Silicon-carbon negative electrode material and fluidization preparation method thereof

Abstract

The invention relates to the technical field of lithium ion battery materials, in particular to a silicon-carbon negative electrode material and a fluidization preparation method thereof. The fluidized preparation method comprises the following steps: performing high-temperature pre-deposition on porous carbon particles, silane and diluent gas in a fluidized state; and then, silane, diluent gas and olefin gas are introduced for olefin-assisted silicon deposition in a fluidized state. According to the fluidized preparation method, the problems of uneven silicon deposition, influence of by-products on carbon coating quality, extensive process control, high energy consumption and the like in the process of preparing the silicon-carbon negative electrode material by an existing fluidized bed CVD (Chemical Vapor Deposition) method are solved, uniform dispersion and compact carbon coating of silicon nanoparticles in porous carbon are realized, and the electrochemical performance of the material is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery materials, in particular to a silicon-carbon negative electrode material and a fluidized preparation method thereof. BACKGROUND

[0002] In recent years, new energy vehicles and large-scale energy storage systems have put forward higher requirements for the energy density of lithium ion batteries, which has greatly promoted the research and development process of new generation negative electrode materials. Silicon-carbon composite negative electrode material has become the focus of the industry because its theoretical specific capacity can be as high as 4200 mAh / g, far superior to traditional graphite materials, and the silicon resource reserves are abundant. However, the silicon-based material has a serious volume expansion effect during the charging and discharging process, with an expansion rate of more than 300%, which easily leads to electrode active material pulverization, continuous rupture and regeneration of the solid electrolyte interface (SEI film), and further causes rapid capacity decay and cycle life decline, which has become a key technical bottleneck restricting its commercial application.

[0003] To overcome the above problems, researchers propose to composite nano-silicon particles with carbon matrix, and use the conductivity and structural stability of carbon material to buffer the volume change and maintain the integrity of the electrode. Among various preparation processes, the fluidized bed chemical vapor deposition (CVD) technology is considered as the most promising method for the preparation of silicon-carbon negative electrode materials due to its high efficiency of gas-solid two-phase contact and reaction, and the potential for continuous production. This technology usually uses silane as the silicon source and acetylene as the carbon source to realize silicon deposition and carbon coating on the surface of porous carbon, thereby constructing a composite material with a "core-shell" structure.

[0004] However, the existing fluidized bed CVD technology still faces many challenges. The silicon particle is easy to agglomerate and grow on the outer surface and orifice of the porous carbon, rather than being ideally filled in the internal pores, which makes the volume effect not effectively alleviated and the material cycle performance poor. At the same time, the by-products produced by the cracking of silane are easy to be adsorbed on the surface of active silicon, hindering the effective contact and deposition of the subsequent carbon source gas, resulting in problems such as discontinuity and non-densification of the carbon coating layer, and reducing its constraint ability on the volume expansion of silicon and the conductivity. In addition, the existing process lacks linkage control of temperature, pressure and gas composition during the reaction process, and the heat release in the deposition stage is concentrated, which easily causes local overheating and leads to sintering of silicon particles; and the direct discharge or incineration treatment of unreacted silane and carbon source gas also increases the production cost and environmental burden.

[0005] Therefore, it is of great significance to develop a new fluidized bed CVD process that can realize uniform deposition of silicon nanoparticles, clean and efficient interface, and energy saving and consumption reduction in the process, for promoting the large-scale application of high-performance silicon-carbon negative electrode materials.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The present application aims to provide a silicon-carbon negative electrode material and a fluidized preparation method thereof. The preparation method provided by the present application can realize uniform dispersion of silicon nanoparticles in porous carbon and compact carbon coating, and significantly improve the electrochemical performance of the material.

[0008] The present application is implemented as follows: In a first aspect, the present application provides a fluidized preparation method of a silicon-carbon negative electrode material, comprising: performing high-temperature pre-deposition of porous carbon particles, silane and dilution gas in a fluidized state, wherein the conditions of high-temperature pre-deposition include: (1) the temperature is 10-30℃ higher than the subsequent olefin-assisted silicon deposition temperature; (2) the volume flow rate of silane is 10-30% of the total volume flow rate of silane and dilution gas; (3) the superficial gas velocity is 0.03-0.15 m / s; and the mass of silicon in high-temperature pre-deposition accounts for 10-25% of the total theoretical deposition mass of silicon. Then, silane, dilution gas and olefin gas are introduced to perform olefin-assisted silicon deposition in a fluidized state; wherein the conditions of olefin-assisted silicon deposition include: (1) the temperature is 450-550℃; (2) the volume flow rate of silane is 10-30% of the total volume flow rate of silane, dilution gas and olefin gas; (3) the superficial gas velocity is 0.03-0.15 m / s; (4) the molar flow rate of olefin gas to silane is (1:20)-(1:10); and the mass of silicon in olefin-assisted silicon deposition accounts for 90-75% of the total theoretical deposition mass of silicon.

[0009] In an optional embodiment, the method further comprises: performing vacuum desorption after the olefin-assisted silicon deposition. The process of vacuum desorption includes: maintaining the temperature of olefin-assisted silicon deposition for 0.5-2 hours under an absolute pressure of 20-90 Pa.

[0010] In an optional embodiment, the method further comprises performing carbon coating after the vacuum desorption. The process of carbon coating includes: introducing carbon source gas and dilution gas to make the material in a fluidized state to perform carbon coating, and the conditions of carbon coating include: (1) the temperature is 450-600℃; (2) the volume flow rate of carbon source gas is 10-30% of the total volume flow rate of carbon source gas and dilution gas; (3) the superficial gas velocity is 0.03-0.15 m / s; and the mass of the coating layer formed by carbon coating accounts for 1-8% of the total mass of the finally formed silicon-carbon negative electrode material.

[0011] In an optional embodiment, the method further comprises: performing pre-heating treatment on the porous carbon particles before the high-temperature pre-deposition.

[0012] In an optional embodiment, the pre-heating treatment comprises: treating at 300-500℃ and 20-90kpa absolute pressure in an inert gas atmosphere and fluidized state for 1-3h; wherein the dilution gas forming the inert gas atmosphere has a superficial flow velocity of 0.03-0.1m / s; and the absolute pressure fluctuation during the pre-heating treatment is controlled within ≤±5Pa.

[0013] In an optional embodiment, the porous carbon particles have a particle size of 2-15μm, a specific surface area of 500-2500m² / g, and a pore volume of 0.5-3.0cm³ / g. Preferably, the porous carbon particles comprise one or more of phenolic resin carbon, coconut shell bio-carbon, pitch carbon, or petroleum coke.

[0014] In an optional embodiment, the dilution gas comprises an inert gas; and the olefin gas comprises ethylene or propylene.

[0015] In an optional embodiment, the silane and the dilution gas are pre-heated at 200-300℃ for 0.5-2s, respectively, before the high-temperature pre-deposition and the olefin-assisted silicon deposition.

[0016] In a second aspect, the present application provides a silicon-carbon negative electrode material prepared by the fluidized preparation method of the silicon-carbon negative electrode material according to any one of the preceding embodiments.

[0017] In an optional embodiment, the silicon-carbon negative electrode material satisfies the following requirements: (1) the silicon content in the silicon-carbon negative electrode material is 40-60% by mass; (2) the silicon in the silicon-carbon negative electrode material is uniformly distributed in the form of nano-particles with a particle size of 5-50nm in the pores and on the surface of the porous carbon particles; (3) the carbon-coated layer formed by the carbon coating has a thickness of 5-50nm; (4) the carbon-coated layer formed by the carbon coating is continuous and uniform amorphous carbon, and the silicon-carbon particles after carbon coating have an electrical conductivity ≥0.2S / cm; (5) the silicon-carbon negative electrode material has a specific surface area of 2-15m² / g and a tap density ≥0.8g / cm³.

[0018] The present application has the following beneficial effects: the embodiments of the present application combine high-temperature pre-deposition and olefin-assisted silicon deposition, which can form stable silicon deposition points on the surface of the porous carbon particles, is conducive to efficient decomposition and uniform deposition of silane, and effectively avoids the agglomeration of silicon particles in the subsequent main deposition process; and significantly improves the silicon deposition efficiency and uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic flowchart of the fluidized bed preparation method for silicon-carbon anode materials provided in this embodiment of the invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] To address the problems of uneven silicon deposition, byproducts affecting carbon coating quality, crude process control, and high energy consumption in the existing fluidized bed CVD method for preparing silicon-carbon anode materials, this invention proposes a novel fluidized bed preparation method for silicon-carbon anode materials. (See schematic diagram of the fluidized bed preparation method for silicon-carbon anode materials.) Figure 1 This preparation method is a process carried out in a fluidized state of raw materials, and therefore it is also called a fluidized bed preparation method.

[0023] The specific process is as follows: S1. Preheating treatment; Porous carbon particles are introduced into a fluidized bed reactor, and a dilution gas is introduced to create an inert gas atmosphere, which also keeps the porous carbon particles in a fluidized state. The reactor is then heat-treated at 300–500℃ and 20–90 kPa absolute pressure for 1–3 hours to remove impurities from the porous carbon particles. The apparent flow rate of the dilution gas is 0.03–0.1 m / s. Simultaneously, during the preheating process, the absolute pressure inside the fluidized bed reactor is monitored in real time using a pressure sensor, and its fluctuation range is controlled to ≤ ±5 Pa.

[0024] The porous carbon particles have a particle size of 2-15 μm, a specific surface area of ​​500-2500 m² / g, and a pore volume of 0.5-3.0 cm³ / g; for example, the porous carbon particles include one or more of phenolic resin carbon, coconut shell biocarbon, asphaltene carbon, or petroleum coke.

[0025] S2, High-temperature pre-deposition; Porous carbon particles, silane, and dilution gas are pre-deposited at high temperature in a fluidized bed. Specifically, a first mixture of silane and dilution gas is introduced into the fluidized bed, and pre-deposition is carried out at a temperature 10-30°C higher than the subsequent olefin-assisted silicon deposition temperature, with the silane volumetric flow rate being 10-30% of the total volumetric flow rate of silane and dilution gas, and an apparent gas velocity of 0.03-0.15 m / s. The mass of silicon pre-deposited at this high temperature accounts for 10-25% of the theoretically total deposited silicon mass.

[0026] In this embodiment of the invention, stable silicon deposition points are formed on the surface of porous carbon particles by high-temperature pre-deposition, which effectively avoids the agglomeration of silicon particles during the subsequent main deposition process.

[0027] Furthermore, before high-temperature pre-deposition, the first mixed gas is preheated at 200-300℃ for 0.5-3 seconds.

[0028] S3, olefin-assisted silicon deposition; Olefin-assisted silicon deposition is then carried out under fluidized conditions by introducing silane, dilution gas, and olefin gas. Specifically, a second mixture of silane, dilution gas, and olefin gas is introduced into the fluidized bed, and olefin-assisted silicon deposition is performed at 450-550°C, with the volumetric flow rate of silane being 10-30% of the total volumetric flow rate of the silane, dilution gas, and olefin gas; an apparent gas velocity of 0.03-0.15 m / s; and a molar flow ratio of olefin to silane of 1:20-1:10. The silicon deposited in this step accounts for 90-75% of the theoretically total silicon deposited. The olefin gas includes, but is not limited to, ethylene and propylene, with ethylene being preferred.

[0029] Olefin-assisted silicon deposition can utilize the active components generated by olefin cracking to promote efficient decomposition and uniform deposition of silanes, significantly improving silicon deposition efficiency and uniformity.

[0030] Furthermore, before olefin-assisted silicon deposition, the silane and dilution gas are preheated at 200-300°C for 0.5-2 seconds.

[0031] It should be noted that the dilution gas used in S2 and S3 is an inert gas, such as, but not limited to, nitrogen, argon or helium.

[0032] S4, Vacuum desorption; Vacuum desorption was performed under an absolute pressure of 20-90 Pa, maintaining the temperature of olefin-assisted silicon deposition for 0.5-2 hours to remove adsorbed byproduct gases.

[0033] The embodiments of the present invention employ vacuum desorption to thoroughly remove adsorption byproducts from the silicon surface, creating a clean interface environment for subsequent dense carbon coating.

[0034] S5, carbon coating; Carbon source gas and dilution gas are then introduced to allow the material to undergo carbon coating in a fluidized state. Specifically, a third mixture of carbon source gas and dilution gas is introduced into the fluidized bed, and carbon coating is carried out at 450-600°C, a carbon source gas volumetric flow rate of 10-30% of the total volumetric flow rate of the carbon source gas and dilution gas, and an apparent gas velocity of 0.03-0.15 m / s, so that the mass of the coating layer formed accounts for 1-8% of the total mass of the final silicon-carbon anode material. The carbon source gas is acetylene, ethylene, or propylene, preferably acetylene.

[0035] Secondly, the present invention provides a silicon-carbon anode material, which is prepared by fluidization method of any of the foregoing embodiments.

[0036] The silicon-carbon anode material contains 40-60% silicon by mass; silicon particles with a diameter of 5-50 nm are uniformly distributed in the pores and surface of the porous carbon particles; the thickness of the carbon coating layer is 5-50 nm; the carbon coating layer is a continuous and uniform amorphous carbon with a resistivity ≤100 μΩ·m; the specific surface area of ​​the silicon-carbon anode material is 2-15 m² / g, and the tap density is ≥0.8 g / cm³.

[0037] The silicon-carbon anode material prepared by the method provided in this invention can be used as a lithium-ion battery anode, and exhibits excellent performance when used as an anode. Specifically, it achieves an initial coulombic efficiency of ≥85% at 0.1C and a capacity retention of ≥90% after 100 cycles at 0.5C.

[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0039] Example 1 This embodiment provides a fluidized bed preparation method for silicon-carbon anode materials, including: S1. Preheating treatment; 10 kg of phenolic resin carbon particles with a particle size D50 of 8 μm, a specific surface area of ​​1800 m² / g, and a pore volume of 1.8 cm³ / g were placed in a stirred fluidized bed reactor. Under a nitrogen atmosphere, the absolute pressure of the fluidized bed reactor was controlled at 50 kPa, and the temperature was increased to 400℃ at a rate of 5℃ / min and held for 2 hours. During the treatment, the apparent flow rate of nitrogen was 0.06 m / s, and the pressure fluctuation was controlled within ±3 Pa.

[0040] Step 2: High-temperature pre-deposition Silane and nitrogen were mixed at a volumetric flow rate ratio of 1:8, preheated to 250°C, and then introduced into a fluidized bed reactor. The apparent gas velocity was controlled at 0.08 m / s, and the reaction temperature was raised to 480°C (20°C higher than the subsequent deposition temperature) for pre-deposition for 2 hours. Calculations showed that the silicon mass pre-deposited at this high temperature accounted for 15% of the theoretically total silicon mass deposited.

[0041] Step 3: Olefin-assisted silicon deposition The temperature was kept at 460℃, and a mixture of silane, nitrogen, and ethylene gas was introduced into the fluidized bed reactor (the volumetric flow rate of silane was 20% of the total volumetric flow rate of silane, dilution gas, and olefin gas, and the molar flow rate ratio of ethylene to silane was 1:15), with an apparent gas velocity of 0.10 m / s, and deposition was carried out for 5 hours. The olefin-assisted silicon deposition accounted for 85% of the theoretically total deposited silicon mass.

[0042] Step 4: Vacuum Desorption After deposition, the absolute pressure of the fluidized bed reactor was reduced to 50 Pa, and desorption was carried out by holding the reactor at 460℃ for 1 hour.

[0043] Step 5: Carbon Coating A mixture of acetylene and nitrogen gas (acetylene partial pressure 25 kPa) was introduced into a fluidized bed reactor at an apparent gas velocity of 0.05 m / s, and the mixture was coated at 550 °C for 3 h.

[0044] Product characterization: The silicon content in the silicon-carbon anode material is 48 wt.%, and the mass of the carbon coating layer accounts for 3.2 wt.% of the total mass of the final silicon-carbon anode material. The silicon particles have a diameter of 20-40 nm and are uniformly distributed in the porous carbon pores. The specific surface area is 3.5 m² / g, and the tap density is 0.95 g / cm³. The initial efficiency at 0.1C is 86.5%, and the capacity retention rate after 100 cycles at 0.5C is 91.2%.

[0045] Example 2 This embodiment provides a fluidized bed preparation method for silicon-carbon anode materials. This preparation method is the same as in Example 1, with the following differences; the remaining operation steps and conditions are consistent with the preparation method in Example 1: Step 1: Take coconut shell biochar (D50=12μm, specific surface area 1500m² / g, pore volume 1.2cm³ / g) and pretreat it at 350℃ and 80kPa absolute pressure for 2.5h.

[0046] Step 3: At 475°C, a mixture of silane, argon and propylene gas (propylene to silane molar ratio 1:18) is introduced and deposited for 4 hours.

[0047] Step 5: Using ethylene as a carbon source (partial pressure 20 kPa), coat the sample at 500°C for 4 hours.

[0048] Product characterization: Silicon content 52 wt.%, carbon coating 4.5 wt.%, silicon particle size 30-50 nm. Specific surface area 5.8 m² / g, initial efficiency at 0.1C 84.8%, capacity retention after 100 cycles 89.5%.

[0049] Example 3 This embodiment provides a fluidized bed preparation method for silicon-carbon anode materials. This preparation method is the same as in Example 1, with the following differences; the remaining operation steps and conditions are consistent with the preparation method in Example 1: Step 1: Pitch peat (D50=5μm, specific surface area 2200m² / g, pore volume 2.5cm³ / g) was pretreated at 450℃ and 30kPa absolute pressure for 1.5h.

[0050] Step 2: The volumetric flow rate of silane is 10% of the total volumetric flow rate of silane and dilution gas, and the apparent gas velocity is 0.04 m / s. Pre-deposit at 520℃ (30℃ higher than the subsequent temperature) for 3 hours. The silicon mass of the high-temperature pre-deposited silicon accounts for 10% of the theoretical total silicon mass.

[0051] Step 3: At 490℃, a mixture of silane, helium and ethylene gas (ethylene to silane molar ratio 1:12) is introduced and deposited for 6 hours.

[0052] Product characterization: Silicon content 58 wt.%, carbon coating 2.8 wt.%, silicon particle size 10-30 nm. Specific surface area 2.1 m² / g, initial efficiency at 0.1C 88.2%, capacity retention after 100 cycles 93.1%.

[0053] Example 4 This embodiment provides a fluidized bed preparation method for silicon-carbon anode materials. This preparation method is the same as in Example 1, with the following differences; the remaining operation steps and conditions are consistent with the preparation method in Example 1: Step 2: The pre-deposition temperature is 10°C higher than the subsequent deposition temperature; Step 3: The molar flow ratio of olefin to silane is 1 / 20; Step 5: The mass of the carbon coating layer accounts for 1% of the total mass of the final silicon-carbon anode material.

[0054] Product characterization: Silicon content 40 wt.%, carbon coating 1.0 wt.%, specific surface area 8.2 m² / g.

[0055] Example 5 This embodiment provides a fluidized bed preparation method for silicon-carbon anode materials. This preparation method is the same as in Example 1, with the following differences; the remaining operation steps and conditions are consistent with the preparation method in Example 1: Step 2: The pre-deposition temperature is 30°C higher than the subsequent deposition temperature; Step 3: The molar flow ratio of olefin to silane is 1 / 10; Step 5: The mass of the carbon coating layer accounts for 8% of the total mass of the final silicon-carbon anode material.

[0056] Product characterization: Silicon content 60 wt.%, carbon coating 8.0 wt.%, specific surface area 4.5 m² / g.

[0057] Comparative Example 1 This comparative example provides a method for preparing a silicon-carbon anode material. The preparation method is the same as that in Example 1, except that the high-temperature pre-deposition of S2 is omitted, that is, all silicon deposition is completed at 460°C; the remaining operation steps and conditions are the same as those in Example 1.

[0058] Product characterization: Silicon content 45 wt.%, but silicon particles are significantly agglomerated (particle size 100-500 nm) and unevenly distributed. Specific surface area 18.5 m² / g, initial efficiency at 0.1C 79.2%, capacity retention after 100 cycles only 68.3%.

[0059] Comparative Example 2 This comparative example provides a method for preparing a silicon-carbon anode material. The preparation method is the same as that in Example 1, except that ethylene is not used in S3, and only silane and nitrogen are introduced, that is, there is no olefin-assisted silicon deposition; the remaining operation steps and conditions are the same as those in Example 1.

[0060] Product characterization: Silicon deposition efficiency decreased, with a silicon content of only 36 wt.%. Although silicon particles did not show significant agglomeration (particle size 50-260 nm), their distribution density was low. Specific surface area was 8.5 m² / g, initial efficiency at 0.1C was 82.1%, and capacity retention after 100 cycles was 75.6%.

[0061] Comparative Example 3 This comparative example provides a method for preparing a silicon-carbon anode material, which is the same as in Example 1, except that step S4 is omitted; the remaining operation steps and conditions are the same as those in Example 1.

[0062] Product characterization: The carbon coating layer has defects and is unevenly coated. The silicon content is 47 wt.%, but the first efficiency at 0.1C drops to 80.5%, and the capacity retention after 100 cycles is 78.9%.

[0063] Comparative Example 4 This comparative example provides a method for preparing a silicon-carbon anode material, which is the same as in Example 3, except that the high-temperature pre-deposition temperature in step 2 is set to 530°C; the remaining operation steps and conditions are consistent with the preparation method in Example 3. This high-temperature pre-deposition temperature is 50°C higher than the subsequent olefin-assisted silicon deposition temperature of 480°C, exceeding the 10-30°C limit specified in this invention.

[0064] Product characterization: Silicon content 53.8 wt.%, carbon content 2.8 wt.%, silicon particles significantly agglomerated (40-80 nm), specific surface area 12.8 m² / g, tap density 0.78 g / cm³ (below the requirement of 0.8 g / cm³), carbon coating thickness uneven and locally cracked, 0.1C first efficiency 80.1%, capacity retention after 100 cycles 65.0%.

[0065] Comparative Example 5 This comparative example provides a method for preparing a silicon-carbon anode material, which is the same as in Example 3, except that the high-temperature pre-deposition temperature in step 2 is set to 450°C; the remaining operation steps and conditions are consistent with the preparation method in Example 3. This high-temperature pre-deposition temperature is 30°C lower than the subsequent olefin-assisted silicon deposition temperature of 480°C, which does not meet the requirement of "above the subsequent olefin-assisted silicon deposition temperature" as defined in this invention.

[0066] Product characterization: Silicon content 52.1 wt.%, carbon content 2.8 wt.%, silicon particles grow disordered and are severely agglomerated (35-60 nm), specific surface area 15.3 m² / g (exceeding the requirement of 2-15 m² / g), carbon coating layer is not tightly bonded to silicon particles and locally peels off, 0.1C first efficiency 78.3%, capacity retention after 100 cycles 58.0%.

[0067] Comparative Example 6 This comparative example provides a method for preparing a silicon-carbon anode material. The preparation method is the same as that in Example 3, except that in step 3, olefin-assisted silicon deposition, propylene is replaced with acetylene; the remaining operation steps and conditions are the same as those in Example 3.

[0068] Product characterization: Silicon content 42.3 wt.%, carbon content 2.8 wt.%, silicon particles locally agglomerated (25-70 nm), specific surface area 9.7 m² / g, carbon coating layer contains crystalline carbon impurities, 0.1C first efficiency 81.5%, capacity retention after 100 cycles 70.0%.

[0069] Comparative Example 7 This comparative example provides a method for preparing a silicon-carbon anode material, which is the same as that in Example 3, except that the olefin-assisted silicon deposition temperature in step 3 is set to 560°C (exceeding the 450-550°C limit of this invention); the remaining operation steps and conditions are the same as those in Example 3.

[0070] Product characterization: Silicon content 55.2 wt.%, carbon content 2.8 wt.%, silicon particles rapidly agglomerate (30-75 nm), specific surface area 16.5 m² / g (exceeding the requirement of 2-15 m² / g), carbon coating layer is discontinuous and thinner, first efficiency at 0.1C 79.4%, capacity retention after 100 cycles 59.0%.

[0071] In summary, the performance results of the silicon-carbon anode materials provided in the embodiments and comparative examples of the present invention are shown in the following table.

[0072]

[0073] As shown in the table above, the embodiments of the present invention effectively solve the problems of silicon particle agglomeration, uneven distribution, and poor carbon coating through multi-step synergy, resulting in silicon-carbon materials with excellent electrochemical performance. The comparative results further demonstrate the necessity and synergistic effect of each step in the present invention.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 fluidization preparation of a silicon-carbon negative electrode material, characterized in that, The method comprises the following steps: high-temperature pre-deposition of porous carbon particles, silane and dilution gas in a fluidized state, wherein the conditions of high-temperature pre-deposition include: (1) the temperature is 10-30℃ higher than the subsequent olefin-assisted silicon deposition temperature; (2) the volume flow rate of silane is 10-30% of the total volume flow rate of silane and dilution gas; (3) the superficial gas velocity is 0.03-0.15m / s; and the silicon mass of high-temperature pre-deposition accounts for 10-25% of the total theoretical deposition silicon mass; then, olefin-assisted silicon deposition is performed by introducing silane, dilution gas and olefin gas in a fluidized state; wherein the conditions of olefin-assisted silicon deposition include: (1) the temperature is 450-550℃; (2) the volume flow rate of silane is 10-30% of the total volume flow rate of silane, dilution gas and olefin gas; (3) the superficial gas velocity is 0.03-0.15m / s; (4) the molar flow rate of olefin gas and silane is (1:20)-(1:10); and the silicon mass of olefin-assisted silicon deposition accounts for 90-75% of the total theoretical deposition silicon mass.

2. The production method according to claim 1, characterized by, The method further comprises the following steps: vacuum desorption after the olefin-assisted silicon deposition; wherein the process of vacuum desorption includes: maintaining the temperature of olefin-assisted silicon deposition for 0.5-2 hours under an absolute pressure of 20-90Pa.

3. The production method according to claim 2, characterized by, The method further comprises the following step: carbon coating after the vacuum desorption; 4. The production method according to any one of claims 1 to 3, characterized by, wherein the process of carbon coating includes: introducing carbon source gas and dilution gas to make the material in a fluidized state for carbon coating, and the conditions of carbon coating include: (1) the temperature is 450-600℃; (2) the volume flow rate of carbon source gas is 10-30% of the total volume flow rate of carbon source gas and dilution gas; (3) the superficial gas velocity is 0.03-0.15m / s; and the mass of the coating layer formed by carbon coating accounts for 1-8% of the total mass of the final formed silicon-carbon negative electrode material.

5. The preparation method according to claim 4, characterized in that, The method further comprises the following step:

6. The preparation method according to claim 4, characterized in that, preheating treatment of the porous carbon particles before high-temperature pre-deposition. The preheating treatment includes: treatment at 300-500℃ and 20-90kpa absolute pressure for 1-3h in an inert gas atmosphere and a fluidized state; wherein the superficial flow rate of dilution gas forming the inert gas atmosphere is 0.03-0.1m / s; and the fluctuation range of absolute pressure during the preheating treatment process is ≤±5Pa.

7. The preparation method according to claim 1, characterized in that, The particle size of the porous carbon particles is 2-15μm, the specific surface area is 500-2500m² / g, and the pore volume is 0.5-3.0cm³ / g.

8. The method of claim 1, wherein, The porous carbon particles include one or more of phenolic resin carbon, coconut bio-carbon, pitch carbon or petroleum coke.

9. A silicon-carbon negative electrode material, characterized by, The dilution gas includes inert gas; and the olefin gas includes ethylene or propylene.

10. The silicon-carbon negative electrode material of claim 9, wherein, The silane and dilution gas are respectively preheated at 200-300℃ for 0.5-2s before high-temperature pre-deposition and olefin-assisted silicon deposition. The method is used for the fluidization preparation of the silicon-carbon negative electrode material according to any one of claims 1-8. The silicon-carbon negative electrode material meets the following requirements: (1) the mass content of silicon in the silicon-carbon negative electrode material is 40-60%; (2) the silicon nanoparticles with a particle size of 5-50nm are uniformly distributed in the pores and on the surface of the porous carbon particles in the form of nanoparticles. (3) the thickness of the carbon coating layer formed by carbon coating is 5-50nm; (4) the carbon coating layer formed by carbon coating is continuous, uniform and amorphous carbon, and the conductivity of the silicon-carbon particles after carbon coating is greater than or equal to 0.2S / cm; (5) the specific surface area of the silicon-carbon negative electrode material is 2-15m² / g, and the tap density is greater than or equal to 0.8g / cm³.

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