Preparation method and application of composite negative electrode material based on silicon-carbon core-shell structure

Abstract

The invention relates to the technical field of lithium ion battery electrode materials, in particular to a preparation method and application of a composite negative electrode material based on a silicon-carbon core-shell structure, and the preparation method of the composite negative electrode material based on the silicon-carbon core-shell structure comprises the following steps: step 1, synthesizing and treating a silicon core; step 2, coating a carbon shell; step 3, heat treatment: the precursor powder is placed in a tubular furnace, heat treatment is carried out in an inert atmosphere, the heat treatment process is divided into two stages, the first stage is carried out at a relatively low temperature to enable a carbon source to be crosslinked and cured, and the second stage is carried out at a relatively high temperature to enable a carbon shell to be completely carbonized and form strong interface bonding with a silicon core, so that the carbon shell is formed; the heat treatment temperature and time are adjusted according to the pyrolysis characteristics of the carbon source and the thermal stability of the silicon core; and 4, post-treatment is carried out. Through coating of the silicon core and the carbon shell, heat treatment and subsequent optimization treatment, the obtained negative electrode material not only has a relatively high specific surface area, but also can relieve the problem of expansion of the silicon material in the charging and discharging process of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode materials technology, and in particular to the preparation method and application of composite anode materials based on silicon-carbon core-shell structure. Background Technology

[0002] Lithium-ion batteries, as the core energy storage devices in modern electronic devices and electric vehicles, directly impact the range and lifespan of these devices. The anode material is a crucial component of lithium-ion batteries. Currently, commercially available anode materials primarily utilize graphite-based carbon materials, but their theoretical specific capacity is relatively low (approximately 372 mAh / g), failing to meet the demands of high-energy-density batteries. Silicon materials, due to their high theoretical specific capacity (approximately 4200 mAh / g), are considered an ideal choice for next-generation anode materials. However, silicon suffers from severe volume expansion during charge and discharge (expansion rates can exceed 300%), leading to electrode material pulverization, instability of the solid electrolyte interface film, and a sharp decline in cycle performance. These problems severely limit the commercial application of silicon-based anode materials.

[0003] To mitigate the volume expansion problem of silicon, existing technologies have proposed silicon-carbon composite structures, among which the silicon-carbon core-shell structure is a common design. In this structure, the silicon core acts as the active material, providing high capacity, while the carbon shell acts as a buffer layer to alleviate volume expansion and improve conductivity. However, existing methods for fabricating silicon-carbon core-shell structures have several problems. First, the core-shell bonding strength is insufficient, making the shell prone to peeling during cycling, leading to rapid capacity decay. Second, the carbon shell coating has poor uniformity, with some silicon cores exposed and in direct contact with the electrolyte, causing side reactions and capacity loss. Furthermore, existing methods often employ high-temperature vapor deposition or mechanical mixing, which are complex, costly, and difficult to mass-produce. For example, chemical vapor deposition requires precise control of gas flow rate and temperature, but is prone to non-uniform coating; while liquid phase coating is simple, the interfacial bonding between the carbon shell and the silicon core is weak, making it prone to cracking after heat treatment. The composite anode materials prepared by these methods exhibit low capacity retention and unsatisfactory initial coulombic efficiency during cycle testing, failing to meet the long-cycle stability requirements of high-power batteries (such as electric vehicles and energy storage systems).

[0004] Therefore, there is an urgent need in the field for a new preparation method that can achieve uniform coating and strong interfacial bonding of silicon-carbon core-shell structures, while simplifying the process and reducing production costs. This invention addresses these issues by proposing a method for preparing composite anode materials based on silicon-carbon core-shell structures. By optimizing raw material selection, coating process, and heat treatment conditions, the stability and electrochemical performance of the core-shell structure are significantly improved. Summary of the Invention

[0005] To achieve the above objectives, this invention provides a method for preparing a composite anode material based on a silicon-carbon core-shell structure and its application. The method for preparing the composite anode material based on a silicon-carbon core-shell structure includes the following steps: Step 1: Synthesis and processing of silicon nuclei. Silane compounds are used as silicon sources. Silane compounds are dissolved in organic solvents to form silicon source solutions. The concentration of the silicon source solution is calculated by the mass of the silane compounds and the volume of the organic solvent. A reducing agent is added dropwise to the silicon source solution under a protective atmosphere to carry out a chemical reduction reaction. The dropping rate is controlled to allow the reduction reaction to proceed slowly, generating nano-silicon particles. After the reaction, the nano-silicon particles are collected by centrifugation. The centrifugation speed is determined based on the particle size and density of the nano-silicon particles. The particle size of the nano-silicon particles is measured by dynamic light scattering. The nano-silicon particles are then washed with an organic solvent to remove impurities. Afterward, the nano-silicon particles are dispersed in an aqueous solution containing a surfactant. The amount of surfactant added is determined based on the specific surface area of ​​the nano-silicon particles, which is measured by nitrogen adsorption. The nano-silicon particles are then uniformly dispersed by ultrasonic treatment to form a silicon nuclei suspension. Step 2: Carbon shell coating. The silicon core suspension is mixed with a carbon source, which is a thermally polymerizable organic compound. The amount of carbon source added is calculated based on the mass of the silicon core and the target carbon shell thickness. The target carbon shell thickness is determined by the silicon core diameter and the expected buffering effect. The silicon core diameter is measured by scanning electron microscopy. During the mixing process, the stirring speed and temperature are controlled to ensure that the carbon source is uniformly adsorbed on the surface of the silicon core. Then, the solvent is removed by evaporation to form a precursor powder. The uniformity of the precursor powder is confirmed by scanning electron microscopy. Step 3: Heat treatment. The precursor powder is placed in a tube furnace and heat-treated under an inert atmosphere. The heat treatment process is divided into two stages. The first stage is carried out at a lower temperature to allow the carbon source to cross-link and solidify. The second stage is carried out at a higher temperature to completely carbonize the carbon shell and form a strong interfacial bond with the silicon core. The heat treatment temperature and time are adjusted according to the pyrolysis characteristics of the carbon source and the thermal stability of the silicon core. Step 4: Post-processing. The heat-treated silicon-carbon core-shell composite powder is pulverized and sieved. Pulverization is carried out using an air jet mill, with control of air pressure and feed rate. Sieving is done using a standard sieve to control the particle size distribution of the powder. The particle size distribution of the powder is measured by a laser particle size analyzer, and the physical properties of the powder are optimized by tap density test and specific surface area measurement.

[0006] Preferably, in step 1, the silane compound is silicon tetrachloride, the organic solvent is ethanol, the reducing agent is sodium borohydride, and the surfactant is sodium dodecyl sulfate. The concentration range of the silicon source solution is the mass of silane compound dissolved per liter of organic solvent, which is calculated by the molecular weight of the silane compound and the yield of the target silicon nanoparticles. The protective atmosphere is nitrogen or argon. The dropping rate is optimized experimentally to avoid agglomeration of nano-silicon particles. The centrifugation speed is calculated based on Stokes' law and the settling velocity of nano-silicon particles. When measuring the particle size of nano-silicon particles using the dynamic light scattering method, the nano-silicon particles are dispersed in deionized water and measured using a laser particle size analyzer. When measuring the specific surface area using the nitrogen adsorption method, the nano-silicon particle sample is degassed under vacuum and then placed in a nitrogen adsorption instrument. The specific surface area is calculated based on the BET model. The amount of surfactant added was determined by specific surface area and surface coverage, and the surface coverage was optimized by adsorption isotherm experiments. Ultrasonic treatment was performed using an ultrasonic disruptor, with power and processing time controlled. Power was determined by testing the dispersion stability of the nano-silicon particles, and processing time was optimized by monitoring particle size distribution.

[0007] Preferably, in step 2, the carbon source is phenolic resin or sucrose, and the concentration of the carbon source solution is calculated by the target carbon shell thickness and the silicon core mass. The target carbon shell thickness is determined based on the silicon core diameter and the volume expansion buffer requirement. The volume expansion buffer requirement is calculated by the expansion rate of the silicon material during the lithium ion insertion and extraction process. The stirring speed is calculated using the Reynolds number to ensure uniform mixing, and the temperature is adjusted based on the solubility and volatility of the carbon source. To remove solvents by evaporation, a rotary evaporator is used, and the evaporation temperature is set according to the boiling point of the solvent to avoid premature decomposition of the carbon source. The uniformity of the precursor powder was checked by observing multiple fields of view using a scanning electron microscope to ensure that the carbon source completely covered the silicon core surface. If there were any uncovered areas, the amount of carbon source added or the mixing time was adjusted.

[0008] Preferably, in step 3, the inert atmosphere is argon, and the heating rate is determined by thermogravimetric analysis curves. The thermogravimetric analysis is performed in an air atmosphere to simulate the heat treatment process. The temperature of the first stage heat treatment is determined by the glass transition temperature of the carbon source, and the temperature of the second stage heat treatment is determined by the pyrolysis peak temperature of the carbon source. The pyrolysis peak temperature is measured by differential scanning calorimetry. The heat treatment time was calculated based on the thickness of the carbon shell and the thermal conductivity of the silicon core to ensure that the carbon shell was free of cracks. The interfacial bonding strength was observed using a high-resolution transmission electron microscope. Ultrathin sections were prepared to check the interfacial continuity between the silicon core and the carbon shell. The interfacial continuity was verified by electron diffraction patterns.

[0009] Preferably, in step 4, the airflow pressure of the air jet mill is adjusted by the hardness and toughness of the powder, and the feed rate is optimized by the flowability of the powder and the target particle size distribution. The mesh size of the standard sieve is selected based on the target particle size distribution, which is determined by the coating requirements of the battery negative electrode material. When using a laser particle size analyzer, the powder is dispersed in ethanol to avoid agglomeration, and multiple measurements are taken to obtain the average value. The tap density test was performed using a tap density meter, with the vibration frequency and number of vibrations optimized based on the powder's packing behavior. The specific surface area was measured again using the nitrogen adsorption method to ensure the integrity of the carbon shell. The specific surface area value was calculated using the BET model and compared with the measurement value in step 1 to evaluate the coating effect.

[0010] Preferably, in step 1, the synthesis of nano-silicon particles further includes size control, which is achieved by adjusting the dropping rate of the reducing agent and the reaction temperature, the reaction temperature being determined by the reduction kinetics of silane compounds; In step 2, the carbon shell coating also includes multiple layers of coating. The number of layers of the multi-layer coating is determined by the target conductivity and buffering effect through repeated mixing and evaporation steps. In step 3, the heat treatment also includes an intermediate annealing step, with the intermediate annealing temperature between the first stage and the second stage, adjusted by the degree of crosslinking of the carbon source, which is analyzed by infrared spectroscopy.

[0011] Preferably, in step 1, the selection of surfactant further includes nonionic surfactants, and the amount of nonionic surfactant added is calculated by the hydrophilic-lipophilic balance value; In step 2, the carbon source also includes a polymer precursor, the molecular weight of which is measured by gel permeation chromatography and the molecular weight distribution is controlled by the polydispersity index. In step 3, the heat treatment atmosphere also includes a reducing gas, the proportion of which is adjusted by the degree of graphitization of the carbon shell, which is determined by Raman spectroscopy.

[0012] Preferably, in step 4, the post-processing further includes surface modification, which is carried out by chemical vapor deposition or atomic layer deposition. The deposition thickness is controlled by the number of cycles, and the deposition material is carbon or metal oxide. The selection of the deposition material is optimized through battery cycle performance testing. The pulverization process also includes a classification step, which is carried out by an air classifier. The classification accuracy is adjusted by the sphericity of the particles, which is measured by image analysis software.

[0013] Preferably, in step 1, the synthesis of the silicon core also includes a doping element, which is boron or phosphorus. The doping concentration is calculated by the ratio of silane compound to doping source, and the doping source is borane or phosphine. The doping effect is verified by electrochemical impedance spectroscopy. In step 2, the carbon shell coating also includes conductive additives, which are carbon nanotubes or graphene. The amount of additives is determined by the electrical conductivity of the composite material, which is measured by the four-probe method. In step 3, the heat treatment also includes a rapid cooling step, the rapid cooling rate of which is optimized by the microstructure of the carbon shell, which is analyzed by X-ray diffraction.

[0014] Accordingly, embodiments of the present invention also provide the application of composite anode materials based on silicon-carbon core-shell structures. The composite anode material is used as the anode of lithium-ion batteries. The composite anode material is mixed with a conductive agent and a binder in a certain proportion. The conductive agent is acetylene black, and the binder is polyvinylidene fluoride. The proportion is optimized through battery capacity and cycle life tests. A solvent is added to form a slurry. The solvent is N-methylpyrrolidone. The viscosity of the slurry is measured by a rheometer. The slurry is coated on a current collector, which is copper foil. The coating thickness is controlled by a doctor blade. After coating, the anode is dried and rolled to form a negative electrode sheet. The drying temperature is determined by the boiling point of the solvent, and the rolling pressure is adjusted by the density of the electrode sheet. The density of the electrode sheet is measured by the Archimedes method. The negative electrode, positive electrode, separator, and electrolyte are assembled into a battery. The positive electrode is lithium cobalt oxide, the separator is a polypropylene membrane, and the electrolyte is an organic carbonate solution containing lithium salt. Assembly is carried out in an argon-protected glove box. The battery undergoes formation and cycle testing. The formation conditions are optimized by initial coulombic efficiency, and the cycle test is carried out by charge-discharge instrument. The test conditions include current density, voltage range, and temperature. The current density is determined by the rate performance of the battery, the voltage range is adjusted by the electrochemical window of the electrode material, and the temperature is selected according to the application environment of the battery.

[0015] The beneficial effects of this invention are: 1. This invention significantly enhances the bonding strength between the silicon core and the carbon shell by optimizing the coating process and heat treatment conditions. Thus, during the charging and discharging process of the battery, the carbon shell layer can effectively prevent peeling, ensuring that the battery capacity remains stable during long-term cycling.

[0016] 2. This invention optimizes the coating process, employing improved raw material selection and precise heat treatment techniques to ensure uniform coating of the carbon shell. This uniform coating effectively reduces the exposed surface area of ​​the silicon core, thereby avoiding unnecessary side reactions and improving the overall capacity and cycle performance of the battery.

[0017] 3. The preparation method proposed in this invention employs a simplified process flow, avoiding complex equipment requirements and reducing production costs. Simultaneously, the simplified process makes material production more operable and scalable, capable of meeting the needs of large-scale production.

[0018] 4. Due to the optimized silicon-carbon core-shell structure, this invention improves the electrochemical performance of the battery. The improved coating technology enhances the stability of the silicon-carbon composite material, especially exhibiting higher capacity retention and initial coulombic efficiency during long-term charge-discharge cycles. This results in the composite anode material of this invention having a longer service life and better stability in high-power battery applications, meeting the long-cycle stability requirements of high-power batteries in electric vehicles and energy storage systems. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the steps of the method of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0022] Please see Figure 1 This invention provides a method for preparing a composite anode material based on a silicon-carbon core-shell structure. In step 1, a silane compound is first used as a silicon source, which is dissolved in an organic solvent to form a silicon source solution. The concentration of the silicon source solution is determined based on the mass of the silane compound and the volume of the solvent. Next, a reducing agent is added dropwise under a protective atmosphere to carry out a chemical reduction reaction, gradually generating nano-silicon particles.

[0023] To ensure reaction stability, the dropping rate was controlled to slow the reduction reaction and avoid excessive byproducts. Nanoscale silicon particles were collected by centrifugation, with the centrifugation speed adjusted according to the particle size and density to ensure uniform particle size. The particle size was measured using dynamic light scattering to ensure it remained within an appropriate range. Impurities were removed by washing with an organic solvent, followed by dispersion in an aqueous solution containing a surfactant. The amount of surfactant added was determined based on the specific surface area of ​​the silicon particles to ensure uniform dispersion.

[0024] Finally, ultrasonic treatment further ensures the uniform dispersion of the silicon nanoparticles, forming a silicon core suspension. This yields high-purity, uniformly dispersed silicon nanoparticles, providing high-quality silicon cores for subsequent carbon shell coating.

[0025] In step 2, the silicon core suspension is mixed with a thermally polymerizable organic carbon source. The amount of carbon source added is calculated based on the silicon core mass and the target carbon shell thickness to ensure uniform coating of the silicon core during the coating process. By controlling the stirring speed and temperature during mixing, the carbon source is ensured to be uniformly adsorbed onto the silicon core surface. Next, the solvent is evaporated to remove the carbon, resulting in a uniform precursor powder. The uniformity of the precursor powder is confirmed by scanning electron microscopy (SEM). By precisely controlling the carbon source coating process, the uniformity of the carbon shell can be ensured, providing an ideal precursor material for subsequent heat treatment.

[0026] In step 3, the precursor powder is placed in a tube furnace and heat-treated under an inert atmosphere. The heat treatment process consists of two stages: the first stage is carried out at a lower temperature to allow the carbon source to crosslink and solidify; the second stage is carried out at a higher temperature to completely carbonize the carbon shell and form a strong interfacial bond with the silicon core. The selection of heat treatment temperature and time is adjusted based on the pyrolysis characteristics of the carbon source and the thermal stability of the silicon core. High-temperature treatment enables a strong interfacial bond between the silicon core and the carbon shell, thereby improving the structural stability of the silicon-carbon composite material and avoiding interfacial separation or delamination problems during subsequent use.

[0027] In step 4, the heat-treated composite powder is pulverized using an air jet mill. The airflow pressure and feed rate are controlled to ensure the desired particle size. A standard sieve is used during sieving to strictly control the particle size distribution, and a laser particle size analyzer is used to measure the particle size and ensure uniformity. The physical properties of the powder are further optimized through tap density testing and specific surface area measurement. This process yields composite anode materials with uniform particle size and suitable specific surface area, laying the foundation for improved battery performance.

[0028] By precisely controlling multiple steps, including silicon core synthesis, carbon shell coating, and heat treatment, the fabrication process of the silicon-carbon core-shell structure was successfully optimized. The resulting composite anode material exhibits high capacity retention, low initial coulombic efficiency loss, and effectively suppresses silicon volume expansion, thus enhancing battery cycle stability. These superior electrochemical properties make the composite anode material of this invention promising for broad applications, especially in high-energy-density batteries (such as electric vehicles and energy storage systems).

[0029] In one possible implementation, silicon tetrachloride was chosen as the silane compound, a common and efficient silicon source that is soluble in the organic solvent ethanol. Ethanol, as a solvent, not only has a low boiling point, which helps control the reaction temperature, but also provides a suitable polar environment for the reaction. Sodium borohydride was chosen as the reducing agent, as it efficiently reduces silicon tetrachloride to generate nano-silicon particles. To ensure the dispersibility and stability of the nano-silicon particles, sodium dodecyl sulfate was added to the solution as a surfactant to help improve particle dispersibility and reduce agglomeration.

[0030] When calculating the concentration of the silicon source solution, the molecular weight of the silane compound and the yield of the target silicon nanoparticles are used to ensure that the mass of silicon source per liter of solvent meets the reaction requirements, avoiding the impact of excessive or insufficient silicon source on the reaction. A nitrogen or argon atmosphere is used as the protective atmosphere, which helps to avoid interference from oxygen in the reduction reaction and ensures its smooth progress.

[0031] The rate of adding the reducing agent was optimized experimentally to avoid excessively rapid reduction reaction that could lead to agglomeration of the nano-silicon particles, thus ensuring particle uniformity and small size. The centrifugation speed was adjusted based on Stokes' law and the settling velocity of the nano-silicon particles to ensure that the nano-silicon particles separated by centrifugation have a suitable particle size distribution.

[0032] The particle size of the silicon nanoparticles was measured using dynamic light scattering. In this process, the particles were first dispersed in deionized water, and then the particle size was measured using a laser particle size analyzer. This method allows for precise determination of the particle size distribution of the silicon nanoparticles, ensuring they meet the requirements for subsequent carbon shell coating.

[0033] Specific surface area was measured using nitrogen adsorption. The sample was degassed under vacuum to remove adsorbed moisture and gas from its surface. The sample was then placed in a nitrogen adsorption instrument, and the specific surface area was calculated using the BET model. This process allows for precise measurement of the specific surface area of ​​nano-silicon particles, thus providing a basis for subsequent surfactant addition.

[0034] The amount of surfactant added was optimized based on specific surface area and surface coverage. Adsorption isotherm experiments were used to determine the optimal surfactant dosage to ensure good dispersibility of the silicon nanoparticles. Ultrasonic treatment was performed using an ultrasonic disruptor, and the dispersion effect was further optimized by controlling the power and treatment time. The selection of ultrasonic power was based on the dispersion stability tests of the silicon nanoparticles, while the treatment time was optimized based on particle size distribution monitoring to ensure that uniformly dispersed silicon nanoparticles were obtained.

[0035] This process effectively improves the quality and performance of silicon core particles by precisely controlling the parameters of each step. In particular, by rationally selecting chemical reagents, optimizing the dropping rate, adjusting the centrifugation speed, and ultrasonic treatment conditions, uniformly sized and stably dispersed nano-silicon particles can be obtained, providing an ideal foundation for subsequent carbon shell coating. Furthermore, the optimized addition of surfactants can significantly improve particle dispersibility, prevent particle aggregation, and thus ensure the high performance and stability of the final composite anode material.

[0036] The embodiments of the present invention result in a silicon-carbon core-shell composite anode material with a high specific surface area, uniform particle distribution and good dispersibility, which can effectively improve the cycle stability and energy density of the battery and has good application prospects, especially suitable for anode materials of high-performance lithium-ion batteries.

[0037] In one possible implementation, the selected carbon source is phenolic resin or sucrose. Phenolic resin, due to its good thermal stability and controllable carbonization characteristics, can form a uniform carbon shell, while sucrose has good solubility and a high carbonization rate, making it suitable for forming high-quality carbon shells. The concentration of the carbon source solution is calculated based on the target carbon shell thickness and the silicon core mass. The carbon shell thickness is determined according to the diameter of the silicon core and its required volume expansion buffering during lithium-ion insertion and extraction. During lithium-ion insertion and extraction, the silicon material undergoes a certain volume expansion; therefore, the carbon shell thickness must be sufficient to alleviate the stress caused by volume expansion and prevent the silicon core from cracking and expanding.

[0038] To ensure uniform mixing of the carbon source and silicon core, the stirring speed needs to be calculated using the Reynolds number. The Reynolds number is a parameter in fluid mechanics that characterizes the flow state of a fluid. It allows adjustment of the stirring speed to ensure that the carbon source solution uniformly covers the silicon core surface, avoiding localized areas of excessively thick or thin carbon shells. Simultaneously, the temperature during stirring needs to be optimized based on the solubility and volatility of the carbon source to ensure complete dissolution and uniform distribution, preventing volatilization or decomposition due to excessively high temperatures.

[0039] To remove solvent from the carbon source solution, a rotary evaporator is used for evaporation. The rotary evaporator improves solvent evaporation efficiency through rotation, and the evaporation rate can be precisely controlled by adjusting the temperature and rotation speed. During this process, the evaporation temperature needs to be set according to the solvent's boiling point to prevent premature decomposition of the carbon source, which would affect the quality and structure of the carbon shell.

[0040] After obtaining the precursor powder, its uniformity needs to be checked using a scanning electron microscope (SEM) to ensure that the carbon source completely covers the surface of the silicon core. SEM can observe the microstructure of the powder surface and check for any uncovered areas. If uneven carbon source coverage is found, the coverage effect needs to be improved by adjusting the amount of carbon source added or the mixing time. Ensuring uniform carbon source coverage is to ensure that the formed carbon shell can provide sufficient protection for the silicon core, improving its ability to withstand volume expansion during battery charging and discharging.

[0041] Through optimization and control of the above steps, a uniform carbon shell with an ideal thickness can be obtained, effectively mitigating the expansion problem of silicon materials during battery cycling and enhancing the cycle stability of the composite anode material. The uniformity and stability of the carbon shell directly affect the battery performance, especially during charge and discharge, effectively improving the battery's specific capacity, cycle life, and safety. Furthermore, this method ensures the dispersion and uniformity of the carbon source and silicon core throughout the preparation process, further enhancing the overall performance of the composite anode material.

[0042] This precise process control not only improves the electrochemical performance of the anode material, but also provides a reliable material basis for the high performance of lithium-ion batteries, with broad application prospects.

[0043] In one possible implementation, argon is used as an inert atmosphere during heat treatment to prevent oxidation. Argon effectively isolates oxygen from the air, thus preventing the silicon material from reacting with oxygen at high temperatures and causing performance degradation. The heating rate is determined using thermogravimetric analysis (TGA), which provides information on the mass changes of the material at different temperatures, simulating its behavior during actual heat treatment. Performing TGA in an air atmosphere allows for a more realistic simulation of the material changes during pyrolysis, providing a theoretical basis for precise control of the heating rate. Precise control of the heating rate helps to achieve uniform heating, thereby preventing material cracking or inhomogeneity caused by rapid heating.

[0044] The temperature of the first stage of heat treatment is determined by the glass transition temperature of the carbon source. The glass transition is the process by which the carbon source softens and hardens; controlling this temperature ensures the successful formation of a stable carbon shell structure. The temperature of the second stage of heat treatment is set based on the pyrolysis peak temperature of the carbon source. The pyrolysis peak temperature is measured using differential scanning calorimetry (DSC), which allows for precise determination of the optimal temperature for carbon source decomposition. By precisely controlling these temperatures, the carbonization process of the carbon shell can be optimized, improving its structural stability.

[0045] The heat treatment time is calculated based on the thickness of the carbon shell and the thermal conductivity of the silicon core. To ensure that the carbon shell does not crack during heat treatment, the heat treatment time needs to be calculated appropriately to ensure that the carbon source decomposes fully and forms a stable carbon shell, while avoiding overheating that could lead to embrittlement or cracking of the carbon shell. Furthermore, the optimization of the heat treatment time also considers the thermal conductivity of the silicon core to ensure that the silicon core can effectively transfer heat and avoid localized overheating.

[0046] To ensure a good bond between the silicon core and the carbon shell, the interface structure was observed using high-resolution transmission electron microscopy (HRTEM). By preparing ultrathin sections, the contact surface between the silicon core and the carbon shell could be clearly observed, allowing for assessment of the strength of the bond. Interface continuity was further verified using electron diffraction patterns, ensuring the absence of interfacial breaks or discontinuities. A good interfacial bond enhances the mechanical strength and electrochemical properties of the composite material, making it more stable during cycling.

[0047] By precisely controlling each parameter in the heat treatment process, the structure of the silicon-carbon core-shell composite material can be effectively optimized, ensuring the uniformity, stability, and crack-free nature of the carbon shell. Furthermore, the excellent bonding between the silicon core and the carbon shell enhances the material's mechanical properties, enabling the composite anode material to better cope with volume expansion during battery charge and discharge, thus improving cycle stability. This method significantly improves the performance of the anode material, resulting in higher specific capacity, longer cycle life, and better safety, making it suitable for the fabrication of high-performance lithium-ion batteries.

[0048] In one possible implementation, the airflow pressure of the air jet mill needs to be adjusted according to the hardness and toughness of the powder. Harder powders, such as silicon-based materials, require higher airflow pressures to ensure effective particle breaking during the milling process and achieve the desired particle size range. Conversely, powders with better toughness can be milled with lower airflow pressures to avoid over-crushing or generating unnecessary heat. Feed rate control needs to be optimized based on the powder's flowability and target particle size distribution. Powders with poor flowability require lower feed rates to avoid clogging the equipment and ensure uniform powder dispersion. In this process, the air jet mill can effectively adjust these parameters to ensure that the particle size distribution of the milled powder meets the requirements of subsequent processes.

[0049] The selection of the standard sieve mesh size is directly related to the target particle size distribution. In the coating process of battery anode materials, the particle size distribution is crucial for coating uniformity and material density. Based on coating requirements, an appropriate sieve mesh size is selected to ensure the particle size distribution meets design specifications. Generally, finer particle sizes help improve coating uniformity and also enhance the surface activity and electrochemical reaction rate of the material.

[0050] To accurately measure the particle size distribution of powder, a laser particle size analyzer is used. During the measurement process, the powder needs to be dispersed in ethanol to effectively avoid powder agglomeration. Agglomeration leads to inaccurate particle size distribution measurements, thus affecting subsequent material design and application performance. By taking multiple measurements and averaging them, the accuracy of the data can be further improved, ensuring precise control of the particle size distribution.

[0051] A tap density meter is used to test the density characteristics of powders. The adjustment of the vibration frequency and number of vibrations is based on the optimization of powder packing behavior. The packing behavior of powders is closely related to their particle size, morphology, and surface properties. By optimizing the vibration frequency and number of vibrations, the close packing of powder particles can be promoted, thereby obtaining a higher density, which helps to improve the energy density and cycle stability of battery anode materials.

[0052] Specific surface area is an important indicator for evaluating the integrity of a carbon shell. Measuring specific surface area using nitrogen adsorption allows for accurate assessment of the surface characteristics of the carbon shell. Changes in specific surface area reflect the integrity and uniformity of the carbon shell. The measurement results are calculated using the BET model and compared with the measured values ​​from step 1 to evaluate the coating effect of the carbon shell. If the specific surface area value matches the expected value, it indicates a good carbon shell coating effect, effectively protecting the silicon core and preventing cracking due to volume expansion, thereby improving the cycling stability of the material.

[0053] Through the embodiments of this invention, it is possible to ensure that the particle size distribution, flowability, density, and other characteristics of the powder meet the requirements of battery anode materials, further optimizing the electrochemical performance of the material. Appropriate airflow pressure and feed rate control ensure powder uniformity, while laser particle size analysis, tap density testing, and specific surface area measurement help to better understand the physical properties of the powder and the quality of the carbon shell. Overall, the embodiments of this invention result in a composite anode material with higher specific capacity, excellent cycle performance, and better battery efficiency, making it suitable for the manufacture of high-performance lithium-ion batteries.

[0054] In one possible implementation, the synthesis of silicon nanoparticles is the first step in the preparation of this composite anode material. Size control is one of the key factors affecting the final material performance. To control the size of the silicon particles, the dropping rate of the reducing agent and the reaction temperature can be adjusted. The dropping rate of the reducing agent directly affects the reaction rate, and thus the growth rate and final size of the silicon particles. If the reducing agent is added too quickly, the particle size may be too small; conversely, if it is too slow, the particles may aggregate, affecting particle uniformity. The reaction temperature is determined by the reduction kinetics of silane compounds. Controlling the temperature can regulate the reaction activity, ensuring the stable progress of the reduction reaction, and thus obtaining uniform silicon nanoparticles. By precisely controlling these parameters during the synthesis process, silicon nanoparticles of ideal size and uniformity can be obtained, providing a high-quality base material for subsequent coating and heat treatment steps.

[0055] After silicon particle synthesis, the next step is to coat the silicon particles with a carbon shell, forming a silicon-carbon core-shell structure. In this process, the number and quality of the coating layers directly affect the material's conductivity and buffering effect. To ensure effective carbon shell coating, a multi-layer coating method can be used, which typically involves repeated mixing and evaporation steps. Each carbon shell layer is formed on the silicon particle surface through evaporation. The number of coating layers is determined by the target conductivity and buffering effect. Increased conductivity enhances the material's electrical conductivity, while the buffering effect helps alleviate stress caused by volume expansion of the silicon material during battery charging and discharging, thereby improving the material's cycle stability. Through multi-layer coating, a uniform and stable carbon shell can be formed on the silicon particle surface, further improving the composite material's performance.

[0056] Heat treatment is a crucial step in the entire preparation process, affecting not only the carbonization of the carbon shell but also the stability of the silicon-carbon core-shell structure. An intermediate annealing step is incorporated into this stage. The intermediate annealing temperature is set between the first and second stages, which helps to further optimize the structure of the carbon shell and the bonding between the silicon and carbon interfaces. The selection of the intermediate annealing temperature is achieved by adjusting the degree of crosslinking of the carbon source, which directly affects the stability and integrity of the carbon shell. The degree of crosslinking is determined by infrared spectroscopy analysis, which provides detailed information on the degree of crosslinking of the carbon source, ensuring that the carbon shell has an appropriate crosslinking density during heat treatment. A suitable degree of crosslinking helps the carbon shell form a more robust structure, reduces crack formation, and improves the mechanical strength and electrochemical properties of the composite material.

[0057] By precisely controlling the size of the silicon nanoparticles, the multi-layer carbon shell coating, and the intermediate annealing step in the heat treatment process, the overall performance of the composite anode material can be significantly improved. Size control ensures the uniformity of silicon particles, avoiding the negative impact of excessively large or small particles on battery performance. Multi-layer carbon shell coating not only improves conductivity but also enhances the material's buffering capacity, effectively reducing the mechanical stress caused by silicon expansion during battery charging and discharging. The intermediate annealing step further optimizes the structure of the carbon shell, ensuring its stability and good bonding between the silicon and carbon interfaces. The embodiments of this invention result in a composite anode material with higher specific capacity, longer cycle life, and better battery performance, making it suitable for the manufacture of high-efficiency lithium-ion batteries.

[0058] In one possible implementation, the selection of surfactant is crucial during the synthesis of silicon particles. Nonionic surfactants, due to their lower degree of ionization, effectively prevent silicon particle agglomeration while minimizing the introduction of impurities, ensuring uniform particle dispersion. The amount of nonionic surfactant added is calculated using its hydrophilic-lipophilic balance (HLB) value. The HLB value measures the balance between the hydrophilicity and lipophilicity of the surfactant, affecting its dispersion in solution. By calculating the HLB value, the amount of surfactant added can be precisely controlled to achieve optimal dispersion. Accurate control of the added amount avoids adverse consequences such as particle agglomeration or uneven dispersion caused by excessive or insufficient surfactant, which in turn affects the performance of the final composite material.

[0059] In the carbon shell coating process of silicon-carbon core-shell structures, the selection of the carbon source is also crucial. In addition to conventional carbon sources, polymer precursors are used to improve the uniformity and stability of the carbon shell. The molecular weight of the polymer precursor is a significant factor affecting the carbon shell structure; excessively high molecular weight may lead to uneven coating, while excessively low molecular weight may result in an unstable carbon shell. To precisely control the molecular weight, gel permeation chromatography (GPC) is used to measure the molecular weight of the polymer precursor to ensure it meets design requirements. Simultaneously, the molecular weight distribution of the polymer is controlled by the polydispersity index (PDI). Optimizing the PDI value can adjust the rheological properties and reactivity of the polymer, thereby optimizing the carbon shell formation process and ensuring that the structure and performance of the carbon shell reach their optimal state.

[0060] Optimizing the atmosphere during heat treatment plays a crucial role in the structure of the carbon shell and the bonding between the silicon-carbon core and shell. This process includes reducing gases such as hydrogen and methane, which promote the reduction of the carbon shell, thereby enhancing its electrical conductivity. The proportion of reducing gases is a significant factor affecting the graphitization degree of the carbon shell. Higher graphitization results in better conductivity, but excessive graphitization can lead to embrittlement and impair its buffering properties. Therefore, by adjusting the proportion of reducing gases, the graphitization degree of the carbon shell can be precisely controlled to achieve optimal electrical conductivity and mechanical properties. The degree of graphitization is assessed using Raman spectroscopy, which reveals the extent of graphitization in carbon materials, helping to optimize the heat treatment process and ensure the stability and conductivity of the carbon shell.

[0061] Through the embodiments of this invention, the performance of the composite anode material has been significantly improved. The precise addition of nonionic surfactants ensures uniform dispersion of silicon particles, avoids agglomeration, and optimizes particle size and morphology. The selection and molecular weight control of the polymer precursor contribute to obtaining a uniform and stable carbon shell, improving coating effect and electrochemical performance. Optimization of the heat treatment atmosphere, especially the precise control of the reducing gas ratio, ensures an appropriate degree of graphitization of the carbon shell, improving conductivity and cycle stability. The embodiments of this invention not only enhance the electrochemical performance of the composite anode material but also improve its application in high-performance lithium-ion batteries, exhibiting higher energy density, better cycle life, and stronger stress resistance.

[0062] In one possible implementation, surface modification is a key post-processing step in the preparation of composite anode materials, aiming to improve the surface properties of the material and enhance the cycle performance and stability of the battery. Surface modification is performed using chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques, both of which can precisely deposit a thin film on the material surface. CVD technology forms a thin film on the surface of a silicon-carbon core-shell structure through chemical reactions, while ALD is a method of depositing material layer by layer on the surface through alternating gas reactions, which allows for more precise control of the deposition thickness. The deposited material can be carbon or metal oxides, such as aluminum oxide or titanium oxide, which can effectively improve the conductivity and stability of the battery and reduce the stress generated during charging and discharging.

[0063] The thickness of the deposit is controlled by the number of cycles. During the battery's charge-discharge cycles, the material undergoes a certain number of charge-discharge cycles, thus determining the number and thickness of the deposited layers. This method allows for precise control of the deposition process, ensuring the surface-modified layer has ideal thickness and stability. The selection of carbon or metal oxides as the deposition material is optimized through battery cycle performance testing. By testing the battery's performance in multiple charge-discharge cycles, the optimal deposition material is selected, ensuring that the surface-modified composite material provides better cycle stability and a longer lifespan.

[0064] After surface modification, the composite material needs to undergo pulverization and classification to optimize the particle morphology and size distribution, thereby improving the material's performance. During pulverization, an air classifier is used to classify the material. The air classifier utilizes the airflow velocity and particle weight differences to separate particles according to size. The classification accuracy is adjusted by the particle sphericity. Sphericity refers to the degree to which the particle shape approximates a sphere; higher sphericity results in better particle dispersibility and flowability, thus contributing to the material's electrochemical performance in batteries.

[0065] Sphericity measurement is performed using image analysis software, which can perform detailed analysis of the particle shape to obtain a sphericity value. This process ensures that the particles have good shape and uniformity, which helps improve battery capacity and cycle performance.

[0066] Surface modification improves the surface properties of the material through a precise deposition process, enhancing its conductivity and stability. Particularly during battery charge and discharge, it effectively reduces silicon expansion and contraction, thereby extending battery life. Furthermore, the pulverization and classification steps optimize particle morphology and distribution, ensuring material uniformity and stability, thus improving battery energy density and cycle performance. In summary, these post-processing optimizations enable silicon-carbon core-shell composite anode materials to exhibit superior electrochemical performance in practical applications, meeting the requirements of high-performance lithium-ion batteries for anode materials.

[0067] In one possible implementation, the selection of dopant elements and the control of doping concentration are crucial for optimizing the performance of silicon materials during the synthesis of silicon nuclei. Doping elements boron or phosphorus can effectively improve the electrochemical properties of silicon, particularly enhancing its conductivity and stability. The doping concentration is calculated using the ratio of a silane compound to the dopant source (such as borane or phosphine). In this way, the concentration of the dopant source can be precisely adjusted to achieve the desired doping effect. The doping effect needs to be verified using electrochemical impedance spectroscopy (EIS), which assesses the charge transport characteristics of the silicon nucleus in the battery, thereby verifying the improvement effect of doping on the conductivity and cycle stability of the silicon material.

[0068] In the coating process, in addition to conventional carbon sources, conductive additives such as carbon nanotubes or graphene are added. These conductive additives can significantly improve the conductivity of the composite material, especially during the expansion and contraction of silicon, maintaining good conductive pathways and preventing battery performance degradation. The amount of conductive additive added is determined based on the conductivity of the composite material. Conductivity is a key indicator for measuring the conductivity of a material and is usually measured using the four-probe method. The four-probe method can accurately measure the conductivity of the material, thus providing a quantitative basis for the amount of additive added and ensuring that the material has optimal conductivity.

[0069] In the heat treatment process, in addition to conventional heating and coating, a rapid cooling step was introduced. Rapid cooling can control the microstructure of the carbon shell, preventing the formation of an inhomogeneous crystal structure during cooling, thereby improving the overall stability of the material. The rapid cooling rate directly affects the microstructure of the carbon shell; excessively rapid cooling may lead to embrittlement, while excessively slow cooling may affect its conductivity and strength. Therefore, by optimizing the cooling rate, the structure of the carbon shell can be adjusted to achieve both good conductivity and strong mechanical strength and stability. To verify the changes in microstructure, X-ray diffraction analysis was used to characterize the heat-treated carbon shell. X-ray diffraction can reveal the crystal structure and graphitization degree of the carbon shell, helping to optimize heat treatment conditions and ensure that the carbon shell has an ideal structure.

[0070] Boron or phosphorus-doped silicon core materials improve conductivity and stability while mitigating silicon expansion during charge and discharge, thus extending battery life. The addition of conductive additives enhances the material's conductivity, ensuring consistent battery performance over long cycles, particularly under high-current charge and discharge conditions. Rapid cooling optimizes the microstructure of the carbon shell, resulting in better conductivity and mechanical properties, improving energy density and cycle stability. The combined application of these optimization measures leads to superior electrochemical performance, longer lifespan, and better stability in high-performance lithium-ion batteries using silicon-carbon core-shell composite anode materials.

[0071] Accordingly, embodiments of the present invention also provide the application of composite anode materials based on silicon-carbon core-shell structures. The composite anode material is used as the anode of lithium-ion batteries. The composite anode material is mixed with a conductive agent and a binder in a certain proportion. The conductive agent is acetylene black, and the binder is polyvinylidene fluoride. The proportion is optimized through battery capacity and cycle life tests. A solvent is added to form a slurry. The solvent is N-methylpyrrolidone. The viscosity of the slurry is measured by a rheometer. The slurry is coated on a current collector, which is copper foil. The coating thickness is controlled by a doctor blade. After coating, the anode is dried and rolled to form a negative electrode sheet. The drying temperature is determined by the boiling point of the solvent, and the rolling pressure is adjusted by the density of the electrode sheet. The density of the electrode sheet is measured by the Archimedes method. The negative electrode, positive electrode, separator, and electrolyte are assembled into a battery. The positive electrode is lithium cobalt oxide, the separator is a polypropylene membrane, and the electrolyte is an organic carbonate solution containing lithium salt. Assembly is carried out in an argon-protected glove box. The battery undergoes formation and cycle testing. The formation conditions are optimized by initial coulombic efficiency, and the cycle test is carried out by charge-discharge instrument. The test conditions include current density, voltage range, and temperature. The current density is determined by the rate performance of the battery, the voltage range is adjusted by the electrochemical window of the electrode material, and the temperature is selected according to the application environment of the battery.

[0072] Specifically, firstly, the composite negative electrode material needs to be mixed with a conductive agent and a binder in a certain proportion. Acetylene black was chosen as the conductive agent, a commonly used conductive material due to its high surface area and good conductivity. Polyvinylidene fluoride (PVDF) was selected as the binder, possessing excellent chemical stability and electrochemical performance, effectively ensuring the structural stability of the battery during cycling. The ratio of conductive agent to binder needs to be optimized through battery capacity and cycle life testing. This means determining the optimal ratio through actual testing to ensure the battery performs best under different usage conditions.

[0073] After mixing, a solvent (N-methylpyrrolidone) is added to form a slurry. The choice of solvent effectively improves the slurry's flowability and uniformity. The viscosity of the slurry needs to be accurately measured using a rheometer to ensure appropriate flowability during coating. Next, the slurry is coated onto a copper foil current collector, which provides good conductivity. The coating thickness is controlled by a doctor blade to ensure uniform thickness for each layer. The coated electrode then undergoes drying and rolling processes. The drying temperature is determined based on the solvent's boiling point to avoid excessive solvent residue affecting battery performance. The rolling pressure is controlled by adjusting the electrode density; excessive density leads to overly dense material, affecting battery performance, while insufficient density may affect the battery's capacity density. The electrode density is measured using the Archimedes method to ensure an ideal density value.

[0074] After the electrode fabrication is complete, the next step is to assemble the negative electrode with the positive electrode, separator, and electrolyte. The positive electrode uses lithium cobalt oxide, which has high energy density and stable electrochemical performance. The separator uses a polypropylene membrane, which has good mechanical strength and electrolyte permeability, effectively isolating the positive and negative electrodes and preventing short circuits. The electrolyte is an organic carbonate solution containing lithium salt, which acts as the ion-conducting medium in the battery.

[0075] The battery assembly process must be carried out in an argon-protected glove box to prevent moisture or oxygen in the air from adversely affecting battery performance. After assembly, the battery needs to undergo formation and cycle testing. Formation refers to the initial charge-discharge process, which is crucial for optimizing the initial coulombic efficiency to ensure the battery's initial charge-discharge efficiency and long-term performance. Afterward, the battery undergoes cycle testing using a charge-discharge instrument. This test simulates the charge-discharge process of the battery in actual use. Test conditions include parameters such as current density, voltage range, and temperature. The current density is selected based on the battery's rate performance to ensure that the battery maintains high efficiency during rapid charge-discharge. The voltage range is adjusted according to the electrochemical window of the electrode materials to avoid excessively high or low voltage affecting battery stability. The temperature parameter needs to be selected according to the battery's application environment to ensure stable operation under different environmental conditions.

[0076] By adjusting the ratio of conductive agents and binders appropriately, the conductivity of the composite anode material is greatly improved, thereby enhancing the battery's capacity and cycle life. Optimized coating and rolling processes of the slurry ensure that the battery electrodes have uniform thickness and suitable density, guaranteeing high energy density and stability. Furthermore, precise battery assembly and formation, along with cycle testing, ensure high efficiency and reliability during long-term use. Ultimately, the application of this silicon-carbon core-shell composite anode material enables lithium-ion batteries with high energy density, high rate performance, and long cycle life, meeting the demands of modern electronic devices and electric vehicles.

[0077] Example Preparation and application of composite anode materials based on silicon-carbon core-shell structure in lithium-ion batteries; 1. Synthesis and processing of silicon nuclei; Input materials: Silicon tetrachloride (SiCl4) is used as the silane compound, anhydrous ethanol is used as the organic solvent, sodium borohydride (NaBH4) is used as the reducing agent, sodium dodecyl sulfate (SDS) is used as the surfactant, and deionized water is used as the dispersion medium.

[0078] Detailed process description: Preparation of silicon source solution: Silicon tetrachloride was dissolved in anhydrous ethanol to form a silicon source solution. The concentration was calculated using the mass of silicon tetrachloride and the volume of anhydrous ethanol, specifically: 50 grams of silicon tetrachloride dissolved per liter of anhydrous ethanol. This concentration was calculated based on the molecular weight of silicon tetrachloride (169.9 g / mol) and the yield of the target silicon nanoparticles (optimized through preliminary experiments, with a target yield of over 90%). The yield was determined by the ratio of the mass of the silicon nanoparticles after the reaction to the theoretical mass of silicon.

[0079] Chemical reduction reaction: Conducted under a protective atmosphere, using high-purity nitrogen (99.999% purity) to eliminate interference from oxygen and moisture. The silicon source solution was heated to 60°C, and a sodium borohydride solution (0.5 mol / L concentration) was slowly added dropwise. The dropping rate was optimized experimentally: small-scale tests were first conducted at different dropping rates (e.g., 1 mL / min, 2 mL / min) to observe the aggregation of the silicon nanoparticles; the final dropping rate was determined to be 1.5 mL / min, which ensured a stable reduction reaction and prevented localized over-concentration leading to aggregation. The reduction reaction mechanism is: SiCl4 + 4NaBH4 → Si + 4NaCl + 2B2H6 + H2, generating silicon nanoparticles.

[0080] Centrifugation: After the reaction, the nano-silicon particles were collected by centrifuging at 8000 rpm for 10 minutes. The centrifugation speed was determined based on the particle size and density of the nano-silicon particles. The particle size was measured using dynamic light scattering. The nano-silicon particles were dispersed in deionized water, and the average particle size was measured using a laser particle size analyzer, yielding an average particle size of 80 nm and a density of approximately 2.3 g / cm³. 3 (Based on silicon crystal density). Rotational speed is calculated using Stokes' law: Settling velocity v = (2r) / (2r) 2 ×(ρ_p×ρ_f)×g) / (9η), where r is the particle radius (40nm), and ρ_p is the particle density (2.3g / cm³). 3 ), where ρ_f is the fluid density (ethanol, 0.789 g / cm³). 3 g is the acceleration due to gravity (9.8 m / s²). 2 η is the fluid viscosity (ethanol, 1.2 mPa·s). The calculated value is v ≈ 1.2 × 10⁻⁶. -6 m / s, thus the rotational speed is set to 8000 rpm to ensure complete settling.

[0081] Washing: Wash the nano-silicon particles three times with anhydrous ethanol to remove residual sodium borohydride and byproducts.

[0082] Surface treatment: Nano-silicon particles were dispersed in an aqueous solution containing sodium dodecyl sulfate. The amount of sodium dodecyl sulfate added was determined based on the specific surface area of ​​the nano-silicon particles. Specific surface area was measured using nitrogen adsorption: Using a specific surface area analyzer, the nano-silicon particle sample was degassed under vacuum at 150°C for 4 hours, and then subjected to nitrogen adsorption at liquid nitrogen temperature (-196°C). The specific surface area was calculated using the BET model. The BET model formula is: 1 / [V×((P0 / P)-1)]=(C-1) / (V_m×C)×(P / P0)+1 / (V_m×C), where V is the adsorption amount, P is the pressure, P0 is the saturated vapor pressure, V_m is the monolayer adsorption amount, and C is a constant. A specific surface area of ​​45 m² was obtained through linear fitting. 2 / g. The amount of sodium dodecyl sulfate added was determined by surface coverage: the target surface coverage was 90%, based on the molecular area of ​​sodium dodecyl sulfate (0.5 nm). 2 The specific surface area of ​​the nano-silicon particles and the molecular weight of the nano-silicon particles were calculated, and the addition amount was 0.1 g of sodium dodecyl sulfate per gram of nano-silicon particles.

[0083] Ultrasonic treatment: An ultrasonic disruptor was used, with a power of 300W and a treatment time of 30 minutes. The power was determined through dispersion stability testing: treatments were performed at different powers (200W, 300W, 400W), and the stability of the suspension was observed after settling. The particle size distribution was most uniform at 300W (confirmed using a laser particle size analyzer). The treatment time was optimized through particle size distribution monitoring: samples were taken and measured every 10 minutes. After 30 minutes, the particle size distribution index (PDI) stabilized below 0.2, indicating uniform dispersion. The final output was a silicon core suspension with a solid content of 10wt%.

[0084] 2. Carbon shell coating; Input materials: silicon core suspension (output from the previous step), carbon source is phenolic resin (molecular weight 1000 g / mol, measured by gel permeation chromatography), solvent is deionized water.

[0085] Detailed process description: Mixing: The silicon core suspension was mixed with a phenolic resin solution. The concentration of the phenolic resin solution was calculated based on the target carbon shell thickness and the silicon core mass. The target carbon shell thickness was determined based on the silicon core diameter and the expected buffering effect: the silicon core diameter was measured using scanning electron microscopy (using a Hitachi SU8000 microscope, with an average diameter of 80 nm for 100 particles); the expected buffering effect was based on the volume expansion rate of silicon during lithium-ion insertion and extraction (300%), requiring a carbon shell thickness of 10% of the silicon core diameter (i.e., 8 nm) to provide sufficient buffering. Carbon shell thickness calculation model: Carbon shell volume V_shell = π / 6 × [(D_shell)] 3 (D_core) 3 [], where D_shell is the diameter after coating, and D_core is the diameter of the silicon core. Based on the silicon core mass (10g) and carbon density (1.8g / cm³). 3 The calculated amount of phenolic resin added is 0.15 grams of phenolic resin per gram of silicon core.

[0086] Stirring control: Mixing is carried out in a stirred reactor, with the stirring speed controlled at 500 rpm and the temperature at 50°C. The stirring speed is calculated using the Reynolds number: Re = ρND 2 / η, where ρ is the fluid density (1 g / cm³) 3N is the stirring speed (500 rpm ≈ 8.33 rpm), D is the impeller diameter (5 cm), and η is the fluid viscosity (1 mPa·s). The calculated Re ≈ 2083, placing it in the turbulent region (Re > 2000), ensuring uniform mixing. The temperature was adjusted based on the solubility and volatility of the phenolic resin: at 50°C, the phenolic resin completely dissolved without decomposition.

[0087] Evaporation: Using a rotary evaporator (such as Buchi R-300), the solvent is removed by evaporation at 60°C. The evaporation temperature is set at 60°C based on the boiling point of water (100°C) to avoid premature cross-linking of the phenolic resin. The precursor powder is obtained after evaporation.

[0088] Uniformity check: Observe the precursor powder in multiple fields of view (at least 5) using a scanning electron microscope to ensure that the carbon source completely covers the silicon core surface. If there are uncovered areas, adjust the amount of carbon source added or the mixing time (in this embodiment, the coverage is complete, so no adjustment is needed).

[0089] 3. Heat treatment; Input materials: precursor powder (output from the previous step), and high-purity argon gas (99.999% purity) is selected as the inert gas.

[0090] Detailed process description: Heat treatment setup: The precursor powder was evenly spread in an alumina crucible and placed in a tube furnace. Argon gas was first introduced for 30 minutes to purge air, then heating was performed at a rate of 5°C / min. The heating rate was determined using thermogravimetric analysis: Using a thermogravimetric analyzer, the weight loss curve was observed at a rate of 5°C / min under air atmosphere, and a rate with stable weight loss was selected.

[0091] Two-stage heat treatment: First stage: Hold at 200°C for 1 hour to allow the phenolic resin to crosslink and cure. The temperature is determined by the glass transition temperature of the phenolic resin: measured using differential scanning calorimetry, the glass transition temperature is 180°C, and 200°C is set to ensure complete crosslinking.

[0092] The second stage involves holding the mixture at 800°C for 2 hours to ensure complete carbonization of the carbon shell. The temperature was determined by the pyrolysis peak temperature of the phenolic resin: differential scanning calorimetry showed the pyrolysis peak at 750°C, so 800°C was set to ensure complete carbonization. The heat treatment time was calculated based on the carbon shell thickness and the thermal conductivity of the silicon core: the carbon shell thickness was 8 nm, and the silicon core thermal conductivity was 150 W / (m·K), resulting in a calculated heat conduction time of approximately 1.5 hours, which was set to 2 hours to ensure uniformity.

[0093] Interface bonding inspection: After heat treatment, the silicon-carbon core-shell composite powder was obtained by furnace cooling to room temperature. The interface bonding strength was observed using a high-resolution transmission electron microscope (e.g., JEOL JEM-2100F): Ultrathin sections (50 nm thick) were prepared to examine the continuity of the interface between the silicon core and the carbon shell. The electron diffraction pattern showed that the lattice fringes of silicon and carbon were continuous and without gaps, indicating strong interface bonding.

[0094] 4. Post-processing; Input material: Silicon-carbon core-shell composite powder (output from the previous step).

[0095] Detailed process description: Pulverization: An air jet mill was used, with the airflow pressure controlled at 0.8 MPa and the feed rate at 5 kg / h. The airflow pressure was adjusted based on the powder's hardness and toughness: hardness was determined using a Mohs hardness test (the silicon-carbon composite has a hardness of approximately 6), and toughness was determined using a compression test (breaking strength 50 MPa). 0.8 MPa effectively pulverized the powder without damaging the core-shell structure. The feed rate was optimized based on the powder's flowability and target particle size distribution: flowability was measured using a Hall effect flowmeter (flow rate 120 s / 50 g), and the target particle size distribution was D50 = 10 μm (determined based on the battery negative electrode coating requirements).

[0096] Sieving: Use a standard sieve (400 mesh, 38μm aperture) for sieving. The mesh size is selected based on the target particle size distribution: if the target D50 = 10μm, a 400 mesh sieve can remove large particles.

[0097] Particle size distribution measurement: The powder was dispersed in ethanol and ultrasonically treated for 5 minutes to prevent agglomeration. The average value of three measurements was taken to obtain D10=5μm, D50=10μm, and D90=20μm.

[0098] Tap density test: A tap density meter was used with a vibration frequency of 200 times / minute and a vibration count of 1000 times. The vibration frequency and number of vibrations were optimized based on the powder's packing behavior: Through testing at different frequencies, the tap density stabilized at 1.2 g / cm³ at 200 times / minute. 3 .

[0099] Specific surface area measurement: Nitrogen adsorption method (BET model) was used again, and the specific surface area was 50 m². 2 / g, compared with the measurement value in step 1 (45m) 2 Compared to the previous example ( / g), the increase in volume comes from the carbon shell, indicating complete coating.

[0100] 5. Application testing; Battery assembly: Slurry preparation: The composite negative electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed in a mass ratio of 90:5:5. The ratio was optimized through battery capacity and cycle life tests: Preliminary experiments tested different ratios (85:10:5, 90:5:5), and the 90:5:5 ratio showed the highest capacity retention. N-methylpyrrolidone was added as a solvent. The viscosity of the slurry was measured using a rheometer (e.g., TA Instruments AR2000), and the viscosity was 5000 mPa·s (shear rate 100 s⁻¹). -1 ).

[0101] Coating and Drying: The slurry was coated onto the copper foil current collector, with the coating thickness controlled to 100 μm using a doctor blade. Drying was carried out in a vacuum oven at 80°C for 2 hours. The drying temperature was set to 80°C based on the boiling point of N-methylpyrrolidone (202°C) to avoid solvent residue. The rolling pressure was 10 MPa, and the electrode density was measured to be 1.5 g / cm³ using the Archimedes method. 3 .

[0102] Battery assembly: In an argon-protected glove box, the negative electrode sheet, positive electrode lithium cobalt oxide, separator polypropylene membrane, and electrolyte (1MLiPF6inEC / DEC=1:1) are assembled into a 2032 coin cell.

[0103] Performance testing: Formation: First, perform formation treatment, charge and discharge once at a rate of 0.1C, with a voltage range of 0.01-2V, and the initial coulombic efficiency is 85% (calculated by charging capacity / discharging capacity).

[0104] Cyclic testing: Using a charge-discharge apparatus, the material was cycled 100 times at a 1C rate. The current density was determined through rate performance testing. Pre-tests were conducted at different rates (0.5C, 1C, 2C), with 1C showing the best capacity retention. The voltage range was 0.01-2V, and the temperature was 25°C. The results showed that the capacity retention was 90% after 100 cycles, indicating that the material has high cycle stability.

[0105] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing composite anode materials based on silicon-carbon core-shell structures, characterized in that, Includes the following steps: Step 1: Synthesis and processing of silicon nuclei. Silane compounds are used as silicon sources. Silane compounds are dissolved in organic solvents to form silicon source solutions. The concentration of the silicon source solution is calculated by the mass of the silane compounds and the volume of the organic solvent. A reducing agent is added dropwise to the silicon source solution under a protective atmosphere to carry out a chemical reduction reaction. The dropping rate is controlled to allow the reduction reaction to proceed slowly, generating nano-silicon particles. After the reaction, the nano-silicon particles are collected by centrifugation. The centrifugation speed is determined based on the particle size and density of the nano-silicon particles. The particle size of the nano-silicon particles is measured by dynamic light scattering. The nano-silicon particles are then washed with an organic solvent to remove impurities. Afterward, the nano-silicon particles are dispersed in an aqueous solution containing a surfactant. The amount of surfactant added is determined based on the specific surface area of ​​the nano-silicon particles, which is measured by nitrogen adsorption. The nano-silicon particles are then uniformly dispersed by ultrasonic treatment to form a silicon nuclei suspension. Step 2: Carbon shell coating. The silicon core suspension is mixed with a carbon source, which is a thermally polymerizable organic compound. The amount of carbon source added is calculated based on the mass of the silicon core and the target carbon shell thickness. The target carbon shell thickness is determined by the silicon core diameter and the expected buffering effect. The silicon core diameter is measured by scanning electron microscopy. During the mixing process, the stirring speed and temperature are controlled to ensure that the carbon source is uniformly adsorbed on the surface of the silicon core. Then, the solvent is removed by evaporation to form a precursor powder. The uniformity of the precursor powder is confirmed by scanning electron microscopy. Step 3: Heat treatment. The precursor powder is placed in a tube furnace and heat-treated under an inert atmosphere. The heat treatment process is divided into two stages. The first stage is carried out at a lower temperature to allow the carbon source to cross-link and solidify. The second stage is carried out at a higher temperature to completely carbonize the carbon shell and form a strong interfacial bond with the silicon core. The heat treatment temperature and time are adjusted according to the pyrolysis characteristics of the carbon source and the thermal stability of the silicon core. Step 4: Post-processing. The heat-treated silicon-carbon core-shell composite powder is pulverized and sieved. Pulverization is carried out using an air jet mill, with control of air pressure and feed rate. Sieving is done using a standard sieve to control the particle size distribution of the powder. The particle size distribution of the powder is measured by a laser particle size analyzer, and the physical properties of the powder are optimized by tap density test and specific surface area measurement.

2. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 1, the silane compound is silicon tetrachloride, the organic solvent is ethanol, the reducing agent is sodium borohydride, and the surfactant is sodium dodecyl sulfate. The concentration range of the silicon source solution is the mass of silane compound dissolved per liter of organic solvent, which is calculated by the molecular weight of the silane compound and the yield of the target silicon nanoparticles. The protective atmosphere is nitrogen or argon. The dropping rate is optimized experimentally to avoid agglomeration of nano-silicon particles. The centrifugation speed is calculated based on Stokes' law and the settling velocity of nano-silicon particles. When measuring the particle size of nano-silicon particles using the dynamic light scattering method, the nano-silicon particles are dispersed in deionized water and measured using a laser particle size analyzer. When measuring the specific surface area using the nitrogen adsorption method, the nano-silicon particle sample is degassed under vacuum and then placed in a nitrogen adsorption instrument. The specific surface area is calculated based on the BET model. The amount of surfactant added was determined by specific surface area and surface coverage, and the surface coverage was optimized by adsorption isotherm experiments. Ultrasonic treatment was performed using an ultrasonic disruptor, with power and processing time controlled. Power was determined by testing the dispersion stability of the nano-silicon particles, and processing time was optimized by monitoring particle size distribution.

3. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 2, the carbon source is phenolic resin or sucrose. The concentration of the carbon source solution is calculated by the target carbon shell thickness and the silicon core mass. The target carbon shell thickness is determined based on the silicon core diameter and the volume expansion buffer requirement. The volume expansion buffer requirement is calculated by the expansion rate of the silicon material during the lithium ion insertion and extraction process. The stirring speed is calculated using the Reynolds number to ensure uniform mixing, and the temperature is adjusted based on the solubility and volatility of the carbon source. To remove solvents by evaporation, a rotary evaporator is used, and the evaporation temperature is set according to the boiling point of the solvent to avoid premature decomposition of the carbon source. The uniformity of the precursor powder was checked by observing multiple fields of view using a scanning electron microscope to ensure that the carbon source completely covered the silicon core surface. If there were any uncovered areas, the amount of carbon source added or the mixing time was adjusted.

4. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 3, the inert atmosphere is argon, and the heating rate is determined by thermogravimetric analysis (TGA) curves. The TGA is performed in an air atmosphere to simulate the heat treatment process. The temperature of the first stage heat treatment is determined by the glass transition temperature of the carbon source, and the temperature of the second stage heat treatment is determined by the pyrolysis peak temperature of the carbon source. The pyrolysis peak temperature is measured by differential scanning calorimetry. The heat treatment time is calculated based on the thickness of the carbon shell and the thermal conductivity of the silicon core to ensure that the carbon shell is free of cracks; The interfacial bonding strength was observed using a high-resolution transmission electron microscope. Ultrathin sections were prepared to examine the interfacial continuity between the silicon core and the carbon shell. The interfacial continuity was verified by electron diffraction patterns.

5. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 4, the airflow pressure of the air jet mill is adjusted by the hardness and toughness of the powder, and the feed rate is optimized by the flowability of the powder and the target particle size distribution. The mesh size of the standard sieve is selected based on the target particle size distribution, which is determined by the coating requirements of the battery negative electrode material. When using a laser particle size analyzer, the powder is dispersed in ethanol to avoid agglomeration, and multiple measurements are taken to obtain the average value. The tap density test was performed using a tap density meter, with the vibration frequency and number of vibrations optimized based on the powder's packing behavior. The specific surface area was measured again using the nitrogen adsorption method to ensure the integrity of the carbon shell. The specific surface area value was calculated using the BET model and compared with the measurement value in step 1 to evaluate the coating effect.

6. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 1, the synthesis of nano-silicon particles also includes size control, which is achieved by adjusting the dropping rate of the reducing agent and the reaction temperature, which is determined by the reduction kinetics of silane compounds. In step 2, the carbon shell coating also includes multiple layers of coating. The number of layers of the multi-layer coating is determined by the target conductivity and buffering effect through repeated mixing and evaporation steps. In step 3, the heat treatment also includes an intermediate annealing step, with the intermediate annealing temperature between the first stage and the second stage, adjusted by the degree of crosslinking of the carbon source, which is analyzed by infrared spectroscopy.

7. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 1, the selection of surfactants also includes nonionic surfactants, and the amount of nonionic surfactants added is calculated based on the hydrophilic-lipophilic balance value; In step 2, the carbon source also includes a polymer precursor, the molecular weight of which is measured by gel permeation chromatography and the molecular weight distribution is controlled by the polydispersity index. In step 3, the heat treatment atmosphere also includes a reducing gas, the proportion of which is adjusted by the degree of graphitization of the carbon shell, which is determined by Raman spectroscopy.

8. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 4, the post-processing also includes surface modification, which is carried out by chemical vapor deposition or atomic layer deposition. The deposition thickness is controlled by the number of cycles. The deposition material is carbon or metal oxide. The selection of the deposition material is optimized through battery cycle performance testing. The pulverization process also includes a classification step, which is carried out by an air classifier. The classification accuracy is adjusted by the sphericity of the particles, which is measured by image analysis software.

9. The method for preparing the composite anode material based on a silicon-carbon core-shell structure according to claim 1, characterized in that, In step 1, the synthesis of silicon cores also includes doping elements, which are boron or phosphorus. The doping concentration is calculated by the ratio of silane compounds to doping sources, and the doping sources are borane or phosphine. The doping effect is verified by electrochemical impedance spectroscopy. In step 2, the carbon shell coating also includes conductive additives, which are carbon nanotubes or graphene. The amount of additives is determined by the electrical conductivity of the composite material, which is measured by the four-probe method. In step 3, the heat treatment also includes a rapid cooling step, the rapid cooling rate of which is optimized by the microstructure of the carbon shell, which is analyzed by X-ray diffraction.

10. The application of composite anode materials based on silicon-carbon core-shell structures, characterized in that, The composite negative electrode material is prepared by the method for preparing a composite negative electrode material based on a silicon-carbon core-shell structure as described in any one of claims 1 to 9. The composite negative electrode material is used as the negative electrode of a lithium-ion battery. The composite negative electrode material is mixed with a conductive agent and a binder in a certain proportion. The conductive agent is acetylene black, and the binder is polyvinylidene fluoride. The proportion is optimized by battery capacity and cycle life tests. A solvent is added to form a slurry. The solvent is N-methylpyrrolidone. The viscosity of the slurry is measured by a rheometer. The slurry is coated on a current collector. The current collector is copper foil. The coating thickness is controlled by a scraper. After coating, the negative electrode sheet is formed by drying and rolling. The drying temperature is determined by the boiling point of the solvent. The rolling pressure is adjusted by the density of the electrode sheet. The density of the electrode sheet is measured by the Archimedes method. The negative electrode, positive electrode, separator, and electrolyte are assembled into a battery. The positive electrode is lithium cobalt oxide, the separator is a polypropylene membrane, and the electrolyte is an organic carbonate solution containing lithium salt. Assembly is carried out in an argon-protected glove box. The battery undergoes formation and cycle testing. The formation conditions are optimized by initial coulombic efficiency, and the cycle test is carried out by charge-discharge instrument. The test conditions include current density, voltage range, and temperature. The current density is determined by the rate performance of the battery, the voltage range is adjusted by the electrochemical window of the electrode material, and the temperature is selected according to the application environment of the battery.

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