A silicon-carbon anode material and its preparation method

Abstract

This invention provides a silicon-carbon anode material and its preparation method, relating to the field of lithium-ion battery technology. The preparation method of the silicon-carbon anode material includes the following steps: S1, mixing, stirring, and heating asphalt, metal powder, and a pore-forming agent; cooling, crushing, and grinding; cleaning and drying with a first organic solvent to form a first material; S2, performing chemical vapor deposition on the first material in a mixed atmosphere of silicon source gas and inert gas, followed by carbon coating treatment in a mixed atmosphere of carbon source gas and inert gas; cooling and grinding until uniform to obtain the silicon-carbon anode material; the silicon-carbon anode material prepared by this method exhibits excellent conductivity.

Description

Technical Field

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

[0002] Compared to traditional energy storage systems, advanced lithium-ion batteries (LIBs) have become one of the most important alternative technologies for energy storage.

[0003] Lithium-ion batteries include anode materials; however, traditional graphite anode materials have a low theoretical capacity (372 mAh·g). -1 However, silicon anode materials cannot meet the requirements for high energy density and high power density. Although silicon anode materials have a high theoretical lithium intercalation capacity (Li1 at room temperature), they cannot meet the requirements for high energy density and high power density. 3.75 Si is 3579 mAh·g -1 Low operating voltage (<0.4V vs. Li / Li) + With its abundant resources and environmental friendliness, silicon has gradually entered the application market. However, silicon materials inherently have low electrical conductivity (~10). -3 S cm -1 This has hindered the large-scale commercial application of silicon anode materials. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a silicon-carbon anode material and its preparation method, solving the technical problem of low conductivity in existing silicon anode materials.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] On one hand, the present invention provides a method for preparing silicon-carbon anode material, comprising the following steps:

[0009] S1. Mix, stir and heat asphalt, metal powder and pore-forming agent, cool and crush and grind, clean and dry with a first organic solvent to form a first material;

[0010] The mass ratio of asphalt to metal powder is 10:1 to 2:1; the mass ratio of asphalt to pore-forming agent is 1:2 to 1:10; the stirring time is 1 to 10 hours; the heating temperature is 300 to 500°C, and the heating time is 1 to 6 hours.

[0011] S2. The first material is subjected to chemical vapor deposition in a mixed atmosphere of silicon source gas and inert gas, and then subjected to carbon coating treatment in a mixed atmosphere of carbon source gas and inert gas. After cooling, it is ground uniformly to obtain silicon-carbon anode material.

[0012] The chemical vapor deposition temperature is 500–700°C and the time is 1–6 h, and the carbon coating treatment temperature is 600–700°C and the time is 1–4 h.

[0013] The present invention discloses a method for preparing silicon-carbon anode material, which involves mixing, stirring, and heating asphalt, metal powder, and a pore-forming agent, followed by cooling, crushing, and grinding to obtain a first material. This process allows the metal powder to form a first conductive metal layer within the first material. The first material is then subjected to chemical vapor deposition in a mixed atmosphere of silicon source gas and inert gas, followed by carbon coating treatment in a mixed atmosphere of carbon source gas and inert gas. After cooling, the material is ground uniformly to obtain the silicon-carbon anode material. The carbon source gas fills the pores not filled by the silicon source gas, forming a complete second conductive layer. This results in the prepared silicon-carbon anode material comprising an inner and outer double-layer conductive network, thereby ensuring the conductivity of the silicon-carbon anode material.

[0014] Preferably, step S1 further includes nitrogen doping treatment of the asphalt, wherein the nitrogen doping treatment includes dissolving the asphalt and nitrogen-containing organic polymer in a second organic solvent, stirring, freeze-drying, and then grinding.

[0015] Preferably, the nitrogen-containing organic polymer is selected from at least one of polyimide, polysulfonamide, and melamine;

[0016] And / or, the mass ratio of the asphalt to the nitrogen-containing organic polymer is 1:1 to 1:10;

[0017] And / or, the mass ratio of the sum of the asphalt and the nitrogen-containing organic polymer to the second organic solvent is 1:5 to 1:10;

[0018] And / or, the second organic solvent is selected from at least one of N-methylpyrrolidone, n-hexane, xylene, carbon disulfide, and carbon tetrachloride;

[0019] And / or, the freeze-drying temperature is -30℃ to -50℃;

[0020] And / or, the freeze-drying time is 12h to 24h.

[0021] After nitrogen doping and freeze-drying of asphalt according to the above process, the first material obtained has a high specific surface area, uniform pore volume and pore size and a large number of reactive sites. The reactive sites allow silicon source gas to better attach and nucleate, increasing the capacity of the material. At the same time, the metal powder can provide attachment sites for the silicon source, which facilitates the uniform deposition of silicon, thereby ensuring the cycle and rate performance of the silicon-carbon anode material.

[0022] Preferably, the preparation method further includes spray pyrolysis treatment of the silicon-carbon anode material, wherein the spray pyrolysis treatment includes mixing and stirring an organic carbon source, a reducing organic solvent and the silicon-carbon anode material, ultrasonic treatment, and spray pyrolysis in a high-temperature atmosphere;

[0023] The spray pyrolysis temperature is 300–500℃, and the spray flow rate is 1–10 mL / min.

[0024] Preferably, the organic carbon source is selected from at least one of citric acid, acetic acid, oxalic acid, formic acid, propionic acid, and stearic acid;

[0025] And / or, the reducing organic solvent is selected from at least one of ethanol, diethyl ether, dichloromethane, acetone and xylene;

[0026] And / or, the mass ratio of the organic carbon source to the reducing organic solvent is 1:5 to 1:20;

[0027] And / or, the total mass ratio of the organic carbon source and the reducing organic solvent to the silicon-carbon anode material is 1:1 to 10:1;

[0028] And / or, the stirring reaction time is 1 to 4 hours, and the ultrasonic treatment time is 10 to 30 minutes.

[0029] After spray pyrolysis, the organic carbon source fills the pores left unfilled by the silicon source gas, forming a complete coating layer. This not only limits the volume expansion of the silicon-carbon anode material, ensuring its cycle and rate performance, but also improves its conductivity. The spray pyrolysis process prevents amorphous silicon from converting to crystalline silicon during high-temperature carbon coating, and the reducing organic solvent prevents the oxidation of nano-silicon particles during pyrolysis, thus ensuring the cycle and rate performance of the silicon-carbon anode material.

[0030] Preferably, the asphalt in step S1 is selected from coal tar pitch, petroleum pitch and natural asphalt, and the D50 of the asphalt is 3 to 5 mm.

[0031] And / or, in step S1, the metal powder is selected from at least one of tin, bismuth, indium, and lithium;

[0032] And / or, in step S1, the pore-forming agent is selected from at least one of phosphoric acid, zinc chloride, potassium hydroxide, and potassium carbonate.

[0033] Preferably, the silicon source gas in step S2 is selected from at least one of silane or its homologues;

[0034] And / or, the inert gas is selected from at least one of helium, argon, and nitrogen;

[0035] And / or, the carbon source gas is selected from at least one of acetylene, methane, or their homologues.

[0036] Preferably, the volume ratio of the inert gas to the silicon source gas is 4:1 to 1:1.

[0037] Preferably, the volume ratio of the inert gas to the carbon source gas is 4:1 to 1:1.

[0038] On the other hand, the present invention provides a silicon-carbon anode material prepared by the preparation method described in the first aspect, wherein the resistivity of the silicon-carbon anode material is 3.9 Ω·cm to 5.1 Ω·cm and the initial coulombic efficiency is 91.9% to 93.1%. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The above are the SEM test results of the silicon-carbon anode material prepared in Example 1 of this invention.

[0041] Figure 2 The results show the charge-discharge capacity test results of the silicon-carbon anode material prepared in Example 1 of this invention and the material in Comparative Example 1.

[0042] Figure 3 The results show the cycle performance test results of the silicon-carbon anode material prepared in Example 1 of this invention and the material in Comparative Example 1. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This application provides a silicon-carbon anode material and its preparation method, which solves the technical problems of low conductivity and poor cycle and rate performance of existing silicon anode materials.

[0045] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0046] Silicon materials in the lithium-intercalated state (Li at room temperature) 3.75The formation of silicon suboxide (Si) results in a massive volume expansion (>300%), leading to the formation of an unstable solid electrolyte interphase (SEI) and particle fragmentation. This ultimately leads to severe capacity decay during battery cycling. Pre-lithiation of the silicon suboxide material, including direct addition of lithium powder and electrochemical pre-lithiation, can improve the initial coulombic efficiency to some extent. However, these modification methods still have many problems. Currently, pre-lithiation processes suffer from high costs, complex processes, and the risk of explosion, making them difficult to apply in actual production.

[0047] Therefore, designing and developing a novel silicon-carbon material that can improve initial coulombic efficiency while maintaining electrode stability and enhancing cycle life is a key technology for realizing the practical application of silicon-based anode materials.

[0048] The present invention discloses a method for preparing silicon-carbon anode material, which involves mixing, stirring, and heating asphalt, metal powder, and a pore-forming agent, followed by cooling, crushing, and grinding to obtain a first material. This process allows the metal powder to form a first conductive metal layer within the first material. The first material is then subjected to chemical vapor deposition in a mixed atmosphere of silicon source gas and inert gas, followed by carbon coating treatment in a mixed atmosphere of carbon source gas and inert gas. After cooling, the material is ground uniformly to obtain the silicon-carbon anode material. The carbon source gas fills the pores not filled by the silicon source gas, forming a complete second conductive layer. This results in the prepared silicon-carbon anode material comprising an inner and outer double-layer conductive network, thereby ensuring the conductivity of the silicon-carbon anode material.

[0049] The present invention also obtains a first material with high specific surface area, uniform pore volume and pore size and a large number of reactive sites by nitrogen doping and freeze-drying asphalt. The reactive sites allow silicon source gas to attach and nucleate better, thereby improving the capacity of the material. At the same time, the metal powder can provide attachment sites for the silicon source, which facilitates the uniform deposition of silicon, thereby ensuring the cycle and rate performance of the silicon-carbon anode material.

[0050] After spray pyrolysis, the organic carbon source fills the pores left unfilled by the silicon source gas, forming a complete coating layer. This not only limits the volume expansion of the silicon-carbon anode material, ensuring its cycle and rate performance, but also improves its conductivity. The spray pyrolysis process prevents amorphous silicon from converting to crystalline silicon during high-temperature carbon coating, and the reducing organic solvent prevents the oxidation of nano-silicon particles during pyrolysis, thus ensuring the cycle and rate performance of the silicon-carbon anode material.

[0051] Therefore, the silicon-carbon anode material prepared by this invention has good conductivity, which can effectively improve the first coulombic efficiency and cycle life of the battery. Moreover, the process is simple and safe, which is conducive to the promotion and application of silicon-carbon anode materials.

[0052] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0053] Example 1

[0054] This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps:

[0055] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry the mixture at -50℃ and normal pressure for 24 hours. Then remove the mixture and grind it to obtain material A.

[0056] S2. Take 100g of material A, 10g of tin metal powder and 200g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir and wash for 2 hours and dry to obtain material B.

[0057] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0058] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0059] This invention first forms nitrogen-doped asphalt, then forms a metal-doped carbon matrix through activation and pore formation, introduces silicon and carbon sources, and finally uses organic carbon source, reducing organic solvent, mixing and stirring, ultrasonic treatment, and spray pyrolysis to form a silicon-carbon anode material with excellent cycle and rate performance and good conductivity.

[0060] Asphalt is inexpensive, abundant, and has a low softening point, making it a good carbon-based material.

[0061] Nitrogen-doped carbon materials possess high specific surface area, uniform pore volume and size, and a large number of reactive sites. These reactive sites allow silicon source gas to better adhere and nucleate, increasing the material's capacity. Metal powder provides adhesion sites for silicon source gas, facilitating uniform deposition and further enhancing the material's conductivity. Organic carbon sources can fill unfilled pores in the silicon source gas, forming a complete coating layer, limiting material volume expansion, and improving conductivity. Spray pyrolysis can prevent amorphous silicon from converting to crystalline silicon at high temperatures during carbon coating, thus avoiding impacts on the material's cycling and rate performance. Reducing organic solvents can prevent the oxidation of nano-silicon particles during pyrolysis. The conductive network formed by the inner and outer double layers also contributes to the material's electrochemical stability.

[0062] Example 2

[0063] This embodiment provides a novel method for preparing silicon-carbon anode materials, including the following steps:

[0064] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 200g of polyimide in a beaker containing 3000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry at -50℃ for 24 hours, then remove and grind to obtain material A.

[0065] S2. Take 100g of material A, 25g of tin metal powder, and 1000g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 6000g of n-hexane solvent. Stir, wash for 2 hours and dry to obtain material B.

[0066] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0067] S4. Place 100g of material C and 100g of citric acid in 600g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0068] Example 3

[0069] This embodiment provides a novel method for preparing silicon-carbon anode materials, including the following steps:

[0070] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry at -50℃ for 24 hours, then remove and grind to obtain material A.

[0071] S2. Take 100g of material A, 50g of lithium metal powder, and 500g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 4 hours. After taking them out, put them in a tube furnace and keep them at 400℃ for 2 hours. After cooling, grind them and place them in a beaker containing 4000g of n-hexane solvent. Stir, wash for 2 hours and dry to obtain material B.

[0072] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0073] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0074] Example 4

[0075] This embodiment provides a novel method for preparing silicon-carbon anode materials, including the following steps:

[0076] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry at -50℃ for 24 hours, then remove and grind to obtain material A.

[0077] S2. Take 100g of material A, 10g of indium metal powder, and 200g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir, wash for 2 hours and dry to obtain material B.

[0078] S3. Place 50g of material B in a rotary kiln, and introduce silane gas and argon gas. The flow rate of silane gas is 5L / h and the flow rate of argon gas is 20L / h. Perform chemical vapor deposition at 600℃ for 4h under the condition that the furnace rotation speed is 1r / min. Then introduce acetylene gas and argon gas. The flow rate of acetylene gas is 5L / h and the flow rate of argon gas is 20L / h. Hold at 700℃ for 4h under the condition that the furnace rotation speed is 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0079] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0080] Comparative Example 1

[0081] This comparative example provides a commercially available SiO / C material (KSP-1 from Hunan Jingui Technology Co., Ltd.) as an anode material.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a silicon-carbon anode material, including the following steps:

[0084] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry at -50℃ for 24 hours, then remove and grind to obtain material A.

[0085] S2. Take 100g of material A and 200g of potassium hydroxide, mix them in a three-dimensional mixer for 2 hours, take them out and put them in a tube furnace, keep them at 350℃ for 2 hours, cool them and grind them, put them in a beaker containing 1550g of n-hexane solvent, stir and wash them for 2 hours, and dry them to obtain material B.

[0086] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0087] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2h, then sonicate for 30min, spray the suspension at 500℃ at a flow rate of 10mL / min, and obtain material D after cooling.

[0088] Comparative Example 3

[0089] This comparative example provides a method for preparing silicon-carbon anode materials, including the following steps:

[0090] S1. Take 100g of coal tar pitch with D50 of 3mm, 10g of tin metal powder, and 200g of potassium hydroxide, mix them, place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir, wash for 2 hours and dry to obtain material B.

[0091] S2. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0092] S3. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0093] Comparative Example 4

[0094] This comparative example provides a method for preparing silicon-carbon anode materials, including the following steps:

[0095] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture and place it in a freeze dryer. Freeze-dry at -50℃ for 24 hours, then remove and grind to obtain material A.

[0096] S2. Take 100g of material A, 10g of tin metal powder and 200g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir and wash for 2 hours and dry to obtain material B.

[0097] S3. Place 20g of material B in a rotary kiln, and introduce silane and argon gases at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then, introduce acetylene and argon gases at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C, which is the silicon-carbon anode material.

[0098] Comparative Example 5

[0099] Specifically, the steps include the following:

[0100] S1. Mix 100g of coal tar pitch with a D50 of 3mm and 100g of polyimide in a beaker containing 1000g of N-methylpyrrolidone solvent. After stirring for 2 hours, remove the mixture, dry it for 24 hours, and grind it to obtain material A.

[0101] S2. Take 100g of material A, 10g of tin metal powder and 200g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir and wash for 2 hours and dry to obtain material B.

[0102] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0103] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0104] Comparative Example 6

[0105] Specifically, the steps include the following:

[0106] S1. Place 100g of coal tar pitch with a D50 of 3mm in a freeze dryer and freeze dry it at -50℃ and normal pressure for 24h. Then take it out and grind it to obtain material A.

[0107] S2. Take 100g of material A, 10g of tin metal powder and 200g of potassium hydroxide and mix them. Place them in a three-dimensional mixer and mix for 2 hours. After taking them out, put them in a tube furnace and keep them at 350℃ for 2 hours. After cooling, grind them and place them in a beaker containing 1550g of n-hexane solvent. Stir and wash for 2 hours and dry to obtain material B.

[0108] S3. Place 20g of material B in a rotary kiln, and introduce silane gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 500℃ for 2h with a kiln rotation speed of 1r / min. Then introduce acetylene gas and argon gas at a flow rate of 5L / h and 5L / h respectively. Perform chemical vapor deposition at 700℃ for 4h with a kiln rotation speed of 1r / min. Cool to room temperature, and then grind in a mechanical mill until D50 is 5μm to obtain material C.

[0109] S4. Place 100g of material C and 100g of citric acid in 500g of anhydrous ethanol, stir and react for 2 hours, then sonicate for 30 minutes. Spray the suspension at 500℃ with a spraying flow rate of 10mL / min. After cooling, material D is obtained, which is the silicon-carbon anode material.

[0110] Test case

[0111] The silicon-carbon anode material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the data, the silicon-carbon anode material prepared in Example 1 has relatively uniform particle size, with a particle size of approximately 6 μm.

[0112] The silicon-carbon anode materials of Examples 1-4 and Comparative Examples 2-6, and the commercial SiO / C material of Comparative Example 1 were used as anode active materials. A paste was prepared and coated according to a mass ratio of anode active material: conductive agent SP: binder LA133 of 8:1:1 to obtain CR2016 coin cells. A 1 mol / L LiPF6 EC + DMC (mass ratio 1:1) solution was used as the electrolyte. Electrochemical performance was tested, and the results are shown in Table 1 and... Figure 2-3 As shown.

[0113] Table 1. Electrochemical performance test results of silicon-carbon anode materials in Examples 1-4 and Comparative Examples 1-6

[0114]

[0115] Table 1, comparing Example 1 and Comparative Example 1, shows that the resistivity of the silicon-carbon anode material prepared in this application is lower than that of commercially available anode materials. Comparative Example 2 shows that the silicon-carbon anode material prepared without tin metal powder has higher resistivity and poorer cycle and rate performance. This is because metal powder can provide adhesion sites for silicon source gas, facilitating uniform silicon deposition and thus improving its initial discharge specific capacity, initial charge specific capacity, and initial coulombic efficiency. Metal powder can further enhance the material's conductivity, resulting in lower resistivity.

[0116] As can be seen from Example 1 and Comparative Examples 3, 5 and 6, the silicon-carbon anode material prepared by simultaneously nitrogen doping and freeze-drying coal tar pitch exhibits excellent cycle and rate performance. This is because after nitrogen doping and freeze-drying the pitch, the first material obtained under the synergistic effect of nitrogen doping and freeze-drying has a high specific surface area, uniform pore volume and pore size, and a large number of reactive sites, thereby ensuring the cycle and rate performance of the silicon-carbon anode material.

[0117] As can be seen from Example 1 and Comparative Example 4, the silicon-carbon anode material prepared by spray pyrolysis without using reducing organic solvents has poor cycle and rate performance. This is because spray pyrolysis can prevent amorphous silicon from converting into crystalline silicon at high temperatures when carbon is coated, thus affecting the cycle and rate performance of the material. Reducing organic solvents can prevent the nano-silicon particles from being oxidized during pyrolysis, thus affecting the cycle and rate performance of the material.

[0118] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: S1. Mix, stir and heat asphalt, metal powder and pore-forming agent, cool and crush and grind, clean and dry with a first organic solvent to form a first material; The mass ratio of asphalt to metal powder is 10:1 to 2:1; the mass ratio of asphalt to pore-forming agent is 1:2 to 1:10; the stirring time is 1 to 10 hours; the heating temperature is 300 to 500°C, and the heating time is 1 to 6 hours. S2. The first material is subjected to chemical vapor deposition in a mixed atmosphere of silicon source gas and inert gas, and then subjected to carbon coating treatment in a mixed atmosphere of carbon source gas and inert gas. After cooling, it is ground uniformly to obtain silicon-carbon anode material. The chemical vapor deposition temperature is 500–700°C and the time is 1–6 h; the carbon coating treatment temperature is 600–700°C and the time is 1–4 h. In step S1, the metal powder is selected from at least one of tin, indium, and lithium.

2. The preparation method according to claim 1, characterized in that, S1 further includes nitrogen doping treatment of asphalt, which includes dissolving asphalt and nitrogen-containing organic polymer in a second organic solvent, stirring, freeze-drying, and then grinding.

3. The preparation method according to claim 2, characterized in that, The nitrogen-containing organic polymer is selected from at least one of polyimide, polysulfonamide, and melamine; And / or, the mass ratio of the asphalt to the nitrogen-containing organic polymer is 1:1 to 1:10; And / or, the mass ratio of the sum of the asphalt and the nitrogen-containing organic polymer to the second organic solvent is 1:5 to 1:10; And / or, the second organic solvent is selected from at least one of N-methylpyrrolidone, n-hexane, xylene, and carbon tetrachloride; And / or, the freeze-drying temperature is -30℃ to -50℃; And / or, the freeze-drying time is 12h to 24h.

4. The preparation method according to claim 1 or 2, characterized in that, The preparation method further includes spray pyrolysis treatment of silicon-carbon anode material, wherein the spray pyrolysis treatment includes mixing and stirring organic carbon source, reducing organic solvent and silicon-carbon anode material, ultrasonic treatment, and spray pyrolysis in a high temperature atmosphere; The spray pyrolysis temperature is 300–500℃, and the spray flow rate is 1–10 mL / min.

5. The preparation method according to claim 4, characterized in that, The organic carbon source is selected from at least one of citric acid, acetic acid, oxalic acid, formic acid, propionic acid, and stearic acid; And / or, the reducing organic solvent is selected from at least one of ethanol, diethyl ether, dichloromethane, acetone and xylene; And / or, the mass ratio of the organic carbon source to the reducing organic solvent is 1:5 to 1:20; And / or, the total mass ratio of the organic carbon source and the reducing organic solvent to the silicon-carbon anode material is 1:1 to 10:1; And / or, the stirring reaction time is 1 to 4 hours, and the ultrasonic treatment time is 10 to 30 minutes.

6. The preparation method according to claim 1, characterized in that, In step S1, the asphalt is selected from coal tar pitch, petroleum pitch and natural asphalt, and the D50 of the asphalt is 3 to 5 mm. And / or, in step S1, the pore-forming agent is selected from at least one of phosphoric acid, zinc chloride, potassium hydroxide, and potassium carbonate.

7. The preparation method according to claim 1, characterized in that, In step S2, the silicon source gas is selected from at least one of silane or its homologues; And / or, the inert gas is selected from at least one of helium, argon, and nitrogen; And / or, the carbon source gas is selected from at least one of acetylene, methane, or their homologues.

8. The preparation method according to claim 1, characterized in that, The volume ratio of the inert gas to the silicon source gas is 4:1 to 1:

1.

9. The preparation method according to claim 1, characterized in that, The volume ratio of the inert gas to the carbon source gas is 4:1 to 1:

1.

10. A silicon-carbon anode material prepared by the preparation method according to any one of claims 1-9, characterized in that, The resistivity of the silicon-carbon anode material is 3.9 Ω·cm to 5.1 Ω·cm, and the initial coulombic efficiency is 91.9% to 93.1%.

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