Multi-layer carbon-coated mesoporous silicon carbon negative electrode material, and preparation method and application thereof

Abstract

The embodiment of the present application relates to a kind of multi-layer carbon-coated mesoporous silicon carbon negative electrode material and its preparation method and application, method includes: in protective atmosphere, into the reaction container loaded with mesoporous carbon matrix, silicon source gas is imported, so that silicon source gas is carried out gas deposition on mesoporous carbon matrix, and mesoporous silicon carbon material is obtained;Continue to import first carbon source gas into the reaction container, and form first carbon layer, and obtain pre-coated mesoporous silicon carbon material;After graphene oxide and positive modification agent are dissolved in solvent, mixed solution is obtained;Pre-coated mesoporous silicon carbon material is added therein, and graphene oxide / pre-coated mesoporous silicon carbon material is obtained by spray drying treatment;Nitrogen-doped graphene layer is formed by importing protective gas into the reaction container and heating the reaction container, and then second carbon source gas is imported into the reaction container, and second carbon layer is formed, so that multi-layer carbon-coated mesoporous silicon carbon negative electrode material is obtained;Second carbon source gas is same with first carbon source gas.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a multilayer carbon-coated mesoporous silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] Traditional graphite anode materials, due to their relatively low theoretical capacity (approximately 372 mAh / g), are no longer sufficient to meet the demands of modern applications for higher energy and power densities. Silicon, on the other hand, is highly favored due to its ultra-high theoretical specific capacity (4200 mAh / g) and low delithiation potential. However, silicon-based anodes experience severe volume expansion during lithium delithiation and lithium intercalation cycles, leading to repeated damage to the solid electrolyte interphase (SEI) and electrode pulverization, ultimately resulting in anode failure. Therefore, developing novel silicon-based anode materials to improve the performance of lithium-ion batteries has become a research hotspot.

[0003] Mesoporous silicon-carbon materials are considered promising anode materials due to their high specific surface area, good conductivity, and excellent structural stability. However, pure mesoporous silicon-carbon materials still face some challenges in practical applications, such as low initial coulombic efficiency, large volume expansion, and poor cycling stability. To address these issues, researchers have explored various modification strategies to improve their electrochemical performance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a multilayer carbon-coated mesoporous silicon-carbon anode material, its preparation method, and its applications. This preparation method effectively combines the advantages of graphene oxide and mesoporous silicon-carbon materials, and adopts an effective coating strategy to optimize performance, thereby improving the electrochemical performance of the multilayer carbon-coated mesoporous carbon anode material.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a multilayer carbon-coated mesoporous silicon-carbon anode material, the method comprising:

[0006] Under a protective atmosphere, silicon source gas is introduced into a reaction vessel containing a mesoporous carbon matrix, and the silicon source gas is vapor-deposited on the mesoporous carbon matrix to obtain a mesoporous silicon-carbon material.

[0007] Stop the supply of silicon source gas, adjust the temperature of the reaction vessel, and introduce a first carbon source gas into the reaction vessel so that the first carbon source gas is pyrolyzed to form a first carbon layer, thereby obtaining a pre-coated mesoporous silicon-carbon material.

[0008] After dissolving graphene oxide and a positively charged modifier in a solvent at a predetermined mass ratio, a mixed solution is obtained.

[0009] The pre-coated mesoporous silicon carbon material is added to the mixed solution and mixed evenly, and then spray-dried to obtain graphene oxide / pre-coated mesoporous silicon carbon material.

[0010] A protective gas is introduced into a reaction vessel containing the graphene oxide / pre-coated mesoporous silicon carbon material, and the reaction vessel is heated so that the graphene oxide is reduced and forms a nitrogen-doped graphene layer with a positively charged modifier. Then, the temperature of the reaction vessel is adjusted, and a second carbon source gas is introduced into the reaction vessel so that the second carbon source gas is pyrolyzed to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material; the second carbon source gas is the same as the first carbon source gas.

[0011] Preferably, the mesoporous carbon matrix has a particle size D50 of 5 μm-20 μm and a specific surface area of ​​1600 m². 2 / g-2400m 2 / g, average pore size of 2nm-10nm, pore volume of 0.5cm³ 3 / g-3.5cm 3 / g, with a porosity of 30%-80% and a mesoporous content of 25%-70%.

[0012] Preferably, the silane gas includes one or more of methylsilane, disilane, gaseous propane, and gaseous trichlorosilane; the flow rate of the silicon source gas is 2L / min-30L / min; the specific conditions for the vapor deposition are: heating to 450℃-600℃ at a heating rate of 1℃ / min-10℃ / min, and continuing for 1 hour-10 hours.

[0013] Preferably, the first carbon source gas includes one or more of methane, ethane, ethylene, acetylene, propane, and propylene; the flow rate of the first carbon source gas is 1 L / min to 20 L / min; the formation conditions of the first carbon layer are specifically: heating to 500℃ to 700℃ at a heating rate of 1℃ / min to 10℃ / min, and continuing for 0.5 hours to 5 hours.

[0014] Preferably, the preset mass ratio is 1:1 to 1:10; the proportion of graphene oxide in the mesoporous silicon carbide material is 0.01wt% to 10wt%.

[0015] Preferably, the conditions for the spray drying process are: inlet temperature 140℃-260℃, outlet temperature 50℃-170℃, and frequency 120Hz-300Hz.

[0016] Preferably, the flow rate of the second carbon source gas is 2 L / min-30 L / min; the formation conditions of the nitrogen-doped graphene layer are: heating to 350℃-550℃ at a heating rate of 1℃ / min-10℃ / min for 1 hour-5 hours; the formation conditions of the second carbon layer are: heating to 500℃-700℃ at a heating rate of 2℃ / min-10℃ / min for 1 hour-20 hours.

[0017] In a second aspect, the present invention provides a multilayer carbon-coated mesoporous silicon-carbon anode material, wherein the multilayer carbon-coated mesoporous silicon-carbon anode material is prepared by any of the preparation methods described in the first aspect above.

[0018] The multilayer carbon-coated mesoporous silicon-carbon anode material includes: a core and a shell;

[0019] The core is a mesoporous silicon-carbon material; the mesoporous silicon-carbon material includes a mesoporous carbon matrix and nano-silicon particles deposited in the pores of the mesoporous carbon matrix.

[0020] The outer shell covers the outside of the core, and the outer shell is a composite carbon layer; the composite carbon layer includes a first carbon layer covering the outside of the core, a nitrogen-doped graphene layer covering the outside of the first carbon layer, and a second carbon layer covering the outside of the graphene layer.

[0021] The particle size D50 of the multilayer carbon-coated mesoporous silicon-carbon anode material is between 7 μm and 25 μm, and the specific surface area is 1 m². 2 / g-20m 2 / g.

[0022] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the multilayer carbon-coated mesoporous silicon-carbon negative electrode material described in the second aspect.

[0023] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the third aspect.

[0024] The method for preparing multilayer carbon-coated mesoporous silicon-carbon anode materials provided in this invention selects a mesoporous carbon matrix with suitable pore size and high pore volume, providing sufficient interface for the subsequent dispersion and deposition of nano-silicon particles, and also providing sufficient buffer space for the expansion of nano-silicon. The pre-coating process optimizes the interfacial performance between the first carbon layer and the mesoporous silicon-carbon material. The first carbon layer can alleviate the volume expansion problem of nano-silicon and prevent contact between the electrolyte and nano-silicon. Graphene oxide reacts chemically with a positively charged modifier to introduce nitrogen atoms into the graphene oxide, resulting in a uniform and highly nitrogen-doped graphene layer, further enhancing the reactivity and conductivity of the graphene layer, thereby further improving the interfacial and electrochemical performance of the graphene layer. The same carbon source gas is used in the process of forming the first and second carbon layers, resulting in amorphous carbon layers with the same structure and properties. The amorphous carbon layers have good bonding, constructing a tightly bonded multilayer carbon coating of amorphous carbon-graphene layer-amorphous carbon, thus forming a stable and complete coating layer. Multilayer carbon coating effectively reduces the contact between nano-silicon and electrolyte in complex application environments, thereby reducing the formation of SE I film and irreversible capacity loss. The graphene layer can form a continuous and conductive interface, optimizing interface properties and enhancing structural stability. When multilayer carbon-coated mesoporous silicon carbon anode materials are used in lithium-ion batteries, they exhibit a low expansion rate during cycling, demonstrating excellent cycle stability, and the coulombic efficiency in the first cycle after compression is significantly improved. Attached Figure Description

[0025] Figure 1 A flowchart illustrating the preparation method of the multilayer carbon-coated mesoporous silicon-carbon anode material provided in this embodiment of the invention;

[0026] Figure 2 This is a schematic diagram of the structure of the multilayer carbon-coated mesoporous silicon-carbon anode material provided in an embodiment of the present invention;

[0027] Figure 3 This is a SEM image of the graphene oxide / pre-coated mesoporous silicon carbide material prepared in Example 1 of the present invention;

[0028] Figure 4 This is a SEM image of the graphene oxide / pre-coated mesoporous silicon carbide material prepared in Comparative Example 1 of this invention.

[0029] Figure 5 This is a SEM image of the multilayer carbon-coated mesoporous silicon-carbon anode material prepared in Example 1 of the present invention;

[0030] Figure 6 The charge-discharge curves of the coin cell assembled from the multilayer carbon-coated mesoporous silicon-carbon anode material prepared in Example 1 of this invention are shown. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] This invention provides a method for preparing a multilayer carbon-coated mesoporous silicon-carbon anode material, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0034] Step 110: Under a protective atmosphere, silicon source gas is introduced into a reaction vessel containing a mesoporous carbon matrix, so that the silicon source gas is vapor-deposited on the mesoporous carbon matrix to obtain a mesoporous silicon-carbon material.

[0035] Specifically, the protective atmosphere can be nitrogen and / or argon, and the gas flow rate of the protective atmosphere can be 2 L / min to 30 L / min, preferably 15 L / min to 25 L / min. The reaction vessel can be a batch or continuous reaction device, specifically including any one of a deposition furnace, rotary furnace, bell furnace, or fluidized bed.

[0036] Mesoporous carbon matrices can be obtained by pulverizing mesoporous carbon materials. These materials can specifically include one or more of the following: biomass-based mesoporous carbon materials, resin-based mesoporous carbon materials, pitch-based mesoporous carbon materials, and graphite-based mesoporous carbon materials. The particle size D50 of the mesoporous carbon matrix is ​​5 μm-20 μm, and the specific surface area is 1600 m². 2 / g-2400m 2 / g, average pore size of 2nm-10nm, pore volume of 0.5cm³ 3 / g-3.5cm 3 / g, with a porosity of 30%-80% and a mesoporous content of 25%-70%. The mesoporous carbon matrix of this application has a suitable pore size and high pore volume, providing a sufficient interface for the subsequent dispersion and deposition of nano-silicon particles, and also providing sufficient buffer space for the expansion of nano-silicon.

[0037] The silane gas may specifically include one or more of the following: methylsilane, disilane, gaseous propane, and gaseous trichlorosilane. The flow rate of the silicon source gas can be 2 L / min-30 L / min, preferably 10 L / min-15 L / min. Specific vapor phase deposition conditions can be: heating to 450℃-600℃ at a heating rate of 1℃ / min-10℃ / min, held for 1 hour-10 hours, preferably heating to 500℃-550℃ at a heating rate of 2℃ / min-5℃ / min, held for 3 hours-5 hours. The silicon content accounts for 20 wt%-65 wt% of the mesoporous silicon-carbon material.

[0038] The resulting mesoporous silicon-carbon material has high specific surface area, good electrical conductivity, and excellent structural stability.

[0039] Step 120: Stop the supply of silicon source gas, adjust the temperature of the reaction vessel, and introduce the first carbon source gas into the reaction vessel so that the first carbon source gas is pyrolyzed to form the first carbon layer, thereby obtaining the pre-coated mesoporous silicon-carbon material.

[0040] Specifically, the first carbon source gas may include one or more of methane, ethane, ethylene, acetylene, propane, and propylene. The flow rate of the first carbon source gas can be 1 L / min to 20 L / min, preferably 6 L / min to 10 L / min. The formation conditions of the first carbon layer are as follows: heating to 500℃-700℃ at a heating rate of 1℃ / min to 10℃ / min, and holding for 0.5 hours to 5 hours, preferably heating to 520℃-600℃ at a heating rate of 2℃ / min to 5℃ / min, and holding for 1 hour to 3 hours.

[0041] The pre-coating process optimizes the interfacial properties between the first carbon layer and the mesoporous silicon-carbon material. The thickness of the first carbon layer is specifically 0.1 nm-50 nm. The first carbon layer can alleviate the volume expansion problem of the silicon nanoparticles and prevent direct contact between the electrolyte and the silicon nanoparticles.

[0042] Step 130: Dissolve graphene oxide and positively charged modifier in a solvent according to a preset mass ratio to obtain a mixed solution;

[0043] Specifically, the graphene oxide is a single-layer solid powder with a particle size D50 between 0.1 μm and 30 μm, an oxygen content between 35 wt% and 50 wt%, and an impurity content of less than 0.1%. The proportion of graphene oxide in the pre-coated mesoporous silicon carbide material is 0.01 wt% to 10 wt%, preferably 0.2 wt% to 3 wt%.

[0044] Graphene oxide is a two-dimensional nanomaterial with good electrical conductivity and excellent polar strength. Introducing graphene oxide into silicon-carbon materials can optimize interfacial resistance and improve the electrochemical performance of materials, such as cycle performance and rate performance, by utilizing its flexibility and mechanical strength.

[0045] Positively charged modifiers include one or both of cationic surfactants and positively charged conductive polymers. Specifically, cationic surfactants include one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and polyethyleneimine. Positively charged conductive polymers include one or more of polypyrrole, polydiallyldimethylammonium chloride, and polyaniline. The nitrogen-containing functional groups of the positively charged modifier and the oxygen-containing functional groups of graphene oxide can be linked through electrostatic interactions.

[0046] The preset mass ratio can be 1:1 to 1:10, preferably 1:2 to 1:5.

[0047] The solvent can be one or more of deionized water, ethanol, isopropanol, and N,N-dimethylformamide.

[0048] Step 140: Add the pre-coated mesoporous silicon carbon material to the mixed solution and mix well. Then, spray dry to obtain graphene oxide / pre-coated mesoporous silicon carbon material.

[0049] Specifically, the mixing time can be 1 hour to 10 hours, preferably 4 hours to 6 hours. The spray drying process can be carried out in a spray dryer, with the following conditions: inlet temperature 140℃-260℃, outlet temperature 50℃-170℃, and frequency 120Hz-300Hz, preferably inlet temperature 165℃-250℃, outlet temperature 85℃-160℃, and frequency 200Hz-220Hz.

[0050] Step 150: A protective gas is introduced into a reaction vessel loaded with graphene oxide / pre-coated mesoporous silicon carbon material, and the reaction vessel is heated so that the graphene oxide is reduced and forms a nitrogen-doped graphene layer with the positively charged modifier. Then, the temperature of the reaction vessel is adjusted, and a second carbon source gas is introduced into the reaction vessel so that the second carbon source gas is pyrolyzed to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0051] Specifically, the formation conditions for graphene structures are as follows: heating to 350℃-550℃ at a heating rate of 1℃ / min-10℃ / min and holding for 1 hour-5 hours, preferably heating to 500℃-550℃ at a heating rate of 5℃ / min-8℃ / min and holding for 1 hour-2 hours.

[0052] The second carbon source gas is the same as the first carbon source gas. The flow rate of the second carbon source gas can be 2 L / min-30 L / min, preferably 10 L / min. The specific conditions for the formation of the second carbon layer are as follows: heating to 500℃-700℃ at a heating rate of 2℃ / min-10℃ / min, and holding for 1 hour-20 hours, preferably heating to 550℃-600℃ at a heating rate of 4℃ / min-9℃ / min, and holding for 4 hours-10 hours.

[0053] In this process, graphene oxide undergoes chemical reactions with positively charged modifiers, such as amidation between carboxyl and amino groups, and ring-opening reactions between epoxy and amino groups. Graphene oxide is reduced, and the nitrogen atoms in the positively charged modifiers provide a positive charge, interacting with the π electrons on the graphene oxide surface to introduce nitrogen atoms into the graphene oxide, resulting in a uniform and highly nitrogen-doped graphene layer. This further enhances the reactivity and conductivity of the graphene layer, thereby improving its interfacial and electrochemical properties. Furthermore, the graphene layer, acting as an intermediate barrier layer, improves pressure resistance, preventing particle breakage under high pressure and affecting electronic conductivity. It also prevents gaseous carbon from entering the mesopores, preserving the expansion space for the nano-silicon particles.

[0054] The same carbon source gas was used in the process of creating the first and second carbon layers, and the resulting amorphous carbon layers have the same structure and properties. The amorphous carbon layers are well bonded together, forming a tightly bonded multilayer carbon coating of amorphous carbon-graphene layer-amorphous carbon, thus forming a stable and complete coating layer.

[0055] The second carbon layer can overcome the problems caused by the sheet-like morphology and large specific surface area of ​​the graphene layer, and can significantly improve the conductivity of the material, reduce the specific surface area, and further reduce the risks caused by the expansion of nano-silicon particles and direct contact with the electrolyte.

[0056] Multilayer carbon coating effectively reduces the contact between nano-silicon and electrolyte in complex application environments, thereby reducing the formation of SE I film and irreversible capacity loss. The graphene layer can form a continuous and conductive interface, optimizing interface properties and enhancing structural stability. When multilayer carbon-coated mesoporous silicon carbon anode materials are used in lithium-ion batteries, they exhibit a low expansion rate during cycling, demonstrating excellent cycle stability, and the coulombic efficiency in the first cycle after compression is significantly improved.

[0057] The multilayer carbon-coated mesoporous silicon-carbon anode material prepared by the above method is as follows: Figure 2As shown, it includes a core and a shell. The core is a mesoporous silicon-carbon material; the mesoporous silicon-carbon material includes a mesoporous carbon matrix and nano-silicon particles deposited in the pores of the mesoporous carbon matrix; the shell covers the outside of the core and is a composite carbon layer; the composite carbon layer includes a first carbon layer covering the outside of the core, a nitrogen-doped graphene layer covering the outside of the first carbon layer, and a second carbon layer covering the outside of the graphene layer; the particle size D50 of the multilayer carbon-coated mesoporous silicon-carbon anode material is between 7 μm and 25 μm, and the specific surface area is 1 m². 2 / g-20m 2 / g.

[0058] In summary, the method for preparing multilayer carbon-coated mesoporous silicon-carbon anode materials provided in this invention selects a mesoporous carbon matrix with suitable pore size and high pore volume, providing sufficient interface for the subsequent dispersion and deposition of nano-silicon particles, and also providing sufficient buffer space for the expansion of nano-silicon. The pre-coating process optimizes the interfacial performance between the first carbon layer and the mesoporous silicon-carbon material. The first carbon layer can alleviate the volume expansion problem of nano-silicon and prevent contact between the electrolyte and nano-silicon. Graphene oxide reacts chemically with a positively charged modifier to introduce nitrogen atoms into the graphene oxide, resulting in a uniform and highly nitrogen-doped graphene layer, further enhancing the reactivity and conductivity of the graphene layer, thereby further improving the interfacial and electrochemical performance of the graphene layer. During the process of creating the first and second carbon layers, the same carbon source gas is used, resulting in amorphous carbon layers with the same structure and properties. The amorphous carbon layers have good bonding, constructing a tightly bonded multilayer carbon coating of amorphous carbon-graphene layer-amorphous carbon, thus forming a stable and complete coating layer. Multilayer coating effectively reduces the contact between nano-silicon and electrolyte in complex application environments, thereby reducing the formation of SE I film and irreversible capacity loss. The graphene layer can form a continuous and conductive interface, optimizing interface properties and enhancing structural stability. When multilayer carbon-coated mesoporous silicon-carbon anode materials are used in lithium-ion batteries, they exhibit a low expansion rate during cycling, demonstrating excellent cycle stability, and the coulombic efficiency in the first cycle after compression is significantly improved.

[0059] The multilayer carbon-coated mesoporous silicon-carbon anode material provided by this invention can be used as an electrode material in energy storage devices such as supercapacitors, lithium-ion batteries, sodium-ion batteries, and solid-state batteries.

[0060] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing multilayer carbon-coated mesoporous silicon-carbon anode materials using the method provided in the above embodiments of the present invention, as well as the electrochemical characteristics of the prepared multilayer carbon-coated mesoporous silicon-carbon anode materials.

[0061] Example 1

[0062] The first step is to crush 5 kg of biomass-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 9 μm and place it in a deposition furnace.

[0063] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 15 L / min to form a nitrogen atmosphere. The temperature is increased to 500°C at a heating rate of 5°C / min. Then, silane is introduced at a gas flow rate of 10 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 4 hours.

[0064] The third step involves stopping the introduction of silane and raising the temperature to 520°C at a rate of 5°C / min. Acetylene is then introduced at a gas flow rate of 6L / min for 2 hours to allow the acetylene to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 2nm and a silicon content of 56wt%.

[0065] Fourth step: Dissolve graphene oxide and hexadecyltrimethylammonium bromide in deionized water at a mass ratio of 1:2 to obtain a mixed solution, wherein the amount of graphene oxide added is 0.5 wt% of the pre-coated mesoporous silicon carbon material.

[0066] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 4 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 170℃, the outlet temperature is 90℃, and the atomizer frequency is 220Hz.

[0067] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 10 L / min, and raise the temperature to 500°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with hexadecyltrimethylammonium bromide. Then raise the temperature to 550°C at a heating rate of 4°C / min, introduce acetylene gas at a flow rate of 10 L / min, and treat for 5 hours to pyrolyze the acetylene to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0068] The prepared multilayer carbon-coated mesoporous silicon-carbon anode material was then subjected to the following tests:

[0069] 1. The specific surface area was characterized according to the methods in the national standard GB / T 38823-2020 "Silicon Carbon".

[0070] 2. An electrode sheet was prepared by using multilayer carbon-coated mesoporous silicon-carbon anode material, and a coin cell was assembled and tested using this electrode sheet, as detailed below:

[0071] First, carbon-phosphorus composite material, conductive additive carbon black, and binder styrene-butadiene rubber are added to deionized water in a mass ratio of 95:2:3 and mixed evenly. The mixture is then prepared into a slurry using a pulping machine, coated onto copper foil, and dried at 80°C for 12 hours to obtain the electrode sheet.

[0072] Then, the electrode sheets are divided into those that have undergone roll forming and those that have not, with a roll forming strength of 100 MPa.

[0073] Subsequently, coin cells were assembled using unrolled and rolled electrodes as negative electrodes, lithium foil as positive electrodes, 1 mol / L LiPF6 (solvent being ethylene carbonate and diethyl carbonate in a 1:1 volume ratio) as the electrolyte, and a Ce L Gard 2400 microporous polypropylene membrane as the separator. The electrochemical performance of the coin cells was tested using a Blue Electric CT2001A battery tester, measuring the initial discharge specific capacity and first-cycle coulombic efficiency under the following conditions: charge / discharge voltage range of 0.005V to 2.0V, and charge / discharge rate of 0.1C. Simultaneously, the rate performance of the coin cells was tested as a percentage of the discharge specific capacity measured at 1C current density divided by the discharge specific capacity measured at 0.1C.

[0074] In addition, a full-charge expansion test was conducted on the rolled coin cells. The specific test process was as follows: the thickness D1 of the rolled electrode was tested, and then the thickness D2 of the electrode was tested when the coin cell was fully charged to 100% SOC (i.e., the battery was fully charged). Then the full-charge expansion rate was calculated as (D2-D1) / D1*100%.

[0075] 3. An electrode sheet was prepared by using multilayer carbon-coated mesoporous silicon-carbon anode material, and a pouch cell was assembled and tested using this electrode sheet, as detailed below:

[0076] Fabrication of the soft-pack battery: A multilayer carbon-coated mesoporous silicon-carbon anode material was mixed with commercial artificial graphite to form a 500 mAh / g capacity anode active material. The anode active material, styrene-butadiene rubber binder, conductive agent SP, and deionized water solvent were dispersed and slurried at a mass ratio of 95.5:4:0.5:300. The anode sheet was obtained through coating, drying, rolling, and slitting processes. For the cathode, NCM811 was used. The cathode material, styrene-butadiene rubber binder, conductive agent SP, and N-methylpyrrolidone solvent were dispersed and slurried at a mass ratio of 92:5:3:200. The cathode sheet was obtained through coating, drying, rolling, and slitting processes. A 2Ah soft-pack battery was prepared using 1 mol / L LiPF6 (solvent being ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte and a Celgard 2400 microporous polypropylene membrane as the separator.

[0077] Cyclic testing: The prepared pouch cells were subjected to charge-discharge cycles under the following conditions: temperature 25±3℃, charge-discharge cut-off voltage 2.5-4.2V, and charge-discharge rate of 1C during the cycle. The capacity retention rate of the pouch cells after 500 cycles was tested.

[0078] Example 2

[0079] The first step is to crush 5 kg of resin-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 12 μm and place it in a deposition furnace.

[0080] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 20 L / min to form a nitrogen atmosphere. The temperature is increased to 550°C at a heating rate of 2°C / min. Then, silane is introduced at a gas flow rate of 15 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 3 hours.

[0081] The third step involves stopping the introduction of silane and raising the temperature to 600°C at a rate of 2°C / min. Propylene is then introduced at a gas flow rate of 10L / min for 1 hour, allowing the propylene to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 1nm and a silicon content of 52wt%.

[0082] Fourth step: Dissolve graphene oxide and polypyrrole in N,N-dimethylformamide at a mass ratio of 1:4 to obtain a mixed solution, wherein the amount of graphene oxide added is 0.2 wt% of the pre-coated mesoporous silicon carbon material.

[0083] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 5 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 250℃, the outlet temperature is 160℃, and the atomizer frequency is 200Hz.

[0084] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 10 L / min, and raise the temperature to 500°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with polypyrrole. Then raise the temperature to 550°C at a heating rate of 5°C / min, introduce propylene gas at a flow rate of 10 L / min, and treat for 6 hours to pyrolyze the propylene to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0085] The testing process is the same as in Example 1.

[0086] Example 3

[0087] The first step is to crush 5 kg of pitch-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 14 μm and place it in a deposition furnace.

[0088] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 15 L / min to form a nitrogen atmosphere. The temperature is increased to 550°C at a heating rate of 5°C / min. Then, gaseous propane is introduced at a gas flow rate of 15 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 5 hours.

[0089] The third step involves stopping the flow of gaseous propane silane and increasing the temperature to 550°C at a rate of 2°C / min. Ethane is then introduced at a flow rate of 10L / min for 3 hours to allow the ethane to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 4nm and a silicon content of 58wt%.

[0090] Fourth step: Dissolve graphene oxide and polydiallyldimethylammonium chloride in deionized water at a mass ratio of 1:2 to obtain a mixed solution, wherein the amount of graphene oxide added is 3 wt% of the pre-coated mesoporous silicon carbon material.

[0091] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 6 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, and the atomizer frequency is 240Hz.

[0092] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 15 L / min, and raise the temperature to 550°C at a heating rate of 5°C / min. Treat for 1 hour to reduce the graphene oxide and form a nitrogen-doped graphene layer with polydiallyldimethylammonium chloride. Then raise the temperature to 600°C at a heating rate of 2°C / min, introduce ethane gas at a flow rate of 10 L / min, and treat for 10 hours to allow the ethane to pyrolyze and form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0093] The testing process is the same as in Example 1.

[0094] Example 4

[0095] The first step is to crush 5 kg of graphite-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 6 μm and place it in a deposition furnace.

[0096] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 25 L / min to form a nitrogen atmosphere. The temperature is increased to 550°C at a heating rate of 5°C / min. Then, gaseous trichlorosilane is introduced at a gas flow rate of 15 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 4 hours.

[0097] The third step involves stopping the flow of gaseous trichlorosilane and raising the temperature to 600°C at a rate of 5°C / min. Propane is then introduced at a gas flow rate of 10L / min for 2 hours to allow the propane to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 3nm and a silicon content of 55wt%.

[0098] Fourth step: Dissolve graphene oxide and polyaniline in N,N-dimethylformamide at a mass ratio of 1:2 to obtain a mixed solution, wherein the amount of graphene oxide added is 1 wt% of the pre-coated mesoporous silicon carbon material.

[0099] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 6 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 250℃, the outlet temperature is 160℃, and the atomizer frequency is 200Hz.

[0100] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 15 L / min, and raise the temperature to 550°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with polyaniline. Then raise the temperature to 600°C at a heating rate of 7°C / min, introduce propane at a flow rate of 10 L / min, and treat for 4 hours to pyrolyze the propane to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0101] The testing process is the same as in Example 1.

[0102] Example 5

[0103] The first step is to crush 5 kg of biomass-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 10 μm and place it in a deposition furnace.

[0104] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 15 L / min to form a nitrogen atmosphere. The temperature is increased to 520°C at a heating rate of 5°C / min. Then, silane is introduced at a gas flow rate of 10 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 3 hours.

[0105] The third step is to stop the introduction of silane, raise the temperature to 600°C at a heating rate of 5°C / min, and introduce methane at a gas flow rate of 6L / min for 3 hours to allow the methane to pyrolyze and form the first carbon layer, thus obtaining a pre-coated mesoporous silicon carbon material with a thickness of 2nm and a silicon content of 49wt% in the mesoporous silicon carbon material.

[0106] Fourth step: Dissolve graphene oxide and polyethyleneimine in isopropanol at a mass ratio of 1:5 to obtain a mixed solution, wherein the amount of graphene oxide added is 1 wt% of the pre-coated mesoporous silicon carbon material.

[0107] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 4 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 180℃, the outlet temperature is 90℃, and the atomizer frequency is 220Hz.

[0108] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 15 L / min, and raise the temperature to 500°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with polyethyleneimine. Then raise the temperature to 600°C at a heating rate of 8°C / min, introduce methane gas at a flow rate of 10 L / min, and treat for 5 hours to allow the methane to pyrolyze and form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0109] The testing process is the same as in Example 1.

[0110] Example 6

[0111] The first step is to crush 5 kg of resin-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 11 μm and place it in a deposition furnace.

[0112] In the second step, argon gas is introduced into the deposition furnace at a gas flow rate of 15 L / min to form an argon atmosphere. The temperature is increased to 550°C at a heating rate of 5°C / min. Then, silane is introduced at a gas flow rate of 15 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 4 hours.

[0113] The third step involves stopping the introduction of silane and raising the temperature to 600°C at a rate of 5°C / min. Ethylene is then introduced at a gas flow rate of 6L / min for 2 hours, allowing the ethylene to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 3nm and a silicon content of 57wt%.

[0114] Fourth step: Dissolve graphene oxide and hexadecyltrimethylammonium chloride in deionized water at a mass ratio of 1:5 to obtain a mixed solution, wherein the amount of graphene oxide added is 0.5 wt% of the pre-coated mesoporous silicon carbon material.

[0115] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 4 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 165℃, the outlet temperature is 85℃, and the atomizer frequency is 220Hz.

[0116] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 10 L / min, and raise the temperature to 500°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with hexadecyltrimethylammonium chloride. Then raise the temperature to 600°C at a heating rate of 9°C / min, introduce ethylene gas at a flow rate of 10 L / min, and treat for 5 hours to pyrolyze the ethylene to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0117] The testing process is the same as in Example 1.

[0118] Example 7

[0119] The first step is to crush 5 kg of pitch-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 5 μm and place it in a deposition furnace.

[0120] In the second step, nitrogen gas is introduced into the deposition furnace at a gas flow rate of 30 L / min to form a nitrogen atmosphere. The temperature is increased to 450°C at a heating rate of 1°C / min. Then, silane is introduced at a gas flow rate of 2 L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 10 hours.

[0121] The third step involves stopping the introduction of silane and increasing the temperature to 500°C at a rate of 1°C / min. Acetylene is then introduced at a gas flow rate of 20L / min for 5 hours to allow the acetylene to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 4nm and a silicon content of 60wt%.

[0122] Fourth step: Dissolve graphene oxide and hexadecyltrimethylammonium bromide in deionized water at a mass ratio of 1:10 to obtain a mixed solution, wherein the amount of graphene oxide added is 2 wt% of the pre-coated mesoporous silicon carbon material.

[0123] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 1 hour, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 140℃, the outlet temperature is 50℃, and the atomizer frequency is 300Hz.

[0124] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 30 L / min, and raise the temperature to 350°C at a heating rate of 1°C / min. Treat for 5 hours to reduce the graphene oxide and form a nitrogen-doped graphene layer with hexadecyltrimethylammonium bromide. Then raise the temperature to 500°C at a heating rate of 3°C / min, introduce acetylene gas at a flow rate of 2 L / min, and treat for 20 hours to pyrolyze the acetylene to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0125] The testing process is the same as in Example 1.

[0126] Example 8

[0127] The first step is to crush 5 kg of graphite-based mesoporous carbon material into a mesoporous carbon matrix with a D50 of 20 μm and place it in a deposition furnace.

[0128] In the second step, argon gas is introduced into the deposition furnace at a gas flow rate of 2L / min to form an argon atmosphere. The temperature is increased to 600℃ at a heating rate of 10℃ / min. Then, trichlorosilane is introduced at a gas flow rate of 30L / min to deposit nano-silicon particles on the mesoporous carbon matrix for 1 hour.

[0129] The third step involves stopping the flow of trichlorosilane and increasing the temperature to 700°C at a rate of 10°C / min. Propane is then introduced at a gas flow rate of 1L / min for 0.5 hours to allow the propane to pyrolyze and form the first carbon layer, resulting in a pre-coated mesoporous silicon-carbon material with a thickness of 1nm and a silicon content of 52wt%.

[0130] Fourth step: Dissolve graphene oxide and polyaniline in N,N-dimethylformamide at a mass ratio of 1:1 to obtain a mixed solution, wherein the amount of graphene oxide added is 10 wt% of the pre-coated mesoporous silicon carbon material.

[0131] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the mixed solution, mixing thoroughly for 10 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 260℃, the outlet temperature is 170℃, and the atomizer frequency is 120Hz.

[0132] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary furnace, introduce argon gas at a flow rate of 2 L / min, and raise the temperature to 400°C at a heating rate of 10°C / min. Treat for 1 hour to reduce the graphene oxide and form a nitrogen-doped graphene layer with polyaniline. Then raise the temperature to 700°C at a heating rate of 10°C / min, introduce propane at a flow rate of 30 L / min, and treat for 1 hour to pyrolyze the propane to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0133] The testing process is the same as in Example 1.

[0134] Comparative Example 1

[0135] Steps one through three are the same as in Example 1.

[0136] The fourth step involves dissolving graphene oxide in deionized water to obtain a solution, wherein the amount of graphene oxide added is 0.5 wt% of the pre-coated mesoporous silicon carbon material.

[0137] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the solution, mixing thoroughly for 4 hours, and then performing spray drying to obtain graphene oxide / pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 170℃, the outlet temperature is 90℃, and the atomizer frequency is 220Hz.

[0138] Step 6: Place the graphene oxide / pre-coated mesoporous silicon carbon material in a rotary kiln, introduce nitrogen gas at a flow rate of 10 L / min, and raise the temperature to 500°C at a heating rate of 5°C / min. Treat for 2 hours to reduce the graphene oxide to form a graphene layer. Then raise the temperature to 550°C at a heating rate of 4°C / min, introduce acetylene gas at a flow rate of 10 L / min, and treat for 5 hours to pyrolyze the acetylene to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material.

[0139] The testing process is the same as in Example 1.

[0140] Comparative Example 2

[0141] Steps one through three are the same as in Example 1.

[0142] The fourth step involves dissolving hexadecyltrimethylammonium bromide in deionized water to obtain a solution, wherein the amount of hexadecyltrimethylammonium bromide added is 1 wt% of the pre-coated mesoporous silica carbon material.

[0143] The fifth step involves adding the pre-coated mesoporous silicon carbon material to the solution, mixing thoroughly for 4 hours, and then performing spray drying to obtain the pre-coated mesoporous silicon carbon material. The inlet temperature of the spray dryer is 170℃, the outlet temperature is 90℃, and the atomizer frequency is 220Hz.

[0144] The sixth step involves placing the pre-coated mesoporous silicon-carbon material in a rotary kiln, introducing nitrogen gas at a flow rate of 10 L / min, and raising the temperature to 500°C at a heating rate of 5°C / min for 2 hours. This process removes the active groups of hexadecyltrimethylammonium bromide, forming a small amount of nitrogen-containing carbon layer and nitrogen-containing oxides. Subsequently, the temperature is raised to 550°C at a heating rate of 4°C / min, and acetylene is introduced at a flow rate of 10 L / min for 5 hours. This process allows the acetylene to pyrolyze and form a second carbon layer, thereby obtaining the mesoporous silicon-carbon anode material.

[0145] The testing process is the same as in Example 1.

[0146] Comparative Example 3

[0147] Steps one through three are the same as in Example 1.

[0148] The fourth step involves placing the pre-coated mesoporous silicon-carbon material in a rotary kiln, introducing nitrogen gas at a flow rate of 10 L / min, then raising the temperature to 550°C at a heating rate of 4°C / min, and introducing acetylene gas at a flow rate of 10 L / min for 8 hours to allow the acetylene to pyrolyze and form a second carbon layer, thereby obtaining a two-layer carbon-coated mesoporous silicon-carbon anode material.

[0149] The testing process is the same as in Example 1.

[0150] Table 1 summarizes the physicochemical parameters and coin cell performance data of the multilayer carbon-coated mesoporous silicon-carbon anode materials prepared in Examples 1-8 and Comparative Examples 1-3 of this invention.

[0151]

[0152]

[0153] Table 1

[0154] As shown in Table 1, the specific surface area of ​​the multilayer carbon-coated mesoporous silicon-carbon anode materials prepared in Examples 1-8 of this invention is smaller than that of Comparative Examples 1-3. However, the coin cells of Examples 1-8 of this invention show significantly better performance than Comparative Examples 1-3 in terms of first discharge specific capacity, first-cycle coulombic efficiency of the electrode before and after rolling, rate capability (1C / 0.1C), and full-charge expansion rate. This is because the coating layer of Examples 1-8 of this invention consists of three layers. The first carbon layer plays a role in alleviating the volume expansion problem of nano-silicon and preventing a small amount of electrolyte from contacting the nano-silicon particles. The second nitrogen-doped graphene layer can improve the pressure resistance and prevent the particles from breaking under high pressure, which would affect the electronic conductivity. At the same time, it can also act as a barrier layer to effectively prevent the gaseous carbon of the second carbon layer from entering the pores and retain the expansion space of the nano-silicon particles. The third layer, namely the second carbon layer, can significantly improve the conductivity of the material, reduce the specific surface area, and further reduce the risk of nano-silicon particle expansion and direct contact with the electrolyte.

[0155] Table 2 summarizes the cycle performance data of the pouch cells prepared by the multilayer carbon-coated mesoporous silicon-carbon anode materials in Examples 1-8 and Comparative Examples 1-3 of this invention.

[0156] serial number Initial cycle capacity retention (%) Capacity retention rate (%) after 500 cycles Example 1 100 97.3 Example 2 100 96.5 Example 3 100 97.8 Example 4 100 96.6 Example 5 100 97.2 Example 6 100 96.4 Example 7 100 96.2 Example 8 100 97.4 Comparative Example 1 100 89.8 Comparative Example 2 100 85.1 Comparative Example 3 100 87.3

[0157] Table 2

[0158] As shown in Table 2, the soft-pack batteries made from the silicon-carbon anode materials provided in Examples 1-8 of the present invention exhibit significantly better cycle performance than those in Comparative Examples 1-3. This is because the anode materials used in Examples 1-8 of the present invention have undergone multi-layer carbon coating and the matrix is ​​a mesoporous carbon material, which results in a low expansion rate of the anode sheet during cycling and demonstrates excellent cycle stability.

[0159] Combination Figure 3 and Figure 4 It can be seen that the graphene oxide / pre-coated mesoporous silicon carbon material prepared in Example 1 of the present invention has a tighter and more uniform coating of graphene oxide on the surface of the mesoporous silicon carbon material due to the modification of graphene oxide by the positively charged modifier.

[0160] Figure 5 It can be seen that the surface coating of the multilayer carbon-coated mesoporous silicon-carbon anode material is very dense and uniform. This is conducive to the formation of a uniform SE I layer in the multilayer carbon-coated mesoporous silicon-carbon anode material during cycling, reducing the occurrence of side reactions, and thus improving the first coulombic efficiency and cycle performance of the battery.

[0161] Figure 6The graph shows the charge-discharge curves of the coin cell assembled from the multilayer carbon-coated mesoporous silicon-carbon anode material prepared in Example 1 of this invention after rolling. It can be seen that the coin cell prepared from the mesoporous silicon-carbon anode material has a discharge specific capacity of up to 2038.1 mAh / g at a voltage of 2V, and a first-week coulombic efficiency of 93.9%. This indicates that the multilayer carbon-coated mesoporous silicon-carbon anode material has good voltage resistance and the first-week coulombic efficiency decreases less after rolling.

[0162] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a multilayer carbon-coated mesoporous silicon-carbon anode material, characterized in that, The preparation method includes: Under a protective atmosphere, silicon source gas is introduced into a reaction vessel containing a mesoporous carbon matrix, and the silicon source gas is vapor-deposited on the mesoporous carbon matrix to obtain a mesoporous silicon-carbon material. Stop the supply of silicon source gas, adjust the temperature of the reaction vessel, and introduce a first carbon source gas into the reaction vessel so that the first carbon source gas is pyrolyzed to form a first carbon layer, thereby obtaining a pre-coated mesoporous silicon-carbon material. After dissolving graphene oxide and a positively charged modifier in a solvent at a predetermined mass ratio, a mixed solution is obtained. The pre-coated mesoporous silicon carbon material is added to the mixed solution and mixed evenly, and then spray-dried to obtain graphene oxide / pre-coated mesoporous silicon carbon material. A protective gas is introduced into a reaction vessel containing the graphene oxide / pre-coated mesoporous silicon carbon material, and the reaction vessel is heated so that the graphene oxide is reduced and forms a nitrogen-doped graphene layer with a positively charged modifier. Then, the temperature of the reaction vessel is adjusted, and a second carbon source gas is introduced into the reaction vessel so that the second carbon source gas is pyrolyzed to form a second carbon layer, thereby obtaining a multilayer carbon-coated mesoporous silicon carbon anode material; the second carbon source gas is the same as the first carbon source gas.

2. The preparation method according to claim 1, characterized in that, The mesoporous carbon matrix has a particle size D50 of 5 μm-20 μm and a specific surface area of ​​1600 m². 2 / g-2400m 2 / g, average pore size of 2nm-10nm, pore volume of 0.5cm³ 3 / g-3.5cm 3 / g, with a porosity of 30%-80% and a mesoporous content of 25%-70%.

3. The preparation method according to claim 1, characterized in that, The silane gas includes one or more of silane, disilane, gaseous propane, and gaseous trichlorosilane; the flow rate of the silicon source gas is 2L / min-30L / min; the specific conditions for the vapor deposition are: heating to 450℃-600℃ at a heating rate of 1℃ / min-10℃ / min, and continuing for 1 hour-10 hours.

4. The preparation method according to claim 1, characterized in that, The first carbon source gas includes one or more of methane, ethane, ethylene, acetylene, propane, and propylene; the flow rate of the first carbon source gas is 1 L / min to 20 L / min; the specific conditions for the formation of the first carbon layer are: heating to 500℃ to 700℃ at a heating rate of 1℃ / min to 10℃ / min, and continuing for 0.5 hours to 5 hours.

5. The preparation method according to claim 1, characterized in that, The preset mass ratio is 1:1 to 1:10; the proportion of graphene oxide in the mesoporous silicon carbide material is 0.01wt% to 10wt%.

6. The preparation method according to claim 1, characterized in that, The conditions for the spray drying process are: inlet temperature 140℃-260℃, outlet temperature 50℃-170℃, and frequency 120Hz-300Hz.

7. The preparation method according to claim 1, characterized in that, The flow rate of the second carbon source gas is 2 L / min-30 L / min; the formation conditions of the nitrogen-doped graphene layer are: heating to 350℃-550℃ at a heating rate of 1℃ / min-10℃ / min for 1 hour-5 hours; the formation conditions of the second carbon layer are: heating to 500℃-700℃ at a heating rate of 2℃ / min-10℃ / min for 1 hour-20 hours.

8. A multilayer carbon-coated mesoporous silicon-carbon anode material, characterized in that, The multilayer carbon-coated mesoporous silicon-carbon anode material is prepared by any of the preparation methods described in claims 1-7. The multilayer carbon-coated mesoporous silicon-carbon anode material includes: a core and a shell; The core is a mesoporous silicon-carbon material; the mesoporous silicon-carbon material includes a mesoporous carbon matrix and nano-silicon particles deposited in the pores of the mesoporous carbon matrix. The outer shell covers the outside of the core, and the outer shell is a composite carbon layer; the composite carbon layer includes a first carbon layer covering the outside of the core, a nitrogen-doped graphene layer covering the outside of the first carbon layer, and a second carbon layer covering the outside of the graphene layer. The particle size D50 of the multilayer carbon-coated mesoporous silicon-carbon anode material is between 7 μm and 25 μm, and the specific surface area is 1 m². 2 / g-20m 2 / g.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the multilayer carbon-coated mesoporous silicon-carbon negative electrode material as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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