A method for preparing a silicon-carbon composite material containing a nitrogen-coated carbon layer

Abstract

The application relates to a preparation method of a silicon-carbon composite material containing a nitrogen-coated carbon layer, which comprises the following steps: dispersing a nitrogen-containing polymer in a microemulsion system, adding a nano-silicon aqueous solution into the system, homogeneously emulsifying, forming stable nitrogen-containing polymer-coated nano-silicon microspheres, separating and drying; dispersing hydrophilic asphalt into an aqueous solution, adding the nitrogen-containing polymer-coated nano-silicon microspheres, using high-speed shearing force to perform secondary coating on the nano-silicon, forming a nano-scale asphalt coating layer on the surface, separating and drying; and carbonizing the silicon-carbon composite material precursor subjected to the secondary coating in an inert atmosphere to obtain the silicon-carbon composite material containing the nitrogen-coated carbon layer. The application has the advantages of good conductivity, excellent mechanical properties of the coating layer, high specific capacity and the like. The application can be applied to the markets of power batteries, consumer batteries and energy storage batteries. The preparation method is simple, raw materials are easy to obtain, and the cost is low, so the application is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a method for preparing a silicon-carbon composite material with a nitrogen-coated carbon layer. Background Technology

[0002] In recent years, industries such as new energy vehicles, energy storage devices, and artificial intelligence have placed increasingly higher demands on the energy density and safety of lithium-ion batteries. Commercially available lithium-ion batteries mainly use graphite as the negative electrode material. The theoretical specific capacity of graphite is 372 mA·h / g, while high-end graphite materials on the market can already reach 360–365 mA·h / g. Therefore, the potential for further improvement in the energy density of lithium-ion batteries is quite limited.

[0003] Against this backdrop, silicon-based anode materials are considered highly promising next-generation high-energy-density lithium-ion battery anode materials due to their advantages such as high theoretical specific capacity (4200 mA·h / g at high temperature, 3580 mA·h / g at room temperature), low delithiation potential (<0.5V), environmental friendliness, abundant reserves, and low cost. Novel nano-silicon-carbon composite anode materials, matched with ternary cathode materials in lithium-ion batteries, are considered the most promising anode materials for achieving energy densities greater than 300 W·h / kg. However, the preparation of nano-silicon, silicon-carbon composite technology, and the electrochemical phenomena of nano-silicon-carbon anode materials during charge and discharge processes still require in-depth research.

[0004] Currently, the industry commonly utilizes pitch-coated silicon-based anode materials. Patent CN 109817957 B discloses a method for preparing pitch-coated silicon-doped natural flake graphite anode materials. This method involves mixing treated natural flake graphite with treated nano-silicon powder, grinding, adding toluene, under nitrogen protection, stirring, filtering, washing, and drying. Then, the NG / Si composite material is mixed with a pitch-toluene solution, collected, air-dried, then dried at a constant temperature, ground, and pyrolyzed to obtain the product. While this method improves the electrochemical cycle performance and discharge specific capacity of natural flake graphite, the pitch transforms into soft graphite carbon after high-temperature carbonization, which cannot meet the requirements for fast charging during high-current charge-discharge processes. Effectively expanding the interlayer spacing of carbon materials is key to developing silicon-carbon composite lithium-ion battery anodes. Patent CN 105047870 A discloses a nitrogen-doped carbon-coated silicon composite material and its preparation method. This method prepares a nitrogen-doped carbon-coated silicon composite material by pyrolyzing a nitrogen-containing organic carbon precursor. This composite material, as a negative electrode material for lithium-ion batteries, exhibits good cycle stability and excellent high-current charge-discharge characteristics. However, some problems exist, such as the high cost of ionic liquids, high volatile content during carbonization, and a high specific surface area, which affects tap density and compaction density. Therefore, this project modulates the nitrogen-doped carbon coating layer. After coating, nano-silicon forms a hard carbon layer with a rigid inner structure and a soft carbon layer with a graphite-like structure. The nitrogen-coated carbon layer is characterized by overall density, resistance to pulverization, and low porosity, effectively inhibiting the pulverization of nano-silicon, improving conductivity, and preventing the irreversible consumption of a large number of active lithium ions during charge-discharge, significantly improving the battery's specific capacity and initial coulombic efficiency. The silicon-carbon composite material of the present invention has high specific capacity, high rate performance, and long cycle life, effectively solving the problems of capacity drop during high current charging and discharging and easy pulverization that exist when silicon-carbon composite materials are used in the actual preparation of lithium battery anodes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a nitrogen-coated carbon-based silicon-carbon composite material. This nitrogen-coated carbon-based silicon-carbon composite material possesses advantages such as good electrical conductivity, excellent mechanical properties of the coating layer, and high specific capacity. It can be applied to the power battery, consumer battery, and energy storage battery markets. The preparation method of this nitrogen-coated carbon-based silicon-carbon composite material is simple, uses readily available raw materials, and is inexpensive, making it suitable for large-scale production.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A method for preparing a silicon-carbon composite material with a nitrogen-coated carbon layer is disclosed. The nitrogen-coated layer can suppress the pulverization of nano-silicon, improve conductivity, and enhance rate performance, while the carbon-coated layer improves density and reduces porosity. The preparation process includes the following steps:

[0008] 1) Disperse the nitrogen-containing polymer in a microemulsion system, then add an aqueous solution of nano-silicon to the system, homogenize and emulsify to form stable nitrogen-containing polymer-coated nano-silicon microspheres, which are then separated and dried;

[0009] 2) Disperse hydrophilic asphalt in an aqueous solution, then add nitrogen-containing polymer-coated silicon microspheres, and use high-speed shear force to perform secondary coating on the silicon nanospheres. Through the valence bond of polar functional groups, a nanoscale asphalt coating layer is formed on the surface, which is then separated and dried.

[0010] 3) The silicon-carbon composite precursor with secondary coating is carbonized in an inert atmosphere, treated at a constant temperature, and cooled to room temperature to obtain a silicon-carbon composite material with nitrogen-coated carbon layer.

[0011] The nitrogen-containing polymer is any one or a mixture of polydopamine, polyvinylpyrrolidone, polybenzimidazole, polyacrylonitrile, polythiophene, polypyrrole, polyaniline, and melamine;

[0012] The microemulsion system is obtained by mixing water, oil, surfactant, and co-surfactant in appropriate proportions; the oil is n-hexane, cyclohexane, n-heptane, or n-octane; the surfactant is anionic or cationic, preferably sulfonate or quaternary ammonium salt; the mass ratio of oil to surfactant is 2.5–200:0.5–100; the co-surfactant is a fatty alcohol, and the mass ratio of surfactant to co-surfactant is 0.5–100:0.1–50; the mass ratio of nitrogen-containing polymer to oil is 1–40:2.5–200; the mass ratio of nitrogen-containing polymer to nano-silicon is 1–40:0.5–5; and the mass ratio of water to nano-silicon is 5–200:0.5–5.

[0013] In step 1) above, the nano-silicon Dv50 is 30-300nm; the homogenization emulsification time is 1-180min, and the emulsification speed is 500-20000rpm; the nitrogen-containing polymer-coated nano-silicon microspheres Dv50 is 50-320nm; the separation method is centrifugation, spray drying, or filtration; and the drying temperature is 60-200℃.

[0014] In step 2) above, the asphalt is one or a mixture of petroleum asphalt and coal tar pitch, wherein the mass ratio of petroleum asphalt to coal tar pitch is 0.1–10:0.3–25 when mixed; the hydrophilic asphalt is asphalt containing hydrophilic groups prepared by oxidation; the hydrophilic groups are -COOH, -OH, -NH2, -C=O, -NO. 2、 One or more of -SO3H; the contact angle between hydrophilic asphalt and water is 0 to 70°.

[0015] The mass ratio of hydrophilic bitumen to nitrogen-containing polymer is 0.1–90:0.1–10; the high-speed shearing time is 10–200 min, and the shearing speed is 2000–28000 rpm; the Dv50 of the secondary coated silicon-carbon composite precursor is 90–360 nm; the separation method is centrifugation, spray drying, or filtration; and the drying temperature is 50–280℃.

[0016] In step 3) above, the inert atmosphere is nitrogen or argon; the carbonization temperature is 500-1400℃; the isothermal treatment time is 10-240 min; and the Dv50 of the silicon-carbon composite material with nitrogen-coated carbon layer is 85-350 nm.

[0017] Compared with existing technologies, the beneficial effects of this invention are:

[0018] 1) The nitrogen-coated carbon layer prepared by the present invention can not only improve the reversible capacity by increasing the interlayer spacing to accelerate the diffusion of lithium ions, but also increase the surface capacitance through capacitive behavior.

[0019] 2) By using microemulsion and high-speed shearing, the interface of nano-silicon is modified to form a silicon-carbon composite material with a hard carbon inner layer of long-range order and short-range disorder and an outer layer of graphite-like structure, thereby preparing a silicon-carbon composite material with high specific capacity, high rate performance and long cycle life.

[0020] 3) After carbonization, nitrogen-containing polymers are transformed into amorphous hard carbon, with a greater interlayer spacing than soft carbon asphalt. Lithium ions can diffuse rapidly in the amorphous carbon. The outermost soft carbon acts as a buffer layer for the rapid diffusion of lithium ions, thereby improving the high-current charge and discharge performance of silicon-carbon composite materials. Therefore, it has excellent rate performance.

[0021] 4) This invention effectively solves the problems of capacity drop during high-current charging and discharging and easy pulverization that exist in the actual application of silicon-carbon composite materials in the preparation of lithium battery anodes. Attached Figure Description

[0022] Figure 1 This is the XRD pattern of nano-silicon used in Example 1 of the present invention.

[0023] Figure 2 The image shows the XRD pattern of the silicon-carbon composite material with a nitrogen-coated carbon layer in Example 1 of this invention.

[0024] Figure 3 This is a SEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer in Example 1 of the present invention.

[0025] Figure 4 This is a TEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer in Example 1 of the present invention.

[0026] Figure 5This is a TEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer in Example 2 of the present invention.

[0027] Figure 6 This is a TEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer in Example 3 of the present invention. Detailed Implementation

[0028] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods, and the equipment used is conventional equipment and commercially available products.

[0029] Example 1:

[0030] S1. Weigh 10g of nano-silicon and dissolve it in 150g of distilled water to form an aqueous phase.

[0031] S2. In a 500mL four-necked flask, add 10g cetyltrimethylammonium bromide, 3g n-pentanol, 100g cyclohexane, and 20g polydopamine in sequence. Emulsify at 1000rpm and 50℃ for 30min to prepare the oil phase.

[0032] S3. Add nano-silica aqueous solution dropwise to the oil phase using a dropping funnel at a rotation speed of 1000 rpm, and homogenize at 50°C for 30 min. Control the HLB value to 3 to form a (W / O) microemulsion. Allow to stand for 10 h to obtain nitrogen-containing polymer-coated nano-silica microspheres, filter, and dry at 100°C in a vacuum drying oven to constant weight.

[0033] S4. Weigh 30g of oxidized hydrophilic coal tar pitch and add it to a four-necked flask containing 200g of distilled water. Stir at 60℃ for 1h. Then add the microspheres prepared in S3 and shear at 20000rpm for 10min to form a uniform and dense nano-coating layer, thus obtaining a secondary coated silicon-carbon composite material precursor.

[0034] S5. The silicon-carbon composite precursor with secondary coating is heated from room temperature to 1200°C at a rate of 3°C / min in a nitrogen atmosphere, held at that temperature for 120 min, and then cooled to room temperature to obtain a silicon-carbon composite material with a nitrogen-coated carbon layer. The XRD pattern of the nano-silicon used in Example 1 is shown below. Figure 1 As shown, the XRD pattern of the obtained silicon-carbon composite material with nitrogen-coated carbon layer is as follows. Figure 2 As shown in the figure, the SEM image is as follows: Figure 3 As shown, TEM image Figure 4 As shown.

[0035] Example 2:

[0036] S1. Weigh 5g of nano-silicon and dissolve it in 75g of distilled water to form an aqueous phase.

[0037] S2. In a 250mL four-necked flask, add 5g sodium dodecylbenzenesulfonate, 3g n-butanol, 50g cyclohexane, and 10g polyvinylpyrrolidone in sequence. Emulsify at 1000rpm and 60℃ for 20min to prepare the oil phase.

[0038] S3. Add nano-silica aqueous solution dropwise to the oil phase using a dropping funnel at a rotation speed of 1000 rpm, and homogenize at 60°C for 20 min. Control the HLB value to 3 to form a (W / O) microemulsion. Allow to stand for 24 h to obtain nitrogen-containing polymer-coated nano-silica microspheres, filter, and dry at 120°C in a vacuum drying oven to constant weight.

[0039] S4. Weigh 20g of oxidized hydrophilic petroleum asphalt and add it to a four-necked flask containing 150g of distilled water. Stir at 40℃ for 30min. Then add the microspheres prepared in S3 and shear at 20000rpm for 10min to form a uniform and dense nano-coating layer, thus obtaining a secondary coated silicon-carbon composite material precursor.

[0040] S5. The silicon-carbon composite precursor with secondary coating is heated from room temperature to 850°C at a rate of 3°C / min in a nitrogen atmosphere, held at that temperature for 120 min, and then cooled to room temperature to obtain a silicon-carbon composite material with a nitrogen-coated carbon layer. The TEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer obtained in Example 2 is shown below. Figure 5 As shown.

[0041] Example 3:

[0042] S1. Weigh 15g of nano-silicon and dissolve it in 225g of distilled water to form an aqueous phase.

[0043] S2. In a 1000mL four-necked flask, add 15g hexadecyl dimethyl allyl ammonium chloride, 15g n-octanol, 150g n-hexane, and 30g polybenzimidazole in sequence. Emulsify at 5000rpm and 60℃ for 50min to prepare the oil phase.

[0044] S3. Add nano-silica aqueous solution dropwise to the oil phase using a dropping funnel at a rotation speed of 5000 rpm and homogenize at 60°C for 50 min. Control the HLB value to 5 to form a (W / O) microemulsion. Allow to stand for 12 h to obtain nitrogen-containing polymer-coated nano-silica microspheres, filter, and dry at 110°C in a vacuum drying oven to constant weight.

[0045] S4. Weigh 20g of oxidized hydrophilic coal tar pitch and 10g of hydrophilic petroleum pitch and add them to a four-necked flask containing 200g of distilled water. Stir at 50°C for 50min. Then add the microspheres prepared in S3 and shear at 25000rpm for 20min to form a uniform and dense nano-coating layer, thus obtaining a secondary coated silicon-carbon composite material precursor.

[0046] S5. The silicon-carbon composite precursor with secondary coating is heated from room temperature to 900°C at a rate of 1°C / min in a nitrogen atmosphere, held at that temperature for 180 min, and then cooled to room temperature to obtain a silicon-carbon composite material with a nitrogen-coated carbon layer. The TEM image of the silicon-carbon composite material with a nitrogen-coated carbon layer obtained in Example 3 is shown below. Figure 6 As shown.

[0047] Example 4:

[0048] S1. Weigh 5g of nano-silicon and dissolve it in 75g of distilled water to form an aqueous phase.

[0049] S2. In a 250 mL four-necked flask, add 5 g of octadecyltrimethylammonium chloride, 3 g of isopropanol, 50 g of n-hexane, and 10 g of polyacrylonitrile in sequence. Emulsify at 10000 rpm for 10 min at a constant temperature of 40 °C to prepare the oil phase.

[0050] S3. Add nano-silica aqueous solution dropwise to the oil phase using a dropping funnel at a rotation speed of 10000 rpm, and homogenize at 40℃ for 10 min. Control the HLB value to 2 to form a (W / O) microemulsion. Allow to stand for 24 h to obtain nitrogen-containing polymer-coated nano-silica microspheres, filter, and dry at 80℃ in a vacuum drying oven to constant weight.

[0051] S4. Weigh 20g of oxidized hydrophilic coal tar pitch and add it to a four-necked flask containing 200g of distilled water. Stir at 60℃ for 30min. Then add the microspheres prepared in S3 and shear at 28000rpm for 15min to form a uniform and dense nano-coating layer, thus obtaining a secondary coated silicon-carbon composite material precursor.

[0052] S5. The silicon-carbon composite precursor that has undergone secondary coating is heated from room temperature to 1400℃ in a nitrogen atmosphere at a rate of 5℃ / min, held at the temperature for 240min, and then cooled to room temperature to obtain a silicon-carbon composite material with a nitrogen-coated carbon layer.

[0053] Example 5:

[0054] S1. Weigh 5g of nano-silicon and dissolve it in 75g of distilled water to form an aqueous phase.

[0055] S2. In a 250 mL four-necked flask, add 5 g of octadecyltrimethylammonium chloride, 3 g of 1-octanol, 50 g of n-octane, and 10 g of melamine in sequence. Emulsify at 10000 rpm for 10 min at a constant temperature to prepare the oil phase.

[0056] S3. Add nano-silica aqueous solution dropwise to the oil phase using a dropping funnel at a rotation speed of 10000 rpm, and homogenize at 60℃ for 10 min. Control the HLB value to 2 to form a (W / O) microemulsion. Allow to stand for 24 h to obtain nitrogen-containing polymer-coated nano-silica microspheres, filter, and dry at 140℃ in a vacuum drying oven to constant weight.

[0057] S4. Weigh 25g of oxidized hydrophilic petroleum asphalt and add it to a four-necked flask containing 150g of distilled water. Stir at 40°C for 30min. Then add the microspheres prepared in S3 and shear at 28000rpm for 15min to form a uniform and dense nano-coating layer, thus obtaining a secondary coated silicon-carbon composite material precursor.

[0058] S5. The silicon-carbon composite precursor that has undergone secondary coating is heated from room temperature to 600℃ at a rate of 5℃ / min in an argon atmosphere, held at the temperature for 240min, and then cooled to room temperature to obtain a silicon-carbon composite material with a nitrogen-coated carbon layer.

[0059] The parameter test results of the silicon-carbon composite anode materials with nitrogen-coated carbon layers prepared in each embodiment are listed in Table 1, and the chemical bonding state content of nitrogen is listed in Table 2.

[0060] Table 1. Parameters of the nitrogen-coated carbon-containing silicon-carbon composite anode materials prepared in each embodiment.

[0061]

[0062] Table 2 shows the chemical bond state content of nitrogen in the nitrogen-coated carbon-containing silicon-carbon composite materials prepared in each example.

[0063] 1 1200 49.0 4.7 46.3 2 850 37.0 22.3 40.7 3 900 40.5 18.3 41.2 4 1400 47.5 6.2 46.3 5 600 36.2 23.4 40.4

[0064] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material with a nitrogen-coated carbon layer, characterized in that, The preparation process includes the following steps: 1) The nitrogen-containing polymer is dispersed in a microemulsion system, and then an aqueous solution of nano-silicon is added to the system. After homogenization and emulsification, nano-silicon microspheres coated with nitrogen-containing polymer are formed, separated, and dried. The nano-silicon Dv50 is 30-300nm; the homogenization emulsification time is 1-180 min, and the emulsification speed is 500-20000 rpm; the nitrogen-containing polymer-coated nano-silicon microspheres have a Dv50 of 50-320nm; the drying temperature is 60-200℃; 2) Disperse hydrophilic asphalt in an aqueous solution, then add nitrogen-containing polymer-coated silicon microspheres. Use shear force to perform secondary coating on the silicon nanospheres. Through the valence bond of polar functional groups, a nanoscale asphalt coating layer is formed on the surface. Separate and dry. The mass ratio of hydrophilic bitumen to nitrogen-containing polymer is 0.1–90:0.1–10; the shearing time is 10–200 min, and the shearing speed is 2000–28000 rpm; the Dv50 of the secondary coated silicon-carbon composite precursor is 90–360 nm; and the drying temperature is 50–280℃. 3) The silicon-carbon composite precursor with secondary coating is carbonized in an inert atmosphere, treated at a constant temperature, and cooled to room temperature to obtain a silicon-carbon composite material with nitrogen-coated carbon layer. The inert atmosphere is nitrogen or argon; the carbonization temperature is 500–1400℃; the isothermal treatment time is 10–240 min; and the Dv50 of the silicon-carbon composite material with nitrogen-coated carbon layer is 85–350 nm. The hydrophilic groups of hydrophilic bitumen are -COOH, -OH, -NH2, -C=O, and -NO. 2、 One or more of -SO3H.

2. The method for preparing a nitrogen-coated carbon-containing silicon-carbon composite material according to claim 1, characterized in that, The nitrogen-containing polymer is any one or a mixture of polydopamine, polyvinylpyrrolidone, polybenzimidazole, polyacrylonitrile, polypyrrole, and polyaniline.

3. The method for preparing a nitrogen-coated carbon layer silicon-carbon composite material according to claim 1 or 2, characterized in that, The microemulsion system is obtained by mixing water, oil, surfactant, and co-surfactant; the oil is n-hexane, cyclohexane, n-heptane, or n-octane; the surfactant is anionic or cationic, and the mass ratio of oil to surfactant is 2.5–200:0.5–100; the co-surfactant is a fatty alcohol, and the mass ratio of surfactant to co-surfactant is 0.5–100:0.1–50; the mass ratio of nitrogen-containing polymer to oil is 1–40:2.5–200; the mass ratio of nitrogen-containing polymer to nano-silicon is 1–40:0.5–5; and the mass ratio of water to nano-silicon is 5–200:0.5–5.

4. The method for preparing a nitrogen-coated carbon layer silicon-carbon composite material according to claim 1, characterized in that, In step 2) above, the asphalt is one or a mixture of petroleum asphalt and coal tar pitch, and when mixed, the mass ratio of petroleum asphalt to coal tar pitch is 0.1-10:0.3-25; the hydrophilic asphalt is asphalt containing hydrophilic groups prepared by oxidation.

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