Preparation method and application of silicon-carbon negative electrode material for lithium ion battery

Abstract

The invention relates to the field of lithium ion battery negative electrode materials, in particular to a method for preparing a silicon-carbon negative electrode material by taking biomass as a raw material and application of the silicon-carbon negative electrode material in a battery. The method comprises the steps of porous carbon skeleton preparation, nanometer silicon layer deposition and vapor carbon coating, and high specific capacity, high first efficiency and excellent cycle performance are achieved by adjusting process parameters. The energy density and the cycle life of the silicon-carbon negative electrode material can be remarkably improved, and a new path is provided for the technical development of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode materials, specifically relating to a method for preparing silicon-carbon anode materials for lithium-ion batteries and their applications. Background Technology

[0002] Lithium-ion batteries, due to their advantages such as light weight, high energy density, and long cycle life, have become important energy storage devices in fields such as new energy vehicles, energy storage power stations, and 3C digital electronic products. However, traditional graphite anode materials are approaching their theoretical capacity limit (372 mAh / g), making it difficult to meet the demands of future high-energy-density batteries. In contrast, silicon, with its theoretical specific capacity of up to 4200 mAh / g and relatively low lithiation potential, is considered a highly promising anode material for next-generation lithium-ion batteries. However, silicon anodes face significant challenges in practical applications, including substantial volume expansion (up to 300-400%), continuous solid electrolyte interphase (SEI) film growth, low intrinsic conductivity, and low lithium-ion diffusion rate. These problems severely limit their large-scale commercial application.

[0003] A search revealed a silicon-carbon anode material for lithium-ion batteries and its preparation method, published on November 24, 2023, with publication number CN114976021B. This patent describes a silicon-carbon anode material prepared by high-temperature calcination after blending modified polyvinyl acrylonitrile, modified nano-silicon, and diphenylmethane diisocyanate, forming a multi-shell core-shell structure on the surface. This effectively alleviates the volume expansion problem of silicon while improving the material's conductivity and cycle stability. However, the preparation process of the multi-shell core-shell structure in this technical solution is relatively complex, especially the high-temperature calcination process, which requires sophisticated equipment and may increase production costs. Furthermore, while the resin-modified porous structure of the modified nano-silicon can alleviate the breakage problem caused by volume expansion, its large specific surface area may lead to a decrease in initial coulombic efficiency, and the coating layer may detach during long-term cycling, affecting the battery's cycle performance.

[0004] A search revealed a silicon-carbon anode material and its preparation method for lithium-ion batteries, with publication number CN111180713B, published on November 1, 2022. This patent designs a core-shell structure for the silicon-carbon anode material, where the core consists of nano-silicon, pyrolytic carbon, and single-walled carbon nanotubes, and the shell is a carbon coating layer formed by vapor deposition. This significantly improves the material's conductivity and cycle performance. However, in this technical solution, the composite process of nano-silicon and pyrolytic carbon requires precise control of particle size and dispersion, making the process quite challenging, especially as it may face consistency issues in large-scale production. Furthermore, the vapor-deposited carbon coating layer is relatively thin (10–200 nm), which may not completely suppress the volume expansion effect of silicon during long-term charge-discharge processes, leading to coating layer cracking and affecting the battery's cycle stability and coulombic efficiency.

[0005] The aforementioned problems indicate that existing silicon-carbon anode materials for lithium-ion batteries still have certain shortcomings in terms of fabrication process complexity, volume expansion suppression, initial coulombic efficiency, and long-term cycle stability. Therefore, this invention provides a novel method for preparing silicon-carbon anode materials for lithium-ion batteries and its application. The method utilizes biomass materials as precursors, uniformly depositing a nano-silicon layer within them using vapor deposition technology, and further coating it with a carbon layer. This effectively alleviates the volume expansion problem of silicon while improving the material's conductivity and cycle stability, meeting the demands of next-generation high-energy-density lithium-ion batteries. Summary of the Invention

[0006] This invention addresses the technical deficiencies of existing lithium-ion battery anode materials in terms of energy density, initial efficiency, and cycle stability by proposing a method for preparing silicon-carbon anode materials using biomass as raw material and its application. Through a composite process involving the construction of a porous carbon framework, the deposition of a nano-silicon layer, and gas-phase carbon coating, a silicon-carbon anode material with high specific capacity, high initial efficiency, and excellent cycle performance is prepared.

[0007] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries, comprising the following steps:

[0008] S1: Preparation of Porous Carbon Framework: Porous carbon materials are obtained by pretreatment, activation, and pulverization of selected biomass raw materials. The specific surface area of ​​the porous carbon material is ≥1000 m² / g, the pore volume is ≥0.8 cm³ / g, and the micropore ratio is ≥80%. The biomass raw materials include one or more combinations of coconut shells, walnut shells, mangosteen shells, or bamboo. Further, the pretreatment includes washing with deionized water to remove surface impurities, followed by drying at 100°C for 12-24 hours. The dried material is placed in a carbonization furnace and carbonized at 400-600°C for 1-3 hours at a heating rate of 5-10°C / min. After carbonization, the material is coarsely crushed to millimeter-sized particles. Specifically, the activation is performed physically using steam or carbon dioxide, with the activation temperature controlled at 800-1100°C and the activation time at 60-180 minutes. After activation, the material is pulverized to achieve a median particle size (D50) of 5-7 μm.

[0009] S2: Nanoscale Silicon Layer Deposition: The porous carbon material obtained in step S1 is placed in a rotary CVD vapor deposition furnace. Under inert gas protection, the temperature is increased and a silane / inert gas mixture is introduced to deposit a nanoscale silicon layer. The inert gas includes one or more combinations of nitrogen or argon. Further, the heating rate is ≤20℃ / min, the deposition temperature is controlled at 450-600℃, the silane concentration is 10-40%, and the deposition time is 4-8 hours. After deposition, the nanoscale silicon layer thickness is ≤2nm, the silicon content is ≤50%, and the specific surface area of ​​the deposited material is reduced to no more than 200m². 2 / g.

[0010] S3: Gas-phase carbon coating: The precursor for depositing the nano-silicon layer in step S2 is further heated, and an acetylene / inert gas mixture is introduced for carbon deposition. The heating rate is ≤20℃ / min, the deposition temperature is controlled at 650-900℃, the acetylene concentration is 30-60%, and the deposition time is 3-5 hours. After deposition, the carbon layer thickness is <5nm, and the specific surface area of ​​the final material is reduced to no more than 5m². 2 / g. After cooling to room temperature, a composite material with an inner carbon skeleton core, an intermediate deposited nano-silicon layer, and an outer carbon coating was obtained, denoted as CPC@Si@C.

[0011] Furthermore, this invention obtains a silicon-carbon anode material with high energy density, high first-pass efficiency, and excellent cycle performance through the above preparation method. The porous carbon framework serves as a substrate, and its abundant microporous structure provides a uniformly distributed deposition space for the nano-silicon layer, while effectively mitigating the internal stress generated by silicon volume expansion during lithium intercalation. The nano-silicon layer deposited within the porous carbon framework avoids silicon particle agglomeration, thereby improving the material's specific capacity and first-pass efficiency. The vapor-phase carbon coating not only enhances the material's conductivity but also further suppresses side reactions between silicon and the electrolyte, significantly improving the material's cycle life.

[0012] Specifically, the technical solution of this invention achieves precise control over the thickness of the nano-silicon layer and the carbon coating layer by adjusting the concentrations of silane and acetylene, the deposition temperature, and the deposition time. The silane concentration and deposition time determine the thickness and silicon content of the nano-silicon layer, while the acetylene concentration and deposition time affect the thickness of the carbon coating layer and the specific surface area of ​​the final material. By optimizing these process parameters, the overall performance of the material is ensured to reach its optimal state.

[0013] The silicon-carbon anode material provided by this invention exhibits excellent electrochemical performance in practical applications. Half-cell tests were conducted using the materials from the examples, and the results showed that all samples possessed high initial charge capacity (≥1650 mAh / g) and high initial efficiency (≥90%). Furthermore, the CPC@Si@C prepared in Example 1 was compounded with artificial graphite to form a 500 mAh / g composite anode material, which was then assembled into a button cell with an NCM811 cathode for cycle testing. The test results showed that after 300 cycles at 1C, the battery capacity retention was as high as 93.44%.

[0014] The beneficial effects of this invention lie in achieving a combination of environmental friendliness and cost-effectiveness by using biomass raw materials to prepare a porous carbon framework. The porous carbon framework possesses a complex microstructure and abundant pore design, providing ideal spatial distribution conditions for the deposition of nano-silicon layers. Furthermore, the nano-silicon layer deposited within the porous carbon framework avoids silicon particle agglomeration, thereby improving the material's specific capacity and initial efficiency. The vapor-phase carbon coating not only enhances the material's conductivity but also effectively suppresses side reactions between silicon and the electrolyte, significantly improving the material's cycle life. In addition, the porous carbon framework and the deposited carbon layer work together to alleviate the internal stress generated by silicon volume expansion during lithium intercalation, maintaining the material's structural integrity.

[0015] In summary, this invention, through a scientifically sound preparation process, solves the technical bottlenecks of traditional silicon anode materials in terms of specific capacity, initial efficiency, and cycle stability, providing a new technical path for the development of lithium-ion battery anode materials. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation method proposed in this invention;

[0017] Figure 2 This is a schematic diagram of the preparation process proposed in this invention;

[0018] Figure 3 This is a SEM image of the porous carbon CPC in Example 1 of the present invention;

[0019] Figure 4 This is a SEM image of the silicon-carbon anode CPC@Si@C in Example 1 of the present invention;

[0020] Figure 5 This is a TEM image of the silicon-carbon anode CPC@Si@C in Example 1 of the present invention;

[0021] Figure 6 The XRD patterns of CPC and CPC@Si@C in Embodiment 1 of the present invention are shown below.

[0022] Figure 7This is a full-electric cycle test diagram of the silicon-carbon anode CPC@Si@C and graphite composite in Example 1 of the present invention.

[0023] The attached figures are labeled as follows:

[0024] CPC: Porous carbon material; CPC@Si: Porous carbon material with deposited nano-silicon layer; CPC@Si@C: Silicon-carbon composite anode material with deposited nano-silicon layer and coated carbon layer; NCM811: Positive electrode material. Detailed Implementation

[0025] This invention provides a method for preparing silicon-carbon anode materials for lithium-ion batteries and their applications, in conjunction with the attached... Figure 1 To be continued Figure 7 The specific implementation method is described in detail. This method achieves the preparation of silicon-carbon anode materials with high specific capacity, high first-pass efficiency, and excellent cycle performance through a composite process of constructing a porous carbon framework, depositing a nano-silicon layer, and vapor-phase carbon coating. The following content will describe in detail the specific operation process, operating principle, and practical application scenarios of each step.

[0026] First, it needs to be clarified that the core technology of this invention lies in preparing a porous carbon framework using biomass as raw material, and on this basis, achieving uniform deposition of a nano-silicon layer and formation of a carbon coating layer by precisely controlling the concentrations of silane and acetylene, deposition temperature, and time. (See attached image) Figure 1 and attached Figure 2 As shown, the entire preparation process is divided into three main stages: the preparation of the porous carbon framework (S1), the deposition of the nano-silicon layer (S2), and the vapor-phase carbon coating (S3). The technical details of each step will be elaborated below.

[0027] In S1, biomass raw materials such as coconut shells, walnut shells, mangosteen shells, or bamboo are selected as starting materials. These materials possess naturally complex microstructures and abundant pore designs, providing an ideal substrate for subsequent nano-silicon deposition. First, the biomass raw materials are repeatedly rinsed three times with deionized water to remove surface impurities, and then placed in a forced-air drying oven and dried at 100℃ for 12-24 hours. After drying, the material is transferred to a carbonization furnace and carbonized at 400-600℃ with a heating rate of 5-10℃ / min for 1-3 hours. During carbonization, the organic components in the biomass are decomposed and transformed into a carbon skeleton, while retaining the macroscopic structural characteristics of its precursor materials. After carbonization, the material is coarsely crushed into millimeter-sized particles to facilitate subsequent activation. Activation is performed physically by introducing steam or carbon dioxide at 800-1100℃ for 60-180 minutes. The activation process further increases the porosity of the material, resulting in a specific surface area ≥1000 m². 2 / g, pore volume ≥0.8cm³3 / g, and the micropore content is ≥80%. After activation, the material is pulverized to a median particle size D50 of 5-7μm to obtain the final porous carbon material, denoted as CPC. (Appendix) Figure 3 The SEM image of CPC is shown, which reveals that its surface exhibits a rich porous structure, providing ample space for the subsequent deposition of nano-silicon layers.

[0028] In stage S2, the porous carbon material CPC prepared in S1 is placed in a rotary CVD vapor deposition furnace for the deposition of a nano-silicon layer. Before deposition, high-purity nitrogen or argon gas is introduced at a flow rate of 1 L / min for 10 minutes to purge air from the furnace and protect the material from oxidation. The furnace temperature is then raised to 450-600℃ at a heating rate of ≤20℃ / min, and a silane / inert gas mixture is introduced at this temperature for deposition. The silane concentration is controlled at 10-40%, and the deposition time is 4-8 hours. During deposition, silane molecules decompose at high temperatures to generate nano-silicon particles, which are uniformly deposited within the pores of the porous carbon framework. This deposition method avoids silicon particle agglomeration, thereby improving the specific capacity and initial efficiency of the material. After deposition, the silane gas is stopped. At this point, the thickness of the nano-silicon layer is ≤2 nm, the silicon content is ≤50%, and the specific surface area of ​​the material is ≤200 m². 2 / g. (Attached) Figure 4 SEM images of CPC@Si@C are shown, revealing that the morphology of the material did not change significantly after nano-silicon deposition, and no aggregation of nano-silicon particles was observed on the surface. This indicates that silane deposition did indeed occur within the porous structure of the porous carbon. Figure 5 TEM images further validated this, showing that diffusely distributed bright spots were uniformly dispersed within the porous carbon of biomass, indicating that the nano-silicon layer was uniformly deposited within the porous carbon framework.

[0029] The next stage, S3, involves further gas-phase carbon coating of the precursor from S2 where the nano-silicon layer was deposited. After stopping the silane gas supply, the furnace temperature is raised to 650-900℃ at a heating rate of ≤20℃ / min, and an acetylene / inert gas mixture is introduced at this temperature for carbon deposition. The acetylene concentration is controlled at 30-60%, and the deposition time is 3-5 hours. During deposition, acetylene molecules decompose at high temperatures to generate carbon atoms, which are uniformly deposited on the surface of the nano-silicon layer, forming a 5nm thick carbon coating. This carbon coating not only enhances the conductivity of the material but also effectively suppresses side reactions between silicon and the electrolyte, significantly improving the cycle life of the material. After deposition, the acetylene gas supply is stopped, while inert gas is continuously introduced for cooling. After cooling to room temperature, the final silicon-carbon composite anode material, denoted as CPC@Si@C, is obtained. Figure 6The XRD patterns of CPC and CPC@Si@C are shown. It can be seen that CPC has broad diffraction peaks near 23° and 43°, indicating low crystallinity and structural disorder. CPC@Si@C, on the other hand, shows obvious diffraction signals at the characteristic peaks of silicon, further verifying the successful deposition of the nano-silicon layer.

[0030] The present invention will be further explained below with reference to specific embodiments.

[0031] Example 1

[0032] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries, the method comprising the following steps:

[0033] S1: First, take 10 kg of Indonesian coconut shells and rinse them three times with deionized water. Then, dry the washed coconut shells in a 100℃ forced-air drying oven for 24 hours. Next, place them in a carbonization furnace and heat them to 400℃ at 10℃ / min, maintaining the temperature for 2 hours. After the reaction, cool them to room temperature. Then, coarsely crush the material to millimeter size and place it in a tube furnace. Heat it to 900℃ at 10℃ / min and maintain the temperature for 60 minutes, during which the carbon dioxide flow rate is 1 L / min. After the reaction, continuously purify the material with high-purity nitrogen (99.999%) and cool it to room temperature to obtain porous carbon material. Crush the material to a median particle size D50 of 6 μm, denoted as CPC.

[0034] S2: Take 1 kg of CPC obtained in step S1 and put it into a rotary CVD vapor deposition furnace. First, introduce high-purity nitrogen at a flow rate of 1 L / min for 10 min, then raise the temperature to 550℃ at 5℃ / min, then introduce 20% silane gas at 1.5 L / min and continue deposition for 4 h. After the deposition is completed, stop introducing silane gas and denote it as CPC@Si.

[0035] S3: After stopping the silane gas in step S2, the temperature is increased to 650℃ at 5℃ / min. Then, 40% acetylene gas is introduced and deposition continues for 2 hours. After deposition is completed, the acetylene gas is stopped and the temperature is cooled down. After cooling to room temperature, a silicon-carbon composite anode material with a carbon skeleton as the core, a nano-silicon layer in the middle, and a carbon coating on the outside is obtained, denoted as CPC@Si@C.

[0036] Example 2

[0037] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries, the method comprising the following steps:

[0038] S1: First, take 10 kg of bamboo strips and rinse them three times with deionized water. Then, place the washed coconut shells in a 100℃ forced-air drying oven and dry them for 24 hours. Next, place them in a carbonization furnace and heat them to 400℃ at 10℃ / min and maintain the temperature for 2 hours. After the reaction, cool them to room temperature. Then, coarsely crush the material to millimeter size and place it in a tube furnace. Heat it to 950℃ at 10℃ / min and maintain the temperature for 120 minutes. During this period, the carbon dioxide flow rate is 1 L / min. After the reaction, continuously introduce high-purity nitrogen (99.999%) and cool it to room temperature to obtain porous carbon material. Crush the material to a median particle size D50 of 7 μm, and denote it as BPC.

[0039] S2: Take 1 kg of BPC obtained in step S1 and put it into a rotary CVD vapor deposition furnace. First, introduce high-purity nitrogen at a flow rate of 1 L / min for 10 min, then raise the temperature to 550℃ at 5℃ / min, then introduce 30% silane gas at 1.5 L / min and continue deposition for 6 h. After the deposition is completed, stop introducing silane gas and denote it as BPC@Si.

[0040] S3: After stopping the silane gas in step S2, the temperature is increased to 650℃ at 5℃ / min. Then, 50% acetylene gas is introduced and deposition continues for 3 hours. After deposition is completed, the acetylene gas is stopped and the temperature is cooled down. After cooling to room temperature, a silicon-carbon composite anode material with a carbon skeleton core, a nano-silicon layer in the middle, and a carbon coating on the outer layer is obtained, denoted as BPC@Si@C.

[0041] Example 3

[0042] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries, the method comprising the following steps:

[0043] S1: First, take 10 kg of walnut shells and rinse them three times with deionized water. Then, place the washed walnut shells in a 100℃ forced-air drying oven and dry them for 24 hours. Next, place them in a carbonization furnace and heat them to 500℃ at 10℃ / min and maintain the temperature for 3 hours. After the reaction, cool them to room temperature. Then, coarsely crush the material to millimeter size and place it in a tube furnace. Heat it to 850℃ at 10℃ / min and maintain the temperature for 180 minutes. During this period, the carbon dioxide flow rate is 1 L / min. After the reaction, continuously introduce high-purity nitrogen (99.999%) and cool it to room temperature to obtain porous carbon material. Crush the material to a median particle size D50 of 6 μm, and denote it as WPC.

[0044] S2: Take 1 kg of WPC obtained in step S1 and put it into a rotary CVD vapor deposition furnace. First, introduce high-purity nitrogen at a flow rate of 1 L / min for 10 min, then raise the temperature to 550℃ at 10℃ / min, then introduce 40% silane gas at 1.5 L / min and continue deposition for 5 h. After the deposition is completed, stop introducing silane gas and denote it as WPC@Si.

[0045] S3: After stopping the silane gas in step S2, the temperature is increased to 600℃ at 5℃ / min. Then, 50% acetylene gas is introduced and deposition continues for 3 hours. After deposition is completed, the acetylene gas is stopped and the temperature is lowered. After cooling to room temperature, a silicon-carbon composite anode material with a carbon skeleton core, a nano-silicon layer in the middle, and a carbon coating on the outer layer is obtained, denoted as WPC@Si@C.

[0046] Comparative Example 1

[0047] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries. The preparation method is the same as in Example 1, except that:

[0048] In step S1, the heat preservation time at 900℃ is 120 minutes.

[0049] In step S2, the silane concentration is 30% and the deposition time is 6 hours.

[0050] In step S3, the acetylene gas concentration was 50%, the deposition time was 3 hours, and the sample was designated CPC@Si@C-1.

[0051] Comparative Example 2

[0052] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries. The preparation method is the same as in Example 2, except that:

[0053] In step S1, the holding time at 900℃ is 180 minutes, and the activation gas is water vapor.

[0054] In step S2, the silane concentration is 40% and the deposition time is 5 hours.

[0055] In step S3, the acetylene gas concentration was 50%, the deposition time was 2 hours, and the sample was designated as BPC@Si@C-1.

[0056] Comparative Example 3

[0057] This invention provides a method for preparing silicon-carbon anode material for lithium-ion batteries. The preparation method is the same as in Example 3, except that:

[0058] In step S2, the silane concentration is 50% and the deposition time is 3 hours.

[0059] In step S3, the acetylene gas concentration was 60%, the deposition time was 2 hours, and the sample was designated WPC@Si@C-1.

[0060] To verify the practical application performance of the silicon-carbon anode material prepared in this invention, it was applied to half-cell and full-cell tests of lithium-ion batteries. In the half-cell test, the silicon-carbon anode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were mixed with styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), and carbon black (SP) at a mass ratio of 95.5:1.7:1.5:1.3 to form a slurry, which was then coated onto a 6 μm copper current collector. The coated electrode was then transferred to an 80°C forced-air drying oven for 2 hours and dried overnight in a 90°C vacuum drying oven. Finally, it was compacted by a roller mill and sliced. Assembly was carried out in an argon-filled glove box. The counter electrode of the battery was a lithium sheet with a thickness of 1 mm, the electrolyte was 1.3 M LiPF6 / (VEC:VDEC = 3:7), and the separator was 20 μm microporous polyethylene. The half-cell was first left to stand for 12 hours and then discharged to 5mV at 0.05C. After standing for 5 minutes, it was discharged to 5mV at 0.05mA. After standing for another 5 minutes, it was discharged to 5mV at 0.01mA. After standing for another 5 minutes, it was charged to 1.5V at 0.1C. The test results are shown in Table 1.

[0061] Table 1

[0062]

[0063] Test results show that all samples exhibit low specific surface area (≤5m²). 2 It exhibits high initial charge capacity (≥1650mAh / g) and high initial efficiency (≥90%). In particular, CPC@Si@C prepared using coconut shell as a carbon precursor shows superior electrochemical performance, which may be related to its intrinsic structure and processing method.

[0064] In full-cell testing, the CPC@Si@C prepared in Example 1 was compounded with artificial graphite to form a 500 mAh / g composite anode material, which was then assembled into a button cell using an NCM811 cathode electrode and its cycle performance was tested. The N / P ratio of the full cell was designed to be 1.08, and the voltage range was set to 2.75-4.2V. Formation was first performed at a 0.1C rate, followed by 300 cycles at a 1C rate. (Appendix) Figure 7 The results of the full-cell cycle performance test are shown, demonstrating that the battery capacity retention rate is as high as 93.44% after 300 cycles at 1C rate. This excellent cycle performance is attributed to the porous carbon framework's ability to withstand the stress generated by silicon lithium insertion / extraction, while the deposited carbon layer maintains the material's structural stability and cycle performance.

[0065] In summary, this invention addresses the technical bottlenecks of traditional silicon anode materials in terms of specific capacity, initial efficiency, and cycle stability through a scientifically sound preparation process. The porous carbon framework, as a substrate, provides ideal spatial distribution conditions for the deposition of nano-silicon layers due to its complex microstructure and abundant pores. The nano-silicon layer, deposited within the porous carbon framework, avoids silicon particle agglomeration, thereby improving the material's specific capacity and initial efficiency. The vapor-phase carbon coating not only enhances the material's conductivity but also effectively suppresses side reactions between silicon and the electrolyte, significantly improving the material's cycle life. Furthermore, the porous carbon framework and the deposited carbon layer work together to alleviate the internal stress generated by silicon volume expansion during lithium intercalation, maintaining the material's structural integrity. This invention not only achieves the preparation of silicon-carbon anode materials with high energy density, high initial efficiency, and excellent cycle performance but also provides a new technical pathway for the development of lithium-ion battery anode materials.

Claims

1. A method for preparing a silicon-carbon anode material for lithium-ion batteries, characterized in that... Includes the following steps: S1: Preparation of porous carbon framework: porous carbon materials are obtained by pretreatment, activation, and pulverization of biomass raw materials. The specific surface area of ​​the porous carbon materials is ≥1000 m². 2 / g, pore volume ≥0.8cm³ 3 / g, micropore content ≥80%, the biomass raw material includes one or more combinations of coconut shell, walnut shell, mangosteen shell or bamboo; S2: nano-silicon layer deposition, the porous carbon material obtained in step S1 is placed in a rotary CVD vapor deposition furnace, heated under inert gas protection and silane / inert gas mixture is introduced to perform nano-silicon layer deposition, after deposition the nano-silicon layer thickness ≤2nm, silicon content ≤50%; S3: gas phase carbon coating, the precursor for depositing nano-silicon layer in step S2 is heated further and acetylene / inert gas mixture is introduced to perform carbon deposition, after deposition the carbon layer thickness <5nm.

2. The preparation method according to claim 1, characterized in that... The pretreatment includes washing with deionized water to remove surface impurities, followed by drying at 100°C for 12-24 hours.

3. The preparation method according to claim 2, characterized in that... The dried material is placed in a carbonization furnace and carbonized at 400-600℃ for 1-3 hours, with a heating rate of 5-10℃ / min.

4. The preparation method according to claim 1, characterized in that... The activation is carried out by physical means, using steam or carbon dioxide, with the activation temperature controlled at 800-1100℃ and the activation time at 60-180 minutes.

5. The preparation method according to claim 1, characterized in that... During the deposition of the nano-silicon layer, the heating rate is ≤20℃ / min, the deposition temperature is controlled at 450-600℃, the silane concentration is 10-40%, and the deposition time is 4-8 hours.

6. The preparation method according to claim 1, characterized in that... During the gas phase carbon coating process, the heating rate is ≤20℃ / min, the deposition temperature is controlled at 650-900℃, the acetylene concentration is 30-60%, and the deposition time is 3-5 hours.

7. The preparation method according to claim 1, characterized in that... The porous carbon material is activated and then pulverized to a median particle size D50 of 5-7 μm.

8. The preparation method according to claim 1, characterized in that... The inert gas includes one or more combinations of nitrogen or argon.

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