsequent processes. (dimensionless) is the molar fraction of the metal silane precursor, representing the molar ratio of the metal silane precursor in the mixed gas. For example, 0.05 - 0.2 (i.e., 5% - 20%), specifically depending on the required deposition rate and the composition of the final deposited layer. (Pa) In the CVD reactor, it depends specifically on the process design. It is directly measured by the pressure sensor in the reactor and 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 when converted to absolute temperature, and is measured by the temperature sensor (thermocouple, infrared thermometer, etc.) in the reactor. (mL / min) The gas flow rate is obtained through a flow meter. In step S2.2, the flow rate range of the composite gas is set at 0.5 - 15 L / min. (min) is the deposition time, set at 100 - 800 minutes.

[0039] Using the formula, engineers can estimate the thickness of the deposited layer based on the set reaction parameters (such as the molar fraction of the metal silane precursor, the total pressure , the temperature , the flow rate This enables process developers to design the deposition process more precisely, ensuring that the deposited layer reaches the desired thickness (the target range may be 200 - 600 nm). The various parameters in the formula (temperature, pressure, flow rate, time, etc.) directly reflect their effects on the deposition rate and the final thickness. For example, the square root relationship between temperature and flow rate indicates that increasing both temperature and flow rate will increase the deposition rate, but the effect is non-linear. This relationship can assist in making fine adjustments during actual operation and optimizing the deposition conditions. Meanwhile, by adjusting the molar fraction of the metal silane precursor and the deposition time, it is possible to precisely control the thickness and uniformity of the deposited layer on the premise of ensuring sufficient chemical reactions. This formula provides theoretical support for on-line monitoring and feedback control. By measuring the deposition thickness in real time (such as using on-line optical measurement or cross-section analysis), the actual thickness can be compared with the predicted value of the formula, and process parameters (such as flow rate and temperature) can be adjusted to achieve fine 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 electron conduction performance. By precisely controlling the deposition thickness, an ideal composite structure can be formed, thereby reducing the internal resistance, improving the electro-chemical reaction kinetics, and enhancing the cycle stability and rate performance.

[0040] S2.3. Continuously introduce the composite gas, raise the temperature to 750 - 850 °C, keep it warm for 10 - 30 minutes, and obtain the pre-product after cooling.

[0041] Under the high-temperature condition of 750 - 850 °C, the metal silicon decomposition products in the deposited layer further undergo partial crystallization and interface fusion to form a more regular grain boundary structure. The high-temperature treatment helps to eliminate the internal stress formed during the deposition process, enhance the interlayer bonding, and at the same time promote the interdiffusion of metal, silicon, and carbon phases, making the composite structure more compact. Through the high-temperature heat preservation treatment, the grain size inside the pre-product is more uniform, the interface structure is more stable, and the electro-chemical performance and structural durability of the overall deposit are improved. This step helps to form an ideal nano-composite layer, laying a foundation for the practical application of the subsequent anode material.

[0042] 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 anode material.

[0043] Mix the obtained pre-product, the siloxane precursor, and magnesium powder in proportion to obtain a mixture. The mass ratio is: pre-product: siloxane precursor: magnesium powder = 1:1:1 (this ratio can be optimized according to the target silicon content). After thorough mixing, ensure that each component is in uniform contact.

[0044] Place the mixture in a quartz boat and put it into a tube furnace. Under the protection of inert nitrogen (nitrogen flow rate is 50 mL / min), heat the temperature to 650 - 700 °C at a heating rate of 5 °C / min and keep it at this temperature range for 2 hours. The siloxane precursor is converted into silicon through the magnesiothermic reduction reaction, and the generated magnesium oxide will be embedded in the mixture. After the reaction, it is naturally cooled to room temperature. Treat the cooled product with dilute hydrochloric acid to dissolve the generated magnesium oxide and unreacted magnesium, and then wash it repeatedly with deionized water until the pH of the washing solution reaches neutral. Dry the washed product at 100 °C for 12 hours. Among them, the siloxane precursor includes at least one of methyltrimethoxysilane, methyltriethoxysilane, and methyltrichlorosilane.

[0045] The siloxane precursor generates a siloxane substance with a (CH3SiO 1-5 )n network structure after hydrolysis and condensation. The magnesium powder is used as a reducing agent to reduce the silicon-oxygen bond in the siloxane precursor to elemental silicon. The original deposition layer of the pre-product contains part of metallic silicon and a carbon network. By adding the siloxane precursor and magnesium powder, additional silicon can be introduced into the original composite structure, which is equivalent to silicon strengthening of the pre-product. Under the protection of inert nitrogen, heat it to 650 - 700 °C at a rate of 5 °C / min, and the magnesium powder and the siloxane precursor undergo a magnesiothermic reduction reaction. The generated silicon is dispersed in the mixture, increasing the silicon content in the pre-product. At the same time, since silicon is often generated in a porous form, the microstructure of the overall composite material becomes more hierarchical and connected.

[0046] The siloxane precursor is converted into silicon through the magnesiothermic reduction reaction, compensating for the shortage of silicon 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 transport and lithium-ion diffusion. The magnesium oxide generated during the magnesiothermic reduction process will be temporarily embedded in the mixture, generating gas locally to form pores. Subsequently, wash away the magnesium oxide and residual magnesium with dilute hydrochloric acid. After repeated washing, a large number of uniform and connected pores will remain on the surface and inside of the product. After the porous silicon and the original modified amorphous carbon material are combined, the specific surface area of the overall material is greatly increased, which is beneficial to the infiltration of the electrolyte and the rapid transport of lithium ions. The high specific surface area and good pore structure provide more ion transport channels, reducing the interfacial impedance and having a positive impact on both the cycling performance and the rate performance.

[0047] By mixing a siloxane precursor, magnesium powder, and a pre-product in a mass ratio of 1:1:1, the organic combination of the solid-state reduction method and the pre-product of CVD deposition is achieved, enabling the material to benefit simultaneously in terms of chemical composition and microstructure. This process not only increases the effective silicon content but also further enhances the kinetic performance of the overall composite material by utilizing the pore generation brought about by high-temperature reduction. The composite material has a higher silicon content, a more abundant pore structure, and an optimized composite interface, which helps to relieve the stress caused by the volume change of silicon during charge and discharge, improve the cycle stability of the material. The higher specific surface area and uniform composite structure promote the rapid transmission of lithium ions and the efficient conduction of electrons, thereby enhancing the rate performance and cycle life of the anode material. By introducing the magnesiothermic reduction method of a siloxane precursor and magnesium powder in the pre-product treatment, using methyltrimethoxysilane, methyltriethoxysilane, or methyltrichlorosilane as the silicon source, and conducting the reduction reaction at 650 - 700 °C under nitrogen protection, not only significantly increases the silicon content in the pre-product but also forms a large number of microporous structures during pickling and drying processes, thus increasing the specific surface area of the composite material. Such a treatment method enables the final metal-doped silicon-carbon anode material to possess more excellent electrochemical kinetics and cycle stability, which is of great significance for improving the overall performance of the battery.

[0048] S3. Heat the pre-product to 750 - 850 °C for a duration of 10 - 30 minutes, cool it down to 500 - 600 °C, and then introduce acetylene gas again and keep it warm for 30 - 300 minutes to obtain the metal-doped silicon-carbon anode material.

[0049] Step S3 includes: S3.1. Continuously heat the pre-product in a chemical vapor deposition reactor with a recommended heating rate of 10 - 20 °C / min, quickly raise the temperature to 800 - 900 °C, and keep it warm for 10 - 30 minutes.

[0050] Under the high-temperature condition of 800 - 900 °C, the metal-silicon mixture in the pre-product further undergoes partial crystallization and interface reconstruction, enhancing atomic diffusion and making the interface between the metal and silicon more firm. The high-temperature condition helps to eliminate internal defects and stresses generated during the deposition process, forming a more regular and dense grain and interface structure. Annealing enables the mutual diffusion and grain reorganization of the metal and silicon, improving the crystallinity and interface bonding degree of the composite deposition layer. By keeping it warm at a high temperature, the internal stress and crystal defects are significantly reduced, thereby improving the uniformity of the subsequent deposited carbon coating layer. The strengthened grain boundaries help to improve the stability of the material under dynamic thermal shock, providing support for subsequent applications (such as rapid charge and discharge in extremely cold environments).

[0051] S3.2. Cool down to 500 - 600 °C, introduce acetylene gas with a flow rate of 0.5 - 10 L / min, keep the temperature for 30 - 300 minutes. After the heating is completed, stop introducing acetylene gas and continue to maintain nitrogen protection, then slowly cool down to room temperature to obtain the metal-doped silicon-carbon anode material.

[0052] At 500 - 600 °C, acetylene gas partially pyrolyzes to generate active carbon atoms or carbon clusters. These active species aggregate on the surface of the precursor, gradually forming a uniform carbon coating layer. The carbon coating layer can fill the tiny defects on the surface of the precursor and at the same time form a continuous and dense covering layer, which helps to improve the electronic conductivity and the mechanical stability of the overall structure. The formed carbon coating layer can effectively prevent the internal metal silicon structure from being eroded by the external environment (such as the electrolyte), improving the cycle stability of the material. The uniform and dense carbon layer is conducive to electron transport, reducing the interfacial impedance and enhancing the electrochemical performance of the anode material. The carbon coating layer, through its heat conduction characteristics, helps to quickly disperse local heat during rapid charge and discharge processes, thereby improving the thermal stability of the material under extreme conditions.

[0053] The present invention provides a metal-doped silicon-carbon anode material, which is prepared by a preparation method of a metal-doped silicon-carbon anode material. The metal-doped silicon-carbon anode material includes 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 the metal silane precursor; The metal silane precursor is used to improve the specific capacity and electrochemical performance of the metal-doped silicon-carbon anode material; The doping auxiliary gas is used to enhance the cycle stability of the metal-doped silicon-carbon anode material; The acetylene gas is used to form a carbon coating layer.

[0054] Example 1: Add 1500 g of a modified amorphous carbon material with a particle size D50 of 8 μm into a chemical vapor deposition reactor, introduce nitrogen at a flow rate of 14 L / min, heat up the temperature in the furnace to 520 °C, introduce methyltriethoxysilane and tetraethoxysilane with a molar ratio of 10:1 at a flow rate of 3 L / min, and at the same time introduce acetylene gas. The gas introduction time is set to 500 min. Raise the temperature to 800 °C, keep the temperature for 20 minutes, and cool to obtain a precursor. Subsequently, in the chemical vapor deposition reactor, introduce nitrogen at a heating rate of 14 L / min, heat up to 850 °C, keep the temperature for 20 minutes and then cool down to 550 °C, and then introduce acetylene gas at a gas flow rate of 3 L / min. The acetylene gas introduction time is set to 200 min, and cool to obtain the metal-doped silicon-carbon anode material.

[0055] Comparative Example 1: Compared with Example 1, the difference lies in that only methyltriethoxysilane is introduced during the silane deposition stage.

[0056] Table 1: Electrical experiment data: 。

[0057] Weigh the metal-doped silicon-carbon anode material, conductive carbon black, and binder CMC, and add deionized water to prepare a homogeneous slurry. The solid content ratio of the metal-doped silicon-carbon anode material: conductive carbon black: binder CMC is 95:1.5:3.5. Use a homogenizer to prepare the sample with a rotation speed of 2000 rpm for 20 minutes. After sieving the slurry, coat it evenly on the copper foil and place it in a vacuum drying oven at 90 °C for drying. After rolling the dried electrode sheet, cut it into circular electrodes of a certain size and record the electrode mass. In an argon atmosphere glove box, use a lithium metal sheet as the counter electrode, and assemble it with the obtained electrode, separator, gasket, etc. into a button cell. The electrolyte uses a special electrolyte for silicon-carbon.

[0058] After performing charge and discharge cycles on Example 1 and Comparative Example 1, the experimental data obtained are shown in Table 1, indicating that the metal-doped silicon-carbon anode material doped with metal has excellent cycle performance, effectively improving the charging efficiency and service life of lithium-ion batteries.

[0059] Figure 1 This is a scanning electron microscope (SEM) image, showing the appearance, size, and surface characteristics of individual particles of the metal-doped silicon-carbon anode material. The particle is generally polyhedral or approximately block-shaped, with a relatively flat surface and distinct edges and corners, indicating that it has certain crystallization or sintering characteristics.

[0060] Figure 2 Based on the SEM image, energy dispersive spectroscopy (EDS) is used for elemental composition analysis, and the distribution information of multiple elements (such as Si, C, O, Ge, etc.) is superimposed on the same image. Through the color or gray-scale distribution, the distribution uniformity and relative content of each element on the surface and inside of the particle can be intuitively seen. It can be seen from the figure that elements such as Si, C, O, Ge, etc. seem to be distributed throughout the particle, indicating that these elements have been successfully doped into the material during the preparation process.

[0061] Figure 3 This is the distribution mapping diagram for germanium element. Each bright or gray-scale point on the diagram represents the presence and intensity of this element in a local area. Through this point cloud distribution, it can be observed that the distribution of germanium in this particle is relatively uniform, without obvious enrichment areas or local deficiencies, indicating that the doping is relatively uniform.

[0062] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a metal-doped silicon-carbon anode material for fabricating a lithium-ion battery, characterized in that the steps Including: S1. Prepare a modified amorphous carbon material and a metal silane precursor respectively. Among them, 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; S2. Place the modified amorphous carbon material in a chemical vapor deposition reactor, introduce nitrogen gas and heat it to 500 - 700 °C, then introduce a composite gas, and carry out a deposition reaction for 100 - 800 minutes to obtain a pre-product. Among them, 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; S3. Heat the pre-product to 750 - 850 °C for a duration of 10 - 30 minutes, cool it to 500 - 600 °C, and introduce acetylene gas again, and keep it warm for 30 - 300 minutes to obtain a metal-doped silicon-carbon anode material.

2. The preparation method of a metal-doped silicon-carbon anode material according to claim 1, wherein, Step S1 includes: S1.

1. Disperse amorphous carbon powder in deionized water, ultrasonically treat it in an ultrasonic cleaner for 10 minutes, transfer it to a reaction kettle, add concentrated nitric acid, the reaction temperature is 120 °C, carry out the reaction under pressure conditions for 2 hours. After the reaction is completed, filter or centrifuge and collect the product, wash it with deionized water until the pH of the filtrate is 7, and then dry it in an oven at 80 °C for 12 hours to obtain etched carbon powder; S1.

2. Mix the etched carbon powder and solid potassium hydroxide in a mass ratio of 1:3, then place it in a tubular furnace under a nitrogen atmosphere and heat it to 800 °C, with a heating rate of 5 °C / min, keep it warm for 2 hours, and after cooling, 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; S1.

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

3. The preparation method of a metal-doped silicon-carbon anode material according to claim 2, wherein, In step S1.3, the silane component includes at least one of methyltriethoxysilane, tetraethoxysilane, and diethoxydimethylsilane, the metal component includes at least one of tetraethoxy germanium, triethoxy arsenic, tetraethoxy tin, triethoxy antimony, and triethoxy gallium. 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, and the catalyst accounts for 1 - 2% of the total mass of the silane component and the metal component.

4. The preparation method of a metal-doped silicon-carbon anode material according to claim 1, characterized in that, Step S2 includes: S2.

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

2. Keep the temperature, stop introducing nitrogen gas, vaporize the metal silane precursor and mix it with the auxiliary doping gas and acetylene gas to form a composite gas, and then introduce the composite gas into the chemical vapor deposition reactor containing the modified amorphous carbon material, and set the deposition reaction duration at 100 - 800 minutes; S2.

3. Continuously introduce the composite gas, raise the temperature to 750 - 850 °C, keep the temperature for 10 - 30 minutes, and obtain the pre-product after cooling.

5. The preparation method of a metal-doped silicon-carbon anode material according to claim 4, characterized in that, 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.

6. The preparation method of a metal-doped silicon-carbon anode material according to claim 5, characterized in that, In step S2.2, calculated by molar ratio, the metal silane precursor: the auxiliary doping gas: the acetylene gas = (10 - 20):1:(5 - 10), the density of the auxiliary doping gas is 1.52 - 1.54 g / cm 3 , the density of the acetylene gas is 0.5 - 1.57 g / cm 3 .

7. The preparation method of a metal-doped silicon-carbon anode material according to claim 1, characterized in that, Step S3 includes: S3.

1. Continuously heat the pre-product in a chemical vapor deposition reactor, with a recommended heating rate of 10 - 20 °C / min, rapidly raise the temperature to 800 - 900 °C, and keep the temperature for 10 - 30 minutes; S3.

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

8. A metal-doped silicon-carbon anode material, characterized in that Prepared by the preparation method of a metal-doped silicon-carbon anode material according to any one of claims 1 - 7, the metal-doped silicon-carbon anode material includes 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 the metal silane precursor; The metal silane precursor is used to improve the specific capacity and electrochemical performance of the metal-doped silicon-carbon anode material; The doping auxiliary gas is used to enhance the cycle stability of the metal-doped silicon-carbon anode material; The acetylene gas is used to form a carbon coating layer.

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