Multilayer silicon-carbon negative electrode material and multistage fluidized bed continuous preparation method thereof

Abstract

The invention discloses a multilayer silicon-carbon negative electrode material and a multistage fluidized bed continuous preparation method thereof. The multilayer silicon-carbon negative electrode material is formed by wrapping silicon layers, SiOx layers and carbon layers at intervals, the silicon layers are isolated by the carbon layers or the SiOx layers, the carbon layers are isolated by the silicon layers or the SiOx layers, and the SiOx layers are isolated by the silicon layers. According to the multi-stage fluidized bed continuous preparation method, different parameters are set in each stage of fluidized bed reactor to adapt to the physical property change of solid particles, so that the continuous process is realized. The multilayer silicon-carbon negative electrode material provided by the invention has a uniform hierarchical structure and the SiOx intermediate layer prepared by limited oxidation, so that the charging capacity and the cycling stability of the silicon-carbon negative electrode material can be effectively improved, and the application value is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to a multi-layer silicon-carbon negative electrode material and a multi-stage fluidized bed continuous preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, high energy density and environmental friendliness. They are widely used in portable electronic devices and have expanded to electric vehicles and energy storage fields.

[0003] Anode materials are a crucial component of lithium-ion batteries, but the most common anode material on the market is graphite, whose reversible specific capacity is already close to its theoretical specific capacity (372 mAh / g), leaving very limited room for improvement and unable to meet future development needs. Therefore, silicon-based materials, with a theoretical specific capacity of up to 4200 mAh / g, are considered the most promising anode materials for lithium-ion batteries. However, silicon has poor conductivity, and as an anode material, it undergoes significant volume expansion during lithium intercalation and deintercalation, leading to silicon particle shattering and severely impacting the battery's cycle performance and service life.

[0004] In order to solve the problems of structural damage caused by the huge volume expansion (≈300%) of silicon negative electrode materials during charging and discharging, and loss of electrical contact between the negative electrode material and the current collector, it is necessary to compound silicon materials with carbon materials with good conductivity and small volume expansion to prepare negative electrode materials that meet relevant standards.

[0005] The Chinese invention patent application with publication number CN117735530A discloses a preparation method for producing silicon-carbon negative electrode materials using a two-stage reactor method, which can produce silicon particles ranging from nanometers to hundreds of nanometers and realize online in-situ carbon coating. However, this method has a complex structure and requires an external plasma device or microwave and medium frequency reaction device, etc., and it is difficult to achieve large-scale production and cannot meet market demand. The Chinese invention patent application with publication number CN117352703A discloses a method for preparing multi-level silicon-carbon negative electrode materials using a fluidized bed, but the process requires continuous switching of silicon source gas, mixed gas and protective gas, making it difficult to achieve continuous production of silicon-carbon negative electrode materials. Moreover, when the silicon deposition temperature and the carbon coating temperature are different, a long heating / cooling and insulation process is required, which greatly reduces the production efficiency and is difficult to meet the needs of industrial production.

[0006] Therefore, there is an urgent need for a multilayer silicon-carbon negative electrode material with a uniform hierarchical structure that can effectively inhibit the volume expansion of the material during charging and discharging, as well as a simple and easy-to-operate continuous preparation method. Summary of the Invention

[0007] Purpose of the invention: In view of the defects of the prior art, the purpose of the present invention is to provide a multilayer silicon-carbon negative electrode material with a uniform hierarchical structure that can effectively inhibit the volume expansion of the material during charging and discharging, as well as a multi-stage fluidized bed continuous preparation method that is easy to operate.

[0008] Technical solution:

[0009] On the one hand, the present invention provides a multilayer silicon-carbon negative electrode material, which comprises a silicon layer, a SiO x Layers and carbon layers are wrapped alternately;

[0010] The silicon layers are separated by a carbon layer or SiO x Layer isolation, the carbon layer and the carbon layer are separated by silicon layer or SiO x Layer isolation, SiO x Layer with SiO x The layers are isolated by silicon layers.

[0011] Furthermore, there is at least one layer of SiO between the silicon layer and the carbon layer. x layer.

[0012] Furthermore, the multilayer silicon-carbon negative electrode material has Si@SiO x @Si@SiO x @CFive-layer structure.

[0013] Another aspect of the present invention provides a multi-stage fluidized bed continuous preparation method for any of the above-mentioned multi-layer silicon-carbon negative electrode materials, wherein the multi-stage fluidized bed continuous preparation method realizes a continuous process by setting different parameters in each stage of the fluidized bed reactor to adapt to the changes in the physical properties of the solid particles;

[0014] The continuous process includes three processes: silicon deposition, restricted oxidation and carbon coating;

[0015] The silicon deposition process is carried out by cracking silicon source gas at high temperature;

[0016] The restricted oxidation process is carried out by using a silicon source gas replacement and oxidation method;

[0017] The carbon coating process is carried out by cracking carbon source gas at high temperature.

[0018] The process sequence of the multi-stage fluidized bed continuous preparation method of the present invention includes but is not limited to: the material obtained in the silicon deposition process is subjected to limited oxidation and / or carbon coating to obtain the silicon-carbon negative electrode material, or the material obtained in the limited oxidation process is subjected to silicon deposition and / or carbon coating to obtain the silicon-carbon negative electrode material, or the material obtained in the carbon coating process is subjected to silicon deposition and / or limited oxidation to obtain the silicon-carbon negative electrode material.

[0019] For example, a silicon-carbon anode material with a Si@C double-layer structure can be made through silicon deposition and carbon coating processes in sequence;

[0020] A silicon-carbon negative electrode material having a Si@C@Si@C four-layer structure can be prepared by sequentially undergoing silicon deposition, carbon coating, silicon deposition, and carbon coating processes;

[0021] Si@SiO can be prepared through the process of silicon deposition, limited oxidation and carbon coating. x @C three-layer silicon-carbon negative electrode material;

[0022] Si@SiO can be prepared by sequentially undergoing the processes of silicon deposition, restricted oxidation, silicon deposition, restricted oxidation and carbon coating. x @Si@SiO x @CFive-layer structure silicon-carbon negative electrode material.

[0023] The multi-stage fluidized bed continuous preparation method of the present invention can quickly transform the reaction environment during the preparation process, achieve more uniform temperature control, coating and oxidation of the material, and thus greatly improve the consistency of the silicon-carbon negative electrode material and improve the overall performance and stability of the material.

[0024] Furthermore, during the silicon deposition process, the temperature in the silicon deposition fluidized bed reactor is controlled to be 300-900° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the silicon deposition fluidized bed reactor is controlled to be 0.5-8 h.

[0025] For example, the temperature in the silicon deposition fluidized bed reactor can be 300°C, 350°C, 400°C, 435°C, 450°C, 500°C, 525°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, the gauge pressure can be 0.10MPa, 0.15MPa, 0.20MPa, 0.25MPa, 0.30MPa, 0.35MPa, 0.40MPa, 0.45MPa, 0.50MPa, and the residence time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h.

[0026] Furthermore, the silicon source gas is selected from one or a mixture of silane, disilane, trisilane, butane, chlorosilane, tetramethoxysilane, tetramethylsilane, tetraethylsilane, tetraethoxysilane, trivinylmethoxysilane, trivinylethoxysilane, divinyldiethoxysilane, divinyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenylsilane, and diphenylsilane.

[0027] Furthermore, in the restricted oxidation process, the silicon source gas replacement stage utilizes an intermediate inert gas continuous reactor to allow the inert gas to replace the unreacted silicon source gas or to completely decompose the residual silicon source gas in an inert atmosphere;

[0028] In the limited oxidation process, the oxidation stage is to partially oxidize the deposited silicon in an oxidation fluidized bed reactor using oxygen and / or air.

[0029] In the multi-stage fluidized bed continuous preparation method of the present invention, a uniform SiO2 layer is successfully formed between the silicon layer and the carbon coating layer by limiting the oxidation process. x The intermediate layer and the rapid conversion of the reaction environment in the preparation method can effectively improve the SiO x The uniformity and density of the intermediate layer can further suppress the coating of the silicon layer material, avoid its volume expansion during charging and discharging, and improve the cycle stability.

[0030] Furthermore, during the silicon source gas replacement process, the temperature in the intermediate inert gas continuous reactor is controlled to be 300-1200° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the intermediate inert gas continuous reactor is controlled to be 0.5-6 hours;

[0031] The inert gas is selected from at least one of N2, Ar, CO2, He, Ne, Kr, and Xe;

[0032] During the oxidation process, the temperature in the oxidation fluidized bed reactor is controlled to be 300-1200° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the oxidation fluidized bed reactor is controlled to be 0.5-6 hours.

[0033] For example, the temperature of the intermediate inert gas continuous reactor can be 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C; the gauge pressure can be 0.10MPa, 0.15MPa, 0.20MPa, 0.25MPa, 0.30MPa, 0.35MPa, 0.40MPa, 0.45MPa, or 0.50MPa; and the residence time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h.

[0034] For example, the temperature of the oxidation fluidized bed reactor can be 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, the gauge pressure can be 0.10MPa, 0.15MPa, 0.20MPa, 0.25MPa, 0.30MPa, 0.35MPa, 0.40MPa, 0.45MPa, 0.50MPa, and the residence time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h.

[0035] Furthermore, during the carbon coating process, the temperature in the carbon coating fluidized bed reactor is controlled to be 300-1500° C., the gauge pressure is controlled to be 0-0.60 MPa, and the residence time of the solid particles in the carbon coating fluidized bed reactor is controlled to be 0.5-6 h.

[0036] For example, the temperature in the carbon-coated fluidized bed reactor can be 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, the gauge pressure can be 0.10MPa, 0.15MPa, 0.20MPa, 0.25MPa, 0.30MPa, 0.35MPa, 0.40MPa, 0.45MPa, 0.50MPa, 0.55MPa, 0.60MPa, and the residence time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h.

[0037] In the multi-stage fluidized bed continuous preparation method of the present invention, fluidized bed reactors are used in the three stages of silicon deposition, restricted oxidation and carbon coating. The temperature control, coating and oxidation degree during the reaction process are more uniform, which greatly improves the consistency of the silicon-carbon negative electrode material.

[0038] Furthermore, the carbon source gas is selected from one or a mixture of cracked carbon, monosaccharides, disaccharides, polysaccharides, sugar derivatives, asphalt, resins, aromatic hydrocarbons, alkanes, alkenes, and alkynes.

[0039] For example, the carbon source gas may be acetylene, asphalt gas, resin gas, or ethylbenzene gas.

[0040] Beneficial effects:

[0041] (1) The multilayer silicon-carbon negative electrode material provided by the present invention has a uniform hierarchical structure, and each layer can form a spherical shell with uniform thickness, which can effectively inhibit the volume expansion of the silicon material during the charge and discharge process, avoid deformation of the material, and thus improve its cycle stability.

[0042] (2) In the multi-layer silicon-carbon negative electrode material and the multi-stage fluidized bed continuous preparation method provided by the present invention, a uniform SiO2 layer is successfully formed between the silicon layer and the carbon coating layer by limiting the oxidation process. x The intermediate layer and the rapid conversion of the reaction environment in the preparation method can effectively improve the SiO x The uniformity and density of the intermediate layer can further suppress the coating of the silicon layer material, avoid its volume expansion during charging and discharging, and improve the cycle stability.

[0043] (3) The raw materials of the multilayer silicon-carbon negative electrode material provided by the present invention are cheap and easily available silicon powder, which is conducive to reducing production costs and gaining advantages in market competition. In addition, silicon powder of various sizes can be purchased in the market to meet different material preparation needs, and the structural design and optimization of the silicon-carbon negative electrode material can be realized, so as to produce silicon-carbon negative electrode materials that meet market demand.

[0044] (4) In the multilayer silicon-carbon negative electrode material provided by the present invention, the SiO obtained by the oxidation reaction is limited. x The intermediate layer can effectively alleviate the volume expansion of silicon, improve the cycle performance and service life of the battery. At the same time, the dense carbon layer generated by the carbon coating process can enhance the conductivity of the negative electrode material and improve the conductivity of the silicon material.

[0045] (5) In the multi-stage fluidized bed continuous preparation method provided by the present invention, fluidized bed reactors are used in the three stages of silicon deposition, restricted oxidation and carbon coating. The temperature control, coating and oxidation degree during the reaction process are more uniform, which greatly improves the consistency of the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Si@SiO x @C Schematic diagram of the structure of the three-layer silicon-carbon negative electrode material, where 1-three-layer silicon-carbon negative electrode material particles; 2-silicon core; 3-SiO x Middle layer; 4-carbon coating layer.

[0047] Figure 2 Si@SiO x @Si@SiO x @C Schematic diagram of the structure of the five-layer silicon-carbon negative electrode material, where 1-five-layer silicon-carbon negative electrode material particles; 2-silicon core; 3-SiO x Intermediate layer; 4-Silicon coating layer; 5-SiO x Middle layer; 6-carbon coating layer.

[0048] Figure 3 This is the cycle stability curve of the negative electrode material. DETAILED DESCRIPTION

[0049] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples are illustrative of the present invention and are intended only to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the scope of the present invention may be made without departing from the spirit or scope of the present invention.

[0050] Example 1

[0051] The multilayer silicon-carbon anode material was prepared by the following steps:

[0052] (1) Silane is introduced into a silicon deposition fluidized bed reactor, and the silane is cracked at 525° C. and 0.45 MPa (gauge pressure) to generate solid silicon core particles, which are then fed together with the silane into an intermediate inert gas continuous reactor;

[0053] (2) Ar is used to displace the silane in the gas and the pores of the solid silicon core particles in the intermediate inert gas continuous reactor, and at the same time, a portion of the silane undergoes a thermal decomposition reaction. During the reaction, the temperature of the intermediate inert gas continuous reactor is maintained at 675°C and the pressure is maintained at 0.30 MPa (gauge pressure). The residence time of the particles in the intermediate inert gas continuous reactor is controlled to be 5 hours, after which the solid particles enter the oxidation fluidized bed with Ar;

[0054] (3) The solid silicon core particles reacted with a certain amount of oxygen in an oxidation fluidized bed reactor at 675 ° C and 0.30 MPa (gauge pressure) for 2 h to obtain a uniformly coated SiO x solid particles;

[0055] (4) Coated SiO x After the solid particles enter the carbon-coated fluidized bed reactor, acetylene undergoes cracking reaction at 750℃ and 0.20Mpa (gauge pressure) and then is evenly coated on the surface of the solid particles. x The residence time of the solid particles in the carbon-coated fluidized bed reactor was 1.5 h, and the Si@SiO x @CThe three-layer solid particles are multi-layer silicon-carbon negative electrode materials.

[0056] Example 2

[0057] The multilayer silicon-carbon anode material was prepared by the following steps:

[0058] (1) Chlorosilane is introduced into a first-stage silicon deposition fluidized bed reactor, and the chlorosilane is cracked at 435° C. and 0.30 MPa (gauge pressure) to generate solid silicon core particles, which are then fed together with the chlorosilane into a first-stage intermediate inert gas continuous reactor;

[0059] (2) using N2 to displace the chlorosilane in the gas and the pores of the solid silicon core particles in a first-stage intermediate inert gas continuous reactor, while causing a portion of the chlorosilane to undergo a thermal decomposition reaction. During the reaction, the temperature of the first-stage intermediate inert gas continuous reactor was maintained at 535°C and the pressure was maintained at 0.20 MPa (gauge pressure). The residence time of the particles in the first-stage intermediate inert gas continuous reactor was controlled to be 2 hours, after which the solid particles entered the first-stage oxidation fluidized bed reactor along with N2;

[0060] (3) The solid silicon core particles react with a certain amount of oxygen in a primary oxidation fluidized bed reactor at 535°C and 0.3 MPa (gauge pressure) for 1 hour to obtain a primary coated SiO x solid particles;

[0061] (4) Primary coating of SiO x The solid particles enter the secondary silicon deposition fluidized bed reactor, disilane is cracked in the secondary silicon deposition fluidized bed reactor at 485℃ and 0.20Mpa (gauge pressure) and then coated on the surface of the solid particles, controlling the SiO coating once. x The solid particles reside in the secondary silicon deposition fluidized bed reactor for 5 hours and then enter the secondary intermediate inert gas continuous reactor;

[0062] (5) In the secondary intermediate inert gas continuous reactor, unreacted disilane is replaced by N2, and a portion of the disilane is thermally decomposed. During the reaction, the temperature of the secondary intermediate inert gas continuous reactor is maintained at 585°C and the pressure is maintained at 0.15 MPa (gauge pressure). The residence time of the solid particles in the secondary intermediate inert gas continuous reactor is controlled to be 2 hours, after which the solid particles enter the secondary oxidation fluidized bed reactor along with N2;

[0063] (6) The solid particles react with a certain amount of oxygen in a secondary oxidation fluidized bed reactor at 585°C and 0.15 MPa (gauge pressure) for 2 h to obtain secondary coated SiO x solid particles;

[0064] (7) Secondary coating SiO x After the solid particles enter the carbon-coated fluidized bed, the asphalt gas undergoes a cracking reaction at 750°C and 0.20 MPa (gauge pressure) and is evenly coated on the surface of the solid particles, controlling the secondary coating of SiO x The residence time of the solid particles in the carbon-coated fluidized bed reactor was 3 h, and the Si@SiO x @Si@SiO x @CThe five-layer solid particles are multi-layer silicon-carbon negative electrode materials.

[0065] Example 3

[0066] A method for preparing a silicon-carbon negative electrode material of the present invention comprises the following steps:

[0067] (1) adding silicon powder to a first-stage intermediate inert gas continuous reactor, and replacing the air in the pores of the silicon powder particles with CO2. During the replacement process, the temperature in the first-stage intermediate inert gas continuous reactor was maintained at 450°C and the pressure was maintained at 0.50 MPa (gauge pressure). The residence time of the silicon powder in the first-stage oxidation fluidized bed reactor was controlled to be 0.5 h, after which the silicon powder particles entered the first-stage oxidation fluidized bed reactor along with CO2.

[0068] (2) Solid silicon powder particles react with a certain amount of oxygen in a primary oxidation fluidized bed reactor at 450 ° C and 0.50 MPa (gauge pressure) for 2 hours to obtain a primary coated SiO x solid particles;

[0069] (3) Primary coating of SiO x The solid particles enter the first-stage silicon deposition fluidized bed reactor, and tetraethoxysilane is cracked in the first-stage silicon deposition fluidized bed reactor at 550℃ and 0.40Mpa (gauge pressure) and then coated on the surface of the solid particles, controlling the SiO coating once. x The solid particles reside in the first-stage silicon deposition fluidized bed reactor for 3 hours, and then enter the second-stage intermediate inert gas continuous reactor;

[0070] (4) In the secondary intermediate inert gas continuous reactor, unreacted tetraethoxysilane is replaced by CO2, and a portion of the tetraethoxysilane is thermally decomposed. During the reaction, the temperature of the secondary intermediate inert gas continuous reactor is maintained at 750°C and the pressure is maintained at 0.25 MPa (gauge pressure). The residence time of the solid particles in the secondary intermediate inert gas continuous reactor is controlled to be 2.5 hours, after which the solid particles enter the secondary oxidation fluidized bed reactor along with CO2;

[0071] (5) The solid particles react with a certain amount of oxygen in a secondary oxidation fluidized bed reactor at 750 ° C and 0.25 MPa (gauge pressure) for 1.5 hours to obtain secondary coated SiO x solid particles;

[0072] (6) Secondary coating SiO x After the solid particles enter the carbon-coated fluidized bed, the resin gas undergoes a cracking reaction at 900°C and 0.20 MPa (gauge pressure) and is evenly coated on the surface of the solid particles, controlling the secondary coating SiO x The residence time of the solid particles in the carbon-coated fluidized bed reactor was 3 h, and the Si@SiO x @Si@SiO x @CThe five-layer solid particles are multi-layer silicon-carbon negative electrode materials.

[0073] Example 4

[0074] A method for preparing a silicon-carbon negative electrode material of the present invention comprises the following steps:

[0075] (1) adding the silicon-carbon material Si / C obtained by silicon deposition on porous carbon into a primary silicon deposition fluidized bed reactor, and cracking the divinyldiethoxysilane in the reactor at 600° C. and 0.20 MPa (gauge pressure) to uniformly coat the surface of the silicon-carbon material. The residence time of the silicon-carbon material in the primary silicon deposition fluidized bed reactor is controlled to be 6 h, after which the solid particles enter the primary intermediate inert gas continuous reactor along with the divinyldiethoxysilane;

[0076] (2) In a first-stage intermediate inert gas continuous reactor, unreacted divinyldiethoxysilane is replaced by He, and a portion of the divinyldiethoxysilane is thermally decomposed. During the reaction, the temperature of the first-stage intermediate inert gas continuous reactor is maintained at 750° C. and the pressure is maintained at 0.20 MPa (gauge pressure). The residence time of the solid particles in the first-stage intermediate inert gas continuous reactor is controlled to be 3 h, after which the solid particles enter the first-stage oxidation fluidized bed reactor along with He;

[0077] (3) The solid particles react with a certain amount of oxygen in a primary oxidation fluidized bed reactor at 750 ° C and 0.20 MPa (gauge pressure) for 2 hours to obtain a primary coated SiO x solid particles;

[0078] (4) Primary coating of SiO x The solid particles enter the secondary silicon deposition fluidized bed reactor, divinyldiethoxysilane is cracked in the secondary silicon deposition fluidized bed reactor at 800℃ and 0.20Mpa (gauge pressure) and then coated on the surface of the solid particles, controlling the SiO coating once. x The solid particles reside in the secondary silicon deposition fluidized bed reactor for 3 hours and then enter the secondary intermediate inert gas continuous reactor;

[0079] (5) In the secondary intermediate inert gas continuous reactor, unreacted divinyldiethoxysilane is replaced by He, and a portion of the divinyldiethoxysilane is thermally decomposed. During the reaction, the temperature of the secondary intermediate inert gas continuous reactor is maintained at 950° C. and the pressure is maintained at 0.20 MPa (gauge pressure). The residence time of the solid particles in the secondary intermediate inert gas continuous reactor is controlled to be 2 h, after which the solid particles enter the carbon-coated fluidized bed reactor along with He;

[0080] (6) Secondary coating SiO xAfter the solid particles enter the carbon-coated fluidized bed, ethylbenzene gas undergoes cracking reaction at 1200℃ and 0.15Mpa (gauge pressure) and then uniformly coats the surface of the solid particles. The residence time of the solid particles with secondary silicon deposition in the carbon-coated fluidized bed reactor is controlled to be 2h. The obtained solid particles are Si / C@Si@SiO x @Si@C five-layer structure silicon-carbon negative electrode material.

[0081] Comparative Example 1

[0082] Solid silicon core particles.

[0083] Performance Testing

[0084] Electrochemical performance test: The silicon-carbon negative electrode materials of Examples 1-4 and Comparative Example 1 were used to make half-cells, and their charge capacities were tested. The test results are shown in Table 1. In particular, half-cell preparation: a button cell was assembled with the active material as the positive electrode and the lithium sheet as the negative electrode. The conductive agent used was conductive carbon Super P, the separator was Celgard 2400, the electrolyte composition was 1 mol / LLiPF6, the solvent was DMC:DEC:EC (vol%) = 1:1:1, 10% FEC, 2.0% VC. The test conditions were: activation twice at a current density of 100 mA / g and the initial specific capacity was tested, followed by 200 cycles at a current density of 500 mA / g. The test results are shown in Table 1. Figure 3 The cyclic stability curve is shown in Table 1 below, and the test data is recorded according to the cyclic stability curve.

[0085]

[0086]

[0087] Table 1

[0088] According to the test results of Examples 1-4, the multilayer silicon-carbon negative electrode material and the multi-stage fluidized bed continuous preparation method provided by the present invention can effectively improve the cycle stability and charging capacity of the silicon-carbon negative electrode material, thereby increasing its application value.

[0089] According to the comparison of the test results of Examples 1-4 and Comparative Example 1, the multi-layer silicon-carbon negative electrode material and the multi-stage fluidized bed continuous preparation method provided by the present invention adopt a fluidized bed reactor in the three stages of silicon deposition, limited oxidation and carbon coating. The temperature control, coating and oxidation degree during the reaction process are more uniform, which greatly improves the consistency of the silicon-carbon negative electrode material and limits the SiO obtained by the oxidation reaction. x The intermediate layer can effectively alleviate the volume expansion of silicon, improve the cycle performance and service life of the battery. At the same time, the dense carbon layer generated by the carbon coating process can enhance the conductivity of the negative electrode material and improve the conductivity of the silicon material.

[0090] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multilayer silicon-carbon negative electrode material, characterized in that: The multilayer silicon-carbon negative electrode material comprises a silicon layer, SiO x Layers and carbon layers are alternately wrapped; The silicon layers are separated by a carbon layer or SiO x Layer isolation, the carbon layer and the carbon layer are separated by silicon layer or SiO x Layer isolation, SiO x Layer with SiO x The layers are isolated by silicon layers.

2. The multilayer silicon-carbon negative electrode material according to claim 1, characterized in that There is at least one layer of SiO between the silicon layer and the carbon layer x layer.

3. The multilayer silicon-carbon negative electrode material according to claim 2, characterized in that: The multilayer silicon-carbon negative electrode material has Si@SiO x @Si@SiO x @CFive-layer structure.

4. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that: The multi-stage fluidized bed continuous preparation method realizes a continuous process by setting different parameters in each stage of the fluidized bed reactor to adapt to the changes in the physical properties of the solid particles; The continuous process includes three processes: silicon deposition, restricted oxidation and carbon coating; The silicon deposition process is carried out by cracking silicon source gas at high temperature; The restricted oxidation process is carried out by using a silicon source gas replacement and oxidation method; The carbon coating process is carried out by cracking carbon source gas at high temperature.

5. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 4, characterized in that: During the silicon deposition process, the temperature in the silicon deposition fluidized bed reactor is controlled to be 300-900° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the silicon deposition fluidized bed reactor is controlled to be 0.5-8 hours.

6. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 4, characterized in that: The silicon source gas is selected from one or a mixture of silane, disilane, trisilane, butane, chlorosilane, tetramethoxysilane, tetramethylsilane, tetraethylsilane, tetraethoxysilane, trivinylmethoxysilane, trivinylethoxysilane, divinyldiethoxysilane, divinyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenylsilane, and diphenylsilane.

7. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 4, characterized in that: In the restricted oxidation process, the silicon source gas replacement stage utilizes an intermediate inert gas continuous reactor to allow the inert gas to replace the unreacted silicon source gas or to completely decompose the residual silicon source gas in an inert atmosphere; In the limited oxidation process, the oxidation stage is to partially oxidize the deposited silicon in an oxidation fluidized bed reactor using oxygen and / or air.

8. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 7, characterized in that: During the silicon source gas replacement process, the temperature in the intermediate inert gas continuous reactor is controlled to be 300-1200° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the intermediate inert gas continuous reactor is controlled to be 0.5-6 hours; The inert gas is selected from at least one of N2, Ar, CO2, He, Ne, Kr, and Xe; During the oxidation process, the temperature in the oxidation fluidized bed reactor is controlled to be 300-1200° C., the gauge pressure is controlled to be 0-0.50 MPa, and the residence time of the solid particles in the oxidation fluidized bed reactor is controlled to be 0.5-6 hours.

9. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 4, characterized in that: During the carbon coating process, the temperature in the carbon coating fluidized bed reactor is controlled to be 300-1500° C., the gauge pressure is controlled to be 0-0.60 MPa, and the residence time of the solid particles in the carbon coating fluidized bed reactor is controlled to be 0.5-6 hours.

10. The multi-stage fluidized bed continuous preparation method of the multilayer silicon-carbon negative electrode material according to claim 4, characterized in that: The carbon source gas is selected from one or a mixture of cracked carbon, monosaccharides, disaccharides, polysaccharides, sugar derivatives, asphalt, resins, aromatic hydrocarbons, alkanes, alkenes, and alkynes.

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