A mixed gas phase segmented coating silicon-carbon negative electrode material, and a preparation method and application thereof

Abstract

This invention relates to a mixed gas-phase segmented coated silicon-carbon anode material, its preparation method, and its application. Under an inert atmosphere, a silicon source is introduced into a reaction chamber, and silicon is uniformly deposited on the surface of a porous carbon matrix to form a silicon-carbon composite material. An organic carbon source is mixed with an inert gas in a specific ratio to perform initial carbon coating on the silicon-carbon composite material, forming an initial carbon coating layer on the surface of the silicon-carbon composite material, thus obtaining a silicon-carbon composite material with an initial carbon coating layer. An oxidizing gaseous carbon source is mixed with an inert gas in a specific ratio to perform a secondary heat treatment on the silicon-carbon composite material with the initial carbon coating layer. The initial carbon coating layer is etched by the oxidizing gaseous carbon source to adjust its structure, and further carbon deposition or adjustment of the carbon layer structure of the silicon-carbon composite material is achieved through the decomposition of the oxidizing gaseous carbon source. This process improves the graphitization degree of the carbon coating layer through carbon layer recombination and structural optimization, resulting in a silicon-carbon anode material optimized by mixed gas-phase segmented coating.

Description

Technical Field

[0001] This invention relates to the field of silicon-carbon anode material technology, and in particular to a mixed gas-phase segmented coated silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] The rapid development of electronic devices and electric vehicles has continuously increased the performance requirements for lithium-ion batteries. As a crucial component of lithium-ion batteries, the performance of the anode material directly affects the battery's energy density and cycle life. Silicon-carbon anode materials, due to their high specific capacity and other advantages, have become one of the current research hotspots.

[0003] In the preparation of silicon-carbon anode materials, carbon coating is an important modification method that can improve the conductivity and structural stability of the materials. Selecting a suitable carbon source for vapor-phase coating is crucial for obtaining high-performance silicon-carbon anode materials. Different gas sources have their own characteristics and advantages as carbon sources. Through research and application of different gas sources, the performance of silicon-carbon anode materials can be further optimized to meet the market demand for personalized customization.

[0004] Currently, there are several technical solutions for gas-phase coating of silicon-carbon anode materials using specific gas sources as carbon sources. For example, there are methods that use acetylene, propylene, propane, etc., as carbon sources and nitrogen or argon as protective gases. By decomposing these organic carbon sources at a certain temperature and forming a carbon coating layer on the surface of the silicon-carbon anode material, the conductivity and cycle stability of the silicon-carbon anode material can be improved to some extent.

[0005] However, using a single gas source as a carbon source for gas-phase coating has some limitations. For example, when methane is used as a carbon source, there may be issues such as high decomposition temperature and the need to improve coating uniformity. Furthermore, different application scenarios place different performance requirements on silicon-carbon anode materials, making it difficult to achieve the preparation of higher-performance silicon-carbon anode materials using existing technologies.

[0006] In summary, existing gas-phase coating methods that use a single gas source as the carbon source have room for improvement. This invention aims to provide a gas-phase coating method that uses different gas sources as carbon sources and adopts segmented gas flow to overcome the shortcomings of existing technologies and improve the overall performance of silicon-carbon anode materials. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing and applying a mixed gas-phase segmented coated silicon-carbon anode material. By introducing organic carbon sources and oxidizing gaseous carbon sources in segments during the coating process, the performance of the carbon coating layer is improved, and the integrity, density, and graphitization of the carbon coating layer are optimized, enhanced, and controllably adjusted. This not only improves the stability of the interface but also effectively enhances the cycle performance and rate performance of the silicon-carbon anode material.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a mixed gas-phase segmented coated silicon-carbon anode material, comprising:

[0009] Step 1: Under the protection of an inert atmosphere, a silicon source is introduced into the reaction chamber. At the set deposition temperature, silicon is uniformly deposited on the surface of a porous carbon matrix by chemical vapor deposition to form a silicon-carbon composite material.

[0010] Step 2: Mix the organic carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform initial carbon coating on the silicon-carbon composite material by chemical vapor deposition to form an initial carbon coating layer on the surface of the silicon-carbon composite material, thereby obtaining a silicon-carbon composite material with an initial carbon coating layer.

[0011] Step 3: Mix the oxidizing gaseous carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform a secondary heat treatment on the silicon-carbon composite material with the initial carbon coating layer. The initial carbon coating layer is etched by the oxidizing gaseous carbon source to adjust its structure. Further carbon deposition or adjustment of the carbon coating layer structure is carried out on the silicon-carbon composite material with the initial carbon coating layer by decomposing the oxidizing gaseous carbon source. In this way, the graphitization degree of the carbon coating layer is improved through carbon layer recombination and structural optimization, and the silicon-carbon anode material after mixed gas phase segmented coating optimization is obtained.

[0012] Preferably, the porous carbon type of the porous carbon matrix includes biomass-based, resin-based, coal-coke-based, and petroleum-based porous carbon materials; the activation method includes physical activation or chemical activation;

[0013] The porous carbon matrix has a particle size (Dv50) ranging from 3 to 20 μm and a specific surface area of ​​200 to 4000 m². 2 / g, total pore volume is 0.2-5cm³ 3 / g, with an average pore size of 1-100nm, a micropore size of 1-2nm, a mesopore size of 2-20nm, a macropore ratio of 0.5%-3%, a micropore ratio of 3%-99%, and a mesopore ratio of 0-80%.

[0014] Preferably, in step 1, the silicon source includes a gaseous silicon source or a liquid silicon source; the gaseous silicon source includes silane and / or silane; the liquid silicon source includes tetraethoxysilane.

[0015] The inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the flow rate of the inert gas is 2-50 L / min;

[0016] The set deposition temperature is 200-1000℃;

[0017] When the silicon source is a gaseous silicon source, the flow rate of the silicon source into the reaction chamber is 2-50 L / min, and the deposition time is 100-500 min;

[0018] When the silicon source is a liquid-phase silicon source, the silicon source is coated onto the porous carbon substrate by impregnation or spraying, and then the porous carbon substrate is placed in the reaction chamber.

[0019] Preferably, in step 2, the flow rate ratio of the organic carbon source to the inert gas is 1:1 to 1:3, the flow rate of the organic carbon source is in the range of 1-30 L / min, the initial carbon coating temperature is 300-1000℃, and the time is 100-1000 min; the organic carbon source includes one or more of acetylene, propylene, or propane.

[0020] Preferably, in step 3, the flow rate ratio of the oxidizing gaseous carbon source to the inert gas is 1:1 to 1:3, the flow rate range of the oxidizing gaseous carbon source is 1-30 L / min, the temperature of the secondary heat treatment is 300-1000℃, and the time is 100-1000 min; the oxidizing gaseous carbon source includes at least carbon dioxide.

[0021] Preferably, the oxidizing gaseous carbon source includes carbon dioxide, and etching the initial carbon coating layer using the oxidizing gaseous carbon source specifically includes:

[0022] C + CO2 → 2CO.

[0023] Preferably, the oxidizing gaseous carbon source includes carbon monoxide and / or carbon dioxide, and further carbon deposition on the silicon-carbon composite material with the initial carbon coating layer is specifically achieved through the decomposition of the oxidizing gaseous carbon source:

[0024] 2CO→2C(solid)+O2; and / or,

[0025] C + CO₂ → 2CO, 2CO → 2C (solid) + O₂.

[0026] Secondly, embodiments of the present invention provide a mixed gas-phase segmented coated silicon-carbon anode material prepared by the preparation method described in the first aspect above.

[0027] Thirdly, embodiments of the present invention provide a negative electrode, comprising a mixed gas-phase segmented coated silicon-carbon negative electrode material prepared by the preparation method described in the first aspect above.

[0028] Fourthly, embodiments of the present invention provide a secondary battery comprising a mixed gas-phase segmented coated silicon-carbon anode material prepared by the preparation method described in the first aspect above.

[0029] The method for preparing mixed gas-phase segmented coated silicon-carbon anode materials provided in this invention involves segmented gas-phase coating using multiple gas sources. By introducing organic carbon sources and oxidizing gaseous carbon sources segmentally during the coating process, the performance of the carbon coating layer is improved, and the carbon layer structure can be adjusted. This optimizes and controllably regulates the integrity, density, and graphitization degree of the carbon coating layer, thereby enhancing interface stability and significantly improving the cycle performance and rate performance of the silicon-carbon anode material. This method offers good process flexibility and adaptability, and has promising application prospects. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for preparing a mixed gas-phase segmented coated silicon-carbon anode material according to an embodiment of the present invention;

[0031] Figure 2 The Raman spectrum of the silicon-carbon anode material provided in Embodiment 1 of the present invention;

[0032] Figure 3 This is a transmission electron microscope (TEM) image of the silicon-carbon anode material provided in Embodiment 1 of the present invention;

[0033] Figure 4 This is a TEM image of the silicon-carbon anode material provided in Embodiment 2 of the present invention;

[0034] Figure 5 The Raman spectrum of the silicon-carbon anode material provided in Comparative Example 1 of this invention;

[0035] Figure 6 This is a TEM image of the silicon-carbon anode material provided in Comparative Example 1 of the present invention;

[0036] Figure 7 This is a TEM image of the silicon-carbon anode material provided in Comparative Example 2 of the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] This invention provides a mixed gas-phase segmented coated silicon-carbon anode material and its preparation method. Figure 1 This is a flowchart of the preparation method of the mixed gas-phase segmented coated silicon-carbon anode material provided in the embodiments of the present invention. The following is in conjunction with... Figure 1 The technical solution of the present invention will be described below.

[0039] like Figure 1 As shown, the preparation method of the mixed gas-phase segmented coated silicon-carbon anode material of the present invention mainly includes the following steps:

[0040] Step 1: Under the protection of an inert atmosphere, a silicon source is introduced into the reaction chamber. At the set deposition temperature, silicon is uniformly deposited on the surface of a porous carbon matrix by chemical vapor deposition to form a silicon-carbon composite material.

[0041] Specifically, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the flow rate of the inert gas is 2-50 L / min.

[0042] Porous carbon matrix types include biomass-based, resin-based, coal-coke-based, and petroleum-based porous carbon materials.

[0043] Activation methods for porous carbon matrices include physical activation and chemical activation. As a framework structure, the porous nature of the porous carbon matrix provides a stable platform for the loading of silicon particles and the deposition of carbon coatings. Physical activation (such as steam treatment at high temperatures) or chemical activation (such as alkali or acid immersion treatment) processes for porous carbon materials can adjust the pore structure, including specific surface area, total pore volume, and pore size distribution, thereby optimizing the distribution of silicon particles and the composite process. Therefore, in the actual implementation of the technical solution of this invention, the activation process of the porous carbon matrix can be controlled to obtain the desired specific surface area and pore size distribution of the porous carbon, thereby increasing the contact area between silicon particles and porous carbon and enhancing the conductivity and stability of the composite material.

[0044] Preferably, the porous carbon matrix of the present invention has a particle size Dv50 ranging from 3 to 20 μm, and may contain fine powder (Dv00 < 1 μm) or not contain fine powder (Dv00 > 1 μm), and a specific surface area of ​​200-4000 m². 2 / g, total pore volume is 0.2-5cm³ 3 / g, with an average pore size of 1-100nm, micropore size of 1-2nm, mesopore size of 2-20nm, macropores accounting for 0.5%-3%, micropores accounting for 3%-99%, and mesopores accounting for 0-80%.

[0045] The silicon source used for silicon deposition can include a gaseous silicon source, such as silane and / or silane, or a liquid silicon source, such as tetraethoxysilane (TEOS). The deposition temperature is set to 200-1000°C.

[0046] When the silicon source is a gaseous silicon source, the flow rate of the silicon source into the reaction chamber is 2-50 L / min, and the deposition time is 100-500 min.

[0047] When the silicon source is a liquid-phase silicon source, the silicon source is coated onto the porous carbon substrate using either an immersion method or a spraying method, and then the porous carbon substrate is placed in the reaction chamber. The immersion method involves immersing the porous carbon substrate in the silicon source solution, ensuring that the solution fully penetrates the porous structure; the spraying method involves using a spraying device to atomize the silicon source solution and uniformly spray it onto the surface of the porous carbon substrate.

[0048] Chemical vapor deposition (CVD) is used to decompose a silicon source at high temperatures, generating silicon that is deposited within a porous carbon matrix. CVD allows for precise control of reaction temperature, gas flow rate, and deposition time, ensuring uniform silicon particle loading and forming a uniformly distributed silicon particle structure within the pores of the porous carbon matrix. This improves the conductivity of the composite material and the unobstructed lithium-ion diffusion path. Furthermore, process control adjusts the silicon particle loading to ensure that the expansion and contraction of silicon does not damage the structure of the carbon matrix.

[0049] Step 2: Mix the organic carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform initial carbon coating on the silicon-carbon composite material by chemical vapor deposition to form an initial carbon coating layer on the surface of the silicon-carbon composite material, thus obtaining a silicon-carbon composite material with an initial carbon coating layer.

[0050] Specifically, the flow rate ratio of organic carbon source to inert gas is 1:1 to 1:3, the flow rate range of organic carbon source is 1-30 L / min, the initial carbon coating temperature is 300-1000℃, and the time is 100-1000 min; the organic carbon source includes one or more of acetylene, propylene, or propane.

[0051] Chemical vapor deposition using organic carbon sources can form a dense carbon layer, improving the coverage of the silicon surface and helping to reduce direct contact between the electrolyte and silicon, thereby reducing irreversible capacity loss caused by the formation of solid electrolyte (SEI) films.

[0052] Step 3: Mix the oxidizing gaseous carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform a secondary heat treatment on the silicon-carbon composite material with the initial carbon coating layer. The initial carbon coating layer is etched by the oxidizing gaseous carbon source to adjust its structure. Further carbon deposition is carried out on the silicon-carbon composite material with the initial carbon coating layer by decomposing the oxidizing gaseous carbon source to adjust the carbon layer structure of the silicon-carbon composite material. In this way, the graphitization degree of the carbon coating layer is improved through carbon layer recombination and structural optimization, and the silicon-carbon anode material after mixed gas phase segmented coating optimization is obtained.

[0053] Specifically, the flow rate ratio of the oxidizing gaseous carbon source to the inert gas is 1:1 to 1:3, the flow rate range of the oxidizing gaseous carbon source is 1-30 L / min, the temperature of the secondary heat treatment is 300-1000℃, and the time is 100-1000 min; the oxidizing gaseous carbon source includes at least carbon dioxide, and may also include carbon monoxide, etc.

[0054] By adjusting the amount of oxidizing gaseous carbon source introduced and the reaction conditions, the carbon surface structure can be finely tuned, further optimizing interfacial contact and gas generation performance, and improving the degree of carbon graphitization, conductivity, and cycle stability.

[0055] Etching the initial carbon coating layer using an oxidizing gaseous carbon source specifically includes:

[0056] C + CO2 → 2CO.

[0057] The carbon layer typically contains disordered carbon atoms or amorphous carbon, which are highly chemically reactive and more readily react with oxidizing carbon source gases (such as CO2). When the disordered carbon is oxidized and removed, the remaining carbon layer is mainly composed of more ordered graphitized carbon, thereby increasing the overall graphitization degree.

[0058] In addition, the oxidative etching process makes it easier for carbon atoms to migrate and rearrange at high temperatures, which can further promote graphitization.

[0059] Further carbon deposition on silicon-carbon composite materials with an initial carbon coating by decomposing an oxidizing gaseous carbon source specifically includes:

[0060] 2CO → C (solid) + CO2; and / or,

[0061] C + CO₂ → 2CO, 2CO → 2C (solid) + O₂.

[0062] When oxidizing carbon source gases (such as CO2 or CO) react with carbon layers, they can generate new carbon-carbon bond rearrangements, eliminating defects within the carbon layers (such as lone pairs of electrons and broken bonds). This process transforms the crystal structure within the carbon layers towards a higher degree of graphitization. This process forms a more ordered carbon coating layer on top of the original carbon coating layer through decomposition.

[0063] Furthermore, at high temperatures, carbon atoms gain enough energy to overcome the energy barrier of lattice defects or disordered arrangement, gradually rearranging themselves into graphitized carbon with a hexagonal honeycomb structure. Simultaneously with the gas-phase reaction, the atomic structure on the carbon layer surface tends towards order, thereby increasing the degree of graphitization.

[0064] Furthermore, gas reactions help remove impurities from the carbon layer that could affect the graphitization process. Purifying the carbon layer can also further enhance its graphitization tendency.

[0065] Through the above process, the disordered structure of the carbon layer is effectively optimized, gradually forming a higher proportion of graphitized regions. This highly graphitized carbon material exhibits higher conductivity, lower interfacial impedance, and superior mechanical and chemical stability, thus yielding a silicon-carbon anode material optimized through mixed gas-phase segmented coating. Simultaneously, the increased graphitization degree and optimized pore and carbon layer structure enhance the material's structural stability, thereby reducing volume expansion and structural damage of the silicon-carbon anode during charge and discharge processes, which is beneficial for extending the battery's cycle life.

[0066] The method for preparing mixed gas-phase segmented coated silicon-carbon anode materials provided in this invention involves segmented gas-phase coating using multiple gas sources. By introducing organic carbon sources and oxidizing gaseous carbon sources segmentally during the coating process, the performance of the carbon coating layer is improved, and the porous structure can be adjusted. This optimizes and controllably regulates the integrity, density, and graphitization degree of the carbon coating layer, thereby enhancing interface stability and significantly improving the cycle performance and rate performance of the silicon-carbon anode material. This method offers good process flexibility and adaptability, and has promising application prospects.

[0067] 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.

[0068] Example 1

[0069] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0070] The second step involves placing 2 kg of silicon-carbon anode material semi-finished product into a coating furnace, introducing nitrogen gas at a flow rate of 12 L / min for protection, raising the temperature of the deposition furnace to 650°C at a heating rate of 10°C / min, and stabilizing it for 30 min; then introducing acetylene, with the flow rate ratio of protective gas to organic carbon source being nitrogen:acetylene = 12 L / min:12 L / min, and holding it at that temperature for 240 min.

[0071] The third step involves stopping the introduction of acetylene and introducing carbon dioxide. The flow rate ratio of the protective gas and the oxidizing gaseous carbon source is nitrogen:carbon dioxide = 12L / min:6L / min. The holding time is 120min. The material is then cooled and discharged to obtain the mixed gas-phase segmented coated silicon-carbon anode material of this embodiment.

[0072] Example 2

[0073] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0074] The second step involves placing 2 kg of silicon-carbon anode material semi-finished product into a coating furnace, introducing nitrogen gas at a flow rate of 12 L / min for protection, raising the temperature of the deposition furnace to 650°C at a heating rate of 10°C / min, and stabilizing it for 30 min; then introducing acetylene, with the flow rate ratio of protective gas to organic carbon source being nitrogen:acetylene = 12 L / min:12 L / min, and holding it at that temperature for 240 min.

[0075] The third step involves stopping the introduction of acetylene and introducing carbon monoxide and carbon dioxide. The flow rate ratio of the protective gas and the oxidizing gaseous carbon source is nitrogen:carbon monoxide:carbon dioxide = 12L / min:4L / min:2L / min. The holding time is 120min. The material is then cooled and discharged to obtain the mixed gas-phase segmented coated silicon-carbon anode material of this embodiment.

[0076] Example 3

[0077] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0078] The second step involves placing 2 kg of silicon-carbon anode material semi-finished product into a coating furnace, introducing nitrogen gas at a flow rate of 12 L / min for protection, raising the temperature of the deposition furnace to 650°C at a heating rate of 10°C / min, and stabilizing it for 30 min; then introducing propylene, with the flow rate ratio of protective gas to organic carbon source being nitrogen:propylene = 12 L / min: 12 L / min, and holding it at that temperature for 240 min.

[0079] The third step involves stopping the flow of propylene and introducing carbon dioxide. The flow rate ratio of the protective gas and the oxidizing gaseous carbon source is nitrogen:carbon dioxide = 12L / min:4L / min. The holding time is 180min. The material is then cooled and discharged to obtain the mixed gas-phase segmented coated silicon-carbon anode material of this embodiment.

[0080] Example 4

[0081] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0082] The second step involves placing 2 kg of silicon-carbon anode material semi-finished product into a coating furnace, introducing nitrogen gas at a flow rate of 12 L / min for protection, raising the temperature of the deposition furnace to 650°C at a heating rate of 10°C / min, and stabilizing it for 30 min; then introducing propylene, with the flow rate ratio of protective gas to organic carbon source being nitrogen:propylene = 12 L / min: 12 L / min, and holding it at that temperature for 240 min.

[0083] The third step involves stopping the flow of propylene and introducing carbon monoxide and carbon dioxide. The flow rate ratio of the protective gas and the oxidizing gaseous carbon source is nitrogen:carbon monoxide:carbon dioxide = 12L / min:2L / min:2L / min. The holding time is 180min. The material is then cooled and discharged to obtain the mixed gas-phase segmented coated silicon-carbon anode material of this embodiment.

[0084] Comparative Example 1

[0085] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0086] The second step involves placing 2 kg of the silicon-carbon anode material semi-finished product into a coating furnace. Nitrogen gas is introduced at a flow rate of 12 L / min for protection. The furnace temperature is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Acetylene is then introduced, with the flow rate ratio of the protective gas to the organic carbon source being nitrogen:acetylene = 12 L / min:12 L / min. The holding time is 240 min. The material is then cooled and discharged to obtain the gas-phase coated silicon-carbon anode material of this comparative example.

[0087] Comparative Example 2

[0088] The first step involves adding 5 kg of porous carbon material with a mesoporous content of 70% into a deposition furnace. Nitrogen gas is introduced at a flow rate of 10 L / min for protection. The temperature of the deposition furnace is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, silane and nitrogen gas are introduced at a gas flow rate ratio of 10 L / min:10 L / min and held at that temperature for 300 min. After cooling, the material is discharged to obtain a carbon / silicon composite material with deposited nano-silicon particles, which is the semi-finished silicon-carbon anode material.

[0089] The second step involves placing 2 kg of the silicon-carbon anode material semi-finished product into a coating furnace. Nitrogen gas is introduced at a flow rate of 12 L / min for protection. The furnace temperature is raised to 650°C at a heating rate of 10°C / min and then stabilized for 30 min. Next, propylene is introduced, with the flow rate ratio of the protective gas to the organic carbon source being nitrogen:propylene = 12 L / min: 12 L / min. The holding time is 240 min. The material is then cooled and discharged to obtain the vapor-phase coated silicon-carbon anode material of this comparative example.

[0090] The coated silicon-carbon anode materials prepared in the above embodiments and comparative examples were used as anode materials for lithium-ion batteries. Coin cells and pouch cells were assembled, and rate performance, cycle performance, and gas generation were tested.

[0091] 1. Assembly of button cell half-cells:

[0092] The coated silicon-carbon composite anode material was used as the cathode material for a coin cell lithium-ion half-cell, and the anode material was a lithium metal sheet. The rate performance of the assembled coin cell half-cell was then tested.

[0093] Coin cell rate testing conditions: Test voltage window: 0.005V-1.5V; Test rates are 0.1C, 0.2C, 0.5C, 1.0C and 2.0C respectively; Test temperature is 25±1℃; Test equipment: Blue Battery Test System; The assembly sequence of coin cell is: positive electrode shell → electrode plate → separator → steel plate → spring plate → negative electrode shell.

[0094] Table 1 compares the rate performance of coin-type lithium-ion half-cells in the examples and comparative examples.

[0095]

[0096] As can be seen from the rate performance comparison data of the examples and comparative examples in Table 1, the silicon-carbon anode using mixed gas-phase segmented coating has better capacity performance at different rates than the silicon-carbon anode using acetylene or propylene as a single gas-phase carbon source.

[0097] 2. Assembly of pouch batteries:

[0098] A coated silicon-carbon anode material and graphite were mixed and compounded to achieve a specific capacity of 500 mAh / g, which was then used as the anode of a pouch cell. This pouch cell was then assembled with NCM811 cathode material. The anode sheet, separator, and cathode sheet were alternately stacked to form the battery cell. The cell was packaged according to conventional pouch cell assembly methods, and an electrolyte—a 1 mol / L solution of ethylene carbonate (EC) / dimethyl carbonate (DEC) of LiPF6 (volume ratio 1:1)—was injected into the packaged cell. The pouch cell was then subjected to cycle performance testing.

[0099] Cyclic performance test conditions: Pack capacity: 2Ah; Cathode material: NCM811; Anode material: a composite material of silicon-carbon anode material and graphite, fixed to 0.8V 500mAh / g; Test temperature: 25℃±1℃; Test cycle: 300 cycles; Test equipment: Blue Battery Test System.

[0100] Table 2 shows the comparison data of cycle performance of the pouch batteries in the examples and comparative examples.

[0101]

[0102] As can be seen from the comparison data of cycle performance of the pouch cells in Table 2 of the embodiments and comparative examples, the capacity retention rate of the silicon-carbon anode using mixed gas phase segmented coating is better than that of the silicon-carbon anode using acetylene or propylene as a gas phase carbon source after 300 cycles.

[0103] 3. Gas generation test conditions: Prepare a slurry with a solid content of 40% by mixing an aqueous solvent (sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 1:1 by volume) with silicon-carbon anode material. Seal the slurry in an aluminum-plastic film and let it stand for a period of time. Then immerse the aluminum-plastic film in silicone oil. Use the water displacement method to test the volume expansion rate after 24 hours and 48 hours. The temperature is kept constant at 60℃ during the test.

[0104] Table 3 shows the gas production comparison data of the slurry in the examples and comparative examples.

[0105]

[0106] As can be seen from the comparison data of gas production of the slurry in the examples and comparative examples in Table 3, the gas production of silicon-carbon anodes using mixed gas phase segmented coating is less than that of silicon-carbon anodes coated with acetylene or propylene as a single gas phase carbon source.

[0107] The above three comparisons further demonstrate that mixed gas-phase segmented coating can improve the integrity, density, and graphitization of the carbon coating layer, thereby improving gas production in silicon-carbon anode materials and enhancing their rate performance and cycle performance.

[0108] 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 hybrid gas-phase segmented-coated silicon-carbon anode material, characterized in that, The preparation method includes: Step 1: Under the protection of an inert atmosphere, a silicon source is introduced into the reaction chamber. At the set deposition temperature, silicon is uniformly deposited on the surface of a porous carbon matrix by chemical vapor deposition to form a silicon-carbon composite material. Step 2: Mix the organic carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform initial carbon coating on the silicon-carbon composite material by chemical vapor deposition to form an initial carbon coating layer on the surface of the silicon-carbon composite material, thereby obtaining a silicon-carbon composite material with an initial carbon coating layer. Step 3: Mix the oxidizing gaseous carbon source with an inert gas in a certain proportion and introduce it into the reaction chamber. At a set temperature, perform a secondary heat treatment on the silicon-carbon composite material with the initial carbon coating layer. The initial carbon coating layer is etched by the oxidizing gaseous carbon source to adjust its structure. Further carbon deposition or adjustment of the carbon coating structure of the silicon-carbon composite material with the initial carbon coating layer is carried out by the decomposition of the oxidizing gaseous carbon source. In this way, the graphitization degree of the carbon coating layer is improved through carbon layer recombination and structural optimization, and the silicon-carbon anode material after mixed gas phase segmented coating optimization is obtained.

2. The production method according to claim 1, characterized by, The porous carbon matrix includes porous carbon types such as biomass-based, resin-based, coal-coke-based, and petroleum-based porous carbon materials; the activation methods include physical activation or chemical activation; The particle size Dv50 of the porous carbon matrix ranges from 3 to 20 μm, the specific surface area ranges from 200 to 4000 m 2 / g, and the total pore volume ranges from 0.2 to 5 cm 3 / g, the average pore size ranges from 1 to 100 nm, the micropore size ranges from 1 to 2 nm, the mesopore size ranges from 2 to 20 nm, the macropore proportion ranges from 0.5% to 3%, the micropore proportion ranges from 3% to 99%, and the mesopore proportion ranges from 0 to 80%.

3. The preparation method according to claim 1, characterized in that, In step 1, the silicon source includes a gaseous silicon source or a liquid silicon source; the gaseous silicon source includes silane and / or silane; the liquid silicon source includes tetraethoxysilane. The inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the flow rate of the inert gas is 2-50 L / min; The set deposition temperature is 200-1000℃; When the silicon source is a gaseous silicon source, the flow rate of the silicon source into the reaction chamber is 2-50 L / min, and the deposition time is 100-500 min; When the silicon source is a liquid-phase silicon source, the silicon source is coated onto the porous carbon substrate by impregnation or spraying, and then the porous carbon substrate is placed in the reaction chamber.

4. The method of claim 1, wherein, In step 2, the flow rate ratio of the organic carbon source to the inert gas is 1:1 to 1:3, the flow rate of the organic carbon source is in the range of 1-30 L / min, the initial carbon coating temperature is 300-1000℃, and the time is 100-1000 min; the organic carbon source includes one or more of acetylene, propylene, or propane.

5. The preparation method according to claim 1, characterized in that, In step 3, the flow rate ratio of the oxidizing gaseous carbon source to the inert gas is 1:1 to 1:3, the flow rate range of the oxidizing gaseous carbon source is 1-30 L / min, the temperature of the secondary heat treatment is 300-1000℃, and the time is 100-1000 min; the oxidizing gaseous carbon source includes at least carbon dioxide.

6. The preparation method according to claim 1, characterized in that, The oxidizing gaseous carbon source includes carbon dioxide, and the etching of the initial carbon coating layer using the oxidizing gaseous carbon source specifically includes: C + CO2 → 2CO.

7. The preparation method according to claim 1, characterized in that, The oxidizing gaseous carbon source includes carbon monoxide and / or carbon dioxide. Further carbon deposition on the silicon-carbon composite material with the initial carbon coating layer is specifically achieved through the decomposition of the oxidizing gaseous carbon source. 2CO→2C(solid)+O2; and / or, C + CO₂ → 2CO, 2CO → 2C (solid) + O₂.

8. A mixed gas-phase segmented coated silicon-carbon anode material prepared by any of the preparation methods described in claims 1-7.

9. A negative electrode, characterized in that, The negative electrode comprises a mixed gas-phase segmented coated silicon-carbon negative electrode material prepared by any of the preparation methods described in claims 1-7.

10. A secondary battery, characterized in that, The secondary battery comprises a mixed gas-phase segmented coated silicon-carbon anode material prepared by any of the preparation methods described in claims 1-7.

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