Fluidized bed integrated preparation method of silicon-carbon composite material and silicon-carbon composite material

Abstract

The invention provides a fluidized bed integrated preparation method of a silicon-carbon composite material and the silicon-carbon composite material, and relates to the technical field of lithium ion batteries. Through process control, construction of carbon skeleton active anchor sites, creation of active sites rich in pyridine nitrogen and / or oxygen-containing functional groups, and utilization of defect sites to guide silane in-situ deposition, the uniformity of silicon deposition is improved, and the interface contact resistance is greatly reduced; a defect site and a Si-H bond are subjected to strong chemical action, so that covalent bonding of silicon and carbon is realized, and the problem of interface instability is fundamentally solved; the three core processes of framework customization, silicon in-situ deposition and carbon packaging are seamlessly integrated on a single reaction platform, so that one-stop continuous production from raw materials to finished products is realized, and the uniformity of carbon coating is improved while the product consistency is improved; therefore, the obtained product shows lower internal resistance, higher rate capability and more stable cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a fluidized bed integrated preparation method for silicon-carbon composite materials and silicon-carbon composite materials. Background Technology

[0002] With the ever-increasing demand for energy density in lithium-ion batteries, silicon-based anode materials have become one of the key materials for next-generation high-energy-density batteries due to their extremely high theoretical specific capacity (approximately 4200 mAh / g). However, silicon exhibits a severe volume expansion effect (>300%) during charge and discharge, which easily leads to electrode structure pulverization, repeated growth of the solid electrolyte interphase (SEI) film, and failure of electrical contact between the active material and the current collector, resulting in rapid capacity decay and shortened cycle life. To overcome these challenges, silicon-carbon composite anode materials have emerged. By combining nano-silicon particles with a carbon matrix, these materials utilize the buffering and conductivity properties of carbon to suppress volume expansion, maintain structural integrity, and improve electron conduction efficiency, making them one of the most promising technological approaches currently available.

[0003] In the preparation of silicon-carbon anode materials, the uniform dispersion of silicon particles and their stable bonding with the carbon matrix are the core factors determining the electrochemical performance of the material. Currently, the industry commonly uses processes such as physical mixing, high-energy ball milling, and chemical vapor deposition (CVD) for preparation, but several common technical challenges remain: First, silicon particles are prone to agglomeration in the carbon matrix, leading to local stress concentration and exacerbating the negative impact of volume expansion; second, the thickness and uniformity of the carbon coating layer are difficult to control precisely; too thin a layer results in insufficient buffering effect, while too thick a layer reduces the overall energy density; third, the interface between silicon and carbon is mostly physical adsorption with weak bonding, making it prone to interface delamination during long-term cycling, leading to rapid capacity decay. Furthermore, existing processes often employ segmented operations, such as first preparing a porous carbon support, then performing silicon deposition and carbon coating. This discrete process flow and frequent equipment changes not only increase production costs and time but also introduce numerous human and environmental variables, resulting in poor batch consistency and difficulty in meeting the needs of large-scale production.

[0004] To address the aforementioned issues, patent CN 117832429 A proposes a continuous preparation scheme: using coking petroleum coke as a carbon source, carbonization and activation are sequentially performed in a fluidized bed reactor to obtain porous carbon materials. Subsequently, silane gas is introduced for two chemical vapor deposition processes to achieve silicon loading and carbon coating. Finally, the silicon-carbon anode material is obtained by cooling under a protective atmosphere. This process achieves a one-step continuous preparation from porous carbon to silicon-carbon composite materials, with a simple process and readily available materials, showing significant advantages in improving process reproducibility and product structure controllability. However, this method still has certain limitations: when silicon is deposited inside the porous carbon, due to the limitation of pore diffusion dynamics, silane gas tends to react and deposit preferentially at the pore inlet, leading to premature pore blockage and reduced internal pore utilization, resulting in uneven distribution of silicon nanoparticles; at the same time, the interaction between silicon and the carbon support mainly relies on physical adsorption, with weak chemical forces and insufficient interfacial stability. During long-term cycling, relative displacement or even detachment may occur, affecting the cycle life and structural integrity of the material.

[0005] In summary, existing silicon-carbon anode fabrication technologies still face two major challenges in pursuing high energy density and long cycle life: firstly, at the process level, segmented operations lead to complex processes, low efficiency, and difficulties in controlling product consistency; secondly, at the material structure level, uneven silicon distribution caused by pore diffusion limitations and weak silicon-carbon interfacial bonding severely restrict the full realization of the electrochemical performance of silicon-carbon composite materials. Therefore, developing a fabrication technology that can achieve uniform silicon loading, enhanced interfacial bonding, and continuous and controllable processes is of paramount importance for promoting the industrial application of silicon-carbon anode materials. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a fluidized bed integrated preparation method for silicon-carbon composite materials and the silicon-carbon composite materials themselves. The main problems solved are: 1) By treating the raw materials, controlling activation, and programmed temperature rise, a large number of chemically active defect sites for capturing silanes are directionally manufactured on the carbon skeleton, and the defect sites guide the in-situ deposition of silanes, thus solving the problems of weak interfacial bonding and uneven silicon distribution; 2) Activation pore formation, defect engineering, silane deposition, and carbon coating are integrated into a single fluidized bed reactor, thus solving the problems of discrete process flow, complex process, and low production efficiency.

[0007] In a first aspect, this application provides a silicon-carbon composite material with a core-shell structure, an outer carbon coating layer, and an inner porous carbon framework with uniformly distributed silicon nanoparticles; the porous carbon framework contains nitrogen-doped defect sites; the porous carbon framework contains active sites rich in pyridine nitrogen and / or oxygen-containing functional groups introduced by nitrogen doping, which chemically interact with Si-H elements to form covalent bonds between silicon and carbon.

[0008] Secondly, this application provides a fluidized bed integrated preparation method for the silicon-carbon composite material described in this application, comprising the following preparation steps:

[0009] 1) Optimize the phenolic resin precursor: Add phenols and aldehydes to an alkaline solution in proportion, stir at a constant temperature I, then add an organic nitrogen source, stir continuously II, wash with water until neutral, and dry to obtain dry powder A;

[0010] 2) Pre-curing treatment: Dry powder A is cured at low temperature in air and then pulverized to obtain dry powder B;

[0011] 3) Constructing carbon skeleton defect sites: Dry powder B is placed in a fluidized bed, and the temperature is increased in an inert atmosphere gradient. During the high-temperature heating process, activation gas is introduced simultaneously to perform physical etching. After high-temperature activation, powder C is obtained.

[0012] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment is cooled to the silane deposition temperature, and silane gas is introduced for deposition to obtain powder D;

[0013] 5) Constructing a dense carbon encapsulation layer: Adjust the temperature to the carbon deposition temperature, introduce acetylene gas to coat the silicon-carbon composite material.

[0014] Further, in step 1), the phenols are any one or a combination of phenol, hydroquinone, catechol, and resorcinol; the aldehydes are any one of formaldehyde, paraformaldehyde, paraformaldehyde, acetaldehyde, and propionaldehyde; the molar ratio of the phenols to the aldehydes is 1:1-2; the alkaline solution is any one of NaOH solution, KOH solution, Na2CO3 solution, NaHCO3 solution, and ammonia water; the concentration of the alkaline solution is 10-35 wt.%; the reaction temperature is 50-80℃; and the stirring time for both stirring I and stirring II is 1-5 h.

[0015] Further, the organic nitrogen source mentioned in step 1) is any one or a combination of p-aminophenol, o-aminophenol, 5-aminosalicylic acid, melamine, and dicyandiamide; the molar ratio of the organic nitrogen source to the phenolic compound is 0.05-0.2:1.

[0016] By controlling the amount of nitrogen doping through organic nitrogen sources, the amount of nitrogen defect sites formed when nitrogen doping is too low will result in most silanes not being effectively fixed, and it will be difficult to change the electronic structure of carbon materials, thereby effectively improving their electronic conductivity; while excessive nitrogen content will lead to a decrease in the stability of the carbon skeleton.

[0017] Furthermore, the low-temperature curing temperature described in step 2) is 150℃-220℃; the curing time is 1-3h; and the heating rate is 1-3℃ / min.

[0018] The pre-curing step mainly allows the resin molecular chains to further cross-link (curing) and release small molecule water, but its main carbon skeleton structure has not yet decomposed, so as to ensure that it will not melt or stick again during the subsequent fluidization process at higher temperatures.

[0019] Furthermore, the D50 of the dry powder B mentioned in step 2) is controlled at 6-8 μm.

[0020] Furthermore, the gradient heating described in step 3) can be divided into two stages: the first stage: heating to 500-600℃ at a rate of 1-3℃ / min and holding for 0.5-2h; the second stage: heating to 800-950℃ at a rate of 2-8℃ / min, during which an activation gas is introduced, the activation gas including water vapor and / or carbon dioxide, the activation gas flow rate being 1-5L / min, and the activation time being 1-5h.

[0021] In the first stage, a large number of polymer chains break down, slowly releasing small volatile molecules. The slow heating rate allows the inert gas flow to carry away these volatiles in time, creating pores. At the same time, it "freezes" a large number of highly active carbon dangling bond defects, and nitrogen elements form highly active pyridine nitrogen inside. In the second stage, etching is carried out while the carbon skeleton is initially formed. This not only creates abundant pores inside, but also creates a large number of chemically active edge carbon atoms and oxygen-containing functional groups (carbonyl (C=O), carboxyl (-COOH) etc.) on the pore walls and particle surfaces, providing active sites for subsequent SiH4 directional deposition.

[0022] Introducing water vapor or CO2 activation not only creates abundant pores inside, but also creates a large number of chemically active edge carbon atoms and oxygen-containing functional groups (carbonyl (C=O), carboxyl (-COOH) etc.) on the pore walls and particle surfaces, providing active sites for subsequent SiH4 directional deposition; KOH activation relies on K etching to create pores, and oxygen-containing functional groups are generated in the process, but in small quantities. In addition, a large amount of alkali is required, which affects the fluidization effect and is corrosive to the equipment.

[0023] The main advantage of using phenolic resin is that nitrogen atoms can be introduced in situ during the polycondensation stage to provide anchoring points for Si-H in the later stage and to provide defect sites to guide the in-situ deposition of silane. The process of this application is well integrated with the characteristics of phenolic resin. Compared with phenolic resin, pitch coke is not easy to modify for defects. In addition, pitch coke has a graphite microcrystalline structure, and generally requires higher temperatures for activation under alkaline activation or physical activation, which also makes it difficult to generate defect sites.

[0024] In this application, small molecules overflow during the nitrogen doping stage, which assists in pore formation and enhances electrical conductivity while generating nitrogen defect sites; water vapor activation is equivalent to etching from the outside in, generating oxygen-containing functional groups while forming pores. These two work together to guide in-situ silane deposition in the later stage, making silicon deposition more uniform.

[0025] Furthermore, the inert gas in the fluidized bed mentioned in step 3) is nitrogen or argon, and the inert gas flow rate is 1-10 L / min.

[0026] Furthermore, the deposition temperature in step 4) is 400℃-550℃, the deposition time is 1-5h, and the silane flow rate is 0.5-3L / min.

[0027] Furthermore, the carbon deposition temperature in step 5) is 500℃-650℃, the deposition time is 1-5h, and the acetylene flow rate is 0.5-3L / min.

[0028] Beneficial effects: 1. This invention constructs active anchor sites for the carbon skeleton through process control. By creating active sites rich in pyridine nitrogen and / or oxygen-containing functional groups, the defect sites guide the in-situ deposition of silane, improving the uniformity of silicon deposition and significantly reducing interfacial contact resistance. The defect sites interact strongly with Si-H bonds, achieving covalent bonding between silicon and carbon, fundamentally solving the problem of interfacial instability. In this application, the three core processes of skeleton customization, in-situ silicon deposition, and carbon encapsulation are seamlessly integrated into a single reaction platform, realizing one-stop continuous production from raw materials to finished products. This improves product consistency while enhancing the uniformity of carbon coating, resulting in products exhibiting lower internal resistance, higher rate performance, and more stable cycle life. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the silicon-carbon composite material according to an embodiment of the present invention;

[0030] Figure 2 The image shows the Raman spectrum of porous carbon (powder C) obtained using the method in Example 1.

[0031] Figure 3 This is an N2 adsorption-desorption curve of porous carbon (powder C) obtained by the method in Example 1;

[0032] Figure 4 The graph shows the resistance test results of the silicon-carbon composite material obtained by the methods of Example 1 and Comparative Examples 1-4.

[0033] Figure 5 This is a high-temperature cycling diagram of the silicon-carbon composite material obtained using the methods of Example 1 and the comparative example. Detailed Implementation

[0034] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1: A fluidized bed integrated preparation method for silicon-carbon composite materials, the preparation process is as follows: Figure 1The preparation steps include the following:

[0036] 1) Optimize the phenolic resin precursor: add resorcinol and formaldehyde in a molar ratio of 1:1.6 to a 28wt% NaOH aqueous solution (the mass of NaOH is 6% of the mass of the phenol monomer), stir at 80℃ for 1h, then add melamine (molar ratio of melamine to phenol monomer is 0.1:1), continue stirring for 4h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0037] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 220℃ at 2℃ / min, calcine it in air atmosphere for 1.5h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0038] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 6L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 2h. Raise the temperature to 950℃ at 5℃ / min, and introduce water vapor (flow rate of 2.8L / min) during the heating process. The activation time is 3.5h, and powder C is obtained after activation.

[0039] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 520℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 0.8L / min, the deposition time was 260min, and powder D was obtained after deposition.

[0040] 5) Constructing a dense carbon encapsulation layer: Heat to 600℃ at 4℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0041] The Raman spectra, nitrogen adsorption-desorption isotherms, pressure-conductivity performance comparison charts, and cycle performance comparison charts of the silicon-carbon composite material obtained by the method in Example 1 are shown in the following figures. Figure 2 , Figure 3 , Figure 4 and Figure 5 .

[0042] Example 2: A fluidized bed integrated preparation method for silicon-carbon composite materials, comprising the following preparation steps:

[0043] 1) Optimize the phenolic resin precursor: Add p-diphenol and formaldehyde in a molar ratio of 1:1.5 to a 25wt% NaOH aqueous solution (the mass of NaOH is 5% of the mass of the phenol monomer), stir at 70℃ for 1h, then add p-aminophenol (molar ratio of 0.1:1 to the phenol monomer), continue stirring for 4h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0044] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 210℃ at 3℃ / min, calcine it in air atmosphere for 2h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0045] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 6L / min), heat to 500℃ at 2℃ / min, and hold for 1.5h. Then heat to 900℃ at 5℃ / min, and introduce water vapor (flow rate of 3L / min) during the heating process. The activation time is 3.5h, and powder C is obtained after activation.

[0046] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 480℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 1L / min, and the deposition time was 210min. Powder D was obtained after the deposition was completed.

[0047] 5) Constructing a dense carbon encapsulation layer: Heat to 580℃ at 5℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0048] Example 3: A fluidized bed integrated preparation method for silicon-carbon composite materials, comprising the following preparation steps:

[0049] 1) Optimize the phenolic resin precursor: add resorcinol and formaldehyde in a molar ratio of 1:1.6 to a 25wt% KOH aqueous solution (KOH mass is 5% of the phenol monomer mass), stir at 80℃ for 1h, then add dicyandiamide (molar ratio to phenol monomer is 0.15:1), continue stirring for 3.5h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0050] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 210℃ at 3℃ / min, calcine it in air atmosphere for 2h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0051] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 5L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 2h. Raise the temperature to 950℃ at 5℃ / min, and introduce water vapor (flow rate of 2L / min) during the heating process. The activation time is 4.5h, and powder C is obtained after activation.

[0052] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 480℃, the nitrogen flow rate was adjusted to 9L / min, the silane flow rate was 1L / min, and the deposition time was 210min. Powder D was obtained after the deposition was completed.

[0053] 5) Constructing a dense carbon encapsulation layer: Heat to 580℃ at 5℃ / min, introduce acetylene gas (flow rate 1.5L / min), carbon deposition time is 280min, and after cooling, the silicon-carbon composite material is obtained.

[0054] Example 4: A fluidized bed integrated preparation method for silicon-carbon composite materials, comprising the following preparation steps:

[0055] 1) Optimization of phenolic resin precursor: add m-diphenol and trioxymethylene in a molar ratio of 1:1.6 to a 30wt% NaOH aqueous solution (NaOH mass is 6% of the phenol monomer mass), stir at 80℃ for 1h, then add 5-aminosalicylic acid (molar ratio with phenol monomer is 0.2:1), continue stirring for 4h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0056] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 200℃ at 1℃ / min, calcine it in air atmosphere for 2h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0057] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 5L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 3h. Raise the temperature to 850℃ at 5℃ / min, and introduce water vapor (flow rate of 3.5L / min) during the heating process. The activation time is 3h, and powder C is obtained after activation.

[0058] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 500℃, the nitrogen flow rate was adjusted to 9L / min, the silane flow rate was 0.7L / min, the deposition time was 300min, and powder D was obtained after deposition.

[0059] 5) Constructing a dense carbon encapsulation layer: Heat to 600℃ at 5℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 210min, and after cooling, the silicon-carbon composite material is obtained.

[0060] Example 5: A fluidized bed integrated preparation method for silicon-carbon composite materials, comprising the following preparation steps:

[0061] 1) Optimization of phenolic resin precursor: p-diphenol and formaldehyde were added to a 25wt% NaOH aqueous solution at a molar ratio of 1:1.5 (the mass of NaOH was 5% of the mass of the phenol monomer). After stirring at 70℃ for 1 h, p-aminophenol (molar ratio of 0.2:1 to the phenol monomer) was added. After stirring for 4 h, the mixture was washed with water until neutral and dried at 80℃ to obtain dry powder A.

[0062] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 210℃ at 3℃ / min, calcine it in air atmosphere for 2h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0063] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 6L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 2h. Raise the temperature to 900℃ at 5℃ / min, and introduce water vapor (flow rate of 2.1L / min) during the heating process. The activation time is 4.8h, and powder C is obtained after activation.

[0064] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 480℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 1L / min, and the deposition time was 210min. Powder D was obtained after the deposition was completed.

[0065] 5) Constructing a dense carbon encapsulation layer: Heat to 580℃ at 2℃ / min, introduce acetylene gas (flow rate 1.5L / min), carbon deposition time is 300min, and after cooling, the silicon-carbon composite material is obtained.

[0066] Comparative Example 1, a fluidized bed integrated preparation method for silicon-carbon composite materials, differs from Example 1 in that: no nitrogen source is used in step 1); and one-step activation is used in step 3).

[0067] The specific steps are as follows:

[0068] 1) Preparation of phenolic resin precursor: add m-diphenol and formaldehyde in a molar ratio of 1:1.6 to 28wt% NaOH aqueous solution (NaOH mass is 6% of the phenol monomer mass), stir at 80℃ for 5h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0069] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 220℃ at 2℃ / min, calcine it in air atmosphere for 1.5h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0070] 3) Constructing the carbon skeleton: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen gas (flow rate of 6L / min) and heat it to 950℃ at 5℃ / min. During the heating process, introduce water vapor (flow rate of 2.8L / min) and activate it for 3.5h. After activation, obtain powder C.

[0071] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 520℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 0.8L / min, the deposition time was 260min, and powder D was obtained after deposition.

[0072] 5) Constructing a dense carbon encapsulation layer: Heat to 600℃ at 4℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0073] Comparative Example 2, a fluidized bed integrated preparation method for silicon-carbon composite materials, differs from Example 1 in that step 3) uses one-step activation.

[0074] The specific steps are as follows:

[0075] 1) Optimize the phenolic resin precursor: add resorcinol and formaldehyde in a molar ratio of 1:1.6 to a 28wt% NaOH aqueous solution (the mass of NaOH is 6% of the mass of the phenol monomer), stir at 80℃ for 1h, then add melamine (molar ratio of melamine to phenol monomer is 0.1:1), continue stirring for 4h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0076] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 220℃ at 2℃ / min, calcine it in air atmosphere for 1.5h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0077] 3) Constructing the carbon skeleton: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen gas (flow rate of 6L / min) and heat it to 950℃ at 5℃ / min. During the heating process, introduce water vapor (flow rate of 2.8L / min). The activation time is 3.5h. After activation, powder C is obtained.

[0078] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 520℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 0.8L / min, the deposition time was 260min, and powder D was obtained after deposition.

[0079] 5) Constructing a dense carbon encapsulation layer: Heat to 600℃ at 4℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0080] Comparative Example 3, a fluidized bed integrated preparation method for silicon-carbon composite materials, differs from Example 1 in that: no nitrogen source is used in step 1).

[0081] The specific steps are as follows:

[0082] 1) Preparation of phenolic resin precursor: add m-diphenol and formaldehyde in a molar ratio of 1:1.6 to 28wt% NaOH aqueous solution (NaOH mass is 6% of the phenol monomer mass), stir at 80℃ for 5h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0083] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 220℃ at 2℃ / min, calcine it in air atmosphere for 1.5h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0084] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a fluidized bed. Introduce nitrogen (flow rate of 6L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 2h. Raise the temperature to 950℃ at 5℃ / min, and introduce water vapor (flow rate of 2.8L / min) during the heating process. The activation time is 3.5h, and powder C is obtained after activation.

[0085] 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment was cooled to 520℃, the nitrogen flow rate was adjusted to 8L / min, the silane flow rate was 0.8L / min, the deposition time was 260min, and powder D was obtained after deposition.

[0086] 5) Constructing a dense carbon encapsulation layer: Heat to 600℃ at 4℃ / min, introduce acetylene gas (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0087] Comparative Example 4, a fluidized bed integrated preparation method for silicon-carbon composite materials, differs from Example 1 in that: in Example 1, steps 3), 4), and 5) are carried out continuously in the same fluidized bed equipment without the need for material replacement, transfer, and repeated heating and cooling; in Comparative Example 4, step 3 is carried out in a rotary kiln, step 4 transfers powder C into the fluidized bed, and step 5 transfers powder D back to the rotary kiln.

[0088] The specific steps are as follows:

[0089] 1) Optimize the phenolic resin precursor: add resorcinol and formaldehyde in a molar ratio of 1:1.6 to a 28wt% NaOH aqueous solution (the mass of NaOH is 6% of the mass of the phenol monomer), stir at 80℃ for 1h, then add melamine (molar ratio of melamine to phenol monomer is 0.1:1), continue stirring for 4h, wash with water until neutral, and dry at 80℃ to obtain dry powder A.

[0090] 2) Pre-curing treatment: Place the dry powder A from step 1) in a muffle furnace, heat it to 220℃ at 2℃ / min, calcine it in air atmosphere for 1.5h, and then pulverize it to obtain dry powder B (D50 is 7±1μm).

[0091] 3) Constructing carbon framework defect sites: Take 500g of dry powder B from step 2) and place it in a rotary kiln. Introduce nitrogen (flow rate of 6L / min), raise the temperature to 550℃ at 2℃ / min, and hold for 2h. Raise the temperature to 950℃ at 5℃ / min, and introduce water vapor (flow rate of 2.8L / min) during the heating process. The activation time is 3.5h, and powder C is obtained after activation.

[0092] 4) In-situ chemical vapor deposition of silane: Powder C from step 3) is transferred into a fluidized bed device, heated to 520°C at 5°C / min, nitrogen flow rate is adjusted to 8L / min, silane flow rate is 0.8L / min, and deposition time is 260min. Powder D is obtained after deposition.

[0093] 5) Constructing a dense carbon encapsulation layer: Powder D from step 4) is transferred to a rotary kiln, heated to 600°C at 4°C / min, acetylene gas is introduced (flow rate 2L / min), carbon deposition time is 240min, and after cooling, the silicon-carbon composite material is obtained.

[0094] Preparation and performance testing of pouch cells:

[0095] The silicon-carbon composite silicon-based anode materials prepared in Examples 1-5 and Comparative Examples 1-4 were mixed with commercial artificial graphite to achieve a capacity of 450 mAh / g. Active materials, binders, and conductive agents were dispersed and slurried at a mass fraction ratio of 96:3.55:0.45. After cell preparation processes including coating, rolling, and slitting, small pouch batteries were fabricated using NCM811 cathodes. The performance of the materials in full-cell batteries was tested, specifically the charge / discharge voltage range at 1.25°C. Rate performance testing was conducted within the range of 2.8–4.2V. First, capacity calibration was performed using a 1 / 3C constant current charge-discharge cycle. The charging rate was 1C, and the discharging rate was 3C. The percentage of the cell's capacity at the high rate was measured relative to that at 1 / 3C. High-temperature cycling performance testing was conducted within the charge-discharge voltage range of 2.8–4.2V at 2.45℃. First, capacity calibration was performed using a 1 / 3C constant current charge-discharge cycle. The charging rate was 0.5C, and the discharging rate was 1C. The high-temperature cycling data of the tested materials are shown in Table 1.

[0096] Figure 2 The Raman spectrum of the porous carbon obtained in Example 1 of this invention (Raman spectrometer used 532nm laser for testing) shows that the obtained porous carbon is rich in defect sites.

[0097] Figure 3 The graph shows the N2 adsorption-desorption curve of the porous carbon obtained in Example 1 of this invention (tested by a BET nitrogen adsorption surface area meter). The curve is type I, mainly representing a microporous structure.

[0098] Figure 4The graph shows the powder resistance test results of the silicon-carbon composite materials obtained in Example 1 and Comparative Examples 1-4 of this invention (tested by Yuaneng Powder Compactor Density Analyzer).

[0099] Figure 5 This is a high-temperature cycling diagram of the silicon-carbon composite material obtained in Example 1 and Comparative Examples 1-4 of the present invention.

[0100] Table 1. Electrochemical properties of silicon-carbon materials obtained in Examples 1-5 and Comparative Examples 1-4

[0101] distinguish 3C Capacity Retention Rate / % Capacity retention rate after 500 cycles / % Example 1 81.46 95.68 Example 2 80.74 95.52 Example 3 82.61 96.01 Example 4 82.88 95.43 Example 5 81.92 96.11 Comparative Example 1 70.31 90.9 Comparative Example 2 74.22 93.78 Comparative Example 3 72.53 92.49 Comparative Example 4 74.86 94.4

[0102] Examples 1-5 exhibit better rate performance and high-temperature cycling performance compared to Comparative Examples 1-4. Example 1 shows improved rate performance and cycling performance compared to Comparative Examples 1-3, mainly because Example 1 has more nitrogen / oxygen defect sites, silane in-situ deposition, improved uniformity of silicon particle deposition and bonding force between silicon and carbon, and nitrogen doping can effectively improve conductivity, thereby improving the overall electrochemical performance of the material.

[0103] Example 1 shows improved rate performance and cycling performance compared to Comparative Example 4, mainly due to fluidized bed activation, which improves the uniformity of porous carbon pores, facilitating the uniform deposition of silicon particles in the later stage. At the same time, the fluidized bed carbon deposition forms a dense carbon encapsulation layer, which helps to improve the electrochemical performance of the material.

[0104] Compared to Example 1, Comparative Example 4 suffers from equipment dispersion, process interruption, air exposure during transfer, introduction of impurities or oxidation of active surfaces, and poor uniformity of defect sites, which in turn leads to poor silicon deposition uniformity and product quality.

[0105] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A silicon-carbon composite material, characterized in that, It has a core-shell structure, with an outer carbon coating layer and an inner porous carbon framework of uniformly distributed silicon nanoparticles; the porous carbon framework contains nitrogen-doped defect sites; the porous carbon framework contains active sites rich in pyridine nitrogen and / or oxygen-containing functional groups introduced by nitrogen doping, which undergo strong chemical reactions with Si-H elements to form covalent bonds between silicon and carbon.

2. A fluidized bed integrated preparation method for the silicon-carbon composite material according to claim 1, characterized in that, The preparation steps include the following: 1) Optimize the phenolic resin precursor: Add phenols and aldehydes to an alkaline solution in proportion, stir at a constant temperature I, then add an organic nitrogen source, stir continuously II, wash with water until neutral, and dry to obtain dry powder A; 2) Pre-curing treatment: Dry powder A is cured at low temperature in air and then pulverized to obtain dry powder B; 3) Constructing carbon skeleton defect sites: Dry powder B is placed in a fluidized bed, and the temperature is increased in an inert atmosphere gradient. During the high-temperature heating process, activation gas is introduced simultaneously to perform physical etching. After high-temperature activation, powder C is obtained. 4) In-situ chemical vapor deposition of silane: The fluidized bed equipment is cooled to the silane deposition temperature, and silane gas is introduced for deposition to obtain powder D; 5) Constructing a dense carbon encapsulation layer: Adjust the temperature to the carbon deposition temperature, introduce acetylene gas to coat the silicon-carbon composite material.

3. The fluidized bed integrated preparation method for silicon-carbon composite materials according to claim 2, characterized in that, In step 1), the phenols are any one or a combination of phenol, hydroquinone, catechol, and resorcinol; the aldehydes are any one of formaldehyde, trioxymethylene, paraformaldehyde, acetaldehyde, and propionaldehyde; the molar ratio of the phenols to the aldehydes is 1:1-2; the alkaline solution is any one of NaOH solution, KOH solution, Na2CO3 solution, NaHCO3 solution, and ammonia water; the concentration of the alkaline solution is 10-35 wt.%; the reaction temperature is 50-80℃, and the stirring time for both stirring I and stirring II is 1-5 h.

4. A fluidized bed integrated preparation method for silicon-carbon composite materials according to claim 2 or 3, characterized in that, The organic nitrogen source mentioned in step 1) is any one or a combination of p-aminophenol, o-aminophenol, 5-aminosalicylic acid, melamine, and dicyandiamide; the molar ratio of the organic nitrogen source to the phenolic compound is 0.05-0.2:

1.

5. The fluidized bed integrated preparation method for silicon-carbon composite materials according to claim 4, characterized in that, The low-temperature curing temperature mentioned in step 2) is 150℃-220℃; the curing time is 1-3h; and the heating rate is 1-3℃ / min.

6. The fluidized bed integrated preparation method of a silicon-carbon composite material according to any one of claims 2-3, 5, characterized in that, The D50 of the dry powder B mentioned in step 2) is controlled at 6-8 μm.

7. The fluidized bed integrated preparation method for silicon-carbon composite materials according to claim 6, characterized in that, The gradient heating described in step 3) can be divided into two stages: the first stage: heating to 500-600℃ at a rate of 1-3℃ / min and holding for 0.5-2h; the second stage: heating to 800-950℃ at a rate of 2-8℃ / min, during which an activation gas is introduced, which includes water vapor and / or carbon dioxide, with a flow rate of 1-5L / min and an activation time of 1-5h.

8. A fluidized bed integrated preparation method for silicon-carbon composite materials according to any one of claims 2-3, 5, and 7, characterized in that, The inert gas in the fluidized bed mentioned in step 3) is nitrogen or argon, and the inert gas flow rate is 1-10 L / min.

9. The fluidized bed integrated preparation method of silicon-carbon composite material according to claim 8, characterized in that... The deposition temperature described in step 4) is 400℃-550℃, the deposition time is 1-5h, and the silane flow rate is 0.5-3L / min.

10. A fluidized bed integrated preparation method for silicon-carbon composite materials according to any one of claims 2-3, 5, 7, and 9, characterized in that, The carbon deposition temperature in step 5) is 500℃-650℃, the deposition time is 1-5h, and the acetylene flow rate is 0.5-3L / min.

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