A substrate-frame-shell structure silicon-carbon anode material, its preparation method and application

Abstract

This invention discloses a substrate-framework-shell structured silicon-carbon anode material, its preparation method, and its applications, belonging to the technical field of lithium-ion battery anode materials. The material comprises a porous carbon substrate in situ doped with an electronically conductive agent, active silicon distributed within the porous carbon substrate, and an outermost N-doped carbon shell. This invention constructs an internal electronically conductive framework by pre-embedding the electronically conductive agent during the porous carbon precursor synthesis stage, and then forms a clever "substrate-framework-shell" composite structure through vapor deposition of silicon and the N-doped carbon shell. This structure not only establishes a highly efficient three-dimensional electron transport network, significantly improving the overall conductivity of the material, but also enhances the material's mechanical strength, effectively buffering the volume expansion of silicon. The silicon-carbon anode material prepared by this invention features high silicon content, high initial coulombic efficiency, excellent rate performance, and long cycle life, making it suitable for high-energy-density lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, and specifically relates to a substrate-shell structure silicon-carbon anode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, energy storage, and portable electronic devices. Traditional graphite anodes have a low theoretical specific capacity, making them unsuitable for the development of high-energy-density batteries. Silicon anode materials, due to their high theoretical specific capacity and abundant reserves, have become an important development direction for high-energy-density anodes.

[0003] However, silicon materials suffer from problems such as severe volume expansion during charge and discharge, low intrinsic conductivity, and poor cycle stability. Currently, silicon-carbon composite structures are often used to modify them. However, existing silicon-carbon anode materials generally suffer from defects such as discontinuous internal conductive networks, low overall conductivity, uneven silicon dispersion, and poor structural stability, making it difficult to simultaneously achieve high silicon content, high initial coulombic efficiency, and excellent rate performance. Summary of the Invention

[0004] Therefore, the present invention aims to provide a substrate-frame-shell structure silicon-carbon anode material, its preparation method and application, with the goal of simultaneously achieving high silicon content, high initial coulombic efficiency, excellent rate performance and long cycle life of silicon-carbon anode materials.

[0005] This invention is implemented as follows: A substrate-framework-shell structured silicon-carbon anode material comprises, from the inside out: a porous carbon skeleton in situ doped with an electronically conductive agent; nano-silicon active material uniformly distributed in the pores and surface of the porous carbon skeleton; and an N-doped carbon shell covering the outermost layer; wherein the electronically conductive agent is embedded in the carbon matrix of the porous carbon skeleton to form a continuous electronically conductive network skeleton.

[0006] Furthermore, the material has an electrical conductivity greater than 50 S / cm, a silicon content of 45% to 60% by mass, an electronic conductive agent content of 0.1% to 0.5% by mass, and an N-doped carbon shell content of 0.5% to 3% by mass.

[0007] Furthermore, the electronically conductive agent is selected from one or more of carbon black, carbon fiber, carbon nanotubes, and graphene; the nitrogen source of the N-doped carbon shell is ammonia, pyridine vapor, or melamine vapor.

[0008] Furthermore, the specific surface area of ​​the porous carbon substrate is 1600~2800 m² / g, the microporosity is ≥92%, the proportion of pores with a pore size of 5nm or larger is ≤0.3%, and the electrical conductivity is greater than 100 S / cm.

[0009] A method for preparing the above-mentioned substrate-shell structured silicon-carbon anode material includes the following steps: S1, precursor preparation: mixing a carbon source, dispersant, crosslinking agent, electronically conductive agent and solvent, heating and gelatinizing, and then spray drying and granulating to obtain composite precursor microspheres; S2, substrate porous carbon preparation: subjecting the composite precursor microspheres to pre-carbonization, pulverization, high-temperature carbonization and activation treatment to obtain highly conductive porous carbon in situ doped with electronically conductive agent; S3, composite and coating: depositing nano-silicon on the highly conductive porous carbon by chemical vapor deposition, and then coating with an N-doped carbon shell under a nitrogen-containing atmosphere to obtain the silicon-carbon anode material.

[0010] Furthermore, in step S1, the carbon source is starch; the heating and gelatinization temperature is 80~99℃, and the holding time is 0.5~4h; the Dv50 particle size of the precursor microspheres obtained by spray drying is 30~100 μm.

[0011] Furthermore, in step S2, the pre-carbonization temperature is 550~750℃, and the time is 1~3 h; the Dv50 particle size of the pulverized powder is 8.0~12.0 μm, and the particle size distribution Span value is ≤0.9; the high-temperature carbonization temperature is 1000~1400℃, and the holding time is 2~6 h; the activation treatment is physical activation, with a temperature of 800~1000℃ and a time of 6~18 h.

[0012] Furthermore, in step S3, the silane gas used for silicon deposition by chemical vapor deposition is selected from one or more of silane, silane, and trichlorosilane, and the deposition temperature is 450~650℃; the atmosphere used for coating the N-doped carbon shell is a mixture of nitrogen source gas and carbon source gas, wherein the volume percentage of nitrogen source is 1~30% and the volume percentage of carbon source is 70~99%, the coating temperature is 500~700℃, and the coating time is 4~10 h.

[0013] Furthermore, the dispersant is selected from one or more of sodium dodecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate; the crosslinking agent is selected from one or more of sodium trimetaphosphate, acetic anhydride, citric acid, and octenyl succinic anhydride.

[0014] A lithium-ion battery, wherein the negative electrode is made of the aforementioned substrate-shell structure silicon-carbon negative electrode material.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention comprises a porous carbon substrate in situ doped with an electronically conductive agent, silicon as an active material distributed within the porous carbon substrate, and an N-doped carbon shell covering the outermost layer. By pre-embedding the electronically conductive agent during the synthesis stage of the porous carbon precursor, an internal electronically conductive framework is constructed. Then, through vapor deposition of silicon and the N-doped carbon shell, a clever composite structure of "substrate framework-shell" is formed. This structure not only establishes a highly efficient three-dimensional electron transport network, significantly improving the overall conductivity of the material (>50 S / cm), but also enhances the mechanical strength of the material, effectively buffering the volume expansion of silicon. The silicon-carbon anode material prepared by this invention features high silicon content (45-60 wt%), high initial coulombic efficiency, excellent rate performance, and long cycle life, making it suitable for high-energy-density lithium-ion batteries. Detailed Implementation

[0016] This invention proposes a solution to the core technical defects of traditional silicon-carbon anode materials for lithium-ion batteries. Traditional silicon-carbon anodes generally suffer from low electron transport efficiency, poor overall conductivity, high volume expansion rate of elemental silicon during lithium insertion and extraction, which easily leads to material pulverization, electrode structure collapse, and a sharp reduction in cycle life. At the same time, the low silicon content results in insufficient battery energy density, and the initial coulombic efficiency and rate performance are difficult to meet the requirements of high-energy-density batteries.

[0017] The core technical objective of this invention is to construct a silicon-carbon anode material that is structurally stable, highly conductive, and resistant to volume expansion. Through a unique three-layer nested substrate-shell structure design, combined with in-situ doping of conductive agents in the precursor, a continuous three-dimensional electron transport network is built, enhancing the overall conductivity of the material. The spatial buffering effect of the high-porosity porous carbon framework alleviates the volume expansion stress of silicon. Furthermore, the outer nitrogen-doped carbon shell further fixes silicon particles, strengthens structural stability, and optimizes interface performance, ultimately achieving high silicon content, high conductivity, high initial coulombic efficiency, excellent rate performance, and long cycle life, meeting the application requirements of high-energy-density lithium-ion batteries.

[0018] Specifically, a substrate-frame-shell structure silicon-carbon anode material comprises, from the inside out: In-situ doped porous carbon framework of substrate; Nano-silicon active material uniformly distributed in the pores and surface of the porous carbon framework of the substrate; The outermost layer is an N-doped carbon shell; The electronically conductive agent is embedded in the carbon matrix of the porous carbon substrate to form a continuous electronically conductive network framework. The first layer of the substrate-shell structure silicon-carbon anode material is a porous carbon framework in situ doped with an electronically conductive agent. This framework serves as the core supporting substrate of the entire material, undertaking the core functions of structural support and electron transport. In-situ doping means that the electronically conductive agent is not physically mixed and attached later, but is incorporated into the raw material system at the initial stage of porous carbon framework synthesis, fully integrated with the carbon source, and ultimately embedded inside the carbon matrix, rather than simply attached to the surface of the carbon framework. This doping method can prevent the conductive agent from falling off later and ensure the stability of the conductive structure. The second layer consists of nano-silicon active material uniformly distributed within the pores and surface of the porous carbon framework of the substrate. Nano-silicon is the core active material of the lithium-ion battery anode, responsible for lithium intercalation and deintercalation to achieve lithium storage. Using nano-sized silicon particles can reduce the volume expansion of a single particle. Uniform distribution within the pores and outer surface of the porous carbon allows the silicon particles to be fully encapsulated and separated by the carbon framework, preventing silicon particle agglomeration. At the same time, the porous space of the carbon provides a buffer for silicon expansion, preventing silicon expansion from compressing and damaging the overall structure. The third layer is an outermost N-doped carbon shell, which serves as both a protective and functional enhancement layer, completely encapsulating the internal porous carbon framework and nano-silicon particles to form a closed shell structure. The N-doped carbon shell possesses excellent conductivity and mechanical toughness, further strengthening electron transport channels and locking in the internal silicon particles to prevent them from detaching. It also optimizes the interfacial compatibility between the material and the electrolyte, reducing side reactions. This invention, through in-situ embedding, allows the conductive agent to interconnect within the carbon matrix, constructing a three-dimensional conductive network that runs through the entire substrate framework, completely solving the problems of broken electron transport paths and insufficient conductivity in traditional silicon-carbon anodes.

[0019] Specifically, the silicon-carbon anode material has a conductivity greater than 50 S / cm, which is much higher than that of traditional silicon-carbon anode materials without in-situ doping of conductive agents. The silicon mass content is 45% to 60%, and the electronic conductive agent mass content is 0.1% to 0.5%. This content is extremely low, which can ensure the formation of a continuous conductive network without taking up too much space due to the addition of conductive agents. The N-doped carbon shell mass content is 0.5% to 3%. The shell content is controlled within this range to achieve complete coating, ensure structural protection and interface optimization, and avoid increasing the overall volume of the material and reducing the volumetric energy density due to excessive shell thickness. At the same time, it avoids the shell thickness from hindering lithium-ion transport. More specifically, the electronic conductive agent is selected from one or more of carbon black, carbon fiber, carbon nanotubes, and graphene. These materials are all carbon-based conductive materials with excellent compatibility with the porous carbon matrix substrate, and will not introduce impurity metal elements, thus avoiding affecting the electrochemical stability of the battery. Among them, carbon black has low cost and good dispersibility, making it suitable for mass production; those skilled in the art can choose to use it alone or in combination according to cost and performance requirements.

[0020] The nitrogen source for N-doped carbon shells can be ammonia, pyridine vapor, or melamine vapor, all of which are gaseous nitrogen sources. These are suitable for in-situ doping under chemical vapor deposition processes, allowing nitrogen atoms to be uniformly incorporated into the carbon shell lattice and achieving a uniform distribution of nitrogen.

[0021] Furthermore, the specific surface area of ​​the porous carbon substrate is 1600 to 2800 square meters per gram. This ultra-high specific surface area can provide a large number of silicon particle attachment sites and pore spaces, ensuring uniform loading of nano-silicon.

[0022] With a microporosity of ≥92%, micropores refer to pores with a diameter of less than 2 nanometers. The ultra-high microporosity ensures that the pores of the porous carbon skeleton are mainly micropores. The micropore structure has high mechanical strength and can effectively support the overall skeleton. At the same time, the micropore space is suitable for loading nano-silicon particles and reserves precise expansion buffer space to avoid the skeleton structure being loose and lacking mechanical strength due to too many large pores.

[0023] The proportion of pores with a diameter of 5 nanometers or larger is less than or equal to 0.3%. The proportion of large-diameter pores is strictly controlled to prevent problems such as fragile framework structure, excessive aggregation of silicon particles, and framework collapse after volume expansion caused by large pores.

[0024] The porous carbon substrate has a conductivity greater than 100 S / cm, and the substrate framework itself has ultra-high conductivity. Combined with in-situ doped electronic conductive agents, the overall conductive network is further enhanced.

[0025] In addition, this invention proposes a method for preparing the above-mentioned substrate-shell structure silicon-carbon anode material, comprising the following steps: S1, precursor preparation: mixing carbon source, dispersant, crosslinking agent, electronically conductive agent and solvent, heating and gelatinizing, and then spray drying and granulating to obtain composite precursor microspheres; S2, substrate porous carbon preparation: pre-carbonizing, pulverizing, high-temperature carbonizing and activation treatment of the composite precursor microspheres to obtain highly conductive porous carbon in situ doped with electronically conductive agent; S3, composite and coating: depositing nano-silicon on the highly conductive porous carbon by chemical vapor deposition, and then coating with an N-doped carbon shell under a nitrogen-containing atmosphere to obtain the silicon-carbon anode material.

[0026] In step S1, starch is selected as the carbon source. Starch is a natural polysaccharide carbon source that is widely available and inexpensive. After pyrolysis, the carbon purity is high and the pore structure is easy to control, making it suitable as a carbon source for porous carbon frameworks. At the same time, the gelatinization process is adapted to the molecular structure of starch, which can achieve uniform mixing with electronic conductive agents.

[0027] The gelatinization temperature is 80 to 99 degrees Celsius, and the holding time is 0.5 to 4 hours. This temperature range is slightly higher than the gelatinization temperature of starch, which allows the starch to fully swell and gelatinize, forming a viscous colloidal system. This ensures that the electronic conductive agent, dispersant, and crosslinking agent are uniformly dispersed in the system, without sedimentation or stratification. The holding time is controlled within this range to ensure complete gelatinization without causing abnormal viscosity of the system due to excessive gelatinization time, which would affect subsequent spray drying.

[0028] The precursor microspheres obtained by spray drying have a Dv50 particle size of 30 to 100 micrometers. Dv50 refers to the median particle size, which represents the average level of the overall particle size of the microspheres. This particle size range is suitable for subsequent pre-carbonization, pulverization and high-temperature carbonization processes. If the particle size is too small, it will easily lead to subsequent powder agglomeration. If the particle size is too large, carbonization and activation will be incomplete, affecting the pore uniformity of the porous carbon skeleton and ensuring that the particle size of the final negative electrode material matches the electrode coating requirements. The pre-carbonization temperature is 550 to 750 degrees Celsius, and the time is 1 to 3 hours. This low-temperature pre-carbonization process allows the volatiles in the precursor microspheres to be released slowly, initially forming a carbon skeleton. This avoids the rapid overflow of volatiles and skeleton breakage caused by direct high-temperature carbonization. The holding time ensures complete pre-carbonization and stabilizes the microsphere structure.

[0029] The Dv50 particle size of the pulverized powder is 8.0 to 12.0 micrometers, and the particle size distribution Span value is less than or equal to 0.9. The Span value represents the uniformity of particle size distribution. The smaller the value, the narrower the distribution. This particle size range is suitable for subsequent vapor deposition silicon and carbon shell coating processes. The narrow particle size distribution ensures that the structure and performance of all powder particles are consistent, avoiding the problems of uneven silicon loading and inconsistent shell coating thickness caused by particle size differences.

[0030] The high-temperature carbonization temperature is 1000 to 1400 degrees Celsius, and the holding time is 2 to 6 hours. This high-temperature range allows the carbon source to be completely graphitized, improving the conductivity of the carbon skeleton. At the same time, it allows the pre-embedded electronic conductive agent to be tightly combined with the carbon matrix to form a continuous conductive network. The holding time ensures complete carbonization and improves the mechanical strength of the carbon skeleton.

[0031] The activation process is physical activation, with a temperature of 800 to 1000 degrees Celsius and a time of 6 to 18 hours. Physical activation typically uses carbon dioxide or water vapor as an activator, leaving no chemical activator residue and avoiding impurities from affecting battery performance. These temperature and time parameters can precisely etch the carbon skeleton to form an ultra-high specific surface area of ​​1600 to 2800 square meters per gram and a microporosity of over 92%, strictly controlling the proportion of large-diameter pores to match the microstructure parameters of claim 4. The silane gas used in chemical vapor deposition for silicon deposition is selected from one or more of silane, silane, and trichlorosilane. These silane gases are commonly used gaseous silicon sources with low pyrolysis temperatures. At deposition temperatures of 450 to 650 degrees Celsius, they can slowly decompose into nanoscale silicon. This temperature range avoids the rapid decomposition of silane, which can lead to the agglomeration of silicon particles. It ensures that silicon particles are uniformly deposited on the pores and surface of porous carbon. The deposition temperature is precisely matched to the heat resistance of the porous carbon framework, without damaging the framework structure.

[0032] The atmosphere used for coating the N-doped carbon shell is a mixture of nitrogen source gas and carbon source gas, with the nitrogen source accounting for 1% to 30% of the volume and the carbon source accounting for 70% to 99% of the volume. The nitrogen doping amount is precisely controlled by the gas ratio to ensure that nitrogen is effectively incorporated into the carbon shell while avoiding excessive nitrogen content that would lead to a loose carbon shell structure. The coating temperature is 500 to 700 degrees Celsius and the coating time is 4 to 10 hours. These process conditions allow the carbon source and nitrogen source to pyrolyze simultaneously, forming a uniform and dense N-doped carbon shell. The shell thickness is controlled within the mass content range of 0.5% to 3%, ensuring the coating effect without affecting lithium-ion transport. The dispersant is selected from one or more of sodium dodecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate. The core function of the dispersant is to reduce the surface tension of the mixture, allowing the electronically conductive agent and carbon source to be uniformly dispersed, avoiding agglomeration, and ensuring the uniformity of in-situ doping. Sodium dodecyl sulfate is an anionic surfactant with high dispersion efficiency; polyvinylpyrrolidone and sodium polystyrene sulfonate are polymeric dispersants that combine dispersing and stabilizing effects, suitable for starch gelatinization systems, and can be used alone or in combination, and are suitable for spray drying granulation processes.

[0033] The crosslinking agent is selected from one or more of sodium trimetaphosphate, acetic anhydride, and octenyl succinic anhydride. The core function of the crosslinking agent is to form a crosslinked structure between starch molecules, improve the viscosity and stability of the gelatinized system, ensure that the microsphere structure formed by spray drying is compact, avoid microsphere breakage during subsequent pre-carbonization and carbonization, and improve the mechanical strength of the porous carbon skeleton. The amount of crosslinking agent is moderate, there will be no residual impurities, and it will not affect the purity of the carbon skeleton.

[0034] The present invention also proposes a lithium-ion battery, wherein the negative electrode is made of the aforementioned substrate-shell structure silicon-carbon negative electrode material.

[0035] Applying the aforementioned silicon-carbon anode material to lithium-ion batteries, using the aforementioned substrate-shell structure silicon-carbon anode material, and following conventional lithium-ion battery anode fabrication processes, combining binders and conductive agents to form anode sheets, and assembling them into lithium-ion batteries, benefits from the high conductivity, high silicon content, and structural stability of silicon-carbon anode materials. This lithium-ion battery possesses high energy density, high initial coulombic efficiency, excellent rate performance, and long cycle life, and can be widely used in new energy vehicles, 3C digital products, energy storage, and other fields.

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] Example 1 A method for preparing a substrate-frame-shell structured silicon-carbon anode material, comprising the following steps: S1. Preparation of precursor: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon black (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotubes with high conductivity porous carbon (specific surface area of ​​2030m² / g, microporosity of 95.0%, pore size greater than 5 nm of 0.2%, and electrical conductivity of 48S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0038] Example 2 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon fiber (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain highly conductive porous carbon with in-situ doped carbon nanotubes (specific surface area of ​​2042m² / g, microporosity of 95.1%, pore size greater than 5 nm of 0.2%, and electrical conductivity of 54S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0039] Example 3 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% graphene (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain highly conductive porous carbon with in-situ doped carbon nanotubes (specific surface area of ​​2034m² / g, microporosity of 94.9%, pore size greater than 5 nm of 0.2%, and electrical conductivity of 26S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0040] Example 4 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0041] Example 5 S1. Preparation of precursor: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.1wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain highly conductive porous carbon with in-situ doped carbon nanotubes (specific surface area of ​​2040m² / g, microporosity of 95%, pore size greater than 5nm of 0.2%, and electrical conductivity of 32S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0042] Example 6 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.5wt% carbon nanotubes (electronic conductive agent) are mixed with deionized water, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2048m² / g, microporosity 95%, pore size greater than 5nm accounting for 0.2%, electrical conductivity 135S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0043] Example 7 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 5% ammonia (nitrogen source) and 95% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 6.3h to obtain silicon-carbon anode material.

[0044] Example 8 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 10% ammonia (nitrogen source) and 90% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 6.6h to obtain silicon-carbon anode material.

[0045] Example 9 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 20% ammonia (nitrogen source) and 80% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7.4h to obtain silicon-carbon anode material.

[0046] Example 10 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 25% ammonia (nitrogen source) and 75% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7.9h to obtain silicon-carbon anode material.

[0047] Example 11 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 4 hours to obtain silicon-carbon anode material.

[0048] Example 12 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 5.5 hours to obtain silicon-carbon anode material.

[0049] Example 13 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 8.5 hours to obtain silicon-carbon anode material.

[0050] Example 14 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain in-situ doped carbon nanotube highly conductive porous carbon (specific surface area 2044m² / g, microporosity 94.9%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 10 hours to obtain silicon-carbon anode material.

[0051] Comparative Example 1 S1. Preparation of precursor: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain porous carbon (specific surface area 2038m² / g, microporosity 95.1%, pore size greater than 5 nm accounting for 0.2%, electrical conductivity 15S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on porous carbon by chemical vapor deposition at 550℃. Then, a mixed gas of 15% ammonia (nitrogen source) and 85% acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, an N-doped carbon shell was coated in a rotary kiln at 600℃ for 7 hours to obtain silicon-carbon anode material.

[0052] Comparative Example 2 S1. Precursor preparation: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent, 0.3wt% carbon nanotubes (electronic conductive agent) and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and after pulverization, powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9 was obtained. Then, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain highly conductive porous carbon with in-situ doped carbon nanotubes (specific surface area of ​​2056m² / g, microporosity of 94.9%, pore size greater than 5 nm of 0.2%, and electrical conductivity of 102S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on highly conductive porous carbon by chemical vapor deposition at 550°C. Then, acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, the carbon shell was coated in a rotary kiln at 600°C for 7 hours to obtain silicon-carbon anode material.

[0053] Comparative Example 3 S1. Preparation of precursor: Starch carbon source, polyvinylpyrrolidone dispersant, sodium trimetaphosphate crosslinking agent and deionized water are mixed, heated and gelatinized at 90℃ and kept at the temperature for 2h, and then spray dried and granulated to obtain composite precursor microspheres with a Dv50 particle size of 60μm. S2. Preparation of porous carbon substrate: The composite precursor microspheres were pre-carbonized at 650℃ for 2h, and then pulverized to obtain powder with Dv50 particle size of 10±1.0μm and particle size distribution Span value ≤0.9. Subsequently, it was carbonized at 1200℃ for 4h, and then physically activated at 900℃ for 12h to obtain porous carbon (specific surface area of ​​2038m² / g, microporosity of 95.2%, pore size greater than 5 nm of 0.2%, and electrical conductivity of 15S / cm). S3. Composite and Coating: Using silane as the silane gas, nano-silicon was deposited on porous carbon by chemical vapor deposition at 550°C. Then, acetylene (carbon source) was introduced to form a pre-coating layer to protect the silicon from oxidation and damage. Finally, the carbon shell was coated in a rotary kiln at 600°C for 7 hours to obtain silicon-carbon anode material.

[0054] Test Example 1 The content of metallic and non-metallic elements was analyzed using a SPECTROI-OES GREEN spectrometer from Germany. The conductivity of the porous carbon and silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3 was tested using the ST2258C four-probe method. The specific surface area of ​​the silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3 was tested using a Quantachrome Autosorb IQ3 3 analyzer. The particle crushing strength of the porous carbon and silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3 was tested using a Yuaneng SPFT2000 particle crushing tester. The particle size of the silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3 was tested using a Mastersizer 3000 particle size analyzer. Table 1. Physicochemical parameters of silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3

[0055] As can be seen from the examples and comparative examples, the electronic conductive agent effectively enhances the conductivity and crush strength of the material. The electronic conductive agent is generated deep in situ within the precursor, which, on the one hand, forms a three-dimensional continuous conductive network, providing a fast channel for electron transport and reducing the contact resistance and internal resistance of the electrodes; on the other hand, the electronic conductive agent itself possesses excellent mechanical strength, acting as physical support and skeletal confinement when silicon particles expand, resisting pressure and preventing particle crushing.

[0056] Based on the powder conductivity data of Examples 1-4 and Comparative Example 3, it can be seen that electronic conductive agents can effectively improve the conductivity of materials, especially carbon nanotubes, which have the most significant effect.

[0057] According to the pressure strength data of Examples 1-4 and Comparative Example 3, on the one hand, the electronic conductive agent improves the crushing strength of the material particles, and on the other hand, the morphology and distribution of the electronic conductive agent affect the crushing strength performance. Carbon nanotubes constitute a three-dimensional network skeleton structure, which has a significant effect on improving particle strength.

[0058] Test Example 2 The silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3 were used as anode materials for lithium-ion batteries. The initial reversible capacity and initial efficiency of the obtained anode materials were tested using the following methods: The silicon-carbon anode materials prepared in Examples 1-7 and Comparative Examples 1-3, the conductive agent Super P (conductive carbon black), and the binder CMC were mixed in pure water at a mass ratio of 95:1.5:3.5 and homogenized (solid content 48wt%) to obtain a slurry. The slurry was coated onto a copper foil current collector, vacuum baked at 100°C for 8 hours, pressed into shape, and punched to obtain anode sheets. A coin cell was assembled in an argon-filled glove box, with a lithium metal sheet as the counter electrode, polyethylene (PE) as the separator, and a 1 mol / L solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) of LiPF6 (EC to DMC volume ratio 1:1). The coin cell was subjected to charge-discharge tests, with the test procedure being 0.2C DC to 0V, 0.05C DC to 0V, 0V CV 50μA, 0.01C DC to 0V, 0V CV 20μA, Rest... 10 min, 0.2C CC to 2V; The testing equipment for the button cell was the LAND battery testing system from Wuhan Landian Electronics Co., Ltd.

[0059] The capacity retention test is conducted using the following method: Silicon-carbon anode material powder was mixed with graphite (mass ratio 15:85) to obtain mixed anode powder. Then, at a mass ratio of 92:4:4, the mixed anode powder, Super P conductive carbon black, and binder BP-7 were mixed in pure water, controlling the solid content at 48 wt%. After homogenization, the mixture was coated onto a current collector with copper foil as the substrate and vacuum-baked in a 90℃ vacuum oven for 4 hours. The electrode was then cold-pressed using a commercial rolling mill, and sliced ​​into small round pieces with a diameter of 22 mm using a commercial slicing machine to prepare the anode electrode. At a mass ratio of 90:7:3, commercial 523 cathode material, Super P conductive carbon black, and Super P conductive carbon black were mixed with graphite. P-type conductive carbon black and polyvinylidene fluoride (PVDF) are mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, controlling the solid content to be 55 wt%. The mixed slurry is coated onto an aluminum foil current collector and placed in a vacuum baking oven at 120℃ for 4 hours. The electrode is then cold-pressed using a commercial rolling mill, and sliced ​​into small round pieces with a diameter of 22 mm using a commercial slicing machine to prepare the positive electrode. The electrode is then dried under vacuum (-0.1 MPa) at 85℃ for 8 hours, weighed, and the weight of the active material is calculated. The separator was made of PE, and the electrolyte was a 1 mol / L LiPF6 EC / DMC solution (EC to DMC volume ratio 1:1). CR2430 coin cells were assembled in a glove box. The coin cells were left to stand at room temperature for 2 hours, then activated by charge-discharge at 0.1C on a Blue Electric test system, followed by 1C or 5C charge-discharge cycles (voltage range 3.0~4.2V) for 1000 cycles. The capacity retention rate of the material = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%.

[0060] The electrode expansion rate test method is as follows: Silicon-carbon anode material powder, Super P conductive carbon black, and binder LA133 were mixed in pure water at a mass ratio of 80:10:10, with the solid content controlled at 30%. After homogenization, the mixture was coated onto a current collector with copper foil as the substrate. The copper foil thickness was 13 μm, and the coating thickness was 75 μm. The mixture was then vacuum-baked in a 120℃ vacuum oven for 2 hours. The electrode was then cold-pressed using a commercial rolling mill, and sliced ​​into small round pieces with a diameter of 14 mm using a commercial slicing machine to prepare the anode electrode. The electrode was weighed, and the weight of the active material was calculated. The thickness of the active material electrode was measured. After weighing, the electrode was placed in a 120℃ vacuum oven. Vacuum baking was performed in a vacuum oven for 2 hours. A PE membrane was used as the separator, and a 1 mol / L LiPF6 EC / EMC / DEC / FEC solution was used as the electrolyte. The negative electrode and counter electrode were lithium sheets. A CR2430 coin cell was assembled in a glove box. The coin cell was left to stand at room temperature for 2 hours. On the Blue Electric testing system, it was first discharged at 0.1C, then at 0.05C, and finally at 0.02C, with a cutoff voltage of 0.005V. After the coin cell was fully charged, it was disassembled, and the thickness of the active material electrode was measured. The electrode expansion rate = (active material electrode thickness 2 - active material electrode thickness 1) / active material electrode thickness 1.

[0061] The electrochemical performance of the silicon-carbon anode materials obtained in Examples 1-14 and Comparative Examples 1-3 was measured and is shown in Table 2.

[0062] Table 2 Electrochemical performance of silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-3

[0063] Table 2 shows that the test data demonstrates that this structural design significantly improves the initial delithiation efficiency, 1C cycle capacity retention, and reduces material expansion. In particular, the silicon-carbon anode material described in Example 4 has an initial delithiation capacity of 2040 mAh / g at 1.5V, achieving an initial efficiency of 94.0%, a capacity retention of 98.9% after 1000 cycles at 1C, and an electrode expansion rate of 45.3%.

[0064] According to the electrochemical data of Comparative Examples 1-3, the "in-situ" generation of electronic conductive agent and the N-doped carbon shell are both beneficial to performance improvement. In particular, the three-dimensional network structure formed by the electronic conductive agent in the material provides a fast channel for electron transport. At the same time, the three-dimensional network confinement formed offsets the expansion stress of silicon particles caused by lithium intercalation.

[0065] Electrochemical data from Examples 1-4 and Comparative Examples 1-3 demonstrate that the material's structural design effectively improves its initial efficiency and cycle retention, and significantly reduces its expansion performance; the electronically conductive carbon nanotube exhibits the best performance in all aspects.

[0066] Examples 4-6 and Comparative Example 1 further investigated the effect of the content of carbon nanotubes as an electronic conductive agent. The results showed that the introduction of carbon nanotubes significantly reduced particle expansion. The appropriate amount of addition can effectively reduce the expansion of the material and reduce the cost.

[0067] Examples 4 and 7-10 further investigated the effect of the N-doped carbon shell coating rate on performance. The results showed that too low or too fast a coating rate is detrimental to the quality of the carbon shell. The first-effect results proved that the quality of the coated carbon affects the first-effect performance.

[0068] Examples 4 and 11-14 further investigated the effect of N-doped shell content on performance. The results showed that the carbon shell content directly affects the specific surface area of ​​the material. Low content will result in some silicon not being completely coated, causing excessive side reactions with the electrolyte and reducing the first efficiency. If the content is too high, the low quality of the carbon shell will lead to excessive consumption of electrolyte, resulting in a reduction in the first efficiency.

[0069] In summary, this invention constructs a silicon-carbon anode material that is structurally stable, highly conductive, and resistant to volume expansion. Through a unique three-layer nested substrate-shell structure design, combined with in-situ doping of conductive agents in the precursor, a continuous three-dimensional electron transport network is built, enhancing the overall conductivity of the material. The spatial buffering effect of the high-porosity porous carbon framework alleviates the volume expansion stress of silicon. Furthermore, the outer nitrogen-doped carbon shell further fixes silicon particles, strengthens structural stability, and optimizes interface performance. Ultimately, this achieves high silicon content, high conductivity, high initial coulombic efficiency, excellent rate performance, and long cycle life, meeting the application requirements of high-energy-density lithium-ion batteries.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A substrate-frame-shell structure silicon-carbon anode material, characterized in that, From the inside out, it includes: a porous carbon framework on the substrate in situ doped with an electronically conductive agent; nano-silicon active material uniformly distributed in the pores and surface of the porous carbon framework on the substrate; and an N-doped carbon shell covering the outermost layer; wherein the electronically conductive agent is embedded in the carbon matrix of the porous carbon substrate to form a continuous electronically conductive network framework.

2. The silicon-carbon anode material according to claim 1, characterized in that, The material has an electrical conductivity greater than 50 S / cm, a silicon mass content of 45%~60%, an electronic conductive agent mass content of 0.1%~0.5%, and an N-doped carbon shell mass content of 0.5%~3%.

3. The silicon-carbon anode material according to claim 1, characterized in that, The electronically conductive agent is selected from one or more of carbon black, carbon fiber, carbon nanotubes, and graphene; the nitrogen source of the N-doped carbon shell is ammonia, pyridine vapor, or melamine vapor.

4. The silicon-carbon anode material according to claim 1, characterized in that, The porous carbon substrate has a specific surface area of ​​1600~2800 m² / g, a microporosity of ≥92%, a pore size of ≥5 nm accounting for ≤0.3%, and an electrical conductivity greater than 100 S / cm.

5. A method for preparing a substrate-frame-shell structured silicon-carbon anode material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Precursor preparation: A carbon source, dispersant, crosslinking agent, electronically conductive agent, and solvent are mixed, heated to gelatinize, and then spray-dried and granulated to obtain composite precursor microspheres; S2. Preparation of porous carbon substrate: The composite precursor microspheres are pre-carbonized, pulverized, subjected to high-temperature carbonization and activation treatment to obtain highly conductive porous carbon in situ doped with electronically conductive agents; S3. Composite and coating: Nano-silicon is deposited on the highly conductive porous carbon by chemical vapor deposition, and then coated with an N-doped carbon shell under a nitrogen-containing atmosphere to obtain the silicon-carbon anode material.

6. The method according to claim 5, characterized in that, In step S1, the carbon source is starch; the heating and gelatinization temperature is 80~99℃, and the holding time is 0.5~4 h; the Dv50 particle size of the precursor microspheres obtained by spray drying is 30~100 μm.

7. The method according to claim 5, characterized in that, In step S2, the pre-carbonization temperature is 550~750℃ and the time is 1~3 h; the Dv50 particle size of the pulverized powder is 8.0~12.0 μm and the particle size distribution Span value is ≤0.9; the high-temperature carbonization temperature is 1000~1400℃ and the holding time is 2~6 h; the activation treatment is physical activation, the temperature is 800~1000℃ and the time is 6~18 h.

8. The method according to claim 5, characterized in that, In step S3, the silane gas used for silicon deposition by chemical vapor deposition is selected from one or more of silane, silane, and trichlorosilane, and the deposition temperature is 450~650℃; the atmosphere used for coating the N-doped carbon shell is a mixture of nitrogen source gas and carbon source gas, wherein the volume percentage of nitrogen source is 1~30% and the volume percentage of carbon source is 70~99%, the coating temperature is 500~700℃, and the coating time is 4~10 h.

9. The method according to claim 5, characterized in that, The dispersant is selected from one or more of sodium dodecyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate; the crosslinking agent is selected from one or more of sodium trimetaphosphate, acetic anhydride, citric acid, and octenyl succinic anhydride.

10. A lithium-ion battery, characterized in that, Its negative electrode is made of silicon-carbon negative electrode material with a substrate-shell structure as described in any one of claims 1-4.

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