Preparation method of a non-metal doped silicon-based anode material

Abstract

The present invention provides a method for preparing a non-metal doped silicon-based anode material, comprising the following steps: preparing a porous carbon substrate having a hierarchical pore structure; sequentially depositing a non-metal doped gas and a silane gas in the porous carbon substrate to obtain a non-metal doped silicon-based material; performing multi-layer carbon coating on the surface of the silicon-based material to obtain a silicon-based anode precursor; and performing heat treatment on the silicon-based anode precursor to obtain a non-metal doped silicon-based anode material. The phenomenon of uneven doping is avoided, and the electrochemical performance of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a preparation method of a non - metal - doped silicon - based anode material. Background Art

[0002] In recent years, silicon - based anodes, with their ultra - high theoretical specific capacity (about 4200 mAh / g), have gradually become strong competitors for the next - generation lithium - ion battery anode materials. Compared with traditional graphite anodes, silicon - based anodes can significantly improve the overall energy density of the battery. However, during the lithium - ion insertion and extraction process of charge and discharge, silicon will experience large volume expansion and contraction (up to 300%), which will lead to damage to the electrode structure, resulting in problems such as poor cycle stability and rapid capacity decay. At the same time, another major practical application difficulty is that the pure silicon anode itself has poor electronic conductivity (1.56×10 -3 s / m), and it must be used by being compounded with carbon materials (such as graphite, carbon nanotubes, etc.) or doped with other elements.

[0003] In silicon - carbon anodes, the porous carbon substrate has a large number of defects, which affect the distribution state of amorphous silicon decomposed from silane on it. Non - metal doping can change the crystal structures of the porous carbon substrate and silicon, help alleviate the volume expansion of silicon during the lithium - insertion and extraction process, and reduce the risk of pulverization and failure of the silicon electrode. However, current doping methods mostly remain in the small - scale experimental stage adopted in laboratories such as sol - gel method and thermal reduction method, and problems such as uneven distribution of doping elements in the substrate and poor performance of the doped anode material are prone to occur. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of a non - metal - doped silicon - based anode material, aiming to solve the problem that the uneven distribution of doping elements leads to poor performance of the anode material.

[0005] To solve the above - mentioned technical problem, the present invention is realized as follows. The present invention provides a preparation method of a non - metal - doped silicon - based anode material, including the following steps:

[0006] S1. Prepare a porous carbon substrate with a hierarchical pore structure, wherein the pore size of the porous carbon substrate is 0.1 - 100 nm. Calculated by percentage, the hierarchical pore structure includes 30 - 90% micropores, 5 - 55% mesopores, and 5 - 55% macropores. The pore diameter of the micropores is 0.1 - 2 nm, the pore diameter of the mesopores is 2 - 50 nm, and the pore diameter of the macropores is 50 - 100 nm;

[0007] S2. Deposit non - metal doping gas and silane gas in the porous carbon substrate in sequence to obtain a non - metal - doped silicon - based material, wherein the non - metal doping gas includes borane gas or phosphine gas;

[0008] S3. Perform multi-layer carbon coating on the surface of the silicon-based material to obtain a silicon-based anode precursor;

[0009] S4. Heat-treat the silicon-based anode precursor to obtain a non-metal doped silicon-based anode material.

[0010] In some embodiments of the present invention, the step S1 includes:

[0011] S1.1. Clean, dry, and pulverize the carbon source material to obtain a uniform particle size distribution, and control the D50 value of the particle size within 5 - 10 μm;

[0012] S1.2. Add a template material to the carbon source material, control the mass ratio of the carbon source material to the template material at 1:2, heat to 800 - 1000 °C, with a heating rate of 5 - 10 °C / min, and hold for 2 - 4 h to obtain a premix;

[0013] S1.3. Transfer the premix to a hydrofluoric acid solution to remove the template material, control the temperature at room temperature, and react for 4 - 6 h to obtain a porous carbon substrate with a hierarchical pore structure.

[0014] In some embodiments of the present invention, in the step S1, the carbon source material includes at least one of porous carbon, natural graphite, artificial graphite mesophase carbon microspheres, and expanded graphite;

[0015] The pore size of the porous carbon substrate is 0.1 - 100 nm. Among them, calculated by percentage, the hierarchical pore structure includes 30 - 90% micropores, 5 - 55% mesopores, and 5 - 55% macropores.

[0016] In some embodiments of the present invention, after the step S1.3, the step S1 further includes:

[0017] S1.4. Immerse the porous carbon substrate in a potassium hydroxide or phosphoric acid solution, with the proportion controlled at 2 - 10% of the carbon source mass. After impregnation for 1 - 4 h, calcine at 500 - 700 °C for 2 - 4 h;

[0018] S1.5. Transfer the porous carbon substrate to a strong oxidant solution, control the temperature at 60 - 100 °C, and react for 2 - 6 h;

[0019] S1.6. Wash repeatedly with deionized water to remove unreacted substances, and dry at a temperature of 100 - 150 °C for 4 - 6 h to obtain an activated porous carbon substrate with a hierarchical pore structure.

[0020] In some embodiments of the present invention, the step S2 includes:

[0021] S2.1. Place the porous carbon substrate in a plasma chemical vapor deposition reactor under an inert atmosphere. The flow rate of the inert gas is 1 - 20 L / min, preheat to 400 - 700 °C, and maintain for 40 - 100 min to remove adsorbed impurities and moisture on the surface;

[0022] S2.2. Stop introducing the inert gas, introduce a non-metal doping gas, control the flow rate of the non-metal doping gas at 0.5 - 10 L / min, the reaction temperature is 400 - 600 °C, the plasma power is 200 - 500 W, and the doping time is 30 - 420 min;

[0023] S2.3. Stop introducing the non-metal doping gas, introduce silane gas, control the flow rate of the silane gas at 0.5 - 10 L / min, the reaction temperature is 500 - 700 °C, the plasma power is 200 - 500 W, and the doping time is 100 - 1500 min;

[0024] S2.4. Stop introducing the silane gas, introduce an inert atmosphere, slowly reduce the temperature to room temperature, and control the cooling rate at 5 - 20 °C / min to obtain a non-metal doped silicon-based material.

[0025] In some embodiments of the present invention, in the step S2,

[0026] The inert gas includes at least one of nitrogen, argon, and hydrogen;

[0027] The borane gas includes at least one of diborane, borane, tetraborane, pentaborane, decaborane, hexaborane, and trimethylborane;

[0028] The phosphine gas includes at least one of phosphine, diphosphine, and triphosphine;

[0029] The silane gas includes at least one of silane, disilane, and silane derivatives.

[0030] In some embodiments of the present invention, the step S3 includes:

[0031] S3.1. Introduce a mixed gas of acetylene and hydrogen into the plasma chemical vapor deposition reactor to perform the first deposition reaction. The gas flow rate of acetylene is 5 - 10 L / min, the gas flow rate of hydrogen is 10 - 20 L / min, the reaction temperature is 500 - 800 °C, the deposition time is 30 - 120 min, and the plasma power is 300 - 600 W to form a first carbon coating layer on the silicon-based material;

[0032] S3.2. Stop introducing the mixed gas of acetylene and hydrogen, and introduce the mixed gas of ethylene or methane gas and nitrogen or argon gas to conduct the second deposition reaction. The gas flow rate of ethylene or methane is 2 - 6 L / min, the gas flow rate of nitrogen or argon is 8 - 12 L / min, the reaction temperature is 700 - 900 °C, the deposition time is 20 - 80 min, and the plasma power is 300 - 600 W. The second carbon coating layer is formed on the first carbon coating layer to obtain the silicon-based anode precursor.

[0033] In some embodiments of the present invention, the thickness of the first carbon coating layer is 5 - 15 nm, and the thickness of the second carbon coating layer is 3 - 10 nm;

[0034] By volume ratio, acetylene: hydrogen = 1:2, ethylene or methane: nitrogen or argon = 1:3.

[0035] In some embodiments of the present invention, the step S4 includes:

[0036] S4.1. Set the heating rate to 5 - 10 °C / min until the temperature of the silicon-based anode precursor reaches 800 - 1000 °C, and the heat preservation time is 120 - 240 min;

[0037] S4.2. Introduce ammonia or hydrazoic gas, the gas flow rate is 5 - 15 L / min, adjust the heating rate to 2 - 5 °C / min until the temperature of the silicon-based anode precursor reaches 1000 - 1200 °C, and the heat preservation time is 120 - 240 min to obtain the non-metal doped silicon-based anode material.

[0038] Compared with the prior art, the beneficial effects of a method for preparing a non-metal doped silicon-based anode material in the present invention are as follows:

[0039] In step S1, by preparing a porous carbon substrate with a hierarchical pore structure, pores of different scales (micropores, mesopores, macropores) are provided, which provides an ideal substrate for the uniform penetration and distribution of doping gases. This structure ensures that the doping gases can be evenly distributed throughout the volume of the material, thus avoiding the situation where doping elements are only limited to the surface or certain local areas in the traditional method.

[0040] In step S2, a gas-phase deposition technique is used to introduce non-metal doping gases such as borane or phosphine. This method can ensure the uniform penetration of doping elements and their reaction with the porous carbon substrate in a short time. Compared with the traditional doping method, this method can ensure the uniform distribution of doping elements in the material and avoid the problem of insufficient local doping.

[0041] The multi-layer carbon coating in step S3 enhances the structural stability of the material and ensures the bonding force between the doped elements and the silicon substrate. The carbon coating layer not only prevents the expansion and cracking of silicon particles but also improves the electrical conductivity of the material by providing an additional conduction path, while enhancing the uniformity and stability of the doped elements throughout the material.

[0042] The heat treatment process in step S4 promotes the chemical bonding between the doped elements and the silicon-based material, ensuring the uniformity and stability of the doping process. By precisely controlling the temperature, time, and atmosphere of the heat treatment, the doped elements can penetrate more deeply into the interior of the silicon-based material, avoiding the phenomenon of uneven doping and further improving the electrochemical performance of the material. Brief Description of the Drawings

[0043] Figure 1 is a schematic flow chart of a method for preparing a non-metal doped silicon-based anode material according to an embodiment of the present invention;

[0044] Figure 2 is a scanning electron microscope image of the boron-doped silicon-based anode material prepared by the present invention;

[0045] Figure 3 is a scanning electron microscope image of the phosphorus-doped silicon-based anode material prepared by the present invention. Detailed Embodiments

[0046] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, 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 used to limit the present invention.

[0047] Please refer to Figure 1 , the present invention provides a method for preparing a non-metal doped silicon-based anode material, including the following steps:

[0048] S1. Prepare a porous carbon substrate with a hierarchical pore structure.

[0049] Specifically, step S1 includes:

[0050] S1.1. Clean, dry, and crush the carbon source material to obtain a uniform particle size distribution, and control the D50 value of the particle size within 5 - 10 μm.

[0051] S1.2. Add a template material to the carbon source material, control the mass ratio of the carbon source material to the template material at 1:2, heat to 800 - 1000 °C, with a heating rate of 5 - 10 °C / min and a holding time of 2 - 4 h to obtain a premix;

[0052] S1.3. Transfer the premix to a hydrofluoric acid solution to remove the template material, control the temperature at room temperature, and react for 4 - 6 h to obtain a porous carbon substrate with a hierarchical pore structure.

[0053] Through the operations of steps S1.1 to S1.3, the prepared hierarchical pore structure effectively increases the specific surface area and pore volume, which helps to improve the electrolyte permeability of the electrode material and the lithium ion transport rate.

[0054] In step S1.2, a predetermined pore structure is formed by adding a template material and carbonizing it at a high temperature. Subsequently, in step S1.3, hydrofluoric acid is used to remove the template to ensure the uniformity and controllability of the pore structure, and avoid the collapse or irregular distribution of pores. The template material is effectively removed by hydrofluoric acid treatment, ensuring the purity of the internal pores of the porous carbon substrate and the stability of the structure, providing a good substrate for subsequent non-metal doping and silicon deposition, and improving the cycle stability and electrochemical performance of the final anode material. In step S1.1, a uniform carbon source material with a D50 value controlled within 5 - 10 μm is obtained through cleaning, drying, and pulverizing processes. The uniform particle size distribution helps to improve the overall uniformity of the porous carbon substrate and avoid structural defects caused by different pore sizes in the subsequent process.

[0055] After step S1.3, step S1 further includes:

[0056] S1.4. Immerse the porous carbon substrate in a potassium hydroxide or phosphoric acid solution, with the proportion controlled at 2 - 10% of the mass of the carbon source, and after immersing for 1 - 4 h, calcine it at 500 - 700 °C for 2 - 4 h.

[0057] By immersing the porous carbon substrate in a potassium hydroxide or phosphoric acid solution and calcining it at 500 - 700 °C, chemical activation is carried out. This process can effectively etch the carbon substrate, increase the number and volume of micropores and mesopores, further optimize the hierarchical pore structure, and increase the specific surface area. The chemical activation treatment can introduce more conductive paths, improve the overall conductivity of the porous carbon substrate, and at the same time, by increasing the complexity of the pore structure, enhance the mechanical stability of the material and reduce the structural damage of silicon during charge and discharge.

[0058] S1.5. Transfer the porous carbon substrate to a strong oxidant solution, control the temperature at 60 - 100 °C, and react for 2 - 6 h.

[0059] Transferring the porous carbon substrate to a strong oxidant solution for treatment can introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups on the carbon surface. These functional groups not only increase the hydrophilicity and chemical activity of the carbon substrate, contribute to subsequent non-metal doping and silicon deposition, but also enhance the bonding force between the carbon layer and silicon particles, improving the structural stability and electrochemical performance of the material. Surface functionalization treatment enhances the lithium-ion insertion and extraction ability by introducing more active sites, improving the capacity and cycle stability of the anode material.

[0060] S1.6. Wash repeatedly with deionized water to remove unreacted substances. The drying temperature is 100 - 150 °C and the duration is 4 - 6 h to obtain the activated porous carbon substrate with a hierarchical pore structure.

[0061] By repeatedly washing with deionized water, the chemical reagents and by-products remaining in the chemical activation and strong oxidant treatment processes are removed, ensuring the purity of the porous carbon substrate. This process effectively prevents impurities from interfering with the subsequent non-metal doping and silicon deposition steps, improving the electrochemical performance and stability of the final anode material. The drying step ensures that the material is completely dry, preventing the residual moisture from affecting the subsequent processes and material properties. At the same time, by optimizing the washing and drying conditions, the pore structure of the porous carbon substrate is further stabilized, ensuring that it maintains a good morphology and performance during the subsequent preparation process.

[0062] In step S1, the carbon source material includes at least one of porous carbon, natural graphite, artificial graphite, mesocarbon microbeads, and expanded graphite; the pore size of the porous carbon substrate is 0.1 - 100 nm. Among them, calculated by percentage, the hierarchical pore structure includes 30 - 90% micropores, 5 - 55% mesopores, and 5 - 55% macropores. Among them, the pore diameter of the micropores is 0.1 - 2 nm, the pore diameter of the mesopores is 2 - 50 nm, and the pore diameter of the macropores is 50 - 100 nm.

[0063] By selecting porous carbon, natural graphite, artificial graphite, mesocarbon microbeads, or expanded graphite as the carbon source material, the microstructure and performance characteristics of the porous carbon substrate can be flexibly adjusted to meet the requirements of different application scenarios for the anode material. Specifying the pore diameter as 0.1 - 100 nm and distributing it in the ratio of 30 - 90% micropores, 5 - 55% mesopores, and 5 - 55% macropores ensures that the porous carbon substrate has a high specific surface area and a hierarchical pore structure. This pore distribution not only provides sufficient lithium-ion storage sites but also effectively buffers the volume change of silicon during charge and discharge, improving the cycle stability.

[0064] The porous carbon substrate with a hierarchical pore structure can significantly improve the electrolyte permeability and lithium-ion transport rate, reduce the ion diffusion resistance, and improve the rate performance and charge-discharge efficiency of the electrode material.

[0065] The hierarchical pore structure provides additional buffer space, which can effectively absorb the volume expansion and contraction generated by silicon particles during charge and discharge, reduce the damage of the material structure, and extend the cycle life of the battery.

[0066] By controlling the selection of different carbon source materials and process parameters, the controllability of the pore size distribution of the porous carbon substrate can be achieved, meeting the specific performance requirements of different battery applications for anode materials, such as high energy density, high power density, or long cycle life, etc.

[0067] S2. Sequentially deposit non-metal doping gas and silane gas in the porous carbon substrate to obtain a non-metal doped silicon-based material, wherein the non-metal doping gas includes borane gas or phosphine gas.

[0068] Step S2 includes:

[0069] S2.1. Place the porous carbon substrate in a plasma chemical vapor deposition reactor under an inert atmosphere. The flow rate of the inert gas is 1 - 20 L / min, preheat to 400 - 700 °C, and maintain for 40 - 100 min to remove the impurities and moisture adsorbed on the surface; the inert gas includes at least one of nitrogen, argon, and hydrogen.

[0070] S2.2. Stop introducing the inert gas and introduce the non-metal doping gas. The flow rate of the non-metal doping gas is controlled at 0.5 - 10 L / min, the reaction temperature is 400 - 600 °C, the plasma power is 200 - 500 W, and the doping time is 30 - 420 min; the borane gas includes at least one of diborane, monoborane, tetraborane, pentaborane, decaborane, hexaborane, and trimethylborane; the phosphine gas includes at least one of phosphine, diphosphine, and triphosphine.

[0071] By introducing boron or phosphorus as doping elements, the conductivity of the carbon substrate is significantly improved. The p-type impurities introduced by boron doping can increase the carrier concentration, while phosphorus doping, as an n-type impurity, can improve the electron mobility. Both can improve the overall conductivity of the anode material and meet the requirements of high-rate charge and discharge. Non-metal doping can introduce more active sites in the carbon substrate, promote the intercalation and deintercalation process of lithium ions, and improve the specific capacity and energy density of the anode material. The doping of boron or phosphorus enhances the interfacial bonding force between the carbon substrate and silicon particles, reduces the structural damage caused by the volume change of silicon during charge and discharge, and extends the cycle life of the battery.

[0072] Through plasma-enhanced chemical vapor deposition, the non-metal doping gas is efficiently activated, and the generated active species can penetrate deep into the porous structure to achieve a uniform and efficient doping distribution, ensuring the consistency of material properties. By precisely controlling the flow rate of the non-metal doping gas and the plasma power, the doping concentration and distribution can be precisely adjusted to meet the specific requirements of different application scenarios for the performance of the anode material.

[0073] S2.3. Stop introducing the non-metal doping gas, and introduce silane gas. The flow rate of the silane gas is controlled at 0.5 - 10 L / min, the reaction temperature is 500 - 700 °C, the plasma power is 200 - 500 W, and the doping time is 100 - 1500 min. The silane gas includes at least one of silane, disilane, and silane derivatives.

[0074] By introducing silicon element, the theoretical specific capacity of the anode material is greatly improved (the theoretical capacity of silicon is about 4200 mAh / g, far exceeding about 372 mAh / g of graphite), significantly increasing the energy density of the battery. The silane gas is activated by the plasma to form nano-scale silicon particles or thin films, which are uniformly distributed in the pores of the porous carbon substrate. This uniform distribution ensures the efficient utilization of silicon particles during charge and discharge, avoiding structural damage caused by local over-expansion.

[0075] A strong interfacial bond is formed between the silicon particles and the carbon substrate. High-energy species during the plasma deposition process promote the formation of chemical bonds between carbon and silicon, enhancing the overall structural stability of the material and reducing capacity decay during cycling. The high specific surface area and good conductivity of the silicon nanoparticles make the process of lithium-ion insertion and extraction more efficient, improving the rate performance of the anode material and meeting the requirements of high-power applications.

[0076] S2.4. Stop introducing the silane gas, introduce an inert atmosphere, and slowly reduce the temperature to room temperature. The cooling rate is controlled at 5 - 20 °C / min to obtain a non-metal doped silicon-based material.

[0077] By controlling the cooling rate at 5 - 20 °C / min, thermal stress and structural defects (such as cracks and pore collapse) caused by rapid cooling of the material are avoided, maintaining the overall structural integrity and pore morphology of the material. The slow cooling process helps to stabilize the distribution positions of the doped non-metal elements and the deposited silicon particles in the porous carbon substrate, ensuring a firm interface between silicon and the carbon substrate and enhancing the mechanical and electrochemical stability of the material. Slow cooling helps to maintain the microstructure of the nano-scale silicon particles and carbon layers, preventing the silicon particles from aggregating or growing due to thermal stress, and ensuring that the anode material has a high specific surface area and high conductivity. Slow cooling in an inert atmosphere prevents the material from reacting with oxygen in the air during the cooling process, maintaining the purity of non-metal doping and silicon deposition, and ensuring the high performance and long life of the material.

[0078] S3. Perform multi-layer carbon coating on the surface of the silicon-based material to obtain a silicon-based anode precursor;

[0079] S3.1. Introduce a mixed gas of acetylene and hydrogen into the plasma chemical vapor deposition reactor to conduct the first deposition reaction. The gas flow rate of acetylene is 5 - 10 L / min, the gas flow rate of hydrogen is 10 - 20 L / min, the reaction temperature is 500 - 800 °C, the deposition time is 30 - 120 min, and the plasma power is 300 - 600 W to form a first carbon coating layer on the silicon-based material.

[0080] Function of the first carbon coating: Through the reaction of the mixed gas of acetylene and hydrogen, the formed carbon coating layer (mainly graphene or graphite-like structure) forms a firm interface on the surface of the silicon-based material. This layer of carbon material provides a good conductive network for the subsequent silicon-based anode material, improves the overall conductivity, and ensures the electron transfer efficiency of silicon particles.

[0081] The first carbon coating layer formed on the surface of the silicon-based material plays a role in buffering the volume expansion of silicon. Silicon undergoes a large volume change during charge and discharge processes, and the carbon coating layer can effectively slow down this change, reduce the cracking and shedding of the material, thereby improving the cycle stability of the material.

[0082] The carbon structure of the coating layer helps to improve the lithium ion transport rate, especially during high-rate charge and discharge processes. The high conductivity of this layer of carbon enables lithium ions to be quickly inserted and extracted, improving the power density and charging rate of the anode material.

[0083] The carbon layer deposited for the first time usually has a certain pore structure, which helps to increase the specific surface area of the material and provides additional space for the storage of lithium ions, further improving the specific capacity of the material.

[0084] S3.2. Stop introducing the mixed gas of acetylene and hydrogen, introduce a mixed gas of ethylene or methane gas and nitrogen or argon gas to conduct the second deposition reaction. The gas flow rate of ethylene or methane is 2 - 6 L / min, the gas flow rate of nitrogen or argon is 8 - 12 L / min, the reaction temperature is 700 - 900 °C, the deposition time is 20 - 80 min, and the plasma power is 300 - 600 W to form a second carbon coating layer on the first carbon coating layer to obtain a silicon-based anode precursor.

[0085] Among them, the thickness of the first carbon coating layer is 5 - 15 nm, and the thickness of the second carbon coating layer is 3 - 10 nm; by volume ratio, acetylene: hydrogen = 1:2, ethylene or methane: nitrogen or argon = 1:3.

[0086] During the deposition process of step S3, in order to precisely control the dynamic changes of temperature and plasma power during the reaction and ensure the best doping effect in different deposition stages.

[0087] The following is the control equation based on the regulation of temperature and power during the reaction process.

[0088]

[0089]

[0090] wherein, is the temperature (°C) inside the reactor, P(t) is the plasma power (W), k is the heat transfer coefficient, representing the heat loss rate (W / °C), is the ambient temperature (°C), assumed to be room temperature, C is the heat capacity (J / °C) of the plasma chemical vapor deposition reactor, depending on the material and volume of the reactor, is the initial plasma power (W), is the maximum plasma power (W), is the maximum deposition time (min), is the control index, adjusting the rate of power increase, with a value between 0.5 and 2. This parameter controls the form of the power growth curve. For example, when = 1, the power increases linearly with time; when > 1, the power increases faster.

[0091] For the deposition of multiple carbon coating layers, a fluidized bed chemical vapor deposition reactor can also be used. A carrier gas is introduced through a gas delivery system, and the gas flow rate is adjusted to ensure that the powder is in a fluidized state in the reactor. The gas flow rate should be controlled within an appropriate range so that the powder particles can be suspended and achieve sufficient contact. Start the heating system and raise the reactor temperature to the required deposition temperature. Temperature control is the key to ensuring the decomposition of the reaction gas and its deposition on the powder surface.

[0092] S4. Heat-treat the silicon-based anode precursor to obtain a non-metal doped silicon-based anode material.

[0093] Step S4 includes:

[0094] S4.1. Set the heating rate to 5 - 10 °C / min until the temperature of the silicon-based anode precursor reaches 800 - 1000 °C, and the holding time is 120 - 240 min.

[0095] The heating process in this step enables a high-temperature reaction between the multi-layer carbon coating layer and the silicon-based material, promoting the structural curing of the silicon-based anode. By precisely controlling the heating rate and holding time, the bonding between the silicon particles and the carbon coating layer becomes tighter, forming a more stable structure. This helps to improve the cycle stability of the material and prevent the silicon material from cracking or peeling due to expansion during charge and discharge.

[0096] During the heating process, non-metallic dopants (such as boron or phosphorus) can undergo solid-state reactions with the silicon-based material, ensuring that the doped elements are evenly distributed within the silicon-based material, thereby improving its electrochemical performance. This process enhances the conductivity and ion migration rate of the material by optimizing the combination of the doped elements and silicon, improving the overall performance of the battery.

[0097] Through this heating process, the interfacial bonding between the formed carbon layer and the silicon-based material is further enhanced. This high-temperature treatment makes the conductive network of the carbon coating more perfect, and the structure of the carbon material tends to a highly conductive graphene or graphite-like phase structure, further improving the electronic conductivity of the silicon-based anode, providing a guarantee for high-power applications.

[0098] During the heat preservation process, the pore structure of the silicon-based anode material is further optimized. The expansion and contraction of silicon are alleviated at high temperatures. At the same time, the pore structure will be refined and enhanced during the heating and heat preservation processes, which helps to increase the specific surface area of the material, provide more lithium-ion insertion and extraction sites, and thus improve the specific capacity and cycling performance of the material.

[0099] S4.2. Introduce ammonia gas or hydrazoic gas with a gas flow rate of 5 - 15 L / min, adjust the heating rate to 2 - 5 °C / min until the temperature of the silicon-based anode precursor reaches 1000 - 1200 °C, and the heat preservation time is 120 - 240 min to obtain a non-metallic doped silicon-based anode material.

[0100] In this step, the introduction of ammonia gas or hydrazoic gas helps to further evenly incorporate non-metallic doping elements (such as boron, phosphorus, etc.) into the silicon-based material at high temperatures. These doping elements can effectively form chemical bonds with silicon or carbon, improving the structural stability, conductivity, and compatibility with the electrolyte of the anode material. This doping helps to improve the cycling performance and rate performance of the material, especially showing better performance under high-temperature conditions.

[0101] The action of ammonia gas or hydrazoic gas at high temperatures can inhibit the degradation of the crystal structure of silicon particles and maintain the good lattice structure of the silicon material. By stabilizing the silicon particles, it is possible to avoid the cracking of silicon particles due to excessive volume expansion and contraction during charge and discharge processes, thereby improving the long-term cycling performance of the anode material.

[0102] Ammonia gas as a nitrogen source gas can introduce nitrogen elements into the silicon-based material. Nitrogen doping can increase the conductivity of the silicon material and improve the efficiency of lithium-ion insertion and extraction. In addition, the incorporation of nitrogen elements can effectively optimize the electrochemical window of the material, reduce the capacity decay caused by side reactions during long-term use of the battery, and further improve the rate performance and cycling stability of the material.

[0103] In an environment of ammonia or hydrazoic gas, high-temperature heat treatment can further optimize the porous structure of the silicon-based anode. The presence of nitrogen and ammonia helps to form micropores or mesopores on the surface of the material. These pores can provide more space for the insertion of lithium ions, improve the lithium ion storage capacity and transmission rate, and enhance the specific capacity and high-rate performance of the anode material.

[0104] The introduction of ammonia or hydrazoic gas can effectively inhibit the occurrence of side reactions in the battery. Especially at high temperatures, it can reduce the reaction between the material and the electrolyte, improving the chemical stability of the material. In this way, the surface protective layer of the material is more stable, which can effectively prevent the rapid decline of the material and improve the service life of the battery.

[0105] Example 1: Add 3000 g of porous carbon with a hierarchical pore structure to a PECVD furnace, introduce nitrogen at a flow rate of 5 L / min and maintain for 60 min. Raise the temperature in the PECVD furnace to 520 °C, introduce diborane gas at a flow rate of 1 L / min and continue for 300 min to obtain a boron-doped porous carbon substrate. Then raise the furnace temperature to 600 °C, introduce silane at a flow rate of 5 L / min and continue for 500 min to obtain a boron-doped silicon-based material. Then introduce a mixed gas of acetylene and hydrogen, with the gas flow rate of acetylene being 5 L / min and that of hydrogen being 10 L / min, and continue for 100 min. Then introduce a mixed gas of ethylene and nitrogen, with the gas flow rate of ethylene being 2 L / min and that of nitrogen being 8 L / min, and continue for 50 min. After heat treatment, a boron-doped silicon-based anode material coated with a carbon layer is obtained.

[0106] Example 2: Add 3000 g of porous carbon with a hierarchical pore structure to a PECVD furnace, introduce nitrogen at a flow rate of 5 L / min and maintain for 60 min. Raise the temperature in the PECVD furnace to 600 °C, introduce diborane gas at a flow rate of 2 L / min and continue for 150 min to obtain a boron-doped porous carbon substrate. Then raise the furnace temperature to 650 °C, introduce silane at a flow rate of 10 L / min and continue for 500 min to obtain a boron-doped silicon-based material. Then introduce a mixed gas of acetylene and hydrogen, with the gas flow rate of acetylene being 10 L / min and that of hydrogen being 20 L / min, and continue for 80 min. Then introduce a mixed gas of methane and argon, with the gas flow rate of methane being 5 L / min and that of argon being 5 L / min, and continue for 80 min. After heat treatment, a boron-doped silicon-based anode material coated with a carbon layer is obtained.

[0107] Example 3: Add 3000 g of porous carbon with a hierarchical pore structure to a PECVD furnace, introduce nitrogen at a flow rate of 5 L / min, and maintain for 60 min. Raise the temperature in the PECVD furnace to 520 °C, introduce phosphine gas at a flow rate of 1 L / min, and continuously introduce it for 300 min to obtain a phosphorus-doped porous carbon substrate. Then raise the furnace temperature to 600 °C, introduce silane at a flow rate of 5 L / min, and continuously introduce it for 500 min to obtain a phosphorus-doped silicon-based material. Then introduce a mixed gas of acetylene and hydrogen, the gas flow rate of acetylene is 5 L / min, the gas flow rate of hydrogen is 10 L / min, and maintain for 100 min. Then introduce a mixed gas of ethylene and nitrogen, the gas flow rate of ethylene is 2 L / min, the gas flow rate of nitrogen is 8 L / min, and maintain for 50 min. After heat treatment, a phosphorus-doped silicon-based anode material coated with a carbon layer is obtained.

[0108] Example 4: Add 3000 g of porous carbon to a PECVD furnace, introduce nitrogen at a flow rate of 5 L / min, and maintain for 60 min. Raise the temperature in the PECVD furnace to 600 °C, introduce phosphine gas at a flow rate of 2 L / min, and continuously introduce it for 150 min to obtain a phosphorus-doped porous carbon substrate. Then raise the furnace temperature to 650 °C and introduce silane at a flow rate of 10 L / min, and continuously introduce it for 500 min to obtain a phosphorus-doped porous silicon-carbon material. Then introduce a mixed gas of acetylene and hydrogen, the gas flow rate of acetylene is 10 L / min, the gas flow rate of hydrogen is 20 L / min, and maintain for 80 min. Then introduce a mixed gas of methane and argon, the gas flow rate of methane is 5 L / min, the gas flow rate of argon is 5 L / min, and maintain for 80 min. After heat treatment, a carbon-coated layer is obtained.

[0109] Figure 2 Upper left corner (SEM image), showing the surface morphology of the boron-doped silicon-based anode material, and the particle morphology of the material can be seen. The surface is smooth and uniform, which is suitable for further analysis of its element distribution.

[0110] Figure 2 Upper right corner (Si element distribution map): The distribution map of silicon element (Si) in the material through X-ray energy spectrum analysis (EDS). This shows that the silicon element is evenly distributed in the material. As the main component of the anode material, silicon plays an important role in the silicon-based anode material.

[0111] Figure 2 Lower left corner (C element distribution map): Showing the distribution of carbon element (C). Since the silicon-based material usually has a carbon coating layer, the distribution map of carbon here can show whether the carbon coating layer evenly covers the surface of the silicon particles.

[0112] Figure 2Lower right corner (distribution map of element B): It shows the distribution of boron element (B) in the material. The boron element is evenly distributed on the surface of silicon particles, proving that the boron element has been successfully doped into the silicon-based anode material.

[0113] This figure shows that through appropriate processes, the boron element has been successfully doped into the silicon-based anode material, and the carbon coating layer is evenly covered, which can improve the conductivity and stability of the material.

[0114] Figure 3 Upper left corner (SEM image): It shows the surface morphology of the phosphorus-doped silicon-based anode material. The appearance of its particles can be seen, which may be different from that of the boron-doped material, and there may be different structural features on the surface.

[0115] Figure 3 Upper right corner (distribution map of element Si): It shows the distribution of silicon element (Si), indicating that silicon is also the main component in this material and is evenly distributed.

[0116] Figure 3 Lower left corner (distribution map of element C): It shows the distribution of carbon element (C). Like the boron-doped sample, a carbon coating layer may exist to ensure that the silicon particles are not oxidized.

[0117] Figure 3 Lower right corner (distribution map of element P): It shows the distribution of phosphorus element (P). The phosphorus element is evenly distributed, indicating that the phosphorus element has been successfully doped into the silicon-based anode material.

[0118] The phosphorus-doped silicon-based anode material also has uniform doping and a carbon coating layer. The phosphorus element can enhance the cycle stability and conductivity of the material.

[0119] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a non-metal-doped silicon-based negative electrode material, characterized in that: The following steps are involved: S1. Preparing a porous carbon substrate with a hierarchical pore structure, wherein the pore size of the porous carbon substrate is 0.1-100 nm, and the hierarchical pore structure includes 30-90% micropores, 5-55% mesopores and 5-55% macropores in percentage, the pore size of the micropores is 0.1-2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is 50-100 nm; S2, sequentially depositing a non-metallic doping gas and a silane gas in the porous carbon substrate to obtain a non-metallic doped silicon-based material, wherein the non-metallic doping gas comprises a borane gas or a phosphine gas; S3, performing multi-layer carbon coating on the surface of the silicon-based material to obtain a silicon-based negative electrode precursor; Step S3 includes: S3.1, introducing a mixed gas of acetylene and hydrogen into a plasma vapor deposition reactor to perform a first deposition reaction, wherein the gas flow rate of acetylene is 5-10 L / min, the gas flow rate of hydrogen is 10-20 L / min, the reaction temperature is 500-800° C., the deposition time is 30-120 min, and the plasma power is 300-600 W to form a first carbon coating layer on the silicon-based material; S3.2, stop introducing the mixed gas of acetylene and hydrogen, and introduce a mixed gas of ethylene or methane gas and nitrogen or argon gas to carry out a second deposition reaction, the gas flow rate of ethylene or methane is 2-6 L / min, the gas flow rate of nitrogen or argon gas is 8-12 L / min, the reaction temperature is 700-900°C, the deposition time is 20-80 min, the plasma power is 300-600 W, and a second carbon coating layer is formed on the first carbon coating layer to obtain a silicon-based negative electrode precursor; The thickness of the first carbon coating layer is 5-15 nm, and the thickness of the second carbon coating layer is 3-10 nm; By volume ratio, acetylene: hydrogen = 1:2, ethylene or methane: nitrogen or argon = 1:3; The relationship between the reaction temperature and the plasma power in step S3 is as follows: in, is the temperature in the reactor (°C), P(t) is the plasma power (W), k is the heat transfer coefficient, which indicates the heat loss rate (W / °C), is the ambient temperature (°C), assumed to be room temperature, C is the heat capacity of the plasma vapor deposition reactor (J / °C), is the initial plasma power (W), is the maximum plasma power (W), is the maximum deposition time (min), To control the index, adjust the speed of power increase, and take the value between 0.5 and 2; S4. Heat-treating the silicon-based negative electrode precursor to obtain a non-metal-doped silicon-based negative electrode material.

2. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 1, characterized in that: The step S1 comprises: S1.

1. Clean, dry and crush the carbon source material to obtain a uniform particle size distribution, and the particle size D50 value is controlled at 5 to 10 μm; S1.2, adding a template material to the carbon source material, the mass ratio of the carbon source material to the template material is controlled at 1:2, heating to 800-1000°C, a heating rate of 5-10°C / min, and a holding time of 2-4h to obtain a premix; S1.3, transferring the premix to a hydrofluoric acid solution to remove the template material, controlling the temperature at room temperature, and reacting for 4 to 6 hours to obtain a porous carbon substrate with a hierarchical pore structure.

3. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 2, characterized in that: In the step S1, the carbon source material includes at least one of porous carbon, natural graphite, artificial graphite mesophase carbon microbeads, and expanded graphite; The pore size of the porous carbon substrate is 0.1-100 nm, wherein, calculated by percentage, the hierarchical pore structure includes 30-90% of micropores, 5-55% of mesopores and 5-55% of macropores.

4. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 2, characterized in that: After step S1.3, step S1 further includes: S1.4, immersing the porous carbon substrate in potassium hydroxide or phosphoric acid solution, the proportion of which is controlled to be 2-10% of the mass of the carbon source, immersing for 1-4 hours, and calcining at 500-700° C. for 2-4 hours; S1.5, transferring the porous carbon substrate to a strong oxidant solution, controlling the temperature at 60-100°C, and reacting for 2-6 hours; S1.

6. Use deionized water to wash repeatedly to remove unreacted products. The drying temperature is 100-150°C for 4-6 hours to obtain a porous carbon substrate with a hierarchical pore structure after activation.

5. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 1, characterized in that: The step S2 comprises: S2.1, placing the porous carbon substrate in a plasma vapor deposition reactor under an inert atmosphere, with an inert gas flow rate of 1-20 L / min, preheating to 400-700°C, and maintaining for 40-100 min to remove impurities and moisture adsorbed on the surface; S2.2, stop introducing the inert gas, introduce the non-metallic doping gas, the flow rate of the non-metallic doping gas is controlled at 0.5-10 L / min, the reaction temperature is 400-600°C, the plasma power is 200-500 W, and the doping time is 30-420 min; S2.3, stop introducing non-metallic doping gas, introduce silane gas, the silane gas flow rate is controlled at 0.5-10L / min, the reaction temperature is 500-700°C, the plasma power is 200-500W, and the doping time is 100-1500min; S2.

4. Stop introducing silane gas, introduce an inert atmosphere, slowly lower the temperature to room temperature, and control the cooling rate at 5 to 20°C / min to obtain a non-metal-doped silicon-based material.

6. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 5, characterized in that: In step S2, The inert gas includes at least one of nitrogen, argon and hydrogen; The borane gas includes at least one of diborane, methylborane, tetraborane, pentaborane, decaborane, hexaborane and trimethylborane; The phosphine gas includes at least one of phosphine, diphosphine and triphosphine; The silane gas includes at least one of monosilane, disilane, and silane derivatives.

7. The method for preparing a non-metal-doped silicon-based negative electrode material according to claim 1, characterized in that: The step S4 comprises: S4.1, setting the heating rate to 5-10°C / min, until the temperature of the silicon-based negative electrode precursor reaches 800-1000°C, and the holding time is 120-240min; S4.

2. Introduce ammonia or nitrogen gas with a gas flow rate of 5 to 15 L / min, adjust the heating rate to 2 to 5°C / min, until the temperature of the silicon-based negative electrode precursor reaches 1000 to 1200°C, and keep warm for 120 to 240 minutes to obtain a non-metal-doped silicon-based negative electrode material.

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